U.S. patent application number 11/555981 was filed with the patent office on 2007-03-22 for method for dechucking a substrate.
This patent application is currently assigned to APPLIED MATERIALS, INC.. Invention is credited to Robert I. Greene, William R. Harshbarger, QUANYUAN SHANG, Ichiro Shimizu.
Application Number | 20070062454 11/555981 |
Document ID | / |
Family ID | 24483658 |
Filed Date | 2007-03-22 |
United States Patent
Application |
20070062454 |
Kind Code |
A1 |
SHANG; QUANYUAN ; et
al. |
March 22, 2007 |
METHOD FOR DECHUCKING A SUBSTRATE
Abstract
A substrate support assembly and method for dechucking a
substrate is provided. In one embodiment, a support assembly
includes a substrate support having a support surface, a first set
of lift pins and one or more other lift pins movably disposed
through the substrate support. The first set of lift pins and the
one or more lift pins project from the support surface when the
pins are in an actuated position. When in the actuated position,
the first set of lift pins project a longer distance from the
support surface than the one or more other lift pins. In another
aspect of the invention, a method for dechucking a substrate from a
substrate support is provided. In one embodiment, the method
includes the steps of projecting a first set of lift pins a first
distance above a surface of a substrate support, and projecting a
second set of lift pins a second distance above the surface of the
substrate support that is less than the first distance.
Inventors: |
SHANG; QUANYUAN; (Saratoga,
CA) ; Harshbarger; William R.; (San Jose, CA)
; Greene; Robert I.; (Fremont, CA) ; Shimizu;
Ichiro; (Itami-shi, JP) |
Correspondence
Address: |
PATTERSON & SHERIDAN, LLP
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Assignee: |
APPLIED MATERIALS, INC.
|
Family ID: |
24483658 |
Appl. No.: |
11/555981 |
Filed: |
November 2, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
10688384 |
Oct 17, 2003 |
7160392 |
|
|
11555981 |
Nov 2, 2006 |
|
|
|
10308385 |
Dec 2, 2002 |
6676761 |
|
|
10688384 |
Oct 17, 2003 |
|
|
|
09619870 |
Jul 20, 2000 |
|
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10308385 |
Dec 2, 2002 |
|
|
|
Current U.S.
Class: |
118/729 ;
156/345.54 |
Current CPC
Class: |
C23C 16/458 20130101;
H01L 21/68742 20130101 |
Class at
Publication: |
118/729 ;
156/345.54 |
International
Class: |
C23F 1/00 20060101
C23F001/00; C23C 16/00 20060101 C23C016/00 |
Claims
1. An apparatus for supporting a substrate, comprising: a support
assembly having a support surface; a first set of lift pins
comprising at least two lift pins having a flared end adapted to
contact the substrate, the first set of lift pins disposed in and
movable relative to the support assembly and extendable upwardly
through the support assembly to a first distance above the support
surface; and a second set of lift pins comprising at least two lift
pins having a flared end adapted to contact the substrate, the
second set of lift pins disposed in and movable relative to the
support assembly and extendable upwardly simultaneously with the
first set of lift pins through the support assembly to a second
distance above the support surface, wherein the second distance is
less than the first distance and wherein the two sets of lift pins
are adapted to simultaneously contact the substrate disposed on the
support surface while the center of the substrate is bowed
downwardly.
2. The apparatus of claim 1, wherein the first set of lift pins
have a length greater than a length of the second set of lift
pins.
3. The apparatus of claim 1, wherein the second set of lift pins
are positioned radially inwards of the first set of lift pins.
4. The apparatus of claim 1, wherein the first set of lift pins and
the second set of lift pins comprise a ceramic material.
5. The apparatus of claim 1, wherein the first set of lift pins are
positioned on a perimeter of the support assembly.
6. The apparatus of claim 1, wherein the first set of lift pins and
the second set of lift pins simultaneously contact a lift surface
of the apparatus when the center of the substrate is bowed
downwardly.
7. The apparatus of claim 1, wherein the support assembly is
coupled to an actuator adapted to move the support assembly
vertically and the first set of lift pins and the second set of
lift pins are extended and retracted based on the vertical position
of the support assembly.
8. An apparatus for supporting a substrate in a chamber having a
lid, sidewalls, and a bottom, the apparatus comprising: a support
assembly having a support surface and an underside opposite the
support surface; a first set of lift pins disposed in and movable
relative to the support assembly and having a first end for
supporting the substrate disposed proximate the support surface and
a second end extending beyond the underside; and a second set of
lift pins disposed in and movable relative to the support assembly
and having a first end for supporting the substrate disposed
proximate the support surface and a second end extending beyond the
underside, wherein the support assembly is adapted to move
vertically within the chamber to displace the first and second sets
of lift pins to a position where the first end of the first set of
lift pins extends a first distance from the support surface and the
first end of the second set of lift pins extends a second distance
from the support surface, wherein the first distance is greater
than the second distance.
9. The apparatus of claim 8, wherein the second set of lift pins
are positioned radially inwards of the first set of lift pins.
10. The apparatus of claim 8, wherein the first end of the first
set of lift pins and the first end of the second set of lift pins
comprises a flared head adapted to contact the substrate.
11. The apparatus of claim 8, wherein the second set of lift pins
further comprises two lift pins positioned opposite a center of the
support assembly.
12. The apparatus of claim 8, wherein the first set of lift pins
comprises at least three or more lift pins.
13. The apparatus of claim 8, wherein the first set of lift pins
and the second set of lift pins comprise a ceramic material.
14. The apparatus of claim 8, wherein the support assembly further
comprise comprises: four sides bounding the support surface,
wherein a respective pair of lift pins are positioned proximate
each side of the support assembly.
15. The apparatus of claim 8, wherein the first set of lift pins
have a first length that is longer than a second length of the
second set of lift pins.
16. The apparatus of claim 15, wherein the first length is at least
2 mm longer than the second length.
17. The apparatus of claim 8, wherein the first and second sets of
lift pins, when respectively extended the first and second
distances, simultaneously support the substrate.
18. The apparatus of claim 8, wherein the first set of lift pins is
adapted to extend to a third distance greater than the first
distance and to support a substrate in a spaced-apart relation to
the support surface while the second set of extended lift pins do
not contact the substrate.
19. An apparatus for supporting a substrate in a chamber having a
lid, sidewalls, and a bottom, the apparatus comprising: a
rectangular support assembly having a support surface and an
underside opposite the support surface; a first set of lift pins
movably disposed through a perimeter of the support assembly and
movable relative to the support assembly, each of the first set of
lift pins having a flared head for supporting the substrate
disposed proximate the support surface and a second end extending
beyond the underside; and a second set of lift pins movably
disposed through the support assembly radially inwards of the first
set of lift pins and movable relative to the support assembly, each
of the second set of lift pins having a flared head for supporting
the substrate disposed proximate the support surface and a second
end extending beyond the underside, wherein the support assembly is
adapted to move vertically within the chamber to displace the first
and second sets of lift pins to a position where the first end of
the first set of lift pins extends a first distance from the
support surface and the first end of the second set of lift pins
extends a second distance from the support surface, wherein the
first distance is greater than the second distance and the first
set and second set of lift pins comprise a ceramic material.
20. The apparatus of claim 19, wherein the first set of lift pins
comprise at least eight lift pins.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/688,384 (Attorney Docket No. 004432.D1),
filed Oct. 17, 2003, which is a divisional of U.S. patent
application Ser. No. 10/308,385 (Attorney Docket No. 004432.C1),
filed Dec. 2, 2002, and issued as U.S. Pat. No. 6,676,761 on Jan.
13, 2004, which is a continuation of U.S. patent application Ser.
No. 09/619,870 (Attorney Docket No. 004432), filed Jul. 20, 2000,
now abandoned, all of which are herein incorporated by reference in
their entireties.
BACKGROUND OF THE DISCLOSURE
[0002] 1. Field of Invention
[0003] The invention relates generally to a method for lifting
(e.g., dechucking) a substrate from a substrate support in a
semiconductor processing chamber.
[0004] 2. Background of the Invention
[0005] Liquid crystal displays or flat panels are commonly used for
active matrix displays, such as computer and television monitors.
Generally, flat panels comprise two glass plates having a layer of
liquid crystal material sandwiched therebetween. At least one of
the glass plates includes at least one conductive film disposed
thereon that is coupled to a power source. Power, supplied to the
conductive film from the power source, changes the orientation of
the crystal material, creating a patterned display. One fabrication
process frequently used to produce flat panels is plasma enhanced
chemical vapor deposition (PECVD).
[0006] Plasma enhanced chemical vapor deposition is generally
employed to deposit thin films on a substrate such as a flat panel
or semiconductor wafer. Plasma enhanced chemical vapor deposition
is generally accomplished by introducing a precursor gas into a
vacuum chamber that contains a substrate. The precursor gas is
typically directed through a distribution plate situated near the
top of the chamber. The precursor gas in the chamber is energized
(e.g., excited) into a plasma by applying RF power to the chamber
from one or more RF sources coupled to the chamber. The excited gas
reacts to form a layer of material on a surface of the substrate
that is positioned on a heated substrate support. A shadow frame,
and optionally a purge gas, is routed through holes in the support
to the edge of the substrate to prevent deposition at the
substrate's edge that may cause the substrate to adhere to the
support. Volatile by-products produced during the reaction are
pumped from the chamber through an exhaust system.
[0007] After the deposition process, the substrate is lifted (e.g.,
dechucked) from the substrate support by a plurality of lift pins
disposed through the substrate support. The lift pins are actuated
upwards to contact the backside of the substrate and raise the
substrate above the substrate support's upper surface. From this
position, a substrate transfer mechanism, typically a blade coupled
to a robot, may be positioned between the substrate and the
substrate support. The lift pins are retracted, leaving the
substrate on the transfer mechanism that is now free to remove the
substrate from the processing chamber.
[0008] During the deposition process, the substrate may become
residually attracted to the substrate support. For example during
plasma processing, charge generally accumulates on the substrate
due to the difference in mobility between ions and electrons within
the plasma. Typically, the more active and mobile electrons reach
the substrate in greater numbers than the ions, resulting in a net
charge accumulation. The accumulated electrons on the substrate's
surface facing the plasma results in a corresponding accumulation
of positive charge on the substrate's backside, creating a static
attraction between the substrate and the substrate support.
[0009] As the lift pins begin to lift the substrate from the
substrate support, the center region of the substrate (i.e., the
region between the lift pins) remains attracted to the substrate
support, causing the substrate to bow. As the lift pins continue to
move farther away from the substrate support, the force separating
the substrate from the substrate support overcomes the static
attraction allowing the substrate to regain a substantially planar
or slightly bowed form as the substrate is supported by the lift
pins in a spaced-apart relation to the substrate support.
[0010] However, if the static attraction is great enough during the
dechucking process, the substrate bows excessively before the
substrate becomes completely separated from the substrate support.
The excessive bowing of the substrate may result in cracking,
breakage or other damage to the substrate and/or material layers or
devices disposed on the substrate. Additionally, excessive bowing
of the substrate may cause the lift pins to slide slightly on the
backside of the substrate, scratching the substrate and increasing
the probability of particulate generation that may contaminate the
substrate or other substrates subsequently processed in the
chamber.
[0011] The static attraction may be dissipated by introducing
plasma formed from an inactive gas in the chamber during the
dechucking process. The plasma redistributes the charges across the
substrate, minimizing the static attraction between the substrate
and the substrate support. This process for reducing the static
attraction was disclosed in U.S. Pat. No. 5,380,566, issued Jun.
10, 1995, by Robertson et al. Although as little as two seconds of
exposure to the plasma formed from the inactive gas may be enough
to dissipate static attraction forces and allow the substrate to be
dechucked without damage, it is desirable to process the substrate
with as few steps as possible and to minimize the consumables such
as gases used during processing.
[0012] Therefore, there is a need for dechucking a substrate from a
substrate support that prevents excessive bowing of the substrate
during dechucking.
SUMMARY OF THE INVENTION
[0013] In one embodiment, an apparatus for supporting a substrate
is described. The apparatus includes a support assembly having a
support surface, a first set of lift pins comprising at least two
lift pins having a flared end adapted to contact the substrate, the
first set of lift pins disposed in and movable relative to the
support assembly and extendable upwardly through the support
assembly to a first distance above the support surface, and a
second set of lift pins comprising at least two lift pins having a
flared end adapted to contact the substrate, the second set of lift
pins disposed in and movable relative to the support assembly and
extendable upwardly simultaneously with the first set of lift pins
through the support assembly to a second distance above the support
surface, wherein the second distance is less than the first
distance and wherein the two sets of lift pins are adapted to
simultaneously contact the substrate disposed on the support
surface while the center of the substrate is bowed downwardly.
[0014] In another embodiment, an apparatus for supporting a
substrate in a chamber having a lid, sidewalls, and a bottom, is
described. The apparatus includes a support assembly having a
support surface and an underside opposite the support surface, a
first set of lift pins disposed in and movable relative to the
support assembly and having a first end for supporting the
substrate disposed proximate the support surface and a second end
extending beyond the underside, and a second set of lift pins
disposed in and movable relative to the support assembly and having
a first end for supporting the substrate disposed proximate the
support surface and a second end extending beyond the underside,
wherein the support assembly is adapted to move vertically within
the chamber to displace the first and second sets of lift pins to a
position where the first end of the first set of lift pins extends
a first distance from the support surface and the first end of the
second set of lift pins extends a second distance from the support
surface, wherein the first distance is greater than the second
distance.
[0015] In another embodiment, an apparatus for supporting a
substrate in a chamber having a lid, sidewalls, and a bottom, is
described. The apparatus includes a rectangular support assembly
having a support surface and an underside opposite the support
surface, a first set of lift pins movably disposed through a
perimeter of the support assembly and movable relative to the
support assembly, each of the first set of lift pins having a
flared head for supporting the substrate disposed proximate the
support surface and a second end extending beyond the underside,
and a second set of lift pins movably disposed through the support
assembly radially inwards of the first set of lift pins and movable
relative to the support assembly, each of the second set of lift
pins having a flared head for supporting the substrate disposed
proximate the support surface and a second end extending beyond the
underside, wherein the support assembly is adapted to move
vertically within the chamber to displace the first and second sets
of lift pins to a position where the first end of the first set of
lift pins extends a first distance from the support surface and the
first end of the second set of lift pins extends a second distance
from the support surface, wherein the first distance is greater
than the second distance and the first set and second set of lift
pins comprise a ceramic material.
BRIEF DESCRIPTION OF DRAWINGS
[0016] The teachings of the present invention can be readily
understood by considering the following detailed description in
conjunction with the accompanying drawings, in which:
[0017] FIG. 1 depicts a schematic sectional view of one embodiment
of a processing chamber of the present invention;
[0018] FIG. 2A is an exaggerated sectional view of one embodiment
of a substrate support depicting a substrate being lifted from the
support;
[0019] FIG. 2B is an exaggerated sectional view of one embodiment
of a substrate support depicting a substrate being lifted from the
support wherein the substrate is bowed beyond its normal sag;
[0020] FIG. 3 is an exaggerated sectional view of one embodiment of
a substrate support depicting a substrate in a lifted position
above the support;
[0021] FIG. 4 is a flow diagram depicting a dechucking process;
and
[0022] FIG. 5 is a sectional view of another embodiment of a
substrate support depicting a substrate being lifted from the
support.
[0023] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures.
DETAIL DESCRIPTION OF INVENTION
[0024] The invention generally provides a substrate support and
method for dechucking a substrate that are advantageous for lifting
a substrate from a substrate support. The invention is
illustratively described below in reference to a plasma enhanced
chemical vapor deposition system, such as a plasma enhanced
chemical vapor deposition (PECVD) system, available from AKT, a
division of Applied Materials, Inc., Santa Clara, Calif. However,
it should be understood that the invention has utility in other
system configurations such as physical vapor deposition systems,
ion implant systems, etch systems, chemical vapor deposition
systems and any other system in which lifting a substrate from a
substrate support is desired.
[0025] FIG. 1 is a cross sectional view of one embodiment of a
plasma enhanced chemical vapor deposition system 100. The system
100 generally includes a chamber 102 coupled to a gas source 104.
The chamber 102 has walls 106, a bottom 108 and a lid assembly 110
that define a process volume 112. The process volume 112 is
typically accessed through a port (not shown) in the walls 106 that
facilitates movement of the substrate 140 into and out of the
chamber 102. The walls 106 and bottom 108 are typically fabricated
from a unitary block of aluminum. The lid assembly 110 contains a
pumping plenum 114 that couples the process volume 112 to an
exhaust port (that includes various pumping components, not
shown).
[0026] The lid assembly 110 is supported by the walls 106 and can
be removed to service the chamber 102. The lid assembly 110 is
generally comprised of aluminum and may additionally contain heat
transfer fluid channels for regulating the temperature of the lid
assembly 110 by flowing heat transfer fluid therethrough.
[0027] A distribution plate 118 is coupled to an interior side 120
of the lid assembly 110. The distribution plate 118 is typically
fabricated from aluminum. The distribution plate generally includes
a perimeter mounting ring that surrounds a "dish-shaped" center
section. The mounting ring includes a plurality of mounting holes
passing therethrough, each accepting a vented mounting screw that
threads into a mating hole in the lid assembly 110. The center
section includes a perforated area through which process and other
gases supplied from the gas source 104 are delivered to the process
volume 112. The perforated area of the distribution plate 118 is
configured to provide uniform distribution of gases passing through
the distribution plate 118 into the chamber 102.
[0028] A heated support assembly 138 is centrally disposed within
the chamber 102. The support assembly 138 supports a substrate 140
during processing. The support assembly 138 generally is fabricated
from aluminum, ceramic or a combination of aluminum and ceramic and
typically includes a vacuum port (not shown) and at least one
embedded heating element 132. The vacuum port is used to apply a
vacuum between the substrate 140 and support assembly 138, securing
the substrate to the substrate support assembly 138 during
processing. The heating element 132, such as an electrode disposed
in the support assembly 138, is coupled to a power source 130,
heating the support assembly 138 and substrate 140 positioned
thereon to a predetermined temperature. In one embodiment, the
heating element 132 maintains the substrate 140 at a uniform
temperature of about 150 to 400 degrees. Alternatively, heating
lamps or other heat sources may be utilized to heat the
substrate.
[0029] Generally, the support assembly 138 is coupled to a stem
142. The stem 142 provides a conduit for electrical leads, vacuum
and gas supply lines between the support assembly 138 and other
components of the system 100. The stem 142 couples the support
assembly 138 to a lift system (not shown) that moves the support
assembly 138 between an elevated position (as shown) and a lowered
position. Bellows 146 provides a vacuum seal between the chamber
volume 112 and the atmosphere outside the chamber 102 while
facilitating the movement of the support assembly 138.
[0030] The support assembly 138 generally is grounded such that RF
power supplied by a power source 122 to the distribution plate 118
(or other electrode positioned within or near the lid assembly of
the chamber) may excite the gases disposed in the process volume
122 between the support assembly 138 and the distribution plate
118. The RF power, generally having a frequency of between a few Hz
to 13 MHz or higher is provided in a wattage suitable for the
substrate surface area. In one embodiment, the power source 122
comprises a dual frequency source that provides a low frequency
power at less than about 2 MHz (preferably about 200 to 500 kHz)
and a high frequency power at greater than 13 MHz (preferably about
13.56 kHz). The frequencies may be fixed or variable.
Illustratively, for a 550 mm.times.650 mm substrate, the low
frequency power is about 0.3 to about 2 kW while the high frequency
power is about 1 to 5 kW. Generally, the power requirements
decrease or increase with a corresponding decrease or increase in
substrate size.
[0031] The support assembly 138 additionally supports a
circumscribing shadow frame 148. The shadow frame 148 is configured
to cover the edge of the substrate 140 and is typically comprised
of ceramic. Generally, the shadow frame 148 prevents deposition at
the edge of the substrate 140 and support assembly 138 so that the
substrate does not stick to the support assembly 138. Optionally, a
purge gas is supplied between the shadow frame 148 and the support
assembly 138 to assist in preventing deposition at the substrate's
edge.
[0032] The support assembly 138 has a plurality of holes 128
disposed therethrough to accept a plurality of lift pins 150
comprising a first set 180 and one or more other lift pins 152 that
comprises a second set 182. The second set 182 of lift pins 152 are
positioned radially inwards the first set 180 of lift pins 150. The
lift pins 150 and 152 are typically comprised of ceramic or
anodized aluminum. Generally, the lift pins 150 and 152 have
respective first ends 160 and 162 that are substantially flush with
or slightly recessed from a support surface 134 of the support
assembly 138 when the lift pins 150 and 152 are in a normal
position (i.e., retracted relative to the support assembly 138).
The first ends 160, 162 are generally flared to prevent the lift
pins 150, 152 from falling through the holes 128. Additionally, the
lift pins 150 and 152 have a respective second end 164 and 166
extending beyond an underside 126 of the support assembly 138.
[0033] The lift pins 150 and 152 may move to a position when
actuated where the pins project from the support surface 134. In
the actuated position, the lift pins 150 project farther from the
support surface 134 than the one or more lift pin 152. Typically,
the first set 180 of lift pins 150 includes three or more lift pins
that are positioned outwards of the one or more lift pins 152. In
one embodiment, the first set 180 of lift pins 150 include eight
pins grouped in pairs wherein a respective pair is positioned
proximate each side of a four-sided substrate. In another
embodiment, the second set 182 of lift pins 152 include two lift
pins positioned to either side of a center of the support assembly
138.
[0034] A lift plate 154 is disposed proximate the underside 126 of
the support surface. The lift plate 154 is disposed below the
second ends 164 and 166 of one or more of the lift pins 150 and
152, respectively. The lift plate 154 is coupled to an actuator
such as a pneumatic cylinder, hydraulic cylinder, lead screw,
solenoid, stepper motor or other motion device (not shown) that is
typically positioned outside of the process volume 112. The lift
plate 154 is connected to the actuator by a collar 156 that
circumscribes a portion of the stem 142. The bellows 146 include an
upper portion 168 and a lower portion 170 that allow the stem 142
and collar 156 to move independently while maintaining the
isolation of the process volume 112 from the environment exterior
to the chamber 102. Alternatively, the motions of the lift plate
154 and support assembly 138 may be controlled via a single
actuator utilizing a spring and a motion stop that controls the
relative motion between the lift plate 154 or support assembly
138.
[0035] Generally, the lift plate 154 is actuated to cause the lift
pins 150, 152 to extend from the support surface 134 as the support
assembly 138 and the lift plate 154 move closer together relative
to one another. The support assembly 138 may move closer relative
to lift plate 154 either by the support assembly 138 lowering, the
lift plate 154 moving upwards, the lift plate 154 lowering at a
rate less than the lowering rate of the support assembly 138 or a
combination thereof.
[0036] FIG. 2A depicts one embodiment of the substrate 140 being
lifted off the support surface 134 of the support assembly 138.
Generally, as the support assembly 138 moves closer relative to
lift plate 154, the first set 180 of lift pins 150 that are
generally longer than the second set 182 of lift pins 152 are
contacted by the lift plate 154 before the second set 182 of lift
pins 152. The first set 180 of lift pins 150 thus extend first the
from the support surface 134 to lift the substrate 140 by its
perimeter. Once the first set 180 of lift pins 150 extend a
distance "L" from the support surface 134, the shorter second set
182 of lift pins 152 contact the lift plate 154. "L" may also
represent the difference in length of the lift pins 150, 152. In
one embodiment, "L" is at least about 2 mm.
[0037] Generally, the substrate 140 has a bow as it is lifted from
the support surface 134. A portion of the bow below the plane of
the lift pins 150 defines a sag "S". The position of the first set
180 of lift pins 150 relative the center of the substrate 140 is
configured such that the sag "S" of the substrate is normally less
than the distance "L". Attributes that effect the sag "S" include
the over-all size of the substrate, the substrate's thickness, the
composition of the layers present on the substrate, the distance
between the lift pins 150 and the temperature of the substrate
among other factors. Thus, as the substrate 140 is lifted from the
support surface 134 by the first set 180 of lift pins 150, the
substrate 140 is prevented from contacting the second set 182 of
lift pins 152 as the substrate 140 is lifted further from the
support surface 134 and the second set 182 of lift pins 152 begin
to extend.
[0038] As depicted in FIG. 3, once the substrate 140 fully lifted
from the support assembly 138, the second set 182 of lift pins 152
protrude a distance D' from the support surface 134 while the first
set of lift pins protrude a distance D'' from the support surface
134. The distance D' is less than the distance D'' such that the
second set 182 of lift pins 152 remain clear of the substrate 140
once the substrate is free of the support surface 134. Thus, as the
substrate 140 is lifted from the support assembly 138, minimal
contact is made with the lift pins (i.e., the lift pins 152 never
touch the substrate 140) thus reducing the probability that the
center portions of the substrate 140 may be scratched.
[0039] As depicted in FIG. 2B, residual forces (such as static
attraction) between a substrate 140' and support assembly 138 may
cause the substrate 140' to bow beyond the predetermined amount
indicated by "S" in FIG. 2A. If the residual forces are great
enough, or cannot sufficiently be discharged, the sag "S" of the
substrate 140' becomes equal to the distance "L" as the substrate
140' is lifted from the support surface 134 by the first set 180 of
lift pins 150. At this point the second set 182 of lift pins 152
contact the center portion of the substrate 140'. As the lift plate
118 and substrate support 138 move closer together, the second set
182 of lift pins 152 contact the substrate 140' radially inwards of
the first set 180 of lift pins 150. The second set 182 of lift pins
152 lift the center portion of the substrate 140' overcoming the
residual attraction therebetween that is generally concentrated at
the substrate's center, thus preventing the substrate from bowing
beyond the predetermined amount of sag S' that may cause damage to
the substrate and/or layers or devices deposited thereon. As the
substrate 140' becomes separated from the support surface 134 of
the support assembly 138, the substrate 140' is no longer subject
to the residual forces that created the sag "S" and returns to its
normal orientation shown in phantom in having the sag "S" wherein
the substrate 140 no longer touches the second set 182 of lift pins
152. As the lift plate 254 continues to place the lift pins 150 and
152 in the fully actuated position, the substrate 140 is positioned
in a space-apart relation to the support surface 134 as depicted in
FIG. 3.
[0040] FIG. 4 is a flow diagram of the method 400 of lifting a
substrate from a support surface (e.g., dechucking) according to
one embodiment of the invention. Starting at step 402 and referring
to FIG. 3, a first set 180 of lift pins 150 are extended a first
distance D'' from a support surface 134 of a support assembly 138.
At step 404, a second set 182 of lift pins 152 are extended a
second distance D' from the support surface 134 of the support
assembly 138. Generally, the second set 182 of lift pins 152 are
located radially inwards of the first set 180 of lift pins 150. At
step 406, the second set 182 of lift pins 152 contact the substrate
140 if the residual attraction between the substrate 140 and the
support assembly 138 causes the substrate to have a sag "S" (see
FIG. 2B) equal to a difference between the first and second
distances (D''-D'=L).
[0041] FIG. 5 depicts another embodiment of a plasma enhanced
chemical vapor deposition system 500. The system 500 generally is
substantially similar to the system 100 described with reference to
FIG. 1-3 except wherein a support assembly 502 includes a first set
580 of lift pins 506 and a second set 582 of lift pins 520 that
have equal length. The lift pins 506, 520 have a first flared end
508, 522, respectively, for lifting the substrate 140 from a
support surface 528 of the substrate support 502. The lift pins
506, 520 have a second end 510, 524, respectively, that extend
beyond an underside 530 of the substrate support 502. A lift plate
512 is disposed under the substrate support 502. The lift plate 512
generally includes a rim 516 that projects above a center portion
514.
[0042] When the lift plate 512 is actuated to elevate the substrate
140 from the support surface 528, the raised rim 516 of the lift
plate 512 contacts the first set 580 of lift pins 506 before the
center portion 514 contacts the second set 582 of lift pins 520.
The difference in elevation "D" between the rim 516 and the center
portion 514 causes the first set 580 of lift pins 506 to protrude
from the support surface 528 before the second set 582 of lift pins
520. The difference in elevation "D" is selected to produce the
same result as the difference in the lift pins "L". Optionally, the
lift plate 512 may be used with lift pins 506, 520 of equal
length.
[0043] In operation, the semiconductor substrate 140 depicted in
FIG. 1 may be processed in a number of methods. For example, to
deposit a silicon nitride layer, the substrate 140 is first secured
to the support assembly 138 by providing a vacuum therebetween. The
support assembly 138 is elevated such that the substrate 140 and
distribution plate 118 are generally between about 500 to 1000 mils
apart. The temperature of the substrate 140 is elevated to a
predetermined process temperature between about 150 to 400 degrees
Celsius primarily by providing power to the electrode 132. Gaseous
components, which in one embodiment may include silane and ammonia
and nitrogen, are supplied from a gas panel to the process chamber
through the distribution plate 118 to form a gaseous mixture. RF
power is applied between the distribution plate 118 and the support
assembly 138 to form a plasma from the gaseous mixture. The gaseous
mixture reacts to form a layer of silicon nitride on the substrate
140.
[0044] After processing, the substrate 140 may optionally be
subjected to a plasma formed from an inactive gas (i.e., a gas that
does not adversely affect the layer disposed on the substrate and
does not cause additional material to be disposed on the substrate)
for about 5 seconds to reduce the attraction between the substrate
and the support assembly 138. Such a process is described in the
previously incorporated U.S. Pat. No. 5,380,566.
[0045] The support assembly 138 is then lowered to allow removal of
the processed substrate 140. The lift plate 154 is actuated to
extend the lift pins 152 and substrate 140 above the support
surface 134. If the residual attraction between the support surface
134 and the substrate 140 causes the substrate to sag a
predetermined amount, the second set 182 of lift pins 152 contacts
the substrate 140 to free the substrate 140 from the support
surface 134. Once freed from the support surface 134, the substrate
140 rest on the first set 180 of lift pins 150 in a position where
a substrate handling robot may enter the chamber 102 and retrieve
the substrate 140 for further processing in other equipment.
[0046] If the residual attraction between the support surface 134
and the substrate 140 is not enough to cause the substrate to sag
equal to the distance "L", the second set 182 of lift pins 152
never contact the substrate 140 and thus cannot leave a mark
thereon.
[0047] Although the teachings of the present invention that have
been shown and described in detail in a plasma enhanced chemical
vapor deposition chamber, those skilled in the art can readily
devise other varied embodiments in other processing chambers that
incorporate the use of lift pins to separate a substrate from a
support surface that still incorporate the teachings and do not
depart from the scope and spirit of the invention.
* * * * *