U.S. patent application number 10/697401 was filed with the patent office on 2005-05-05 for low/high temperature substrate holder to reduce edge rolloff and backside damage.
Invention is credited to Goodman, Matthew G., Keeton, Tony J., Stamp, Michael R..
Application Number | 20050092439 10/697401 |
Document ID | / |
Family ID | 34550353 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050092439 |
Kind Code |
A1 |
Keeton, Tony J. ; et
al. |
May 5, 2005 |
Low/high temperature substrate holder to reduce edge rolloff and
backside damage
Abstract
A substrate holder for processing a semiconductor substrate that
minimizes substrate non-uniformities as well as backside damage.
The substrate holder includes one or more support elements, such as
a plurality of veins configured in an annular ring to support an
outer edge of a substrate. The veins are configured to support a
substrate of a particular size in a support plane defined by the
top surfaces of the veins. The substrate holder also has one or
more annular grooves formed in the top surface of the holder. In a
preferred embodiment, the substrate holder also has a raised
annular ring positioned radially inward of the grooves and the
support elements. The top surface of the raised annular ring is no
higher that the top surfaces of the veins.
Inventors: |
Keeton, Tony J.; (Mesa,
AZ) ; Goodman, Matthew G.; (Chandler, AZ) ;
Stamp, Michael R.; (Chandler, AZ) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
34550353 |
Appl. No.: |
10/697401 |
Filed: |
October 29, 2003 |
Current U.S.
Class: |
156/345.51 |
Current CPC
Class: |
H01L 21/68735 20130101;
C23C 16/4585 20130101; H01L 21/6833 20130101 |
Class at
Publication: |
156/345.51 |
International
Class: |
C23F 001/00 |
Claims
1. An apparatus for processing a semiconductor substrate,
comprising a substrate holder comprising a support element
configured to support a substrate of a particular size in a support
plane defined by the support element, wherein the support element
comprises an annular veined ring supporting an outer edge of the
substrate when the substrate is supported on the support
element.
2. The apparatus of claim 1, wherein the support element comprises
at least 300 veins.
3. The apparatus of claim 1, further comprising a first annular
groove on the substrate holder, the first annular groove being
positioned radially inward from the support element.
4. The apparatus of claim 3, wherein the first annular groove has a
generally uniform annular thickness.
5. The apparatus of claim 3, wherein the substrate holder further
comprises a substrate pocket and the first annular groove is formed
such that the first annular groove is lower than a surface of the
substrate pocket.
6. The apparatus of claim 3, further comprising a second annular
groove on the substrate holder, the second annular groove being
positioned radially outward from the support element.
7. The apparatus of claim 6, wherein a vertical depth of the first
annular groove is greater than a vertical depth of the second
annular groove.
8. The apparatus of claim 5, further comprising an annular ring
raised above the substrate pocket and positioned radially inward of
the support element.
9. The apparatus of claim 1, wherein the substrate holder is
configured to be supported by a spider structure comprising a
vertical shaft and at least three substrate holder supporters
extending radially outward and upward from the shaft, the substrate
holder supporters configured to support the bottom surface of the
substrate holder.
10. The apparatus of claim 9, wherein the bottom surface of the
substrate holder includes a recess configured to receive upper ends
of the substrate holder supporters of the spider structure.
11. The apparatus of claim 9, wherein the bottom surface of the
substrate holder includes a circular groove centered about a
central vertical axis of the substrate holder, the circular groove
configured to receive upper ends of the substrate holder supporters
of the spider structure, the circular groove of the bottom surface
being interrupted in one location.
12. An apparatus for processing a substrate, comprising: a reaction
chamber; a plurality of radiant heating elements configured to heat
the reaction chamber; and a substrate holder in the reaction
chamber, the substrate holder having a plurality of support
elements configured to support a substrate of a particular size
within a support plane defined by the plurality of support
elements, wherein the support elements comprise a plurality of
spaced veins configured in an annular ring to support an outer edge
of the substrate.
13. The apparatus of claim 12, wherein the substrate holder further
comprises: a substrate pocket; and an annular groove formed in the
substrate pocket and configured to surround an outer edge of the
substrate when the substrate is supported on the plurality support
elements.
14. The apparatus of claim 12, wherein the support plane is formed
by top surfaces of the plurality of spaced veins.
15. The apparatus of claim 13, further comprising an annular recess
in the substrate pocket, the annular recess positioned radially
inward of the support elements.
16. The apparatus of claim 12, further comprising a support
structure configured to support the substrate holder, the support
structure comprising a vertical shaft and a plurality of support
arms extending generally radially outward and upward from the
shaft, the support arms having upper ends configured to support the
substrate holder.
17. The apparatus of claim 13, further comprising an annular ring
on the substrate holder, the annular ring being positioned radially
inward of the support elements and having a raised surface higher
than a surface of the substrate pocket but no higher than the
support plane.
18. An apparatus for processing a substrate, comprising a susceptor
having a support surface sized to support a substrate of a
particular size in a support plane, wherein the support plane is
formed by top surfaces of a plurality of veins.
19. The apparatus of claim 18, wherein the plurality of veins are
formed in an annular ring to support an outer edge of the
substrate.
20. The apparatus of claim 19, further comprising a plurality of
annular recesses in the susceptor, wherein a first of the plurality
of recesses is positioned radially outward of the plurality of
veins and a second of the plurality of recesses is positioned
radially inward of the plurality of veins.
21. The apparatus of claim 18, further comprising an annular ring
on the susceptor, the annular ring being positioned radially inward
of the plurality of veins and having a raised surface no higher
than the support plane.
22. The apparatus of claim 20, further comprising an annular ring
on the susceptor, the annular ring being positioned radially inward
of the second of the plurality of recesses and having a raised
surface no higher than the support plane.
23. A method of manufacturing an apparatus for processing a
substrate, comprising: forming a substrate holder out of graphite,
the substrate holder having one or more support elements configured
to support a substrate of a particular size in a support plane
defined by the one or more support elements, wherein the one or
more support elements comprise a plurality of veins configured on
an annular ring to support an outer edge of the substrate when the
substrate is supported on the one or more support elements; forming
a first annular groove in the substrate holder, the first annular
groove configured to surround an outer edge of the substrate when
the substrate is supported on the one or more support elements;
forming a second annular groove in the substrate holder, the second
annular groove being positioned radially inward of the one or more
support elements; and coating the substrate holder with SiC.
24. The method of claim 23, further comprising forming a raised
annular ring positioned radially inward of the second annular
groove.
25. The method of claim 24, wherein a top surface of the raised
annular ring is no higher than a top surface of support plane.
26. The method of claim 23, further comprising forming a spider
structure configured to support the substrate holder, the spider
structure comprising a vertical shaft and at least three substrate
holder supporters extending radially outward and upward from the
shaft, the substrate holder supporters configured to support the
bottom surface of the substrate holder.
27. An apparatus for processing a semiconductor substrate,
comprising a substrate holder having an annular ring of veins
configured to support a substrate of a particular size, wherein
each vein is generally parallel to two adjacent veins,
substantially all of the veins being angled with respect to a
center of the ring.
28. The apparatus of claim 27, wherein the ring of veins is
configured to support an outer edge portion of the substrate.
29. The apparatus of claim 27, wherein at least some of the veins
are curved.
Description
RELATED APPLICATION
[0001] This application incorporates by reference the entire
disclosure of U.S. patent application Ser. No. 10/331,444, entitled
"SUBSTRATE HOLDER WITH DEEP ANNULAR GROOVE TO PREVENT EDGE HEAT
LOSS," filed Dec. 22, 2002.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to substrate holders
in semiconductor manufacturing apparatuses and, in particular, to
substrate holders configured to maintain uniform heating.
[0004] 2. Description of the Related Art
[0005] High-temperature ovens, or reactors, are used to process
substrates for a variety of reasons. In the electronics industry,
substrates such as semiconductor wafers are processed to form
integrated circuits. A substrate, typically a circular silicon
wafer, is placed on a substrate holder. If the substrate holder
helps to attract radiant heat, it is called a susceptor. The
substrate and substrate holder are enclosed in a reaction chamber,
typically made of quartz, and heated to high temperatures by a
plurality of radiant heat lamps placed around the quartz chamber.
In an exemplary high temperature process, a reactant gas is passed
over the heated substrate, causing the chemical vapor deposition
(CVD) of a thin layer of the reactant material onto a surface of
the substrate. Through subsequent processes, these layers are made
into integrated circuits.
[0006] It is generally desirable to maintain a uniform temperature
throughout the substrate holder during substrate processing.
Typically, the substrate temperature closely tracks that of the
substrate holder. Non-uniformities in the temperature of the
substrate holder result in non-uniformities in the substrate
temperature. These temperature gradients can leave the substrate
susceptible to crystallographic slip in the single-crystal
substrate and epitaxial layers, and possible device failure. Thus,
temperature uniformity is desirable to minimize these problems.
Another reason why it is desirable to maintain a uniform
temperature throughout the substrate holder is to prevent
differences in the quality of the filn deposited on the substrate.
Generally, for other semiconductor fabrication processes (e.g.,
etching, annealing, deposition), temperature gradients in the
substrate result in different rates of reaction, and thus
non-uniformities, throughout the substrate.
[0007] Using state of the art apparatuses and methods, temperature
uniformity has been achieved throughout most of the combination of
the substrate and the substrate holder. However, it has recently
been found that with larger substrates (e.g., 300 mm wafers), it is
difficult to keep the radially outer region of the substrate/holder
combination (the "combination") as hot as the inner region. This is
because the radially outer region experiences greater convective
and conductive heat loss and, in many existing apparatuses,
receives less direct radiation.
[0008] The radially outer region of the substrate/holder
combination experiences greater convective heat loss than the
remainder of the combination because the outer region has a
generally vertical side edge and, hence, a larger surface area at
which heat loss occurs for a given volume or mass. The outer region
of the combination can also lose conductive heat due to contact
with other equipment. These disparities in heat loss between the
radially outer region and the remainder of the combination result
in a lower temperature in the outer region. This temperature
disparity produces a different deposition rate and deposited film
thickness near the outer edge of the substrate. Accordingly, a
processed substrate is typically characterized by an "exclusion
zone" near the substrate edge, within which active devices are not
manufactured and within which the deposited film has non-uniform
qualities.
[0009] Some prior art attempts to minimize or remove the exclusion
zone have focused upon directing a greater amount of radiant energy
to the radially outer, as opposed to inner, region of the substrate
holder during processing, in order to lessen the disparity in heat
loss between such regions. Other attempts have focused upon
providing a hot annular structure (e.g., a temperature compensation
ring) near the periphery of the substrate holder, to reduce the
heat loss from the outer region. While these efforts have been
helpful, some disparity in heat loss between the inner and outer
regions remains. Using state of the art processing methods and
apparatuses, the annular thickness of exclusion zones is generally
about 10-20 mm, while chip manufacturers strive to enforce
exclusion zones to as small as 1 mm to 3 mm to maximize yield. A
need exists to further shrink the exclusion zone.
SUMMARY OF THE INVENTION
[0010] In one aspect, an apparatus for processing a substrate is
provided. The apparatus comprises a substrate holder having a
support element configured to support a substrate of a particular
size in a support plane defined by the support element. The support
element comprises an annular veined ring supporting an outer edge
of the substrate when the substrate is supported on the support
element. In a preferred embodiment of the invention, the support
element comprises an annular ring having a plurality of veins,
where the veins are angled or spiraled to stop gas flow to the
backside of the substrate. In this embodiment, there are preferably
at least 300 veins in the annular veined ring. In a preferred
embodiment, the substrate holder also has a raised annular ring
positioned radially inward of the support element.
[0011] In another aspect, an apparatus for processing a substrate
is provided, comprising a reaction chamber, a plurality of radiant
heating elements configured to heat the reaction chamber, and a
substrate holder in the reaction chamber. The substrate holder has
a thickness defined as a distance between generally parallel top
and bottom surfaces of the substrate holder. The substrate holder
has one or more support elements configured to support a substrate
of a particular size within a support plane defined by the one or
more support elements. The support elements comprise a plurality of
veins configured in an annular ring to support an outer edge of the
substrate.
[0012] In another aspect, an apparatus for processing a substrate
is provided. The apparatus comprises a susceptor having a support
surface sized to support a substrate of a particular size in a
support plane, wherein the support plane is formed by top surfaces
of a plurality of veins.
[0013] In yet another aspect, a method of manufacturing an
apparatus for processing a substrate is provided. A substrate
holder is formed of graphite. The substrate holder has one or more
support elements configured to support a substrate of a particular
size in a support plane defined by the one or more support element.
The one or more support elements comprise a plurality of veins
configured on an annular ring to support an outer edge of the
substrate. A first annular groove is formed in the substrate holder
and is configured to surround an outer edge of the substrate when
the substrate is supported on the one or more support elements. A
second annular groove is also formed in the substrate holder and is
positioned radially inward of the one or more support elements.
Finally, the substrate holder is coated with SiC.
[0014] For purposes of summarizing the invention and the advantages
achieved over the prior art, certain objects and advantages of the
invention have been described herein above. Of course, it is to be
understood that not necessarily all such objects or advantages may
be achieved in accordance with any particular embodiment of the
invention. Thus, for example, those skilled in the art will
recognize that the invention may be embodied or carried out in a
manner that achieves or optimizes one advantage or group of
advantages as taught herein without necessarily achieving other
objects or advantages as may be taught or suggested herein.
[0015] All of these embodiments are intended to be within the scope
of the invention herein disclosed. These and other embodiments of
the present invention will become readily apparent to those skilled
in the art from the following detailed description of the preferred
embodiments having reference to the attached figures, the invention
not being limited to any particular preferred embodiment(s)
disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1A is a top plan view of a conventional substrate
holder;
[0017] FIG. 1B is a partial cross-sectional view of the substrate
holder of FIG. 1A, taken along line 1B-1B of FIG. 1A;
[0018] FIG. 1C is a partial cross-sectional view of the substrate
holder of FIGS. 1A and 1B, shown with a substrate held thereon;
[0019] FIG. 1D is a graph illustrating the thickness of a deposited
chemical layer across the surface of a semiconductor substrate,
using a conventional substrate holder;
[0020] FIG. 2 is a schematic, cross-sectional view of an exemplary
reaction chamber with a substrate supported on a substrate holder
therein;
[0021] FIG. 3A is a top plan view of a substrate holder according
to an embodiment of the present invention, in which the holder has
a veined substrate support surface defined by a plurality of veins
configured in an annular ring;
[0022] FIG. 3B is a partial cross-sectional view of the substrate
holder of FIG. 3A, taken along line 3B-3B in FIG. 3A;
[0023] FIG. 3C is an enlarged view of a portion of FIG. 3A
indicated by arrows 3C-3C in FIG. 3A;
[0024] FIG. 3D is an enlarged view of a portion of FIG. 3C
indicated by arrows 3D-3D in FIG. 3C;
[0025] FIG. 3E is a cross-sectional view of an of the substrate
holder 200 along the line 3E-3E in FIG. 3D;
[0026] FIG. 4 is a bottom plan view of the substrate holder of
FIGS. 3A-3E;
[0027] FIG. 5A is a top plan view of a substrate holder according
to another embodiment of the present invention, in which the holder
has a raised feature near the edge of the holder; and
[0028] FIG. 5B is a schematic cross-sectional view, taken along
line 6B-6B in FIG. 5A, of a portion of a substrate holder according
to the embodiment of the present invention shown in FIG. 5A.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0029] While the claimed invention is described in the context of
CVD, it will be understood that the invention described herein is
applicable to other types of thermal processing, including etching
annealing, oxidation, nitridation, reduction and ALD. As noted
above in the Background of the Invention section, processed
substrates are typically characterized by an exclusion zone at the
outer radial portion of each substrate, within which the deposited
film has non-uniform qualities. This non-uniformity of the
substrate is due in part to non-uniformity in temperature of the
substrate holder upon which the substrate is supported. The outer
radial portion of a typical substrate holder loses heat
convectively at a greater rate than the remainder of the substrate
holder. This disparity in the rate of heat loss is due to the outer
radial portion of the substrate holder having a larger surface area
over which heat loss can occur. The outer radial edge of the
substrate holder also loses some heat conductively due to contact
with other equipment. In addition, in most existing semiconductor
processing apparatuses, the vertical side edge of the substrate
holder receives less direct radiant heat than the remainder of the
substrate holder. As a result, the outer radial portion of the
substrate holder has a lower temperature than the remainder of the
holder, which in turn results in the aforementioned
non-uniformities in the outer radial portion of the processed
substrate supported by the substrate holder.
[0030] FIGS. 1A-1D illustrate this concept. FIGS. 1A-1C show a
conventional substrate holder 1 for supporting a substrate 2, such
as a semiconductor wafer, during processing. FIGS. 1A and 1B show
the substrate holder 1 alone without the substrate 2. FIG. 1A is a
top plan view, and FIG. 1B is cross-sectional view of one side of
the substrate holder 1. FIG. 1C is a view similar to that of FIG.
1B, showing a substrate 2 supported on the substrate holder 1. The
substrate holder 1 includes an inner pocket area 3 defined by an
annular wall 4. The pocket area 3 is sized and configured to
receive and support the substrate 2 (e.g., circular and slightly
larger than a 300 mm wafer). The wall 4 separates the pocket area 3
from a raised annular shoulder 5. The shoulder 5 is located
radially outward of the pocket 3. The substrate holder 1 has an
annular side surface 6 and a bottom surface 7.
[0031] During substrate processing, the substrate holder 1 absorbs
heat, typically from radiant heat lamps surrounding the reaction
chamber. U.S. Pat. No. 6,121,061, which is incorporated by
reference, describes a typical configuration of radiant heat
sources in an exemplary CVD reactor. The substrate holder 1 also
loses heat to the surrounding environment (e.g., to the chamber
walls, which are not perfectly reflective). Some of this lost heat
is re-radiated to the substrate holder 1, while the rest is lost by
convection and conduction. With reference to FIG. 1C, the substrate
holder 1 loses heat from its upper surfaces 3 and 5, side surface
6, and bottom surface 7, and the substrate 2 loses heat from its
upper surface 9. The arrows H.sub.T schematically illustrate the
heat loss at the upper surfaces 3, 5, and 9. Similarly, the arrows
H.sub.S and H.sub.B schematically illustrate the heat loss at the
side surface 6 and the bottom surface 7, respectively. Throughout
most of the holder/substrate combination, the heat loss H.sub.T and
H.sub.B is typically compensated with uniform heat input across the
combination surface of the holder/substrate. Thus, there is a
relatively uniform temperature throughout the upper surface of the
holder/substrate combination (there may be some vertical
temperature gradients). However, there is additional heat loss Hs
at the outer radial edge of the holder/substrate combination, which
receives less direct radiation from the radiant heat lamps and is
thus not compensated by heat input. This additional heat loss
results in a lower temperature at the outer radial edge of the
holder 1 and substrate 2. Consequently, the substrate holder design
shown in FIGS. 1A-1C normally results in some degree of processing
non-uniformities within an "exclusion zone" bordering the substrate
edge 8. Furthermore, the additional heat loss at the edges induces
temperature gradients from the center of the substrate to the
edges, as heat flows radially outward.
[0032] FIG. 1D is a graph that illustrates the thickness of a
chemical vapor deposited (CVD) layer across the surface of a 200-mm
semiconductor substrate, using a conventional substrate holder such
as the substrate holder 1 shown in FIGS. 1A-C. This test was
conducted on a rotating substrate (i.e., the substrate was rotated
about its vertical center axis). In FIG. 1D, the horizontal axis
represents the horizontal location on the surface of the substrate.
The value 0 mm represents the leading edge of the substrate, and
200 mm represents the trailing edge. The vertical axis represents
the localized layer thickness divided by the mean layer thickness
throughout the surface of the substrate. The localized layer
thickness of the deposited layer is shown only from 3-197 mm on the
horizontal axis. This is because it is very difficult to measure
the thickness of the chemical deposition layer within the three
millimeters bordering the substrate edge, which is often rounded.
As shown in FIG. 1D, the use of a conventional substrate holder
leads to a significant reduction of the thickness of the deposited
layer at the edges of the substrate. This "edge roll-off" effect is
caused by the lower temperature at, the outer radial edge of the
substrate/holder combination.
[0033] Previous studies have indicated that the substrate holder is
generally cooler than the substrate during processes such as CVD.
During low temperature processes, the normal contact point, which
is usually the edge perimeter of the substrate, between the
substrate holder and the substrate has the best conductive thermal
contact and is the point where most heat loss from the substrate to
the substrate holder occurs. There are other mechanisms that also
contribute to the temperature losses between the edge of the
substrate and the environment. The edge roll-off compensation
features of the preferred embodiments permit additional heat input
to the substrate from the front, side, and rear radiant heat lamps
of the apparatus, and thermally isolate this additional heat input
as close to the edge of the substrate as possible.
[0034] The preferred embodiments help to achieve a smaller
exclusion zone. A substrate holder design that significantly
reduces heat losses at the outer radial edge of the
holder/substrate combination and, thus, helps to shrink the
achievable size of the exclusion zone is provided. Before
presenting the details of a preferred embodiment of the substrate
holder of the invention, it will be instructive to illustrate an
exemplary reactor within which the inventive substrate holder can
be used for processing substrates, such as semiconductor
wafers.
[0035] FIG. 2 illustrates an exemplary chemical vapor deposition
(CVD) reactor 10, including a quartz reaction chamber 12. Radiant
heating elements 14 are supported outside the transparent chamber
12, to provide heat energy to the chamber 12 without appreciable
absorption by the chamber walls. Although the preferred embodiments
are described in the context of a "cold wall" CVD reactor, it will
be understood that the substrate support systems described herein
can be used in other types of reactors and semiconductor processing
equipment. Skilled artisans will appreciate that the claimed
invention is not limited to use within the particular reactor 10
disclosed herein. In particular, one of skill in the art can find
application for the substrate support systems described herein for
other semiconductor processing equipment, wherein a substrate is
supported while being uniformly heated or cooled, particularly
where the support is subject to edge losses near the substrate
edge. Moreover, while illustrated in the context of standard
silicon wafers, the supports described herein can be used to
support other kinds of substrates, such as glass, which are
subjected to treatments such as CVD, physical vapor deposition
(PVD), etching, annealing, dopant diffusion, photolithography, etc.
The supports are of particular utility for supporting substrates
during treatment processes at elevated temperatures.
[0036] The radiant heating elements 14 typically include two banks
of elongated tube-type heating lamps arranged in orthogonal or
crossed directions above and below a susceptor holding a
semiconductor substrate. Each of the upper and lower surfaces of
the substrate faces one of the two banks of heating lamps 14. A
controller within the thermal reactor adjusts the relative power to
each lamp 14 to maintain a desired temperature during wafer
processing. There are also spot lamps that are used for
compensating for the heat sink effect of lower support
structures.
[0037] The illustrated substrate comprises a semiconductor wafer 16
with a generally circular edge 17, shown in FIG. 2 supported within
the reaction chamber 12 upon a substrate support structure 20. The
illustrated support structure 2b includes a substrate holder 100,
upon which the wafer 16 rests, and a spider 22 that supports the
holder 100. The substrate holder 100, shown in greater detail in
FIGS. 3A-3E (described below), is only one of a number of preferred
embodiments of the present invention. The spider 22 is preferably
made of a transparent and non-metallic (to reduce contamination)
material. The spider 22 is mounted to a shaft 24, which extends
downwardly through a tube 26 depending from the lower wall of the
chamber 12. The spider 22 has at least three substrate holder
supporters or arms 25, which extend radially outward and upward
from the shaft 24. The arms 25 are preferably separated by equal
angles about a vertical center axis of the shaft 24, which is
preferably aligned with a vertical center axis of the substrate
holder 100 and wafer 16. For example, if there are three arms 25,
they are preferably separated from one another by 120.degree.. The
arms 25 are configured to support the bottom surface of the
substrate holder 100. In a preferred embodiment, the substrate
holder 100 comprises a susceptor capable of absorbing radiant
energy from the heating elements 14 and re-radiating such energy.
It is preferable that the upper surface of the holder 100 is solid
and made of one piece. Preferably, the shaft 24, spider 22, and
holder 100 are configured to be rotated in unison about a vertical
center axis during substrate processing.
[0038] A central temperature sensor or thermocouple 28 extends
through the shaft 24 and the spider 22 in proximity to the
substrate holder 100. Additional peripheral temperature sensors or
thermocouples 30 are also shown housed within a slip ring or
temperature compensation ring 32, which surrounds the substrate
holder 100 and the wafer 16. The thermocouples 28, 30 are connected
to a temperature controller (not shown), which controls and sets
the power of the various radiant heating elements 14 in response to
the readings of the thermocouples 28, 30.
[0039] In addition to housing the thermocouples 30, the slip ring
32 also absorbs radiant heat during high temperature processing. As
noted in the Background section, the heated slip ring 32 helps to
reduce, but not eliminate, heat loss at the wafer edge 17. The slip
ring 32 can be suspended by any suitable means. For example, the
illustrated slip ring 32 rests upon elbows 34, which depend from
the quartz chamber dividers 36.
[0040] U.S. patent application Ser. No. 09/747,173, which is
incorporated by reference, discloses a substrate holder designed to
minimize problems associated with substrate "slide," "stick," and
"curl." Slide occurs when the substrate is dropped onto the
substrate holder from above. Slide is normally caused by a cushion
of gas above the holder (e.g., in a recess or pocket sized to
receive a substrate) that is unable to escape fast enough to allow
the substrate to fall immediately onto the holder. The substrate
floats momentarily above the holder as the gas slowly escapes,
causing the substrate to slide off center. Conversely, stick is the
tendency of the substrate holder to cling to the substrate when the
substrate is picked up from the substrate holder. Stick occurs
because gas is slow to flow into the small space between the
substrate and the holder, creating a vacuum effect between the
substrate and the holder. Curl refers to warping of the substrate
caused by a combination of both radial and axial temperature
gradients therein. Typically, when a substrate is initially
inserted into a heated reaction chamber and held above a substrate
holder, the center of the substrate is heated disproportionately
from below, causing the substrate to curl slightly into a "bowl" or
concave-up shape. When the slightly curled substrate is dropped
onto a hot wafer holder that does not conform in shape to the
substrate (e.g., a flat holder), the curl can be greatly
exacerbated. Slide and curl often lead to non-uniformities in
processed substrates, and stick can cause particle contamination in
the reaction chamber.
[0041] The substrate holder disclosed in U.S. patent application
Ser. No. 09/747,173 substantially prevents substrate slide and
stick by providing a plurality of intersecting grooves underneath
the substrate, which permit the flow of gas to and from the region
between the substrate and the holder. The embodiments of the
present invention discussed below and shown in FIGS. 3A-E and 5
represent further modifications of the substrate holder of U.S.
patent application Ser. No. 09/747,173.
[0042] FIGS. 3A-E show a substrate holder 200 according to a
preferred embodiment. The holder 200, preferably a susceptor
capable of absorbing and re-radiating radiant energy, has features
similar to the holder disclosed in U.S. patent application Ser. No.
09/747,173. The holder 200 is preferably circular and made of
graphite coated with silicon carbide, although the skilled artisan
will appreciate that other materials are also suitable. The
substrate holder 200 has a thickness t.sub.h defined as the
distance between upper and lower surfaces.
[0043] FIG. 3A shows the holder 200 as viewed from the top, that
is, looking into a recessed pocket 202. The recessed pocket 202 is
a substantially flat surface sized to accommodate a substrate of a
particular size (e.g. 200 mm or 300 mm wafer). The substrate holder
200 has an annular veined ring 220 on its upper surface configured
to support a substrate in a support plane. The veined ring 220 is
surrounded by a shallow annular groove 204, as shown in FIGS.
3A-3C. The shallow annular groove 204 resides radially inward of
the annular peripheral side surface 211 of the holder 200. A raised
shoulder 206 surrounds the shallow annular groove 204. FIG. 3C is
an enlarged view of a portion of FIG. 3A, illustrating more clearly
the configuration of the annular veined ring 220, shallow annular
groove 204, and raised shoulder 206 of the substrate holder
200.
[0044] With continued reference to FIGS. 3A-3C, the shallow annular
groove 204 has an annular thickness t.sub.s (along a radial
direction for the illustrated round substrate holder). In a
preferred embodiment, the thickness t.sub.s is generally uniform.
In other embodiments, the thickness t.sub.s varies along its
length. The shallow annular groove 204 helps to minimize radiation
losses from the substrate to the substrate holder 200. The skilled
artisan will understand that as the annular thickness t.sub.s
becomes larger, the structural integrity of the holder 200 becomes
more compromised, particularly during the silicon carbide coating
process during manufacture of the holder, which warps the holder
shape. The average annular thickness t.sub.s of the shallow annular
groove 204 is preferably less than 1.5 mm. The annular thickness
t.sub.s is preferably in the range of 0.5 mm to 2.5 mm, and more
preferably 0.7 mm to 1.5 mm.
[0045] The shallow annular groove 204 has a vertical depth, defined
as the vertical distance between the top surface of the veins 221
and bottom point of the shallow annular groove 204. The vertical
depth of the shallow annular groove 204 is preferably at least 15%
of the thickness t.sub.h of the substrate holder 200. The vertical
depth of the shallow annular groove 204 is in the range of 0.1 mm
to 2 mm, and more preferably in the range of 0.4 mm to 0.6 mm. In
one embodiment, the vertical depth of the shallow annular groove
204 is preferably at least 0.43 mm.
[0046] FIGS. 3A-3C also show a thermal isolation groove 215 on the
substrate holder 200. The thermal isolation groove 215 is an
annular groove in the substrate holder 200 positioned radially
inward from the annular veined ring 220 and the shallow annular
groove 204. The thermal isolation groove 215 is provided to
compensate for the heat conduction from the substrate to the
substrate holder in the area of the annular veined ring 220, where
the substrate is supported by and in thermal contact with the
substrate holder. Those of ordinary skill in the art will
understand that the groove 215 can have many different, possibly
irregular shapes.
[0047] The thermal isolation groove 215 has an annular thickness
t.sub.g (along a radial direction for the illustrated round
substrate holder). In a preferred embodiment, the thickness t.sub.g
is generally uniform. In other embodiments, the thickness t.sub.g
varies along its length. Preferably, the annular thickness t.sub.g
is large enough to substantially reduce the flow of heat radially
outward through the holder 200 and to reduce the gap conductive
heat loss by the substrate to the substrate holder 200, and to
permit the application of a complete coating of silicon carbide
over the entire inner surface of the thermal isolation groove 215.
The annular thickness t.sub.g is also preferably small enough to
prevent significant flow of gas, and thus convective heat loss,
within the thermal isolation groove 215. Also, the skilled artisan
will understand that as the annular thickness t.sub.g becomes
larger, the structural integrity of the holder 200 becomes more
compromised, particularly during the silicon carbide coating
process during manufacture of the holder, which warps the holder
shape. Such warping introduces concavity to the holder shape, which
creates more room to avoid slide and creates less contact between
the holder and the substrate in the middle. The average annular
thickness t.sub.g of the thermal isolation groove 215 is in the
range of 0.3 mm to 5 mm, and more preferably 0.6 mm to 2 mm. In a
preferred embodiment, the average annular thickness t.sub.g of the
thermal isolation groove 215 is less than 2 mm, more preferably
less than 1.5 mm, and more preferably less than 1 mm.
[0048] The thermal isolation groove 215 has a vertical depth,
defined as the vertical distance between the top surface of the
veins 221 and bottom point of the thermal isolation groove 215,
that is preferably larger than the vertical depth of the shallow
annular groove 204. Preferably, the vertical depth of the thermal
isolation groove 215 is large enough to compensate for the
conductive heat loss to the substrate from contact with the annular
veined ring 220, while also small enough to prevent significant
compromise of the structural integrity of the substrate holder 200.
The vertical depth of the thermal isolation-groove 215 is
preferably at least 20% of the thickness t.sub.h of the substrate
holder 200. In one embodiment, the vertical depth of the thermal
isolation groove 215 is preferably at least 0.5 mm, and no more
than 3 mm. More preferably, the vertical depth of the thermal
isolation groove 215 is in the range of 0.8 mm to 1.2 mm from the
top surface of the veined annular ring 220.
[0049] In order to improve thickness uniformity of the substrate
and reduce the achievable size of the exclusion zone, it is
desirable to further thermally isolate the substrate 16 from the
substrate holder 200 to reduce heat loss from the substrate 16 to
the substrate holder 200. FIGS. 3A-3C also show an annular veined
ring 220 on the substrate holder 200 in the area between the
shallow annular groove 204 and the thermal isolation groove
215.
[0050] In this embodiment of the invention, the veined ring 220 has
a plurality of veins 221 separated by gaps or channels. The top
surfaces of the veins 221 form a substantially flat coplanar (or
angled 0 to 10 degrees, and preferably angled 3 degrees) surface
configured to support a substrate of a particular size in a support
plane defined by the top surfaces of the veins 221. In this
embodiment, the annular veined ring 220 supports the substrate 16
only in the area of the "exclusion zone" approximately 1-3 mm
radially inward from the edge of the substrate. The annular veined
ring 220 is preferably the only point of contact between the
substrate 16 and the substrate holder 200 during processing, at
least after any curl settles. Aside from this point of contact,
there is no other contact between the substrate 16 and the
substrate holder 200. As there is little contact between the
substrate 16 and the substrate holder 200 in this embodiment, the
possibility of damaging the backside of the substrate is reduced.
In another embodiment, the top surfaces of the veins collectively
form a concave surface that minimizes problems associated with
substrate curl. In a preferred embodiment, the veins 221 are
oriented at an angle to avoid alignment of the veins 221 with the
crystal orientation of the substrate.
[0051] Preferably, many veins 221 are provided on the substrate
holder 200 to keep the substrate holder 200 cooler because the
veins 221 increase heat conduction from the substrate holder 200 to
the substrate 16 in the veined region of the substrate holder 200
at the outer edge of the substrate 16. The skilled artisan will
appreciate that as the substrate holder 200 is generally at a
cooler temperature than the substrate, conduction dominates at the
contact points and the channel depths around and in between the
veins 221 are selected to compensate for the conductive,
convective, and gap conduction interface between the substrate and
the substrate holder 200. The veins 221 also provide a gas path for
Bernoulli wand pickup as they allow the Bernoulli wand gas to
penetrate underneath the substrate. In an embodiment of the
invention, there are between 300 and 720 veins 221 in the veined
ring 220. Typically, in a preferred embodiment of the invention
intended to process a 200 mm wafer, there are more than 300 veins.
In an embodiment of the invention intended to process a 300 mm
wafer, there are more than 700 veins. Preferably, for a 300 mm
wafer, there are between 250 and 300 veins. The skilled artisan
will appreciate that the number of veins is selected to minimize
contact damage (e.g., crystalline defects to the substrate).
[0052] FIG. 3D is an enlarged view of a portion of FIG. 3C
indicated by arrows 3D-3D. FIG. 3E is a cross-sectional view of an
of the substrate holder 200 along the line 3E-3E in FIG. 3D. As
shown in FIGS. 3D and 3E, the veins 221 are angled, illustrated in
a counterclockwise direction at about 45 degrees to the radial
direction, and are designed to stop, or promote, gas flow to the
backside of the substrate during rotation of the substrate.
Alternatively, the veins 221 may be angled in a clockwise
direction. Typically, the veins 221 are angled at 30 degrees, more
preferably at 45 degrees to the radial direction. FIG. 3E shows
that the veins 221 are separated from each other by gaps or
channels 250.
[0053] The thickness t.sub.v of each vein 221 is preferably between
0.2 mm and 2 mm. In a preferred embodiment, the thickness t.sub.v
of each vein 221 is 1 mm. Each vein 221 has side walls 244 that
slant outward, as shown in FIG. 3E. With continued reference to
FIG. 3E, in a preferred embodiment, the side walls 244 of adjacent
veins 221 form a 45-degree angle. There is preferably a flat
surface 242 on the bottom of each groove 250 between the veins 221
as shown in FIG. 3E. The height of each vein 221, which is defined
as the distance between the top surface of a vein 221 and the flat
surface 242, is preferably between 0.2 mm and 1 mm. In a preferred
embodiment, the height of each vein 221 is 0.4 mm. The distances
d.sub.v between the veins 221 is preferably small enough such that
there are enough veins 221 provided in the ring 220 to increase
heat conduction from the substrate holder 200 to the substrate 16
in the area of the veined ring 220. Preferably, the distance
d.sub.v between each vein 221 is between 0.5 mm and 3 mm. In a
preferred embodiment, the distance d.sub.v between each vein 221 is
about 1.5 mm.
[0054] The vertical depth of each channel 250 between veins 221 is
equal to the height of each vein 221 in the illustrated embodiment.
The vertical depth of each such channel 250 is preferably deep
enough to inhibit heat loss at the edge of the substrate by
inhibiting the conductive flow of heat radially outward through the
substrate holder 200. By doing so, the veins 221 reduce the heat
loss from the peripheral side surface 211 of the substrate holder
200. It is believed preferable to have many veins 221 in the veined
ring 220 because: (1) the veins 221 reduce most backside
deposition, which reduces warping of the wafer during lithographic
processes; and (2) they reduce slip and enhance uniformity of the
substrate.
[0055] The annular veined ring 220 also helps minimize the problems
associated with slide, stick, and curl. The veined ring 220 allows
gas to penetrate underneath the substrate 16 to minimize "stick"
when a substrate 16 is picked up from the substrate holder 200. The
veined ring 220, combined with the volume of area underneath the
substrate 16, also provides enough area for gas to escape to allow
the wafer to drop onto the substrate holder 200 without
sliding.
[0056] FIG. 3B is a cross-sectional view of an area near the
periphery of the substrate holder 200 along the line 3B-3B in FIG.
3A. The shallow annular groove 204, the raised shoulder 206, the
thermal isolation groove 215, and the annular veined ring 220 are
shown in FIG. 3B. Preferably, the top surfaces of the veins 221 are
substantially parallel to the top surface of the raised shoulder
206. In an alternative embodiment, the top surfaces of the veins
221 are angled to the top surface of the raised shoulder 206.
[0057] On a bottom surface 210, the substrate holder 200 has a
bottom groove 208 centered about a central vertical axis of the
substrate holder 200. The bottom groove 208 is configured to
receive upper ends of the substrate holder supporters or arms 25 of
the spider 22 (FIG. 2). FIG. 4, which shows a bottom plan view of
the holder 200, illustrates a preferred configuration of the bottom
groove 208. The illustrated bottom groove 208 comprises a single
groove and does not form a complete circle but is interrupted by a
section 114, shown on the right side of FIG. 4. The interrupting
section 114 ensures that the spider 22 cannot rotate independently
of the substrate holder 200 once it has locked in position against
section 114. A more detailed description of a bottom groove such as
bottom groove 208 is provided in U.S. patent application Ser. No.
09/747,173. In an alternative embodiment, the substrate holder does
not have a bottom groove. Instead, the holder has a plurality of
recesses, each configured to closely receive one of the upper ends
of the substrate holder supporters 25 of the spider 22. The skilled
artisan will appreciate that there are alternative methods of
centering the substrate holder to the holder support.
[0058] In a preferred embodiment of the invention, the substrate
holder 200 includes a raised feature 230 approximately near the
edge of the substrate (assuming the substrate is centered on the
substrate holder, where the substrate and the substrate holder have
the same center), as shown in FIGS. 5A and 5B. FIG. 5A is a top
plan view of the substrate holder 200 according to this embodiment,
and FIG. 5B is a cross-sectional view, taken along line 6B-6B in
FIG. 5A. The view in FIG. 5B extends from a vertical center axis
240 of the substrate holder to the raised shoulder 206. Only a
portion of the raised shoulder 206 is shown in FIG. 5B.
[0059] The region of the substrate holder 200 in which the raised
feature 230 s preferably located is approximately near the edge of
the substrate. For example, on a 300 mm substrate, the raised
feature is preferably in an area that is approximately 100 mm to
140 mm from the vertical center axis 240 and radially inward from a
radially inward edge of the shallow annular groove 204. The raised
feature 230 is a raised annular ring that, when a substrate 16 is
supported on the substrate holder 200, is very close to, but not
touching, the substrate 16, as shown in FIG. 5B. Due to the
configuration of the radiant heat lamps 14 in the apparatus
described in connection with this embodiment, the substrate 16 is
generally at a higher temperature than the substrate holder 200 in
the region of the raised feature 230. As the raised feature 230 is
so close to the substrate 16, the raised feature 230 also increases
heat loss from the substrate 16 to the substrate holder 200 in this
region of the substrate holder 200 to compensate for the higher
temperature of the substrate 16 in this region caused by the
configuration of the radiant heat lamps 14 in this embodiment,
which is also described in U.S. Pat. No. 6,121,061. The raised
feature 230 pulls out additional heat energy from the substrate 16
to the substrate holder 200 as there is more heat flow in the
substrate 16 in the raised feature 230 region. The raised feature
230 also reduces the effects of the overlapping radiation view
angle from the front, side, and rear radiant heat lamps 14 with the
center radiant heat lamps 14 of the apparatus during steady state
CVD deposition (generally at temperatures under 950.degree. C.
[0060] Although this invention has been disclosed in the context of
certain preferred embodiments and examples, it will be understood
by those skilled in the art that the present invention extends
beyond the specifically disclosed embodiments to other alternative
embodiments and/or uses of the invention and obvious modifications
and equivalents thereof. Further, the various features of this
invention can be used alone, or in combination with other features
of this invention other than as expressly described above. Thus, it
is intended that the scope of the present invention herein
disclosed should not be limited by the particular disclosed
embodiments described above, but should be determined only by a
fair reading of the claims that follow.
* * * * *