Note: Descriptions are shown in the official language in which they were submitted.
FIELD OE THE INVENTION
This invention relates to a chemical vapor
deposition apparatus.
3ACKGROUND 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 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
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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.
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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
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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
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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
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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
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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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