Page 1 of 8
`
`Samsung Exhibit 1014
`Samsung Electronics Co., Ltd. v. Daniel L. Flamm
`
`

`
`Oct. 22, 1991
`
`Sheet 1 of 2
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`5,059,770
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`Page 2 of 8
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`

`
`U.S. Patent
`
`Oct. 22, 1991
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`Sheet 2 of 2
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`5,059,770
`
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`POWER
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`Page 3 of 8
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`

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`1
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`5,059,770
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`MULTI-ZONE PLANAR HEATER ASSEMBLY
`AND METHOD OF OPERATION
`
`FIELD OF THE INVENTION
`
`The present invention relates to a heater assembly
`and method of its operation for use in processing a
`substrate such as a semiconductor wafer and more par-
`ticularly to such a heater assembly and method of oper-
`ation for use in a chemical vapor deposition (CVD)
`reactor.
`
`BACKGROUND OF THE INVENTION
`
`for example,
`In semiconductor wafer processing,
`CVD, and similar methods, substrates such as silicon
`wafers are typically heated to various temperatures in
`order to carry out different thin film deposition or etch
`operations. Various techniques have been employed in
`the prior art for heating these thin substrates, including:
`(1) infrared heating; (2) visible light source heating; (3)
`radio frequency coupled heaters; and (4) hot plate heat-
`ers.
`
`In the first type of heater, the substrate was physi-
`cally rotated past an array of infrared lamps in an effort
`to achieve required uniform temperatures throughout
`the silicon wafer. However, the physical rotation step
`tended to interfere with distribution of gas flow over
`and onto the wafer, thus resulting in processing limita-
`tions.
`In the second heating method, temperature unifor-
`mity was attempted by employing very complex and
`expensive optical reflectors. Stability and uniformity of
`temperatures were determined by complex radiative
`interaction of the various surfaces according to their
`respective emissivities.
`The third method, while also complex and expensive,
`has been commonly employed particularly for process-
`ing temperatures in the range of 1,000—l,200 degrees
`Centigrade (°C.). However,
`this method has offered
`sub-optimal
`temperature uniformity on the substrate
`while being very difficult to manipulate in order to
`achieve even a moderate level of temperature unifor-
`mity.
`The fourth method has typically been employed for
`low temperature applications, for example below 500“
`C. Such hot plate heaters have commonly consisted of
`an embedded resistance wire in a ceramic or dielectric
`plate or a high thermally conductive metal such as
`aluminum. While satisfactory temperature uniformity
`has been achieved by this method, it has not been found
`suitable for use in high temperature processing due, for
`example, to limits established by metal melting points,
`bonding materials employed and the emission of con-
`taminants from the heating element and the metals par-
`ticularly at such higher temperatures.
`SUMMARY OF THE INVENTION
`
`Accordingly, there has been found to remain a need
`for an improved heater assembly and method of opera-
`tion for use in such techniques. Generally, semiconduc-
`tor wafer processing techniques such as those described
`above require temperature uniformity across the entire
`wafer area, typically with a variation of no more than
`i2“ C.
`in order to achieve uniform film processing
`(deposition or etch, for example) on the wafer or sub-
`strate. Such temperature uniformity is required in pro-
`
`35
`
`2
`cesses which may be carried out in a temperature range
`of typically 250°—l,250° C.
`Semiconductor processing techniques are further
`complicated by the requirement for heating of the wa-
`fers or substrates from one side only in order to allow a
`gas delivery system (on the other side of the substrate)
`to be at a different temperature for optimal chemical
`processing. A fundamental problem arises in such heat-
`ing techniques in that heat losses in central portions of
`the substrate tend to be very different from heat losses
`in edge portions. Thus, if a substrate is uniformly heated
`across its area, heat loss characteristics of the substrate
`normally cause it
`to assume a temperature profile
`which, when viewed in diametric cross-section, will be
`relatively low at the diametric edges and relatively high
`midway between those diametric extremities. Further-
`more, relative heat losses and the temperature profile
`referred to above vary at different temperature levels
`and at different pressures. Thus, as processing tempera-
`tures are increased for a substrate, there will be a corre-
`sponding increase in the temperature profile, that is, a
`greater contrast between maximum and minimum tem-
`peratures in different areas of the substrate. In addition,
`the temperature profile is also affected by processing
`pressure. This is due in part to the fact that, at pressures
`below about 5 Torr, the heat transfer mechanism is
`mostly by radiation whereas, above about 10 Torr, the
`heat transfer mechanism involves a combination of radi-
`ation and convection.
`In any event, the preceding discussion is set forth in
`order to further emphasize the difficulties in maintain-
`ing uniform surface temperatures throughout a sub-
`strate, particularly where the substrate is being pro-
`cessed at a variety of temperatures and/or pressures.
`It is therefore an object of the invention to provide an
`improved heater assembly and method of operation for
`the heater assembly in the processing of substrates or
`wafers in order to overcome one or more problems as
`discussed above.
`More specifically, it is an object of the invention to
`provide a heater assembly for use in the processing of
`substrates or wafers in order to develop and maintain a
`uniform elevated temperature throughout the substrate,
`the heater assembly including a dielectric heater base
`having a generally circular surface, a plurality of heater
`elements forming radially spaced and circumferentially
`extending segments which substantially cover the circu-
`lar surface of the heater base, a heater shroud arranged
`in spaced apart relation from the heater element seg-
`ments and intermediate the heater elements and the
`substrate, separate means for operating the plurality of
`heater elements and means for maintaining a blanket of
`inert gas adjacent the heater element segments.
`Such a combination provides a multi-zone planar
`heater assembly and method of operation therefor per-
`mitting modification in heating patterns for the sub-
`strate in order to eliminate or minimize temperature
`profile effects as discussed above. In particular,
`the
`heater assembly may be provided with any number of
`heater element segments which are preferably radially
`separated and circumferentially extending in configura-
`tion. With such a heater configuration,
`the different
`heater element segments can be adjusted to achieve
`different heating temperatures in order to either com-
`pensate for or substantially eliminate temperature varia-
`tions throughout the substrate.
`The heater element segments are preferably formed
`from electrically conductive material or metal capable
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`Page 4 of 8
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`5,059,770
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`3
`of resistance heating. The dielectric heater base is then
`preferably formed from a dielectric material having a
`similar coefficient of thermal expansion as the heater
`element segments while also being selected to resist
`separation from the heater elements and to remain di-
`mensionally stable during rapid and extensive tempera-
`ture variations. A particularly preferred combination of
`materials is a heater base formed from boron nitride
`with the heater element segments being formed from
`pyrolytic graphite.
`In a preferred method of construction, the conduc-
`tive material for the heater elements is uniformly depos-
`ited upon the heater base, circumferential regions of the
`conductive material then being removed, for example
`by machining, to define the radially spaced apart heater
`element segments. Each heater element segment is also
`preferably interrupted by a radially extending line or
`region so that electric contact can be made on opposite
`end portions of each heater segment for causing resis-
`tance heating.
`It is yet a further object of the invention to provide a
`heater assembly and method of operation including
`means for maintaining an inert gas blanket over the
`heater element, for example, to prevent oxidation, etc.
`Preferably, a central opening in the heater base forms an
`inlet for the inert gas so that it flows radially outwardly
`over the heater elements. The inert gas can then be
`exhausted about the periphery of the heater shroud.
`Preferably, the heater assembly is adapted for use in
`reactor chambers, more particularly in a CVD reactor
`chamber. For example, the heater assembly of the pres-
`ent invention is contemplated for use in a CVD deposi-
`tion method as disclosed in a copending U.S. patent
`application Ser. No. 07/370,331 filed June 22, 1989 by
`the present inventor and entitled METHOD OF DE-
`POSITING SILICON DIOXIDE FILM AND
`PRODUCT. In addition, the heater assembly of the
`present invention is also contemplated for use within a
`CVD reactor chamber of the type disclosed in another
`copending U.S. patent application Ser. No. 07/386,903
`filed July 28, 1989 by the present inventor and entitled
`CHEMICAL VAPOR DEPOSITION REACTOR
`AND METHOD OF OPERATION. Those two co-
`pending applications are accordingly incorporated
`herein by reference as though set forth in their entirety
`in order to assure a more complete understanding of the
`present invention.
`It is a further related object of the invention to pro-
`vide a method of operation for a heater assembly as
`summarized above. In both the heater assembly design
`and method of operation,
`it is contemplated that the
`means for regulating operation of the multiple heating
`elements and also the means for regulating flow of inert
`gas can be varied in order to facilitate processing of the
`wafer. In particular, by adjusting the heating effect of 55
`the different heater elements,
`temperature variations
`occurring diametrically across a substrate can readily be
`substantially eliminated or reduced to a satisfactory
`level, even for a wide variety of operating temperatures
`and/or pressures. Furthermore, heating capacities of 60
`the respective heating elements are selected in order to
`permit rapid heating of the substrate to greatly elevated
`temperatures in a very short period of time. For exam-
`ple, it is contemplated that the heater assembly of the
`present invention may be employed to heat a substrate
`or semiconductor wafer from ambient to a desired pro-
`cessing temperature, typically l,00O°—l,l0O° C., over a
`time interval of about one minute.
`
`4
`At the same time, the ability to adjust the flow rate
`and/or the type of inert gas even further enhances ver-
`satility of the heater assembly. For example, in addition
`to preventing oxidation, increased inert gas flow may be
`provided, for example, between processing operations
`in order to more rapidly cool down both the heater
`assembly and the substrate to facilitate interchange of
`substrates where sequential operations are contem-
`plated.
`Additional objects and advantages of the invention
`are made apparent in the following description having
`reference to the accompany drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a plan View of the heater assembly with a
`substrate or silicon wafer in the form of a cylindrical
`disk being mounted thereupon.
`FIG. 2 is a side view, with parts in section, taken
`along section line II—II of FIG. 1 in order better illus-
`trate intemal construction of the heater assembly.
`FIG. 3 is a plan View of the heater assembly, similar
`to FIG. 1 but with the substrate and heater shroud
`removed to better illustrate a plurality of heating ele-
`ment segments.
`FIG. 4 is a schematic representation of the heater
`assembly, generally in side view, arranged within a
`CVD reactor.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`Referring now to the drawings and particularly
`FIGS. 1-3, a heater assembly constructed according to
`the present invention is generally indicated at 10. The
`heater assembly 10 is preferably adapted for use within
`a reactor such as that schematically indicated at 12 in
`FIG. 4. The CVD reactor 12 may, for example, be of a
`type contemplated and described in greater detail
`within either of the copending references noted above.
`Accordingly, no further description of the CVD reac-
`tor or its general mode of operation is believed neces-
`sary within the scope of the present invention.
`Referring particularly to FIG. 2, the heater assembly
`10 includes a water cooled, heater support monolith 14
`capable of being mounted within a reactor chamber as
`illustrated in FIG. 4.
`A tubular riser 16 is centrally secured to the monolith
`with a heater support point 18 being mounted there-
`upon. Both the tubular riser 16 and heater support point
`18 are preferably formed from nickel plated stainless
`steel in order to withstand contemplated high tempera-
`tures and to avoid introducing contaminants thereinto.
`A disk-shaped heater base 20 formed from a suitable
`dielectric material as described in greater detail below is
`mounted upon the support plate 18 with a plurality of
`heater elements, collectively indicated at 22, being ar-
`ranged on a generally circular surface 24 of the heater
`base. Construction of the heater base 20 and heater
`elements 22 is described in greater detail below.
`As for the overall construction of the heater assem-
`bly, a cover or shroud 26 is also supported by the mono-
`lith 14 in spaced apart relation from the heater elements
`22. Preferably, the shroud 26 is formed from a material
`such as quartz and includes means for supporting a
`substrate or silicon wafer 26 on its upper surface di-
`rectly above the heater elements 22.
`The shroud 26 includes a flange or skirt extending
`downwardly in spaced apart relation about both the
`heater base 20 and support plate 18. The skirt 30 is also
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`Page 5 of 8
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`5,059,770
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`5
`spaced apart from a cylindrical flange portion 30 of the
`monolith 14. Thus, the shroud 26 serves both to support
`the substrate 28 above the heater elements and also to
`enclose a space above the heater elements to assure
`formation of an inert gas blanket over the heater ele-
`ments as described in greater detail below.
`Referring particularly to FIG. 3 in combination with
`FIG. 2, the heater elements 22 include a plurality of
`heater element segments indicated respectively at 22A,
`22B and 22C which are slightly spaced apart radially
`from each other while being circumferentially extend-
`ing to cover substantially the entire surface 24 of the
`heater base 20. Although the heater assembly of the
`present invention is thus described with three specific
`heater element segments, it will be apparent that any
`number of such segments could be employed as neces-
`sary for assuring uniform temperature control over the
`substrate 28.
`The heater element segments 22A—C are preferably
`formed from an electrically conductive material, more
`preferably a metal, deposited directly upon the heater
`base 20. The deposited material is then removed, for
`example, by means of machining in order to form cir-
`cumferential regions or gaps 34 and 36 providing radial
`spacing between the respective heater element seg-
`ments 22A—C.
`A radially extending region or gap 38 is also formed
`to intersect all three heater element segments. With the
`heater element segments thus being formed upon the
`heater base, electrode pairs 40A—C extend upwardly
`through the support plate 18 and heater base 20 as illus-
`trated in FIG. 2 for respective connection with the
`heater element segments 22A-C on opposite sides of the
`radial gap 38. The electrode pairs are coupled with a
`suitable power source 42, see FIG. 4, the power source
`being capable of individually regulating power supply
`to the respective heater element segments in order to
`closely and accurately adjust heating temperatures de-
`veloped by the respective segments.
`Central portions of the heater element segments
`22A—C opposite the electrode pairs 40A—C, are inter-
`connected with thermocouple pairs 44A—C respec-
`tively. The thermocouple pairs 44A—C form part of a
`standard
`proportional/integral/differentially
`(PID)
`electronic temperature controller (forming part of the
`power source 42 and not otherwise illustrated) in order
`to provide individual control for the respective heater
`element segments.
`In any event, with the capability of sensing the output
`energy or temperature of each heater element segment
`or zone 22A—C, a temperature profile across a diametri-
`cal section of the heater can be electronically manipu-
`lated, in a manner well known to those skilled in the art,
`in order to achieve close regulation and minimum varia-
`tion over the temperature profile. In any event, such
`controls permit the maintenance of a desired tempera-
`ture profile under widely varying conditions of pressure
`and temperature in order to maintain a uniform temper-
`ature field within :2” C. across the substrate 28.
`As noted above, an inert gas blanket is preferably
`maintained over the heater element segments 22A—C in
`order to prevent oxidation of the segments and also to
`facilitate and enhance operation of the heater assembly.
`In that regard, an inert gas such as nitrogen, helium,
`argon, etc. is supplied from a source 46 (see FIG. 4)
`through a flow regulating device 48 into a passage 50
`extending axially upwardly through the monolith 14,
`riser 16 and heater support plate 18 to an opening 52
`
`6
`formed centrally in the heater base 20. With the opening
`52 being formed in the heater base 20, the surface 24
`covered by the heater element segments 22A—C is actu-
`ally an annulus as best illustrated in FIG. 3.
`In any event, when inert gas is introduced through
`the opening 52 in the heater base 20, it enters the space
`32 between the heater element segments and the shroud
`26, the inert gas flowing radially outwardly to blanket
`all of the heater element segments. As the inert gas
`flows radially outwardly past the heater element seg-
`ments and heater base, it then flows around an exhaust
`passage formed by the skirt 30 and escapes into the
`reactor chamber 12 to be exhausted along with other
`gases from the reactor in a conventional manner.
`Within the heater assembly 10 as described above, the
`heater element segments 22A-C are preferably formed
`from pyrolytic graphite which is particularly suited for
`withstanding high temperatures contemplated by the
`invention. At the same time,
`it
`is important that the
`dielectric material forming the heater base 20 be formed
`from a material having a similar coefficient of thermal
`expansion as the heater element segments in order to
`prevent separation therebetween, the dielectric material
`of the heater base 20 further being selected to remain
`dimensionally stable and to prevent emission of contam-
`inants during rapid and extensive temperature varia-
`tions. Most preferably, the heater base 20 is formed
`from boron nitride which satisfies the requirements
`summarized above. In addition, the boron nitride mate-
`rial has a white color tending to reflect heat upwardly
`toward the substrate (see FIGS. 2-4). In addition, the
`pyrolytic graphite can be deposited with good adhesion
`onto the boron nitride and readily machined away in
`order to form the circumferential and radial gaps 34-38
`as described above.
`The pyrolytic graphite is preferably deposited to a
`thickness of about 0.040 inches in order to provide de-
`sired or required film resistance. The heater base 20 may
`be formed with a typical diameter of about 10 inches
`and a thickness of about 0.25 inches.
`As noted above, a wide variety of power capabilities
`is provided by the power source 42 for the respective
`heater element segments 22A-C. In one example, the
`outer heater element segment 22A may be designed
`with a power delivery capability of up to about 4,000
`watts,
`the intermediate heater element segment 22B
`with a power delivery capability of up to about 3,500
`watts and the inner heater element segment 22C with a
`power delivery capability of up to about 2,500 watts.
`With such a configuration and with materials as pref-
`erably noted above, the heater assembly is capable of
`operation under a wide variety of operating parameters
`contemplated in various processing techniques.
`The method of operation for the heater assembly is
`believed apparent
`from the preceding description.
`However, the method of operation is described briefly
`below in order to assure a complete understanding of
`the invention.
`Initially, the heater assembly is constructed and ar-
`ranged as described above, preferably within a reactor
`chamber such as that illustrated in FIG. 4.
`A substrate such as the silicon wafer indicated at 28 is
`then mounted upon the heater shroud 26. Operation of
`the heater assembly 10 is initiated by actuating the
`power source 42 under a desired set of operating param-
`eters according to the particular application and by
`initiating the flow of inert gas from the source 46.
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`5,059,770
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`7
`With appropriate power levels being supplied to the
`heater element segments 22A—C,
`they are rapidly
`heated to respective temperatures assuring a generally
`uniform temperature profile across any selected diamet-
`ric section of the substrate 28.
`The material of the heater element segments 22A-C
`is protected from oxidation under the severe tempera-
`tures developed by inert gas flow as described above.
`With the substrate uniformly heated as described
`above, a deposition or etch process may then be carried
`out within the reactor chamber 12 in a manner contem-
`plated and well known to those skilled in the art.
`The heater assembly of the present invention further
`facilitates such operations in that where successive de-
`position or etching processes are contemplated, power
`from the power source 42 may be interrupted and flow
`of inert gas from the source 46 increased in order to
`rapidly cool various portions of the heater assembly 10
`and the substrate 28. Thus, rapid interchange of sub-
`strates is made possible with greater efficiency for both
`the heater assembly and reactor chamber 12. Even
`greater cooling may be achieved, for example, by sup-
`plying a different
`inert gas capable of high thermal
`conductivity than an inert gas employed during the
`particular process. When the heater assembly is cooled
`and the substrate 28 cooled and replaced, the operating
`steps described above may then be repeated for simi-
`larly processing the subsequent substrate.
`The heater assembly 10 is contemplated for develop-
`ing temperatures over a wide range as noted above. For
`example,
`typical temperatures developed in the sub-
`strate may range from approximately 200° C. to about
`1,200“ C. and the heater assembly 10 is particularly
`effective for assuring uniform temperatures over that
`entire temperature range.
`Thus, there has been described an effective heater
`assembly and method of operation for developing and
`maintaining uniform elevated temperatures in a sub-
`strate. Numerous variations and modifications in addi-
`tion to those specifically described above will be appar-
`ent from the preceding description. Accordingly, the
`scope of the present invention is defined only by the
`following appended claims which provide further ex-
`amples of the invention.
`What is claimed is:
`1. A heater assembly for use in semiconductor wafer
`processing for developing and maintaining a uniform
`elevated temperature in the wafer, comprising
`a dielectric heater base having a circular surface,
`a plurality of heater elements arranged on the circular
`surface of the heater base and formed from conduc-
`tive material capable of resistive heating, the plu-
`rality of heater elements forming radially spaced,
`circumferentially extending segments which,
`in
`combination, substantially cover the circular sur-
`face, the heater element segments being separated
`from each other by circumferentially extending
`regions, each heater element segment being inter-
`rupted by a radially extending region,
`separate means for respectively regulating operation
`of the plurality of heater elements, the separate
`means for respectively regulating operation of the
`plurality of heater elements comprising electrical
`couplings operatively coupled with each heater
`element segment opposite the respective radially
`extending region,
`heater shroud arranged in spaced apart relation
`from the plurality of heater elements and interme-
`
`8
`diate the heater elements and the semiconductor
`wafer, and
`means for maintaining a blanket of inert gas between
`the heater elements and the heater shroud.
`2. The heater assembly of claim 1 wherein the heater
`elements are formed from pyrolytic graphite.
`3. The heater assembly of claim 1 wherein the heater
`elements are formed by uniformly depositing the con-
`ductive material over the circular surface of the dielec-
`tric heater base and then selectively removing portions
`of the conductive material to form the heater elements.
`4. The heater assembly of claim 3 wherein the heater
`element segments are separated from each other by
`circumferentially extending regions, each heater ele-
`ment segment being interrupted by a radially extending
`region, the separate means for respectively regulating
`operation of the plurality of heater elements comprising
`electrical couplings formed on portions of each heater
`element segment opposite the respective radially ex-
`tending region.
`5. The heater assembly of claim 1 wherein the heater
`base is formed from dielectric material selected to have
`a similar coefficient of thermal expansion as the conduc-
`tive metal in the heater elements, the dielectric material
`also being selected to resist separation from the conduc-
`tive metal and to remain dimensionally stable during
`rapid an extensive temperature variations.
`6. The heater assembly of claim 5 wherein the heater
`base is formed from boron nitride and the heater ele-
`ment segments are formed pyrolytic graphite.
`7. The heater assembly of claim 1 wherein the heater
`shroud includes means for supporting the wafer there-
`upon.
`8. The heater assembly of claim 1 wherein the means
`for maintaining an inert gas blanket comprises a central
`opening in the heater base forming an inert gas inlet so
`that inert gas from the central inlet flows radially out-
`wardly between the heater element segments and the
`heater shroud.
`9. The heater assembly of claim 8 further comprising
`means formed about a peripheral portion of the heater
`shroud for venting the inert gas.
`10. The heater assembly of claim 8 further comprising
`means for regulating inert gas flow through the central
`opening for facilitating processing of the semiconductor
`wafer.
`11. The heater assembly of claim 1 wherein the mcrms
`for maintaining an inert gas blanket comprises a central
`opening in the heater base forming an inert gas inlet so
`that inert gas from the central inlet flows radially out-
`wardly between the heater element segments and the
`heater shroud.
`12. The heater assembly of claim 11 further compris-
`ing means formed about a peripheral portion of the
`heater shroud for venting the inert gas.
`13. The heater assembly of claim 11 further compris-
`ing means for regulating inert gas flow through the
`central opening for facilitating processing of the semi-
`conductor wafer.
`14. The heater assembly of claim 1 wherein the heater
`assembly and wafer are arranged in a chemical vapor
`deposition (CVD) reactor chamber.
`15. A method of heating a substrate during semicon-
`ductor wafer processing and for developing and main-
`taining a uniform elevated temperature in the substrate,
`comprising the steps of
`forming a heater assembly to include a dielectric
`heater base having a circular surface. a plurality of
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`Page 7 of 8
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`

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`9
`heater elements arranged on the circular surface of
`the heater base, the plurality of heater elements
`forming radially spaced, circumferentially extend-
`ing segments which, in combination, substantially
`cover the circular surface, and a heater shroud
`arranged in spaced apart relation from the plurality
`of heater elements and intermediate the heater
`elements and the substrate,
`maintaining a blanket of inert gas between the heater 10
`elements and the heater shroud during operation of
`the heater assembly, and
`separately regulating operation of the plurality of
`heater elements in order to achieve different heat-
`ing temperatures in the respective heater elements
`and thereby substantially eliminate temperature
`variations throughout the substrate for facilitating
`and enhancing processing of the substrate.
`16. The method of claim 15 wherein the heater ele-
`ments are formed from a conductive material selected
`for resistive heating.
`17. The method of claim 16 wherein the heater ele-
`ments are formed from pyrolytic graphite.
`18. The method of claim 16 wherein the heater ele-
`ments are formed by uniformly depositing the conduc-
`tive material on the circular surface of the heater base
`and then selectively removing portions of the metal to
`form the heater elements.
`
`15
`
`5,059,770
`
`10
`19. The method of claim 15 further comprising the
`step of supporting the substrate in thermally conductive
`relation upon the heater shroud.
`20. The method of claim 15 wherein the inert gas
`blanket is maintained by introducing inert gas through a
`central opening in the heater base and allowing the inert
`gas to flow radially outwardly over the heater elements.
`21. The method of claim 20 further comprising the
`step of venting the radially flowing inert gas about a
`peripheral portion of the heater shroud.
`22. The method of claim 21 further comprising the
`step of regulating inert gas flow through the central
`opening of the heater base for facilitating processing of
`the substrate.
`23. The method of claim 22 further comprising the
`step of mounting the heater assembly and substrate
`within a chemical vapor deposition (CVD) reactor
`chamber and thereafter operating the heater assembly
`as part of a CVD process for treating the substrate.
`24. The method of claim 15 further comprising the
`step of regulating inert gas flow through a central open-
`ing of the heater base for facilitating processing of the
`substrate.
`25. The method of claim 24 further comprising the
`step of mounting the heater assembly and substrate
`within a chemical vapor deposition (CVD) reactor
`chamber and thereafter operating the heater assembly
`*
`I
`3
`I
`I
`as part of a CVD process for treating the substrate.
`
`Page 8 of 8