U.S. patent application number 10/232364 was filed with the patent office on 2004-03-11 for wafer processing apparatus, wafer stage, and wafer processing method.
Invention is credited to Edamura, Manabu, Kanai, Saburou, Kanno, Seiichiro, Kihara, Hideki, Nishio, Ryoji, Okuda, Koji, Yoshioka, Ken.
Application Number | 20040045813 10/232364 |
Document ID | / |
Family ID | 31990406 |
Filed Date | 2004-03-11 |
United States Patent
Application |
20040045813 |
Kind Code |
A1 |
Kanno, Seiichiro ; et
al. |
March 11, 2004 |
Wafer processing apparatus, wafer stage, and wafer processing
method
Abstract
A heater function and an electrostatic chuck function are
incorporated in a ceramic plate for placing a wafer, and the
ceramic plate is fixed to a cooling jacket with ceramic bolts
having a low coefficient of thermal conductivity with an
intervening heat insulating member. In order to transmit heat input
in the wafer to the water-cooling jacket with high repeatability, a
heat-conducting member having elasticity in the vertical direction
is sandwiched between the ceramic plate and the cooling jacket. The
degradation of temperature distribution of wafers due to the
radiant heat radiation from the sidewall of the ceramic plate to
the chamber can be minimized by covering the circumference of the
ceramic plate with a radiation insulator.
Inventors: |
Kanno, Seiichiro;
(Niihari-gun, JP) ; Yoshioka, Ken; (Hikari-shi,
JP) ; Nishio, Ryoji; (Kudamatsu-shi, JP) ;
Kanai, Saburou; (Hikari-shi, JP) ; Kihara,
Hideki; (Kudamatsu-shi, JP) ; Okuda, Koji;
(Kudamatsu-shi, JP) ; Edamura, Manabu;
(Niihari-gun, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-9889
US
|
Family ID: |
31990406 |
Appl. No.: |
10/232364 |
Filed: |
September 3, 2002 |
Current U.S.
Class: |
204/242 ;
204/286.1 |
Current CPC
Class: |
C25D 7/123 20130101;
H01L 21/67109 20130101; C25D 21/02 20130101; H01J 2237/2001
20130101; H01L 21/67069 20130101; H01L 21/6831 20130101; C25D 7/00
20130101; C25D 17/001 20130101 |
Class at
Publication: |
204/242 ;
204/286.1 |
International
Class: |
C25D 017/00 |
Claims
What is claimed is:
1. A wafer stage for supporting semiconductor wafers comprising an
internal electrode for impressing a direct-current voltage and a
radio-frequency voltage and a ceramic plate incorporating a heater
wiring fixed with bolts to a cooling jacket whose inside is cooled
with a cooling medium, wherein said ceramic plate is
vacuum-insulated from said cooling jacket, and heat transfer
between said ceramic plate and said cooling jacket is performed by
radiant heat transmission.
2. A wafer stage for supporting semiconductor wafers comprising an
internal electrode for impressing a direct-current voltage and a
radio-frequency voltage and a ceramic plate incorporating a heater
wiring fixed with bolts to a cooling jacket whose inside is cooled
with a cooling medium, wherein a heat-conducting member having
elasticity in the vertical direction is inserted between said
ceramic plate and said cooling jacket so that both ends of said
heat-conducting member contact said ceramic plate and said cooling
jacket, and heat transfer between said ceramic plate and said
cooling jacket is performed by radiant heat transmission and the
heat conduction of said heat-conducting member.
3. A wafer processing apparatus for the plasma treatment of
semiconductor wafers having a wafer stage for supporting
semiconductor wafers comprising an internal electrode for
impressing a direct-current voltage and a radio-frequency voltage
and a ceramic plate incorporating a heater wiring fixed with bolts
to a cooling jacket whose inside is cooled with a cooling medium,
wherein said ceramic plate is vacuum-insulated from said cooling
jacket, the temperature of the member of said wafer processing
apparatus facing said ceramic plate is controlled with a
temperature control means, and said ceramic plate is cooled by heat
transfer by radiant heat transmission to said cooling jacket and
said member.
4. A wafer processing apparatus for the plasma treatment of
semiconductor wafers having a wafer stage for supporting
semiconductor wafers comprising an internal electrode for
impressing a direct-current voltage and a radio-frequency voltage
and a ceramic plate incorporating a heater wiring fixed with bolts
to a cooling jacket whose inside is cooled with a cooling medium,
wherein a heat-conducting member having elasticity in the vertical
direction is inserted between said ceramic plate and said cooling
jacket so that both ends of said heat-conducting member contact
said ceramic plate and said cooling jacket, the temperature of the
member of said wafer processing apparatus facing said ceramic plate
is controlled with a temperature control means, and said ceramic
plate is cooled by radiant heat transmission and heat conduction to
said cooling jacket and heat transfer by radiant heat transmission
to said member.
5. A wafer stage or a wafer processing apparatus according to
claims 1 to 4, wherein at least three heat insulating members of a
constant height are inserted between said ceramic plate and said
cooling jacket.
6. A wafer processing method wherein the temperature of said
ceramic plate according to claims 1 to 4 is controlled by
controlling at least one of electric power supplied to said heater,
the temperature of said member, the temperature of said cooling
medium, or the flow rate of said cooling medium.
7. The wafer stage or wafer processing apparatus according to
claims 1 to 4, wherein a black paint is applied onto the surface of
said cooling jacket.
8. The wafer stage or wafer processing apparatus according to
claims 1 to 4, wherein an irregularity is formed on onto the
surface of said cooling jacket.
9. The wafer stage or wafer processing apparatus according to
claims 2 or 4, wherein the material of said heat-conducting member
is a stainless steel or Inconel.
10. The wafer stage or wafer processing apparatus according to
claims 2 or 4, wherein the number of said heat-conducting member
can be adjusted.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a technique for
manufacturing a semiconductor. More specifically, the present
invention relates to an apparatus for processing wafers at a high
temperature, and to a wafer stage provided in the apparatus.
[0003] 2. Description of the Related Art
[0004] Examples of Known Technique
[0005] Japanese Patent Application Laid-open No. 11-87245
[0006] Ruthenium, the oxides thereof, and platinum are promising
candidates for materials used in the capacitor electrode of
next-generation semiconductor devices for the compatibility or the
like with capacitor insulating films of high dielectric constant.
Zirconium oxide, hafnium oxide, and the like have been studied as a
material for a gate insulating film substituting silicon oxide; and
PZT (a compound of platinum, zirconium, and titanium), BST (a
compound of barium, strontium, and titanium) have also been studied
as a capacitor film. For future semiconductor devices, the use of
various types of novel materials is studied. These novel materials
are thermally and chemically stable, and since the volatility of
these materials is extremely low, they are often called nonvolatile
materials.
[0007] In etching these nonvolatile materials, it is essential to
maintain the temperature of wafers in process high. Although the
temperature of wafers in conventional etching apparatus is
generally as low as -50.degree. C. to about 100.degree. C.,
nonvolatile materials are too stable to be etched in this range of
temperature. Nonvolatile materials must be processed at a
temperature as high as 200.degree. C. to 500.degree. C.
[0008] Therefore, a processing apparatus that can process wafers at
a high temperature has recently been required. In order to realize
such a processing apparatus, there is required a wafer stage that
can not only heat wafers to a high temperature, but also control
temperature with good response without degrading the temperature
distribution of wafers even if heat is inputted from plasma.
[0009] A method for controlling the temperature of wafers in
process is disclosed in Japanese Patent Application Laid-open No.
11-87245. In this example, a substrate holder for supporting wafers
is fabricated by bonding a plurality of blocks consisting of same
or different metals including heating blocks having built-in
heaters for heating wafers with high heat conduction and high
air-tightness using diffusion bonding.
[0010] In the disclosure of Japanese Patent Application Laid-open
No. 11-87245, since the electrostatic attraction block for
supporting wafers is integrated with the heat-conducting block, the
heating block, and the cooling block by diffusion bonding,
temperature difference between blocks is small, and the temperature
is easy to control; however, there are problems in that when the
usable life of the electrostatic attraction block is expired and
the block must be replaced, the entire substrate holder must be
replaced resulting in much labor and high costs.
[0011] In addition, since heat from the heater is directly
transmitted to the cooling block, there is a problem that a large
electric power must be inputted to the heater in operation
particularly at a high temperature.
[0012] Furthermore, since the dissipation of heat due to radiation
that affects the temperature distribution of wafers in process is
not taken into consideration, the temperature distribution of
wafers tends to degrade, and in the embodiments, a method for
supplying electric power independently to the center and the
circumference of the heater for improving the temperature
distribution of wafers is disclosed. However, there is a problem of
increase in costs in this case.
[0013] Therefore, the object of the present invention is to
provided a wafer stage and a wafer processing apparatus that can
maintain the temperature distribution of wafers uniform within a
wide temperature range between 200.degree. C. and about 500.degree.
C., and can prevent the temperature elevation of wafers by removing
heat input to the wafers when treated with plasma.
SUMMARY OF THE INVENTION
[0014] The above object can be achieved by incorporating a heater
function and an electrostatic chuck function in a ceramic plate for
placing a wafer, and fixing the ceramic plate to a cooling jacket
with ceramic bolts having a low coefficient of thermal conductivity
with an intervening heat insulating member; sandwiching a
heat-conducting member having elasticity in the vertical direction
between the ceramic plate and the cooling jacket, in order to
transmit heat input in the wafer to the water-cooling jacket with
high repeatability; and covering the circumference of the ceramic
plate with a radiation insulator in order to minimize the
degradation of temperature distribution of wafers due to the
radiant heat transmission from the sidewall of the ceramic plate to
the chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a sectional view showing a wafer processing
apparatus according to Embodiment 1 of the present invention;
[0016] FIG. 2 is a sectional view showing a wafer stage according
to Embodiment 1 of the present invention;
[0017] FIG. 3 is a diagram showing a model of heat balance
according to the embodiment of the present invention;
[0018] FIG. 4 is a table showing the heat balance of Embodiment 1
of the present invention;
[0019] FIG. 5 is a table showing the heat balance of Embodiment 1
of the present invention when a black paint is applied to the
surface of the cooling jacket;
[0020] FIG. 6 is a sectional view showing Embodiment 2 of the
present invention;
[0021] FIG. 7 is a perspective view showing the cooling jacket of
Embodiment 2 of the present invention;
[0022] FIG. 8 is a perspective view showing the heat-conducting
member of Embodiment 2 of the present invention;
[0023] FIG. 9 is a sectional view showing the heat-conducting
member of Embodiment 2 of the present invention;
[0024] FIG. 10 is a table showing the heat balance of Embodiment 2
of the present invention;
[0025] FIG. 11 is a graph showing the temperature distribution of
wafers according to Embodiment 2 of the present invention;
[0026] FIG. 12 is a perspective view showing the cooling jacket
according to Embodiment 3 of the present invention; and
[0027] FIG. 13 is a table showing the heat balance of Embodiment 3
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] The embodiments of the present invention will be described
below referring to the drawings.
[0029] FIGS. 1 and 2 show Embodiment 1 of the present invention.
FIG. 1 is a sectional view of a wafer stage of the present
invention actually applied to a plasma treatment apparatus; and
FIG. 2 is an enlarged sectional view of the wafer stage of the
present invention.
[0030] As illustrated in FIG. 1, an etching gas 11 is introduced
into a vacuum chamber 9, and the pressure in the chamber is
maintained at an adequate pressure by controlling the opening of a
valve 12 installed upstream the turbo-molecular pump 13. Above the
vacuum chamber is placed an alumina bell jar 10, and around the
bell jar 10 is install a coil 7. By connecting the coil 7 to a
radio frequency (RF) power source 8, and impressing an RF voltage
(e.g., 13.56 MHz) across the coil 7, inductively coupled plasma 6
is generated. A plurality of fans 27 are installed around the bell
jar 10 to maintain the temperature of the bell jar 10 constant
(about 70.degree. C. to 120.degree. C.). When a wafer 1 is exposed
to the plasma, etching is performed. During etching, the wafer 1 is
placed on the wafer stage 2, and the temperature of the wafer 1 is
controlled.
[0031] In order to impress a bias voltage to the wafer, a RF power
source 5 is connected to the wafer stage 2. A DC power source 22 is
connected to the power supply line 19 of the RF voltage to impart
an electrostatic chuck function to the wafer stage 2. In FIG. 1,
reference numeral 3 denotes a flow rate controller for controlling
the flow rate of the etching gas, 4 denotes a gate valve that opens
when the wafer is conveyed, enabling the forward-backward movement
of a conveying arm (not shown).
[0032] In Embodiment 1, in the state where a cooling jacket 14 and
a ceramic plate 15 are installed to form a layered structure, the
above-described space is constituted by a gap 37 formed on the
surface of the cooling jacket 14 facing the ceramic plate 15. In
order to adjust the distance between the cooling jacket 14 and the
ceramic plate 15, spacers 23 made of zirconia is sandwiched between
them, and fixed with bolts 36 made of zirconia. Since the distance
of the space constituted by the gap 37 must be adjusted accurately
in order to adjust the temperature of the wafer stage 2 in good
response, or to reproduce it accurately, the shape of the spacers
23, which affect the distance, is important.
[0033] The protruded portion of the cooling jacket 14 formed around
a hole linked to a through hole 29 (described later), formed in the
center portion of the cooling jacket 14 in the state combined with
the ceramic plate 15, contacts the lower surface of the ceramic
plate 15; and in the circumferential portion of the cooling jacket
14, the spacers 23 contact the upper surface of the cooling jacket
14 and the lower surface of the ceramic plate 15. A seal member is
provided on the protruded portion to maintain the hole linked to a
through hole 29 airtight from the gap 37. In the space constituted
by the gap 37, a communicating path (not shown) for communicating
with the space in the vacuum chamber 9 so that the space is
maintained at a high degree of vacuum when the vacuum chamber 9 is
evacuated and maintained at a high degree of vacuum. Thus, the
excessive heat transmission between the cooling jacket 14 and the
ceramic plate 15 through the fluid in the space can be prevented.
Also, ventilation can be performed through a ventilation means
directly linked to the space produced by the gap 37. If a large
quantity of heat conduction is required, a heat-conducting fluid
can be flowed in this space as required.
[0034] The reason why zirconia is used as the material of the bolts
36 for fixing the ceramic plate 15 is that the coefficient of
thermal conductivity is as low as about 3 W/mK, has a high fracture
toughness, and excels in mechanical strength. Therefore, the
quantity of heat escaped to the cooling jacket 14 through the bolts
64 can be minimized, and the local degradation of temperature
distribution of wafers can be prevented. However, the material of
the bolts 64 is not limited to zirconia, but other ceramic bolts or
metal bolts may be used as long as they can achieve the required
perform the material of the ceramic plate 15 is aluminum nitride,
which has a large coefficient of thermal conductivity, and a heater
16 is embedded therein. Therefore, the ceramic plate 15 can be
heated by inputting electric power to the heater 16. The reason why
the ceramic plate 15 is composed of aluminum nitride is that since
aluminum nitride has a large coefficient of thermal conductivity,
little temperature difference is produced on the surface, and the
degradation of temperature distribution of wafers can be prevented.
However, the material of the ceramic plate 15 is not limited to
aluminum nitride, but other materials may also be used.
[0035] An internal electrode 17 that imparts an electrostatic chuck
function and supplies an RF bias voltage to the wafer stage 2 is
embedded above the heater 16 in the ceramic plate 15. When a DC
voltage is impressed to the internal electrode 17, a potential
difference is generated between the internal electrode 17 and the
wafer 1 (the wafer 1 is exposed to plasma, and has a potential
which is substantially ground potential), an electric charge is
stored between the internal electrode 17 and the back of the wafer
1, and the wafer 1 is attracted and fixed to the ceramic plate 15.
In addition to the DC voltage, an RF voltage for inputting bias
power to the wager 1 is impressed to the internal electrode 17. The
RF power source 5 in FIG. 1 plays this role. As the electric
circuit, a DC power source 22 for the electrostatic chuck is
connected to the power supply line 19 through the coil 21. In
Embodiment 1, what is equivalent to the power supply line is a
hollow shaft 20 installed in the support member. Since a bias
voltage can be impressed to the wafer 1 when an RF voltage is
impressed to the internal electrode 17, ions in the plasma can be
drawn, and effects such as the increase of the etching rate and the
improvement of the shape after etching can be expected.
[0036] The reference numeral 55 denotes a sheathed thermocouple for
measuring the temperature of the ceramic plate 15. A through hole
54 is formed in a part of the cooling jacket 14, and a dent 53 is
formed on the back of the ceramic plate 15 corresponding to the
location of the through hole 54. The sheathed thermocouple 55 is
inserted so that the end of the sheathed thermocouple 55 contacts
the bottom of the dent 53. Since the measured temperature changes
if the contacting condition of the end of the sheathed thermocouple
55 changes, a flange 56 is installed on the thermocouple, a coil
spring 57 is inserted in the flange 56, and the entire sheathed
thermocouple 55 is fixed to the cooling jacket 14 with a holding
member 58. Therefore, even if the installing condition of the
ceramic plate 15 is somewhat changed, the contacting pressure of
the end of the sheathed thermocouple 55 and ceramic plate 15 is
maintained substantially constant, and a method for measuring
temperature with high repeatability can be provided. Based on the
temperature information, electric power to be supplied to the
heater 16 is controlled power is supplied to the heater 16 through
a through hole 39 formed in the cooling jacket 14. A socket 41
electrically connected to the heater 16 is built in the ceramic
plate 15, and an electric plug 42 connected to an external power
source is provided to meet the socket 41. Although only one
electric connecting portion to the heater 16 is described in
Embodiment 1, since a connector of the opposite polarity is
required, there are actually two electric connecting portions.
[0037] The reference numeral 38 denotes a radiation insulator for
reducing the dissipation of heat from the circumference of the
ceramic plate 15, and the surface of the radiation insulator is
chromium-plated. When the radiation insulator is provided, radiant
heat escaping to the internal wall of the vacuum chamber is reduced
to a half or less, and the degradation of temperature distribution
in the surface of the wafer stage 2 can be prevented.
[0038] In order to transmit heat inputted to the wafer in process
effectively to the wafer stage 2, and to improve the
controllability of the temperature of wafers, a heat-conducting gas
such as helium gas must be introduced between the back of the wafer
and the ceramic plate 15. In Embodiment 1, the heat-conducting gas
is supplied through a hollow shaft built in the supporting member
for impressing an RF voltage and a DC voltage to the internal
electrode 17. In other words, helium gas is introduced to the back
of the wafer 1 through the through hole 29 formed in the center of
the ceramic plate 15.
[0039] Channels 46 for circulating the cooling medium are formed
inside the cooling jacket 14. In Embodiment 1, cooling water
prepared in the clean room is used as the cooling medium. The
cooling water is fed to and discharged from the channel 46 through
flexible pipes 30. The flexible pipes 30 are used because the
entire wafer stage 2 moves up and down as described later. In FIG.
2, only the feeding side of the cooling water is shown, and the
return side is omitted. Although water is used as the cooling
medium in Embodiment 1, the cooling medium is not limited to water.
For example, chlorofluorocarbon-based cooling medium, such as
Fluorinert.TM. and Galden, can also be used. However, the use of
water is advantageous in that heat transfer quantity between water
and the ceramic plate 15 can be large when the pressure between
gaps is identical, because the heat transfer coefficient with the
portion for circulating the cooling medium (cooling jacket 14 in
Embodiment 1) is large. In other words, the pressure for securing
the same heat transfer quantity may be low. This moderates the
requirements for sealing helium, and becomes significantly
advantageous in designing the apparatus.
[0040] Wafers are conveyed by ascending and descending the wafer
stage 2 by the expansion and contraction of a bellows 35, and by
lifting the wafers with a pusher pin 32.
[0041] When a wafer is processed by thus impressing a bias voltage,
the temperature of the wafer is elevated by the heat inputted from
plasma. Although temperature rise may not arise problems if the
quantity of the heat input is small, normally, etching may be
poorly performed unless the temperature of wafers is well
controlled in the manufacturing process of semiconductors.
Therefore, in order to maintain wafer temperature high, the ceramic
plate 15 must be heated with the heater when there is no heat
input, and when processing is started and heat is inputted from
plasma, electric power supplied to the heater must be lowered to
adjust the wafer temperature. As the method for this, heat exchange
is performed between the ceramic plate 15 and the cooling jacket 14
by radiant heat transmission in Embodiment 1. The heat balance of
Embodiment 1, which is the basis of the concept of Embodiment 1,
will be described below referring to FIG. 3.
[0042] In FIG. 3, the reference numeral 15 denotes the output of
the heater; 31 denotes the radiant heat transmission to the cooling
jacket 14; and 33 denotes the radiant heat transmission to the bell
jar facing the wafer stage 2. Although heat conduction through
zirconia bolts for fixing the wafer stage 2 to the cooling jacket
14 is present, it can be ignored in Embodiment 1 because of a low
heat transfer coefficient, so explanation thereof is omitted. Heat
input from plasma during processing is denoted by reference numeral
34. First, in order to maintain the temperature of the wafer at as
high as 200.degree. C. to 500.degree. C., the wafer stage 2 must be
heated to 200.degree. C. to 500.degree. C. In this case, Equation
(1) must be satisfied in a steady state.
Heater output=Radiant heat transmission to the cooling
jacket+Radiant heat transmission to the bell jar (1)
[0043] On the other hand, when there is heat input to the wafer
stage during plasma treatment, Equation (2) must be met in order to
maintain the temperature of the wafer stage constant.
Heater output+Heat input from plasma=Radiant heat transmission to
the cooling jacket+Radiant heat transmission to the bell jar
(2)
[0044] The temperature of the wafer stage 2 can be maintained
constant if the apparatus is operated by the heater output of (1)
before starting processing and the heater output is lowered by the
heat input from plasma after starting processing. In other words,
if the heat input from plasma is the same or more than the radiant
heat transmission to the cooling jacket and the bell jar, the
temperature of the wafer elevates even if the power to the heater
is 0 W, and the apparatus is out of control. FIG. 4 shows the
results of calculation of the heat balance of Embodiment 1. From
FIG. 4, it is known that when the apparatus is operated at
400.degree. C., since the heater output without heat input from
plasma is 501 W, the allowable heat input from plasma is 501 W. In
the cases of 300.degree. C. and 200.degree. C., since the quantity
of radiant heat transmission reduces, the allowable heat input from
plasma is 246 W and 101 W, respectively.
[0045] Therefore, according to Embodiment 1, since the wafer stage
2 is fixed to the cooling jacket 14 using zirconia bolts, and heat
is transmitted to and from the cooling jacket and the bell jar by
radiant heat transmission, a wafer stage 2 is provided that can
realize uniform temperature distribution within a wide temperature
range of as high as 200.degree. C. to 400.degree. C. with a simple
structure, if the heat input to the wafer is 101 W or below.
[0046] Next, a method for further controllably increasing the heat
input to wafers than the above-described example will be described.
In Embodiment 1, the material of the cooling jacket is stainless
steel, and the surface facing the ceramic plate is simply a cut
surface. The emissivity of the surface is 0.3. The emissivity can
be measured using a direct method wherein a sample is heated and
the emissivity is measured, or an indirect method wherein the
emissivity is calculated based on the spectral reflectance obtained
from reflection spectrum measured by FTIR. When a black paint is
applied onto the surface for increasing the emissivity and the
radiant heat transmission to the cooling jacket, the radiant heat
transmission of the ceramic plate can be increased. FIG. 5 shows
the heat balance when the radiation factor is 0.9. From FIG. 5, it
is known that when the temperature of the ceramic plate is
400.degree. C., 300.degree. C., and 200.degree. C., the electric
power that can be supplied increases to 818 W, 403 W, and 157 W,
respectively.
[0047] Other than this method, a method wherein the surface of the
cooling jacket is made irregular to enlarge the surface area; or if
the material of the cooling jacket is aluminum, a method wherein
the surface is converted to black alumite can be considered.
However, what is important is to increase the emissivity of the
surface of the cooling jacket, and the means for this does not
limit the scope of the present invention.
[0048] FIG. 6 shows Embodiment 2 of the present invention.
[0049] In the structure of Embodiment 2, a ring-shaped
heat-conducting member 24 using Inconel is sandwiched between a
ceramic plate and a cooling jacket, so that the temperature of the
wafer 1 can be controlled even if the quantity of heat inputted to
the wafer 1 is larger than the quantity of heat in Embodiment 1.
The cooling jacket is provided with a groove 25 for aligning the
heat-conducting member 24 as illustrated in FIG. 7. FIG. 8 shows a
perspective view of the heat-conducting member 24, and FIG. 9 shows
a sectional view thereof.
[0050] When the vertical direction of FIGS. 8 and 9 is made the
height direction, the heat-conducting member 24 of Embodiment 2 has
a larger height than the height of the spacer 23. Thereby, the
upper end of the heat-conducting member 24 contacts the ceramic
plate 15, and the lower end thereof contacts the cooling jacket 14
with the ceramic plate 15 and the cooling jacket 14 attached
thereto. Furthermore, the heat-conducting member 24 has an elastic
portion that can expand or contract, and when the ceramic plate 15
and the cooling jacket 14 are attached or detached, the expanding
or contracting force of the elastic portion pushes the upper and
lower end against the ceramic plate 15 and the cooling jacket 14 to
enhance contracting, and lowers the resistance of heat conduction.
This elastic portion is connected so as to enhance heat conduction
to the end portions, and especially in Embodiment 2, it is
integrally constituted using the same material.
[0051] The elastic portion is bent or curved in the direction that
the plate having the thickness that can exert elasticity intersects
the expanding or contracting direction. By such a constitution,
both ends of the heat-conducting member contact the ceramic plate
and the cooling jacket with high repeatability when the ceramic
plate fitted to the groove of the cooling jacket is fixed to the
cooling jacket.
[0052] Although the cross-sectional shape of the heat-conducting
member has a W-shape as illustrated in FIG. 9, the cross-sectional
shape of a U-shape or a C-shape can also be considered. What is
important is that the heat-conducting member has elasticity in the
height (thickness) direction. Since the purpose of the
heat-conducting member is to control the quantity of heat
conduction from the ceramic plate to the cooling jacket, the
preferable properties of the material is that it has heat
resistance, can easily have more reduced thickness, and has an
ensured elasticity in the thickness direction after its thickness
reduced, the heat resistance of the heat-conducting member after
processing realizes the expected quantity of heat conduction, and
the costs are low. Although Inconel is used in Embodiment 2 as the
material to meet these requirements, a stainless steel is also
considered as a candidate.
[0053] The elasticity secures the repeatability of the contacting
of the both ends of the heat-conducting member, and the thermal
resistance is determined by the length in the thickness direction
and the thickness. However, these should be determined by
experiments for actual applications. The estimated values of the
heat-conducting member of Embodiment 2 by calculation are: the
coefficient of thermal conductivity of Inconel is 12 W/mK, the
thickness is 0.3 mm, the length in the thickness direction is 16
mm, the diameter is 210 mm, and the thermal resistance is 6.7 K/W.
The thermal resistance actually evaluated is 6.4 K/W, which
substantially agrees with the calculated value. This shows that the
contacting thermal resistance is as small as can be ignored due to
the elasticity of the heat-conducting member, and if the thickness,
length, and the like are controlled, substantially desired thermal
resistance can be realized.
[0054] FIG. 10 shows the heat balance of Embodiment 2 whereto a
heat-conducting member of a thermal conductance of 0.3 W/K is
applied. From FIG. 10, it is known that when the temperature of the
ceramic plate is 400.degree. C., 300.degree. C., and 200.degree.
C., the electric power that can be supplied increases to 921 W, 477
W, and 202 W, respectively.
[0055] Therefore, according to Embodiment 2, since a
heat-conducting member is sandwiched between the ceramic plate and
the cooling jacket, if the heat input is 202 W or less, a uniform
temperature distribution can be realized within a wide temperature
range as high as between 200.degree. C. and 500.degree. C. by the
simple structure as in Embodiment 1.
[0056] Although the heat-conducting member of Embodiment 2 is
ring-shaped, and is disposed coaxially with the center axis of the
cooling jacket, and this is because the distribution of heat
transfer is made axisymmetric, the present invention is not limited
to this structure. For example, a plurality of small ring-shaped
heat-conducting members maybe arranged. What is important is that
the heat-conducting member has elasticity in the thickness
direction, and the thermal resistance is controlled. When the
heat-conducting member is disposed in the vicinity of the
circumference as Embodiment 2, since the wraparound of the reaction
products or gases that can deposit is reduced, and the effects such
as decrease in the number of cleaning and the elongation of usable
life can be expected.
[0057] FIG. 11 shows the results of measurement of temperature
distribution on the surface of the wafer when the wafer is held
using the wafer processing apparatus of Embodiment 2. The
temperature of the wafer is measured using a thermocouple
manufactured by SensArray Japan Corporation buried in the wafer.
From FIG. 11, it is known that substantially uniform temperature
distribution of within .+-.7.degree. C. from the mean temperature
of the wafer from 283.degree. C. to 414.degree. C. can be
realized.
[0058] FIG. 12 shows the surface of the cooling jacket of
Embodiment 3 of the present invention. In Embodiment 3, a groove 26
is added inside the groove 25 in order to introduce two
heat-conducting members of Embodiment 2. This example is an
effective means for further improving the heat conduction capacity
of the heat-conducting member when the heat input to the wafer is
larger than the heat input of Embodiment 2. FIG. 13 shows the heat
balance when the thickness and the shape of the heat-conducting
member are reviewed, two heat-conducting members are used, and the
thermal conductance is made 1 W/K. From FIG. 13, it is known that
when the temperature of the ceramic plate is 400.degree. C.,
300.degree. C., and 200.degree. C., the electric power that can be
supplied increases to 1168 W, 652 W, and 307 W, respectively.
[0059] Although the surface of the heat-conducting member is not
specially treated in the above embodiments, if the surface is
plated by a soft metal such as nickel and gold, the repeatability
of contacting of the ceramic plate with the cooling jacket will
further be improved.
[0060] Although the case where the temperature of the bell jar
facing the wafer stage is controlled to 70.degree. C. to
120.degree. C. is described in the embodiments of the present
invention, the temperature control is not always necessary. When
the temperature control is not performed, the structure of the
processing apparatus can be simplified, and the effect of cost
reduction can be expected. However, in such a case, the temperature
of the bell jar elevates with increase in the number of processed
wafers, the effect of exhaust heat by radiation to the bell jar
reduces, and the above-described controllable wafer bias power
lowers. Also, there is a problem of change in etching properties
due to change in depositing state under the conditions where
reaction products deposit on the internal wall of the bell jar, and
whether temperature control is performed or not should be
determined by the users of the apparatus.
[0061] Although the electrostatic chuck for fixing wafers is a
chuck having a monopolar internal electrode, known as a monopole
system, the present invention is not limited thereto. The
electrostatic chuck may have two independent internal electrodes,
known as a bipolar system. Although this system has disadvantages
that the structure is complicated because of the need of two
internal electrodes, and two power sources are required, it can
attract wafers without plasma, and since the cooling gas can be
introduced to the back of the wafers before starting plasma
treatment, this system has the advantage of excelling in
temperature controllability.
[0062] Although the plasma source of the processing apparatus in
the embodiments of the present invention is induction-coupling
plasma, the present invention is not limited thereto. For example,
a plasma source may be of the parallel plate system, the UHF-band
electromagnetic radiation discharge system or the microwave system,
or the plasma system using the VHF band of several ten to about 300
megahertz. Other than these, for example, a magnetron-type plasma
treatment apparatus using magnetic fields may also be used. The
adoption of plasma source among these should be selected according
to the properties of the material to be actually treated.
[0063] According to the present invention, as described above, the
temperature distribution of wafers can be maintained uniform within
a wide range from 200.degree. C. to a high temperature such as
500.degree. C., and the temperature variation can be minimized even
during processing. Therefore, nonvolatile materials, which cannot
be etched by normal processes, can be subjected to etching
treatment.
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