U.S. patent application number 09/871854 was filed with the patent office on 2002-12-05 for temperature-controlled chuck and method for controlling the temperature of a substantially flat object.
This patent application is currently assigned to Motorola, Inc.. Invention is credited to Charles, Alain B., Maltabes, John G., Mautz, Karl E..
Application Number | 20020179585 09/871854 |
Document ID | / |
Family ID | 25358296 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020179585 |
Kind Code |
A1 |
Maltabes, John G. ; et
al. |
December 5, 2002 |
TEMPERATURE-CONTROLLED CHUCK AND METHOD FOR CONTROLLING THE
TEMPERATURE OF A SUBSTANTIALLY FLAT OBJECT
Abstract
The present invention generally relates to a method for
controlling the temperature of a substantially flat object and to a
temperature-controlled chuck comprising a chuck body (20) having an
object support side (21) and a back side (22). Said object support
side (21) holds a substantially flat object (1) having a front side
(2) and a back side (3) on said back side (3) of said object (1). A
plurality of temperature sensing elements (4) is distributed on
said object support side (1) to measure the temperature
distribution of said flat object (1). A plurality of individual
temperature influencing elements (6; 8; 9) is distributed on said
object support side (21) to face said back side (3) of said flat
object (1), each of said temperature influencing elements (6; 8; 9)
being arranged to influence the temperature of a partial area of
said object's back side (3) as desired.
Inventors: |
Maltabes, John G.; (Austin,
TX) ; Charles, Alain B.; (Singapore, SG) ;
Mautz, Karl E.; (Round Rock, TX) |
Correspondence
Address: |
Jim Clingan
Motorola, Inc
Austin Intellectual Property Law Section
7700 West Parmer Lane
Austin
TX
78729
US
|
Assignee: |
Motorola, Inc.
|
Family ID: |
25358296 |
Appl. No.: |
09/871854 |
Filed: |
May 31, 2001 |
Current U.S.
Class: |
219/390 ;
219/444.1 |
Current CPC
Class: |
H01L 21/67103
20130101 |
Class at
Publication: |
219/390 ;
219/444.1 |
International
Class: |
H05B 003/68; F27D
011/00 |
Claims
1. A temperature-controlled chuck to hold a substantially flat
object comprising: a chuck body having an object support side and a
backside, said object support side holding a substantially flat
object having a front side and a backside on said backside of said
object, a plurality of temperature sensing elements being
distributed on said object support side to measure the temperature
distribution of said flat object, a plurality of individual
temperature influencing elements being distributed on said object
support side to face said backside of said flat object, each of
said temperature influencing elements being arranged to influence
the temperature of a partial area of said object's backside as
desired.
2. The temperature-controlled chuck of claim 1, wherein said
temperature influencing elements are piezoelectric elements, each
piezoelectric element being individually controllable.
3. The temperature-controlled chuck of claim 2, wherein said
temperature influencing piezoelectric elements contact said
backside of said flat object.
4. The temperature-controlled chuck of claim 2, wherein a plurality
of support pin elements are distributed on said object support side
and being arranged to contact said backside of said flat
object.
5. The temperature-controlled chuck of claim 1, wherein said
temperature influencing elements are individual fiber optics, said
fiber optics being illuminated with infrared radiation.
6. The temperature-controlled chuck of claim 5, wherein said
temperature influencing fiber optics are spaced from said object's
backside.
7. The temperature-controlled chuck of claim 1, wherein said
temperature influencing elements comprise a plurality of fiber
optics illuminated with infrared radiation and a plurality of
piezoelectric elements.
8. The temperature-controlled chuck of claim 1, wherein said
temperature influencing elements comprise heat sink pins and
heating elements.
9. The temperature-controlled chuck of claim 1, wherein said
temperature influencing elements are selectively movable into close
proximity with and away from said backside of said flat object.
10. The temperature-controlled chuck of claim 1, wherein a
temperature controller is connected to said plurality of individual
temperature influencing elements to control the temperature
distribution of said flat object as desired.
11. A temperature-controlled wafer chuck comprising: a chuck body
having a wafer support side, said wafer support side being adapted
to hold a wafer having a front side and a backside on the wafer's
backside, a plurality of temperature sensing elements distributed
on said wafer support side, each of said temperature sensing
elements being arranged to sense the temperature of a partial area
of said wafer back side, a plurality of individual temperature
influencing elements distributed on said wafer support surface,
each of said temperature influencing elements being arranged to
influence the temperature of a partial area of said wafer back
side, and a temperature controller connected to said plurality of
temperature sensing elements and said plurality of individual
temperature influencing elements to control the temperature
distribution of said flat object as desired.
12. The temperature-controlled wafer chuck of claim 12, wherein
said temperature controller includes at least one temperature
detector and a control unit connected with said at least one
temperature detector and controlling said temperature influencing
elements.
13. A method for controlling the temperature of a substantially
flat object having a front side and a backside and being supported
on said backside, comprising the method steps: sensing the
temperature of partial areas of said backside of said flat object,
determining the object's temperature distribution on the basis of
the temperatures measured in said temperature sensing step,
changing the temperature in some of said partial areas of said
backside of said flat object as desired.
14. The method of claim 13, wherein said flat object is a
wafer.
15. The method of claim 13, wherein the temperature of the partial
areas of said flat object is measured by a temperature sensing
element of a plurality of temperature sensing elements distributed
over the backside of said flat object.
16. The method of claim 15, wherein each temperature sensing
element is a piezoelectric element.
17. The method of claim 13, wherein the temperature of the partial
areas of said flat object is influenced by a temperature
influencing element of a plurality of temperature influencing
elements distributed over the backside of said flat object.
18. The method of claim 17, wherein each temperature influencing
element is an IR-optical fiber.
19. The method of claim 17, wherein each temperature influencing
element is a heat sink pin.
20. The method of claim 17, wherein each temperature influencing
element is a piezoelectric element.
21. The method of claim 17, wherein said plurality of temperature
influencing elements comprise IR-optical fibers and piezoelectric
elements and heat sink pins.
22. The method of claim 14 that allows for the wafer temperature to
be made more uniform prior to the exposure step to prevent the
production of non-linear errors from the lithography
processing.
23. The method of claim 14, wherein the wafer temperature can be
made purposely different on specific areas of the wafer to assist
the exposure tool in the compensation of the known non-linear
errors during the exposure step.
24. A pre-align station of an exposure tool for wafers comprising a
wafer chuck having a chuck body having a wafer support side, said
wafer support side being adapted to hold a wafer having a front
side and a backside on the object's backside, a plurality of
temperature sensing elements distributed on said wafer support
side, each of said temperature sensing elements being arranged to
sense the temperature of a partial area of said wafer back side, a
plurality of individual temperature influencing elements
distributed on said wafer support surface, each of said temperature
influencing elements being arranged to influence the temperature of
a partial area of said wafer back side, and a temperature
controller connected to said plurality of temperature sensing
elements and said plurality of individual temperature influencing
elements to control the temperature distribution of said flat
object as desired.
25. An exposure chuck in an exposure tool for wafers comprising: a
chuck body having a wafer support side, said wafer support side
being adapted to hold a wafer having a front side and a backside on
the object's backside, a plurality of temperature sensing elements
distributed on said wafer support side, each of said temperature
sensing elements being arranged to sense the temperature of a
partial area of said wafer back side, a plurality of individual
temperature influencing elements distributed on said wafer support
surface, each of said temperature influencing elements being
arranged to influence the temperature of a partial area of said
wafer back side, and a temperature controller connected to said
plurality of temperature sensing elements and said plurality of
individual temperature influencing elements to control the
temperature distribution of said flat object as desired.
26. The exposure chuck of claim 25, wherein said temperature
influencing elements are arranged to be adjustable such that
distortions of a wafer will be at least reduced during the exposure
of said wafer.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to controlling the
temperature of partial areas of a substantially flat object. More
particularly, the present invention relates to a
temperature-controlled chuck to hold a substantially flat object.
With such a temperature-controlled chuck the temperature
distribution of the substantially flat object can be sensed or
measured, and due to temperature influencing elements the
temperature of partial areas of said object's back side can be
altered to obtain a more uniform temperature distribution.
Furthermore, the present invention relates also to a
temperature-controlled wafer chuck and a method for controlling the
temperature of a substantially flat object such as a wafer.
Finally, the invention relates also to a pre-align station of an
exposure tool for wafers comprising a temperature-controlled wafer
chuck, and relates to an exposure wafer chuck in an exposure tool
for wafers comprising a wafer chuck with which the temperature of a
wafer can be measured and influenced as desired.
BACKGROUND OF THE INVENTION
[0002] Integrated circuits are typically constructed by depositing
a series of individual layers of predetermined materials on a
wafer-shaped semi-conductor substrate, or "wafer". The individual
layers of the integrated circuit are in turn produced by a series
of manufacturing steps. For example, in forming an individual
circuit layer on a wafer containing a previously formed circuit
layer, an oxide such as silicon dioxide is deposited over the
previously formed circuit layer to provide an insulating layer for
the circuit. A pattern for the next circuit layer is then formed on
the wafer using a radiation alterable material, known as
photoresist.
[0003] Photoresist materials are generally composed of a mixture of
organic resins, sensitizers and solvents. Sensitizers are compounds
such as diazonaphthaquinones, that under go a chemical change upon
exposure to radiant energy, such as visible and ultraviolet light.
The irradiated sensitizer material has different solution
characteristics with respect to various solvents than the
non-irradiated material allowing for selective removal of the
photoresist. Resins are used to provide mechanical strength to the
photoresist and the solvents serve to lower the viscosity of the
photoresist so that it can be uniformly applied to the surface of
the wafers.
[0004] After a photoresist layer is applied to the wafer surface,
the solvents are evaporated and the photoresist layer is hardened,
usually by heat treating the wafer. The photoresist layer is then
selectively irradiated through the use of a radiation opaque mask.
The mask contains transparent portions that define the pattern for
the next circuit layer. The mask is placed over the photoresist
layer and the photoresist covered by the transparent portion is
irradiated. The wafer is removed and the photoresist layer is
exposed to a process liquid, known as developer. The developer
selectively solubilizes and removes either the irradiated or the
nonirradiated photoresist exposing portions of the underlying
insulating layer.
[0005] The exposed portions of the insulating layer can be
selectively removed using an etchant to expose corresponding
sections of the underlying circuit layer. In this process, the
photoresist should be more resistant to the etchant than the
insulating layer to limit the attack of the etchant to only the
exposed portions of the insulating layer. Alternatively, the
exposed underlying layer(s) can be implanted with ions which do not
penetrate the photoresist layer thereby selectively penetrating
only those portions of the underlying layer not covered by the
photoresist. The remaining photoresist is then stripped using
either a solvent, or a strong oxidizer in the form of a liquid or a
gas in the plasma state. The next layer is then deposited and the
process is repeated until fabrication of the semiconductor device
is complete.
[0006] Thermal gradients in wafers during lithography exposure
create linear pattern transfer effects due to expansion or
contraction. Wafers can have temperature instability due to
previous processing from a photoresist track hot plate. If this
bake is non-uniform or the cooling prior to wafer transfer into the
exposure tool is not complete, non-linear effects will occur.
During the transfer from the track to the exposure tool there may
not be adequate time for the wafer to thermally stabilize prior to
exposure. This effect causes pattern transfer errors, seen as
overlay or grid distortion and chip magnification errors. Other
sources of non-linear errors can occur outside of lithography
processing. These sources include rapid thermal processing such as
anneal (RTA), film deposition processing (such as diffusion or
chemical vapor deposition-CVD), and chemical mechanical polishing
(CMP). These non-linear errors are variable across the wafer and
are difficult to correct when severe.
[0007] A temperature difference as small as 0.1.degree. C. can
affect overlay. Wafers can only equilibrate through conduction with
the exposure tool environment or contact with non-temperature
regulated surfaces, so-called chucks. There are defects during
lithography processing known as "banana effect" problems due to
wafer contact non-uniformity on the track hotplate that cause
significant temperature gradients over the wafer that result in
overlay issues in these areas. Banana effect non-linear errors
typically occur on the edge regions of the wafer in a semicircle
pattern that resembles a banana shape. The magnitude of these
non-linear errors varies significantly across the effected region,
and therefore are difficult to correct using normal lithography
processing.
[0008] Thus, it is apparent that a need exists for an improved
chuck to hold a substantially flat object such as a wafer and a
method for controlling the temperature of a wafer in a pre-align
station or an exposure tool, which overcomes, among other things,
the above-discussed problems to produce a more uniform temperature
distribution over the surface of the wafer.
[0009] Furthermore, it is an object to provide an improved chuck
with which the temperature of localized areas of a generally flat
object, particularly a wafer, can be influenced in a desired manner
to reduce significant temperature gradients over the wafer or to
use defined temperature peaks or temperature depths in localized
areas of a wafer to reduce or eliminate distortions of the wafer
grid.
BRIEF SUMMARY OF THE INVENTION
[0010] The above objects and others are accomplished by a
temperature-controlled chuck and a method for controlling the
temperature of a substantially flat object such as a semiconductor
wafer, in accordance with the present invention. The
temperature-controlled chuck according to the invention comprises a
chuck body having an object support side and a back side, said
object support side holding a substantially flat object having a
front side and a back side on said back side of said object. A
plurality of temperature sensing elements is distributed on said
object support side to measure the temperature distribution of said
object. A plurality of individual temperature influencing elements
is distributed on said object support side to face said back side
of said flat object, each of said temperature influencing elements
being arranged to influence the temperature of a partial area of
said object's back side as desired.
[0011] A temperature-controlled chuck according to the invention
provides the possibility to influence the temperature of a wafer,
particularly the back side of a wafer, in a partial area in a
manner as desired. For example, by use of an inventive
temperature-controlled chuck the temperature can be varied
precisely in tenths of a degree centigrade and be controlled
overall to .+-.1.degree. C. Hence, a good temperature uniformity
across the whole wafer would be provided. It is also possible to
provide local modification to correct process distortions on a
wafer. If, for example, the temperature in partial areas of the
wafer can be precisely controlled, then it is also possible to use
a variation of the chuck temperature to adjust for chip
magnification error, instead of changing lens, housing pressure or
having an extra field lens for magnification adjustment. It could
also be used in conjunction with current lens magnification
correction systems, so that a coarse chip mag correction would be
done using temperature adjustment while the fine correction will be
still done as of today. With such a preferred embodiment of the
invention, a simpler lens design for an exposure tool is possible,
and hence such an exposure tool can be constructed more
cheaply.
[0012] A preferred embodiment of an inventive
temperature-controlled chuck comprises a plurality of piezoelectric
elements, each piezoelectric element being individually
controllable, such that each piezoelectric element is able to
influence a localized area or a partial area of the object's back
side. Due to a variation of the current and/or the voltage applied
to the piezoelectric elements, the temperature of the object's back
side can be controlled in a desired manner.
[0013] A further embodiment of an inventive temperature-controlled
chuck comprises the above-mentioned temperature influencing
piezoelectric elements. At least some of these piezoelectric
elements are arranged such that they are able to contact the back
side of a flat object such as a wafer. Due to the contact of the
piezoelectric elements with said back side of said flat object,
influencing of the temperature of the back side of said flat object
is improved.
[0014] In an alternate embodiment of the invention a plurality of
support pin elements are distributed on said object support side
and arranged to contact said back side of said flat object. In such
an embodiment of the invention, the wafer is held on the support
pin elements and piezoelectric elements also distributed between
the support pin elements serve to measure or sense the temperature
and serve to influence the temperature in a desired manner.
[0015] Another embodiment of the invention comprises individual
fiber optics being illuminated with infrared radiation to influence
the temperature of localized areas of the object's back side.
[0016] If fiber optics as mentioned above are used to influence the
temperature of localized areas of the object's back side, in a
preferred embodiment of the invention the tops of these temperature
influencing fiber optics are arranged such that they are spaced
from the object's back side.
[0017] A further preferred embodiment of the invention comprises a
plurality of fiber optics illuminated with infrared radiation and a
plurality of piezoelectric elements as temperature influencing
elements. Due to the combination of fiber optics and piezoelectric
elements a better temperature distribution of the object's back
side and a better influence of the temperature distribution can be
achieved.
[0018] An alternative embodiment of the invention comprises also
heat sink pins and heating elements as temperature influencing
elements. Hence, in such an embodiment localized areas of the
object's back side can not only be heated but also be cooled.
[0019] Due to the use of temperature influencing elements which are
selectively movable in close proximity with and away from said back
side of said flat object, a better influence of the temperature of
a localized area of the object's back side is achievable.
[0020] Another embodiment of the invention comprises a temperature
controller connected to that plurality of individual temperature
influencing elements to control the temperature distribution of
said flat object in a desired manner.
[0021] A preferred embodiment of the invention refers to a
temperature-controlled wafer chuck comprising a chuck body having a
wafer support side and a back side opposing said wafer support
side, said wafer support side being adapted to hold a wafer having
a front side and a back side on the object's back side. A plurality
of temperature sensing elements is distributed on said wafer
support side, each of said temperature sensing elements being
arranged to sense the temperature of a partial area of said wafer
back side. A plurality of individual temperature influencing
elements is distributed on said wafer support surface, each of said
temperature influencing elements being arranged to influence the
temperature of a partial area of said wafer back side. A
temperature controller is connected to said plurality of
temperature sensing elements and said plurality of individual
temperature influencing elements to control and/or regulate the
temperature distribution of said flat object in a desired
manner.
[0022] A preferred embodiment of such a temperature-controlled
wafer chuck comprises a temperature controller including at least
one temperature detector and a control unit connected with said at
least one temperature detector and controlling said temperature
influencing elements.
[0023] A preferred inventive method for controlling the temperature
of a substantially flat object having a front side and a back side
and being supported on said back side comprises the method steps of
sensing the temperature of partial areas of the back side of said
flat object, determining the object's temperature distribution on
the basis of the temperatures measured in said temperature sensing
step, and changing the temperature in at least some of said partial
areas of said back side of said flat object in a desired
manner.
[0024] The method is particularly for controlling the temperature
of a wafer held on a wafer chuck.
[0025] In a preferred method according to the invention, the
temperature of a partial area of said flat object is measured by a
temperature sensing element of a plurality of temperature sensing
elements distributed over the back side of said flat object.
[0026] In a preferred embodiment these temperature sensing elements
consist of a piezoelectric element.
[0027] In a preferred method according to the invention the
temperature of a partial area of said flat object is influenced by
a temperature influencing element of a plurality of temperature
influencing elements distributed over the back side of said flat
object.
[0028] In a preferred embodiment each temperature influencing
element is an IR-optical fiber.
[0029] In another preferred embodiment of the inventive method each
temperature influencing element is a heat sink pin.
[0030] In an alternative embodiment of the inventive method a
piezoelectric element is used as a temperature influencing
element.
[0031] Another embodiment of the inventive method includes
IR-optical fibers and piezoelectric elements and heat sink pins as
temperature influencing elements.
[0032] A preferred embodiment of a pre-align station of an exposure
tool for wafers comprises:
[0033] a chuck body having a wafer support side and a back side
opposing said wafer support side, said wafer support side being
adapted to hold a wafer having a front side and a back side on the
object's back side. A plurality of temperature sensing elements is
distributed on said wafer support side, each of said temperature
sensing elements being arranged to sense the temperature of a
partial area of said wafer back side. A plurality of individual
temperature influencing elements is distributed on said wafer
support surface, each of said temperature influencing elements
being arranged to influence the temperature of a partial area of
said wafer back side. A temperature controller is connected to said
plurality of temperature sensing elements and said plurality of
individual temperature influencing elements to control the
temperature distribution of said flat object as desired.
[0034] A preferred embodiment of an exposure chuck in an exposure
tool for wafers comprises
[0035] a chuck body having a wafer support side and a back side
opposing said wafer support side, said wafer support side being
adapted to hold a wafer having a front side and a back side on the
object's back side. A plurality of temperature sensing elements is
distributed on said wafer support side, each of said temperature
sensing elements being arranged to sense the temperature of a
partial area of said wafer back side. A plurality of individual
temperature influencing elements is distributed on said wafer
support surface, each of said temperature influencing elements
being arranged to influence the temperature of a partial area of
said wafer back side. A temperature controller is connected to said
plurality of temperature sensing elements and said plurality of
individual temperature influencing elements to control the
temperature distribution of said flat object as desired.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Preferred embodiments of the present invention will be
described in greater detail with reference to the accompanying
drawings, wherein like members bear like reference numerals and
wherein:
[0037] FIG. 1 is a schematic side view of a wafer chuck according
to a first embodiment of the present invention;
[0038] FIG. 2 is a schematic top plan view of the wafer chuck in
FIG. 1 showing the distribution of piezoelectric elements and
IR-fiber optics;
[0039] FIG. 3 is a schematic side view of a second embodiment of a
wafer chuck according to the present invention;
[0040] FIG. 4 is a schematic top plan view of the second embodiment
of the wafer chuck of FIG. 3;
[0041] FIG. 5 is a schematic side view of a third embodiment of a
wafer chuck according to the invention;
[0042] FIG. 6 is a schematic top plan view of the third embodiment
of the wafer chuck according to the invention;
[0043] FIG. 7 is a schematic side view of a fourth embodiment of
the wafer chuck according to the invention;
[0044] FIG. 8 is a schematic top plan view of the fourth embodiment
of the wafer chuck of FIG. 7;
[0045] FIG. 9 is a schematic top plan view of the back side of a
wafer having a localized area with a localized area having a
temperature lower than the average temperature of the wafer's back
side; and
[0046] FIG. 10 is a schematic flow diagram of a preferred
embodiment of the method according to the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0047] The present invention provides an improved wafer chuck,
especially an improved lithography wafer chuck, that is especially
useful for holding small as well as large wafers, such as having a
diameter of, for example, 300 mm.
[0048] FIG. 1 illustrates simplified a side view of a wafer chuck
body 20 having a wafer support side 21 and a back side 22 opposing
said wafer support side. On the wafer support side 21 a plurality
of piezoelectric pin elements 4 are distributed. These
piezoelectric pins 4 have a top surface 5 arranged to support a
back side 3 of a wafer 1. The wafer 1 has also a front side 2
opposing the wafer's back side 3, which will be exposed in an
exposure tool.
[0049] Each piezoelectric pin 4 projects from the wafer support
side 21 of the wafer chuck body 20 and are evenly distributed on
the wafer support side 21, as illustrated in FIG. 2. If preferred,
the piezoelectric elements 4 can also be unevenly distributed.
Between the piezoelectric elements IR-fiber optics 6 are arranged.
These fiber optics 6 project from the wafer support side 21 of the
chuck body 20, but the tops of these fiber optics are not as high
as the tops of the piezoelectric elements 4. Hence, the tops of the
fiber optics 6 do not contact the wafer's back side 3. As shown in
FIG. 1, a temperature controller 30 is connected with each
piezoelectric element 4 and each IR-fiber optic 6 via a lead
31.
[0050] Referring to FIG. 2, a partial area of the wafer chuck body
20 is shown in a top plan view.
[0051] Here, the tops of the piezo electric elements 4 and the
IR-fiber optics 6 are illustrated. The operation of a wafer chuck
shown in FIGS. 1 and 2 is as follows:
[0052] A wafer 1 is laid down on the top surface 5 of the
piezoelectric pins 4 such that the wafer 1 lies on the top surface
5 of the piezoelectric pins 4 with the wafer's back side 3. Now, by
sensing or measuring a .DELTA.V (voltage difference) of each
piezoelectric pin 4 a .DELTA.T on the wafer's back side is
measured. Hence, the temperature distribution on the wafer's back
side 3 is available. In the preferred embodiment according to FIGS.
1 and 2 the temperature is now adjusted by using the IR-fiber
optics 6. Due to the temperature controller 30 it is possible to
control each IR-fiber optic such that the temperature of a partial
area of the wafer's back side 3 can be influenced in a desired
manner, that means here the temperature can be increased. The
temperature increase of the partial area accompanying a fiber optic
6 can be achieved by varying the pulse and intensity of the IR
radiation.
[0053] Then again, the wafer distribution is measured by the
piezoelectric elements 4. Again, if necessary, one or more fiber
optics 6 are activated as necessary to achieve a temperature
distribution within a desired temperature range, for example,
0.1.degree. C.
[0054] It is to be noted that it is also possible to use holding
pins instead of piezoelectric pins. The temperature is in such an
embodiment measured by normal temperature sensing elements. The
second embodiment of the wafer chuck according to the invention is
shown in FIGS. 3 and 4. Here, contrary to the first embodiment of
FIGS. 1 and 2, the IR-fiber optics 8 are arranged in the center of
the piezoelectric pins 4. The distribution of the piezoelectric
pins 4 and the centered IR-fiber optics 8 is illustrated in FIG. 4.
With such an arrangement a higher density of piezoelectric elements
and temperature influencing fiber optics 8 is achievable. Hence,
the temperature distribution of the wafer's back side 3 can be
measured in a higher number of partial areas of the wafer's back
side 3.
[0055] The operation of the second embodiment according to FIGS. 3
and 4 is similar to the operation of the first embodiment.
[0056] A third embodiment of the wafer chuck according to the
invention is shown in FIGS. 5 and 6. Contrary to the second
embodiment shown in FIGS. 3 and 4, here heat sink pins 9 are
distributed between the piezoelectric pins 4 having in the center a
fiber optic 8. Again, the distribution of these elements mentioned
above is shown in FIG. 6 in a schematic manner.
[0057] Here, the temperature of a partial area of the wafer's back
side 3 can be influenced such that the temperature can be increased
or decreased. The temperature of a partial area of the wafer's back
side 3 can now be increased or decreased by activating one or more
fiber optic elements 8 and heat sink pins 9, respectively. Again, a
temperature controller is arranged to control the heat sink pins 9,
the IR-fiber optic elements 8 and the piezoelectric elements 4.
[0058] It is to be noted that the top surfaces 10 of the heat sink
pins 9 do not contact the wafer's back side 3. If desired, it is
also possible that these surfaces 10 contact the wafer's back side
3 to carry off heat from the wafer's back side 3.
[0059] In a further preferred embodiment according to FIGS. 7 and
8, the fiber optics 8 are not arranged in the center of the
piezoelectric elements 4, but are separate elements. All other
features are similar to the embodiments shown in FIGS. 5 and 6. In
FIG. 8 the distribution of the piezoelectric elements 4, the heat
sink pins 9 and the IR-fiber optic elements 8 is illustrated
schematically.
[0060] If, as for example shown in FIG. 9, a wafer's back side 3
has a localized area 11 with a temperature lower than the average
temperature of the wafer 1, these temperature influencing elements
4, 8, 9 facing this localized area 11 of the wafer 1 can be
activated such that a more even temperature distribution of the
wafer's back side 3 is achievable.
[0061] In the flow diagram of FIG. 10 the various method steps of
the method according to the invention are shown. In a method step
S1 the temperature difference AT on the wafer's back side is
measured. If necessary, to obtain a more even temperature
distribution of the wafer in a method step S2 the temperature is
adjusted by activating one or more IR fiber optics or heat sinks or
a combination of IR fiber optics and heat sinks or of piezo
electric elements. If .DELTA.T is equal or less than
.DELTA.T.sub.max then the wafer is exposed in a method step S4. If
.DELTA.T is greater than .DELTA.T.sub.max again the temperature
difference .DELTA.T on the wafer's back side is measured and in a
method step S2 the temperature is adjusted. Here, .DELTA.T.sub.max
is about 0.1.degree. C. or within the range of 0.1.degree. C. and
1.degree. C.
* * * * *