U.S. patent application number 09/209735 was filed with the patent office on 2001-06-07 for gas driven rotating susceptor for rapid thermal processing (rtp) system.
This patent application is currently assigned to Rodney T. Hodgson. Invention is credited to ASCHNER, HELMUT, HAUKE, ANDREAS, WEBER, KARSTEN, ZERNICKEL, DIETER.
Application Number | 20010002948 09/209735 |
Document ID | / |
Family ID | 22780044 |
Filed Date | 2001-06-07 |
United States Patent
Application |
20010002948 |
Kind Code |
A1 |
ASCHNER, HELMUT ; et
al. |
June 7, 2001 |
GAS DRIVEN ROTATING SUSCEPTOR FOR RAPID THERMAL PROCESSING (RTP)
SYSTEM
Abstract
An apparatus for preventing warping of a rotatable base for
supporting an object being processed in a Rapid Thermal Processing
(RTP) system due to non uniform heating of the base by radiation
from the object being processed is disclosed.
Inventors: |
ASCHNER, HELMUT;
(BEIMERSTETTEN, DE) ; HAUKE, ANDREAS; (NEU ULM,
DE) ; WEBER, KARSTEN; (LEUTENBACH, DE) ;
ZERNICKEL, DIETER; (AMSTETTEN, DE) |
Correspondence
Address: |
RODNEY T HODGSON
822 PINESBRIDGE ROAD
OSSINING
NY
10562
|
Assignee: |
Rodney T. Hodgson
|
Family ID: |
22780044 |
Appl. No.: |
09/209735 |
Filed: |
December 11, 1998 |
Current U.S.
Class: |
392/418 ;
119/730; 219/390 |
Current CPC
Class: |
C30B 25/12 20130101;
H01L 21/67115 20130101; C30B 31/14 20130101 |
Class at
Publication: |
392/418 ;
219/390; 119/730 |
International
Class: |
F27B 005/14 |
Claims
1. An apparatus, comprising: a rotatable base for supporting an
object being processed in a Rapid Thermal Processing (RTP) system;
and a first means for preventing warping of the base due to non
uniform heating of the base by radiation from the object being
processed.
2. The apparatus of claim 1, wherein the base is rotated by
impinging a flowing fluid on the base.
3. The apparatus of claim 2, wherein the first means comprises a
radiation absorbing plate interposed between the base and the
object.
4. The apparatus of claim 2, wherein the first means comprises a
reflective coating applied to a surface of the base.
5. The apparatus of claim 2, wherein the first means comprises an
absorptive coating applied to a surface of the base.
6. The apparatus of claim 2, wherein the first means comprises a
slot cut in the base.
7. The apparatus of claim 2, wherein the first means comprises a
plate separate from the base, the plate supported by the base at a
plurality of points and the plate supporting the object.
8. The apparatus of claim 7, wherein the plate is engaged with the
base so that orientation of the plate with respect to the base is
constant as the base rotates.
9. The apparatus of claim 2, wherein the first means comprises a
plate joined to the base, the plate joined to the base at a
plurality of points by joining means which allow relative expansion
between the base and the plate.
10. The apparatus of claim 2, wherein the first means comprises a
spatial variation of the material of the base which results a
spacial variation in the absorption of radiation from the
object.
11. The apparatus of claim 2, wherein the first means comprises an
apparatus for controlling the temperature and distribution of the
fluid impinging on the base, so that the temperature distribution
of the base is controlled.
12. The apparatus of claim 2, wherein the first means comprises a
guard ring about the object.
13. The apparatus of claim 2, wherein the angular position of the
base is determined by optical means.
14. The apparatus of claim 13, wherein the base is formed from
quartz, the quartz having optical markings impressed by
sandblasting.
15. The apparatus of claim 2, wherein the angular position of the
base is determined by magnetic means.
16. A method of rapid thermal processing (RTP) of an object,
comprising: supporting the object on a rotatable base; processing
the object with radiation from radiation sources of an RTP system
while rotating the object on the rotatable base; and preventing the
base from warping due to non-uniform heating of the base by
radiation from the object being processed.
17. The method of claim 16, wherein the base is rotated by
impinging a flowing fluid on the base.
18. The method of claim 17, wherein a is plate interposed between
the base and the object to prevent the base from warping.
19. The method of claim 17, wherein a slot cut in the base to
prevent the base from warping.
20. The method of claim 17, wherein a plate separate from the base
is used to support the object, where the plate is supported by the
base at a plurality of points, and wherein the plate receives most
of the radiation from the object and thus prevents the base from
warping.
21. The method of claim 20, wherein the plate is engaged with the
base so that orientation of the plate with respect to the base is
constant as the base rotates.
22. The method of claim 17, wherein a plate joined to the base at a
plurality of points is used to support the object, and wherein the
plate receives most of the radiation from the object and thus
prevents the base from warping.
23. A system for rapid thermal processing (RTP) of an object,
comprising: a radiation source for producing radiation to heat the
object; a chamber for containing the object to be processed, the
chamber having at least a part of at least one wall transparent to
the radiation from the radiation source; a gas handling system for
controlling the gas in the chamber; a means for monitoring the
temperature of the object; a computer system for controlling the
gas handling system and the radiation sources; a rotatable base for
supporting an object being processed within the chamber; and a
first means for preventing warping of the rotatable base due to non
uniform heating of the base by radiation from the object being
processed.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a system, apparatus, and
method for more uniformly heating objects in a Rapid Thermal
Processing (RTP) system. More specifically, the present invention
discloses a convenient, inexpensive way to rotate semiconductor
wafers treated in such system.
BACKGROUND OF THE INVENTION
[0002] The major problem faced by the field of RTP has been the
uniformity of heating of the semiconductor wafers treated in the
RTP systems. RTP systems generally have a chamber with at least one
wall transparent to radiation from sources of radiation such as
lamps. The object to be processed is placed in the chamber and
irradiated with radiation from the radiation source so that the
object is heated. The chamber with the transparent wall is not
strictly necessary in the system, provided that the system controls
the atmosphere in which the object is placed during processing. The
lamps could then be placed in proximity to the object without the
intervening window. Much progress has been made in using batteries
of lamps with individual control of each lamp to increase
uniformity of the illuminating radiation. However, the uniformity
of the resulting material is not sufficient for present and future
demands from the industry.
[0003] One way to increase the uniformity of result in such systems
is to rotate the substrate under the lamps. Many prior art systems
have been published to effect this rotation. However, these many
systems generally used only one bank of lamps on one side of the
semiconductor wafer. The other side of the wafer could then be used
for various shafts which penetrated through the chamber walls to
mechanically rotate the wafer with respect to the lamps. The prior
art is deficient in that the systems are expensive and difficult to
seal. The prior art systems also allow contaminants scrubbed from
the relatively moving parts to contaminate the chamber. The prior
art systems can not be used with banks of lights on either side of
the wafer since the shaft, the rotating base holding the wafer, and
the fittings necessary to allow the shaft to rotate with respect to
the chamber block or otherwise interfere with light from the bank
on the same side of the wafer as the shaft, and the resulting light
impinging on the wafer is no longer uniform.
RELATED APPLICATIONS
[0004] Reactors based on the RTP principle often have the entire
cross section of one end of the reactor chamber open during the
wafer handling process. This construction has been established
because the various wafer holders, guard rings, and gas
distribution plates, which have significantly greater dimensions
and may be thicker than the wafers, must also be introduced into
the chamber and must be easily and quickly changed when the process
is changed or when different wafer sizes, for example, are used.
The reaction chamber dimensions are designed with these ancillary
pieces in mind. U.S. Pat. No. 5,580,830 teaches the importance of
the gas flow and the use of an aperture in the door to regulate gas
flow and control impurities in the process chamber.
[0005] The importance of measuring the temperature of the wafer
using a pyrometer of very broad spectral response is taught in U.S.
Pat. No. 5,628,564.
[0006] A method and apparatus for improved temperature control is
taught in U.S. Pat. No. 5,841,110.
[0007] The wafer to be heated in a conventional RTP system
typically rests on a plurality of quartz pins which hold the wafer
accurately parallel to the reflector walls of the system. Prior art
systems have rested the wafer on an instrumented susceptor,
typically a uniform silicon wafer. Patent application Ser. No.
08/537,409, now U.S. Pat. No. 5,841,110 teaches the importance
susceptor plates separated from the wafer.
[0008] Rapid thermal processing of III-IV semiconductors has not
been as successful as RTP of silicon. One reason for this is that
the surface has a relatively high vapor pressure of, for example,
arsenic (As) in the case of gallium arsenide (GaAs). The surface
region becomes depleted of As, and the material quality suffers.
Patent application Ser. No. 08/631,265, now U.S. Pat. No.
5,837,555, supplies a method and apparatus for overcoming this
problem.
[0009] A method of raising the emissivity of a lightly doped,
relatively low temperature wafer by locally heating the wafer with
a pulse of light is disclosed in application Ser. No. 08/632,364,
now U.S. Pat. No. 5,727,017.
[0010] An inflatable seal for an RTP system is disclosed in
copending allowed application Ser. No. 08/895,655, filed Jul. 17,
1997, by Aschner et al.
[0011] A method, apparatus, and system for RTP an object is
disclosed in copending application Ser. No. 08/953,590, filed Oct.
17, 1997, by Lerch et al.
[0012] A method of RTP of a substrate where a small amount of a
reactive gas is used to control the etching of oxides or
semiconductor is disclosed in copending application Ser. No.
08/886,215, by Nenyei et al, filed Jul. 1, 1997.
[0013] A method of RTP of a substrate where evaporation of the
silicon is controlled is disclosed in copending application Ser.
No. 09/015,441, by Marcus et al. filed Jan. 29, 1998.
[0014] Methods of rotating the wafer in an RTP system are disclosed
in application Ser. Nos. 08/960,150 and 08/977,019 by Blersch et
al. and Aschner et al. filed on Oct. 29, 1997 and Nov. 24, 1997
respectively.
[0015] The above identified lpatents and applications are assigned
to the assignee of the present invention and are hereby
incorporated herein by reference.
SUMMARY OF THE INVENTION
[0016] According to this invention, the object to be processed in
an RTP system is placed on a rotating susceptor which is protected
from warping due to uneven heating of the susceptor from radiation
from the hot object.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows a prior art RTP processing system.
[0018] FIG. 2 shows a rotating base or susceptor 210 holding a
wafer 110.
[0019] FIG. 3 shows an alternative embodiment of the invention.
[0020] FIG. 4 shows a cross section of the most preferred
embodiment of the invention.
[0021] FIG. 5 shows an alternative embodiment of the invention.
[0022] FIG. 6 shows an alternative embodiment of the invention.
[0023] FIG. 7 shows an expanded view of an enhanced version of the
most preferred embodiment of the invention.
[0024] FIGS. 8A-E show detailed views of the most preferred
embodiment of the invention.
[0025] FIGS. 9A-G show detailed views of the most preferred
embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0026] FIG. 1 shows a prior art RTP processing system. A
semiconductor wafer 110 or other object to be processed is
supported in a quartz RTP chamber 120 by quartz support pins 160
(only one shown). A guard ring 170 is used to lessen edge effects
of radiation from the edge of the wafer 110. An end plate 190 seals
to the chamber 120, and a door 180 allows entry of the wafer 110
and, when closed, allows the chamber to be sealed and a process gas
125 to be introduced into the chamber. Two banks of radiation
sources 130 and 140 are shown on either side of the wafer 110. A
computer 175 or other control means as are known in the art is used
to control the lamps 130 and 140, and to control the gas flow
controller 185, the door 180, and the temperature measuring system,
denoted here as a pyrometer 165. The gas flow may be an inert gas
which does not react with the wafer, or it may be a reactive gas
such as oxygen or nitrogen which reacts with the material of the
semiconductor wafer to form a layer of on the semiconductor wafer,
or the gas flow may be a gas which may contain a silicon compound
which reacts at the heated surface of the object being processed to
form a layer on the heated surface without consuming any material
from the surface of the object. When the gas flow reacts to form a
layer on the surface, the process is called rapid thermal-chemical
vapor deposition (RT-CVD). An electrical current may be run through
the atmosphere in the RTP system to produce ions which are reactive
with or at the surface, and to impart extra energy to the surface
by bombarding the surface with energetic ions.
[0027] FIG. 2 shows a rotating base or susceptor 210 holding a
wafer 110. Such a rotating base driven by a gas flow has been
described in great detail in application Ser. No. 08/977,019 by
Aschner et al. filed on Nov. 24, 1997. The base 210 is supported by
air bearings 220. A gas flow 230 impinging on the rotating base
causes the base to rotate about axis 240. A means for centering the
base 210 is not shown in FIG. 2. When the device described in
application Ser. No. 08/977,019 is used for heating wafer 110 to
high temperatures and relatively long times, the infra red
radiation from the hot wafer 110 is partially absorbed by the base
which is made of quartz or other material transparent to the
radiation from the lamps 140 and may cause warping of the base so
that the flat surfaces of the base needed to ride on the air
bearings 220, and the rotation may stop. The present invention
details apparatus and methods to prevent such warping. One such
method of preventing absorption and warping is shown in FIG. 2,
where a layer 250 is shown deposited on or part of base 210. The
layer 250 may be a reflective layer which reflects the infrared
radiation from the wafer, but transmits the visible and near
infrared radiation from the lamps 140. Such a reflective layer may
be uniform over the base as shown, or it may be non uniformly
applied to counteract the non-uniformity of the infrared radiation
from the wafer impinging on the base. The layer 250 may also be an
absorbing layer which absorbs radiation in a pattern to counteract
the non uniform radiation from the wafer 110. Another preferred
embodiment of the invention is to dope the quartz glass of the base
210 with atoms or molecules which absorb radiation from the wafer,
so that a radial gradient in concentration of the molecules or
atoms, preferably increasing from the inner to the outer portions
of the base 210, is provided. The doping will result in a more
uniform radial temperature profile of the base 210, if the base is
non uniformly irradiated mainly in the center region. Due to the
more uniform radial temperature distribution of the base 210,
buckling of the wafer and the base is prevented.
[0028] FIG. 3 shows an alternative embodiment to prevent the infra
red radiation from the wafer 110 heating and warping the base 210.
A plate 310 is interposed between wafer 110 and base 210 which
absorbs radiation from the wafer 110 and prevents the infra red
radiation from heating the base 210. The plate 310 is preferably
made of quartz, so that the heating radiation from the lamps 140
will be transmitted, while the longer wavelength radiation from the
wafer 110 will be absorbed. The plate 310 may also be coated with a
reflective or absorptive layer to control the temperature
distribution of the plate 310 and the base 210. A further solution
is to dope the quartz glass of the plate 310 with atoms or
molecules to get a radial gradient in concentration of the
molecules or atoms which absorb radiation from the wafer,
preferably increasing from the inner to the outer portions of the
plate 310. The doping will result in a more uniform radial
temperature profile of the susceptor 310, if the susceptor is non
uniformly irradiated mainly in the center region. Due to the more
uniform radial temperature distribution of the plate 310, buckling
of the wafer is prevented. The diameter of plate 310 is preferably
approximately the same as the diameter of the wafer 110.
[0029] FIG. 4 shows a cross section of the most preferred
embodiment of the invention. The rotating base 410 of the invention
is a ring which is supported by the air bearings 220. The ring
supports a plate 420 which is supported at a plurality of points
430. The plate 420 is shown having a plurality of projections 440
for support (only one shown). Now, when plate 420 is heated by
radiation from wafer 110, it may expand within the ring of base
410, and base 410 which receives relatively little radiation from
wafer 110 will not be under so much stress to warp and cause
problems riding on air bearings 220. While projections 440 are
shown attached to plate 410, such projections could equally well be
attached to base 410 to support plate 420 from the bottom. Once
again, a centering post or detent arrangement which forces the base
410 and plate 420 to rotate about axis 240 is not shown.
[0030] FIG. 4 also shows a method of determining the angular
position of base 410. A light beam 450 shines through the base 410
and is detected by a detector 460. Features 470 are placed on base
410 which change the light beam and thus may be detected by
detector 460. The preferred features are sandblasted features,
which scatter the light beam 450 but do not otherwise interfere
with the radiation from the lamps 140. The most preferred features
are the teeth of application Ser. No. 08/977,019 which have been
sandblasted to interrupt light from a laser. As a convenience,
there are 360 teeth arranged equidistant around the circumference
of base 410. An extra tooth is additionally used inserted in
between two of the 360 teeth to produce an extra reference signal.
Other preferred features may be absorptive features or reflective
features. Features 470 may also be magnetic features which may be
detected by a magnetic detector in place of an optical
detector.
[0031] In order to prevent plate 420 rotating with respect to base
410, plate 420 may engage base 410 with a tooth projecting from
plate 420 into a detent in base 410, or with the projections 440
engaged in detents in base 410, or any suitable combination or
other means as would be obvious to one skilled in the art.
[0032] To prevent imbalance of the ring 410 and the plate 420, the
features of the apparatus such as the projections 440, the pin
holding means for holding pins 160, the detent in base 410, the
extra tooth of plate 410 are arranged in a suitable way to balance
the whole apparatus.
[0033] An alternative embodiment of the invention is shown in FIG.
5. A base 510 in the form of a ring is joined to a plate 520 by a
plurality of rods 530. The rods 530 are sufficiently elastic to
ensure that little stress is placed on base 510 when plate 520 is
heated by radiation from the wafer.
[0034] An alternative embodiment of the invention is shown in FIG.
6. A base 610 has a series of cuts 640 formed in the plate to
ensure that stress will not be transmitted from the inner part 620
to the outer part 630.
[0035] The advantage of the embodiments described in FIGS. 2, 5,
and 6 is that the distortion of the rotatable substrate is
extremely reduced, since the inner part of the rotating system is
mechanically decoupled from the outer part, but the outer part is
the essential part of the rotation means regarding the
functionality of the air bearings. As a result, the bearing
surfaces of the outer parts remain very parallel to the surfaces of
the air bearings, even if the diameter of the rotating system is
large or if the temperature of the wafer and inner parts of the
rotation means is very high.
[0036] FIG. 7 shows an expanded view of an enhanced version of the
most preferred embodiment of the invention. A lower quartz plate
701 has gas lines 702 to deliver gas to gas bearings 220 A center
bearing 703, preferably made of sapphire, serves to center the
apparatus with respect to the plate 701. The base 410 and plate 420
of FIG. 4 ride on the air bearings and are rotated by gas blown
from an external tube (not shown). A series of optional elements
707-716 are shown, which control the infra red radiation from the
wafer 110. Elements 707 are hollow cylinders which hold pins 160 to
support wafer 110. An additional holding means 708 holds a ring
comprised of segments such as 710 and 711. Holding means 708 and
ring segments 710 and 711 do not rotate, but are held by plate 701.
The ring segments 710 and 711 are preferably made from quartz, and
shield the rotating base 410 from radiation reflected and radiated
from the wafer 110 and especially from the guard ring, 714, 715,
and 712. The guard ring, 714, 715, and 712 is shown made from
segments. The ring 710 and 711 and the guard ring, 714, 715, and
712 are made from segments for cost reasons, and for ease of
replacement if one segment is broken. However, these rings could be
made from single pieces of material. The guard ring, 714, 715, and
712 is preferably made from silicon, and the silicon is preferably
coated to make sure that the guard ring is stable and the
reflectivity and absorption characteristics do not change with
time.
[0037] The holding means 708 is engaged with the quartz plate 701
via pins 704 and 709. The ring segments 710 and 711 are supported
on the hollow cylindrical shaped pins 708A of the holding means
708. Pins 713 are inserted into the hollow pins 708A, and project
through the ring segments 710 and 711 to support the guard ring
segments 712, 714, and 715. One segment 712 is shown displaced from
the plane of the other segments 714 and 715 to show that a segment
may optionally be placed out of the plane (either higher or lower)
of the guard ring to allow withdrawal of a robot arm which has
introduced wafer 110 into the system and lowered it so that wafer
110 is coplanar with guard ring segments 714 and 715.
[0038] An additional quartz plate 716 resting on quartz pins 709
has the advantage that turbulence of the hot gas above the wafer is
minimized.
[0039] FIGS. 8A-E and 9A-G show detailed views of the most
preferred embodiment of the invention. In particular, a notch 822
in ring 410 received a tooth 932 on plate 420 so that ring 410 may
drive plate 420. Also shown are the sandblasted teeth 450, and an
extra tooth 825 which gives the computer a calibration point from
which to count the number of teeth rotating past the optical
detection means.
[0040] Obviously, many modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that, withing the scope of the appended
claims, the invention may be practiced otherwise then as
specifically described.
* * * * *