CA1216075A - Wafer fabrication by implanting through protective layer - Google Patents

Wafer fabrication by implanting through protective layer

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Publication number
CA1216075A
CA1216075A CA000458075A CA458075A CA1216075A CA 1216075 A CA1216075 A CA 1216075A CA 000458075 A CA000458075 A CA 000458075A CA 458075 A CA458075 A CA 458075A CA 1216075 A CA1216075 A CA 1216075A
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Prior art keywords
epitaxial
layer
regions
base
implanting
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Expired
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CA000458075A
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French (fr)
Inventor
Paul J. Howell
Gregory B. Currier
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Fairchild Semiconductor Corp
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Fairchild Camera and Instrument Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/66007—Multistep manufacturing processes
    • H01L29/66075—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials
    • H01L29/66227—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
    • H01L29/66234—Bipolar junction transistors [BJT]
    • H01L29/66272—Silicon vertical transistors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02107—Forming insulating materials on a substrate
    • H01L21/02225—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer
    • H01L21/0226—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a deposition process
    • H01L21/02263—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a deposition process deposition from the gas or vapour phase
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/027—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34
    • H01L21/033—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising inorganic layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/26—Bombardment with radiation
    • H01L21/263—Bombardment with radiation with high-energy radiation
    • H01L21/265—Bombardment with radiation with high-energy radiation producing ion implantation
    • H01L21/26506—Bombardment with radiation with high-energy radiation producing ion implantation in group IV semiconductors
    • H01L21/26513—Bombardment with radiation with high-energy radiation producing ion implantation in group IV semiconductors of electrically active species
    • H01L21/2652—Through-implantation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
    • H01L21/314—Inorganic layers
    • H01L21/3143—Inorganic layers composed of alternated layers or of mixtures of nitrides and oxides or of oxinitrides, e.g. formation of oxinitride by oxidation of nitride layers
    • H01L21/3145—Inorganic layers composed of alternated layers or of mixtures of nitrides and oxides or of oxinitrides, e.g. formation of oxinitride by oxidation of nitride layers formed by deposition from a gas or vapour
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
    • H01L21/76—Making of isolation regions between components
    • H01L21/762—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers
    • H01L21/76202—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using a local oxidation of silicon, e.g. LOCOS, SWAMI, SILO
    • H01L21/76205—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using a local oxidation of silicon, e.g. LOCOS, SWAMI, SILO in a region being recessed from the surface, e.g. in a recess, groove, tub or trench region
    • H01L21/7621—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using a local oxidation of silicon, e.g. LOCOS, SWAMI, SILO in a region being recessed from the surface, e.g. in a recess, groove, tub or trench region the recessed region having a shape other than rectangular, e.g. rounded or oblique shape
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
    • H01L21/76—Making of isolation regions between components
    • H01L21/762—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers
    • H01L21/76202—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using a local oxidation of silicon, e.g. LOCOS, SWAMI, SILO
    • H01L21/76213—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using a local oxidation of silicon, e.g. LOCOS, SWAMI, SILO introducing electrical inactive or active impurities in the local oxidation region, e.g. to alter LOCOS oxide growth characteristics or for additional isolation purpose
    • H01L21/76216—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using a local oxidation of silicon, e.g. LOCOS, SWAMI, SILO introducing electrical inactive or active impurities in the local oxidation region, e.g. to alter LOCOS oxide growth characteristics or for additional isolation purpose introducing electrical active impurities in the local oxidation region for the sole purpose of creating channel stoppers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/77—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate
    • H01L21/78—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices
    • H01L21/82—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices to produce devices, e.g. integrated circuits, each consisting of a plurality of components
    • H01L21/822—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices to produce devices, e.g. integrated circuits, each consisting of a plurality of components the substrate being a semiconductor, using silicon technology
    • H01L21/8222—Bipolar technology

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  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
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Abstract

WAFER FABRICATION BY IMPLANTING THROUGH PROTECTIVE LAYER
Abstract of the Disclosure Manufacture of bipolar substantially isoplanar integrated circuit structures is accomplished by rearrangement of the conventional masking steps and by the substitution and full integration of implanting methods for diffusion methods. A uniform nitride layer is deposited over the basic structure of epitaxial islands separated by isolation oxide regions thereby passivating and protecting the isolation oxide regions, epitaxial oxide buffer layer and epitaxial layer from environmental contaminants. The nitride layer which forms part of a composite protective layer is maintained in place throughout a major portion of the fully integrated sequential implanting steps during which the collector sink, base and emitter regions are introduced into the epitaxial islands. At least a portion of the composite protective layer is a barrier to environmental contaminants throughout the process. The overall number of steps is reduced, etching steps minimized, and overall reliability of the structure improved. The process also includes field implanting of phosphorus in the isolation oxide for continuous gettering of ionic contaminants.

Description

)7~

50.4311 WAFER FABRICATION BY IMPLANTING THROUGH PROTECTIVE LAYER
Techni al Field This invention relates ~o an improved isoplanar process for fabricating integrated circuits with reduced number o~ process steps and improved reliability by implanting the integrated circuit elements through a protective layer.
Background Art The basic method for fabricating bipolar isoplanar integrated circuits with oxidized isolation is described by Douglas L. Peltzer in United States Patent No. 3,648,125.
A thin silicon epitaxial layer, formed on a silicon substrate is subdivided into electrically isolate~ islands 15 or mesas by a grid of oxidized regions of epitaxial silicon material referred to as oxidized isolation regions or isolation oxide regions. The annular shaped isolation oxide regions defining and separating the epitaxial islands are oxidized through the epitaxial layer to the laterally 20 extending PN junction between the epitaxial layer and substrate, referred to as the isolation junction. The top surfaces of the epitaxial islands and the isolation oxide regions are substantially coplanar.
In the conventional isoplanar process the active a~d 25 passive integrated circuit elements are then formed in the epitaxial islands by a complex sequence of masking and diffusion steps for selectively introducing P-type and N-type dopant materials into different regions of the epitaxial islands defined by the sequence of masks. In the 30 original isoplanar process all of the bipolar regions of P-type conductivity or N-type conductivity are introduced by diffusion. In a typical diffusion sequence, a uniform oxide layer is grown across the epitaxial layer although a layer of other mask material such as nitride layer may be 35 used. A photoresist layer is spun on the oxide layer, the photoresist layer is exposed ~hrough a light mask to a pattern of light, and the exposed or unexposed portions of the photoresist are developed and washed away leaving a photoresist mzsk pattern. The sequence of ~steps involved 7~) in for~ing the photoresist mask are sometimes referred to as a dry mask step or dry mask sequence. A dry mask sequence results in an overlying photoresist mask pattern.
The overlying photoresist mask pattern is then used as an etching mask for etching the exposed portions of the underlying layPr. Typically the portions of the underlying layer exposed through the photoresist mask are selectively removed by a chemical etchant which does not effect the photoresist material. A plasma etch, however, may also be 10 used. The photoresist material is then ehemically removed leaving a mask of oxide, nitride or other mask material.
The sequence of steps by which an underlying layer is etched through the photoresist mask to produce a mask for introducing dopant material is sometimes referred to as a 15 wet mask step or wet mask sequence because of the typical use of chemical etchants.
A traditional isoplanar process is characterized by the following mask sequences:
1.0 Buried Collector Mask
2.0 Isolation Oxide Mask
3.0 Collector Sink Mask
4.0 Nitride or Self-Aligned Transistor Mask
5.0 Emitter Mask or N+ Mask
6.0 Base Mask or P+ Mask
7.0 Gontact Mask
8.0 Etc. Metalization Masks Each of the foregoing mask steps in the sequence with the exception of Base Mask ~.Q involves both a dry mask sequence for forming a photoresist mask pattern, and a wet 30 mask sequence for etching the underlying o~:ide layer to form an oxide mask. The etching, of course, may be accomplished by either a chemical etch or a plasma etch.
The typical diffusion sequence introduce~ selective regions of N-type or r-type conductivity material in the 35 epitaxial islands. The alternating dry mask procedure and wct mask procedure result in the o~iae mask, or other material mask, which then serves zs z diffusion mask for diffusing a dopant material of rhe des-ired conducti~ity type through the openin~s in the m?.s~ lz~;cr. Upon 607~

completio~ of the diffusion step, the oxide mask must be stripped away and a new oxide layer grown. The further diffusion steps then follow, each involving both dry mask and wet mask sequences. A complete account of the diffusion steps of the traditional isoplanar process may be found, for example, in the Peltzer U.S. Patent No.
3,648,125 referred to above.
While Peltzer made a basic contribution to the isoplanar fabrication process by the introduction of 10 isolation oxide regions for isolating the epitaxial islands, a number of disadvantages are attendant upon the continued use of diffusion methods. First, the so called dry mask and wet mask sequences result in exposure of the epitaxial layer to environmental contaminants once the 15 oxide layer has been etched. Furthermore, upon completion of a diffusion step, the oxide layer must be stripped away briefly exposing the entire epitaxial layer to environmental contaminants before the new oxide layer is grown. Second, diffusion affords only imprecise control 20 over introduction of the dopant material because diffusion proceeds laterally away from the mask opening as well as axially into the epitaxial layer. Third, the diffusion sequence of dry masks and wet masks requires an inordinate number of steps which increase the time and expense of the 25 manufacturing process.
As a result, modifications have been introduced bv semiconductor man~facturers into the isoplanar process to reduce the number of steps and to increase reliability.
For example, some of the diffusion steps have been replaced 30 by implant steps in which the dopant material o the selected conductivity type is introduced into the epitaxial layer by a directed ion beam. The present isoplanar processes for forming active and passive elemcnts in the epitaxial islands may therefore typically comprise a hybrid process of diffusion and implanting sLeps. Such hybrid isoplanar processes arc exemplified by the Farrell et al, United States Patent No. 4,199,380.
The isoplanar process has been modified at Fairchild Camera ~ Instrument Corporation o Mountain ~1iew, 3~,'Z~.tj~'7~

California, to substitute an emitter implant step for the emitter diffusion step. Thus, the 5.0 emitter mask involves a dry mask step only in which the photoresist mask pattern is formed and used for selectively implanting the emitter regions. An ion beam of, for example, N~ type dopant material is directed through the selective openings in the photoresist mask for introducing the dopant material into the emitter regions. Similarly, the base regions may be implanted so that the 6.0 base mask step involves a dry mask sequence only, forming a photoresist mask pattern for directing an ion beam, for example, of P+ type dopant material into the base regions.
The hybrid processes of which applicant is aware generally suffer the disadvantage that at one or more occasions through the fabrication process, the protective insulation layer, be it an oxide layer or a nitride layer must be etched or stripped away exposing the underlying epitaxial layer to environmental contaminants. Futhermore, none of the hybrid processes have achieved a full integration of the implant method for introducing dopant material into the fabrication process while retaining in place a passivating nitride layer as a barrier to environmental contaminants. For example, Wen C. Ko et al in U.S. Patent No.
4,433,471, filed 18 January 1982, entitled "Ion Implanted ~emory Cells for High Density Ram", while fully converting to implant methods, do not retain a nitride layer for passivating the structure. While the partial introduction of implant methods increases raliability, there is further opportunity fox substantial ()75 - ~a -reduction in the number of process steps and therefore the fabrication time and expense while passivating the structure substantially throughout the process.
Objects of the Invention It is therefore an object of the present invention to provide a new and improved isoplanar process which fully integrates ion implant methods into the isoplanar process and fully substitutes the ion implant methods for diffusion methods.

Another object of the invention is to provide an improved isoplanar process in which a passivating protective layer is provided over the epitaxial layer throughout the fabrication process. According to this object of the invention there is no stripback of the protective insulating layer and no exposure of the epitaxial layer to environmental contaminants throughout the formation of active and passive elements in the epitaxial islands.
A further object of the invention is to substan-tially reduce the number of steps and sequences in the bipolar isoplanar process thereby reducing fabrication time and expense.
The invention also seeks to increase reliability of devices by, for example, dramatically reducing the parasitic MOS transistor effect caused by contaminant ions in the isolation oxide.
Disclosure of the Invention According to one aspect of the present invention there is provided a method for fabricating a bipolar substantially isoplanar integrated circuit structure on a substrate of semicon-ductor material of a first conductivity type, said substrate being processed by depositing an epitaxial layer of semiconductor material over the substrate thereby forming an isolation junction extending laterally through the structure between the epitaxial layer and substrate, forming a thin epitaxial oxide buffer layer over the epitaxial layer, subdividing said structure into a plurality of epitaxial islands in which active and passive elements are fabricated, and isolating said epitaxial islands relative to each other by forming annular shaped isolation oxide regions of - 5a -oxidized semiconductor material extending through the epitaxlal layer to the isolation junction, wherein the improvement in the method of fabricating said structure comprises:
depositing a uniform nitride layer over the structure thereby passivating the structure and protecting the isolation oxide regions, epitaxial oxide buffer layer and epitaxial layer from contaminants;
implanting collector sink regions in the epitaxial islands by selectively directing a beam of ions of second conduc-~ivity type through the nitride layer and epitaxial oxide buffer layer into the epitaxial layer at collector sink region surface locations;
retaining the nitride layer and epitaxial ox~de buffer layer in place as a barrier to environmental contaminants;
implanting base regions in the epitaxial islands by selectively directing a beam of ions of first conductivity type through the nitride layer and epitaxial oxide buffer layer into the epitaxial layer at base region surface locations before implanting emitter regions;
retaining the nitride layer and epitaxial oxide buffer layer in place as a barrier to environmental contaminants;
forming a self-aligned transistor mask pattern over the nitride layer for defining the surface locations of collector sink, base and emitter regions in self-alignment relative to each other on the epitaxial islands through openings in the self-aligned transistor mask pattern;

l~Z16~75 - 5b -etching the underlying nitride layer through the openings in the self-aligned transistor mask pattern and removing the nitride layer at the surface locations of the collector sink, base and emitter regions while retaining the epitaxial oxide buffer layer in place as a barrier to environmental contaminants;
removing the self-aligned transistor mask pattern, retaining the unetched remainder of the nitride layer in place, and retaining the epitaxial oxide buffer layer in place at the surface locations where the nitride layer was removed by etching;
implanting emitter regions in base regions pre-viously implanted in the epitaxial islands by selectively directing a beam of ions of second conductivity type through the epitaxial oxide buffer layer into the epitaxial layer;
simultaneously annealing the implanted collector sink base and emitter regions thereby providing a substantially isoplanar integrated circuit structure of active and passive elements in the epitaxial islands separated by said isolation oxide regions.
The process of manufacturing a bipolar substantially isoplanar integrated circuit structure begins with a substrate of semiconductor material of first conductivity type. The substrate is typically processed by introducing at least one buried region of dopant material of a second conductivity type in the substrate to function as a buried collector. However, there need not necessarily be in each instance a buried collector layer. An epitaxial layer of semiconductor material is deposited over the ~Zl~ 5 - 5c -substrate and buried region. An isolation PN junction therefore extends laterally through the structure between the epitaxial layer and substrate. A thin epitaxial oxide buffer layer is formed over -the epitaxial layer. The fabrication normally continues by sub-dividing the structure into a plurality of epitaxial islands in which active and passive elements are to be formed, and isolating the epitaxial islands relative to each other by forming annular shaped isolation oxide regions of oxidized semiconductor material extending through the epitaxial layer to the isolation junction.
The objects of the present invention are achieved by depositing a uniform nitride layer or layer of other insulating material over the basic structure, thereby ll'~16~75 passivating the structure and protecting the isolation o~ide regions, epitaxial oxide buffer layer and epitaxial layer from environmental contam;nants. A feature and advantage of the invention is that the uniform layer of nîtride or other insulating material in combination with the epitaxial oxide buffer layer forms a composite protective layer over the structure. According to the invention the composite protective layer is maintained in place throughout a major portion of the steps during which 10 the collector sink, base and emitter regions are introduced into the epitaxial islands. Furthermore, at least a portion of the composite protective layer is a barrier to environmental contaminants throughout the process of introducing collector sink, base and emitter regions into 15 the epitaxial islands. The surface of the epitaxial silicon layer thus remains protected and unexposed until it is finally necessary to deposit the metalization contacts at the surface locations of the respective collector sink, base and emitter regions.
The invention contemplates that the entire sequence of fabricating active and passive elements in the epitaxial islands by introducing selective N-type and P-type regions be accomplished through a passivating protective layer and that such layer be maintained in place throughout the 25 introduction of selectively doped regions un-til the respective surface locations of the collector sink, base and emitter regions are exposed for the deposit of metaliz~tion contacts. This is accomplished according to the present invention by a rearrangement of the 30 conventional masking steps and by the substitution and full integration of implanting methods for diffusion methods.
The present invention therefore provides a fully integrated sequential implanting process directed throu~,h a continuously maintained passivating protective laver.
35 feature and advantage of this asp-ct of the invention is that the wet mask or etchin ,ctepS are minimized and the overall number of steps re~uired for the isoplanar process are reduced. Another feat~re of the inventic,n is that the integrated circuit structure is passivated and protected from environmental contaminants throughout the fabrication of active and passive elements in the epitaxial islands until the metalization contacts are deposited.
In order to accomplish these results 9 the present invention provides the steps of for~ing a sink implant mask of resist material in a pattern over the nitride layer for defining collector sink regions in the epitaxial islands and implanting through the sink implant mask openings by directing a beam of ions of a second conductivity type 10 through the composite protective layer comprising the nitride layer and epitaxial oxide buffer layer. The, energy of the beam is adjusted to implant the collector sink regions in the,epitaxial layer. After removing the sink implant mask while retaining the nitride layer and 15 epitaxial oxide buffer layer in place, the invention contemplates forming a base implant mask of resist material in a pattern over the nitride layer for defining base regions in the epitaxial islands and implanting through the base implant mask openings by directing a beam of ions of 20 first conductivity type through the composite protective layer. The beam energy is adjusted for implanting base regions in the epitaxial layer. This aspect of the present invention provides a further modification and simplification of the isoplanar process by implanting the 25 base before implanting the emitter regions.
The process proceeds by removing the base implant mask, retaining the nitride layer and epitaxial oxide buffer in place as a barrier to environmental contaminants, and for,ming a self-aligned transistor mask pattern over the 30 nitride layer for defining the surface locations of the collector sink, base and emitter regions in alignment relative to each,other. At this point in the improved isoplanar process the invention retains a wet mask or etching step by etching the underlying nitride layer 35 through the openings in the self-aligned transistor mask pattern removing the nitride layer at the surface locations of the collector sink, base and emitter regions.
Importantly, however,the e~itaxial oxide buffer layer, being a portion of the composite passivating protective 6~75 layer is retained in place as a barrier to environmental contaminants. ~fter removing the photoresist self-aligned transistor mask pattern, the invention therefore contemplates retaining the epitaxial oxide buffer layer in place at the surface locations where the nitride layer was removed by etching. Thus, throughout the fabrication of active and passive elements at least a portion of the composite passivating and protective layer is retained in place. According to another aspect of the invention the 10 unetched remainder of the nitride layer is retained in place to function as a nitride self-aligned transistor mask as hereafter described.
Further steps in the improved process comprise forming an emitter implant mask pattern of resist material over the 15 nitride layer and exposed portions of epitaxial oxide buffer layer for defining the emitter regions in the epitaxial islands and implanting through the emitter implant mask openings by directing a beam of ions of second conductivity type through the epitaxial oxide buffer layer.
20 The energy of the ion beam is adjusted for implanting the emitter regions in base regions previously implanted in the epitaxial islands. The successive implanting steps through successive implant masks is followed by the single reduced annealing step of simultaneously annealing the implanted 25 collector sink, base and emitter regions thereby providing the substantially isoplanar integrated circuit structure of active and passive elements which coincide with the epitaxial islands separated by isolation oxide regions.
The invention contemplates a number of additional 30 features and variations. According to further steps the improved process contemplates removing the emitter implant mask while retaining the unetched portions of the nitride layer in place for use of the nitride layer as a nitride layer self-aligned transistor mask. An etching step 35 follo~s by etching the epitaxial oxide buffer layer at the surface locations of the collector sink, base and emitter regions through thè nitride layer self-aligned transistor mask exposing the epitaxial layer at the collector sink, base and emitter surface locations for deposit of metalized lZ1~075 contacts through the nitride layer self-aligned transistor mask. A feature and advantage of the present invention is that the exposure of the epitaxial layer at the collector sin~, bas~ and emitter surface locations may be accomplished by a blanket etching of the portions of the epitaxial oxide layer exposed through the nitride layer self-aligned transistor mask pattern. A contact mask step is therefore entirely eliminated.
Further efficiency is achieved by using the current 10 practice of providing an emitter implant mask pattern formed with openings defining the collector sink regions in addition to the emitter regions. The step of implanting through the emitter implant mask openings therefore comprises directing a beam of ions of second conductivity 15 type for implanting emitter regions while at the same time overdoping the surface locations of the collector sink regions to reduce surface contact resistance. In another improvement according to the invention, the sink implant mask pattern is formed with openings defining the isolation 20 oxide regions in addition to the collector sink surface locations. The step of implanting through the sink implant mask openings therefore comprises directing a beam of ions of second conductivity type for implanting collector sink regions and for field implanting ions of phosphorus into 25 the isolation oxide regions for continuous gettering and for passivating the isolation oxide regions.
The present invention affords a number of advantages and improvements over the conventional fabrication process.
For example, the present invention increases the 30 reliability of the integrated circuit structures. The phosphorus ions field implanted in the isolation oxide getter and passivate contaminant ions in the oxide such as, for example, sodium and potassium ions which typicall,v occur in the oxide as a result of normal manufact~ring 35 processes. Even minute amounts of ccntaminant sodium and potassium ions will migrate in an el~ctric field in the o~ide to the bottom of the o~;ide when a positive charge is applied to an overlying metal ~ontact of the device. The migrating contaminant ions carry positive charges eliciting i;~l6~75 N-type carriers in the underlying silicon substrate. As a result, the underlying P-type material may become effectively N-type forming a parasitic MOS FET transistor with the overlying metal contact. The parasitic MOS
transistor effect produced by contaminant ions in the isolation oxide is responsible for a substantial percentage of the defective devices in any batch produced according to conventional fabrication processes. According to the present invention, the field implant phosphorus ions getter 10 the contaminant ions, passivate the isolation oxide regions, prevent the threshold voltage of the parasitic MOS
transistors from being achieved or exceeded by motion of contaminant ions, and substantially eliminate parasitic MOS
transistor field inversion effects caused by contaminant 15 ions. The percentage of defective devices is therefore dramatically reduced and the percentage of defective devices atrributable to contaminant ion parasitic MOS
transistor effect is substantially eliminated.
According to another feature of the invention, in the 20 growth of isolation oxide regions, the te~perature and other parameters are selected to minimize fracturing of epitaxial islands by the expanding oxide of the isolation oxide regions.
It is apparent that the overall objectives of the 25 present invention are achieved by full integration of implanting techniques in the introduction of active and passive elements into the epitaxial islands, reordering and reduction of masking steps in combination with the implanting methods to simplify the fabrication process, and 30 by maintaining in place at least a portion of a composite passivating protective layer over the entire structure throughout fabrication and introduction of the active and passive elements into the epitaxial islands.
Other objects, features and advantages of the present 35 invention are apparent in the following specification and accompanying drawings.
Brief Fi~ure Description Figure 1 is a fragmentary view in diagrammatic cross section of a portion of an integrated circuit structure at a location where an epitaxial island is to be formed and showing a buried collector layer introduced in the substrate.
Figure 2 is a diagrammatic cross section of the same portion of the integrated eircuit structure showing formation of the epitaxial layer, epitaxial oxide layer and nitride layer.
Figure 3 is a diagrammatic cross section at the same location showing formation of the epitaxial island, mesa, 10 or pedestal.
Figure 4 is a diagrammatic cross section of the epitaxial island showing formation of the isolation oxide regions.
Figure 5 is a diagrammatic cross section of the 15 epitaxial island showing implanting of the collector sink region with simultaneous field implanting of the isolation oxide regions.
Figure 6 is a diagrammatic cross section of the epitaxial island showing implant of the base region.
Figures 6A and 6B are diagrammatic fragmentary cross sections showing the prior art process for introducing the emitter and base regions.
Figure 7 is a diagrammatic cross section of the epitaxial island showing implant of the emitter region w;th 25 simultaneous overdoping of the collector sink surface location for minimizing surface contact resistance.
Figure 8 is a diagrammatic cross section of the epitaxial island showing after etching in preparation for deposition of metalization contacts at the surface 30 locations of the collector sink, base and emitter regions.
Description of Preferred Example_Embodiments and Best Mode of the Invention Figure 1 shows in diagrammatic cross section a ira~mentary portion of a substrate 10 of, for example, 35 P-type silicon in which N-type impurity or dopant material has been introduced to form the buried collector region 12.
The thic~ness of the substrate 10 is not shown to scale and would of course be many times greater. The buried collector region is introduced by the following convention method. First, a silicon oxide layer 14 is grown uniformly across the entire substrate. A dry mask procedure follows in which a photoresist material is spun on the oxide layer to form a uniform photoresist layer. The photoresist is exposed through ~ light mask with openings defining the buried regions. The exposed portions of the photoresist layer are washed away with the developer leaving the photoresist material as an etching mask.
The so-called "dry mask" sequence is followed by &
10 wet mask sequence in which the underlying oxide layer 14 is etched to expose the substrate 10 at the sur~ace locations whe~e impurities are introduced to form the buried collector layers 12. The photoresist mask pattern is then removed leavin~ the oxide layer 14 in the pattern shown in 15 Figure 1 to serve as a diffusion mask. Typically a chemical etchant is used to etch the oxide layer, however, a dry plasma etch may also be used. Upon completion of the so-called "wet mask" sequence, N-type conductivity material is diffused through the openings in diffusion mask 14 to 20 form the buried collector layers 12 as shown in Figure 1.
The buried collector region 12 is doped to a very high level indicated by the notation N~ to increase conductivity of the silicon in the vicinity of the buried collector region. The buried layer 12 serves to collect electrons 25 ejected by the emitter re~ion to the collector sink region hereafter described. While a buried collector region is typical, other collector structures may also be used.
The oxide layer 14 is then stripped off the substrate and epitaxial layer 15 shown in Figure 2 is formed over the 30 substrate. The epitaxial layer 15 is comprised of N-type silicon precipitated on to the substrate in the form of a single-~crystsl layer by an epitaxial chemical vapor deposition type process. h'h le the epitaxial layer and substrate are typically of opposite conductivity type, they 35 may also be of the same conductivity type material. The surface of epitaxial layer 15 is oxidized to form a thin epitaxial oxide layer 16 of silicon dioxide tSiO2).
Epitaxial oxide layer 16 comprises an isoplanar oxide layer which provides stress relief for the next layer, nitride layer 180 ~pitaxial layer 15 must remain a monocrystalline layer which, however, may be stressed and broken ~y the nitride layer 18. Th~ "epi-o~" layer 16 therefor~ provides the buffer for stress relief. Nitride layer 18 is deposited o~er the epitaxial oxide buffer la~er 16 by chemical vapor deposition from an external source. The silicon nitride layer is of the chemical form SiXNyOz ideally comprising Si3N4. The silicon nitride layer is generally referred to herein as the nitride layer 18.
In order to establish the epitaxial islands a nitride masking procedures follows including both dry mask and wet mask sequences. First, the photoresist layer is spun on the nitride layer and exposed through a light mask defining the surface locations of the isolation oxide regions. The 15 exposed or unexposed portions of the photoresist layer are washed away according to whether a positive or negative photoresist material is used, leaving the photoresist mask to function as an etching mask. The dry mask sequence is followed by a wet mask sequence involving three etching 20 steps which may be wet chemical etches or dry plasma etches. In the first etch step the nitride layer 18 is etched through the photoresist mask using a silicon nitride selective etchant and the photoresist mask may then be removed. The underlying epitaxial oxide layer 16 is then 25 etched with an oxide etch using the nitride layer 18 as an etching mask. Finally, the epitaxial layer 15 of N-type silicon is etched in a silicon etching step at locations 2a on either side of the buried layer 12 to form the epitaxial island, mesa or pedestal 25 having a hat or cover formed by 30 the une~ched portions of silicon nitride layer 18 and silicon dioxide layer 16. The silicon etch i5 carried out to a depth of approximately one-half of the epitaxial layer 15.
According to one variation of the present invention, 35 the silicon etching step is carried to a depth slightly greater than the conventional depth and oxide is grown in the isolation o~;ide spaces 20 at a temperature slightly higher than the conventional temperature of 1000C, for example, in the range of 1050C to 1100C. As a result of iZl61D7S

the oxidation of the silicon at a slightly higher temperature range, the fracturing effect of the isolation oxide on the epitaxial island 25 is minimized or eliminated.
Before growth of the isolation oxide, P-type impurities or dopant material is diffused into ~he very top surfaces of the substrate 10 and epitaxial layer 15 underlying the isolation oxide spaces 20. The introduction of P-type conductivity material into the surface locations 1~ lOa and 15a respectively of the substrate 10 and epitaxial layer 15 underlying the isolation oxide regions in combination with the gettering of ion contaminants in the isolation oxide by field implant of phosphorus ions as hereafter described, assures the reliabili~y of the 15 integrated circuit structure by substantially eliminating the proble~ of parasitic MOS (FET) transistor effects between adjacent epitaxial islands. The P-type implant or diffusion, comprised, for example, of boron introduced into the surface areas lOa and l5a provides a channel stop 20 between adjacent mesas or islands. The P-type diffusion of boron may be carried out to a P or P+ level and may be introduced alternatively by implanting with an ion beam or diffusion.
After p~eparation of the surface channel stops, the 25 isolation oxide 22 is grown in the isolation oxide regions or spaces 20 isolating the epitaxial islands 25 from each other by annular shaped isolation oxide regions. During oxidation and growth of the isolation oxide, the epitaxial layer 15 in the vicinity of the isolation oxide regions is 30 entirely consumed so that the isolation oxide portions extend through the epitaxial layer to the isolation junction between epitaxial layer 15 and substrate 10. The silicon oxide grown from silicon in the isolation oxide regions generally occupies twice the volume of the original silicon so that the isolation oxide 22 in the region 20 and the epitaxial islands 25 are substantially isoplanar.
During growth of the isolation oxide, the characteristic birds' heads 22a and birds' beaks 16a form on either side o~ the epitaxial island 25.
I

iZ~075 - .
The remaining portions of the original nitride layer 18 are then stripped off the surface of the integrated circuit structure and a new silicon nitride layer 28 is grown uni~ormLy over the structure as shown in Figur~ 5.
According to conventional procedures, instead of regrowing the silicon nitride layer 28, 2 thick oxide layer would be formed over the structure followed by dry mask and wet mask sequences for introducing the collector sink region hereafter described. Instead, according to the present 10 invention, the new uniform nitride layer 28 is formed over the entire structure which in combination with epitaxial oxide layer 16 forms a composite passivating protective layer across the entire integrated circuit structure.
~ccording to the present invention, there is no need to 15 grow another oxide layer and further steps of etching and growing oxide are eliminated. As hereafter described according to the present invention, implanting techniques are fully integrated into the isoplanar process for fabricating the active and passive elements in the 20 epitaxial islands 25. Nitride provides a sound protective layer for all the elements below including the epitaxial oxide layer 16, isolation oxide 22 and epitaxial silicon 15. The nitride layer 28 prevents accumulation of environmental contaminants and ions in the structure, 25 passivating the wafer. To this end the new nitride layer 28 is formed immediately as shown in Figure 5 after completion of o~idation and growth of the isolation oxide 22 as shown in Figure 4. On the other hand in the conventional process there may be a long period o~ up to 30 six steps during which portion~ of the epitaxial laver and other underlying elements are exposed to environmental contaminants. The improved isoplanar process according to the present invention passivates the wafer in~luding the epi~cxial layer, epitaxi21 oxide layer and isolation oxide 35 immediately.
The collector sink region 30 is then implanted through the passivating silicon nitride ~2ver 28 and epitaxial layer 16 with the layers 28 and 16 re,~ined in place. This is accomplished by ion implantation directing an ion beam lZ~6075 of N-type conductivity, impurity or dopant material, for example, phosphorus, through the respective layers. The ion beam is generated according to conventional procedures and equipment stripping an electron from the phosphorus S atom, applying an accelerating field, and focusing the phosphorus ion beam with plates or magnets. The mass spectrometer effect of the equipment filters out the phosphorus ion beam for implanting at the selective locations in the integrated circuit structure. The ion 10 beam is generated at energy high enough to pass through the nitride layer 28 and epitaxial oxide layer 16 to implant the N-type epitaxial layer 15 with pure phosphorus in the collector sink region 30 to provide an N or N++ implant.
Selective implantation is accomplished by use of a dry 15 mask sequence only. A photoresist layer 35 is spun on the nitride layer 28 and exposed through a light mask pattern which according to the present invention defines through openings, not only the collector sink regions 30, but also the isolation oxide regions 20 and isolation oxide 22. The 20 photoresist layer 35 is developed by washing away the exposed or unexposed portion of photoresist according to whether a positive or negative photoresist material is used, leaving a photoresist mask 35 which functions as an implant mask not only for implanting the collector sink 25 regions 30 but also for field implanting phosphorus ions in-the isolation oxide regions. A typical ion beam energy for implanting a phosphorus ion beam of N-type carriers to achieve an N concentration of carriers in the collector sink region while at the same time field implantin~
30 phosphorus ions for continuous gettering of the isolation oxide is, for example, 180 kev. Such a beam energy - achieves implant of the collector sink region in the epitaxial layer 15 through the passivating nitride layer 28 and the epitaxial oxide layer 16. The collector sink 35 implant and field implant for passivating the isolation oxide may therefore be accomplished simultaneously according to the method of the present invention. The collector sink implant and field implant may, of course, be carried out seouentially. Where the ~-type carrier is 12i6075 phosphorus, however, the invention contemplates simultaneous implant. The phosphorus ion beam is scanned over the surface locations of the isolation oxide regions in addition to the collector sink regions. This may be 5 done simultaneously, according to the present invention, because the passivating phosphorus ion implants will not be etched away in a subsequent oxide etch, as all such etching steps have been eliminated as hereafter more fully appears.
Any contaminants which enter the oxide regions are lOtherefore chemically contained by the gettering ions withou~ any modification in the device performance. Thus, the device performance remains intact and furthermore throughout the step of the sink implant and concurrent field implant, the passivating nitride layer 28 remains in 15place as a barrier to environmental contaminants.
The silicon nitride layer 28 and epitaxial oxide layer 16 are retained while the sin~ i~plant photoresist mask 35 is removed. A new photoresist layer is then spun on the nitride layer 28, exposed through a light mask, and the 20 exposed or unexposed portions are washed away by developer according to whether a positive or negative photoresist material is used, leaving the photoresist mask pattern 36 for implanting the base regions as illustrated in Figure 6.
The photoresist mask pattern 36 thus serves as an implant 25 mask for implanting the base region 40 by directing an ion beam of impurities of P-type conductivity such as a boron ion beam through openings in the photoresist mask with sufficient energy to penetrate the nitride layer 28 and epitaxial oxide layer 16 thereby introducing the P-type 30 base region 40 into the epitaxial layer 15 of epitaxial island 25.
Contrary to the conventional isoplanar process, base region 40 is implanted before the emitter region is introduced into the epitaxial island. This affords a 35 number of advantages. First, implanting the base region permits retaining the protective layer in place. Second, implanting the base 40 as shown in Figures 6 affords a base region of uniform thickness and flat profile. Third, because of the greater control over introduction of i impurities afforded by implanting techniques, there is little l~teral diffusion and the base region 40 and sink region 3D remain separated and non-contiguous. The boron ion beam implant may be carried out with an ener~y of 9 for 5 example, 80 Kev. Furthermore, by implanting the base before the emitter an adequate base width or clearance can be maintained between the lower limit of the emitter region and the lower limit of the base region as hereafter illustrated with reference to Figure 7. This is to be lOcontrasted with the standard process shown in Figure 6A
according to which the emitter 150 is first introduced through the epitaxisl oxide layer 116 and openings in the photoresist mask layer 138 and nitride layer 128 before the base is introduced. As shown in Figure 6B, the base 140 is 15thereafter introduced through openings in the photoresist mask layer 136 and nitride layer 128. Due to the lowe~
total implant stopping power at the openings in the nitride layer 128, the base profile runs deeper below the openings than in the adjacent regions. The uneven depth and profile 200f the base 140 combined with lateral diffusion of the emitter 150 prod~ces a narrow widt-n or separation between the lower limit of the emitter region 150 and the lower limit of the base region 140 at points 145. This narrow separation produces high field regions on the edges of the 25emitters and consequent "leaky" transistors. Not only does the method of the present invention eliminate the problem of uneven base width and profile, but also implanting of the base region i5 accomplished by retaining the co~posite protective layer in place consisting of both the 30passivating nitride layer 28 and epitaxial oxide layer 16.
The photoresist base implant mask 36 is then removed - while retaining the nitride layer 28 in place. A new photoresist layer is spun on the nitride layer and the photoresist layer is then exposed to a self-aligned 35transistor mask pattern. The exposed or unexposed portions of the photoresist layer are developed and washed away according to whether a positive or negative photoresist material is used, leaving a self-zligned transistor (SAT) mask pattern for etching the underlying nitride layer.
I

(375 Such a self-aligned transistor mask pattern is described in the Farrell et al U.S. Patent No. 4,199,380 and the Ko et al Patent No.
4,433,471 referred to above. After formation of the photoresist SAT etching mask pattern, the nitride layer 28 is etched for the first time in the improved isoplanar process according to the invention. Thus, all steps are completed that can be completed with the nitride layer 28 in place before the nitride etch step.
The etching of nitride layer 28 through the photoresist SAT mask pattern results in the nitride layer pattern 28 illustrated in Figure 7. Importantly, only the nitride layer 28 is etched and not the underlying epitaxial oxide layer 16. Epitaxial oxide layer 16 is exposed through the openings etched in the nitride layer 28 at the surface locations of the collector sink base and emitter regions as shown in Figure 7. Viewing the nitride layer 28 and epitaxial oxide layer 16 as a composite protective layer, therefore only a portion of the composite is etched and removed as may be required for the emitter implant step while retaining the epitaxial oxide layer 16 in place as a protective barrier for the epitaxial islands.
After completion of the nitride etch the photoresist SAT mask pattern is removed and a new photoresist layer is spun on the etched nitride layer 28 in preparation for the emitter implant sequence. The new photoresist layer is exposed through a light mask pattern and the exposed or unexposed portions of photoresist are developed and washed away leaving a photoresist emitter region implant mask pattern 38 as illustrated in Figure 7. According to the present practice, openings formed in the photoresist mask pattern - l9a -38 permit not only implanting selective impurities in the emitter regions 50, but also overdoping a surface portion 31 of the collec-tor sink reg.ion 30 to reduce surface contact resistance at the collector sink region.
The emitter implant step is designed to implant, for example, N-type conductivity impurities to a greater concentra-tion of carriers designated by the symbol N++ in Figure 7. The higher concentration and higher conductivity implant is accomplished by directing an ion beam of N-type - - - - l ,Z1f~07-5 .
eonductivity ion impurities such as arsenic ions through the epitaxial oxide layer 16 and into the epitaxial layer thereby implanting the emitter region 50 and the overdoped collector sink surfaee location 31, all as shown in Figure 7. Typically, the ion beam energy for implanting arsenic ions in the emitter region and surface location of the collector sink region is in the order of 100 kev. The progressive migration or diffusion of the collector sink region 30 as illustrated sequentially in Figures S, 6 and 7 10 until the collector sink region 30 contacts the buried collector 12 follows as a result of various heating steps, etc. during ~he isoplanar fabrication process as is well known in the art. The portion 28a of nitride layer 28 serves as a barrier to the N-type conductivity ion beam to 15 maintain separation of the collector sink region 30 and base region 40. Implanting the emitter regions and overdoping the surface locations of the collector sink regions through the epitaxial oxide layer 16 according to the present invention saves additional etching and masking 20 steps required in the conventional isoplanar process.
The photoresist emitter implant mask pattern 38 is then removed and all the implants for the collector sink, base and emitter regions are then simultaneously annealed in a single step also driving the implants for the 25 collector sink region 30 and emitter region 50 to the --appropIiate desired depths are illustrated in Figure 7.
The present invention thus consolidates the separate annealing steps of the conventional process into a single step upon completion of all implants. Prior annealing 30 steps are eliminated thereby simplifying the improved process.
The final step of the improved isoplanar process modifications, according to the present invention, is a blanket etching away of the portions of epitaxial oxide 35 layer 16 exposed through the openings etched in nitride layer 28 as shown in Figure 8. No further masking steps are required for selectively etching away and removing thc portions of epitaxial oxide layer 16 overlying the surface locations of the collector sink, base and emitter regions.

l'Z~t75 Whereas prior art methods would require a further contact masking step to protect the diffused areas while etching a~ay the oxide to prevent undercutting, the present invention merely requires a blanket etching step through the openings in nitride layer 28 which functions effectively as a nitride layer SAT mask for etching and removing the exposed portions of epitaxial oxide layer 16.
Metalization contacts may be deposited directly on the surface locations of the collector sink, base and emitter lO regions without further masking using the etched nitride layer 28 as the effective mask for selective deposition of metalization contacts.
A summary of the improved bipolar isoplanar process steps according to the present invention is as follows:
1.0 Buried Collector Mask 2.0 Isolation Oxide Mask 3.0 Collector Sink Mask (Dry Mask Sequence Only) 6.0 Base Mask or P Mask (Dry Mask Sequence Only) 4.0 Nitride or Self-Aligned Transistor (SAT) Mask 5.0 Emitter Mask or N+ Mask (Dry Mask Sequence Only) The improved isoplanar process of the invention therefore eliminates the 7.0 Contact Mask steps, the 3.0 Collector Sink Mask wet mask or etching sequence and 5.0 25 Emitter Mask wet mask or etching sequence. The passi~ating nitride layer is retained in place until all steps which can be completed with the nitride layer in place are in fact completed. The steps are rearranged to permit optimization of the process with the nitride layer in place 30 and the nitride layer is then etched through the SAT mask sequence only before implanting of the emitter region.
Neverthele~s,-the epitaxial oxide layer, part of the composite protective layer is retained in place even for the emitter implant step. Overall, the number of wet 35etching sequences in comparison with conventional isoplanar processes is reduced from 6 to 2, dry mask sequences reduced from 5 to 4, implant steps increased from 2 to 3, while the annealing steps are consolidated thereby reducing the number of thermal heating steps.

.. .... . .. . _ . .. _ __ _ ._ .. _ . _ i~l6~7~

While the invention has been described with reference to particular example embodiments of bipolar devices with particula. sequences of N-type and P-type conductivity semiconductor materials and regions, the polarity may be reversed with N-type conductivity materials substituted for P-type conductivity materials and vice-versa in accordance with the invention while still preserving all features and advantages. Furthenmore, the invention is intended to cover all modifications and equivalents within the scope of 10 the following claims.

L

Claims (19)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for fabricating a bipolar substantially isoplanar integrated circuit structure on a substrate of semicon-ductor material of a first conductivity type, said substrate being processed by depositing an epitaxial layer of semiconductor material over the substrate thereby forming an isolation junction extending laterally through the structure between the epitaxial layer and substrate, forming a thin epitaxial oxide buffer layer over the epitaxial layer, subdividing said structure into a plurality of epitaxial islands in which active and passive elements are fabri-cated, and isolating said epitaxial islands relative to each other by forming annular shaped isolation oxide regions of oxidized semi-conductor material extending through the epitaxial layer to the isolation junction, wherein the improvement in the method of fabri-cating said structure comprises:
depositing a uniform nitride layer over the structure thereby passivating the structure and protecting the isolation oxide regions, epitaxial oxide buffer layer and epitaxial layer from contaminants;
implanting collector sink regions in the epitaxial islands by selectively directing a beam of ions of second conducti-vity type through the nitride layer and epitaxial oxide buffer layer into the epitaxial layer at collector sink region surface locations;
retaining the nitride layer and epitaxial oxide - 23a -buffer layer in place as a barrier to environmental contaminants;
implanting base regions in the epitaxial islands by selectively directing a beam of ions of first conductivity type through the nitride layer and epitaxial oxide buffer layer into the epitaxial layer at base region surface locations before implanting emitter regions;
retaining the nitride layer and epitaxial oxide buffer layer in place as a barrier to environmental contaminants;
forming a self-aligned transistor mask pattern over the nitride layer for defining the surface locations of collector sink, base and emitter regions in self-alignment relative to each other on the epitaxial islands through openings in the self-aligned transistor mask pattern;
etching the underlying nitride layer through the openings in the self-aligned transistor mask pattern and removing the nitride layer at the surface locations of the collector sink, base and emitter regions while retaining the epitaxial oxide buffer layer in place as a barrier to environmental contaminants;
removing the self-aligned transistor mask pattern, retaining the unetched remainder of the nitride layer in place, and retaining the epitaxial oxide buffer layer in place at the surface locations where the nitride layer was removed by etching;
implanting emitter regions in base regions previously implanted in the epitaxial islands by selectively directing a beam of ions of second conductivity type through the epitaxial oxide buffer layer into the epitaxial layer;
simultaneously annealing the implanted collector sink, base and emitter regions thereby providing a substantially isoplanar integrated circuit structure of active and passive elements in the epitaxial islands separated by said isolation oxide regions.
2. The method of Claim 1 further comprising the step of:
etching the epitaxial oxide buffer layer at the surface locations of the collector sink, base and emitter regions defined by the openings in the nitride layer using the nitride layer as a self-aligned transistor mask thereby exposing the epitaxial layer at the collector sink, base and emitter surface locations on the epitaxial islands of the integrated circuit structure.
3. The method of Claim 2 further comprising the step of depositing metalized contacts at the etched and exposed surface locations of the collector sink, base and emitter regions through the nitride layer self-aligned transistor mask thereby eliminating a contact masking step.
4. The method of Claim 1 comprising the step of directing a beam of ions of second conductivity type into the collector sink regions a second time while implanting emitter regions thereby overdoping the surface locations of the collector sink regions to reduce surface contact resistance.
5. The method of Claim 1 comprising the step of field implanting by selectively directing a beam of phosphorus ions into the isolation oxide regions for continuous gettering and for passivating the isolation oxide regions.
6. The method of Claim 1 comprising the preliminary step of forming the isolation oxide regions in the preferred temperature range of 1050°C to 1100°C thereby substantially reducing the viscosity of the oxidized semiconductor material and eliminating the fracturing of epitaxial islands.
7. The method of Claim 1 comprising the step of field implanting gettering ions of phosphorus in the isolation oxide regions.
8. A method for fabricating elements in a bipolar substantially isoplanar integrated circuit structure comprising a substrate of semiconductor material of a first conductivity type, at least one buried region of dopant material of a second conductivity type introduced in the substrate, an epitaxial layer of semiconductor material deposited over the substrate and buried region thereby forming an isolation junction extending laterally through the structure between the epitaxial layer and substrate, a thin epitaxial oxide buffer layer formed over the epitaxial layer, said structure being subdivided into a plurality of epitaxial islands in which the elements are fabricated, said epitaxial islands being isolated relative to each other by annular shaped isolation oxide regions of oxidized semiconductor material extending through the epitaxial layer to the isolation junction and wherein the improvement in the method of fabricating the elements comprises:
depositing a uniform nitride layer over the structure thereby passivating the structure and protecting the isolation oxide regions, epitaxial oxide buffer layer and epitaxial layer from contaminants;
forming a sink implant mask of resist material in a pattern over the nitride layer for defining collector sink regions in the epitaxial islands through openings formed in the sink implant mask;
implanting through said sink implant mask openings by directing a beam of ions of second conductivity type through the nitride layer and epitaxial oxide buffer layer into the epitaxial layer for implanting collector sink regions in the epitaxial islands;
removing the sink implant mask and retaining the nitride layer and epitaxial oxide buffer layer in place as a barrier to environmental contaminants;
forming a base implant mask of resist material in a pattern over the nitride layer for defining base regions in the epitaxial islands through openings formed in the base implant mask;
implanting through said base implant mask openings by directing a beam of ions of first conductivity type through the nitride layer and epitaxial oxide buffer layer into the epitaxial layer for implanting base regions before implanting the emitter regions;
removing the base implant mask and retaining the nitride layer and epitaxial oxide buffer layer in place as a barrier to environmental contaminants;
forming a self-aligned transistor mask pattern over the nitride layer for defining the surface locations of the collector sink, base and emitter regions in alignment relative to each other through openings in the self-aligned transistor mask pattern;
etching the underlying nitride layer through the openings in the self-aligned transistor mask pattern and removing the nitride layer at the surface locations of the collector sink, base and emitter regions while retaining the epitaxial oxide buffer layer in place as a barrier to environmental contaminants;
removing the self-aligned transistor mask pattern retaining the unetched remainder of the nitride layer in place, and retaining the epitaxial oxide buffer layer in place at the surface locations where the nitride layer was removed by etching;

forming an emitter implant mask pattern of resist material over the nitride layer and exposed portions of epitaxial oxide buffer layer for defining the emitter regions in the epitaxial islands through openings in the emitter implant mask;
implanting through said emitter implant mask openings by directing a beam of ions of second conductivity type through the epitaxial oxide buffer layer and into the epitaxial layer for implanting emitter regions in base regions previously implanted in the epitaxial islands;
simultaneously annealing the implanted collector sink, base and emitter regions thereby providing a substantially isoplanar integrated circuit structure of active elements coinciding with epitaxial islands separated by said isolation oxide regions.
9. The method of Claim 8 further comprising the steps of:
removing the emitter implant mask while retaining the unetched portions of the nitride layer in place for use of the nitride layer as a nitride layer self-aligned transistor mask;
etching the epitaxial oxide buffer layer at the surface locations of the collector sink, base and emitter regions defined by the openings in the nitride layer self-aligned transistor mask thereby eliminating a further masking step and exposing the epitaxial layer at the collector sink, base and emitter surface locations on the epitaxial islands of the integrated circuit structure.
10. The method of Claim 9 wherein said etching step comprises a blanket etching of oxidized semiconductor material through the nitride layer self-aligned transistor mask.
11. The method of Claim 9 further comprising the step of depositing metalized contacts at the etched and exposed surface locations of the collector sink, base and emitter regions through the nitride layer self-aligned transistor mask thereby eliminating a contact mask step.
12. The method of Claim 8 wherein the emitter implant mask pattern is also formed with openings defining the collector sink regions and wherein the step of implanting through said emitter implant mask openings comprises directing a beam of ions of second conductivity type for implanting emitter regions and for overdoping the surface locations of the collector sink regions to reduce surface contact resistance.
13. The method of Claim 8 wherein the sink implant mask is also formed with openings defining the isolation oxide regions and wherein the step of implanting through said sink implant mask openings comprises directing a beam of ions of second conductivity type for implanting collector sink regions and for field implanting ions of phosphorus into the isolation oxide regions for continuous gettering and for passivating the isolation oxide regions.
14. The method of Claim 8 wherein the integrated circuit structure is formed with dopant material of the first conductivity type introduced at the surface of the epitaxial layer and substrate portions which underlie the isolation oxide regions.
15. A method for fabricating a bipolar substantially isoplanar integrated circuit structure comprising a substrate of first conductivity type semiconductor material, an epitaxial layer semiconductor material on the substrate forming an isolation junction extending laterally through the structure between the epitaxial layer and substrate, said structure divided into a plurality of epitaxial islands by annular shaped isolation oxide regions of oxidized semiconductor material extending through the epitaxial layer to the isolation junction, at least some of said isolation islands comprising a collector sink region, a base region, and an emitter region, said collector sink, base and emitter regions having surface locations at the surface of the epitaxial layer, wherein the improvement in the method of fabrication comprises:
forming a passivating composite protective layer across the epitaxial layer including the epitaxial islands and isolation oxide regions prior to fabricating the collector sink, base and emitter regions in the epitaxial islands;

forming a sink implant mask pattern over the composite protective layer and implanting the sink regions according to the sink implant mask pattern by directing a beam of ions of a second conductivity type through the composite protective layer into the epitaxial layer;
removing the sink implant mask pattern while retaining the composite protective layer in place and forming a base implant mask pattern over the composite protective layer;
forming a base implant mask pattern over the composite protective layer and implanting the base regions according to the base implant mask pattern by directing a beam of ions of first conductivity type through the composite protective layer into the epitaxial layer thereby implanting the base regions before the emitter regions;
removing the base implant mask pattern while retaining the composite protective layer in place and forming a self-aligned transistor mask pattern over the composite protective layer;
etching part way through the underlying composite protective layer through the self-aligned transistor mask pattern for removing one component portion of the composite protective layer at the surface locations of the collector sink, base and emitter regions for aligning the surface locations of the collector sink, base and emitter regions while retaining a component portion of the composite protective layer as a barrier to contaminants;
removing the self-aligned transistor mask pattern and forming an emitter implant mask pattern over the partially etched composite protective layer;
implanting the emitter regions according to the emitter implant mask pattern by directing a beam of ions of the second conductivity type through the retained component portion of the composite protective layer and into the base regions of the epitaxial layer;
whereby at least some of said isolation islands are transformed into active elements having implanted collector sink, base and emitter regions with aligned surface locations and whereby the collector sink, base and emitter regions are formed by implanting through a composite protective layer which passivates the structure and protects the epitaxial layer and isolation oxide regions from contamination throughout the fabrication process.
16. The method of Claim 15 further comprising the step of simultaneously annealing the implanted collector sink, base and emitter regions.
17. The method of Claim 15 further comprising the step of blanket etching and removing the remaining component portion of the protective layer etched through the self-aligned transistor mask at the surface locations of the collector sink, base and emitter regions in preparation for depositing metalized contacts at said aligned surface locations.
18. The method of Claim 15 wherein the sink implant mask pattern comprises openings defining the surface locations of the sink regions and the isolation oxide regions and further comprising the step of field implanting gettering ions through the retained component portion of the composite protective layer into the isolation oxide regions for continuous gettering of the oxidized semiconductor material in the isolation oxide regions at the same time as implanting the sink regions.
19. The method of Claim 15 wherein said etching step comprises wet etching.
The method of Claim 15 wherein said etching step comprises plasma etching.
CA000458075A 1983-07-05 1984-07-04 Wafer fabrication by implanting through protective layer Expired CA1216075A (en)

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EP0134166A1 (en) 1985-03-13
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US4498227A (en) 1985-02-12

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