CA1236970A - Chemical vapor deposition apparatus - Google Patents

Abstract

Abstract of the Invention Chemical vapor deposition reaction chamber glassware includes an upper reaction chamber cover and a wafer boat support plate. A gas collector means has an upper edge supporting the wafer boat support, and the upper portion thereof communicates with gas flow openings in the wafer support plate for removal of spent CVD gases from the reaction chamber. Gas injectors enclosed within the gas collectors pass upwardly through the wafer support plate.
Unique wafer boats of several types are supported on the wafer boat support.

Description

FIELD OE THE INVENTION

This invention relates to a chemical vapor deposition apparatus.

Chemical Vapor Deposition (CVD) is the process of depositing a solid material from a gaseous phase onto a substrate by means of a chemical reaction. The deposition reaction involved is generally thermal decomposition, chemical oxidation, or chemical reduction. In one example of thermal decomposition, organometallic compounds are transported to the substrate surface as a vapor and are reduced to the elemental metal state on the substrate surface.

For chemical reduction, the reducing agent most usually employed is hydrogen, although metal vapors can also be used. The substrate can also act as a reductant as in the case of tungsten hexafluoride reduction by silicon. The substrate can also supply one element of a compound or a]loy deposit. The CVD process can be used to deposit many elements and alloys as well as compounds including oxides, nitrides and carbides.

In the present invention, CVD technology can be used to manufacture deposits on substrates for a variety of purposes.
Tungsten carbide and aluminum oxide wear coatings on cutting tools; corrosion resistant coatings of tantalum, boron nitride, -silicon carbide and the like and tungsten coatings on steel to reduce erosion can be applied according to this invention. The apparatus and method is particularly advantageous in manufacturing solid state electronic devices and energy conversion devices.
Chemical vapor deposition of electronic materials is described by T.L. Chu et al, J. Bac. Sci. Technol. 10, 1 (1973) and B.E. Watts, Thin Solid Films 18, 1 ~1973).
They describe the formation and doping of epitaxial films of such materials as silicon, germanium and GaAs, for example. In the field of energy conversion, the CVD
process provides materials for nuclear fission product retention, solar energy collection, and superconduction. A
summary of the chemical vapor deposition field is provided by W~A. Bryant, "The Fundamentals of Chemical Vapour Deposition" in Journal of Materials Science 12, 1285 (1977)~
The deposition parameters of temperature, pressure, the ratio of reactant gases, and amount and distribution of gas flow critically determine the deposition rates and the ability of a particular system to provide the desired uniformity and quality of deposition. The }imitations of prior art systems stem from their inability to adequately control one or more of these factors or from deposit contamination.
DESCRIPTION OF THE PRIOR ART
The reaction chambers employed for chemical vapor deposition are generally classified as cold wall or as hot wall systems. In cold wall systems, the substrate is heated by inductive coupling, radiant heating or direct electrical resistance heating of internal support elements.
Hot wall systems rely on radiant heatiny elements arranged to create a heated reaction and deposition zone. Con-duction and convection heating approaches have also been used in hot wall systems.

:~ 3 Cold wall systems for chemical vapor deposition are described in U.S Patents 3,594,227, 3,699,298, 3,704,987, and ~,263,872. In these systems, the semiconductor wafers are positioned inside a vacuum chamber, and induction coils are arranged exterior to the vacuum chamber. The wafers are mounted on a susceptible material adapted for heating by RF energy. By localizing heat to the immediate semi-conductor wafer area, chemical vapor deposition is limited to the heated areas. Since the unheated walls are below CVD temperatures, deposition on the walls is reduced. The temperatures in the reaction zone are usually not as uniform as those obtained with hot wall systems.
.S. Patent 3,705,567 is directed to a system for doping semiconductor wafers with a doping compound. The chamber containing the wafers extends into the oven in a cantilever supported system. Heating elements are provided along the sides, and the temperatures of the centrally located wafers would vary substantially from those at the ends Diffusion of vapor is perpendicular to the wafer orientation, and the wafers are not exposed to uniform concentrations of doping compound. The edge to center, wafer to wafer, and batch to batch uniformity required for advanced semiconductor devices such as VLSI (very large scale integration) devices can not be achieved with this system. This is a closed, vapor deposition system and does not provide for positive gas flow using a carrier gas.
Hot will CVD systems currently used in making semi-conductor materials are most commonly converted doping ovens. These have long tubular reactors of quart or similar inert material, and heat is provided by heating elements coiled around the outside of the cylindrical 7~

portion. The reactor ends are not heated, and tempera-ture variance is so severe that only a portion in the center of the deposition chamber (typically one-third of the heated total) is useful. Equilibrium temperature variations between parts of the limited reaction zone typically exceeds 4C. The tube walls become coated, are difficult to remove and clean, and are a source of debris. The wafers are positioned in a boat which is cantilevered from beyond the end of the tubular reactor, the wafers being reloaded by full retraction of the cantilevered support from the chamber. The floor area occupied by a single converted doping oven and associated equipment (for a 30 inch effective reaction zone) is about 70 to 80 sq. feet. These converted ovens have severe limitations for use in manufacturing advanced integrated circuit components, frequently contaminating the semiconductor wafers and causing a high rejection rate. Sustaining power requirements are excessive, and the unit capacity i5 limited by the lengthy time required to reach thermal equilibrium Prior to this invention, apparatus has not been available to manu-facture the precision, high quality coatings desired by the semiconductor industry for the most advanced integrated circuit components such as VLSI devices.
This is a consequence of the increased requirements for the uniform and homogeneous physical and electrical properties such as dielectric strength, resistivity and the like.

SUMMARY OE THE INVENTION

7~:3 A chemical vapor deposition reaction chamber of this invention comprises an upper reaction chamber cover means and a wafer boat support plate means, the upper reaction cover means having a top and sidewalls with lower edges contact-ing the wafer boat support plate to define the reaction chamber, gas collector means having an upper edge supporting the wafer boat support and defining a gas removal means, the passageway defined by the upper portions thereof communicating with gas flow openings in the wafer support plate to provide for removal of spent CVD gases from the reaction chamber, gas injec-tor means enclosed within the gas removal means and passing upward through the wafer support plate.

According to a preferred embodiment of the invention the components of the reaction chamber are quartz glass.

According to an aspect of the invention the gas injector means comprises at least one gas supply tube, the lower end thereof having a flared connecting means for frictionally engaging a gas supply means, the upper end thereof comprising a gas distributor means. The axis of the gas distributor means is substantially perpendicular to the axis of the gas supply tube and the gas distributor means has a plurality of holes in the walls in the walls thereof for directing CVD gas flow into the reaction chamber.

BRIEF DESCRIPTION OF THE DRAWINGS
-Figure 1 is a cross-sectional view of the CVD device of this invention.
Figure 2 is a par-tial, cross-sectional view of the detailed flange construction of the CVD device shown in Figure 1, left portion.
Figure 3 is a partial, cross-sectional view of the detailed flange construction of the CVD device shown in Figure 1, right portion.
Figure 4 is a cross-sectional, detailed vlew of the construction of the mounting flange of the inner vacuum chamber base.
Figure 5 is a cross-sectional view of the inner deposition reaction chamber and gas collector construction.
Figure 6 is a cross-sectional view of the lower support structure for the inner deposition reaction chamber and gas distributorO
Detailed DescriDtion of the Invention The terms chemical vapor deposition" and "CVD", as used herein, are defined to include modifications of the process which increase or change the reactivity, chemical properties or chemical composition of the reactant gases while retaining the basic characteristics of chemical vapor deposition processes. Thus, processes such as plasma assisted chemical vapor deposition, uv excited (ultraviolet light excited) chemical vapor deposition, microwave excited chemical vapor deposition and the like in which reactant gas molecules are converted to more reactive entities are included within the meaning of these terms as used herein.
The term "radiant heat source(s)", as used herein, includes any device, system or means for heating whereby at least a part of the heat is transferred by radiation.
It is recognized and intended that heat transfer by conduction and convection will also occur. The "radiant heat source" can be any material having an elevated temperature, without limitations as to how the temperature elevation was affected. Resistance heating elements and ''3~f~

coatings, heat lamps, heated liquids and solutions, and microwave or induction heated materials can function as "radiant heat sources", for example.
Referring to Figure 1, a cross-sectional view of the chemical vapor deposition device of this invention is shown. The environment for the chemical vapor deposition is controlled within a zone defined by the domed housing 2 and domed base 4. These are constructed from a composition which is substantially transparent to radient heat.
Resistance heating elements 6 and 8 are illustrated. The radient heat passing through the walls of the domed housing 2 and domed base 4 heats the chemical vapor deposition zone defined by these components. The resistance heating elements 6 and 8 are separated from the respective domed housing wall 2 and dome base 4 by an air space 10 and 12, respectively. By avoiding conductive heat transfer from the heating elements 6 and 8 to the walls of the domed housing 2 and domed base 4, the heat load thereon is reduced and as is described in greater detail hereinafter, thermal damage to heat sensitive sealing components is prevented.
The resistance heating elements 6 are supported on the inner housing wall 14 which is separated from the outer housing shell 16 by insulation 18. The resistance heating element 8 is separated from the support base 20 by insulation 22.
The term "dome" as used herein with respect to the housing 2 and base 4 can have a variety of configurations.
For example, the top 24 of the domed housing 2 can be hemispherical. Preferably, the top has a flattened configuration, that is, has a spherical radius which is greater than the radius of the cylindrical sidewall 26.

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In a similar manner, the top 28 of the dome base 4 can have a flattened configuration, the radius of curvature thereof in a vertical plane through the central axis being greater than the radius of the base of the sidewall 30. The upper end of the axially concentric inner cylinder 29 of the domed base flares outwardly to become the upper portion 28 integral therewith. The inner deposition reaction chamber is defined by the upper reaction chamber wall 32 and support plate 34. The plate 34 which supports wafers 36 held in a vertical plane by the boats 38 can also be a plurality of rods. The domed reaction chamber wall 32 has outwardly extending projections ~0 which are engaged by projections 42 when the outer housing components are lifted to expose the inner deposition chamber. The gas supply conduit 44 extenas from the inner deposition reaction chamber defined by the domed reaction chamber housing 32 through the support plate 34 and down the center of the gas collector 46. Conduit 48 passing through the support base 20 can be used to reduce gas pressure in the interior of the domed base 4.
The temperature uniformity in the inner deposition reaction chamber achieved with the apparatus of this invention is substantially better than is obtainable with prior art CVD devices. This provides a far more uniform ~5 coating on wafers, or example.
A major improvement has been achieved wherein the radiant heating means are all at a temperature which, at steady state, is the same as the temperature desired in the inner deposition reaction chamber. In a preferred embodiment of this invention, this uniform radiant heater temperature is obtained by using resistance heating elements 6 having the same cross-sectional area and by passing the same current through each o the heating elements. Suitable power supplies are commerclally available as stock items and employ conventional technology which is well known in the art. If the heating elements 6 are formed from a continuous wire or are in a series configuration, this effect can be automatically achieved with a simple power source. If several resistance element circuits are used and each is made of wire having the same cross-sectional area and same length, the constant current can be obtained with a single power supply by placing the resistance heating elements in parallel.
Figures 2 and 3 are partial, enlarged cross-sectional views of the flanged area of the device shown in Figure 1.
Figure 2 shows the left portion and Figure 3 shows the right portion. The bottom edge 50 of the domed housing 2 engages the seal 52 supported by the annular plate 54 to establish a vacuum seal. The seal 52, being of organic polymeric elastomeric material such as a high temperature synthetic rubber O-ring is quickly destroyed if exposed to the elevated temperatures which are present in the chemical vapor deposition reaction chamber during normal use of the apparatus. The annular seal plate 54 constitutes a heat sink which is cooled by a cooling liquid circulating in the channel 56. A conductive ring of metal or similar material 58 having a wedge-shaped cross-section is held in a thermoconductive relationship with the outer wall surface 60 of the domed housing 2 and a sloped surface of the plate 54~ The ring 58 can be preormed of highly conductive metal such as copper or can be formed in place by packing a metal wool such as copper wool in the wedge shaped cavity. The conductive ring 58 is pressed against l ¢~

the heat transfer surfaces by the pressure ox annular plate 62 and nut 64. The end of the air gap or air space 10 is closed by the insulating ceramic seal 65. With this configuration, the portions of the domed housing wall 2 directly exposed to the highest temperatures, those directly surrounding the inner deposition reaction chamber, are thermally isolated from the destructible seal 5~. The lower portions of the domed housing wall 26 are not directly exposed to elevated temperatures. Heated gas in the air space 10 is blocked by the sealing ceramic ring 65. Heat conducted down the wall of the domed housing 2 is removed by the conductive ring 58, further reducing the temperature to which the seal 52 is exposed. Similar vacuum seals 66 and 68 are protected by physical separation from the hottest components and further are cooled by the annular plate 70 which has a coolant channel 72 through which a cooling liquid is passed.
The sidewall 30 of the domed base 4 terminates in the outward extending flange 74 by which it is held by plate 7~ against support plate 20. The lower portion of the domed base 4 is insulated from the zone of highest temperature by insulation 22. The projection 42 which engages and raises the domed reaction chamber housing 32 by engaging projection 40 extending therefrom (see Pigure 1) extends from the annular plate 54. The exposed surface thereof is covered with quartz or other suitable sleeve 76 which prevents contamination of the deposition zone my the`
metal during opening and closing of the apparatus.
Referring to Figure 3, the cooling channel 56 is supplied with cooling water through cooling water conduit 78, conduit 80 removing the cooling water rom the channel.
Passageway 82 communicates with gas space 84 between ye the dome housing 2 and dome base 4. Gas supplied through the passageway 82 from the non-reactive gas supply connector 86 provides the positive pressure between these two walls, thereby preventing escape of reaction gases from the reaction chamber. The non-reactive or inert gas can be nitrogen, hydrogen, etc. depending upon the CVD reaction being carried out.
The dome base 4 preferably has a specially constructed mounting flange 74. This component is subjected to high stress when the inner chamber is evacuated, and we have discovered that the most severe stresses are concentrated adjacent the flange 74. Therefore, the lower wall portion 88 of the sidewall 30, the zone marked E in Figure 4, must have a minimum thickness in order to provide the requisite strength. The thickness D should be at least 0.029 times the inside diameter of the flange 74 which constitutes the terminus of the sidewall 30. In a reaction chamber wherein the domed base has a flange with an inner diameter in the horizontal plane of 16 in., for example, the dimensions ox the other portions of the flange and lower sidewall can be as follows: A=0.75 in., B=1.5 in., C=0.375 in., D=0.56 in and E=2.125 in.
igure 5 is a cross-sectional view of the inner deposition reaction chamber and associated components.
The domed reaction chamber upper wall portion 3~ rests on the support plate 34. The projections 40 extend beyond the edge of support plate 34 for lifting engagement with the projections 42 see figure l The reaction zone is therefor defined by the upper wall portion 3~ and the support plate 34. The wafer boats 38 rest on the support plate 34, and the wafers 36 are supported in a vertical orientation thereon.

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The gas collector 46 has a cylindrical lower portion 90 and an upper section 92 which flares outwardly to form a bowl section integral therewith. The upper portion 92 in conjunction with the plate 34 forms a gas collection chamber 94 which communicates with the reaction zone through the gas collecting por,s 96 and 98. The ports 96 and 98 are preferably located adjacent the outer edge the plate 34 but within the area defined by the flared upper portion 92. The plate 34 and flared gas collector portion 92 can be separate or integral. The gas supply 44 extends through the center of the plate 34 and terminates in the gas outlet 97. The gas collector cylinder 90 is enclosed within the inner cylinder portion_29 of the sidewall 28.
Gas emerging from the gas outlet 97 passes between the vertically oriented wafers 36 in a single pass and immediately through collecting ports 96 and 98. Gas composition gradients resulting from depletion of reactive components is thereby minimized.
Figure 6 is a detailed cross-sectional view of the lower portion of the gas collector system The inner cylinder 29 of the domed base 4 is sealed against the upper edge 99 of the cylindrical vacuum sleeve plate 101 by the seal ~00. The sloped annular surface 103 of the plate 20 provides sealing pressure against seal 100. The bottom edge 105 of the inner cylinder 29 rests on the supporting annular shelf 102.
The cylindrical lower portion 90 of the gas collector 46 is enclosed within the cylindrical portion ~9 of the domed base 4, and the lower terminus 107 thereof rests on the annular supporting shelf 104. The projections 106 and 108 engage corresponding respective notches 110 and 112 in the terminus, thereby precisely orienting the gas collector about it vertical axis. The gas supply conduit 44 extends down the center of the cylindrical portlon 90, and the lower end 114 thereof has an enlarged and flared configuration. rhe gas supply system has a male outlet 116 which engages and supports the flared portion 114.
The seals (O-rings) 118 form a sealing engagement with the inner surface of glass supply conduit flared portion 114.
Gases supplied to the male member 116 through the gas supply linkage connector t20. Gas exhausted from the reaction chamber zone through ports 96 and 98 and through the gas collector 46 passes down the cylindrical section 90 and is exhausted through the outlet port 122 communi cating therewith.
The internal components of the gas delivery and collection system as well as the components defining the reaction chamber are preferably made of quartz glass or similar material which is transparent to radiant heat and which can be easily cleaned to remove all trace of metal or other chemicals deposited thereon during operation of the equipment. One or more of the internal components can be removed for cleaning when the equipment is opened during the loading cycle. These elements can be quickly removed and replaced. The domed housing 32 rests on the support plate 34 and lifted from it for replacement of wafers. Gas supply tubing 44 is lifted vertically to disengage it from the gas supply fitting 116. Replacement tubing is inserted from above, the flanged terminal end thereof facilitating re-engagement with the male portion 116. The gas collector 90, supported on the shelf 104 can be removed by lifting it vertically, and a replacment gas collector can be inserted by lowering it and rotating it until the projections 106 and 108 engage the notches 110 and 11~ and the terminus rests on the shelf 1~4.

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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1, A chemical vapor deposition reaction chamber comprising an upper reaction chamber cover means and a wafer boat support plate means, the upper reaction cover means having a top and sidewalls with lower edges contacting the wafer boat support plate to define the reaction chamber, gas collector means having an upper edge supporting the wafer boat support and defining a gas removal means, the passageway defin-ed by the upper portions thereof communicating with gas flow openings in the wafer support plate to provide for removal of spent CVD gases from the reaction chamber, gas injector means enclosed within the gas removal means and passing upward through the wafer support plate.

2. The chemical vapor deposition reaction chamber of Claim 1 wherein the components are quartz glass.

3. The chemical vapor deposition reaction chamber of Claim 2 wherein the gas injector means comprises at least one gas supply tube, the lower end thereof having a flared connecting means for frictionally engaging a gas supply means, the upper end thereof comprising a gas distributor means, the axis of the gas distributor means being substantially per-pendicular to the axis of the gas supply tube, the gas distributor means having a plurality of holes in the walls thereof for directing CVD gas flow into the reaction chamber.

4. The chemical vapor deposition reaction chamber of Claim 2 wherein the wafer boat support plate has a central passageway for receiving gas distributor tubing therethrough and gas flow openings adjacent opposite edges thereof.

5. The chemical vapor deposition reaction chamber of Claim 4 wherein the wafer boat support plate has two wafer boat support zones in parallel relationship, the central passageway between the zones, and the gas flow openings being along the outer edges of the zones.

6. The chemical vapor deposition reaction chamber of Claim 2 wherein the upper reaction chamber cover means has outwardly extending projections for engaging means for lifting it from the wafer boat support plate to expose the reaction chamber.

7. The chemical vapor deposition reaction chamber of Claim 2 including a wafer boat support means supported on the wafer boat support plate and comprising means for individually supporting a plurality of wafers in an evenly spaced, vertical orientation, the bottom edge of the wafer support means having leg means extending therefrom for supporting the wafer support means above the upper surface of the wafer support plate means, the leg means being spaced apart for engaging a loading projection of a wafer boat load-ing and unloading means.