U.S. patent application number 14/704602 was filed with the patent office on 2015-08-20 for system and method for performing hot water seal on electrostatic chuck.
This patent application is currently assigned to LAM RESEARCH CORPORATION. The applicant listed for this patent is Lam Research Corporation. Invention is credited to Ambarish Chhatre, John Daugherty, Tuochuan Huang, Clifford La Croix, David Schaefer, Hong Shih, MingHang Wu.
Application Number | 20150235889 14/704602 |
Document ID | / |
Family ID | 47744091 |
Filed Date | 2015-08-20 |
United States Patent
Application |
20150235889 |
Kind Code |
A1 |
Shih; Hong ; et al. |
August 20, 2015 |
SYSTEM AND METHOD FOR PERFORMING HOT WATER SEAL ON ELECTROSTATIC
CHUCK
Abstract
A method is provided for treating a bipolar ESC having a front
surface and a back surface, the front surface including an anodized
layer. The method includes eliminating the anodized layer,
disposing a new anodized layer onto the front surface, and treating
the new anodized layer with water to seal the new anodized
layer.
Inventors: |
Shih; Hong; (Santa Clara,
CA) ; Huang; Tuochuan; (Saratoga, CA) ;
Schaefer; David; (Fremont, CA) ; Chhatre;
Ambarish; (San Ramon, CA) ; Daugherty; John;
(Fremont, CA) ; Wu; MingHang; (Renton, WA)
; La Croix; Clifford; (Livermore, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lam Research Corporation |
Fremont |
CA |
US |
|
|
Assignee: |
LAM RESEARCH CORPORATION
Fremont
CA
|
Family ID: |
47744091 |
Appl. No.: |
14/704602 |
Filed: |
May 5, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13219540 |
Aug 26, 2011 |
9054148 |
|
|
14704602 |
|
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|
Current U.S.
Class: |
279/128 |
Current CPC
Class: |
B05D 5/12 20130101; B05D
7/52 20130101; H01L 21/6833 20130101; Y10T 279/23 20150115; C23C
8/02 20130101; C23C 22/66 20130101; H01L 21/6831 20130101 |
International
Class: |
H01L 21/683 20060101
H01L021/683 |
Claims
1. A bipolar ESC having a front surface and a back surface, the
front surface having an anodized layer comprising a first layer of
Al.sub.2O.sub.3 and a second layer of Al.sub.2O.sub.3, wherein the
first layer of Al.sub.2O.sub.3 has a first thickness and a first
density, wherein the second layer of Al.sub.2O.sub.3 has a second
thickness and a second density, wherein the first thickness is less
than the second thickness, and wherein the first density is greater
than the second density.
2. The bipolar ESC of claim 1, wherein the second layer of
Al.sub.2O.sub.3 is a layer of porous Al.sub.2O.sub.3 treated with
hot deionized water to create AlO(OH).
3. The bipolar ESC of claim 1, wherein the second layer of
Al.sub.2O.sub.3 is a layer of porous Al.sub.2O.sub.3 treated with
water to create AlO(OH) by reacting the second layer of porous
Al.sub.2O.sub.3 with the water to create boehmite.
4. The bipolar ESC of claim 1, wherein the first layer is under the
second layer, the first layer has a thickness of about 750 to 800
angstroms and the second layer has a thickness of about 2 mils.
5. The bipolar ESC of claim 1, wherein the anodized layer has a
dielectric constant of about 10.
6. The bipolar ESC of claim 1, wherein the second layer consists
essentially of pore-free AlO(OH).
7. The bipolar ESC of claim 1, wherein the second layer has an
exposed surface on which a semiconductor wafer can be
electrostatically clamped.
8. The bipolar ESC of claim 1, wherein the anodized layer has a
consistent dielectric constant effective to avoid failure
associated with chucking or de-chucking wafers thereon.
9. The bipolar ESC of claim 1, wherein the anodized layer is an
anodized surface of an aluminum alloy.
Description
[0001] This application is a divisional application of U.S.
application Ser. No. 13/219,540 entitled SYSTEM AND METHOD FOR
PERFORMING HOT WATER SEAL ON ELECTROSTATIC CHUCK, filed Aug. 26,
2011, the entire content of which is hereby incorporated by
reference.
BACKGROUND
[0002] Bipolar electrostatic chucks (ESCs or ESC for singular) are
commonly used in semiconductor wafer fabrication. These ESCs use
electrostatic forces to hold a semiconductor wafer in place during
the manufacturing process. Over time, the chucks develop wear from
use and their performance degrades.
[0003] Methods for refurbishing ESCs have been developed, however
the known anodization process for refurbishment may present
consistency issues associated with the dielectric constant for an
anodized layer.
[0004] What is needed is a method for ESC refurbishment enabling
fabrication of an anodized layer with a consistent dielectric
constant.
BRIEF SUMMARY
[0005] The present invention provides a method for refurbishing an
ESC with an anodized layer performed by application of a deionized
water seal for supplying an anodized layer.
[0006] In accordance with an aspect of the present invention, a
method is provided for treating a bipolar ESC having a front
surface and a back surface, the front surface including an anodized
layer. The method includes eliminating the anodized layer,
disposing a new anodized layer onto the front surface, and treating
the new anodized layer with water to seal the new anodized
layer.
[0007] Additional advantages and novel features of the invention
are set forth in part in the description which follows, and in part
will become apparent to those skilled in the art upon examination
of the following or may be learned by practice of the invention.
The advantages of the invention may be realized and attained by
means of the instrumentalities and combinations particularly
pointed out in the appended claims.
BRIEF SUMMARY OF THE DRAWINGS
[0008] The accompanying drawings, which are incorporated in and
form a part of the specification, illustrate an exemplary
embodiment of the present invention and, together with the
description, serve to explain the principles of the invention. In
the drawings:
[0009] FIG. 1 illustrates a cross-sectional view of an exemplary
ESC, in accordance with an aspect of the present invention;
[0010] FIG. 2 illustrates a cross-sectional view of an exemplary
partial ESC as described with reference to FIG. 1 where a layer
portion has been removed, in accordance with an aspect of the
present invention;
[0011] FIG. 3 illustrates a cross-sectional view of an example
partially refurbished ESC wherein a defective or deformed layer
portion has been replaced with a new layer portion, in accordance
with an aspect of the present invention;
[0012] FIG. 4 illustrates a cross-sectional view of an example ESC,
wherein a defective or deformed layer portion has been replaced
with a functional layer portion, in accordance with an aspect of
the present invention; and
[0013] FIG. 5 illustrates an example method for refurbishing a
semiconductor wafer, in accordance with an aspect of the present
invention.
DETAILED DESCRIPTION
[0014] In accordance with aspects of the present invention, an
anodized layer is removed from an ESC. A replacement anodized layer
is then added to ESC. The new anodized layer is treated with hot
water to eliminate pores therein. The hot water treated anodized
layer is more resistant to corrosion and maintains consistent
electromagnetic properties for longer periods than anodized layers
that are not treated with hot water.
[0015] FIG. 1 illustrates a cross-sectional view of a portion of an
example ESC 100, to be refurbished in accordance with an aspect of
the present invention.
[0016] As seen in the figure, ESC 100 includes an electrode 102 and
an anodized layer 104. ESC 100 is used to hold a semiconductor
wafer (not shown) in place during the manufacturing process via
electrostatic attraction between the semiconductor wafer and ESC
100. Electrode 102 may be positively or negatively charged. The
charge applied to electrode 102 is developed by applying a voltage
difference between electrode 102 and a second electrode (not
shown). Anodized layer 104 prevents unwanted oxidation of electrode
102.
[0017] Anodized layer 104 includes a porous layer 106 and a barrier
layer 108. As a non-limiting example, porous layer 106 and barrier
layer 108 may be formed of Al.sub.2O.sub.3. Anodized layer 104
resides on a top surface 110 of electrode 102. Barrier layer 108
resides between electrode 102 and porous layer 106 and resides on
top surface 110. Typically, the thickness of barrier layer 108 is
smaller than the thickness of porous layer 106. Furthermore, in
general, the density of barrier layer 108 is greater than that of
porous layer 106.
[0018] Anodizing an aluminum alloy such as Al.sub.2O.sub.3 produces
a porous layer (e.g. porous layer 106) containing a high density of
microscopic pores with a sampling denoted as a pore 122. As a
result of the pores, the anodized aluminum alloy reacts readily or
oxidizes with oxygen in air resulting in undesirable oxidation,
i.e., corrosion. The resulting oxidation varies throughout the
volume of the material producing variable electromagnetic
properties (i.e. permittivity or .epsilon..sub.0 associated with
electrical properties and permeability or .mu..sub.0 associated
with magnetic properties) for the material. The variable
electromagnetic properties results in inconsistent operation and
negatively affects the performance of an ESC for fabricating
semiconductor wafers.
[0019] An ESC is used to hold wafers via an electrostatic
attraction also known as chucking a wafer. Furthermore, wafers are
released from an ESC via an electrostatic repulsion also known as
de-chucking. As the electromagnetic properties (i.e.
.epsilon..sub.0 and .mu..sub.0) of an ESC begin to vary as a result
of unwanted oxidation, the parameters associated with chucking and
de-chucking a wafer also vary. Furthermore, due to the precision
required for fabricating a semiconductor, the efficiency,
effectiveness and ability to chuck and de-chuck a wafer is
negatively affected as a result of unwanted oxidation and the
undesirable variance associated with the electromagnetic properties
distributed throughout the volume of Al.sub.2O.sub.3.
[0020] Furthermore, ESC 100 will wear over time by developing
cracks, dents, pits, scratches and deep scratches. The degradation
may occur as a result of surface conditions that may develop with
use. Due to the physical defects associated with ESC 100, the
processing of semiconductor wafers may be not be performed
correctly, may not be performed sufficiently and/or may not be
performed efficiently.
[0021] Several types of wear may develop for ESC 100. Particulate
matter may stick to a top surface 111, with example particulate
matter illustrated as a particulate matter 112 and a particulate
matter 120. Scratches or marks may occur in anodized layer 104 with
example scratches illustrated as a scratch 114, a scratch 116 and a
scratch 118.
[0022] A wafer handling system, which uses ESC 100, is operated
under very precise conditions. When the electromagnetic properties
of ESC 100 change, the efficiency of the operation of the entire
wafer handling system degrades. As such, it is important to
maintain the electromagnetic properties of ESC 100. In order to
maintain the electromagnetic properties of ESC 100, the issues
resulting from operational wear over time should be addressed.
Particulate matter 112 and 120 may be removed from the surface of
ESC 100 by known methods, however scratches 114, 116 and 118
require more intensive repair.
[0023] ESC 100 with a damaged anodized layer 104 may be refurbished
in order to restore its electromagnetic properties. The process of
refurbishment of ESC 100 includes removal and replacement of
anodized layer 104.
[0024] FIG. 1 illustrates a cross-sectional view of ESC 100,
wherein anodized layer 104 has become physically damages during
operation. Anodized layer 104 may be removed and replaced in order
to restore the electromagnetic properties of ESC 100. Removal and
replacement of an anodized layer will be described with reference
to FIGS. 2-3.
[0025] FIG. 2 illustrates a cross-sectional view of ESC 100 of FIG.
1, wherein anodized layer 104 has been removed. Removal of anodized
layer 104 may be performed by any known method, non-limiting
examples of which include lathing (stripping).
[0026] Anodized layer 104 may be accurately stripped with a
controlled resolution of 30 seconds or less, followed by deionized
water rinsing and measurement. Stripping is controlled in order to
cease material removal process when previous anodic material has
been removed. Top surface 110 is then polished to remove 1 to 2
mils of electrode 102. With the anodized layer removed, top surface
110 of electrode 102 is ready to receive a new anodized layer.
[0027] FIG. 3 illustrates a cross-sectional view of an example
partially refurbished ESC 300, wherein a defective anodized layer
has been replaced with a new anodized layer, in accordance with an
aspect of the present invention.
[0028] Partially refurbished ESC 300 includes electrode 102, a
barrier layer 302 and a layer 308. The term "partially" is used in
partially refurbished ESC 300 because the ESC will not be
completely refurbished, in accordance with aspects of the present
invention, until the new anodized layer is treated with hot water.
This will be described later.
[0029] Layer 308 forms on top of barrier layer 302. Barrier layer
302 is formed with a thickness 304 and layer 308 is formed with a
thickness 312. As a non-limiting example, layer 308 may be
fabricated with Al.sub.2O.sub.3. Layer 308 has been formed with
thickness 312 above a top surface 306.
[0030] Barrier layer 302 and layer 308 form a layer portion
310.
[0031] When forming layer portion 310, barrier layer 302 and layer
308 form simultaneously. Since the density of barrier layer 302 is
greater than layer 308, a thickness 408 of barrier layer 302
increases at a faster rate than thickness 304 of barrier layer 302.
The layer forming process initiates with zero electrical current
and the current is increased. As the current is increased, the
voltage on the surface of the newly forming layer portion 310
begins to increase. Surface nucleation operates to aid in
generation of layer portion 310. Surface nucleation is a process
where components in a solution precipitate out and form nuclei that
attracted additional precipitate.
[0032] To maintain precise quality, many fabrication parameters may
be controlled. In a non-limiting example, with a voltage potential
of 75 Volts, thickness 304 is approximately 750 Angstroms to 800
Angstroms. Furthermore, the pH for application of layer portion 310
is controlled, wherein in an example embodiment, the pH is
maintained between 5.6 and 6.2. Still further, the temperate for
application of layer portion 310 is controlled, wherein in an
example embodiment, the temperature is maintained between
96.degree.-99.degree. Celsius. With these example parameters,
approximately 1 mil of layer portion 310 is formed for every 75
minutes. Accordingly, with these parameters, the time for forming 2
mils of layer portion 310 is approximately 150 minutes.
[0033] Following formation of layer portion 310, an ESC may
function to process wafers in accordance with conventional systems.
However, unwanted effects associated with oxidation as described
with reference to FIG. 1 will be experienced as a result of the
porous nature of layer 308. To prevent oxidation and the unwanted
negative performance associated with the oxidation, layer 308 is
treated in accordance with aspects of the present invention as
discussed below with reference to FIG. 4.
[0034] FIG. 4 illustrates a cross-sectional view of an example ESC
400, in accordance with an aspect of the present invention.
[0035] Refurbished ESC 400 includes electrode 102, barrier layer
302 and a layer 402.
[0036] Layer 402 has been formed by treating layer 308 (FIG. 3)
with a water seal. As a non-limiting example, a water seal may be
performed via application of hot deionized water.
[0037] Deionized water is produced by processing water to the point
where the water is free of ions. A common method for producing
deionized water is to pass a relatively pure source of water
through a reverse osmosis filter. Reverse osmosis filtering may be
performed by applying pressure to the water when it is located on
one side of a selective membrane, resulting in solute being
retained on pressurized side of membrane with deionized water
passing to depressurized side of the membrane. The membrane allows
small particles to pass, but larger particles, such as ions, to not
pass.
[0038] Layer 402 is created via a reaction of hot deionized water
with the porous Al.sub.2O.sub.3 of layer 308 (FIG. 3). The reaction
of the Al.sub.2O.sub.3 with the deionized water creates AlO(OH). In
some embodiments, the AlO(OH) takes the form of boehmite.
[0039] Layer 402 with thickness 408 and includes properties of high
corrosion resistance for preventing corrosion and/or oxidation.
Furthermore, layer 402 includes a consistent dielectric constant
for avoiding failures associated with chucking or de-chucking. As a
non-limiting example, a dielectric constant of 10 may be attributed
to layer 402.
[0040] Pores (e.g. pore 316) as described with reference to FIG. 3
(which have the potential to cause unwanted oxidation) have been
removed as illustrated by layer 402 of FIG. 4. In particular, the
pores have been removed via treatment of the Al.sub.2O.sub.3 with
hot water. More specifically, the Al.sub.2O.sub.3 reacts with the
hot water and is converted into AlO(OH), as illustrated in FIG. 4.
The AlO(OH) as illustrated in FIG. 4 is much less porous than the
Al.sub.2O.sub.3 of FIG. 3, and as a result, is much less
susceptible to unwanted oxidation.
[0041] The AlO(OH) of FIG. 4 retains consistent electromagnetic
properties for a much longer period of time than the
Al.sub.2O.sub.3 described with reference to FIG. 1.
[0042] Although the electromagnetic properties (i.e. those
associated with .epsilon..sub.0 and .mu..sub.0) of the AlO(OH)
layer of FIG. 4 are slightly different than the electromagnetic
properties of Al.sub.2O.sub.3 of FIG. 1, refurbished ESC 400
adequately performs chucking and de-chucking operations.
Furthermore, refurbished ESC 400 performs chucking and de-chucking
for a longer period of time and operates more efficiently over time
as compared to ESC 100, which is more susceptible to oxidation.
[0043] Thickness 408 for layer 402 is greater than the thickness
304 for barrier layer 302.
[0044] The density of barrier layer 302 is greater than the density
of layer 402.
[0045] The chuck force for refurbished ESC 400 is characterized by
Equation (1) shown below:
F=(1/2).epsilon.o.epsilon..sub.rV.sup.2/D.sup.2 (1)
[0046] The variable F represents the chuck force for refurbished
ESC 400, .epsilon.o=8.85.times.10.sup.-12 F/m and represents the
permittivity of free space, .epsilon..sub.r, relative permittivity,
represents the dielectric constant of layer 402, variable V
represents the applied chuck voltage and variable D represents the
thickness of the anodic film or a thickness 410.
[0047] The consistent dielectric constant associated with layer 402
results in a reliable chucking/de-chucking force as the
chucking/de-chucking force is proportional to the dielectric
constant as illustrated with reference to Equation (1). The
consistent dielectric constant associated with layer 402 prevents a
too low dielectric constant and enables proper chucking.
Furthermore, the consistent dielectric constant aids in preventing
high helium flow from leakage during chamber testing and wafer
production as a result of a too low chucking force. Furthermore,
helium may be used for controlling temperature of semiconductor
process and an insufficient chucking force may result if an
excessive amount of helium applied for semiconductor manufacturing
process, thereby resulting in defective wafers.
[0048] For too large of a dielectric constant, water moisture
becomes trapped inside pores of anodic film, resulting in poor
de-chucking.
[0049] A problem that arises with the use of an ESC is the
difficulty of removing the residual electrostatic force between the
wafer and the ESC during "de-chucking". This residual force results
from electric charges having accumulated at the interface between
the wafer and the ESC support surface. One technique for
de-chucking involves connecting the electrode and the wafer to
ground. Another technique reverses the polarity of the DC chucking
voltage applied to the electrodes to discharge the electrodes.
However, these techniques are not completely effective at removing
the charge on the electrodes and the wafer. Consequently, a
mechanical force is often needed to overcome the remaining
attractive electrostatic force due to residual charges on the
electrodes and wafer. At times, the mechanical force used to
release the wafer may cause the wafer to "pop", i.e., to be
released from the chuck in some unpredictable manner, which may
cause either wafer damage or difficulty in retrieving the wafer
from unintended position. Therefore, a successful de-chucking
operation is one which leaves the wafer in a state subject to
acceptably low residual electrostatic attractive force without
"popping" the wafer.
[0050] The voltage control of an ESC is used for the operation of
the device, as the voltage differential created also generates an
electric field used to attract and hold a wafer for processing. The
capacitance of refurbished ESC 400 is a parameter which affects
voltage control and therefore is maintained consistent in order to
maintain a consistent voltage control.
[0051] The capacitance of refurbished ESC 400 is characterized by
Equation (2) as shown below:
C=.epsilon.o.epsilon..sub.rA/D (2)
[0052] The variable C represents the capacitance of refurbished ESC
400 and variable A represents the surface area for the stop surface
of the refurbished ESC 400. Furthermore, refurbished ESC 400
receives a semiconductor wafer 412 on a top surface 414 of
refurbished ESC 400.
[0053] As can be observed by Equation (2), the capacitance, C, is
proportional to the dielectric constant, .epsilon..sub.r, so in
order to maintain a consistent capacitance, a consistent dielectric
constant is maintained.
[0054] The resistance of refurbished ESC 400 is a parameter which
affects arcing and therefore is consistently maintained in order to
prevent arcing. In some instances, it is possible for arcing to
occur as a result of a low resistance point associated with an ESC.
In order to prevent arcing, resistance is maintained at a
consistently high value. The permittivity, .epsilon..sub.r, of a
material is given by Equation (3) shown below:
.epsilon.=.epsilon..sub.o.epsilon..sub.r (3)
[0055] Permittivity, .epsilon., is a measure of how much resistance
is encountered when forming an electric field in a medium.
Permittivity is a measure of how an electric field affects, and is
affected by, a dielectric medium. Permittivity is determined by the
ability of a material to polarize in response to an electric field,
and thereby reduce the total electric field inside the material.
Permittivity describes a material's ability to transmit (i.e.
permit) an electric field. Less electric flux exists in a medium
with a high permittivity due to polarization effects. Processing of
layer 402 via deionized water contributes to a permittivity such
that arcing is reduced.
[0056] FIG. 5 illustrates an example method for refurbishing a
semiconductor wafer, in accordance with an aspect of the present
invention.
[0057] In the example embodiment, a method 500 starts (S502) and a
portion of a second layer (e.g. porous layer 106 (FIG. 1)) is
removed if it exists or a portion of a barrier layer (e.g. barrier
layer 108 (FIG. 1)) is removed if second layer does not exist for
an ESC (S504).
[0058] Removal of layers may be performed via any know means or
method for removal of layers. Non-limiting examples of means and
methods for removal of layer includes, mechanical, chemical and
electrical.
[0059] A determination is performed as to whether the second layer
and the barrier layer have been removed (S506).
[0060] Dimensions of ESC are measured using coordinate measurement
machine. Based upon the measured dimensions, a determination is
performed as to whether additional layer material is to be
removed.
[0061] Following a determination for adequate removal of layer
material (S506), ESC is configured as described with reference to
FIG. 2.
[0062] A new layer portion (e.g. layer portion 310 (FIG. 3)) is
added to ESC (S510).
[0063] Layer portion may be added to ESC using any known means or
method.
[0064] A determination is performed as to whether addition of layer
portion has been completed (S512).
[0065] Dimensions of ESC are measured using coordinate measurement
machine. Based on the measured dimensions, a determination is
performed as to whether additional layer material is to be
added.
[0066] Following a determination for adequate addition of layer
material (S512), ESC is configured as described with reference to
FIG. 3.
[0067] Deionized water seal is applied to layer portion 310 (FIG.
3) (S514).
[0068] An anodic film (e.g. layer 402 (FIG. 4)) is created via a
reaction of hot deionized water with the porous Al.sub.2O.sub.3 of
layer 308 (FIG. 3). The reaction of the Al.sub.2O.sub.3 with the
deionized water creates AlO(OH) also known as boehmite.
[0069] A determination is performed as to whether a multiplicity of
wafers have been refurbished successfully (S516).
[0070] Measurements, testing and analysis are performed for
determining whether refurbishment of a multiplicity of ESCs have
been performed successfully.
[0071] For a determination of not having processed a multiplicity
of ESCs successfully, the process of refurbishing an ESC is
initiated (S518).
[0072] An ESC previously refurbished unsuccessfully may be
processed again, or an entirely different ESC which has not been
attempted to be refurbished may be processed again.
[0073] For a determination of having successfully processed a
multiplicity of ESCs (S516), a process specification is
developed.
[0074] Process specification is developed based upon the
measurements and other associated information determined while
successfully processing a multiplicity of ESCs (S520).
[0075] Method 500 ceases operation (S522).
[0076] An ESC is subject to wear and/or degradation from conditions
associated with operation. ESC may be refurbished by replacing
degraded anodized layer with a new anodized layer which has been
subject to a water seal for realizing an anodized layer with
properties conducive to the successful operation of refurbished
ESC.
[0077] The foregoing description of various preferred embodiments
of the invention have been presented for purposes of illustration
and description. It is not intended to be exhaustive or to limit
the invention to the precise forms disclosed, and obviously many
modifications and variations are possible in light of the above
teaching. The example embodiments, as described above, were chosen
and described in order to best explain the principles of the
invention and its practical application to thereby enable others
skilled in the art to best utilize the invention in various
embodiments and with various modifications as are suited to the
particular use contemplated. It is intended that the scope of the
invention be defined by the claims appended hereto.
* * * * *