U.S. patent application number 10/929577 was filed with the patent office on 2005-03-03 for method for plasma etching a wafer.
Invention is credited to Hofer, Willard L., Johnson, David R., Langley, Rodney C..
Application Number | 20050048781 10/929577 |
Document ID | / |
Family ID | 22120407 |
Filed Date | 2005-03-03 |
United States Patent
Application |
20050048781 |
Kind Code |
A1 |
Langley, Rodney C. ; et
al. |
March 3, 2005 |
Method for plasma etching a wafer
Abstract
A method for plasma etching a wafer in a process chamber. The
wafer is coupled to an internally cooled chuck and is rotated
therewith. In the case of electrostatic coupling of the wafer to
the chuck, the bias applied to the chuck may be coupled with the
use of a rotational roller to allow the bias to be applied to the
chuck for the duration of the etch process. Plasma is introduced
into the chamber to etch the rotating wafer. A spider assembly is
disposed in the chamber so that the spider pushes up on the wafer
in response to actuation of a lift mechanism upon completion of the
etching process.
Inventors: |
Langley, Rodney C.; (Boise,
ID) ; Johnson, David R.; (Meridian, ID) ;
Hofer, Willard L.; (Boise, ID) |
Correspondence
Address: |
DICKSTEIN SHAPIRO MORIN & OSHINSKY LLP
2101 L STREET, NW
WASHINGTON
DC
20037
US
|
Family ID: |
22120407 |
Appl. No.: |
10/929577 |
Filed: |
August 31, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10929577 |
Aug 31, 2004 |
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09507465 |
Feb 22, 2000 |
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6838390 |
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09507465 |
Feb 22, 2000 |
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09074591 |
May 8, 1998 |
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6080272 |
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Current U.S.
Class: |
438/689 |
Current CPC
Class: |
H01J 37/32082 20130101;
H01J 2237/2001 20130101; H01L 21/67069 20130101; Y10T 279/23
20150115 |
Class at
Publication: |
438/689 |
International
Class: |
H01L 021/302; H01L
021/461 |
Claims
What is claimed as new and desired to be protected by Letters
Patent of the United States is:
1. A chuck assembly for use with a semiconductor wafer plasma
etching device, the assembly comprising: a chuck; a pedestal
coupled to the chuck and having a longitudinal axis; and a drive
motor coupled to the pedestal for rotating the pedestal about the
longitudinal axis.
2. A chuck assembly comprising: an internally cooled chuck; a clamp
coupled to the chuck; a pedestal coupled to the chuck and having a
central bore and a longitudinal axis, the chuck and pedestal
cooperating to define a coolant chamber that communicates with the
central bore; and a drive motor coupled to the shaft for rotating
the shaft about the longitudinal axis.
3. The assembly of claim 2 wherein the clamp includes an
electrostatic clamp.
4. The assembly of claim 3 wherein the electrostatic clamp includes
an electrostatic bias roller disposed in contact with the
shaft.
5. The assembly of claim 2 further comprising a spider disposed in
the coolant chamber and a push rod coupled to the spider and
disposed in the central bore, the push rod including a coolant
passage in communication with the coolant chamber.
6. A chuck assembly for use with a plasma etching device, the
assembly comprising: a chuck including a top surface having a
plurality of slots; a pedestal coupled to the chuck and defining
therewith a coolant chamber in communication with the slots, the
pedestal having a longitudinally extending passage in fluid
communication with the coolant chamber, the pedestal being
rotatable about a longitudinal axis; a plurality of lift pins
disposed in the coolant chamber and coupled to a longitudinally
extending push rod disposed in the pedestal, the push rod including
a coolant passage in communication with the coolant chamber; and an
electrostatic clamp including an electrostatic voltage source
coupled to the shaft.
7. The assembly of claim 6 further including a bellows assembly
coupled to the pedestal and a lift actuator coupled to the bellows
assembly, the push rod moving between a wafer unloading position
and a wafer clamping position and the bellows moving between a
compressed position and a relaxed position in response to movement
of the lift actuator.
8. The assembly of claim 7 further including a rotational coupler
coupled to the push rod and a source of coolant, the rotational
coupler moving with the push rod in response to actuation of the
lift actuator.
9. The assembly of claim 6 further including a block coupled to a
process chamber, the pedestal being coupled to the block for
rotation therein, the block including a plurality of bearings for
supporting the pedestal during rotation and a plurality of seals,
the seals cooperating with the pedestal to seal the process
chamber.
10. A method for plasma etching wafer comprising the steps of:
coupling a chuck to a pedestal; coupling the wafer to the chuck;
rotating the pedestal; and plasma etching the wafer while the
pedestal is rotating.
11. The method of claim 10 further comprising the steps of
internally cooling the chuck.
12. The method of claim 11, wherein the pedestal cooperates with
the chuck to define a coolant chamber and includes a shaft having a
coolant passage in communication with the coolant chamber, the step
of internally cooling further including the step of introducing
coolant to the coolant chamber through the coolant passage.
13. The method of claim 10 wherein the pedestal includes a push rod
having a coolant passage, the coolant passage being in
communication with a coolant source and a coolant chamber defined
by the chuck and the pedestal.
14. The method of claim 10 wherein the chuck includes an
electrostatic clamp.
15. The-method of claim 10 further comprising the steps of
initializing process parameters, the process parameters including
gas flow, process chamber pressure, water temperature, and pedestal
rotation speed.
16. The method of claim 10 further including the step of unloading
the wafer from the chuck after plasma etching, the unloading step
including the steps of providing a lift actuator coupled to a push
rod and a spider and actuating the lift actuator, the push rod
pushing the spider to move the wafer away from the chuck in
response to actuation of the lift actuator.
17. A plasma etching machine comprising: a process chamber; a
rotatable, internally cooled chuck disposed in the process chamber,
and a controller coupled to the process chamber and chuck for
controlling gas flow and pressure in the process chamber and
rotation of the chuck.
18. The machine of claim 17 further comprising a pedestal coupled
to the chuck and cooperating therewith to define a coolant chamber,
the pedestal including a coolant passage in fluid communication
with a coolant source and the coolant chamber.
19. The machine of claim 18 further including a lift actuator
coupled to the coolant passage, the coolant passage moving in the
pedestal in response to actuation of the lift mechanism to lift a
wafer from the chuck.
20. The machine of claim 17 further including a pedestal coupled to
the chuck, a block coupled to the process chamber, the pedestal
being disposed in the block for rotation therein, and a bellows
assembly coupled to the pedestal, the block, pedestal, and bellows
assembly cooperating with each other to seal the process
chamber.
21. A plasma etching machine comprising: a process chamber; a chuck
disposed in the process chamber; a pedestal coupled to the chuck
and cooperating therewith to define a coolant chamber, the pedestal
including a coolant passage in communication with the coolant
chamber; a drive motor coupled to the pedestal for rotating the
pedestal during plasma etching.
22. The machine of claim 21 further comprising a bellows assembly
coupled to the pedestal and to a source of coolant, and a lift
mechanism coupled to the bellows assembly, the lift mechanism
including a lift plate coupled to a push rod disposed in the
pedestal, the push rod including the coolant passage and being
coupled to a plurality of lift pins, the lift pins lifting a wafer
from the chuck in response to movement of the lift plate.
23. A plasma etching machine comprising: a process chamber defining
an interior region and including a bottom wall having an aperture;
a block disposed in the aperture and including a longitudinally
extending bore; a shaft extending through the bore and including a
spider push rod extending longitudinally therethrough, the shaft
being supported for rotation in the bore; a chuck coupled to the
shaft and disposed in the interior region, the chuck cooperating
with the shaft to define a coolant chamber; a spider disposed in
the coolant chamber and coupled to the spider push rod; a lift
mechanism coupled to the spider push rod, the spider pushing up on
a wafer in response to actuation of the lift mechanism; and a drive
motor coupled to the shaft for rotating the shaft during a plasma
etching process.
24. The machine of claim 23 wherein the block includes a plurality
of bearings for supporting the shaft for rotation in the block and
a plurality of seals for sealing the process chamber.
25. The machine of claim 23 further comprising a bellows assembly
coupled to the shaft and to a coolant source, the lift mechanism
including a lift plate coupled to the bellows assembly, the lift
plate and bellows assembly being movable between a wafer lifting
position and a disengaged position, the spider push rod including a
coolant passage in communication with the chamber and being movable
in response to movement of the lift plate and bellows assembly.
Description
[0001] The present invention relates to a method and apparatus for
plasma etching a wafer and particularly to plasma etching a wafer
using a rotatable chuck. More particularly, the invention relates
to an internally cooled rotatable chuck for use in a plasma etching
process.
BACKGROUND OF THE INVENTION
[0002] Plasma etching apparatus for processing wafers is known.
Typically, a chuck serves as a lower electrode in a process chamber
which can be set in a vacuum state. A wafer is placed on and fixed
to the chuck, and then subjected to the plasma etching process.
There are two commonly used ways of fixing a wafer to a chuck,
mechanical supporting means such as a clamp, and an electrostatic
chuck for attaching a wafer by means of an electrostatic attractive
force. A typical electrostatic chuck includes a metallic base plate
that is coated with a thick layer of slightly conductive dielectric
material. A silicon wafer of approximately the same size as the
chuck is placed on top of the chuck and a potential difference is
applied between the silicon wafer and the base plate of the
electrostatic chuck. This causes an electrostatic attraction
proportional to the square of the electric field in the gap between
the silicon wafer and the chuck face.
[0003] When the chuck is used in a plasma filled chamber, the
electric potential of the wafer tends to be fixed by the effective
potential of the plasma. The purpose of the dielectric layer on the
chuck is to prevent the silicon wafer from coming into direct
electrical contact with the metallic part of the chuck and shorting
out the potential difference. On the other hand, a small amount of
conductivity appears to be desirable in the dielectric coating so
that much of its free surface between points of contact with the
silicon wafer is maintained near the potential of the metallic base
plate; otherwise, a much larger potential difference would be
needed to produce a sufficiently large electric field in the vacuum
gap between the wafer and chuck.
[0004] During plasma etching of pattern wafers, the plasma raises
the temperature of the wafer to an undesirable level that could
damage the wafer. Accordingly, the chuck must be kept as cool as
possible. The current preferred method of cooling a plasma chuck is
with conductive cooling of the backside of the chuck through the
use of helium. The face of the chuck generally includes a pattern
of grooves in which helium gas is maintained. This gas provides
cooling by thermal contact between the wafer and the chuck. To
contain the helium at the chuck and prevent it from escaping into
the reaction, a clamp must be incorporated with the chuck to hold
the wafer down.
[0005] In conventional pattern plasma etched apparatus, the chuck
is stationary to allow for cooling. Non-uniform etching occurs,
however, due to chamber design or process parameters resulting in
undesirable film thickness deviations. These deviations in film
thickness can be localized or spread across the entire film
surface.
SUMMARY OF THE INVENTION
[0006] The present invention overcomes these shortcomings by
providing an internally cooled rotatable chuck for use in a
semiconductor wafer plasma etching apparatus. By rotating the chuck
and the wafer in an etching chamber, the effect of the inherent
lack or excess of ions due to chamber design or process parameters
can be minimized. The lack or excess of ions creating the etch can
be spread across the entire wafer surface assuring all locations
see the same etch parameters. Accordingly, a more efficient process
with better film uniformity will be realized.
[0007] According to the present invention, a plasma etching machine
comprises a process chamber defining an interior region and
including a bottom wall having an aperture and a block disposed in
the aperture and including a longitudinally extending bore. A shaft
extends through the bore and includes a spider push rod extending
longitudinally therethrough. The shaft is supported for rotation in
the bore. A controller controls the speed, direction and duration
of the shaft rotation.
[0008] An internally cooled chuck is coupled to the shaft and
disposed in the interior region and cooperates with the shaft to
define a chamber. The chuck includes a clamp, either electrostatic
or mechanical, for retaining the wafer on the chuck. The wafer can
be retained on the chuck in a conventional face up orientation, an
upside down orientation, or on its side within the process
chamber.
[0009] A spider is disposed in the chamber and is coupled to a
spider push rod. A lift mechanism is coupled to the shaft and the
spider push rod so that the spider pushes up on a wafer in response
to actuation of the lift mechanism. A drive motor is coupled to the
shaft for rotating the shaft during a plasma etching process. A
bellows assembly couples the shaft end to a coolant source. The
lift mechanism includes a lift plate coupled to the bellows
assembly, the lift plate and bellows assembly being movable between
a wafer lifting position and a disengaged position, the spider push
rod including a coolant passage in communication with the chamber
and being movable in response to movement of the lift plate and
bellows assembly.
[0010] Further according to the invention, a method for plasma
etching a wafer comprises the steps of coupling a chuck to a
pedestal, coupling the wafer to the chuck, rotating the pedestal,
and etching the wafer.
[0011] The present invention to provide a rotatable chuck for use
with apparatus for plasma etching a wafer. The invention also
provides a rotatable electrostatic chuck for use with apparatus for
plasma etching a patterned wafer. The invention further provides a
rotatable chuck having coolant passages for conveying coolant to
the chuck.
[0012] These and other features and advantages of the invention
will become apparent from the following detailed description of
preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a perspective view of a plasma etching apparatus
according to the present invention;
[0014] FIG. 2 is a side view a plasma etching apparatus;
[0015] FIG. 3 is a front view of the apparatus of FIG. 2; and
[0016] FIG. 4 is a flow chart of a control process for controlling
the apparatus of FIGS. 1-3.
DETAILED DESCRIPTION OF THE DRAWING
[0017] A plasma etching machine 10 for use in plasma etching
pattern wafers is illustrated in FIGS. 1-3. The machine 10 includes
a process chamber 12, a mounting assembly 14, a chuck 16, and a
pedestal 18 coupled to the chamber 12 and mounting plate 14. A
drive motor 20 is attached to the mounting assembly 14 for rotating
the chuck and pedestal 16, 18.
[0018] The process chamber 12 includes a plurality of sidewalls 22
and a bottom wall 24 and a dome 30 (FIG. 2) that cooperate to
define an interior region 32. The bottom wall 24 includes a central
aperture 34.
[0019] The mounting assembly 14, best seen in FIG. 2, includes a
vertical member 14a, a pair of vertically oriented upper gussets
14b and a pair of vertically oriented lower gussets 14c projecting
orthogonally from the vertical plate 14a, and a pair of
horizontally oriented mounting plates 14d, 14e projecting
orthogonally from opposite sides of the vertical member 14a. The
upper gussets 14b include flanges extending outwardly from the
upper edges thereof for retaining the mounting assembly 14 to the
bottom wall 24 of the chamber 12. The lower gussets 14c are
attached to, and provide rigid support for, the mounting plate 14d.
Mounting plate 14e supports the drive motor 20.
[0020] A cylindrical bearing and seal block 36 having a first end
36a and a second end 36b is disposed in the central aperture 34.
The block 36 includes an angular flange 38 extending radially
outwardly from the first end 36a. A radially outer surface 40 of
the first end 36a and the flange 38 cooperate to define a shoulder
that engages the central aperture 34. When so engaged, the flange
38 abuts the bottom wall 24 and extends between the upper gussets
14b. The flange 38 includes a plurality of bolt-receiving bores 42
evenly spaced around the flange 38, and a plurality of bolts 44
attach the flange 38 to the bottom wall 24. An O-ring 46 is
disposed between the flange 38 and the bottom wall 24. The block 36
further includes a central bore 52 extending longitudinally
therethrough for receiving the pedestal 18. The bore 52 includes a
pair of annular grooves at the first end 36a for receiving a pair
of O-rings 56. O-rings 46 and 56 cooperate to seal the interior
region 32. The bore 52 further includes an annular recess 58
extending longitudinally upwardly from the second end 36b. A pair
of bearings 60a and 60b are disposed in the recess 58 and separated
by a spacer 62. An annular bearing cap 64, attached to the second
end 36b, retains the bearings 60a, 60b and the spacer 62 in
position. An end play adjustment nut 66 threadedly engages the
pedestal 18.
[0021] The pedestal 18 includes a cylindrical shaft 72 having a
first end 72a and a second end 72b and a circular plate 74 attached
to the first end 72a. The shaft 72 includes 3 sections 76, 78, 80.
The first section 76 extends downwardly from the plate 74 to a
first shoulder 76a that defines the beginning of the second section
78. The O-rings 56 in the block 36 engage the first section 76. The
second section 78 includes a reduced outer diameter and extends
downwardly from first shoulder 76a to shoulder 78a. The bearings
60a, 60b and spacer 62 engage the second section 78. A portion of
the second section 78 extending from the second shoulder 78a
includes threads to engage the end play adjustment nut 66. A pulley
86 is coupled to the second section 78 adjacent the second shoulder
78. A woodruff key 87 rotationally locks the pulley 86 to the shaft
72. The third section 80 extends from the second shoulder 78a to
the second end 72b of the shaft 72 and includes a threaded portion
adjacent the second shoulder 78a. A pulley lock nut 88 threadedly
engages the portion of the treaded third section 80 adjacent the
second shoulder 78a to axially retain the pulley 86 on the shaft
72. Thus, the pedestal 18 is free to rotate in the block 36., but
is substantially axially fixed in the block 36.
[0022] The pedestal 18 further includes a conductive ring assembly
90 and a bellows assembly 92 attached to the second end 72b. The
conductive ring assembly 90 includes a conductive ring 90a
sandwiched between a pair of insulators 90b, 90c. O-rings provide a
seal between the insulators 90b, 90c and the second end 72b and
bellows assembly 92, respectively, and to the conductive ring 90a.
The bellows assembly 92 includes an upper flange 92a and a lower
flange 92b. A plurality of mounting bolts 93 extend through aligned
apertures in the upper flange 92a, the conductive ring 90a and
insulators 90b, 90c to attach the bellows assembly 92 and
conductive ring assembly 90 to the second end 72b of the pedestal
18.
[0023] A plunger assembly 94, attached to the mounting assembly
vertical plate 14a, includes a electrostatic bias roller 96, such
as a DC roller, that engages the conductive ring 90a. A high
tension wire 98 couples the electrostatic bias roller 96 to a
voltage source (not shown). An electrostatic lead 98a extends from
the conductive ring 90a to the chuck 16 to provide electrostatic
voltage to the chuck 16, causing the chuck 16 to become an
electrode. An annular lip 16b, preferably made from a thin film
insulator, extends around the periphery of the chuck 16. The lip
16b retains the wafer in a spaced relationship with the
electrostatically charged chuck 16 and prevents the wafer from
contacting the chuck 16.
[0024] A pneumatic lift actuator 104 is attached to the horizontal
mounting plate 14e and includes air lines 104a, 104b and a lift
piston 106. A lift piston 106 engages a lift plate 108 that engages
the lower bellows flange 92b. The lower flange 92b includes a
circumferential groove formed in the radially outer surface
thereof. A pair of thrust washers 110a, lob are disposed in the
circumferential groove between the lift plate 108 and the lower
bellows flange 92b. Actuation of the lift actuator 104 causes the
bellows assembly 92 to move between a compressed upper position
(not shown) and a relaxed lower position (FIGS. 2-3).
[0025] The pedestal 18 includes a longitudinal central bore 72c
extending through the shaft 72 and plate 74. The chuck 16 is
mounted to the top of the plate 74 and cooperates with the plate 74
to define a coolant chamber 100. A plurality of slots 16a formed in
the face of the chuck 16 are in fluid communication with the
chamber 100. A spider assembly 102 includes a spider 102a disposed
in the coolant chamber 100 and a hollow lift rod 102b disposed in
the central bore 72c. As the bellows assembly 92 moves in response
to actuation of the lift actuator 104, the push rod 102b moves
between a wafer unloading position, corresponding to the compressed
position of the bellows assembly 92, and a wafer clamping position,
corresponding to the relaxed position of the bellows assembly
92.
[0026] A rotational coupler 114 couples a helium source (not shown)
to the lower bellows flange 92b and the pedestal 18. The rotational
coupler 114 is coupled to a vented screw 116 that allows helium to
pass from the rotational coupler 114 to the hollow lift rod 118.
Thus, the rotational coupler 114 and the vented screw 116 move with
the lift rod 118 in response to actuation of the lift actuator 104.
The lift rod 118 conveys helium to the coolant chamber 100 and the
slots 16a.
[0027] The dome 30 includes an upper electrode 128. The upper
electrode 128 includes a gas inlet 130 and a header 132 formed to
include a plurality of gas outlets 134. Preferably, the upper
electrode 128 is made of a conductive material such as aluminum
having an anodic oxide surface. The upper electrode 128 faces the
chuck 16 which serves as a lower electrode. The lower electrode 16
is grounded and an RF source 138 (FIG. 1) is applied to the upper
electrode 128 and provides energy to the interior region 32 to
ionize the gas and form the plasma for etching the wafer.
[0028] A representative plasma etching process is illustrated in
FIG. 4. A wafer is loaded into the process chamber 12 and the
machine 201 is started at step 201 to begin the process. Based on a
predefined process, a controller 131 establishes process
parameters. Initially, the controller 131 establishes a gas flow
into the process chamber 12 at step 204. The gas enters through the
gas inlet 130 and passes out of the header 132 through the outlets
134 into the process chamber 12. The controller 131 continues the
gas flow 204 to establish a chamber pressure at a set point during
step 206. Depending on the process involved, the gas flow can vary
from less than 1 SCCM to a few SLM and the pressure can vary from a
few millitorr to 2.5 torr and beyond.
[0029] The controller 131 also establishes backside cooling of the
chuck 16 in step 208 by sending helium through the rotational
coupler 114 and push rod 102b to the coolant chamber 122 and allows
the temperature to stabilize. The controller 131 also energizes the
ELECTROSTATIC BIAS ROLLER 96 to electrostatically charge the chuck
16 in step 210 and signals the drive motor 20 to begin pedestal
rotation at a predetermined RPM at step 212. When all of the
process parameters are stabilized, the controller 131 activates RF
power by energizing the RF source 138 to generate the etching
plasma at step 214. Power settings can vary, depending on the
process involved, from a few watts to an excess of 2 megawatts.
When the plasma is generated, the process continues until the
expiration of a pre-set time or an end point occurs at step 218. At
that point, the controller 131 stops the process, stopping the
chuck rotation, rotating the chuck to the unload position, and
deenergizing the RF source during step 220. The controller 131 also
stops the gas flow at step 222 and returns the pressure, backside
cooling, and electrostatic voltage to the idle state at steps 224,
226, 228, respectively. When the system is returned to the idle
state, the controller 131 unloads the wafer at step 230 by
signaling the lift actuator 104 to push up on the lift plate 108.
The lift plate 108, in turn, pushes on the lift rod 102b and the
spider 102a, which contacts the wafer and lifts the wafer from the
chuck 16. At that point, during step 230, a new wafer can be loaded
into the process chamber 12 and the process repeated, or the
process can be terminated, as at step 232.
[0030] The present invention has been described with reference to
an electrostatic chuck. It will be appreciated by those of ordinary
skill in the art that a mechanical clamp can be used, although it
is not preferred. A mechanical clamp adds more mass to the rotating
pedestal and must be carefully machined to ensure that it is
balanced about the rotational axis of the pedestal.
[0031] The above descriptions and drawings are only illustrative of
the preferred embodiments which present the features and advantages
of the present invention, and it is not intended that the present
invention be limited thereto. Any modification of the present
invention which comes within the spirit and scope of the following
claims is considered part of the present invention.
* * * * *