llllllllllllllIlllllllIIlIlIlllllllll||||lllllllllilllllllllllllllIIIIIIIII
`USOOOOOIMSH
`Umted States Statutory Invention Registration 119]
`[11] Reg. Number:
`
`H1145
`
`Anderson
`{43] Published:
`Mar. 2, 1993
`
`
`[54] RAPID TEMPERATURE RESPONSE WAFER
`CHUCK
`
`[75]
`
`Inventor: Richard L. Anderson, Austin, Tex.
`.
`.
`[73} “5‘8"”: 5mm“! Inc-4 Aus“n1Tex'
`[21] App]. No; 790 098
`’
`Nov. 6, 1991
`
`[22] Filed:
`
`~
`-
`Relmd U'S' Appl'cam“ Data
`Continuation of Ser. No. 587,718, Sep. 25, 1990, aban-
`doned.
`
`[63]
`
`Int. Cl.5 ........................ F258 19/02; F25B 29/00
`[51]
`152] US. Cl. ....................................... 165/61;62/51.1;
`62/5“; 118/724; 118/725; 118/728; 165/64;
`l65/80.4; 165/ 104.33; 165/908; 165/911;
`250/4922
`[58] Field of Search ................. .. 165/908, 104.33, 911,
`165/61, 64, 80.4; 118/724, 725, 728; 250/4922;
`62/51.], 52.1
`
`[56]
`
`4,628,991 12/1986 Hsiao et al.
`..
`........... 165/80
`
`
`4,635,709
`1/1987 Attoz ...... ..
`165/10433
`. . . . . . . . .. 118/59
`4,671,204
`6/1987 Ballou . . . . ..
`
`7/1987 Lamont . . . . . . . .. . .
`. . . . .. 148/15
`4,680,061
`
`.. 250/4421
`4,705,951 11/1987 Layman et a1.
`
`..
`..... .. 34/218
`2/1988 Hobson et a1.
`4,724,621
`
`4/1988 Kisa .... ... ..........
`..... 156/643
`4,738,748
`4,771,730 9/1988 Tezuka . . . . .
`. .. .. 118/723
`
`
`3/1989 Inoue .................. .. 204/192
`4,810,342
`6/1989 Bellows et al.
`.
`....... .. 165/908
`4,838,041
`
`4,912,600
`3/1990 Jaeger et al.
`165/104.33
`
`........ 165/80.1
`4,949,783
`8/1990 Lakioset al.
`4,969,511 11/1990 Person ................................ 165/80.4
`FOREIGN PATENT DOCUMENTS
`0136349
`7/1985 J
`“55/104 33
`aPan -----------------------------
`-
`1001239
`2/1983 U.S.S.R.
`.............................. 165/908
`Primary Examiner—David H. Brown
`Attorney, Agent, or Firm—William W. Kidd
`
`ABSTRACT
`[57]
`A wafer chuck having a substantially hollow cavity
`therein utilizes the latent vaporization of a liquid to
`extract heat from the wafer. An insulated heater pro-
`vides for heating the wafer to its desired operating point
`as rapidly as WSSible in “def ‘0 bring the wafer ‘0 its
`Operating 1301'mt before Plasma “Chins 01' dePOSition
`OCCUIS-
`
`_
`References cued
`U.S. PATENT DOCUMENTS
`165/908
`3 109 485 11/1963 Fortier ......
`.................
`H
`1...: 165/908
`3:414:753 12/1968 Hruda
`
`3/1970 Chu . . . .. . . . .
`. .. . .. 148/175
`3,501,356
`
`...... .. 165/26
`3,669,812 6/1972 Ensslin
`
`3,724,536 4/1973 Baxter
`165/27
`3,843,910 10/1974 Ringuet ..........
`165/908
`
`5/1975 Corboy et a1.
`.
`.. 117/201
`3,885,061
`4/1981 King ...............
`4,261,762
`148/15
`
`A statutory invention registration is not a patent. It has
`4,274,476
`6/1931 Gaffe"
`165/80
`
`the defensive attributes of a patent but does not have the
`1,339; g/iggl gm I.I.i''
`'‘'‘''" 165/80
`
`enforceable attributes of a patent. No article or advertise-
`' 165/104'33
`4’457’359 17/
`2
`man
`.
`/1984 Holden ...................... 165/80
`,
`,
`
`1/1985 McNeilly et a1.
`.
`4,496,609
`427/55 mm 0', the 111“! my use the tern patent, or any term
`
`9/1985 Holden ..............
`250/4431
`4,542,298
`“We”Ive 0’ ‘ Pm”, "he" “fem” ‘0 ‘ mmmry “1'
`
`4,549,407 113/1985 Grubs,- ,,,,,"
`165/911
`vention registration. For more specific information on the
`
`... .. 29/569
`4,603,466
`5/1986 Morley . .. .. . .
`rights associated with a statutory invention registration
`4,615,755 10/1986 Tracy et a1. ......................... 156/345
`see 35 U.S.C. 157.
`
`7
`12 Chums, 2 Drawing Sheets
`
`#
`
`l5
`.g::::=========‘--“-"-‘--
`gmwfixgwa;= ’3
`F““““““““““““;«'
`//
`
`
`
`Page 1 of 8
`
`Samsung Exhibit 1011
`
`
`
`Page 1 of 8
`
`Samsung Exhibit 1011
`
`

`

`US. Patent
`
`Mar. 2, 1993
`
`Sheet 1 of 2
`
`H 0,001,145
`
`
`
`Page 2 of 8
`
`
`
`Page 2 of 8
`
`

`

`_ US. Patent
`
`Mar. 2, 1993
`
`Sheet 2 of 2
`
`H 0,001,145
`
`u»\
`
`b\
`
`MV
`
`\\
`
`"““““““““‘“"““‘
`"““"“:“:““““““l
`"'..I.|'lll‘.'|.l'lIIII"I.t
`
`
`Page 3 of 8
`
`
`
`Page 3 of 8
`
`

`

`H1145
`
`1
`
`RAPID TEMPERATURE RESPONSE WAFER
`CHUCK
`
`This application is a continuation of application Ser.
`No. 587,718, filed on Sep. 25, 1990, now abandoned.
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates to the field of semicon-
`ductor manufacturing devices and, more particularly, to
`chucks for controlling wafer temperature.
`2. Prior Art
`.
`
`In the manufacture of semiconductor integrated cir-
`cuit devices, various circuit elements are formed in or
`on a base substrate, such as a silicon substrate. Gener—
`ally, the process of forming these various circuit ele—
`ments starts from a base wafer, which is typically flat
`and is circular in shape. On each of these flat circular
`wafers, a number of integrated circuit devices, typically
`known as “chips” are formed by the use of various
`well-known techniques,
`including photolithography,
`doping, depositing, etching, and annealing techniques,
`just to name a few.
`In performing some of these steps, a wafer is placed in
`a chamber in order for the wafer to undergo a necessary
`processing step, such as deposition or etching. When
`these wafers are loaded into a given chamber, the wafer
`is placed on a wafer chuck, which is a type of semicon-
`ductor platen. These platens, or chucks, are used to
`control the wafer temperature during a given process
`cycle. Because the wafer resides on the platen, by con-
`trolling the temperature of the platen, wafer tempera-
`ture can be controlled. Accordingly, elaborate mea-
`sures have been devised to address the various means
`available for controlling the temperature of the platen.
`Some of these prior art techniques are described in US.
`Pat. Nos. 3,501,356; 4,496,609; 3,669,812; 4,542,298;
`4,628,991;
`4,671,204;
`4,457,359;
`4,282,924;
`and
`3,885,061. These patents teach a technique of cooling
`the wafer by circulating liquids, such as water. Either
`the cooling of the apparatus as a whole is provided by
`the circulating cooling water, or in more sophisticated
`systems, channels or passages are provided in the base
`of the chuck to directly cool the wafer chuck.
`Another prior art device is described in US. Pat. No.
`4,274,476,
`in which heat created inside the wafer is
`transferred to an expandable heat pipe, wherein the heat
`causes the fluid in the heat pipe to boil and vaporize.
`The vaporizable liquid is inside the cavity for expanding
`the heat pipe when heated and for transferring heat
`from one plate to the other. Furthermore, another
`scheme is described in US. Pat. No. 3,724,536, in which
`a fluid coolant, such as carbon dioxide, undergoes a
`rapid expansion upon entering an expansion chamber,
`thereby cooling the conductive element and conse-
`quently the device under control.
`In practice, the temperature of the chuck must fre-
`quently be controlled at a temperature substantially
`below that of the wafer process temperature, especially
`when there is substantial energy input into the wafer.
`Substantial energy input to the wafer will usually occur
`when processing techniques such as plasma etch, chemi-
`cal vapor depositions (CVD), and electron cyclotron
`resonance-chemical vapor deposition (ECR-CVD), just
`to name a few, are used. In some of these processes, the
`power input to the wafer can be as much as 8 W/cmz.
`As an example, for a 6-inch wafer, this is equivalent to
`
`Page 4 of 8
`
`2
`a total power input of nearly 1500 watts. To maintain
`the wafer at the desired process temperature requires
`this amount of heat energy be removed from the wafer
`during the process. Thus, a substantial difference in
`temperature (AT) between the wafer and the chuck
`must be maintained in order to realize the required heat
`energy extraction from the wafer.
`In a prior art system utilizing the circulation of cool-
`ing water, a considerable amount of cooling water flow
`must be maintained in order to dissipate the heat gener-
`ated by such energy input. For example, an 1800 W
`energy input system would require approximately 0.5
`liter/second (6.6 gallons/minute) flow of cooling water
`having a AT value of 1° C. from inlet to outlet. Thus,
`considerable amount of cooling water must be circu-
`lated in order to dissipate the required energy. Al-
`though it is possible to substitute other cooling fluids to
`reduce the required volume of flow of the coolant,
`significant amount of liquid is still needed and the liquid
`must be maintained in a closed system for recirculation.
`In many instances condensation or other processes for
`reclaiming the liquid is needed within the closed system.
`Furthermore, with most prior art closed loop sys-
`tems, fluid passages are typically present within the
`wafer chuck to circulate the cooling fluid in order to
`dissipate the heat from the chuck. Additionally, in a
`closed loop system, the temperature of the circulating
`fluid will typically need to be controlled. In some in-
`stances where an expansion chamber is used, such as in
`a system utilizing liquid gas which is expanded to re-
`move the heat, a sophisticated closed loop system must
`be present in order to control the temperature of the
`chuck, as well as maintaining the proper flow of a spe-
`cially designated coolant, other than water, to the wafer
`chuck.
`-
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`In those special processes, such as plasma etch and
`ECR-CVD processes, additional temperature control
`problems are encountered. These processes deposit
`substantial amounts of energy into the wafer and the
`wafer must be cooled by the wafer chuck to keep it at
`the selected process temperature. For example, in one
`CVD-SiOz deposition process, the temperature of the
`chuck is controlled to a value in the range of 65' to 90°
`C. by circulating thermostated liquid through the base
`of the chuck. If a cold (room temperature) wafer is
`loaded onto the chuck, the wafer will be heated to the
`temperature of the chuck within a few seconds. The
`wafer temperature, however, is still 200°- to 400° C.
`below the optimum deposition temperature. If the film
`deposition is begun before the wafer is at this tempera-
`ture, the quality of the initial layer of the film will be
`inferior to that deposited at the optimum process tem-
`perature. Alternatively, with no silane flow into the
`reactor the plasma can be used to heat the wafer with-
`out deposition, but at the cost of an additional 15 to 20
`seconds added to the process. For a 120 second process
`that represents an increase in process time of about 16%
`or a proportional decrease in yield in the number of
`wafers that can be processed per hour.
`For maximum throughput of the tool in certain high
`energy processes, such as plasma processes, it is impera-
`tive that the wafer be brought up to its operating tem-
`perature as quickly as possible and once the operating
`temperature has been reached, to remove the process
`generated heat from the wafer in a controlled manner.
`_ In order to provide these objectives, it is preferred that
`a chuck be designed to accommodate the thermal shock
`of drastic temperature changes of the order of 200°
`
`55
`
`65
`
`
`
`Page 4 of 8
`
`

`

`3
`C./sec and yet maintain the ability to dissipate heat
`energy in order to control the temperature of the wafer.
`In such a design, it is preferable to design an economi-
`' cal, yet efficient system, to reach the desired objectives.
`SUMMARY OF THE INVENTION
`
`A wafer chuck which utilizes the latent heat of va-
`
`porization of water or other liquids to extract heat to
`cool the wafer is described. The chuck has a substan-
`
`10
`
`tially flat upper surface for the placement of a semicon-
`ductor wafer, but the chuck is substantially hollow in
`the interior. At the lower portion of the chuck, spray
`mechanisms are positioned into the cavity for spraying
`liquid in the cavity. The nozzles spray a mist of liquid to
`the underside surface of the chuck having the wafer 15
`residing thereon. Upon contact the liquid vaporizes if
`the chuck temperature is greater than the boiling point
`of the liquid. Heat extraction from the wafer is en-
`hanced by using the latent heat of vaporization of the
`liquid. The operating temperature of the chuck can be
`established by the selection of a liquid of suitable boiling
`point. A central exhaust opening is also provided at the
`lower portion of the chuck to remove vapor from the
`cavity. When water is used, the steam can be readily
`exhausted into the air. For other fluids, an external
`condenser can be used to recycle the fluid.
`An insulated heater is provided on the upper surface
`of the chuck, disposed between the chuck and the wa-
`fer, in order to raise the temperature of the wafer to its
`operating range. Thus, the wafer can be rapidly brought
`up to its operating temperature, prior to the commence-
`ment of the wafer process cycle.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`20
`
`25
`
`30
`
`FIG. 1 is pictorial view of a wafer chuck of the pres- 35
`ent invention.
`FIG. 2 is a cross-sectional view of the wafer chuck of
`FIG. 1.
`
`FIG. 3 is a drawing of the wafer chuck of the present
`invention, showing the placement of various inlet and 40
`exhaust openings.
`DETAILED DESCRIPTION OF THE
`
`50
`
`55
`
`PREFERRED EMBODIMENT
`A wafer chuck for using the vaporization of water to 45
`remove excess heat energy from a semiconductor wafer
`is described. In the following description, numerous
`specific details are set forth, such as specific shapes,
`materials, etc., in order to provide a thorough under-
`standing of the present invention. It will be obvious,
`however, to one skilled in the art that the present inven-
`tion may be practiced without these specific details. In
`other instances, well-known techniques have not been
`described in detail in order not to unnecessarily obscure
`the present invention.
`The present invention provides for a wafer chuck
`which is to be utilized in processing wafers in a temper-
`ature range of —150° to +500“ C. It is especially de-
`signed for use with processes where substantial energy
`input to the wafer is encountered, such as during plasma
`etch, CVD and ECR«CVD depositions, but not neces-
`sarily limited to these. Although the present invention is
`described in reference to its use in a plasma environ-
`ment, it is to be noted that the present invention can be
`used in non-plasma environment as well.
`In a typical plasma process a given semiconductor
`wafer is loaded into a chamber and onto a chuck which
`is most likely at or near room temperature. Then some
`
`65
`
`Page 5 of 8
`
`H1145
`
`4
`form of heating means will be required to raise the
`temperature of the wafer to the desired operating point
`if it is above room temperature. Conversely, if the de-
`sired operating point is below room temperature, then
`some form of cooling means, typically that provided by
`a lower boiling point liquid, will lower the temperature
`of the wafer below room temperature.
`Usually, the operating point falls within a tempera-
`ture range of — 150° to +500° C. Some finite amount of
`time is required to change the wafer temperature from
`room temperature to the operating temperature. If, in a
`plasma system, plasma is used to heat the wafer to raise
`it to the operating temperature, a significant portion of
`the total process time may be devoted to changing (rais-
`ing the temperature in this instance) the temperature of
`the wafer to the desired operating temperature. For
`process efficiency it is desirable to reach this operating
`temperature in the minimum amount of time possible, so
`that critical processing time is not utilized in the prepa-
`ration stage, but instead is used in the actual plasma
`processing stage for etching or depositing. However,
`once the operating temperature has been reached, the
`temperature of the wafer will continue to rise unless the
`chuck is capable of dissipating the process generated
`heat in order to maintain the wafer at a controllable
`operating temperature. Thus, for an efficient plasma
`processing operation, the wafer is brought to the oper-
`ating temperature as rapidly as possible by electrical
`heating. Once the operating temperature has been
`reached, the plasma process is switched on, the electri—
`cal heater is switched off and the liquid spray is started
`to provide cooling of the chuck in order to maintain the
`wafer at
`the desired operating temperature. When
`water is used as the cooling liquid, a cooling rate of
`greater than 200” C./sec can be realized.
`The wafer chuck of the present invention provides
`for rapid cooling to quickly change the chuck tempera-
`ture to maintain the wafer at the desired operating tem-
`perature when the plasma is switched on in a plasma
`etching or deposition reactor chamber. Optionally, the
`chuck of the present invention provides a means for
`heating the chuck and the wafer by introducing heat
`energy by the use of an electrical heater to bring the
`wafer quickly up to its operating temperature. In order
`to provide for the desired rapid heating and/or the
`rapid cooling of the chuck, the chuck must be capable
`of withstanding the severe thermal shock (temperature
`change per unit time) that the chuck will necessarily
`undergo during the cooling and heating cycles. The
`wafer chuck of the present invention provides for these
`requirements.
`Referring to FIGS. 1, 2, and 3, a .wafer chuck ll of
`the present invention is shown. Chuck 11 is a three-di-
`mensional disk which is circular in shape and substan-
`tially flat on its upper surface to accommodate a typical
`circular semiconductor wafer 20. The interior of chuck
`11 is substantially hollow, thereby forming a cavity 12
`At the lower surface 18 of chuck 11, a plurality
`of inlet openings 21 are disposed at various predeter-
`mined locations. Also along the bottom surface 18 of
`chuck 11, an outlet opening 25 is located. In the pre-
`ferred embodiment, outlet opening 25 is centrally dis-
`posed while inlet openings 21 are distributed concentri-
`cally and having equidistant separation. The actual
`number and position of the openings 21 are a design
`choice as long as the cooling constraints below are met.
`Furthermore, it is to be noted that although the present
`invention is described in terms of using water as the
`
`
`
`Page 5 of 8
`
`

`

`H1145
`
`6
`
`5
`cooling liquid, various other liquids ca be readily used
`without departing from the spirit and scope of the pres-
`ent invention.
`
`A liquid mist spray mechanism 22, such as a means
`having a jet or a spray nozzle 23, is inserted into each of
`the inlet openings 21. Nozzle (jet) 23 of each spray
`means 22 can reside within opening 21 without pene-
`trating into cavity 12 or, alternatively, it can actually
`penetrate into and reside within the region of cavity 12,
`as is shown in FIG. 2. The actual height of the penetra-
`tion of each nozzle 23 into cavity 12 (as well as the
`number and positioning of the nozzles) is a design
`choice, as long as the liquid mist spray from all nozzles
`23 covers substantially all of the underside surface area
`16 of chuck 11. The other end of each spray mechanism
`22, which end is external to cavity 12, is coupled to a
`pressurized liquid source. The exhaust opening 25 is
`coupled to an exhaust pipe 26 which provides a passage
`for the exhaust gas to an exhaust opening 27.
`In operation, the pressurized liquid causes each spray
`mechanism 22 to spray liquid in form of a mist to the
`underside 16 of chuck 11. If the chuck 11 is above the
`liquid temperature,
`the liquid will vaporize upon
`contact. The vaporization causes heat to be extracted
`from chuck 11. The cavity 12 provides for the expan-
`sion to take place when liquid is vaporized to gas. The
`gas is then exhausted through opening 27 without the
`use of forced exhaust and/or vacuum. In the preferred
`mode, water is expanded and exhausted as steam.
`The actual number and placement of the spray mech-
`anisms 22, is a design choice, as long as the spray 24
`from nozzles 23 are capable of spraying all of the under-
`side surface 16 of chuck 11. As shown in FIG. 3, the
`preferred embodiment has eight openings 21 disposed
`radially in a circular pattern about the center of chuck
`11. Each of the nozzles 23 cover a certain predeter-
`mined area of the underlying surface 16, such that all of
`the eight nozzles 23 are capable of spraying, substan-
`tially all of the underlying surface 16 of chuck 11.
`The chuck 11 of the preferred embodiment is con-
`structed from stainless steel. The other associated ele-
`ments 22, 23, and 26 are also constructed from stainless
`steel in order to have the same expansion properties as
`chuck 11. For operation below room temperature, alu-
`minum alloys or copper can be used. Two factors affect
`the choice of materials for the body of the chuck. The
`material of the chuck must be compatible with the
`chosen fluid over the temperature range of operation.
`For example, aluminum and water may not be acom-
`patible combination at higher temperatures. The second
`factor is the thermal expansion coefficient of the chuck
`material. The thermal expansion of the chuck materials
`must match closely the thermal expansion coefficient of
`the insulating materials bonded to the top of the chuck.
`Overlying the upper surface of chuck are two insulat-
`ing layers 13 and 14 having a heating layer 15 dispose
`there between. A wafer 20 is then positioned onto the
`upper insulating layer 14. The purpose of the insulating
`layers 13 and 14 is to previde insulation between the
`heater element 15 and the chuck 11, as well as the heater
`element 15 and wafer 20.
`The purpose of the heater element 15 is to rapidly
`heat the wafer 20 to raise the temperature of the wafer
`from room temperature to the operating temperature as
`rapidly as possible prior to the turning on of plasma
`energy. The preferred embodiment uses electrical en-
`ergy, wherein heater element 15 converts this electrical
`
`Page 6 of 8
`
`energy to heat energy. A variety of well-known materi-
`als can be readily used for element 15. Some of these are
`described below. The insulating layers 13 and 14 of the
`preferred embodiment are constructed from a cermet
`material. Cerment materials are used because of the
`property of readily transferring heat, while providing
`the necessary insulation of the electric heater element
`15.
`Some of the heater/cermet combinations are tungsten
`electrode embedded in a Ti-Alumina cermet, platinum
`with a Pt-Alumina cermet, or Nichrome (or Ni—Cr al-
`loy) with Cr-Alumina cermet. A critical consideration
`is to match the coefficient of thermal expansion of the
`heater material and the associated cermet. A desirable
`feature of the heater material is to have a low tempera-
`ture coefficient of resistance. It is to be noted that other
`combinations can be readily used.
`When the process temperature is above room temper-
`ature, the present invention provides for the wafer 20 to
`be rapidly heated to the process operating temperature
`and once that temperature is reached, it provides for the
`extraction of excess heat energy when the plasma is
`turned on. In practice, the preferred embodiment
`is
`capable of heating the chuck 11 from room temperature
`to an operating temperature of 100° to 500° C.
`in a
`matter of seconds, due to the low thermal mass heater
`employed. Then, once the plasma is switched on, the
`present invention is capable of quickly lowering the
`chuck temperature by the use of latent heat of vaporiza-
`tion of liquid.
`The cooling means takes advantage of the large latent
`heat of vaporization of the liquid applied as a mist (i.e.,
`suspension of tiny liquid droplets). The quantity of liq~
`uid vaporized in g/s for a unit heat input per unit area (1
`>_ W/cmz) is
`
`5
`
`10
`
`l5
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`fl _
`_q_
`t _ h,
`
`(Equation 1)
`
`where m is the mass of the liquid vaporized in grams, t
`is the time in seconds, q is the heat input per unit area
`per second (W/cm2=J/s-cm2), and h, is the heat of
`vaporization of the liquid in Joules/gram. The volume
`flow of liquid that is vaporized by the unit heat input
`per unit area is
`
`V”? = _I;n_ x
`
`'DIv-n
`
`(Equation 2)
`
`where p is the density of the liquid at 25" C. in g/cm3.
`The volume of gas exhausted to the atmosphere (press-
`ure=l atm) at ambient temperature (T =25“ C. or 298
`K) is
`
`55
`
`-"'— x 0.0327" x so
`Vm= M
`
`(Eqm‘i‘m 3)
`
`where M is the molecular weight in g/mol, 0.082 is the
`gas constant in liter-atm/mol-K, T is the temperature in
`K, and 60 converts the flow rate tk standard liters per
`minute (SLM). As an example, four liquids of different
`boiling points that might be used as the liquid for the
`wafer chuck of the present invention is provided in
`Table 1 below. The last two columns of Table 1 give the
`volumes of gas for two different heat
`inputs of l
`W/cm2 and 8 W/cm2 for a lSO—mm—diameter wafer.
`
`65
`
`
`
`Page 6 of 8
`
`

`

`H1145
`
`7
`
`TABLE 1
`Volume of Volume of
`V (gas SLM)
`Liquid for
`Gas for
`Heat of
`Boiling
`Point
`Vaporization
`1 W/cm2
`1 W/cm2
`for 150mm Wafer
`
`Liquid
`cc.)
`(J/g)
`(cm3)
`(SLM)
`@ 1 W/cmZ
`@ 8 W/cm2
`Nitrogen
`— 196
`199
`6.2 13-03
`2.6 13—01
`47.9
`383.1
`Freon m —R—22
`—40
`232
`3.6 15-03
`7.3 12-02
`13.3
`106.4
`Water
`100
`2260
`4.4 E—O4
`3.6 13-02
`6.5
`52.5
`
`Ethylene glycol
`197
`800
`1.1 13413
`2.9 5-02
`5.4
`3.0
`
`8
`
`Since, for water
`
`h,=2260 j/gm
`
`(Equation 4)
`
`with a heat energy input (qm) of 8 w/cm2 into a 150 mm
`diameter wafer is:
`
`9in=l4l3.7 watts (j/s)
`
`(Equation 5)
`
`This will be balanced by the heat extracted (qom) by
`the vaporizing the water, which is defined by:
`
`Gin — Gout = 0
`and
`
`gout = by)?—
`
`(Equation 6)
`
`'7
`'
`(Equauon )
`
`To extract this quantity of heat will require:
`
`L".I
`
`9am
`hv
`
`(Equation 8)
`
`signifying the
`In calculation rn/t=0.626 _gm/s,
`amount of water required to extract heat. Since the
`density of water p is l gm/cm3, the volume of liquid
`water evaporated and, therefore, which must be sup-
`plied is (m/t)/p=0.627 cm3/s.
`For a 120 second plasma process, the volume of
`water required to maintain the chuck temperature at
`100° C. is 75.3 cm3.
`The volume of gas (steam) that will be generated by
`the vaporization of 75.3 cm3 of water can be readily
`calculated. The number of moles of vaporized liquid is:
`
`0.626 gm/18 gm/mol = 3.48 ><10’2 mols/s
`
`(Equation 9)
`
`Using the perfect gas law
`
`
`V _ nRT
`_ P
`
`(Equation l0)
`
`where R=0.082 liter-atm/mole-K,
`T=373.15K (100° C.), and P=l atm,
`,
`so that V=849 std. cm3/s,
`which is approximately 51 standard liters/min.
`By the application of the above formulated steps, the
`amount of liquid input, as welI as the resultant gas ex-
`haust, can be readily calculated for various temperature
`differences. The particular examples above are for cool-
`ing the chuck to various temperatures from — 150° C. to
`197° C. Further,
`the specific example illustrated in
`Equations 4-10 apply to the use of water as the cooling
`liquid and similar calculations apply if other liquids are
`used.
`It is to be noted that when water is used, the exhaust
`gas is steam. That is, ordinary water (preferably distilled
`water) is sprayed to the underside of the wafer chuck to
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`cool the chuck temperature. It is the latent heat of va-
`porization of water which provides the rapid cooling.
`For certain liquids, such as water or nitrogen, no spe-
`cialized reclamation process and/or system is needed
`(although one can be utilized) and the converted gas
`can be readily exhausted to the atmosphere. Thus, a
`closed 100p system need not be required.
`However, with certain liquids, recovery may or will
`be necessary. For example, because of the expense and
`possible environmental problems with exhausting Fre-
`ons TM or ethylene glycol to the atmOSphere, a recov-
`ery condenser and recycling system will prove most
`practical. Although specific examples are detailed in
`Table 1, other liquids can be used to practice the present
`invention. Water is particularly desirable because of its
`large heat of vaporization, it is inexpensive and it is
`environmentally acceptable to exhaust
`to the atmo-
`Sphere as steam.
`Further, it is to be appreciated that a variety of heat-
`ing and insulating elements can be used for the elements
`13—15 of the present invention for heating the chuck to
`rapidly raise the temperature of the wafer to its process
`operating temperature. Due to properties exhibiting
`good thermal shock resistance, as well as good electri-
`cal resistance, cermet materials are recommended.
`Thus, a rapid temperature response wafer chuck is
`described.
`I claim:
`
`1. An apparatus for cooling a semiconductor wafer
`disposed thereon comprising:
`a body for having said semiconductor wafer reside
`thereon and said body having a hollow cavity
`therein;
`spray means coupled to said body and disposed
`within said cavity for spraying a liquid to at least a
`portion of an interior surface of said cavity which
`is proximal
`to said semiconductor wafer, but
`wherein said liquid is prevented from physically
`contacting said wafer;
`said liquid for extracting heat from said wafer by the
`use of latent heat of vaporization of said liquid
`when said liquid is sprayed onto said portion of said
`interior surface of said cavity and is vaporized
`upon contact with said interior surface of said cav-
`ity, such that said wafer is maintained at a predeter-
`mined temperature;
`exhaust means coupled to said cavity of said body for
`exhausting vaporized liquid from said cavity.
`2. The apparatus of claim 1 further including heating
`means coupled to a surface of said body upon which
`said semiconductor wafer resides, wherein said semi-
`conductor wafer is disposed onto said heating means
`and said heating means is utilized to rapidly heat said
`semiconductor wafer to a predetermined temperature.
`3. The apparatus of claim 1 wherein said apparatus
`utilizes wafer as said liquid.
`
`Page 7 of 8
`
`
`
`Page 7 of 8
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`

`

`H1145
`
`10
`9. A chuck for cooling a semiconductor wafer dis-
`posed thereon during plasma processing of said wafer
`comprising:
`a body having a substantially flat upper surface and a
`hollow cavity disposed therein;
`a heater having a substantially flat shape coupled to
`said upper surface of said body, wherein said semi-
`conductor wafer resides thereon;
`a plurality of spray jets coupled to said cavity of said
`chuck for spraying water to at least a portion of an
`interior surface of said cavity, including the under-
`side of said flat upper surface, but wherein said
`water is retained in said cavity and isolated from
`said semiconductor wafer;
`said water for extracting heat from said water by the
`use of latent heat of vaporization of said water
`when said water is sprayed onto said interior sur-
`face and is vaporized upon contact with said inte-
`rior surface of said cavity, such that said wafer is
`maintained at a predetermined temperature;
`said cavity having an exhaust opening for exhausting
`steam from said cavity to an atmospheric ambient.
`10. The chuck of claim 9 wherein said body is fabri-
`cated from stainless steel.
`11. The chuck of claim 10 wherein said heater is
`comprised of an electric heating element disposed be-
`tween a dielectric material.
`12. The chuck of claim 11 wherein said dielectric
`material is a cermet material.
`t
`t
`t
`
`t
`
`it
`
`9
`4. The apparatus of claim 1 wherein said apparatus
`utilizes liquid nitrogen as‘said liquid.
`5. A chuck for cooling a semiconductor wafer dis-
`posed thereon during processing of said wafer compris-
`mg:
`a body having a substantially flat upper surface for
`having said semiconductor wafer reside thereon
`and said body having a hollow cavity therein;
`a plurality of spray nozzles coupled to said cavity of
`said chuck for spraying water to at least a portion
`of an interior surface of said cavity, including the
`underside of said flat upper surface, but wherein
`said water is prevented from physically contacting
`said wafer;
`said water for extracting heat from said wafer by use
`of the latent heat of vaporization of said water
`when said water is sprayed onto said interior sur-
`face and is vaporized upon contact with said inte-
`rior surface of said cavity, such that said wafer is
`maintained at a predetermined temperature;
`said cavity having an exhaust opening for exhausting
`steam from said cavity to an atmospheric ambient.
`6. The chuck of claim 5 wherein said body is fabri-
`cated from stainless steel.
`7. The chuck of claim 5 further including a heater
`coupled to said upper surface of said body wherein said
`semiconductor wafer is disposed onto said heater and
`said heater is utilized to heat said semiconductor wafer.
`8. The chuck of claim 7 wherein said body is fabri-
`cated from stainless steel.
`
`5
`
`10
`
`15
`
`20
`
`25
`
`3O
`
`35
`
`45
`
`50
`
`55
`
`65
`
`Page 8 of 8
`
`
`
`Page 8 of 8
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`