Chemical vapor deposition apparatus

An improved chemical vapor deposition device having heating means substantially surrounding an inner deposition chamber for providing isothermal or precisely controlled gradient temperature conditions therein. The internal components of the chamber are quartz or similar radiant energy transparent material. Also included are special cooling means to protect thermally sensitive seals, structural configurations strengthening areas of glass components subjected to severe stress during operation, and specific designs permitting easy removal and replacement of all glass components exposed to deposition gas.

FIELD OF THE INVENTION 
This invention relates to a chemical vapor deposition apparatus. In 
particular, this invention relates to an apparatus for the chemical vapor 
deposition of highly uniform, uncontaminated coatings of selected elements 
and compounds on substrates, and to components thereof. 
BACKGROUND OF THE INVENTION 
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 alloy 
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), and is hereby 
incorporated by reference. 
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 limitations 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 heating elements arranged to create a heated 
reaction and deposition zone. Conduction and convection heating approaches 
have also been used in hot wall systems. 
Cold wall systems for chemical vapor deposition are described in U.S. Pat. 
Nos. 3,594,227, 3,699,298, 3,704,987, and 4,263,872. 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 semiconductor 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. 
U.S. Pat. No. 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 wall CVD systems currently used in making semiconductor materials are 
most commonly converted doping ovens. These have long tubular reactors of 
quartz or similar inert material, and heat is provided by heating elements 
coiled around the outside of the cylindrical portion. The reactor ends are 
not heated, and temperature 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 4.degree. C. 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 is limited by the lengthy time required 
to reach thermal equilibrium. Prior to this invention, apparatus has not 
been available to manufacture 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 AND OBJECTS OF THE INVENTION 
The controlled temperature deposition device of this invention comprises an 
inner deposition chamber having gas distribution means for introducing gas 
into the inner chamber and removing gas therefrom and a vacuum chamber 
means surrounding the inner deposition reaction chamber and spaced from 
the walls thereof for maintaining a minimum vacuum therein. The vacuum 
chamber means comprises a domed housing and a base cooperating therewith, 
the material of the domed housing and base being substantially transparent 
to radiation. Radiant heating means are positioned over the outer surface 
of the domed housing and base surrounding the inner deposition chamber for 
providing precisely controlled temperatures in the reaction chamber. The 
radiant heating means and the outer surface of the domed housing and base 
are in a non-conducting relationship. The radiant heating means preferably 
have the same temperature achieved by having the same cross-sectional 
areas and currents. 
The domed housing has a base which engages a support plate. Seals are 
positioned between the base and support plate to form a vacuum seal. 
Cooling means engage the outer wall of the domed housing between the base 
and the portion thereof surrounding the inner deposition chamber for 
removing heat therefrom, thereby protecting the seals. 
The quartz vacuum chamber base has an outer dome portion and an axially 
concentric inner cylindrical portion integral therewith. The lower 
terminus of the outer domed portion comprises an outwardly extending 
annular mounting flange integrally joined to the sidewall thereof by a 
connecting wall portion having a thickness of at least 0.029 times the 
inside diameter of the lower terminus. 
The inner deposition chamber has a domed portion removab1y supported on a 
gas collector. The gas collector has a lower cylindrical portion, the 
terminus thereof being removably supported on an annular support surface. 
Preferably, the lower edge of the cylindrical portion and the support 
therefor having mutually engaging indexing means for orienting the gas 
collector about its vertical axis. The inner deposition chamber is defined 
by a domed portion and a plate support means therefor. The support means 
has a central opening receiving a gas distributor. The flared inlet 
opening of the gas distributor forms a detachable, sealing engagement with 
a male gas source member upon which it is supported. The inner components 
can thus be easily removed for cleaning. 
It is an object of this invention to provide a chemical vapor deposition 
system which provides a more uniform temperature in the inner deposition 
reaction chamber thereof. It is a further object to reduce the temperature 
of the vacuum chamber seal engaging surfaces to a level which does not 
destroy the integrity of the seals. It is a still further object of this 
invention to provide internal components, components which form the inner 
deposition reaction chamber and gas distribution means, which are easily 
removed for cleaning or replacement.

DETAILED DESCRIPTION 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 coatings, heat lamps, heated liquids and solutions, and microwave or 
induction heated materials can function as "radiant heat sources", for 
example. 
Referring to FIG. 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 radiant 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. 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 4 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 40 which are 
engaged by projections 42 when the outer housing components are lifted to 
expose the inner deposition chamber. The gas supply conduit 44 extends 
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 
coating on wafers, for 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 of 
the heating elements. Suitable power supplies are commercially 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. 
FIGS. 2 and 3 are partial, enlarged cross-sectional views of the flanged 
area of the device shown in FIG. 1. FIG. 2 shows the left portion and FIG. 
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 
preformed 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 the heat transfer 
surfaces by the pressure of 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 52. 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 70 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 FIG. 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 by the metal during opening 
and closing of the apparatus. 
Referring to FIG. 3, the cooling channel 56 is supplied with cooling water 
through cooling water conduit 78, conduit 80 removing the cooling water 
from the channel. 
Passageway 82 communicates with gas space 84 between 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 FIG. 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 of 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. 
FIG. 5 is a cross-sectional view of the inner deposition reaction chamber 
and associated components. The domed reaction chamber upper wall portion 
32 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 FIG. 1). The reaction zone is therefor defined by the upper wall 
portion 32 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. 
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 ports 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 99. 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. 
FIG. 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 100. 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 29 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 its vertical axis. The 
gas supply conduit 44 extends down the center of the cylindrical portion 
90, and the lower end 114 thereof has an enlarged and flared 
configuration. The gas supply system has a male gas supply 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 120. 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 exhaust port 
122 communicating 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 traces 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 112 and 
the terminus rests on the shelf 104.