U.S. patent application number 10/011418 was filed with the patent office on 2002-07-11 for method and apparatus for heating a wafer, and method and apparatus for baking a photoresist film on a wafer.
Invention is credited to Park, Chan-Hoon.
Application Number | 20020088608 10/011418 |
Document ID | / |
Family ID | 27350033 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020088608 |
Kind Code |
A1 |
Park, Chan-Hoon |
July 11, 2002 |
Method and apparatus for heating a wafer, and method and apparatus
for baking a photoresist film on a wafer
Abstract
To heat an object, a first solid heat transfer medium is
supplied with heat. The heat is transmitted from the first solid
heat transfer medium to a fluid heat transfer medium which is
partitioned into an interconnected plurality of evaporation
cavities each containing a liquid. The heat causes the liquid to
evaporate into a plurality of vapor parts in the respective
plurality of evaporation cavities, and the plurality of vapor parts
are guided in parallel in an upward direction towards the object.
The vapor parts contact a second solid heat transfer medium to heat
the second solid heat transfer medium, thereby transmitting the
heat to the second solid heat transfer medium. The second solid
heat transfer medium is thermally contacted with the object to
transmit the heat from the second solid heat transfer medium to the
object.
Inventors: |
Park, Chan-Hoon; (Seoul,
KR) |
Correspondence
Address: |
VOLENTINE FRANCOS, P.L.LC.
SUITE 150
12200 SUNRISE VALLEY DRIVE
RESTON
VA
20191
US
|
Family ID: |
27350033 |
Appl. No.: |
10/011418 |
Filed: |
December 11, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10011418 |
Dec 11, 2001 |
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09624776 |
Jul 25, 2000 |
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09624776 |
Jul 25, 2000 |
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09484051 |
Jan 18, 2000 |
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Current U.S.
Class: |
165/80.3 ;
165/104.21 |
Current CPC
Class: |
H01L 21/67103 20130101;
H01L 21/67109 20130101; F28D 15/0233 20130101 |
Class at
Publication: |
165/80.3 ;
165/104.21 |
International
Class: |
F28D 015/00; F28F
007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 26, 1999 |
KR |
99-30350 |
Claims
What is claimed is:
1. A method for uniformly heating an object, comprising: supplying
a first solid heat transfer medium with heat; transmitting the heat
from the first solid heat transfer medium to a fluid heat transfer
medium which is partitioned into an interconnected plurality of
evaporation cavities each containing a liquid, wherein the heat
causes the liquid to evaporate into a plurality of vapor parts in
the respective plurality of evaporation cavities, and wherein the
plurality of vapor parts are guided in parallel in an upward
direction towards the object; contacting the vapor parts with a
second solid heat transfer medium to heat the second solid heat
transfer medium, thereby transmitting the heat to the second solid
heat transfer medium; and thermally contacting the second solid
heat transfer medium with the object to transmit the heat from the
second solid heat transfer medium to the object.
2. The method for heating an object as claimed in claim 1, further
comprising: generating the heat; transmitting the heat to a lower
solid heat transfer medium to heat the lower solid heat transfer
medium; and thermally contacting the lower solid heat transfer
medium with the first solid heat transfer medium to transmit the
heat to the first solid heat transfer medium.
3. The method for heating an object as claimed in claim 1, wherein
an upper portion of each of the plurality of evaporation cavities
has a curved cross-sectional configuration, and wherein the
plurality of vapor parts contact the second solid heat transfer
medium at the upper portion of the respective plurality of
evaporation cavities.
4. The method for heating an object as claimed in claim 3, wherein
the plurality of vapor parts partially condense to generate a
latent heat which is transmitted to the second solid heat transfer
medium.
5. The method for heating an object as claimed in claim 1, further
comprising condensing the plurality of vapor parts to reform the
liquid, wherein the liquid is repeatedly evaporated into the vapor
parts and the vapor parts are repeatedly condensed into the liquid
so as to circulate within each the evaporation cavities of the
fluid heat transfer medium.
6. The method for heating an object as claimed in claim 1, wherein
each of the vapor parts is partially mixed with a vapor part
contained in an adjacent evaporation cavity of the fluid heat
transfer medium while being guided toward the object.
7. The method for heating an object as claimed in claim 6, wherein
the fluid heat transfer medium has a circular outer periphery, and
wherein each of the vapor parts is mixed with a vapor part
contained in a radially or circularly adjacent evaporation
cavity.
8. The method for heating an object as claimed in claim 1, wherein
the fluid heat transfer medium has a circular outer periphery, and
wherein the plurality of evaporation cavities are partitioned into
a plurality of concentric or spiral circles which are divided into
a plurality of radial sectors.
9. The method for heating an object as claimed in claim 8, wherein
a sector angle of each of the plurality of radial sectors is about
10 to 20 degrees.
10. The method for heating an object as claimed in claim 1, wherein
the object is a photoresist film coated on a wafer.
11. The method for heating an object as claimed in claim 1, wherein
the liquid is an inert perfluorocabon-type solvent which has a
higher critical temperature under an atmosphere than the sum of a
target temperature for the object plus 100.degree. C.
12. A method for baking a photoresist film on a wafer, comprising:
coating a photoresist solution on a wafer to form the photoresist
film; exposing the photoresist film to a light; supplying a first
solid heat transfer medium with heat; transmitting the heat from
the first solid heat transfer medium to a fluid heat transfer
medium which is partitioned into an interconnected plurality of
evaporation cavities each containing a liquid, wherein the heat
causes the liquid to evaporate into a plurality of vapor parts in
the respective plurality of evaporation cavities, and wherein the
plurality of vapor parts are guided in parallel in an upward
direction towards the wafer; contacting the vapor parts with a
second solid heat transfer medium to heat the second solid heat
transfer medium, thereby transmitting the heat to the second solid
heat transfer medium; and thermally contacting the second solid
heat transfer medium with the wafer to transmit the heat from the
second solid heat transfer medium to the wafer, thereby baking the
photoresist film on the wafer.
13. The method for baking a photoresist film on a wafer as claimed
in claim 12, wherein the light is a deep ultraviolet light.
14. The method for baking a photoresist film on a wafer as claimed
in claim 12, wherein the photoresist film is baked at a temperature
of about 140 to 150.degree. C. for 0.5 to 1.5 minutes.
15. A method for forming a photoresist pattern, comprising coating
a photoresist solution on a wafer to form a photoresist film,
exposing the photoresist film to a light, developing the exposed
photoresist film to form a first photoresist pattern having a first
opening of a first size, and reflowing the first photoresist
pattern to form a second photoresist pattern having a second
opening of a second size which is smaller than the first size,
wherein said reflowing of the first photoresist pattern comprises:
supplying a first solid heat transfer medium with heat;
transmitting the heat from the first solid heat transfer medium to
a fluid heat transfer medium which is partitioned into an
interconnected plurality of evaporation cavities each containing a
liquid, wherein the heat causes the liquid to evaporate into a
plurality of vapor parts in the respective plurality of evaporation
cavities, and wherein the plurality of vapor parts are guided in
parallel in an upward direction towards the wafer; contacting the
vapor parts with a second solid heat transfer medium to heat the
second solid heat transfer medium, thereby transmitting the heat to
the second solid heat transfer medium; and thermally contacting the
second solid heat transfer medium with the wafer to transmit the
heat from the second solid heat transfer medium to the wafer,
whereby the first photoresist pattern is heated to reflow.
16. An apparatus for heating an object, said apparatus comprising:
a first solid heat transfer medium; a fluid heat transfer medium,
thermally coupled to the first solid heat transfer medium, which is
partitioned into an interconnected plurality evaporation cavities;
a second solid heat transfer medium, thermally coupled to the fluid
heat transfer medium, for making thermal contact with the object;
wherein the plurality of evaporation cavities extend in a same
plane between the first and second solid heat transfer mediums.
17. An apparatus for heating an object as claimed in claim 16,
further comprising a liquid sealed within the plurality of
evaporation cavities of the fluid heat transfer medium.
18. The apparatus for heating an object as claimed in claim 16,
further comprising a heating element, and a lower solid heat
transfer medium thermally coupled between the heating element and
the first solid heat transfer medium.
19. The apparatus for heating an object as claimed in claim 18,
wherein the heating element is at least partially contained in a
groove formed at a lower surface of the lower solid heat transfer
medium.
20. The apparatus for heating an object as claimed in claim 19,
wherein the groove has a spiral configuration, and wherein a pitch
of the spiral configuration is shorter at an outer peripheral
region than at a central region of the lower surface portion.
21. The apparatus for heating an object as claimed in claim 16,
wherein said second solid heat transfer medium is integrally formed
with said first solid heat transfer medium.
22. The apparatus for heating an object as claimed in claim 16,
wherein the first and second solid heat transfer media and the
fluid heat transfer medium each have a circular and planar
configuration.
23. The apparatus for heating an object as claimed in claim 22,
wherein a diameter of the fluid heat transfer medium is equal to
about 0.9 to 0.98 times a diameter of the first and second solid
heat transfer media.
24. The apparatus for heating an object as claimed in claim 22,
wherein the fluid heat transfer medium has a circular outer
periphery, and wherein the plurality of evaporation cavities are
partitioned into a plurality of concentric or spiral circles which
are divided into a plurality of radial sectors.
25. The apparatus for heating an object as claimed in claim 17,
wherein an occupied volume of the liquid within the fluid heat
transfer medium is about 15 to 25% of a volume of fluid heat
transfer medium.
26. The apparatus for heating an object as claimed in claim 16,
wherein a thickness of the fluid heat transfer medium is about 40%
to 60% of a combined thickness of the first and second solid heat
transfer media and the fluid heat transfer medium.
27. The apparatus for heating an object as claimed in claim 17,
wherein said fluid is an inert perfluorocabon-type solvent which
has a higher critical temperature under an atmosphere than the sum
of an object target temperature plus 100.degree. C.
28. An apparatus for heating a wafer, said apparatus comprising: a
heating element; a lower solid heat transfer medium thermally
coupled to the heating element; a first solid heat transfer medium
thermally coupled to an upper surface of the lower solid heat
medium; a second solid heat transfer medium having a wafer mounting
surface and thermally coupled to said first solid heat transfer
medium opposite said wafer mounting surface; a fluid heat transfer
medium defined by a plurality of interconnected evaporation
cavities interposed between said first and second solid heat
transfer media.
29. The apparatus for heating a wafer as claimed in claim 28,
wherein the plurality of evaporation cavities are partitioned into
a plurality of concentric or spiral circles which are radially
divided into a plurality of radial sectors.
30. The apparatus for heating a wafer as claimed in claim 29,
further comprising a liquid sealed within the plurality of
evaporation cavities.
31. The apparatus for heating a wafer as claimed in claim 29,
wherein the first and second solid heat transfer media are circular
and have a diameter which is greater than a diameter of the wafer
mounting surface.
32. The apparatus for heating a wafer as claimed in claim 31,
wherein the first and second solid heat transfer media are
integrally formed.
33. The apparatus for heating a wafer as claimed in claim 28,
wherein the heating element is located in a spiral groove formed in
a lower surface of the lower solid heat transfer medium.
34. The method for heating an object as claimed in claim 28,
wherein an upper portion of each of the plurality of evaporation
cavities has a curved cross-sectional configuration.
Description
CROSS-REFERENCE OF RELATED APPLICATIONS
[0001] This application is a Continuation-in-part application of
"WAFER HEATING APPARATUS HAVING FLUID HEAT TRANSFER MEDIUM AND
METHOD OF HEATING A WAFER USING THE SAME", by the present inventor,
Ser. No. 09/484,051, filed on Jan. 18, 2000, the contents of which
are herein incorporated by reference in their entirety. This
application also relies for priority upon Korean Patent Application
No. 99-30350 filed on Jul. 26, 1999, the contents of which are
herein incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method for heating a
wafer, a method for baking a photoresist film on a wafer, an
apparatus for heating a wafer, and an apparatus for baking a
photoresist film on the wafer. More particularly, the present
invention relates to a method for uniformly heating a wafer during
a photolithography process for forming a photoresist pattern, a
method for uniformly baking a photoresist film on a wafer for
forming a photoresist pattern, an apparatus for performing this
heating method, and an apparatus for performing this baking
method.
[0004] 2. Description of the Related Art
[0005] The fabricating of semiconductor devices typically includes
a photolithography process in which a wafer is coated with liquid
photoresist (PR) to form a PR film. The PR film is patterned by
being exposed to light produced by an optical source and passed
through a mask or reticle. The pattern is then developed, and the
wafer is heated to a predetermined temperature several times
throughout the course of these steps.
[0006] Apparatus for performing this photolithography process thus
requires a PR coater, an exposure device, a developer, and a baking
unit. The current trend in such technology is the use of a system
in which the PR coater, the developer and the baking unit are
clustered in one place, whereby the distance required to move the
wafer between the devices and hence, the time required to move the
wafer therebetween, is minimized. In other words, the clustered
system is capable of performing the conventional photolithography
process with a high degree of efficiency.
[0007] The PR coater is typically of a type which performs a spin
coating method in which the wafer is rotated at a predetermined
speed, and photoresist solution is sprayed onto the rotating wafer.
As a result, the photoresist is uniformly spread over the wafer by
centrifugal force.
[0008] The heating of the wafer during the fabricating of a
semiconductor device is generally considered to include four steps.
The first step is a pre-baking step of heating a wafer at a
predetermined temperature to evaporate organic materials or foreign
materials from the surface of the wafer. The second step is a
soft-baking step of heating the wafer just after the wafer is
coated with the photoresist in order to dry the photoresist and to
strongly attach the film of photoresist to the surface of the
wafer. The third step is a post-exposure-baking (PEB) step
(described below) of heating the photoresist which has been
exposed. The fourth step is a hard-baking step of heating a wafer
just after the photoresist film has been developed so as to
strongly attach the resultant photoresist pattern to the wafer
surface.
[0009] When the exposure device comprises a source of ultra violet
(UV) and deep ultra violet (DUV) light, the light diffracts and
produces interference according to the reflectivity and refractive
index of the substrate, such as a wafer, and the optical
absorptivity of the photoresist film, which is irradiated with the
light. The phenomena of interference, in turn, causes both the
profile of the pattern of the photoresist to be abnormal, and the
critical dimensions of the pattern to be non-uniform. The PEB step
is performed to compensate for these problems. In the PEB step, the
exposed photoresist film is heated at a predetermined temperature
to rearrange the resins which were optically decomposed due to
thermal diffusion, thereby cleaning the cross section of a profile
of the exposed pattern. When the exposure light is a DUV light, a
chemically-amplified resist is used as the photoresist. A portion
of the chemically-amplified resist, which is exposed by thermal
treatment, changes into an acid which is soluble in a developing
solution. Also, the alteration of the chemically-amplified resist
occurs due to a chain reaction, so that the balance of heat applied
to the entire wafer in the PEB step has the greatest effect on the
uniformity of the critical dimensions of the photoresist
pattern.
[0010] Hence, a uniform heating of the entire surface of the wafer
is very important in increasing the yield. A heating device of a
conventional baking unit, as shown in FIG. 1, includes a lower
plate 2 in which an electrical heat source, that is, a heater 21 is
installed. The heater 21 is situated just below the lower surface
of an upper plate 1 on which a wafer 100 is supported. Referring to
FIGS. 2 and 3, a spiral groove 22 is formed in the upper surface of
the lower plate 2, and the heater 21 is seated in the groove 22. In
this structure, heat generated by the heater 21 is transferred from
the lower plate 2 to the upper plate 1 to heat the wafer 100 on the
upper plate 1. Also, the power of the heater 21 is
feedback-controlled, by detecting the temperature of the upper
plate 1 using a temperature sensor (not shown) which is installed
on the lower plate 2, so that the temperature is kept within a
predetermined range. In the conventional heating device, heat is
conducted via the bodies of the upper and lower plates 1 and 2,
respectively. Consequently, as discussed below, an uneven thermal
distribution occurs at the surface of the upper plate 1.
[0011] FIG. 4 is a temperature distribution diagram illustrating
the temperature at the surface of a wafer heated by the
conventional heating device, wherein the temperature difference
between adjacent isotherms is 0.02.degree. C. As shown in FIG. 4,
the temperature distribution is irregular and abnormally distorted,
and the difference in the temperature between the coolest and
warmest regions is about 1.76.degree. C. In this figure, bold
isotherm A crossing the center of a wafer indicates a temperature
of 145.31.degree. C., isotherm B indicates a temperature of
146.28.degree. C., and isotherm C indicates a temperature of
144.32.degree. C. As can be seen from this temperature
distribution, the temperature of the surface of the wafer gradually
increases on one side of the bold isotherm A and reaches
146.28.degree. C. at one peripheral portion of the wafer, gradually
decreases on the other side of the bold isotherm A, and reaches
144.32.degree. C. at another peripheral portion of the wafer. This
irregular temperature distribution and wide temperature difference
greatly affects the yield as described above. Therefore, the
temperature distribution produced by heating the wafer must be
improved by all means.
[0012] FIG. 5 is a temperature-time graph showing variations in
temperature of regions of a wafer while the wafer is being heated
by the conventional heating apparatus, and FIG. 6 shows the
locations at which the temperature of the wafer surface are
measured. These locations include the center of the wafer surface,
and various points on two circles, which are concentric with the
center of the wafer surface.
[0013] Referring to the variations in the temperature obtained by
taking temperature readings at the above-described points, as shown
in FIG. 5, the temperature differs greatly amongst the measuring
points at any given time. Moreover, after a predetermined time
passes, the temperature drops sharply (zone D in figure). Such
great differences in temperature imparts a serious thermal shock
not only to the wafer but also to the photoresist film formed on
the wafer. Such a thermal shock adversely affects the
physicochemical properties of the photoresist film.
[0014] Therefore, the conventional heating apparatus described
above impedes the success of the photolithography process in
forming a photoresist having a normal profile and uniform critical
dimension on a wafer. This problem becomes particularly acute as
the design rule of patterns becomes finer and finer (for example,
0.25 .mu.m, 0.18 .mu.m, and 0.15 .mu.m) in response to the demand
for increased levels of circuit integration. Thus, the conventional
heating apparatus is an impediment to enhancing yield.
SUMMARY OF THE INVENTION
[0015] In view of the foregoing, it is a first object of the
present invention to provide a method and apparatus for uniformly
heating an object, such as a wafer.
[0016] It is another object of the present invention to provides a
method and apparatus for uniformly heating a wafer in order to
avoid or at least minimize the application of thermal shock to the
wafer and to a photoresist film formed on the wafer.
[0017] It is yet another object of the present invention is to
provide a method and apparatus for uniformly baking a photoresist
film on a wafer in order to avoid or at least minimize the
application of thermal shock so as to reduce critical dimension
variance induced therefrom.
[0018] According to one aspect of the present invention, in a
method for uniformly heating an object, a first solid heat transfer
medium is supplied with heat. The heat is transmitted from the
first solid heat transfer medium to a fluid heat transfer medium
which is partitioned into an interconnected plurality of
evaporation cavities each containing a liquid. The heat causes the
liquid to evaporate into a plurality of vapor parts in the
respective plurality of evaporation cavities, and the plurality of
vapor parts are guided in parallel in an upward direction towards
the object. The vapor parts contact a second solid heat transfer
medium to heat the second solid heat transfer medium, thereby
transmitting the heat to the second solid heat transfer medium. The
second solid heat transfer medium is thermally contacted with the
object to transmit the heat from the second solid heat transfer
medium to the object.
[0019] According to another aspect of the present invention, in a
method for baking a photoresist film on a wafer, a photoresist
solution is coated on a wafer to form the photoresist film. After
the photoresist film is exposed to a light, the wafer is
transported onto a hot plate. In the hot plate, a first solid heat
transfer medium is supplied with heat. The heat is transmitted from
the first solid heat transfer medium to a fluid heat transfer
medium which is partitioned into an interconnected plurality of
evaporation cavities each containing a liquid. The heat causes the
liquid to evaporate into a plurality of vapor parts in the
respective plurality of evaporation cavities, and the plurality of
vapor parts are guided in parallel in an upward direction towards
the wafer. The vapor parts contact a second solid heat transfer
medium to heat the second solid heat transfer medium, thereby
transmitting the heat to the second solid heat transfer medium. The
second solid heat transfer medium is thermally contacted with the
object to transmit the heat from the second solid heat transfer
medium to the wafer.
[0020] According to another aspect of the present invention, the
above-described method for heating a wafer may be used for forming
a photoresist pattern. After coating a photoresist solution on a
wafer to form a photoresist film, the photoresist film is exposed
to light, such as deep ultra violet light. The exposed photoresist
film is developed to form a first photoresist pattern having a
first opening of a first size. The wafer is heated by the
above-describe heating method at a predetermined temperature, so as
to reflow the first photoresist pattern to form a second
photoresist pattern having a second opening of a second size which
is smaller than the first size.
[0021] According to still another aspect of the present invention,
an apparatus for heating an object includes a first solid heat
transfer medium and a fluid heat transfer medium, thermally coupled
to the first solid heat transfer medium, which is partitioned into
an interconnected plurality evaporation cavities. The apparatus
further includes a second solid heat transfer medium, thermally
coupled to the fluid heat transfer medium, for making thermal
contact with the object. The plurality of evaporation cavities
extend in a same plane between the first and second solid heat
transfer mediums.
[0022] According to still another aspect of the present invention,
an apparatus for heating a wafer includes a heating element, a
lower solid heat transfer medium thermally coupled to the heating
element, a first solid heat transfer medium thermally coupled to an
upper surface of the lower solid heat medium, and a second solid
heat transfer medium having a wafer mounting surface and thermally
coupled to said first solid heat transfer medium opposite said
wafer mounting surface. The apparatus further includes a fluid heat
transfer medium defined by a plurality of interconnected
evaporation cavities interposed between said first and second solid
heat transfer media.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The above objects and other advantages of the present
invention will become more apparent by describing in detail
embodiments thereof with reference to the attached drawings in
which:
[0024] FIG. 1 is a schematic cross-sectional view of a wafer
heating apparatus of a conventional baking unit;
[0025] FIG. 2 is a plan view of the heat source of the conventional
wafer heating apparatus;
[0026] FIG. 3 is an enlarged view of part of the heat source of the
conventional wafer heating apparatus;
[0027] FIG. 4 is a temperature distribution diagram of a wafer
surface heated by the conventional wafer heating apparatus;
[0028] FIG. 5 is a graph showing variations in the temperatures of
regions of a wafer with respect to time while the wafer is being
heated by the conventional wafer heating apparatus;
[0029] FIG. 6 show the locations where the surface temperature of a
wafer heated by the conventional wafer heating apparatus were
measured to yield the temperature distribution diagram shown in
FIG. 5;
[0030] FIG. 7 is a schematic side view of a first embodiment of the
wafer heating apparatus according to the present invention;
[0031] FIG. 8 is a schematic cross-sectional view of the heat
source of the wafer heating apparatus according to the present
invention;
[0032] FIG. 9 is an enlarged view of part of the heat source;
[0033] FIG. 10 is a schematic side view of a second embodiment of
the wafer heating apparatus according to the present invention;
[0034] FIG. 11A is a schematic perspective view of a lattice, which
may be employed in the second embodiment of the wafer heating
apparatus according to the present invention;
[0035] FIG. 11B is a schematic perspective view of another form of
the lattice suitable for use in the second embodiment of the wafer
heating apparatus according to the present invention;
[0036] FIG. 12 is a schematic side view of a third embodiment of
the wafer heating apparatus according to the present invention;
[0037] FIG. 13 is a schematic side view of a fourth embodiment of
the wafer heating apparatus according to the present invention;
[0038] FIG. 14 is a schematic cross-sectional view of a fifth
embodiment of the wafer heating apparatus according to the present
invention;
[0039] FIG. 15 is a bottom view of a solid heating medium which may
be employed in the fifth embodiment of the wafer heating apparatus
according to the present invention;
[0040] FIG. 16 is a schematic cross-sectional view of a sixth
embodiment of the wafer heating apparatus according to the present
invention;
[0041] FIG. 17 is a cross-sectional view of part of a seventh
embodiment of the wafer heating apparatus according to the present
invention;
[0042] FIG. 18 is a schematic cross-sectional view of a coronary
body, which can be employed in the seventh embodiment of the wafer
heating apparatus according to the present invention;
[0043] FIG. 19 is a surface temperature distribution diagram of a
wafer being heated by the wafer heating apparatus according to the
present invention;
[0044] FIG. 20 is a surface temperature distribution diagram of
another wafer heated by the wafer heating apparatus according to
the present invention;
[0045] FIG. 21 is a graph showing variations in the temperatures of
regions of a wafer with respect to time while the wafer is being
heated by the wafer heating apparatus according to the present
invention;
[0046] FIG. 22 is a schematic perspective view showing an eighth
embodiment of an apparatus for heating a wafer according to the
present invention;
[0047] FIG. 23 is a sectional view of the wafer heating apparatus
taken along line E-E' as shown in FIG. 22;
[0048] FIG. 24 is an enlarged view of a portion F of FIG. 23;
[0049] FIG. 25 is a sectional plan view of a layout of the inner
partition walls of an embodiment of the main heat transfer
body;
[0050] FIG. 26 is a sectional plan view of a layout of the inner
partition walls of another embodiment of the main heat transfer
body;
[0051] FIG. 27 is a perspective bottom view of the lower solid heat
transfer medium;
[0052] FIG. 28 is a sectional view of a conventional heat transfer
medium to which a heat block is attached thereunder including
isotherm diagrams for illustrating the temperature
distribution;
[0053] FIG. 29 is a sectional view of a heat transfer medium
according to one embodiment of the present invention, to which a
heat block is attached thereunder, including isotherm diagrams for
illustrating the temperature distribution;
[0054] FIG. 30 is a sectional view of a heat transfer medium
according to another embodiment of the present invention, to which
a heat block is attached thereunder including isotherm diagrams for
illustrating the temperature distribution;
[0055] FIG. 31 is a graph illustrating a top surface temperature of
the main heat transfer body as shown in FIGS. 28 to 30.
[0056] FIGS. 32A to 32D are sectional view s illustrating a method
for forming a photoresist pattern in accordance with one embodiment
of the present invention, utilizing the heating apparatus of the
present invention;
[0057] FIG. 33 is an isotherm diagram showing the distribution of
the surface temperature of a wafer heated by using the main heat
transfer as shown in FIG. 25;
[0058] FIG. 34 is an isotherm diagram showing the distribution of
the surface temperature of a wafer heated by using the main heat
transfer as shown in FIG. 26;
[0059] FIG. 35 is a critical dimension (CD) distribution diagram of
a first opening obtained after developing the exposed photoresist
film which has been post-baked using the main heat transfer medium
as in FIGS. 22 and 26.
[0060] FIG. 36 is a critical dimension distribution diagram of the
second opening obtained by using the main heat transfer medium as
in FIGS. 1 and 2; and
[0061] FIG. 37 is a critical dimension distribution diagram of the
second opening obtained by using the main heat transfer medium as
in FIGS. 22 and 26.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0062] The preferred embodiments of the present invention will now
be described in detail below.
[0063] Referring first to FIG. 7, the wafer heating apparatus
according to a first embodiment of the present invention includes a
sold heat transfer medium 10 which supports a wafer 100 in direct
contact therewith, a heat source 20, and a fluid heat transfer
medium 30, which is interposed between the solid medium 10 and heat
source 20. The state of the fluid medium 30 is changeable between a
vapor and liquid state by heating the medium with the heat source
20 and allowing the medium to cool. Here, the arrows in the solid
heat transfer medium 10 and the heat source 20 indicate the
direction of movement of heat, and the arrows in the fluid heat
transfer medium 30 indicate the direction of movement of the fluid
medium. A portion of the fluid heat transfer medium 30 adjacent the
solid heat transfer medium 10 is in a vapor state, and a portion of
the fluid heat transfer medium 30 adjacent the heat source 20 is in
a liquid state. The fluid heat transfer medium 30 absorbs heat from
the heat source 20, and moves toward the solid heat transfer medium
10 while being vaporized. When the vapor of the fluid heat transfer
medium 30 contacts the solid heat transfer medium 10, it transmits
heat to the solid heat transfer medium 10. The transfer of heat
cools the vapor, causing it to condense, whereby the resultant
liquid moves toward the heat source 20. The absorption of heat from
the heat source 20 by the fluid heat transfer medium 30, and the
transfer of heat to the solid medium 10 is a continuous cycle,
during which a phase change of the fluid heat transfer medium 30
occurs continuously. The phase change of the fluid heat transfer
medium is dependent upon the critical temperature and pressure of
the fluid medium.
[0064] The cycle of heat transfer occurs within a closed space
according to the present invention, and is very fast as compared to
the cycle of heat transfer which occurs in the conventional heating
apparatus. The fluid medium of the present invention transfers the
heat to the surface of the solid heat transfer medium 10 rapidly
and evenly, whereupon the heat is uniformly transferred to the
wafer 100, which is supported on the solid medium 10. Therefore,
the surface of the wafer 100 is rapidly and uniformly heated by the
heat, which is evenly distributed throughout the solid heat
transfer medium 10.
[0065] As shown in FIGS. 8 and 9, the heat source 20 includes a
heater 203 comprising an electrical heating coil, and upper and
lower heater blocks 201 and 202 which contain the heater 203. More
specifically, the heater 203 is contained within a groove 204
formed in the lower surface of the upper heater block 201 or in the
upper surface of the lower heater block 202.
[0066] According to a second embodiment of the present invention,
the space in which the fluid heat transfer medium 30 is contained
can be partitioned into a plurality of areas, as shown in FIG.
10.
[0067] Referring now to FIG. 10, a plurality of partitions 301 are
installed between the solid heat transfer medium 10 and the heat
source 20. Accordingly, the fluid heat transfer medium 30 exists
within the area partitioned by the plurality of partitions 301, and
a phase change occurs in independent spaces delimited by the
plurality of partitions 301.
[0068] The partitions 301 can constitute a lattice 302 having
rectangular or honeycomb-shaped units, as shown in FIGS. 11A and
11B. Preferably, the cross sections of the units of the lattice 302
are designed so that the units will act as capillary tubes for the
fluid heat transfer medium 30.
[0069] Referring to FIG. 12, according to a third embodiment of the
present invention, a refractory porous body 303 having discrete
sections is provided within the units of the lattice 302 in contact
with the heat source 20. The fluid heat transfer medium 30 thus
fills the cavities of the porous body 303. The fluid heat transfer
medium 30 thus contained in the cavities of the refractory porous
body 303 will be rapidly heated and evaporated. Also, the cavities
act as capillary tubes, which promote the mobility of the fluid
heat transfer medium 30.
[0070] Alternatively, as shown in FIG. 13, the refractory porous
body 303 of a fourth embodiment of the present invention is a
single body interposed between the solid heat transfer medium 10
and the heat source 20. In this case, the refractory porous body
303 closely adheres to the inner surfaces of both the heat source
20 and the solid heat transfer medium 10, or to the inner surface
of either the heat source 20 or the solid heat transfer medium.
[0071] FIGS. 14 and 15 show a fifth embodiment of the heating
apparatus according to the present invention. In this embodiment,
the solid heat transfer medium 10 adheres to the heat source 20,
and a groove 101 containing the fluid heat transfer medium 30 is
formed at the interface between the solid heat transfer medium 10
and the heat source 20.
[0072] In particular, the groove 101 is formed in the bottom
surface of the solid heat transfer medium 10, but can be formed in
the surface of the heat source 20 in some circumstances. The groove
101 forms a closed loop at the interface between the solid heat
transfer medium 10 and the heat source 20, through which the fluid
heat transfer medium 30 can circulate. The end 101a of the groove
101 is open at the side surface of the solid heat transfer medium
10 or the heat source 20 so that the fluid heat transfer medium 30
can be placed in the groove 101. A plug 10a closes the open end
101a of the groove 101.
[0073] In this structure, while the fluid heat transfer medium 30
circulates along the groove 101, the phase of the fluid heat
transfer medium 30 is changed due to heat absorption and heat
transmission as described above. The loop of fluid heat transfer
medium 30 leaves portions where the solid heat transfer medium 10
and the heat source 20 directly contact each other. Accordingly,
heat is also transmitted from the heat source 20 to the solid heat
transfer medium 10 via the contacting portions of the solid heat
transfer medium 10 and the heat source 20.
[0074] However, heat transfer via the fluid medium 30 circulating
in the groove 101 occurs at a faster rate than the direct heat
transfer via the contacting portions of the solid medium 10 and the
heat source 20.
[0075] Meanwhile, the groove 101 can have a shape other than that
of a single closed loop. That is, a plurality of grooves 101 can be
formed in the lower surface of the solid heat transfer medium 10 or
in the surface of the heat source 20. The plurality of grooves 101
are laid out at regular intervals across the interface between the
solid heat transfer medium 10 and the heat source 20. The
independent grooves form discrete closed spaces in which the phase
of the fluid heat transfer medium 30 is changed.
[0076] FIG. 16 shows a sixth embodiment of the present invention in
which the grooves 101 form a plurality of independent spaces as
described above. Referring now to FIG. 16, a plurality of grooves
101 are formed in the upper surface of the heat source 20. Walls
104, which isolate the grooves 101 from each other, have triangular
profiles. A vertex of each triangular wall 104 contacts the lower
surface of the solid heat transfer medium 10. This minimal contact
between the wall 104 and the solid heat transfer medium 10
minimizes heat transfer from the former to the latter.
[0077] FIG. 17 shows a seventh embodiment of the present invention
in which a coronary (tubular) body 102 extends in the groove 101.
The fluid heat transfer medium is contained in the coronary body
102. In this structure, the groove 101 extends in a closed loop at
the interface between the solid heat transfer medium 10 and the
heat source 20.
[0078] Referring to FIG. 18, the coronary body 102 includes fins
103 which contact the fluid heat transfer medium 30 in order to
promote the phase change of the fluid heat transfer medium 30. The
fins 103 extend axially in the direction of movement of the fluid
transfer medium 30 along the coronary body 102. As an alternative
to the fins 103, a porous layer of a predetermined thickness can be
formed on the inner wall of the coronary body 102.
[0079] According to the present invention as described above, the
fluid heat transfer medium must be one whose phase can be changed
between vapor and liquid within a predetermined range of
temperatures targeted for heating a wafer during a semiconductor
manufacturing process, e.g., in the photolithography process. When
considering that the targeted temperature to which a wafer is
heated is between 200.degree. C. and 300.degree. C., the fluid heat
transfer medium can be, but it is not limited to, water, ethanol,
methanol, acetone, ammonia, or Freon.
[0080] In particular, the choice of liquid to be used in the
various embodiments of the present invention will largely depend on
the temperature ranges to which an object is to be heated. Although
the invention is not so limited, the table below shows examples of
various liquids which may be employed within the indicated
temperature ranges.
1 -273.degree. C. to -120.degree. C. -120.degree. C. to 470.degree.
C. 450.degree. C. to 2700.degree. C. Helium Water Cesium Argon
Ethanol Sodium Nitrogen Methanol Lithium Acetone Ammonia Freon
[0081] Likewise, the choice of material for the solid heat transfer
mediums will largely depend on the liquid employed. Although the
invention is not so limited, the table that follows shows examples
of materials which are recommended and not recommended for the
indicated fluids.
2 Recommended Not Recommended Ammonia Aluminum, Carbon steel,
Copper Stainless steel, Nickel Acetone Aluminum, Copper, Stainless
steel, Silica Methanol Copper, Stainless steel, Aluminum Nickel,
Silica Water Copper, 347 stainless Aluminum, Stainless steel steel,
Nickel, Carbon steel, Inconel, Silica Thermex Copper, Silica,
Stainless steel
[0082] Surface Temperature Distribution I
[0083] FIGS. 19 and 20 are isotherm diagrams showing the
distribution of surface temperatures of a wafer heated by the
heating apparatus according to an embodiment of the present
invention. As can be seen from these figures, the isotherms are
annular, the center of the wafer has the highest temperature, and
the temperature decreases in a uniform pattern beginning from the
center and moving out toward the periphery of the wafer. It is also
clear that the isotherm distribution shown in FIG. 20 is preferable
to that shown in FIG. 19.
[0084] In the isotherm diagram of FIG. 19, the difference between
the highest and lowest temperatures is 0.73.degree. C., the bold
isotherms indicate a temperature of 1 55.63.degree. C., the
temperature of the center of the wafer is 156.00.degree. C., and
the lowest temperature of the wafer periphery is 155.26.degree. C.
In the isotherm diagram of FIG. 20, the difference between the
highest and lowest temperatures is 0.72.degree. C., the bold
isotherm indicates a temperature of 155.63.degree. C., the
temperature of the center of the wafer is 155.96.degree. C., and
the lowest temperature of the wafer periphery is 155.32.degree.
C.
[0085] As can be seen from FIGS. 19 and 20, the temperature of a
wafer has an even distribution over the surface of the wafer, and
particularly, the deviations between the highest and lowest
temperatures of 0.73.degree. C. and 0.72.degree. C. are excellent
results which cannot be obtained by the conventional wafer heating
apparatus.
[0086] FIG. 21 is a graph showing temperature-time variations
obtained from a plurality of measuring points while a wafer was
heated by the heating apparatus according to an embodiment of the
present invention. As shown in FIG. 21, after heating starts, the
temperature increases sharply, and thermal vibration, that is, a
temperature variation with respect to the lapse of time, is gentle.
In particular, a sudden drop in temperature, as occurs when using
the conventional heating apparatus, does not occur when practicing
the embodiment of the present invention. This tiny temperature
variation over the wafer, and the small thermal vibration show that
a very weak thermal shock is applied to the wafer and to the
photoresist film formed on the wafer.
[0087] According to the embodiments of the present invention as
described above, stable heating of a wafer with a very small
temperature deviation greatly reduces the intensity of the thermal
shock on the wafer and the photoresist film formed on the wafer, in
particular, the wafer can be heated with a regular and uniform
temperature distribution. Accordingly, the present invention allows
finer patterns to be formed successfully even when the design rule
in the critical dimension is 0.25 .mu.m, 0.18 .mu.m, or 0.15 .mu.m,
with an increase in the level of the integration of circuits, thus
greatly increasing the yield.
[0088] FIG. 22 is a schematic perspective view showing an eighth
embodiment of an apparatus for heating a wafer according to the
present invention.
[0089] Referring to FIG. 22, the hot plate 500 functioning as a
wafer heating apparatus includes a main heat transfer body 510 and
a lower solid heat transfer medium 520, each configured as a
circular plate of the same size and larger than a wafer to be
heated. The lower solid heat transfer medium 520 is placed under
the lower surface of the main heat transfer body 510.
[0090] At the upper surface portion of the main heat transfer body
510, a round and shallow trench 512 is formed for receiving a wafer
to be heated. Also, a plurality of wafer guides 513 are provided at
a peripheral region of the upper surface portion. The wafer guides
513 guide a wafer when it is placed onto the trench 512. The trench
512 reduces the introduction of the ambient air onto the wafer,
thereby lowering the undesired influence of the ambient air.
[0091] FIG. 23 is a sectional view of the hot plate 500 taken along
line E-E' as shown in FIG. 22. FIG. 24 is an enlarged view of a
portion F of FIG. 23.
[0092] Referring to FIG. 23, the main heat transfer body 510
includes a first solid heat transfer medium 514 and a second solid
heat transfer medium 516. Preferably, the media 514 and 516 are
integrally formed and configured as a circular plate which is
larger than a size of a wafer. The first solid heat transfer medium
514 is provided at a lower portion of the main heat transfer body
510 and the second solid heat transfer medium 516 is provided at an
upper portion of the main heat transfer body 510. As mentioned
earlier, the trench 512 for receiving a wafer is formed at an upper
portion of the second solid heat transfer medium 516.
[0093] As shown in the figures, an outer side wall 518 having a
ring shape is formed at an outer periphery of the first solid heat
transfer medium 514 and the second solid heat transfer medium 516.
That is, the first solid heat transfer medium 514 and the second
solid heat transfer medium 516 are integrally formed by way of the
outer side wall 518. Also, a cavity 515 which forms a fluid heat
transfer medium is defined between the first and second solid heat
transfer media 514 and 516.
[0094] The cavity 515 is located below the trench 512 and an outer
region thereof also has a generally circular configuration. When
the diameter 2r of the cavity 515 is less than about 0.9 times the
diameter 2R.sub.0 of the main heat transfer body 510 (or first and
second solid heat transfer mediums 514 and 516), undesirable heat
transfer can occur when baking a photoresist film coated on a
wafer. When the diameter 2r of the cavity 515 exceeds 0.98 times
the diameter 2R.sub.0 of the main heat transfer body 510,
manufacturing of the main heat transfer body 510 having the cavity
515 becomes difficult. Thus, the diameter 2r of the cavity 515 is
preferably about 0.9 to 0.98 times, and more preferably about 0.94
to 0.98 times the diameter 2R.sub.0 of the main heat transfer body
510. Particularly, when the main heat transfer body 510 for heating
an eight-inch wafer has a diameter 2R.sub.0 of 240 mm, the diameter
2r of the cavity 515 is about 225 to 235 mm, and more specifically
about 230 mm.
[0095] In the cavity 515, a plurality of inner partition walls 530
are provided for dividing the cavity 515 into an interconnected
plurality of smaller evaporation cavities 515a, 515b, 515c, etc.,
whereby a plurality of vapor parts are guided in parallel from the
first solid heat transfer medium 514 to the second solid heat
transfer medium 516.
[0096] As shown in FIG. 24, a liquid 540 is placed in the cavity
515. Each of the evaporation cavities 515a, 515b, 515c, etc.
forming the cavity 515 have a curved cross-sectional shape at an
upper portion thereof. The liquid 540 is evaporated upon receiving
heat from the first solid medium 514. The vaporized liquid, i.e.
vapor 542 is guided in parallel in the evaporation cavities 515a,
515b, 515c, etc. toward the second solid heat transfer medium 516.
At the top of each cavity, the vapor 542 comes in contact with the
second solid heat transfer medium 516 to partially condense into a
liquid state while transferring the latent heat of the vapor 542 to
the second solid heat transfer medium 516. The condensed liquid 544
returns to the first solid heat transfer medium 514 along a path
formed on the inner surface (the curved ceiling and side wall) of
the inner partition walls 530.
[0097] The heat transfer from the first solid heat transfer medium
514 to the second solid heat transfer medium 516 is continuously
performed while the liquid 540 is evaporated and the vapor 542 is
condensed, thereby uniformly transferring heat from the first solid
heat transfer medium 514 to the second solid heat transfer medium
516.
[0098] As mentioned above, the cavity 515 is divided into a
plurality of smaller evaporation cavities 515a, 515b, 515c, etc. by
a plurality of inner partition walls 530, for guiding the vapor 542
in parallel toward the second solid heat transfer medium 516.
[0099] When a volume occupied by the liquid 540 is less than about
15% of the volume of the cavity 515, the generation of vapor may
become insufficient. On the other hand, when the volume occupied by
the liquid 540 exceeds about 25% of the volume of the cavity 515,
mixing of the generated vapor may be insufficient due to the short
distance from the liquid 540 to the second solid heat transfer
medium 516, thus causing a non-uniform heat transfer. Thus, the
volume occupied by the liquid 540 is preferably about 15 to 25%,
but more preferably, 20% of the volume of the cavity 515.
[0100] As a liquid medium, a perfluorocarbon-type inert solvent is
preferably used in the present embodiment. Examples of the
perfluorocarbon-type inert solvent include FC-72, FC-40, FC-43,
FC-70 (trade names manufactured by 3M Korea Co. Ltd.) etc. Among
them, a solvent is preferred which has a higher critical
temperature (under an atmosphere) than the sum of the target
temperature plus 100.degree. C. For example, FC-40 solvent has a
boiling point of 155.degree. C. and a critical point of 270.degree.
C.
[0101] The thickness of the main transfer body 500 is about 10 to
12 mm, preferably 11 mm. When the thickness of the main transfer
body 500 is 11 mm, the evaporation cavities 515a, 515b, 515c, etc.
defined by the inner partition walls 530 have a width W of 5 to 7
mm, preferably, 6 mm, and a height H of 5 to 6 mm, preferably 5.5
mm.
[0102] Due to the presence of the evaporation cavities 515a, 515b,
515c, etc., the thickness of the first solid heat transfer medium
514 may vary within a range of 2 to 4 mm, and the thickness of the
second solid heat transfer medium 516 may vary within a range of 1
to 2 mm, preferably 1.5 mm at a trench 512. Also, the thickness Wp
of the inner partition walls 530 may vary within a range of about 2
to 3 mm.
[0103] In this embodiment, the thicknesses of the first and second
solid heat media 514 and 516 are not limited to the above so long
as the main heat transfer body 510 is capable of manufacture. The
height H of the isolated space 515 is preferably 0.4 to 0.6 times
of the thickness T of the main heat transfer body 510.
[0104] FIG. 25 is a sectional plan view of an embodiment of the
main heat transfer body 510, in particular showing a layout of the
inner partition walls 530.
[0105] Referring to FIG. 25, the horizontal area of the cavity 515
is circular as defined by the outer sidewall 518. Also, a plurality
of inner partition walls 530 are provided in the cavity 515 so as
to both radially and spirally (or circularly) divide the cavity 515
into a plurality of evaporation cavities 515a, 515b, 515c, etc.
[0106] In particular, the inner partition walls 530 are first
formed in a spiral configuration within the cavity 515. Then, the
inner partition walls 530 are cut in a radial direction so as to
form five radial mixing paths from the center to the periphery of
the main heat transfer body 510. Thus, as shown in FIG. 25, each
spiral is divided into five radial sectors, each having an angle
.theta..sub.1 of about 72 degrees.
[0107] Reference number 505 denotes screw holes which may be
provided for coupling the main heat transfer body 510 to the lower
solid heat transfer medium 520.
[0108] FIG. 26 is a sectional plan view of another embodiment of
the main heat transfer body 510, particularly showing another
layout of the inner partition walls 530.
[0109] Referring to FIG. 26, the inner partition walls 530 are
arranged as concentric circles and are more densely provided in the
cavity 515 than those of the embodiment shown in FIG. 25. That is,
in this embodiment, each circle of the evaporation cavities 515a,
515b, 515c, etc. is divided into twenty four radial sectors, each
having an angle .theta..sub.2 of about 15 degrees.
[0110] More particularly, the cavity 515 is divided in a circular
direction into a plurality of concentric circle-shaped evaporation
cavities 515ca, 515cb, 515cc, etc. Further, each of the
circle-shaped evaporation cavities 515ca, 515cb, 515cc are further
divided in a radial direction into a plurality of arc-shaped
evaporation cavities 515ca1, 515ca2, . . . 515cb1, 515cb2, . . .
515cc1, 515cc2 . . . etc.
[0111] FIG. 27 is a perspective bottom view of the lower solid heat
transfer medium 520. As shown in the figure, a spiral groove 522 is
formed at the lower surface of the lower solid heat transfer
medium. In the spiral groove 522, a heater 524 such as a heating
coil is provided. The heater 524 is connected to an electrical
source (not shown). When electric current is applied to the heater
524, heat is generated to first heat the lower solid heat transfer
medium 520.
[0112] At the peripheral region of the main heat transfer body 510,
a larger amount of heat loss occurs due to contact with ambient
air. Thus, in a preferred embodiment of the present invention, the
pitch Po at an outer peripheral region (where radius r is greater
than about 0.75 Ro, and wherein Ro is the radius of the main heat
transfer body 510) of the bottom surface of the lower solid heat
transfer medium 520 is shorter than the pitch Pc at a central
portion. This configuration compensates for the heat loss at the
peripheral region. According to the experiments of the present
inventor, the pitch Po at the outer peripheral region is preferably
0.1 to 0.5 times the pitch Pc at the central portion.
[0113] Hereinafter, the heating mechanism of a wafer will be
explained in detail.
[0114] First, an electrical current is supplied to the heater 524
which is provided in the spiral groove 522 at the bottom surface of
the lower solid heat transfer medium 520, to thereby generate heat.
The heat is transferred to the lower solid heat transfer medium 520
which is in contact with the first solid heat transfer medium
514.
[0115] Then, the heat is transferred from the lower solid heat
transfer medium 510 to the first solid heat transfer medium
514.
[0116] On the first solid heat transfer medium 514, a cavity 515
contain a liquid 540, an outer sidewall 518, and a plurality of
inner partition walls 530 are provided.
[0117] From the first solid heat transfer medium 514, the heat may
be transferred to the second solid medium 516 by conduction through
the outer sidewall 518 and the inner partition walls 530. However,
this heat conduction is very small when compared to the heat
transfer via the liquid 540 contained in the cavity 515.
[0118] That is, most of the heat of the first solid heat transfer
medium 514 is used for heating the liquid 540, thereby evaporating
the liquid 540 into a vapor. The vapor is guided in parallel in an
upward direction toward the second solid heat transfer medium 516.
thereby transferring the heat to the second solid heat transfer
medium 516, which has the trench 512 for receiving a wafer.
[0119] Referring to FIGS. 25 and 26, the inner partition walls 530
are formed so as to have an arc shape. The inner partition walls
530 divide the cavity 515 into a plurality of the evaporation
cavities 515a, 515b, 515c, etc. in both radial and circular (or
spiral) directions. Thus, when the vapor moves in the upward
direction, the vapor in the evaporation cavities 515a, 515b, 515c,
etc. is partially mixed with vapor from adjacent evaporation
cavities, thus contributing to a uniform temperature distribution,
and thereby uniformly transferring the heat to the second solid
heat transfer medium 516.
[0120] Also, each of the evaporation cavities 515a, 515b, 515c,
etc. has an upper surface which is curved (or circular) in
cross-section. When each vapor part guided by the inner partition
wall 530 reaches the upper surface of the evaporation cavities
515a, 515b, 515c, etc., and comes in contact with the second solid
heat transfer medium 516, the vapor partially condenses into liquid
to generate latent heat to the second solid heat transfer medium
516, thereby heating the second solid heat transfer medium 516.
Then, the condensed liquid 544 returns to the first solid heat
transfer medium 514 and receives heat from the first solid heat
transfer medium 514.
[0121] In the meantime, the vapor which is not condensed, but is
simply cooled, is also circulated toward the first solid heat
transfer medium 514. Then, the returned vapor contacts the first
solid heat transfer medium 514 to absorb heat again and is guided
upward toward the second solid heat transfer medium 516. That is,
heat transfer is also performed by convection.
[0122] As shown in FIGS. 25 and 26, the vapor mixing paths are
formed in a radial pattern from the center to the periphery and in
a circular direction. Since the direct mixing of the vapor in the
radial direction may occur from the center out toward the periphery
of the main heat transfer body 510, the temperature difference of
the vapor at the central portion of the main heat transfer body 510
and at the peripheral portion of the main heat transfer body 510 is
greatly reduced.
[0123] As described above, the second solid heat transfer medium
516 receives heat via the evaporation cavities from the first heat
solid medium 514. The thus heated solid heat transfer medium 516 is
in contact with a wafer, which is located in the trench 512. As
such, the heat is transferred from the uniformly heated solid heat
transfer medium 516 to the wafer to uniformly heat the wafer to a
desired temperature.
[0124] FIGS. 28 to 30 are sectional views of the heat transfer
medium to which a heat block is attached thereunder, and in
particular isotherm diagrams for illustrating temperature
distributions.
[0125] FIG. 28 illustrates a conventional heat transfer medium as
shown in FIGS. 1 and 2. As shown in FIG. 28, the observed maximum
temperature was 152.447.degree. C. and the minimum temperature was
151.566.degree. C.
[0126] FIG. 29 illustrates one embodiment of the present invention
wherein the cavity is formed under the trench, and the heating coil
is provided in a groove which has a regular pitch. As shown in this
figure, the observed maximum temperature was 152.769.degree. C. and
the minimum temperature was 151.259.degree. C.
[0127] FIG. 30 illustrates another embodiment of the present
invention wherein the cavity is formed so as to have a diameter
equal to about 0.96 times a diameter of the main heat transfer
body, and heating coil provided in a groove in which the pitch
thereof at a peripheral region is shorter than at a central region.
As shown in this figure, the observed maximum temperature was
152.765.degree. C. and the minimum temperature was 151.492.degree.
C.
[0128] As can be seen in the figures, the temperature distribution
of the hot plate of FIG. 30 is most uniform, followed by the hot
plate of FIG. 29, and then by the hot plate of FIG. 28.
[0129] FIG. 31 is a graph illustrating a top surface temperature
distribution of the main heat transfer bodies of FIGS. 28 to 30. In
FIG. 31, the line interconnected by triangles was obtained from the
main heat transfer body of FIG. 28. The line interconnected by
circles was obtained from the main heat transfer body of FIG. 29.
The line interconnected by rectangles was obtained from the main
heat transfer body of FIG. 30.
[0130] As can be seen in FIG. 31, a more uniform temperature
distribution of the top surface of the main heat transfer body may
be obtained in the present invention. Also, by increasing the
cavity and by reducing the heating element pitch at a peripheral
region, the temperature distribution of the top surface is further
improved.
[0131] Photoresist Pattern Formation
[0132] FIGS. 32A to 32D are sectional views illustrating a method
for forming a photoresist pattern in accordance with one embodiment
of the present invention, utilizing the above heating
apparatus.
[0133] Referring to FIG. 32A, a positive-type photoresist
composition containing a novolak resin is coated on a silicon wafer
610 utilizing a spin coater to form a photoresist film 612. Then,
the photoresist film 612 is soft-baked utilizing a conventional hot
plate at 90-120.degree. C. for 60 seconds. The thickness of the
photoresist film 612 is 0.8 to 0.9 .mu.m.
[0134] Referring to FIG. 32B, the photoresist film 612 is
selectively exposed to deep ultra violet light 614 utilizing a
stepper and a photo mask (not shown). Thereafter, the exposed
photoresist film 612 is post-baked utilizing a heating method
according to the present invention and a hot plate including a main
heat transfer body 510 as shown in FIGS. 22 and 26. The post-baking
is performed at a temperature of 140.degree. C. to 150.degree. C.
for 30 to 90 seconds.
[0135] Referring to FIG. 32C, the exposed photoresist film 612 is
developed using a developer for one minute, then washed using water
for about 30 seconds, and then dried to remove the exposed portion
of the photoresist film. A first photoresist pattern 612a is formed
which has an opening portion 616 of a first size to expose a
portion of the silicon wafer 610.
[0136] Referring to FIG. 32D, the first photoresist pattern 612a is
heated at a temperature of about 140 to about 160.degree. C. for
about one to three minutes. At this time, a heating method
according to the present invention and a hot plate including a main
heat transfer body 510 as shown in FIGS. 22 and 26 are also
utilized. Then, the first photoresist pattern 612a is reflowed to
form a final photoresist pattern 612b (as shown by a dotted line)
having a second opening portion 616a of a second size which is
smaller than the first opening size of the first photoresist
pattern 612a.
[0137] Surface Temperature Measurement of a Wafer
[0138] FIG. 33 is an isotherm diagram showing the distribution of
the surface temperature of a wafer which was heated by using the
main heat transfer body shown in FIG. 25. In FIG. 33, the
temperature difference between one isotherm and its adjacent
isotherm is 0.04.degree. C. In this figure, the highest temperature
is 155.02.degree. C. at a central portion of the wafer and the
lowest temperature is 153.91.degree. C. at a peripheral region of
the wafer. The temperature range (the temperature difference
between the highest temperature and the lowest temperature) is
0.97.degree. C. The mean temperature indicated by a bold isotherm
is 154.65.degree. C., and the standard deviation of the surface
temperature is 0.31.degree. C.
[0139] FIG. 34 is an isotherm diagram showing the distribution of
the surface temperature of a wafer which was heated by using the
main heat transfer body shown in FIG. 26. In FIG. 34, the
temperature difference between one isotherm and its adjacent
isotherm is 0.03.degree. C. In this figure, the highest temperature
is 137.97.degree. C. at a central portion of the wafer and the
lowest temperature is 137.42.degree. C. at a peripheral region of
the wafer. The temperature range (the temperature difference
between the highest temperature and the lowest temperature) is
0.55.degree. C. The mean temperature indicated by a bold isotherm
is 137.68.degree. C., and the standard deviation of the surface
temperature is 0.15.degree. C.
[0140] As can been seen from a comparison of FIGS. 33 and 34, when
the cavities 515 is more densely divided by the inner partition
walls in a radial direction as in FIG. 26, a more uniform
temperature distribution is obtained. As a result of many
experiments, it has been determined that the evaporation cavities
515a, 515b, 515c, etc. are radial divided into eighteen to
thirty-six radial sectors each having an angle of 10 to 20 degrees,
more preferably 15 degrees, the temperature range was less than
0.6.degree. C., and thus a more uniform temperature distribution is
obtained.
[0141] Measurement of the Critical Dimension After Post-Exposure
Baking of the Photoresist Pattern
[0142] Referring again to FIG. 32A, a photoresist solution was
coated on a wafer 610 to form a photoresist layer 612 and the thus
obtained photoresist layer 612 was pre-baked at a temperature of
110.degree. C. for about 60 seconds.
[0143] Then, as shown in FIG. 32B, the photoresist layer 612 was
exposed to deep ultra violet rays 614. At this time, a mask having
a pattern for forming a 135 nm (target dimension) contact hole was
used. The exposed photoresist layer 612 was post-baked. At this
time, a hot plate including a main heat transfer body 510 as shown
in FIGS. 22 and 26 was used. For manufacturing a main heat transfer
body 510, the first and second solid heat transfer media 514 and
516, the outer sidewall 518, and the inner partition walls 530 were
manufactured by using an aluminum alloy. As th liquid 540, FC-40
(trade name purchased from 3M Korea LTD) was selected which has a
boiling point and critical temperature of about 155.degree. C. and
270.degree. C., respectively. After forming the main heat transfer
body 510, the cavity 515 was evacuated to 10.sup.7 Torr, and then
about 20% of the volume of the cavity 515 was filled with the
liquid 540. The cavity 515 was then sealed.
[0144] Thereafter, as shown in FIG. 32C, the exposed photoresist
layer 612 was developed to form a first photoresist pattern 612a
having a first opening portion 616.
[0145] FIG. 35 is a critical dimension (CD) distribution diagram of
a first opening obtained after developing the exposed photoresist
film which has been post-baked using the main heat transfer medium
as in FIGS. 22 and 26.
[0146] When the hot plate according to the present invention was
used, the maximum and minimum CD was 140 nm and 129 nm,
respectively. Also, the average CD was 135 nm and the dimension
range was only 11 nm. When the acceptable dimension range is set at
120 to 150 nm, all measured contact holes had a size within an
acceptable dimension range.
[0147] Measurement of the Critical Dimension of the Photoresist
Pattern After Reflowing the Photoresist Pattern
[0148] Referring yet again to FIG. 32A, a photoresist solution was
coated on a wafer 610 to form a photoresist layer 612, and the thus
obtained photoresist layer 612 was pre-baked at a temperature of
110.degree. C. for about 60 seconds.
[0149] Then, as shown in FIG. 32B, the photoresist layer 612 was
exposed to deep ultra violet rays 614. At this time, a mask having
a pattern for forming a 185 nm contact hole was used. The exposed
photoresist layer 612 was post-baked. At this time, a hot plate
including a main heat transfer body as shown in FIGS. 22 and 26 was
used. This hot plate was the same as that used for the
above-described measurement of the CD after post-exposure baking of
the photoresist pattern.
[0150] The exposed photoresist layer 612 was developed to form a
first photoresist pattern 612a having a first opening portion 616
as shown in FIG. 32C. Then, the first photoresist pattern 612a was
heated at a temperature of 150.degree. C. for two minutes. At this
time, the same hot plate was used. As a result, as shown in FIG.
32D, a second photoresist pattern 612b was obtained having a second
opening portion 616a which was smaller size than the first opening
portion 616.
[0151] For comparison, the same procedure was performed using a
conventional hot plate in both post-baking and reflowing steps.
That is, the hot plate of FIGS. 1 and 2 was used instead of the hot
plate according to the present invention.
[0152] The critical dimension (size) of the second opening was
measured per one map throughout the whole wafer.
[0153] FIG. 36 is a critical dimension (CD) distribution diagram of
the second opening obtained by using the conventional main heat
transfer medium as in FIGS. 1 and 2. FIG. 37 is a critical
dimension (CD) distribution diagram obtained by using the main heat
transfer medium of the present invention as in FIGS. 22 and 26.
[0154] As can be noted from FIG. 36, when the conventional hot
plate was used, the maximum and minimum CD was 201 nm and 159 nm,
respectively. Also, the average CD was 177 nm, and the dimension
range was 42 nm.
[0155] When the hot plate according to the present invention was
used, the maximum and minimum CD was 205 nm and 182 nm,
respectively. Also, the average CD was 194 nm, and the dimension
range was 23 nm, as shown in FIG. 37.
[0156] From the above, it can be noted that the critical dimension
range was improved from 42 nm to 23 nm.
[0157] As mentioned above, when the wafer is heated by the heating
method of the present invention, the wafer can be uniformly heated
with a temperature deviation of less than 1.degree. C., and further
less than 0.6.degree. C.
[0158] Thus, thermal shock which may be applied to the wafer and
the photoresist film coated on the wafer is greatly reduced.
Consequently, in a case where the heating method and apparatus of
the present invention is used in the post-exposure baking step, a
photoresist pattern having a uniform size may be formed on the
wafer. Also, the heating method and apparatus of the present
invention may be advantageously used for reflowing the photoresist
pattern so as to form a finer photoresist pattern.
[0159] The heating method and apparatus of the present invention
may be used in other fields for uniformly heating an object
preferably having a plate shape. Of course, in semiconductor fields
which require the uniform heating of a wafer, the heating method
and apparatus of the present invention may be advantageously
used.
[0160] While the present invention has been particularly shown and
described with reference to particular embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be effected therein without departing from the
spirit and scope of the invention as defined by the appended
claims.
* * * * *