US20050017325A1 - Method for fabricating an NPN transistor in a BICMOS technology - Google Patents
Method for fabricating an NPN transistor in a BICMOS technology Download PDFInfo
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- US20050017325A1 US20050017325A1 US10/781,329 US78132904A US2005017325A1 US 20050017325 A1 US20050017325 A1 US 20050017325A1 US 78132904 A US78132904 A US 78132904A US 2005017325 A1 US2005017325 A1 US 2005017325A1
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- 229910052814 silicon oxide Inorganic materials 0.000 claims description 34
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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
- 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
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
- H01L29/08—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions with semiconductor regions connected to an electrode carrying current to be rectified, amplified or switched and such electrode being part of a semiconductor device which comprises three or more electrodes
- H01L29/0804—Emitter regions of bipolar transistors
-
- 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
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
- H01L29/10—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions with semiconductor regions connected to an electrode not carrying current to be rectified, amplified or switched and such electrode being part of a semiconductor device which comprises three or more electrodes
- H01L29/1004—Base region of bipolar transistors
-
- 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
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/70—Bipolar devices
- H01L29/72—Transistor-type devices, i.e. able to continuously respond to applied control signals
- H01L29/73—Bipolar junction transistors
- H01L29/732—Vertical transistors
Definitions
- the present invention relates to the field of integrated circuits and more specifically to the fabrication of an NPN transistor.
- FIG. 12A of this patent application An example of NPN transistor obtained by using this technology is shown in FIG. 12A of this patent application, which is reproduced identically in appended FIG. 1 .
- This NPN transistor is formed in an epitaxial layer 2 which is above a buried layer 3 formed in a P-type silicon substrate (not shown). The transistor is formed in a window made in a thick oxide layer 5 . References 21 and 22 designate thin silicon oxide and silicon nitride layers which are not necessary for the description of the bipolar transistor. Region 23 is a P-type doped polysilicon layer called the base polysilicon since the base contact diffusion 32 is formed from this silicon layer. Polysilicon layer 23 is coated with an encapsulation silicon oxide layer 24 . A central emitter-base opening is formed in layers 22 and 23 altogether. A thin silicon oxide layer 31 covers the sides of polysilicon layer 23 and the bottom of the opening.
- an N-type high energy implant 30 meant for the forming of a sub-collector region with a selected doping level is performed.
- the walls of the emitter-base opening are coated with a silicon nitride layer 44 .
- Polysilicon lateral spacers 43 are formed on the sides of the opening.
- an intrinsic base implant 33 is formed before the forming of silicon nitride region 44 and of polysilicon spacers 43 .
- a highly-doped N-type polysilicon layer 46 from which is formed emitter region 49 is deposited.
- Polysilicon layer 46 is coated with an encapsulation oxide layer 47 .
- the general structure is coated with an insulating and planarizing layer 51 through which are formed emitter contact openings 55 joining polysilicon layer 46 and base contact openings 56 joining polysilicon layer 23 . Further, a collector contact (not shown) is made via an N-type drive-in towards buried layer 3 .
- the emitter-base opening penetrates slightly into the thickness of epitaxial layer 2 . This inevitably results from the fabrication process and possible defects in the selectivity of the etching of polysilicon layer 23 with respect to the etching of the substrate silicon.
- the depth of the penetration is not precisely controlled and can for example vary of ⁇ 20 nm around a provided value of 30 nm according to slight variations of the fabrication parameters. This results in variable characteristics for the NPN transistor, having a variable distance between the extrinsic base and the intrinsic base and thus having a fluctuating resistance of access to the base. Further, the bottom surface area of the opening—emitter surface area—results from an end of doped polysilicon etching and risks of being of poor quality, which is also prejudicial to the stability of the characteristics of the transistor.
- An object of the present invention is to provide an NPN transistor of the same type as that of FIG. 1 but the parameters of which can be controlled accurately independently from the fluctuations of the fabrication parameters.
- Another object of the present invention is to provide such a transistor wherein the stray capacitance between the extrinsic base and the collector is reduced.
- Another object of the present invention is to provide such a transistor wherein the stray capacitances and the resistance of access to the base are adjustable.
- the present invention provides a transistor of NPN type implemented in an epitaxial layer within a window defined in a thick oxide layer, including an opening formed substantially at the center of the window, this opening penetrating into the epitaxial layer down to a depth of at least the order of magnitude of the thick oxide layer, the walls of the opening being coated with a layer of silicon oxide and with a layer of silicon nitride; a polysilicon spacer formed on the lateral walls and a portion of the bottom wall of the opening; an N-type highly-doped polysilicon layer formed in the opening and in contact with the epitaxied layer at the bottom of the opening within the space defined by the spacer; an N-type doped region at the bottom of the opening; a first P-type doped base region at the bottom of the opening; a second lightly-doped P-type region on the sides of the opening; and a third highly-doped P-type region formed in the vicinity of the upper part of the opening, this third region being in contact with an
- the transistor further includes a fourth P-type doped intermediary region between the third and second regions.
- the collector is formed vertically of a portion of the epitaxied layer, of an overdoped region resulting from an implant in the opening and of a buried layer.
- the present invention also provides a method for fabricating an NPN transistor in an epitaxial layer of type N, including the steps of defining a window in a thick oxide region; depositing a polysilicon layer and a silicon oxide layer; substantially opening at the center of the window the silicon oxide and polysilicon layers; performing a thermal oxidation; forming in the opening an insulating layer of a first material which is selectively etchable with respect to the silicon oxide; forming spacers in a second material which are selectively etchable with respect to the silicon oxide and to the first material; opening the bottom of the opening within the area defined by the spacers; depositing an N-type doped polysilicon layer; and after the step of opening of the polysilicon and silicon oxide layers, the step of further opening to a determined depth the epitaxial layer and of implanting a P-type doping in the epitaxial layer at the bottom of the opening and on the walls thereof.
- the implant step is a step of oblique implant under low incidence.
- the method further includes a second step of oblique implant under strong incidence and at high dose of a P-type doping.
- the method includes, after the step of formation of an opening in the epitaxial layer, the step of implanting an N-type doping to form in the epitaxial layer an N-type collector region at a higher doping level close to a buried layer of type N + formed under this epitaxial layer.
- the first material is silicon nitride.
- the second material is polysilicon.
- the present invention also aims at a transistor obtained by this method.
- FIG. 1 shows an NPN transistor fabricated by a method described the incorporated by reference patent application referred to above;
- FIGS. 2 to 7 show successive steps of fabrication of a transistor according to the present invention.
- FIG. 8 shows a curve of the doping concentration according to the depth.
- FIG. 2 shows an initial step of fabrication of an NPN-type bipolar transistor according to the present invention.
- a window is defined in a thick oxide layer 102 .
- a layer 103 open more widely than window 102 and which may have been used in a previous step of protection of this window during the performing of other steps has also been shown.
- Layer 103 is for example a silicon oxide layer of a thickness of 20 to 30 nanometers covered with a silicon nitride layer also of a thickness of 20 to 30 nanometers. This layer 103 will not be shown in the following drawings since it has no functional role in the bipolar transistor to be described.
- a highly-doped for example by implant after deposition (typically BF 2 at a dose of 5 10 15 under 20 keV), P-type silicon layer 105 , a silicon oxide layer 106 , and a masking resist layer 108 are successively deposited.
- implant after deposition typically BF 2 at a dose of 5 10 15 under 20 keV
- the thickness of thick oxide layer 102 can be around 500 nm, the thickness of silicon oxide layer 105 around 200 nm, the thickness of silicon oxide layer 106 around 300 nm, and the thickness of resist layer 108 around 1000 nm (1 ⁇ m).
- an opening is made by photolithography in masking layer 108 .
- This opening is disposed substantially centrally in the window formed in thick oxide layer 102 . If the window in thick oxide layer 102 has a width of around 1200 nm, the opening in the resist layer has a width of around 400 to 800 nm, for example 600 nm.
- an anisotropic etching of the monosilicon of epitaxial layer 101 is also performed. This etching is continued for a determined duration to reach a selected depth of penetration into the silicon. This depth will for example be around 300 to 1000 nm, for example 600 nm. It should be noted that this depth is far from being negligible and is of the order of magnitude of thick oxide layer 102 (500 nm). As will be seen hereafter, the choice of this depth enables selection of desired characteristics for the NPN transistor.
- resist layer 108 is removed and an oxidizing annealing is performed to develop a silicon layer 110 within the previously formed opening.
- This layer develops on the apparent surfaces of monosilicon 101 and polysilicon 105 .
- an annealing in the presence of oxygen at a temperature of 850 to 900° C. can be performed for one quarter of an hour.
- the boron or other P-type doping contained in polysilicon 105 diffuses into the underlying silicon to form a base contact region 112 , of type P, the junction depth of which is for example around 100 nm.
- the first implant is performed under oblique incidence at an angle from 1° to 10° as the wafer turns with respect to the axis of implant.
- a doped area which, after the annealing, has the shape illustrated in the drawing, and includes a deeper implanted area 114 at the bottom of the opening and a shallower implanted area 115 on the sides of the opening is thus obtained.
- This first implant is for example a boron implant performed under 5 keV with a dose of 2.10 13 at./cm 2 .
- the second implant is also performed under oblique incidence, as the wafer is rotated, but with a larger angle of incidence than the preceding angle, from 30° to 50°, for example 45°, to implant a doping only in an upper part of the sides of the opening formed in epitaxied layer 101 .
- An implanted region 117 the doping level of which is intermediary between the level of doping of regions 114 - 115 and that of region 112 is thus obtained.
- This second implant is for example an implant performed from a boron fluoride (BF 2 ) under high energy (45 keV) and with a relatively high dose, for example 10 14 atoms/cm 2 .
- this second implant although constituting a preferred embodiment of the present invention, is optional.
- FIG. 7 shows the structure according to the present invention at a practically final step of fabrication.
- a silicon nitride layer 120 has first been deposited on the entire surface of the device, and especially inside the opening, after which a polysilicon layer 121 has been deposited.
- the polysilicon layer has been etched, as shown in the drawing, to only leave in place spacers along the walls of the opening.
- the portions of the silicon nitride layer unprotected by spacers 121 are removed.
- the apparent portion of thermal silicon oxide layer 110 is removed at the bottom of the opening and an in situ highly-doped N-type polysilicon layer 123 is deposited.
- a thermal annealing is then performed to diffuse at the bottom of the opening an N-type doped region 125 forming the emitter of the bipolar transistor.
- the collector part of the bipolar transistor according to the present invention which has not been shown in FIGS. 2 to 6 is also shown in FIG. 7 .
- This collector part corresponds to a portion of epitaxial layer 101 located under the base-emitter opening and more specifically includes a region 130 formed by implant from the opening immediately after the step illustrated in FIG. 4 (before removal of resist layer 108 ) aid developing above a buried layer of type N + 131 (itself formed on a silicon wafer of type P, not shown).
- a collector region 130 effectively localized laterally and in depth under emitter region 125 and intrinsic base region 114 is thus obtained.
- FIG. 8 shows an example of doping concentration which can be obtained according to the present invention in a cross-sectional view taken along the axis of the base-emitter opening. There successively appear:
- emitter region 125 the surface concentration of which is around 10 20 at./cm 3 ,
- the maximum doping level of which is around 10 19 at./cm 3 .
- the doping level of which is for example around 10 15 at./cm 3 .
- the thickness of region 125 can be around 60 nm
- the total thickness of region 114 under the bottom of the opening can be around 120 nm
- the thickness of the epitaxial layer free of overdoping can be around 200 nm
- the thickness of the adapted doping collector region 130 can be around 200 nm.
- An essential characteristic of the present invention is to provide an opening of non-negligible depth in epitaxial layer 101 and to provide several levels of base doping around and at the bottom of this opening.
- the doping level of intrinsic base region 114 can be set as desired and the resistance of the extrinsic base including regions 115 and 117 towards base contact region 112 can be adjusted as desired to optimize the base resistance, to reduce the base-emitter and base-collector capacitances, and to improve the reverse characteristics of the emitter-base junction.
- these base-emitter and base-collector capacitances essentially depend on the distance between the more doped part 112 and emitter region 114 on the one hand, and the more doped regions of collector 130 on the other hand.
- the depth of the opening and the base doping levels can be adjusted according to the desired results.
- the deposition of a silicon nitride layer may be provided at the interface between polysilicon layer 105 and silicon oxide layer 106 .
- the apparent edge, on the side of the opening of this additional silicon nitride layer, will weld with silicon nitride layer 120 upon deposition thereof.
- silicon nitride layer 120 and polysilicon layer 121 may be used. These two materials only have to be etched selectively with respect to each other and with respect to the silicon oxide, and the second material has to be etchable so as to form spacers.
Abstract
The present invention relates to a bipolar transistor of NPN type implemented in an epitaxial layer within a window defined in a thick oxide layer, including an opening formed substantially at the center of the window, this opening penetrating into the epitaxial layer down to a depth of at least the order of magnitude of the thick oxide layer, an N-type doped region at the bottom of the opening, a first P-type doped region at the bottom of the opening, a second lightly-doped P-type region on the sides of the opening, and a third highly-doped P-type region in the vicinity of the upper part of the opening, the three P-type regions being contiguous and forming the base of the transistor.
Description
- 1. Field of the Invention
- The present invention relates to the field of integrated circuits and more specifically to the fabrication of an NPN transistor.
- 2. Discussion of the Related Art
- In a patent application filed on even day herewith under attorney docket number S1022/7945 and incorporated herein by reference, a method for fabricating a bipolar transistor compatible with a BICMOS technology (that is, a technology enabling the simultaneous fabrication of bipolar transistors and of complementary MOS transistors) is described.
- An example of NPN transistor obtained by using this technology is shown in
FIG. 12A of this patent application, which is reproduced identically in appendedFIG. 1 . - This NPN transistor is formed in an
epitaxial layer 2 which is above a buriedlayer 3 formed in a P-type silicon substrate (not shown). The transistor is formed in a window made in athick oxide layer 5.References Region 23 is a P-type doped polysilicon layer called the base polysilicon since thebase contact diffusion 32 is formed from this silicon layer.Polysilicon layer 23 is coated with an encapsulationsilicon oxide layer 24. A central emitter-base opening is formed inlayers silicon oxide layer 31 covers the sides ofpolysilicon layer 23 and the bottom of the opening. In this opening, an N-typehigh energy implant 30 meant for the forming of a sub-collector region with a selected doping level is performed. The walls of the emitter-base opening are coated with asilicon nitride layer 44. Polysiliconlateral spacers 43 are formed on the sides of the opening. Before the forming ofsilicon nitride region 44 and ofpolysilicon spacers 43, anintrinsic base implant 33 is formed. After the spacers have been formed, a highly-doped N-type polysilicon layer 46 from which is formedemitter region 49 is deposited. Polysiliconlayer 46 is coated with anencapsulation oxide layer 47. The general structure is coated with an insulating and planarizinglayer 51 through which are formedemitter contact openings 55 joiningpolysilicon layer 46 andbase contact openings 56 joiningpolysilicon layer 23. Further, a collector contact (not shown) is made via an N-type drive-in towards buriedlayer 3. - Referring to
FIG. 1 , the emitter-base opening penetrates slightly into the thickness ofepitaxial layer 2. This inevitably results from the fabrication process and possible defects in the selectivity of the etching ofpolysilicon layer 23 with respect to the etching of the substrate silicon. - Actually, the depth of the penetration is not precisely controlled and can for example vary of±20 nm around a provided value of 30 nm according to slight variations of the fabrication parameters. This results in variable characteristics for the NPN transistor, having a variable distance between the extrinsic base and the intrinsic base and thus having a fluctuating resistance of access to the base. Further, the bottom surface area of the opening—emitter surface area—results from an end of doped polysilicon etching and risks of being of poor quality, which is also prejudicial to the stability of the characteristics of the transistor.
- An object of the present invention is to provide an NPN transistor of the same type as that of
FIG. 1 but the parameters of which can be controlled accurately independently from the fluctuations of the fabrication parameters. - Another object of the present invention is to provide such a transistor wherein the stray capacitance between the extrinsic base and the collector is reduced.
- Another object of the present invention is to provide such a transistor wherein the stray capacitances and the resistance of access to the base are adjustable.
- To achieve these and other objects, the present invention provides a transistor of NPN type implemented in an epitaxial layer within a window defined in a thick oxide layer, including an opening formed substantially at the center of the window, this opening penetrating into the epitaxial layer down to a depth of at least the order of magnitude of the thick oxide layer, the walls of the opening being coated with a layer of silicon oxide and with a layer of silicon nitride; a polysilicon spacer formed on the lateral walls and a portion of the bottom wall of the opening; an N-type highly-doped polysilicon layer formed in the opening and in contact with the epitaxied layer at the bottom of the opening within the space defined by the spacer; an N-type doped region at the bottom of the opening; a first P-type doped base region at the bottom of the opening; a second lightly-doped P-type region on the sides of the opening; and a third highly-doped P-type region formed in the vicinity of the upper part of the opening, this third region being in contact with an N-type doped polysilicon layer, the three P-type regions being contiguous and forming the base of the transistor.
- According to an embodiment of the present invention, the transistor further includes a fourth P-type doped intermediary region between the third and second regions.
- According to an embodiment of the present invention, the collector is formed vertically of a portion of the epitaxied layer, of an overdoped region resulting from an implant in the opening and of a buried layer.
- The present invention also provides a method for fabricating an NPN transistor in an epitaxial layer of type N, including the steps of defining a window in a thick oxide region; depositing a polysilicon layer and a silicon oxide layer; substantially opening at the center of the window the silicon oxide and polysilicon layers; performing a thermal oxidation; forming in the opening an insulating layer of a first material which is selectively etchable with respect to the silicon oxide; forming spacers in a second material which are selectively etchable with respect to the silicon oxide and to the first material; opening the bottom of the opening within the area defined by the spacers; depositing an N-type doped polysilicon layer; and after the step of opening of the polysilicon and silicon oxide layers, the step of further opening to a determined depth the epitaxial layer and of implanting a P-type doping in the epitaxial layer at the bottom of the opening and on the walls thereof.
- According to an embodiment of the present invention, the implant step is a step of oblique implant under low incidence.
- According to an embodiment of the present invention, the method further includes a second step of oblique implant under strong incidence and at high dose of a P-type doping.
- According to an embodiment of the present invention, the method includes, after the step of formation of an opening in the epitaxial layer, the step of implanting an N-type doping to form in the epitaxial layer an N-type collector region at a higher doping level close to a buried layer of type N+ formed under this epitaxial layer.
- According to an embodiment of the present invention, the first material is silicon nitride.
- According to an embodiment of the present invention, the second material is polysilicon.
- The present invention also aims at a transistor obtained by this method.
- These objects, characteristics and advantages as well as others, of the present invention, will be discussed in detail in the following non-limiting description of specific embodiments of the present invention, in relation with the accompanying drawings.
-
FIG. 1 shows an NPN transistor fabricated by a method described the incorporated by reference patent application referred to above; - FIGS. 2 to 7 show successive steps of fabrication of a transistor according to the present invention; and
-
FIG. 8 shows a curve of the doping concentration according to the depth. -
FIG. 2 shows an initial step of fabrication of an NPN-type bipolar transistor according to the present invention. On an N-typeepitaxial layer 101, a window is defined in athick oxide layer 102. As an example, alayer 103 open more widely thanwindow 102 and which may have been used in a previous step of protection of this window during the performing of other steps has also been shown.Layer 103 is for example a silicon oxide layer of a thickness of 20 to 30 nanometers covered with a silicon nitride layer also of a thickness of 20 to 30 nanometers. Thislayer 103 will not be shown in the following drawings since it has no functional role in the bipolar transistor to be described. - At the step illustrated in
FIG. 3 , a highly-doped, for example by implant after deposition (typically BF2 at a dose of 5 1015 under 20 keV), P-type silicon layer 105, asilicon oxide layer 106, and amasking resist layer 108 are successively deposited. - As an example of numeric values, in an embodiment adapted to the fabrication of submicron dimensioned integrated circuits, the thickness of
thick oxide layer 102 can be around 500 nm, the thickness ofsilicon oxide layer 105 around 200 nm, the thickness ofsilicon oxide layer 106 around 300 nm, and the thickness ofresist layer 108 around 1000 nm (1 μm). - Then, an opening is made by photolithography in
masking layer 108. This opening is disposed substantially centrally in the window formed inthick oxide layer 102. If the window inthick oxide layer 102 has a width of around 1200 nm, the opening in the resist layer has a width of around 400 to 800 nm, for example 600 nm. - At the step illustrated in
FIG. 4 , successive anisotropic plasma etchings ofsilicon oxide layer 106 andpolysilicon layer 105 have been performed. - According to an aspect of the present invention, an anisotropic etching of the monosilicon of
epitaxial layer 101 is also performed. This etching is continued for a determined duration to reach a selected depth of penetration into the silicon. This depth will for example be around 300 to 1000 nm, for example 600 nm. It should be noted that this depth is far from being negligible and is of the order of magnitude of thick oxide layer 102 (500 nm). As will be seen hereafter, the choice of this depth enables selection of desired characteristics for the NPN transistor. - At the step illustrated in
FIG. 5 , resistlayer 108 is removed and an oxidizing annealing is performed to develop asilicon layer 110 within the previously formed opening. This layer develops on the apparent surfaces ofmonosilicon 101 andpolysilicon 105. To reach an oxide thickness of around 5 nm, an annealing in the presence of oxygen at a temperature of 850 to 900° C. can be performed for one quarter of an hour. During this annealing step, the boron or other P-type doping contained inpolysilicon 105 diffuses into the underlying silicon to form abase contact region 112, of type P, the junction depth of which is for example around 100 nm. - At the following step illustrated in
FIG. 6 , two successive implants of a P-type doping arc performed. - The first implant is performed under oblique incidence at an angle from 1° to 10° as the wafer turns with respect to the axis of implant. A doped area which, after the annealing, has the shape illustrated in the drawing, and includes a deeper implanted
area 114 at the bottom of the opening and a shallower implantedarea 115 on the sides of the opening is thus obtained. This first implant is for example a boron implant performed under 5 keV with a dose of 2.1013 at./cm2. - The second implant is also performed under oblique incidence, as the wafer is rotated, but with a larger angle of incidence than the preceding angle, from 30° to 50°, for example 45°, to implant a doping only in an upper part of the sides of the opening formed in
epitaxied layer 101. An implantedregion 117, the doping level of which is intermediary between the level of doping of regions 114-115 and that ofregion 112 is thus obtained. This second implant is for example an implant performed from a boron fluoride (BF2) under high energy (45 keV) and with a relatively high dose, for example 1014 atoms/cm2. - The implementation of this second implant, although constituting a preferred embodiment of the present invention, is optional.
-
FIG. 7 shows the structure according to the present invention at a practically final step of fabrication. Asilicon nitride layer 120 has first been deposited on the entire surface of the device, and especially inside the opening, after which apolysilicon layer 121 has been deposited. The polysilicon layer has been etched, as shown in the drawing, to only leave in place spacers along the walls of the opening. Then, the portions of the silicon nitride layer unprotected byspacers 121 are removed. Afterwards, the apparent portion of thermalsilicon oxide layer 110 is removed at the bottom of the opening and an in situ highly-doped N-type polysilicon layer 123 is deposited. A thermal annealing is then performed to diffuse at the bottom of the opening an N-type dopedregion 125 forming the emitter of the bipolar transistor. - The collector part of the bipolar transistor according to the present invention which has not been shown in FIGS. 2 to 6 is also shown in
FIG. 7 . This collector part corresponds to a portion ofepitaxial layer 101 located under the base-emitter opening and more specifically includes aregion 130 formed by implant from the opening immediately after the step illustrated inFIG. 4 (before removal of resist layer 108) aid developing above a buried layer of type N+ 131 (itself formed on a silicon wafer of type P, not shown). Acollector region 130 effectively localized laterally and in depth underemitter region 125 andintrinsic base region 114 is thus obtained. -
FIG. 8 shows an example of doping concentration which can be obtained according to the present invention in a cross-sectional view taken along the axis of the base-emitter opening. There successively appear: -
emitter region 125, the surface concentration of which is around 1020 at./cm3, -
intrinsic base region 114, the junction concentration of which is around some 1018 at./cm3, - a portion of
epitaxial layer 101, the doping level of which is around 1016 at./cm3, -
region 130, the maximum doping level of which is around 1017 at./cm3, - buried
layer 131, the maximum doping level of which is around 1019 at./cm3, and - the P-type substrate on which the structure is formed, the doping level of which is for example around 1015 at./cm3.
- On the assumption that the thickness of the epitaxial layer is around 1.4 μm (1400 nm) and that the bottom of the opening is at 600 nm from the surface, the thickness of
region 125 can be around 60 nm, the total thickness ofregion 114 under the bottom of the opening can be around 120 nm, the thickness of the epitaxial layer free of overdoping can be around 200 nm, and the thickness of the adapteddoping collector region 130 can be around 200 nm. - An essential characteristic of the present invention is to provide an opening of non-negligible depth in
epitaxial layer 101 and to provide several levels of base doping around and at the bottom of this opening. Thus, the doping level ofintrinsic base region 114 can be set as desired and the resistance of the extrinsicbase including regions base contact region 112 can be adjusted as desired to optimize the base resistance, to reduce the base-emitter and base-collector capacitances, and to improve the reverse characteristics of the emitter-base junction. Indeed, these base-emitter and base-collector capacitances essentially depend on the distance between the moredoped part 112 andemitter region 114 on the one hand, and the more doped regions ofcollector 130 on the other hand. The depth of the opening and the base doping levels can be adjusted according to the desired results. - Of course, the present invention is likely to have various alterations, modifications, and improvements which will readily occur to those skilled in the art. In particular, the base contact, emitter contact and collector contact recoveries have not been described but can be performed in the way described in relation with
FIG. 1 . - To avoid any risk of short-circuit between
base polysilicon region 105 andemitter polysilicon region 123, the deposition of a silicon nitride layer may be provided at the interface betweenpolysilicon layer 105 andsilicon oxide layer 106. The apparent edge, on the side of the opening of this additional silicon nitride layer, will weld withsilicon nitride layer 120 upon deposition thereof. Thus, any risk of penetration of etching agent or any etching during a plasma etching at the interface between the edges ofsilicon oxide layer 106 and the external wall ofsilicon nitride layer 120 is avoided. - Several numeric values have been indicated as an example, to show that the invention applies to structures of very small dimensions, but the present invention also applies more generally to the implementation of NPN transistors of different dimensions wherein it is desired to optimize the resistances and stray capacitances. Similarly, the use of specific dopings and implant modes has been indicated as an example. Those skilled in the art may use several known variants for the implementation of the dopings.
- Several variants of materials can also be performed. For example, other materials may be used for
silicon nitride layer 120 andpolysilicon layer 121. These two materials only have to be etched selectively with respect to each other and with respect to the silicon oxide, and the second material has to be etchable so as to form spacers. - Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only as defined in the following claims and the equivalents thereto.
Claims (31)
1-9. Canceled
10. A central base bipolar transistor made according to a method for fabricating an integrated circuit including complementary MOS transistors and an NPN-type bipolar transistor, comprising the steps of:
forming an N-type epitaxial layer on a P-type substrate, a buried layer being provided at least at a location of the bipolar transistor,
forming a thick oxide layer at locations other than locations of wells of the MOS transistors, of a collector well region of the bipolar transistor and of a base-emitter region of the bipolar transistor,
forming the wells of the MOS transistors and the collector well of the bipolar transistor,
forming the insulated gates, the spacers and sources and drains of the MOS transistors,
covering the entire structure with a protection layer including a first layer of silicon oxide and a first layer of silicon nitride,
opening the protection layer at the base-emitter location of the bipolar transistor,
forming a first P-type doped layer of polysilicon or amorphous silicon and a second layer of encapsulation oxide,
opening these last two layers at a center of the emitter-base region of the bipolar transistor,
diffusing the doping contained in the first silicon layer into the underlying epitaxial layer, to form the extrinsic base of the bipolar transistor,
implanting an N-type collector doping,
implanting a P-type doping to form an intrinsic base of the bipolar transistor,
depositing a second silicon nitride layer, depositing a second layer of polysilicon, anisotropically etching the second polysilicon layer to leave in place spacers in the vertical portions thereof, and removing the silicon nitride,
depositing a third N-type doped polysilicon layer and diffusing the doping to form the emitter of the bipolar transistor,
clearing the areas to be silicided,
performing a silicidation,
depositing a planarized insulating layer, and
performing the metallizations;
wherein the opening of the first silicon layer and of the second encapsulation layers performed so as to leave in place a central area of these layers.
11. A method according to claim 10 , wherein the first layer of silicon oxide has a thickness of around 20 nm and the first silicon nitride layer has a thickness of around 30 nm.
12. A method according to claim 10 , wherein the first silicon layer has a thickness of around 200 nm and the second silicon oxide layer has a thickness of around 300 nm.
13. A method according to claim 10 , wherein the first silicon layer is obtained by deposition of undoped amorphous silicon, and then by superficial implant of BF2.
14. A method according to claim 10 , wherein a surface area of the collector well is doped at a same time as the sources and drains of the N-channel MOS transistors.
15. A method according to claim 10 , wherein the opening of the protection layer at the emitter-base location is of smaller extent than the corresponding opening in the thick oxide.
16. A lateral PNP transistor made according to a method for fabricating an integrated circuit including complementary MOS transistors and an NPN-type bipolar transistor, comprising the steps of:
forming an N-type epitaxial layer on a P-type substrate, a buried layer being provided at least at a location of the bipolar transistor,
forming a thick oxide layer at locations other than locations of wells of the MOS transistors, of a collector well region of the bipolar transistor and of a base-emitter region of the bipolar transistor,
forming the wells of the MOS transistors and the collector well of the bipolar transistor,
forming the insulated gates, the spacers and sources and drains of the MOS transistors,
covering the entire structure with a protection layer including a first layer of silicon oxide and a first layer of silicon nitride,
opening the protection layer at the base-emitter location of the bipolar transistor,
forming a first P-type doped layer of polysilicon or amorphous silicon and a second layer of encapsulation oxide,
opening these last two layers at a center of the emitter-base region of the bipolar transistor,
diffusing the doping contained in the first silicon layer into the underlying epitaxial layer, to form the extrinsic base of the bipolar transistor,
implanting an N-type collector doping,
implanting a P-type doping to form an intrinsic base of the bipolar transistor,
depositing a second silicon nitride layer, depositing a second layer of polysilicon, anisotropically etching the second polysilicon layer to leave in place spacers in the vertical portions thereof, and removing the silicon nitride,
depositing a third N-type doped polysilicon layer and diffusing the doping to form the emitter of the bipolar transistor,
clearing the areas to be silicided,
performing a silicidation,
depositing a planarized insulating layer, and
performing the metallizations;
wherein:
the base region corresponds to the epitaxial layer formed above a buried layer of type N+,
the emitter region is formed by the same implant as the sources and drains of the P-channel MOS transistors, and
the collector region is formed from a portion of the first polysilicon layer.
17. A method according to claim 16 , wherein the first layer of silicon oxide has a thickness of around 20 nm and the first silicon nitride layer has a thickness of around 30 nm.
18. A method according to claim 16 , wherein the first silicon layer has a thickness of around 200 nm and the second silicon oxide layer has a thickness of around 300 nm.
19. A method according to claim 16 , wherein the first silicon layer is obtained by deposition of undoped amorphous silicon, and then by superficial implant of BF2.
20. A method according to claim 16 , wherein a surface area of the collector well is doped at a same time as the sources and drains of the N-channel MOS transistors.
21. A method according to claim 16 , wherein the opening of the protection layer at the emitter-base location is of smaller extent than the corresponding opening in the thick oxide.
22. A MOS transistor resistant to electrostatic discharges made according to a method for fabricating an integrated circuit including complementary MOS transistors and an NPN-type bipolar transistor, comprising the steps of:
forming an N-type epitaxial layer on a P-type substrate, a buried layer being provided at least at a location of the bipolar transistor,
forming a thick oxide layer at locations other than locations of wells of the MOS transistors, of a collector well region of the bipolar transistor and of a base-emitter region of the bipolar transistor,
forming the wells of the MOS transistors and the collector well of the bipolar transistor,
forming the insulated gates, the spacers and sources and drains of the MOS transistors,
covering the entire structure with a protection layer including a first layer of silicon oxide and a first layer of silicon nitride,
opening the protection layer at the base-emitter location of the bipolar transistor,
forming a first P-type doped layer of polysilicon or amorphous silicon and a second layer of encapsulation oxide,
opening these last two layers at a center of the emitter-base region of the bipolar transistor,
diffusing the doping contained in the first silicon layer into the underlying epitaxial layer, to form the extrinsic base of the bipolar transistor,
implanting an N-type collector doping,
implanting a P-type doping to form an intrinsic base of the bipolar transistor,
depositing a second silicon nitride layer, depositing a second layer of polysilicon, anisotropically etching the second polysilicon layer to leave in place spacers in the vertical portions thereof, and removing the silicon nitride,
depositing a third N-type doped polysilicon layer and diffusing the doping to form the emitter of the bipolar transistor,
clearing the areas to be silicided,
performing a silicidation,
depositing a planarized insulating layer, and performing the metallizations;
wherein the contact drain of the MOS transistor is recovered by a portion of the first polysilicon layer extending above a portion of the substrate and is also used to establish a diffusion continuing at the drain area.
23. A method according to claim 22 , wherein the first layer of silicon oxide has a thickness of around 20 nm and the first silicon nitride layer has a thickness of around 30 nm.
24. A method according to claim 22 , wherein the first silicon layer has a thickness of around 200 nm and the second silicon oxide layer has a thickness of around 300 nm.
25. A method according to claim 22 , wherein the first silicon layer is obtained by deposition of undoped amorphous silicon, and then by superficial implant of BF2.
26. A method according to claim 22 , wherein a surface area of the collector well is doped at a same time as the sources and drains of the N-channel MOS transistors.
27. A method according to claim 22 , wherein the opening of the protection layer at the emitter-base location is of smaller extent than the corresponding opening in the thick oxide.
28. A high voltage MOS transistor made according to a method for fabricating an integrated circuit including complementary MOS transistors and an NPN-type bipolar transistor, comprising the steps of:
forming an N-type epitaxial layer on a P-type substrate, a buried layer being provided at least at a location of the bipolar transistor,
forming a thick oxide layer at locations other than locations of wells of the MOS transistors, of a collector well region of the bipolar transistor and of a base-emitter region of the bipolar transistor,
forming the wells of the MOS transistors and the collector well of the bipolar transistor,
forming the insulated gates, the spacers and sources and drains of the MOS transistors,
covering the entire structure with a protection layer including a first layer of silicon oxide and a first layer of silicon nitride,
opening the protection layer at the base-emitter location of the bipolar transistor,
forming a first P-type doped layer of polysilicon or amorphous silicon and a second layer of encapsulation oxide,
opening these last two layers at a center of the emitter-base region of the bipolar transistor,
diffusing the doping contained in the first silicon layer into the underlying epitaxial layer, to form the extrinsic base of the bipolar transistor,
implanting an N-type collector doping,
implanting a P-type doping to form an intrinsic base of the bipolar transistor,
depositing a second silicon nitride layer, depositing a second layer of polysilicon, anisotropically etching the second polysilicon layer to leave in place spacers in the vertical portions thereof, and removing the silicon nitride,
depositing a third N-type doped polysilicon layer and diffusing the doping to form the emitter of the bipolar transistor,
clearing the areas to be silicided,
performing a silicidation,
depositing a planarized insulating layer, and performing the metallizations;
wherein:
the high voltage MOS transistor is formed in an insulated P well;
the gate insulating layer of the high voltage MOS transistor corresponds to a portion of the protection layer including a first layer of silicon oxide and a first layer of silicon nitride;
the gate of the high voltage MOS transistor is formed from the first layer of doped polysilicon and is coated with the second layer of encapsulation oxide, the gate being laterally framed with spacers formed by the second silicon nitride layer and the second polysilicon layer; and
the source and drain contact recovery regions of the high voltage MOS transistor are formed of areas doped by diffusion from a deposition of a portion of the third polysilicon layer.
29. A method according to claim 28 , wherein the first layer of silicon oxide has a thickness of around 20 nm and the first silicon nitride layer has a thickness of around 30 nm.
30. A method according to claim 28 , wherein the first silicon layer has a thickness of around 200 nm and the second silicon oxide layer has a thickness of around 300 nm.
31. A method according to claim 28 , wherein the first silicon layer is obtained by deposition of undoped amorphous silicon, and then by superficial implant of BF2.
32. A method according to claim 28 , wherein a surface area of the collector well is doped at a same time as the sources and drains of the N-channel MOS transistors.
33. A method according to claim 28 , wherein the opening of the protection layer at the emitter-base location is of smaller extent than the corresponding opening in the thick oxide.
34. An EPROM transistor made according to a method for fabricating an integrated circuit including complementary MOS transistors and an NPN-type bipolar transistor, comprising the steps of:
forming an N-type epitaxial layer on a P-type substrate, a buried layer being provided at least at a location of the bipolar transistor,
forming a thick oxide layer at locations other than locations of wells of the MOS transistors, of a collector well region of the bipolar transistor and of a base-emitter region of the bipolar transistor,
forming the wells of the MOS transistors and the collector well of the bipolar transistor,
forming the insulated gates, the spacers and sources and drains of the MOS transistors,
covering the entire structure with a protection layer including a first layer of silicon oxide and a first layer of silicon nitride,
opening the protection layer at the base-emitter location of the bipolar transistor,
forming a first P-type doped layer of polysilicon or amorphous silicon and a second layer of encapsulation oxide,
opening these last two layers at a center of the emitter-base region of the bipolar transistor,
diffusing the doping contained in the first silicon layer into the underlying epitaxial layer, to form the extrinsic base of the bipolar transistor,
implanting an N-type collector doping,
implanting a P-type doping to form an intrinsic base of the bipolar transistor,
depositing a second silicon nitride layer, depositing a second layer of polysilicon, anisotropically etching the second polysilicon layer to leave in place spacers in the vertical portions thereof, and removing the silicon nitride,
depositing a third N-type doped polysilicon layer and diffusing the doping to form the emitter of the bipolar transistor,
clearing the areas to be silicided,
performing a silicidation,
depositing a planarized insulating layer, and performing the metallizations;
wherein:
a first gate of the EPROM transistor, the associated spacers and a source and drain of the EPROM transistors are formed at the same time as those of the MOS transistors;
an insulator between gates corresponds to a portion of the protection layer, and a second gate of the EPROM transistor corresponds to the first polysilicon layer.
35. A method according to claim 34 , wherein the first layer of silicon oxide has a thickness of around 20 nm and the first silicon nitride layer has a thickness of around 30 nm.
36. A method according to claim 34 , wherein the first silicon layer has a thickness of around 200 nm and the second silicon oxide layer has a thickness of around 300 nm.
37. A method according to claim 34 , wherein the first silicon layer is obtained by deposition of undoped amorphous silicon, and then by superficial implant of BF2.
38. A method according to claim 34 , wherein a surface area of the collector well is doped at a same time as the sources and drains of the N-channel MOS transistors.
39. A method according to claim 34 , wherein the opening of the protection layer at the emitter-base location is of smaller extent than the corresponding opening in the thick oxide.
Priority Applications (1)
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US10/781,329 US20050017325A1 (en) | 1996-11-19 | 2004-02-18 | Method for fabricating an NPN transistor in a BICMOS technology |
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FR9614411A FR2756101B1 (en) | 1996-11-19 | 1996-11-19 | METHOD FOR MANUFACTURING AN NPN TRANSISTOR IN BICMOS TECHNOLOGY |
US08/969,800 US6156616A (en) | 1996-11-19 | 1997-11-13 | Method for fabricating an NPN transistor in a BICMOS technology |
US69663300A | 2000-10-25 | 2000-10-25 | |
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US10/785,667 Expired - Lifetime US6984872B2 (en) | 1996-11-19 | 2004-02-24 | Method for fabricating an NPN transistor in a BICMOS technology |
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US20080230872A1 (en) * | 2007-03-19 | 2008-09-25 | Nam-Joo Kim | Bipolar transistor and method for manufacturing the same |
US7494887B1 (en) * | 2004-08-17 | 2009-02-24 | Hrl Laboratories, Llc | Method and apparatus for fabricating heterojunction bipolar transistors with simultaneous low base resistance and short base transit time |
US20090212365A1 (en) * | 2008-02-25 | 2009-08-27 | Elpida Memory, Inc. | Semiconductor device and method of manufacturing the same |
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US6940151B2 (en) * | 2002-09-30 | 2005-09-06 | Agere Systems, Inc. | Silicon-rich low thermal budget silicon nitride for integrated circuits |
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US7494887B1 (en) * | 2004-08-17 | 2009-02-24 | Hrl Laboratories, Llc | Method and apparatus for fabricating heterojunction bipolar transistors with simultaneous low base resistance and short base transit time |
US20080230872A1 (en) * | 2007-03-19 | 2008-09-25 | Nam-Joo Kim | Bipolar transistor and method for manufacturing the same |
US20090212365A1 (en) * | 2008-02-25 | 2009-08-27 | Elpida Memory, Inc. | Semiconductor device and method of manufacturing the same |
US7888737B2 (en) * | 2008-02-25 | 2011-02-15 | Elpida Memory, Inc. | Semiconductor device and method of manufacturing the same |
Also Published As
Publication number | Publication date |
---|---|
FR2756101A1 (en) | 1998-05-22 |
FR2756101B1 (en) | 1999-02-12 |
EP0843351A1 (en) | 1998-05-20 |
JP3065006B2 (en) | 2000-07-12 |
US6156616A (en) | 2000-12-05 |
US6984872B2 (en) | 2006-01-10 |
US20040164378A1 (en) | 2004-08-26 |
JPH10189788A (en) | 1998-07-21 |
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