United States Patent [191
`Carman et al.
`
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`SOO5294778A
`[11] Patent Number:
`[45] Date of Patent:
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`5 294 77s
`9
`9
`Mar. 15, 1994
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`54 CVD LA NH TE
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`1 CONgEN-I-TEIC
`ELEMENTS
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`533311 11;
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`Monkowski, Danville, all of Calif.
`[73] Assign“: Lam R
`ch corpon?on, Fremont,
`Calif.
`
`_
`[21] App!’ No" 757’921
`[22] Filed:
`Sep. 11, 1991
`Cé‘ls """"""""
`Hon‘ ugly/33291211’
`‘ ‘
`' """
`338/2l7’_ 118/725’
`[58] Field of Search
`’219/385 ’445_45o
`’
`219/455, 466_
`/4l6,"11éj338/285’ 287 283:
`’
`217 218’, 118/724: 725’ 730
`’ _
`’
`'
`’
`References cued
`us. PATENT DOCUMENTS
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`[56l
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`,
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`"""""" "
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`2,330,867 10/1943 Challet .... ..
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`219/446
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`3,381,114 4/1968 Nakanuma . . . . . . . .
`
`. . . . .. 338/217
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`4,511,789 4/1985 Goessler et a]. .................. .. 219/446
`
`FOREIGN PATENT DOCUMENTS
`3545443 6/1987 Fed. Rep. of Germany .... .. 219/445
`59-44819 3/1984 Japan ................................. .. 118/728
`61-142743 6/1986 Japan .
`.
`63-196033 8/1988 In an .
`1-27715 1/1990 115m .
`773-80530 4/1991 Japan ................................. .. 118/725
`Primary Examiner-Geoffrey S. Evans
`Assistant Examiner-John A. Jeffery
`Attorney, Agent, or Firm—James P. Hillman
`[57] '
`ABSTRACI.
`A wafer support platen heating system for low pressure
`chemical vapor deposition of apparatus includes multi
`ple resistance heaters for individual heating of multiple
`portions of the platen to provide a predetermined uni
`form or non-uniform temperature gradient/profile
`across the platen. The multiple graphite resistance heat
`ers of the preferred embodiment include a spiral shaped
`mainhiresistance heatgr and tlwo igglefaal @529 1058
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`t e mner
`wit
`grap te resistance eaters ocat
`diameter and along the periphery of the outer diameter
`respectively of the main spiral shaped resistance heater.
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`9 Claims, 6 Drawing Sheets
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`EXHIBIT 2001
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`US. Patent '
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`Mail-.15, 1994
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`Sheet 1 of 6
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`5,294,778
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`EXHIBIT 2001
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`US. Patent
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`Mar. 15, 1994
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`Sheet 2 of 6
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`U.S. Patent
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`Mar. 15, 1994
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`Sheet 3 of 6
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`5,294,778
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`FIG 3
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`U.S. Patent
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`Mar. 15, 1994
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`Sheet 4 of 6
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`5,294,778
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`H i
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`FIGURE 4
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`EI'ZIZIZIZIZIZFZI ?. \w
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`US. Patent
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`Mar. 15, 1994
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`Sheet 5 of 6
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`5,294,778
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`l| WZON Ewm<>> Z0035 Ill.
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`FIG 5
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`Mar.15, 1994
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`Sheet 6 of 6
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`FIGURE 6
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`1
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`CVD PLATEN HEATER SYSTEM UTILIZING
`CONCENTRIC ELECTRIC HEATING ELEMENTS
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`5,294,778
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`if the main heater were circular). A circular shaped,
`single turn (alternate embodiments can have multiple
`turns if desired) resistance heater is located within the
`spiral shaped main heater’s inner space. An additional
`single turn (multiple turns are optional) heater is located
`on the outside of the outer space of the spiral shaped
`main heater. Temperature sensing means such as a cali
`brated thermocouple may be located proximate the
`platen at predetermined locations to sense the tempera
`ture of the platen at those predetermined locations.
`Power control means can then adjust the power input to
`the individual platen resistance heaters to provide a
`uniform flat pro?le) or smooth temperature gradient
`pro?le across the platen as desired. In the preferred
`embodiment of the invention, the temperature sensing
`means are located proximate the inner space, middle
`and outer space, respectively of the main spiral heater.
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`10
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`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention relates to apparatus and methods for
`chemical vapor deposition of thin ?lms on silicon wa
`fers. More particularly, this invention relates to appara
`tus and methods for heating semiconductor wafers by
`creating a predetermined temperature pro?le across a
`support platen by means of multiple heaters.
`2. Description of the Prior Art
`In chemical vapor deposition systems, it is important
`to have complete control of heating the semiconductor
`wafer substrate. Sometimes it is necessary to heat the
`substrate uniformly. Non-uniform heating at these times
`can result in non-uniform deposition. At other times it is
`desirable to create a non-uniform temperature pro?le
`across the wafer in one direction while maintaining a
`uniform temperature pro?le in another direction.
`Chemical vapor deposition heating systems of the prior
`art, such as heat lamp or induction systems, have dif?
`culty maintaining a desired heat pro?le across the wa
`fers. These systems heat the wafer satisfactorily, but the
`dif?culty occurs from their lack of control.
`Since the chamber in which low pressure chemical
`vapor deposition occurs is evacuated during the opera
`tion, it is important that the voltage applied to the
`heater be kept low so as to prevent arcing across the
`terminals. There is a trade off‘ of sufficient voltage to
`provide enough power to heat the wafer but not so
`much voltage as to initiate arcing across the heater
`terminals.
`Accordingly, it would be desirable to have a platen
`heater for a chemical vapor deposition system that is
`capable of providing a desired temperature pro?le or
`gradient across a support platen. Furthermore it would
`be desirable to have a platen heater for a chemical vapor
`deposition system that has low cost and high efficiency.
`40
`Furthermore, it would be desirable to have this platen
`heater operate at suf?ciently low voltage as to inhibit
`arcing at the terminals or elsewhere (enhances person
`nel safety also). These bene?ts and others will become
`apparent as the platen heater system is described ac
`45
`cording to the teachings of the invention.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The invention may be better understood and further
`advantages and uses thereof more readily apparent,
`when considered in view of the following detailed de
`scription of exemplary embodiments, taken with the
`accompanying drawings in which;
`FIG. 1 is a schematic view of the multiple resistance
`heaters constructed according to the teaching of the
`invention;
`FIG. 2 is a bottom view of the support platen con
`structed according to the teachings of the invention,
`showing the recessed grooves for the temperature sens
`ing means;
`FIG. 3 is a cross sectional view of the support platen
`of FIG. 2 taken along the line 3’—3' showing the loca
`tion of the multiple resistance heaters and temperature
`sensors of FIG. 1;
`FIG. 4 is a cross sectional view of a chemical vapor
`deposition reaction chamber constructed according to
`the teachings of the invention, showing the location of
`the support, platen of FIG. 2 and the multiple resistance
`heaters of FIG. 1; and
`FIG. 5 is a graph of several possible platen tempera
`ture pro?les.
`FIG. 6 depicts an alternate embodiment of a single
`turn edge loss heater having portions removed along its
`length.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`There has been a long felt need in the chemical vapor
`deposition arts for a platen heating system that has low
`capital costs, efficient operation to provide low operat
`ing costs and moderate voltage requirements to prevent
`arcing in the vacuum environment of chemical vapor
`deposition apparatus, especially at the heater terminals.
`The platen heating system constructed according to the
`teachings of the present invention satisfies all these
`criteria. In addition, the platen heating system of the
`invention can provide a predetermined uniform (?at) or
`non-uniform (tilted) temperature pro?le/ gradient
`across the platen as desired.
`Referring now to the drawings and to FIG. 1 in par
`ticular there is shown platen heating system 10 con
`structed according to the teachings of the invention.
`Platen heating system 10 includes individual resistance
`heaters 12, 14, and 16 respectively. Resistance heaters
`12, 14, and 16 may be made from standard resistance or
`graphite and coated with silicon carbide after suitable
`
`35
`
`SUMMARY OF THE INVENTION
`Brie?y the present invention is a novel heating means
`and method for heating a chemical vapor deposition
`chamber wafer support platen by providing a desired
`uniform or non-uniform temperature pro?le across the
`platen as desired. The novel heating means of the inven
`tion is able to create this temperature pro?le or gradient
`because it comprises two’or more individual heating
`means for heating at least first and second portions of
`the platen to predetermined temperatures. A preferred
`embodiment of the invention includes three or more
`individually controlled and powered heaters. The indi
`vidual heating means of the invention could be any type
`of heater and take any desired shape. The preferred
`embodiments of the invention include resistance heaters
`formed in annular shapes. More particularly, the platen
`heating system includes a spiral shaped main resistance
`heater that de?nes both an inner space (that area within
`what would be referred to as the inner diameter if the
`main heater was circular) and an outer space (that area
`outside what would be referred to as the outer diameter,
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`surface preparation including puri?cation. Resistance
`slightly greater at either inner heat zone 34 or outer heat
`zone 36 by simply turning up the power on inner edge
`heater 12 is the main heater for platen heating system 10
`and is in the shape of a spiral de?ning an inner spaced 22
`loss heater 14 or outer edge loss heater 16 as shown
`generally at graphs 84 and 86, respectively. Since sup
`and an outer space 24 respectively. Inner space 22 and
`port platen 52 is slowly rotating, it can be seen that a
`outer space 24 may be thought of at the space within
`uniform temperature pro?le is maintained across sup
`and without the inner diameter and outer diameter,
`port platen 52 in the circumferential direction while the
`respectively, of main heater 12, if main heater 12 was
`temperature pro?le in the radial direction can be tilted
`circular shaped. Main resistance heater 12 provides
`slightly, that is raised slightly in the center or at the
`uniform heat except at inner and outer spaces 22 and 24
`periphery of the support platen 52, as illustrated in
`respectively. Single turn edge loss resistance heaters 14
`graphs of 84 and 86. A typical range of temperature
`and 16 respectively provide the capacity to heat the
`elevations for the tilt is l°-30".
`portion of the platen within the inner space 22 and the
`portion of the platen near the inner periphery of the
`Referring now to FIG. 6 there is shown an alternate
`embodiment of a single turn edge loss heater 92 that
`outer space 24. Therefore three heat zones with individ
`ually controllable power supplies (any type of resis
`may used for either inner or outer edge loss heaters 14
`and 16 respectively. Edge loss heater 92 has portions
`tance heater power supply, as is well known in the art,
`along its length removed such as slots 94 to increase its
`may be used - generally three zone SCR ?xed control)
`resistance by presenting a convoluting path for current
`are created and are shown generally at 32, 34, and 36
`respectively and correspond to spiral resistance heater
`flow. Another alternative would be to use wire wound
`in a spiral for the single turn edge loss heaters length.
`12, inner edge loss heater 14 and outer edge loss heater
`In conclusion, the present invention discloses means
`16 respectively. Three temperature sensors shown at 42,
`and methods for creating a uniform circumferential
`44 and 46 sense the platen temperature of the three heat
`temperature gradient and a non-uniform radial tempera
`zones 32, 34 and 36 respectively and provide feedback
`ture gradient across a CVD reaction chamber support
`to the operator. The operator may then adjust the set
`platen. The invention teaches the use of multiple, indi
`points. In this way, platen heating system 10 will indi
`vidual, independently powered heating means such as
`cate when the predetermined temperature gradient has
`multiple resistance heaters disposed in ?xed radial posi
`been created by the individual heaters 12, 14 and 16 or
`tions along a support platen while the support platen is
`whether the power input to the individual heaters 12, 14
`rotatably disposed within the reaction chamber. By
`and 16 must be adjusted. Although a manual adjustment
`simply adjusting the power applied to the independent
`scheme has just been described for purposes of illustra
`heating means, a uniform ?at or non-uniform tilted
`tion, it is to be understood the teachings of the invention
`radial temperature pro?le can be created. When the
`encompass an automated control such as, for example a
`platen is rotated, the circumferential temperatures along
`microprocessor or computer controlled system.
`the platen will be integrated to create a uniform circum
`Referring now to FIGS. 2 and 3, there are shown a
`ferential temperature gradient/pro?le even when the
`bottom view and cross sectional view along the lines
`platen is subject to the non-uniform radial temperature
`3'—3’, respectively, of support platen 52. Support
`gradient. The non-uniform radial temperature gra
`platen 52 has recessed grooves 54, 56 and 58 machined
`dient/pro?le can be tilted in a range from one to thirty
`into its bottom surface. Temperature sensors 42, 44 and
`degrees centigrade towards either the center or the
`46, are mounted to ?t within grooves 54, 56- and 58,
`periphery of the support platen. The use of multiple
`respectively, as shown in FIG. 3. Also shown in FIG. 3
`independent heating means provides for reducing the
`is the location of main spiral resistance heater 12 and
`voltage requirements of each individual heating means.
`edge loss heaters 14 and 16, respectively, directly below
`Operating the heating system at reduced voltages pro
`and proximate bottom surface 62 of support platen 52.
`vide greater safety for operating personnel and inhibits
`Referring now to FIG. 4, there is shown a cross sec
`arcing at the heater terminals.
`tional view of chemical vapor deposition reaction
`45
`chamber 72 constructed according to the teachings of
`I claim:
`1. A heating system for heating a chemical vapor
`the invention. FIG. 4 shows the location of support
`deposition reaction chamber support platen, compris
`platen 52 and platen heating system 10 within chemical
`deposition reaction chamber 72. Platen heating system
`mg:
`a) ?rst and second heating means for heating ?rst and
`10 is mounted stationary within chemical vapor deposi
`second portions of said platen;
`tion reaction chamber 72 while wafer support platen 52
`b) ?rst and second temperature sensing means for
`is rotatably mounted within chemical vapor deposition
`sensing the temperature of said ?rst and second
`reaction chamber 72.
`portions of said platen respectively;
`In operation, chemical vapor deposition reaction
`c) ?rst and second power control means responsive
`chamber 72 wafer support platen 52 is rotated slowly
`respectively to said ?rst and second temperature
`while power is applied to stationary heating system 10,
`sensing means for varying the power input to said
`whereupon support platen 52 and any semiconductor
`?rst and second heating means to provide individ
`wafers supported thereon are raised to a predetermined
`ual temperature control of said ?rst and second
`temperature, for instance 800 degrees Fahrenheit. Re
`portions of said platen;
`ferring now to FIG. 3, main spiral heater 12, heats heat
`d) a third heating means for heating a third portion of
`zone 32 while edge loss heaters 14 and 16 heat heat
`the platen;
`zones 34 and 36, respectively. Referring now to FIG. 5,
`e) a third temperature sensing means for sensing the
`since all three individual heaters 12, 14 and 16 are indi
`temperature of said third portion of the platen; and
`vidually powered and controlled, the temperature of
`f) a third power control means for varying the power
`each individual heat zone 32, 34 and 36 may adjusted to
`65
`input to said third heating means to provide indi
`provide either a ?at uniform temperature pro?le across
`vidual temperature control of said third portion of
`support platen 52 such as shown generally at graph 82,
`the platen;
`or the temperature of support platen 52 may be adjusted
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`along its length to provide a convoluted path and
`wherein the ?rst heating means has a spiral shape
`thereby increased resistance to current ?ow.
`de?ning both an inner diameter and an outer diam
`6. The platen heating system of claim 2 wherein the
`eter, the second heating means has a single turn
`third graphite resistance heater is made of wire wound
`circular shape and the third heating means has a
`single turn circular shape, the second heating
`in a spiral to provide increased resistance.
`7. The platen heating system of claim 5_ wherein the
`means has a diameter less than the inner diameter of
`third graphite resistance heater has a cylindrical shape
`‘the ?rst heating means and is located within the
`having both a top and bottom surface and wherein the
`inner diameter of the ?rst heating means, the third
`missing portions are slits disposed along the top and
`heating means as a diameter greater than the outer
`bottom surfaces to a predetermined depth.
`diameter of the ?rst heating means and is located
`8. The platen heating system of claim 5 wherein the
`outside the outer diameter of the ?rst heating
`second graphite resistance heater has portions removed
`means.
`along its length to provide a convoluted path for cur
`2. The platen heating system of claim 1 wherein the
`rent ?ow and increased resistance to reduce current
`?rst, second and third heating means are resistance
`heaters.
`?ow.
`-
`9. The platen heating system of claim 8 wherein the
`3. The platen heating system of claim 2 wherein the
`second graphite resistance heater has a cylindrical
`?rst, second and third resistance heaters are made of
`shape having a top and bottom surface and inner and
`graphite and coated with silicon carbide.
`4. The platen heating system of claim 2 wherein the
`outer sidewall surfaces and wherein the removed por
`tions ar slits disposed along either the top or bottom
`?rst, second and third resistance heaters are made of
`20
`surface at predetermined locations and to predeter
`one of the materials from the group nickel chromium,
`mined depths along the inner and outer sidewall sur
`tungsten or other standard resistance wire.
`5. The platen heating system of claim 2 wherein the
`faces.
`third graphite resistance heater has portions missing
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