Patent US5346578 - Induction plasma source

[merged small][merged small][merged small][table][merged small][merged small]

INDUCTION PLASMA SOURCE

BACKGROUND OF THE INVENTION

1. Field of the Invention 5 The present invention relates to plasma sources, and

more particularly to induction plasma sources for integrated circuit fabrication.

2. Description of Related Art

Plasma etching is useful in many fields, but particu- 10 larly in the field of microelectronic fabrication. Microelectronic fabrication of integrated circuits requires mass replication of tightly controlled, submicron-sized features in a variety of materials, as well as selective removal of material without causing damage to sensi- 15 tive structures and remaining materials. Illustrative application of plasma etching to microelectronic fabrication of integrated circuits includes ion sputter cleaning, dielectric gap filling involving simultaneous chemical vapor deposition ("CVD") and etch, chemical blan- 20 ket etchback without resist, and chemical pattern etch with resist.

Various plasma source methods and geometric designs for reactors are known for use in plasma deposition and etching. For example, electron cyclotron reso- 25 nance ("ECR") sources are available from Applied Science and Technology, Inc., Woburn, Mass. and from the WAVEMAT Corporation, Plymouth, Mass. Also, wafer cleaning and etching processes have commonly been done with equipment using various cylindrical 30 shaped quartz vessels of various diameters having induction windings of various pitches, either constant or variable, as well as with flat spiral induction windings mounted above the dielectric chamber top plate. Radio frequency ("rf') diode and triode configurations are 35 also known in which the wafer electrode and possibly other electrodes are powered at 13.56 MHz to produce the plasma.

Physical sputtering, one of several plasma etching mechanisms, involves the removal of material by ener- 40 getic ions, which cross the sheath and transfer energy and momentum to the material being etched. As implemented on a great many of the prior art inductively coupled cavity and/or diode and triode machines, physical sputtering suffers from a number of disadvantages, 45 including low material removal rate, poor etch uniformity due to poor ion current uniformity, and electrical damage to the substrate from ion bombardment and implantation due to high ion energies. The ECR sources provide improved performance, but with considerably 50 greater complexity than induction-type sources.

Hence, a need continues for plasma source systems that are able to provide good ion density to achieve high etch rates, ion current uniformity to achieve uniform removal of material over large diameter sub- 55 strates, and operational stability at low pressure to achieve a more uniform ion distribution in the plasma and better directionality of ions in high aspect ratio structures, all in a generally simple machine implementation. 60

SUMMARY OF THE INVENTION

The present invention achieves high ion density, good ion current uniformity, and stable low pressure operation in a generally simple machine implementa- 65 tion.

In one embodiment of the present invention, an induction plasma source, the induction coil is hemispheri

cal in shape. A chamber into which a substrate may be introduced is disposed inside the induction coil. In a further embodiment, the induction coil follows the contour of a hemispherically shaped vessel, which contains the chamber. In yet a further embodiment, the power source is a low frequency source having a frequency of about 450 KHz and a power in the range of 200-2000 watts, and the pressure is a low pressure of about 0.1-100 mTorr.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section view of a hemispherical induction plasma source and related components of a plasma etch system.

FIG. 2 is a perspective cut-away view of the hemispherical induction plasma source of FIG. 1.

FIG. 3 is a plan view of the connection between the hemispherical inductor and the rf matching network of FIG. 1.

FIG. 4 is a plan view of the connection between the hemispherical inductor and the plasma chamber of FIG. 1.

FIG. 5 is an equivalent circuit of the hemispherical induction plasma source of FIG. 1.

FIG. 6 is a graph of etch rate versus ion source power for the hemispherical induction ion source of FIG. 1.

FIG. 7 is a graph of ion current uniformity for the hemispherical induction ion source of FIG. 1 and a standard diode etch apparatus.

DESCRIPTION OF THE PREFERRED
EMBODIMENT

A hemispherical induction plasma source 1 is shown in cross-section in FIG. 1 and in a simplified perspective in FIG. 2. The hemispherical induction plasma source 1 is contained within a stainless steel source housing 10 measuring 26.62 cm high and 43.82 cm wide, and includes a hemispherical induction coil 18 that is provided in an expanding spiral pattern on four winding forms—only forms 12 and 14 are illustrated for clarity. Four forms are used to simplify assembly of the induction coil 18, although other form types such as a unitary form are suitable as well, depending on the manufacturing techniques employed. The winding forms, e.g. forms 12 and 14, are made of any suitable material, which include dielectric materials such as nylon. The induction coil 18 is held in place inside channels in the winding forms, e.g. 12 and 14, by any suitable dielectric strapping, adhesive, or cement. The winding forms, including forms 12 and 14, are securely attached to the housing 10 in any convenient manner, as by bolts or adhesive.

The induction coil 18 is copper tubing having an inner diameter of 3.0 mm and an outer diameter of 4.75 mm. The hemispherical induction coil 18 has a radius to centerline of 7.75 cm. The expanding spiral pattern of the induction coil 18 is made of thirty-six windings. The first winding is nearly coplanar with substrate 32 and each subsequent winding spirals upward with a 2.432 degree angular displacement for a total of 36 coils.

During processing operations, the induction coil 18 is positioned about a vacuum chamber 30 contained within a quartz vessel or bell jar 20, in conjunction with a stainless steel chamber top plate 24 of any suitable thickness, illustratively 1.91 cm thick. Preferably, the vessel 20 is hemispherically shaped so that there is a balanced coupling of rf (uniform dielectric spacing) into the vacuum cavity. Generally, the vessel material is an

3 4

insulating dielectric having sufficient structural integ- sputter clean involves the use of a plasma obtained from

rity to withstand a vacuum. Suitable materials include a suitable inert gas such as argon at low pressure to

quartz, pyrex, aluminum oxide (AI2O3, also known as remove material from the surface of the substrate by

sapphire), polyamide, and other oxide or nitride com- momentum transfer. In the illustrative arrangement of

posites. Illustratively, the radius of the vessel 20 is 17.78 5 the induction system 1 for etch clean shown in FIG. 1,

cm, and the vessel material is quartz having a thickness argon gas is introduced into the chamber 30 through a

of 0.51 cm. The induction coil 18 follows the hemi- single port 58 (FIG. 1) located in the chamber sidewall

spherical contour of the vessel 20, which is capable of just below the platen 40. Chemical etching uses reactive

holding a vacuum and contains the substrate, illustra- gases instead of an inert gas in typically a higher pres

tively a semiconductor wafer 32 containing integrated 10 sure regime than an ion sputter clean, and is suitable for

circuit chips in fabrication. etchback or for pattern etch where a photoresist or

The housing 10 is mounted onto the chamber top other masking material is present. Because of the higher

plate 24 in any convenient manner. FIG. 1 shows the pressure or greater reactivity of species, an arrangement

housing 10 as being engaged by an rf seal 22, which of the induction system for chemical etching (not

includes copper leaves to prevent spurious rf emissions 15 shown) preferably uses a symmetrical multiple port

from the induction plasma source 1. arrangement about the substrate for introducing the

The semiconductor wafer 32, illustratively 200 mm in reactive gases. PECVD uses different reactive gases

diameter, is supported within the chamber 30 by an that induce film deposition. An arrangement of the

electrically conductive (e.g. stainless steel) wafer sup- induction system for PECVD (not shown) preferably

port pedestal 42 that includes a platen 40 having a stain- 20 uses the symmetrical multiple port arrangement. When

less steel portion 44 underlying the wafer 32 and a ce- used with careful substrate bias control, the induction

ramie dark space ring 46 extending beyond and in the system for PECVD is suitable for dielectric gap filling, plane of the platen portion 44. The diameter of the A vacuum system (not shown) of any suitable type is

portion 44 is 18.35 cm, and the outer diameter of the connected to the transfer region 60 for evacuating the

dark space ring 46 is 28.62 cm. Under the platen 40 is a 25 chamber 30. Suitable vacuum systems are well known

dark space shield 50, which has an outer diameter of in the art. After chamber 30 is evacuated, process gas,

20.32 cm. which for an ion sputter clean is preferably argon, is

The pedestal 42 is capable of vertical motion, which furnished to the chamber 30 through the port 58 to

is imparted by any suitable mechanism (not shown). The attain a desired pressure of process gas. Illustratively for

position of the pedestal depends on whether the plasma 30 an ion sputter clean, sufficient argon is introduced to

etch system is operating in process mode or in wafer establish a low pressure in the range of about 0.1-100

transfer mode. In process mode, the platen 40 is posi- mTorr, and preferably 0.1-10 mTorr. tioned within the chamber 30, as shown in FIG. 1. Bel- The radio frequency ("rf') subsystem of the induc

lows 52, which is provided to isolate the mechanical tion plasma source 1 includes matching capacitors 6 and

components of the pedestal drive system at atmospheric 35 8, which are enclosed within a stainless steel rf match

pressure from the vacuum in chambers 30 and 60, is well enclosure 2. Capacitors 6 and 8 are connected to bus

extended. The wafer 32 rests on the pedestal 40, within bars (only bus bar 4 shown), and the assembly is

the process chamber 30. mounted onto a dielectric block 5 which is mounted on

For wafer unloading and loading, the pedestal 40 is the housing 10. lowered into a wafer transfer region 60, which is 7.54 40 The induction coil 18 is coupled to the rf matching cm in height and includes at one end a sealable wafer network capacitors 6 and 8 as shown in the detail of transfer opening 26 having a height of 4.60 cm. The FIG. 3. Capacitors 6 and 8 each have one terminal bellows 52 is well compressed, and three lifter pin- screwed into the copper bus bar 4 and the other termis—only pins 54 and 56 are shown—protrude through nal screwed into copper bus bar 204. Bus bar 4 is conholes (not shown) in the platen 40 so as to support the 45 nected to the low frequency source 410 (FIG. 5). Bus wafer 32 in a stationary position within the transfer bar 204 is connected to end 206 of the copper tubing of region 60 as the pedestal 42 lowers. The sealable wafer which the induction coil 18 is formed through fitting transfer opening 26 is provided to permit a wafer trans- 208. Fitting 208 is screwed into a channel through the port arm (not shown) access beyond the wafer transfer bus bar 204. Another fitting 210 is screwed into the flange 28 into the transfer region 60 during wafer trans- 50 other end of the channel. Teflon tubing 212 is connected fer mode. Suitable wafer transport arms and associated to the fitting 210 for delivering a cooling fluid. The mechanisms are well known in the art. In a wafer trans- induction coil 18 is coupled to the grounded top plate 24 fer operation, tines on the end of the transport arm are as shown in the detail of FIG. 4. Bus bar 302 is bolted to inserted under the wafer 32 as it is supported by the the housing 10 by bolt 304, and is connected to end 306 lifter pins (e.g. pins 54 and 56). The transport arm is 55 of the copper tubing of which the induction coil 18 is raised to lift the wafer 32 off of the lifter pins, so that formed through fitting 308. Fitting 308 is screwed into when the transport arm is retracted, the wafer 32 is a channel through the bus bar 302. Another fitting 310 removed from the transfer region 60. A new wafer is is screwed into the other end of the channel. Teflon substituted on the tines, and the transport arm is then tubing 312 is connected to the fitting 310 for draining a moved into a position over the lifter pins (e.g. 54 and 60 cooling fluid.

56). The transport arm is lowered to deposit the wafer The rf subsystem of the induction plasma source 1 is 32 onto the lifter pins, and then withdrawn. The pedes- represented in FIG. 5. The power source includes a low tal 42 is raised to cause the wafer 32 to be deposited on frequency source 410 and a high frequency source 420. the platen 40. The low frequency source 410 has a frequency of about The induction source 1 is suitable for use in a variety 65 450 KHz and a power in the operating range of of applications, including ion sputter clean, chemical 200-2000 watts. The low frequency source 410 is conblanket etchback, chemical pattern etch, and plasma- nected to the induction wiring 18 through a low freenhanced chemical vapor deposition ("PECVD"). Ion quency matching network that includes the capacitors 6

« ZurückWeiter »

Patente

Induction plasma source