U.S. patent application number 12/078244 was filed with the patent office on 2008-08-14 for dummy substrate and substrate processing method using the same.
This patent application is currently assigned to MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.. Invention is credited to Kenichi Ishihara.
Application Number | 20080193779 12/078244 |
Document ID | / |
Family ID | 34988028 |
Filed Date | 2008-08-14 |
United States Patent
Application |
20080193779 |
Kind Code |
A1 |
Ishihara; Kenichi |
August 14, 2008 |
Dummy substrate and substrate processing method using the same
Abstract
A dummy substrate is obtained by covering a silicon substrate
with a resin coating. This increases the strength of the dummy
substrate, prevents pieces and particles of the silicon substrate
from scattering, and even when the dummy substrate is damaged
during processing, prevents them from contaminating a processing
apparatus. The use of a chemical-resistant resin for the resin
coating restrains the dummy substrate from being etched by a
cleaning process using a chemical solution and increases the number
of times that the dummy substrate can repeatedly be used.
Inventors: |
Ishihara; Kenichi; (Toyama,
JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, NW
WASHINGTON
DC
20005-3096
US
|
Assignee: |
MATSUSHITA ELECTRIC INDUSTRIAL CO.,
LTD.
Osaka
JP
|
Family ID: |
34988028 |
Appl. No.: |
12/078244 |
Filed: |
March 28, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11079332 |
Mar 15, 2005 |
7392599 |
|
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12078244 |
|
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Current U.S.
Class: |
428/440 ;
428/64.1 |
Current CPC
Class: |
Y10T 428/31641 20150401;
H01L 21/67051 20130101; Y10T 428/21 20150115; H01L 21/67028
20130101 |
Class at
Publication: |
428/440 ;
428/64.1 |
International
Class: |
B32B 17/10 20060101
B32B017/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2004 |
JP |
2004-084430 |
Claims
1. A dummy substrate having substantially the same mass as each of
to-be-processed substrates and made of a plate material, at least
the outer edge of said plate material being coated with a
resin.
2. The dummy substrate of claim 1, wherein the entire surfaces of
the plate material are coated with the resin.
3. The dummy substrate of claim 1, wherein the dummy substrate has
substantially the same shape and size as each said to-be-processed
substrate.
4. The dummy substrate of claim 1, wherein the resin is
chemical-resistant.
5. The dummy substrate of claim 1, wherein the resin is
conductive.
6. The dummy substrate of claim 1, wherein any one of the principal
surfaces of the dummy substrate is marked.
7. The dummy substrate of claim 1, wherein the plate material is a
single crystal silicon substrate or a substrate containing single
crystal silicon.
8-15. (canceled)
16. The dummy substrate of claim 2, wherein the dummy substrate has
substantially the same shape and size as each said to-be-processed
substrate.
17. The dummy substrate of claim 2, wherein the resin layer is a
fluorine-containing resin.
18. The dummy substrate of claim 2, wherein the resin layer is
conductive.
19. The dummy substrate of claim 2, wherein the plate material is a
single crystal silicon substrate or a substrate containing single
crystal silicon.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. .sctn.119
on Patent Application No. 2004-84430 filed in Japan on Mar. 23,
2004, the entire contents of which are hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] (1) Field of the Invention
[0003] The present invention relates to processing of a substrate
such as a semiconductor wafer, and more particularly relates to a
dummy substrate used for cleaning and drying and to a semiconductor
processing method using the dummy substrate.
[0004] (2) Description of Related Art
[0005] Basic processes for fabricating a semiconductor integrated
circuit device include a cleaning process and a drying process of
the semiconductor wafer. A cleaning method using a basin has been
widely used in a cleaning process step. In this method, a
semiconductor substrate is soaked into a chemical solution which
contains acid or alkali and with which a chemical-resistant basin
is filled, thereby removing contaminants on the surface of the
semiconductor substrate.
[0006] A chemical-solution-circulation-type cleaning apparatus with
a basin cleans each of lots of semiconductor substrates (for
example, a set of twenty-five semiconductor substrates that will be
fabricated together) by circulating, through a pump and a filter, a
chemical solution filling in a basin. This apparatus has a problem
in saving the chemical solution because a large volume of the
solution is used for cleaning. Furthermore, since the cleaning by
the apparatus is a batch treatment, there also exists another
problem that the states of cleaned surfaces of semiconductor
substrates are varied in each production lot.
[0007] In order to solve the above problems, drum-type spin
cleaning apparatuses using rotating drums have been developed. Such
an apparatus requires only a small volume of chemical solution for
cleaning and provides stable cleaning so that cleaning is rapidly
completed and a solution is not left after cleaning. This can
reduce variations in the states of cleaned surfaces of
semiconductor substrates in a lot. Therefore, drum-type spin
cleaning apparatuses are now used frequently (see, for example,
Japanese Unexamined Patent Publication No. 2002-52358).
[0008] A drum-type spin cleaning apparatus, a known art, will be
described hereinafter with reference to the drawings.
[0009] FIG. 5 is a diagram illustrating an example of an internal
structure of a drum-type spin cleaning apparatus when viewed from
side.
[0010] As shown in FIG. 5, a turntable 11 is placed inside a
cylindrical chamber 10, and a shaft 12 is coupled to the lower
surface of the turntable 11 at the site of a rotation axis of the
turntable 11 and furthermore is connected to a motor 13 located
below the chamber 10. The rotation of the motor 13 allows the
turntable 11 to rotate through the shaft 12 at a high speed of, for
example, 1000 rpm or more.
[0011] Bar guides 15 are placed on the turntable 11 to fix
cassettes 14 into which a plurality of substrates including a
plurality of to-be-processed substrates 16, such as semiconductor
substrates, and at least one dummy substrate 17 are inserted. The
use of the guides 15 allows the cassettes 14 to be placed
symmetrically about the rotation axis of the turntable 11. The
arrangement of the cassettes 14 and guides 15 will be described
later in detail with reference to FIG. 6.
[0012] The dummy substrate 17 represents herein a substrate on
which an electronic device for providing an actual product is not
formed, for example, a silicon substrate or the like on which an
oxide film or a silicon nitride film is formed.
[0013] A spray nozzle 19 protrudes from the middle part of a top
lid 18 of the cleaning apparatus to be perpendicular to the top lid
18. The closure of the top lid 18 allows the spray nozzle 19 to be
located above the rotation axis of the turntable 11. During
cleaning, a chemical solution for cleaning 20 containing acid or
alkali can be horizontally sprayed from the spray nozzle 19 onto
the to-be-processed substrates 16 or the dummy substrate 17. The
chemical solution 20 is supplied from the outside of the cleaning
apparatus to the inside of the cleaning apparatus through a
chemical solution supply pipe 21.
[0014] Cleaning is carried out by spraying the chemical solution 20
onto the to-be-processed substrates 16 and the dummy substrate 17
and rotating the cassettes 14 together with the turntable 11. This
makes uniform cleaning possible.
[0015] Not only a chemical solution but also pure water can be
sprayed by the spray nozzle 19. At least one side spray nozzle 22
for supplying additional pure water during the cleaning is also
mounted in the vicinity of and with a certain distance from the
turntable 11. Pure water is supplied through a pure water supply
pipe 23.
[0016] FIG. 6 is a diagram illustrating an example of the internal
structure of the drum-type spin cleaning apparatus when viewed from
above.
[0017] FIG. 6 illustrates a turntable 11, cassettes 14 placed on
the turntable 11, guides 15 through which the cassettes 14 are
fixed, a plurality of substrates including a plurality of
to-be-processed substrates 16 and at least one dummy substrate 17
and put into each cassette 14. The other components are not shown.
As illustrated in FIG. 6, four sets of (eight) guides 15 are placed
on the turntable 11, and the cassette 14 is fixed by the associated
sets of guides 15. These guides 15 allow two or four cassettes 14
to be placed symmetrically about the rotation axis.
[0018] The dummy substrate 17 is often used for cleaning or drying
process by the above-mentioned drum-type spin cleaning apparatus.
The dummy substrate 17 is used mainly for two purposes.
[0019] One of the purposes is to prevent particles from being
deposited on the to-be-processed substrates 16.
[0020] As seen from FIG. 5, the cassettes 14 are longitudinally
fixed in the chamber 10 of the drum-type spin cleaning apparatus.
Spin drying is carried out immediately after cleaning. During this
drying, some of particles in the chamber 10 are raised with the
rotation of the turntable 11 and floats in the chamber 10. Such
particles are deposited on the to-be-processed substrates 16 or the
like put into the cassettes 14, leading to reduced production
yields. Particles are likely to be deposited, in particular, to the
uppermost one of the plurality of to-be-processed substrates 16 put
into each cassette 14.
[0021] To cope with this, not the to-be-processed substrate 16 on
which an electronic device is formed but the dummy substrate 17 is
placed in the uppermost part of each cassette 14. This allows
particles to be deposited almost intensively on the dummy substrate
17. Therefore, particles are much less likely to be deposited on
the to-be-processed substrates 16. This can prevent reduction in
yields.
[0022] The other purpose is to achieve balanced rotation.
[0023] As long as the gross mass of a combination of each cassette
14 and the plurality of substrates including the to-be-processed
substrates 16 and the dummy substrate 17 and contained in the
cassette 14 (hereinafter, referred to as "cassette gross mass")
does not vary from cassette to cassette, the cassettes 14 are
placed on the turntable 11 symmetrically about the rotation axis of
the turntable 11. This makes balanced rotation possible. However,
if at least one of the plurality of cassettes 14 has a different
cassette gross mass from that of each of the other cassettes, this
makes balanced rotation impossible. To avoid this, the cassette
gross masses of all the cassettes 14 are allowed to coincide with
one another by adding a necessary number of dummy substrates 17 to
the cassette 14 having a different cassette gross mass. Dummy
substrates 17 are used for this purpose.
[0024] This will be described below in detail by citing a specific
example.
[0025] Four cassettes 14 can be provided for the drum-type spin
cleaning apparatus shown in FIG. 6. Therefore, if the number of the
to-be-processed substrates 16 to be cleaned or dried at the same
time is a multiple of 4, the same number of the to-be-processed
substrates 16 can be contained in each cassette 14. In this case,
each cassette 16 has the same cassette gross mass. Therefore, the
masses of the cassettes 14 are balanced, resulting in balanced
rotation kept.
[0026] However, if the number of the to-be-processed substrates 16
to be processed at the same time is not a multiple of 4, more
to-be-processed substrates 16 will be contained in at least one of
the cassettes 14 than in each of the other cassettes 14. As a
result, the at least one of the cassettes 14 has a different
cassette gross mass from that of each of the other cassettes 14.
Thus, if cleaning and drying are carried out by rotating the
cassettes 14, eccentric rotation is caused.
[0027] Furthermore, only two cassettes 14 may be used for the
drum-type spin cleaning apparatus shown in FIG. 6. In this case, if
the number of the to-be-processed substrates 16 to be processed at
the same time is odd, eccentric rotation is caused likewise.
[0028] If the turntable 11 is allowed to rapidly spin with such
eccentricity, the drum-type spin cleaning apparatus itself vibrates
due to centrifugal force. The increase of the vibrations of the
drum-type spin cleaning apparatus might cause the drum-type spin
cleaning apparatus itself, the to-be-processed substrates 16 and
the dummy substrate 17 to be broken.
[0029] The drum-type spin cleaning apparatus usually has an
interlock. Thus, if eccentricity is caused, the apparatus will
stop. However, in order to perform cleaning, electric rotation
itself must be prevented. Therefore, each cassette 14 need have the
same cassette gross mass. A necessary number of dummy substrates 17
are added to the cassette 14 having less to-be-processed substrates
16 than the other cassettes 14. This allows the total number of
substrates in any one cassette 14 including the to-be-processed
substrates 16 and the at least one dummy substrate 17 (hereinafter,
referred to as "the total number of contained substrates") to be
the same as that for any other cassette 14. This provides balanced
mass, because the mass of the to-be-processed substrate 16 is
substantially the same as that of the dummy substrate 17.
[0030] Lots often have different numbers of the to-be-processed
substrates 16. Therefore, the number of the dummy substrate to be
used is adjusted for each lot, thereby balancing rotation.
[0031] An electronic device fabricating process includes 100 or
more individual process steps. Substrates on which electronic
devices are not formed are used also in process steps other than
the above-mentioned cleaning and drying process steps. Such
substrates on which electronic devices are not formed are referred
to as "dummy substrates" herein. For example, the dummy substrates
include substrates used to determine electronic device fabrication
conditions for each process step and dummy substrates used to
stabilize conditions on which an electronic device is fabricated in
a dry etching process step and a CVD process step.
[0032] More dummy substrates are required with increase in the
production of semiconductor devices or the like. This leads to
increased cost. Therefore, inexpensive dummy substrates that can
repeatedly be used have been desired (see, for example, Japanese
Unexamined Patent Publication No. 2000-272910).
[0033] Conventional dummy substrates have the following
problems.
[0034] The conventional dummy substrates used in a semiconductor
fabricating process include a silicon substrate, a silicon
substrate whose top surface is covered with an insulating film,
such as a silicon oxide film or a silicon nitride film, and the
like.
[0035] The dummy substrates repeatedly used for semiconductor
fabricating process steps are highly chemical-resistant. In spite
of this, in a cleaning process step using a high-temperature
chemical solution with etching ability, such as a mixed solution of
NH.sub.4OH and H.sub.2O.sub.2, the dummy substrate is etched little
by little with increase in the number of electronic device
fabricating processes, leading to the decreased thickness of the
dummy substrate. Since a mechanical strength of the dummy substrate
is consequently deteriorated, the dummy substrate that has been
used for a certain period must be exchanged.
[0036] If the dummy substrate with the deteriorated strength keeps
being used, this increases the possibility that it will be broken
in the cleaning apparatus during process steps requiring high-speed
rotation. The breakage of the dummy substrate will produce broken
pieces and particles of the dummy substrate. The produced broken
pieces and particles contaminate substrates on which electronic
device products are formed and which are processed in the same
batch, leading to the reduced yields. Furthermore, they also
contaminate the chamber of the drum-type spin cleaning
apparatus.
[0037] Such a state provides the necessity for cleaning the inside
of the chamber to recover the particle level to the extent that an
integrated circuit can be fabricated. Since this cleaning is
nevertheless very difficult, the chamber itself is usually not
cleaned but exchanged. It is expensive to repair a drum-type spin
cleaning apparatus in this manner, and the spin cleaning apparatus
cannot be operated during repair.
[0038] As seen from the above, the known method using dummy
substrates has a problem that production cost becomes high.
SUMMARY OF THE INVENTION
[0039] In view of the above, an object of the present invention is
to provide a dummy substrate of excellent durability used in each
semiconductor device fabricating process step, in particular,
cleaning and drying process steps. Furthermore, another object of
the present invention is to provide a substrate processing method,
which can reduce the number of times that dummy substrates are
exchanged, the probability that the dummy substrate will be broken,
the frequency that processing apparatuses such as the drum-type
spin cleaning apparatuses are stopped, and production cost.
[0040] In order to achieve the above object, a dummy substrate of
the present invention has substantially the same mass as each of
to-be-processed substrates and made of a plate material, at least
the outer edge of said plate material being coated with a
resin.
[0041] In this way, the resin coating increases the strength of the
dummy substrate, restrains the dummy substrate from being damaged
and, even when the dummy substrate is damaged, suppresses the
scattering of pieces thereof. The adjustment of the total number of
the at least one dummy substrate and the to-be-processed substrates
permits the adjustment of the gross mass of the dummy substrate and
the to-be-processed substrates, because the dummy substrate has
substantially the same mass as each to-be-processed substrate.
[0042] According to the dummy substrate of the present invention,
the entire surfaces of the plate material are preferably coated
with the resin.
[0043] This further ensures that the resin coating can restrain the
dummy substrate from being damaged and, when the dummy substrate is
damaged, suppress the scattering of pieces thereof.
[0044] The dummy substrate preferably has substantially the same
shape and size as each said to-be-processed substrate.
[0045] This allows the dummy substrate to be handled like the
to-be-processed substrates when various processes, such as
cleaning, are performed to fabricate electronic devices.
[0046] The resin with which the dummy substrate is coated is
preferably chemical-resistant.
[0047] This can reduce an influence of etching on the dummy
substrate when the to-be-processed substrates are processed by a
chemical solution. Therefore, the number of times that the dummy
substrate can repeatedly be used can be increased.
[0048] The resin with which the dummy substrate is coated is
preferably conductive.
[0049] This can prevent static electricity from being produced by
friction between a processing atmosphere and the resin when the
cassettes or the like containing the to-be-processed substrates are
cleaned or dried while being rotated. This can restrain particles
from being deposited on the dummy substrate due to static
electricity.
[0050] Any one of the principal surfaces of the dummy substrate is
preferably marked.
[0051] This facilitates discrimination between the two principal
surfaces of the dummy substrate. The marking can be utilized to
discriminate between the dummy substrate and each to-be-processed
substrate.
[0052] The plate material is preferably a single crystal silicon
substrate or a substrate containing single crystal silicon.
[0053] This can increase the number of times that the dummy
substrate can repeatedly be used, because the single crystal
silicon is resistant to a chemical solution containing acid or
alkali. In addition, the to-be-processed substrates can be
prevented from being contaminated, because a substance leading to
contamination never leaks out of the dummy substrate and dissolves
in a cleaning solution.
[0054] In this case, the substrate containing single crystal
silicon means a substrate including a part of the substrate made of
single crystal silicon and a part thereof made of a material other
than single crystal silicon, e.g., Silicon on Insulator (SOI) or
the like.
[0055] In order to solve the above problem, a substrate processing
method according to a first aspect of the present invention
comprises the steps of: containing a plurality of to-be-processed
substrates in each of a plurality of containers; containing the at
least one dummy substrate of Claim 1 in each said container as
necessary to place the same total number of the to-be-processed
substrates and said at least one dummy substrate in each said
container; and placing the plurality of containers containing the
dummy substrates to be symmetric about a rotation axis and
processing the to-be-processed substrates while rotating the
containers about the rotation axis.
[0056] In this way, if the same total number of the to-be-processed
substrates and the necessary number of the dummy substrates is
contained in each of containers (for example, cassettes), the gross
mass of any one cassette and the necessary number of the dummy
substrates and the to-be-processed substrates both contained in the
container (cassette gross mass) can be the same as that for any
other container. The reason for this is that the dummy substrate
has substantially the same mass as each to-be-processed substrate.
In view of the above, a balanced mass can be achieved when the
to-be-processed substrates are processed while being rotated. In
addition, various effects of the dummy substrate of the present
invention can be utilized.
[0057] In the substrate processing method according to the first
aspect of the present invention, in the step of processing the
to-be-processed substrates, the to-be-processed substrates are
preferably cleaned by spraying a chemical solution onto the
to-be-processed substrates with the plurality of containers
rotated.
[0058] The sprayed chemical solution preferably contains acid or
alkali.
[0059] In this way, for example, the number of times that the dummy
substrate is exchanged can be reduced in a cleaning process.
[0060] In the substrate processing method according to the first
aspect of the present invention, in the step of processing the
to-be-processed substrates, the to-be-processed substrates are
preferably dried with the plurality of containers rotated.
[0061] In this way, for example, the number of times that the dummy
substrate is exchanged can be reduced in a drying process. If in
this case the resin with which the dummy substrate is coated is a
conductive resin, this can prevent static electricity from being
produced.
[0062] A substrate processing method according to a second aspect
of the present invention comprises the steps of: containing a
plurality of to-be-processed substrates in a container to create
such a row that the principal surfaces of the adjacent
to-be-processed substrates are faced to each other; containing the
at least one dummy substrate of Claim 1 in the container such that
the principal surface of the dummy substrate is faced to the
principal surface of the to-be-processed substrate located at the
end of the row; and processing the to-be-processed substrates
together with the container containing the dummy substrate.
[0063] This allows particles raised with the rotation of the
container to be deposited almost intensively on the dummy
substrate. Therefore, particles can be prevented from being
deposited on the to-be-processed substrates. In addition, various
effects of the dummy substrate of the present invention can be
utilized. For example, the number of times that the dummy substrate
is exchanged can be reduced.
[0064] A substrate processing method according to a third aspect of
the present invention comprises the steps of: containing a
plurality of to-be-processed substrates in a container to create
such a row that the principal surfaces of the adjacent
to-be-processed substrates are faced to each other; containing the
at least one dummy substrate of Claim 1 in the container by holding
any one of the two principal surfaces of the dummy substrate by a
substrate holder, the other principal surface of the dummy
substrate different from the held principal surface being faced to
the principal surface of the to-be-processed substrate located at
the end of the row; and processing the to-be-processed substrates
together with the container containing the dummy substrate.
[0065] In this case, for example, vacuum tweezers can be used as
the substrate holder.
[0066] This allows particles raised with the rotation of the
container to be deposited almost intensively on the dummy
substrate. Therefore, particles can be prevented from being
deposited on the to-be-processed substrates.
[0067] Furthermore, particles deposited on the dummy substrate
during the handling of the dummy substrate can be prevented from
being transferred to the to-be-processed substrates. The reason for
this is that the principal surface of the dummy substrate on which
particles are deposited is not faced to the principal surface of
each to-be-processed substrate.
[0068] In addition, various effects of the dummy substrate of the
present invention can be utilized. For example, the number of times
that the dummy substrate is exchanged can be reduced.
[0069] In the substrate processing method according to the third
aspect of the present invention, it is preferable that any one of
the two principal surfaces of the dummy substrate is marked, that
when any one of the two principal surfaces is held, the marked
principal surface is held, and that the other principal surface
different from the held principal surface is not marked.
[0070] In this way, the marking facilitates discrimination between
two surfaces of the dummy substrate. Therefore, the opposite
surface of the dummy substrate to the held surface thereof can
easily be faced to each to-be-processed substrate.
[0071] A substrate processing method according to a fourth aspect
of the present invention comprises the steps of: containing a
plurality of to-be-processed substrates and the dummy substrate of
Claim 1 in a container; and soaking the plurality of
to-be-processed substrates into a chemical solution together with
the container containing the dummy substrate, thereby processing
the to-be-processed substrates.
[0072] In this way, when the to-be-processed substrates are soaked
into a chemical solution, the effects of the dummy substrate of the
present invention can be realized.
[0073] As described above, the dummy substrate of the present
invention is obtained by covering a plate material with a resin to
have substantially the same mass as each to-be-processed substrate.
The adjustment of the total number of the dummy substrate and the
to-be-processed substrates permits the adjustment of the gross mass
of the dummy substrate and the to-be-processed substrates, because
the dummy substrate has substantially the same mass as each
to-be-processed substrate. Furthermore, the resin coating can
restrain the dummy substrate from being deteriorated by gradually
etching the dummy substrate through a cleaning treatment using a
caustic chemical solution and suppress reduction in the mechanical
strength of the dummy substrate with the deterioration thereof.
Since the resin coating can prevent pieces and particles of the
damaged dummy substrate from scattering, this eliminates the need
for exchanging a chamber of a processing apparatus and can suppress
contamination of the to-be-processed substrates.
[0074] According to the substrate processing method using the dummy
substrate, the dummy substrate can be restrained from being damaged
during a process including high-speed rotation, such as cleaning
using a drum-type spin cleaning apparatus, and the number of times
that the dummy substrate can repeatedly be used can be increased.
Therefore, the frequency of the exchange of the dummy substrate can
be reduced.
[0075] In view of the above, the production cost of a semiconductor
device can be reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0076] FIGS. 1A and 1B are a side view and a plan view,
respectively, illustrating the structure of a dummy substrate
according to an embodiment of the present invention.
[0077] FIG. 2 is a diagram illustrating a method for containing a
dummy substrate 100 and to-be-processed substrates 104 in a
cassette 204 according to the embodiment of the present
invention.
[0078] FIG. 3 is a side view illustrating an internal structure of
a drum-type spin cleaning apparatus used for a substrate processing
method according to the embodiment of the present invention.
[0079] FIG. 4 is a top view illustrating the internal structure of
the drum-type spin cleaning apparatus used for the substrate
processing method according to the embodiment of the present
invention.
[0080] FIG. 5 is a side view illustrating an internal structure of
a known drum-type spin cleaning apparatus.
[0081] FIG. 6 is a top view illustrating the internal structure of
the known drum-type spin cleaning apparatus.
DETAILED DESCRIPTION OF THE INVENTION
[0082] A dummy substrate according to an embodiment of the present
invention will be described hereinafter with reference to the
drawings.
[0083] FIGS. 1A and 1B are a side view and a plan view,
respectively, illustrating the structure of a dummy substrate 100
according to the embodiment of the present invention.
[0084] The dummy substrate 100 is obtained by covering, for
example, the entire surfaces of a single crystalline silicon
substrate 101 for forming an electronic device with a resin coating
102. The entire surfaces of the single crystal silicon substrate
101 include the side surface thereof. In this case, the two
principal surfaces of the single crystal silicon substrate 101,
i.e., mirror parts thereof, are previously grinded to provide a
surface roughness (Ra) of 2 .mu.m or more. The irregularities of
the principal surfaces 103 thus provided facilitate bringing the
resin coating 102 into strong contact with the silicon substrate
101.
[0085] It is desirable that a material resistant to a chemical
solution for cleaning (a mixed solution of H.sub.2SO.sub.4 and
H.sub.2O.sub.2 or a mixed solution of NH.sub.4OH and H.sub.2O.sub.2
both having a temperature of approximately 50.degree. C. through
160.degree. C.) used in a semiconductor fabricating process is
selected as a material of the resin coating 102. Perfluoroalkoxy
polymer made of a fluorine-containing resin or the like has
excellent chemical resistance. The polymer has desirable
properties, e.g., excellent heat resistance.
[0086] The resin coating 102 is formed, for example, in the
following manner: a plate material to which coating is applied,
such as the silicon substrate 101, is put on a base; the plate
material is coated with resin powders by a spray gun; and then the
resin is cured using a furnace. The opposite surface of the plate
material to the coated surface thereof is also coated with resin
powders and then the resin is cured likewise.
[0087] In this relation, it is one of the intended purposes of the
dummy substrate 100 to strike a balance of masses among
semiconductor substrate cassettes 204 (which are containers shown
in FIG. 2 and will be described later) during high-speed rotation
in a batch-type and drum-type spin cleaning apparatus (which is an
apparatus shown in FIGS. 3 and 4 and will be described in detail
later). In order to facilitate this, the dummy substrate 100 need
have substantially the same weight as a to-be-processed substrate.
More specifically, the dummy substrate 100 need weigh 95% through
105%, both inclusive, of the weight of the to-be-processed
substrate.
[0088] When an 8-inch or 200-mm wafer is taken as an example, its
weight is 51 g through 55 g both inclusive, for example, and
therefore the weight of the dummy substrate 100 need also be 51 g
through 55 g both inclusive.
[0089] To cope with this, adjustment is made to how much the
principal surfaces 103 are to be grinded and the thickness of the
resin coating 102. Since the weight of a resin depends on types of
the resin, the thickness of the resin coating 102 is determined
depending on the type of the resin used therefor.
[0090] Furthermore, the dummy substrate 100 preferably has
substantially the same shape and dimensions as the to-be-processed
substrate. For example, the dummy substrate 100 is adapted to the
to-be-processed substrate and thus allowed to have a diameter of
200 mm and a thickness falling within a range of 545 .mu.m through
555 .mu.m both inclusive.
[0091] This allows the dummy substrate 100 and the to-be-processed
substrates to be handled likewise by vacuum tweezers or the
like.
[0092] As described above, the dummy substrate 100 of this
embodiment uses the silicon substrate 101 as a base, is obtained by
covering the entire surfaces of the silicon substrate 101 with the
resin coating 102, and has the same shape and size as the silicon
substrate on which an electronic device is formed. Therefore, the
resin coating 102 increases the strength of the dummy substrate
100. In addition, the dummy substrate 100 is hardly affected by a
chemical solution during the cleaning process step or the other
process steps and thus the thickness of the silicon substrate
inside the dummy substrate 100 is not decreased. As a result, the
strength of the dummy substrate 100 is very unlikely to be
deteriorated. Therefore, there is very little possibility that the
dummy substrate 100 will be damaged during a cleaning process using
the drum-type spin cleaning apparatus.
[0093] In view of the above, the number of uses of the dummy
substrate 100 of this embodiment can significantly be increased as
compared with the known dummy substrate. As a result, the number of
exchanges of the dummy substrates can be reduced, resulting in the
reduced production cost of semiconductor devices.
[0094] Furthermore, even if the silicon substrate 101 is damaged
inside the dummy substrate 100, the viscosity of the resin coating
102 can prevent pieces of the silicon substrate 101 from being
scattered inside a chamber of the cleaning apparatus. This
eliminates the need for exchanging the chamber itself every time
the dummy substrate is broken. This also contributes to reduction
in the production cost of semiconductor devices.
[0095] For the dummy substrate 100 of this embodiment, the entire
surfaces of the silicon substrate 101 serving as a base as shown in
FIG. 1 are covered with the resin coating 102. For a dummy
substrate obtained by covering only a part of the silicon substrate
101 with the resin coating 102, a chemical solution penetrates
between the silicon substrate 101 and the resin coating 102, and
the silicon substrate 101 is etched due to the chemical solution.
However, the use of the dummy substrate 100 obtained by covering
the entire surfaces of the silicon substrate 101 with the resin
coating 102 as described above can prevent such a chemical solution
from penetrating therebetween and the silicon substrate 101 from
being etched. Therefore, it is an optimum substrate as a dummy
substrate of this embodiment. However, in some cases, a dummy
substrate 100 obtained by covering only the outer edges of the two
principal surfaces of the silicon substrate 101 with the
chemical-resistant resin coating 102 is also available.
[0096] Such a dummy substrate 100 obtained by covering only the
outer edges with the resin coating 102 may be likely to be
deteriorated from the border between a part of the silicon
substrate 101 that is covered with the resin coating 102 and a part
thereof that is not covered with the resin coating 102. In other
words, it may be likely that a chemical solution will penetrate
from the border and the penetration of the chemical solution will
cause the resin to peel off.
[0097] In spite of this problem, during the spin drying of a
substrate on which a semiconductor integrated circuit is formed,
the dummy substrate 101 obtained by covering only the outer edges
with the resin coating 102 is also available without any problem.
During high-speed rotation for drying, forces due to centrifugal
force are applied to an edge part of the dummy substrate 101
including the side surface thereof and coming into contact with a
cassette. In spite of this, since the resin coating 102 increases
the strength of this part, the dummy substrate 101 can be
restrained from being damaged. Furthermore, the above-mentioned
dummy substrate 101 obtained by covering only the outer edge with
the resin coating 102 can be produced at a lower cost than the
dummy substrate 100 obtained by covering the entire surfaces of the
silicon substrate 101 with the resin coating 102. The reason for
this is that the amount of a resin used for the resin coating 102
is small.
[0098] The top surface of the dummy substrate 100 cannot easily be
discriminated from the back surface thereof as it is. To cope with
this, for example, before covering the dummy substrate 100 with the
resin coating 102, a marking, such as "back", "back surface",
"backside", or the like, should be applied to the back surface of
the silicon substrate 101 by a laser or the like.
[0099] This facilitates discriminating between the top surface and
the back surface of the dummy substrate 100 and discriminating
between the dummy substrate 100 and each to-be-processed substrate.
However, a marking method and specific marking contents are not
specifically limited. Marking may be applied not to the back
surface of the dummy substrate 100 but to the top surface thereof.
If necessary, marking may be applied to both the top and back
surfaces thereof.
[0100] The resin coating 102 is preferably formed of a resin
allowed to have conductivity, for example, by combining conductive
particles or fibers (for example, particles or fibers made of a
substance for suppressing the amount of charges on the resin, such
as carbon) into the resin coating 102. When the silicon substrate
101 is covered with the resin coating 102 of a conductive resin as
described above, this can reduce the amount of static electricity
generated on the dummy substrate 100. As a result, particles can be
restrained from being deposited on the dummy substrate 100 due to
static electricity. This can prevent particles from being
transferred to the to-be-processed substrate 104 if the dummy
substrate 100 and the to-be-processed substrates 104 are contained
in each cassette 204 with one principal surface of the dummy
substrate 100 faced to that of the adjacent to-be-processed
substrates 104 as will be described later. This can improve the
production yield of semiconductor devices.
[0101] A silicon single-crystal substrate is used as the
above-mentioned plate material serving as the base of the dummy
substrate 100. As long as the dummy substrate 100 is formed to have
the same shape and size as a silicon substrate that is to be
processed together and on which an electronic device is to be
formed, a substrate containing a silicon single crystal or a quartz
glass substrate may be used instead of the silicon single-crystal
substrate.
[0102] Furthermore, when the entire surfaces of the silicon
substrate 101 is covered with a chemical-resistant resin, further
various materials can be used instead of the silicon single-crystal
substrate. The reason for this is that the base is not exposed at
the surface of the dummy substrate 100. For example, metals,
alloys, metal compounds, or ceramic, or a combination of these
materials can also be used. The dummy substrate 100 need only have
a mass similar to the mass of the substrate on which an electronic
device is formed. In this case, electronic devices can further be
reduced in production cost by reducing the cost of the dummy
substrate 100. The reason for this is that a material having a
lower cost than the silicon substrate can be selected as a material
of the base.
[0103] Next, a method for processing a semiconductor device using
dummy substrates according to this embodiment will be described
with reference to the drawings by using a cleaning process as an
example.
[0104] First, as shown in FIG. 2, a dummy substrate 100 and a
plurality of to-be-processed substrates 104 are contained in a
cassette 204. FIG. 2 shows the cassette but does not show a part
thereof along the horizontal direction.
[0105] Initially, attention is given to the case where the number
of the to-be-processed substrates 104 to be processed together can
be divided so that the same number of to-be-processed substrates
104 can be contained in each of a plurality of cassettes 204. In
other words, attention is given to the case where the number of the
to-be-processed substrates 104 for each lot is a multiple of the
number of the cassettes 204 to be used.
[0106] In this case, a single dummy substrate 100 is placed in the
uppermost part of each cassette 204. More particularly, as shown in
FIG. 2, a predetermined number of to-be-processed substrates 104
are arranged and contained in each cassette 204 in bottom-to-top
order or in top-to-bottom order to form a row, and further the
dummy substrate 100 is placed above this row. In this relation,
FIG. 2 shows how the single dummy substrate 100 is contained in the
uppermost part of the cassette 204 and a maximum number of
to-be-processed substrates 104 that can be contained in the
cassette 204 are contained therein.
[0107] Next, attention is given to the case where the number of the
to-be-processed substrates 104 to be processed together does not
allow the same number of to-be-processed substrates 104 to be
contained in each cassette 204. In other words, attention is given
to the case where the number of the to-be-processed substrates 104
for each lot is not a multiple of the number of the cassettes 204
to be used.
[0108] In this case, the same total number of at least one dummy
substrate 100 and to-be-processed substrates 104 (the total number
of contained substrates) need be contained in each of all the
cassettes 204 to be used together. As a result, additional dummy
substrates 100 are contained in some of the cassettes 204.
[0109] Dummy substrates 100 to additionally be contained in some of
the cassettes 204 need be contained above the to-be-processed
substrates 104, for example, contained in the some of the cassettes
204 in bottom-to-top order or in top-to-bottom order. A plurality
of dummy substrates 100 are placed above this row of the
to-be-processed substrates 104 to align therewith. However, this
method for containing substrates is not restrictive.
[0110] The to-be-processed substrates 104 may be contained in the
cassettes 204 after the dummy substrates 100 have been contained
therein.
[0111] If the same total number of contained substrates are placed
in each cassette 204 in the above-mentioned manner, the gross mass
of any one cassette 204 and at least one dummy substrate 100 and
to-be-processed substrates 104 both contained in the cassette
(cassette gross mass) can be the same as that for any other
cassette 204. The reason for this is that the dummy substrate 100
has substantially the same mass as the to-be-processed substrate
104.
[0112] Thus, eccentricity can be prevented from being caused during
spin cleaning. Although the dummy substrate 100 and the
to-be-processed substrates 104 might be damaged due to strong
vibrations or the like caused by the eccentric spinning of the
dummy substrate 100 and the to-be-processed substrates 104, the
above-mentioned prevention of eccentricity can prevent such damage.
This increases the number of times that the dummy substrate 100 can
repeatedly be used and improves the production yield of
semiconductor devices. In addition, the effect of the dummy
substrate of this embodiment can be utilized. The above contributes
to reduction in production cost of semiconductor devices.
[0113] Either the top or back surfaces of the to-be-processed
substrates 104 may be directed upward in the containment of the
to-be-processed substrates 104. On the other hand, when the dummy
substrate 100 is contained in the cassette 204, the top surface of
the dummy substrate 100 is preferably discriminated from the back
surface thereof. The reason for this is as follows.
[0114] When the dummy substrate 100 is contained in the cassette
204, the dummy substrate 100 is handled by unshown vacuum tweezers
or the like with any one of its two principal surfaces held. The
principal surface of the dummy substrate 100 thus held is referred
to as "held surface 105". During the handling of the dummy
substrate 100, particles may be transferred from the vacuum
tweezers or the like to the held surface 105. In this case, if the
dummy substrate 100 is contained in the cassette 204 with its held
surface 105 faced to the adjacent to-be-processed substrate 104,
particles might be transferred from the held surface 105 to the
to-be-processed substrate 104. In order to avoid this, the dummy
substrate 100 is contained in the cassette 204 such that its
non-held surface 106 opposite to its held surface 105 is faced to
the adjacent to-be-processed substrate 104.
[0115] This can prevent particles from being transferred to the
to-be-processed substrates 104 and avoid deterioration in the
qualities of semiconductor devices due to particles and reduction
in the yield of semiconductor devices.
[0116] In this relation, in order to facilitate discriminating
between the top and back surfaces of such a dummy substrate 100,
there is preferably used a dummy substrate 100 marked to
discriminate between its top and back.
[0117] Thus, the dummy substrate 100 can be contained in the
cassette 204 such that the non-held surface 106 is certainly faced
to the to-be-processed substrate 104. This can facilitate
preventing particles from being transferred from the dummy
substrate 100 to the to-be-processed substrate 104.
[0118] Next, a description will be given of a drum-type spin
cleaning apparatus for executing processes, such as cleaning, with
reference to FIGS. 3 and 4. Cassettes 204 each containing at least
one dummy substrate 100 and a plurality of to-be-processed
substrates 104 are provided for the drum-type spin cleaning
apparatus.
[0119] FIG. 3 is a diagram illustrating an example of an internal
structure of a drum-type spin cleaning apparatus used in this
embodiment when viewed from side.
[0120] As shown in FIG. 3, a turntable 201 is placed inside a
cylindrical chamber 200, and a shaft 202 is coupled to the lower
surface of the turntable 201 at the site of a rotation axis of the
turntable 201 and furthermore is connected to a motor 203 located
below the chamber 200. The rotation of the motor 203 allows the
turntable 201 to rotate at a high speed of, for example, 1000 rpm
or more, with the shaft 202 interposed between the motor 203 and
the turntable 201.
[0121] Bar guides 205 are placed on the turntable 201 to fix
cassettes 204 into which a plurality of substrates including a
plurality of to-be-processed substrates 104, such as semiconductor
substrates, and at least one dummy substrate 100 are inserted. The
use of the guides 205 allows the cassettes 204 to be placed
symmetrically about the rotation axis of the turntable 201. The
arrangement of the cassettes 204 and guides 205 will be described
later in detail with reference to FIG. 4.
[0122] A spray nozzle 207 protrudes from the middle part of a top
lid 206 of the cleaning apparatus to be perpendicular to the top
lid 206. The closure of the top lid 206 allows the spray nozzle 207
to be located above the rotation axis of the turntable 201. During
cleaning, a chemical solution for cleaning 208 containing acid or
alkali can be horizontally sprayed from the spray nozzle 207 onto
the to-be-processed substrates 104 or the dummy substrate 100. The
chemical solution for cleaning 208 is supplied from the outside of
the cleaning apparatus to the spray nozzle 207 through a chemical
solution supply pipe 209.
[0123] Cleaning is carried out by spraying the chemical solution
for cleaning 208 onto the to-be-processed substrates 104 and the
dummy substrate 100 and rotating the cassettes 204 together with
the turntable 201. This makes uniform cleaning possible.
[0124] Not only a chemical solution for cleaning but also pure
water can be sprayed by the spray nozzle 207. At least one side
spray nozzle 210 for supplying additional pure water is also
mounted in the vicinity of and with a certain distance from the
turntable 201. Pure water is supplied through a pure water supply
pipe 211.
[0125] FIG. 4 is a diagram illustrating an example of the internal
structure of the drum-type spin cleaning apparatus when viewed from
above.
[0126] FIG. 4 illustrates a turntable 201, cassettes 204 placed on
the turntable 201, guides 205 through which the cassettes 204 are
fixed, a plurality of substrates including a plurality of
to-be-processed substrates 104 and at least one dummy substrate 100
and put into each cassette 204. The other components are not shown.
As illustrated in FIG. 4, four sets of (eight) guides 205 are
placed on the turntable 201, and the cassette 204 is fixed by the
associated sets of guides 205. The use of these guides 205 allows
two or four cassettes 204 to be placed symmetrically about the
rotation axis.
[0127] Next, a cleaning method using the drum-type spin cleaning
apparatus shown in FIGS. 3 and 4 will be described.
[0128] First, as described above, the cassettes 204 each containing
at least one dummy substrate 100 and a plurality of to-be-processed
substrates 104 are placed inside the chamber 200 of the drum-type
spin cleaning apparatus shown in FIGS. 3 and 4 by using the guides
205. At this time, the cassettes 204 are arranged to be symmetric
about the rotation axis of the turntable 201. For example, two or
four cassettes 204 can be processed together by the drum-type spin
cleaning apparatus shown in FIGS. 3 and 4. If in this case four
cassettes 204 are used, the cassettes 204 can be placed
symmetrically about the rotation axis of the turntable 201 by
mounting the cassettes 204 to four sets of guides 205,
respectively. If only two cassettes 204 are used, they are mounted
to two sets of guides 205 faced to each other with the rotation
axis interposed therebetween.
[0129] In this way, balanced rotation can be achieved, because the
cassette gross mass of each cassette is the same.
[0130] Next, the top lid 206 is closed, and then the rotation of
the turntable 201 allows the cassettes 204 to rotate at a high
speed. In addition, the chemical solution for cleaning 208 is
sprayed from the spray nozzle 207 toward the cassettes 204, thereby
performing cleaning.
[0131] In this relation, a chemical solution containing acid or
alkali is preferably used as the chemical solution for cleaning 208
for the above cleaning process. For example, a mixed solution of
H.sub.2SO.sub.4 and H.sub.2O.sub.2 (to be used at approximately
100.degree. C.) or a mixed solution of NH.sub.4OH and
H.sub.2O.sub.2 (to be used at approximately 70 through 80.degree.
C.) is used thereas. These chemical solutions are used mainly for
cleaning before resist ashing, oxidation or the deposition of a CVD
film. As long as an appropriate chemical solution for cleaning 208
is selected, the chemical solution can be used for cleaning for
removing organic materials produced by etching reaction after
contact etching or via etching or the removal of reaction products
produced by etching for forming metal interconnects.
[0132] The use of the dummy substrate 100 covered with the
chemical-resistant resin coating 102 can prevent the dummy
substrate 100 from being etched by a cleaning process. This
increases the number of times that the dummy substrate 100 can
repeatedly be used, leading to the reduced production cost of
semiconductor devices.
[0133] By the way, the high-speed rotation of the turntable 201
allows particles in the chamber 200 to be raised. If such particles
are deposited on the to-be-processed substrates 104, this causes
reduction in the qualities of fabricated semiconductor devices.
However, as described above, the dummy substrate 100 is contained
in the uppermost part of a row of the to-be-processed substrates
104 located in each cassette 204, thereby depositing most particles
to the dummy substrate 100 and preventing the particles from being
deposited on the to-be-processed substrates 104.
[0134] Furthermore, the to-be-processed substrates 104 are cleaned
by the drum-type spin cleaning apparatus, and then the
to-be-processed substrates 104 are subjected to spin drying in the
same chamber 200. At this time, static electricity might be
produced by friction between the atmosphere in the chamber and the
dummy substrate, because the cleaning apparatus is of a spinning
type.
[0135] This production of static electricity is likely to deposite
particles to the dummy substrate 100. Therefore, secondary
contamination arising from particles is likely to be caused, for
example, on the to-be-processed substrate 104 placed immediately
below the dummy substrate 100 shown in FIG. 2.
[0136] However, the use of the dummy substrate 100 covered with the
conductive resin coating 102 can suppress the production of static
electricity during drying. This prevents particles from being
deposited on the to-be-processed substrates 104, resulting in
reduced secondary contamination.
[0137] Even when the to-be-processed substrates 104 are not dried
in the chamber 200 of the drum-type spin cleaning apparatus but
dried separately by a spin dryer, the use of the dummy substrate
100 covered with the conductive resin coating 102 can again
suppress static electricity.
[0138] Although in this embodiment processes using a drum-type spin
cleaning apparatus and a drum-type spin drying apparatus (including
an apparatus that can perform functions of both the apparatuses)
have been described, the dummy substrate 100 of this embodiment can
be used also for apparatuses of other kinds. For example, as
described above, it can also be used for a processing method in
which, for example, the dummy substrate 100 and the to-be-processed
substrates 104 are contained in each cassette 204 and soaked into a
chemical solution together with each cassette 204 to clean the
to-be-processed substrates 104. Also in this case, the effects of
the dummy substrate 100 of this embodiment can be utilized. For
example, the number of times that the dummy substrate 100 can
repeatedly be used is increased more than in the use of a known
dummy substrate by covering the dummy substrate 100 with the resin
coating 102. This can reduce the production cost of semiconductor
devices.
* * * * *