U.S. patent application number 10/656745 was filed with the patent office on 2004-03-18 for method and apparatus for coating a wafer.
Invention is credited to Courtenay, Robert William.
Application Number | 20040052956 10/656745 |
Document ID | / |
Family ID | 24021179 |
Filed Date | 2004-03-18 |
United States Patent
Application |
20040052956 |
Kind Code |
A1 |
Courtenay, Robert William |
March 18, 2004 |
Method and apparatus for coating a wafer
Abstract
Disclosed is a method and apparatus for coating liquid films on
to the surface of a wafer substrate by rotating the substrate at a
speed sufficient to cause a liquid, through centrifugal effect, to
flow outwardly toward the perimeter of the surface and form a
substantially uniform thickness liquid coating thereon and starting
at the central region of the wafer surface and moving radially
outward therefrom, spraying a fine mist of the liquid to the
surface of the wafer.
Inventors: |
Courtenay, Robert William;
(Boise, ID) |
Correspondence
Address: |
Charles Brantley
Micron Technology, Inc.
MS 1-525
8000 S Federal Way
Boise
ID
83716
US
|
Family ID: |
24021179 |
Appl. No.: |
10/656745 |
Filed: |
September 5, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10656745 |
Sep 5, 2003 |
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10155450 |
May 22, 2002 |
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6666917 |
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10155450 |
May 22, 2002 |
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09292081 |
Apr 14, 1999 |
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6423380 |
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09292081 |
Apr 14, 1999 |
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08949072 |
Oct 10, 1997 |
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5902399 |
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08949072 |
Oct 10, 1997 |
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08508051 |
Jul 27, 1995 |
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Current U.S.
Class: |
438/780 ;
118/722; 427/425; 427/96.7; 438/782 |
Current CPC
Class: |
B05C 11/08 20130101;
G03F 7/162 20130101; B05B 13/0228 20130101 |
Class at
Publication: |
427/421 ;
427/425 |
International
Class: |
B05D 001/02 |
Claims
I claim:
1. A process for applying solutions on a semiconductor wafer which
comprises: (a) rotating a substrate about a central point thereof;
(b) dispensing a solution mist from a spray nozzle onto a top
surface of said rotating substrate; (c) said dispensing nozzle
moving radially between the central axis and an edge of the
substrate while dispensing said solution.
2. The process of claim 1 wherein the rotational speed of the
semiconductor wafer is. less than 2500 rpm.
3. The process of claim 2 wherein the spray nozzle is selected from
the list consisting of atomizer nozzle and airless spray-mist
nozzle.
4. A method for forming a coating upon a planar substrate having an
upper surface which comprises (a) rotating the substrate at a speed
sufficient through centrifugal effect to cause a solution to flow
outwardly toward the perimeter of the surface and form a
substantially uniform thickness liquid coating thereon, (b)
starting at the central region of the planar surface and moving
radially outward therefrom, and (c) spraying a mist of the liquid
to the surface.
5. The process of claim 4 wherein the rotational speed of the
semiconductor wafer is less than 2500 rpm.
6. A process for applying solutions on a substrate which comprises:
(a) rotating a substrate about a central point thereof; (b)
dispensing a polymer dielectric mist from a spray nozzle onto a top
surface of said rotating substrate; (c) said dispensing nozzle
moving radially between the central axis and an edge of the
substrate while dispensing said solution.
7. An coating apparatus for coating a wafer of known diameter with
a substantially uniform coating of a solution, the apparatus
comprising: (a) a containment bowl; (b) a rotatable spin chuck
mounted inside the containment bowl; (c) a wafer attachment surface
on the chuck; (d) a dispersing mist spray nozzle moveably
positioned above the wafer attachment surface.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 09/292,081, filed Apr. 14, 1999; which is a continuation of
U.S. application Ser. No. 08/949,072, filed Oct. 10, 1997 and
issued as U.S. Pat. No. 5,902,399; which is a continuation of U.S.
application Ser. No. 08/508,051, filed Jul. 27, 1995, and now
abandoned.
TECHNICAL FIELD
[0002] The present invention relates to an apparatus and process
for coating solutions on to the surface of semiconductor
wafers.
BACKGROUND
[0003] The current practice in semiconductor manufacturing is to
use thin film fabrication techniques. A large variety of materials
can be deposited using thin films, including metals,
semiconductors, insulators and the like. The composition and
uniformity of these thin layers must be strictly controlled to
facilitate etching of submicron features. Many of these materials
are best suited to application of the substrate with a liquid which
is then dried to form the solid thin film. The liquid materials are
most often deposited using either spin or spray coating
methods.
[0004] In a conventional spin coating process the semiconductor
wafer to be processed is placed on a rotatable chuck and held in
place by vacuum. The chuck is referred to by a variety of names,
including spin chuck and vacuum chuck. The spin chuck has a
diameter slightly less than that of the semiconductor wafer. The
wafer is positioned on the chuck such that it is resting in a level
horizontal plane with the inactive surface, designated as the
bottom, in contact with the chuck and the opposite top surface is
coated with the desired solution. In standard systems the chuck is
powered and rotated by a motor.
[0005] In the spin coating process, the solution can be dispensed
prior to spinning the wafer, which is referred to as static
dispense or after the semiconductor wafer has been set in motion,
which is termed dynamic dispense. In either case after the solution
has been dispensed onto the top surface, the wafer is spun at a
constant speed to establish a desired relatively uniform thickness
of the solution across the wafer. Once the liquid layer acquires
the relatively uniform and symmetrical profile, the remainder of
the spin cycle allows the solvent in the solution to evaporate to
produce a solid film on the wafer top surface.
[0006] The supply of the solution is dispensed onto the wafer from
a supply nozzle. The nozzle can either be configured to simply drop
a specific quantity onto the semiconductor wafer surface in the
form of a puddle or to spray the desired quantity onto the wafer
surface in the form of a mist.
[0007] After the solution is dispensed onto the wafer it is
distributed uniformly over the surface largely as a result of the
radial distribution of the liquid due to centrifugal and drag
forces created by the spinning of the wafer.
[0008] The solution deposited on the wafer goes through a number of
stages during the spin process, primarily due to the fluid dynamics
created by the spinning substrate. At the start of the spinning a
wave of solution is created that moves towards the edge of the
wafer. As the major portion of the solution in the wave reaches the
edge of the wafer it forms a ridge, this is referred to as the
corona stage. A bead subsequently forms along the edge of the wafer
as the solvent evaporates from the ridge formed in the corona
stage. As the corona disappears the remaining solution leaves the
surface in the form of a fine spiral-like mist. This spiral stage
results in thousands of droplets spinning off the wafer and
splashing back onto the wafer off of the surrounding spinner bowl.
Bowls and splashguards have been designed to prevent this
splashing. Additionally, solvent washing of the bottom of the wafer
can eliminate the edge bead that forms during the spin coating.
[0009] Every layer deposited on the top surface of the wafer that
possesses irregularities and variations in its uniformity has an
adverse affect during all subsequent processing steps that the
wafer undergoes. Uniformity of the layers is a critical factor in
semiconductor wafer production. The film thickness uniformity
obtained using the spin coating process is largely a function of
size and shape of the wafer, because of the influence centrifugal
force has in the spin coat process. The fluid dynamics described
above become more pronounced as the diameter of the wafer used
increases and the trend is towards using larger wafers.
[0010] To compensate for these undesirable influences the standard
practice is to use a large starting volume of solution in the spin
coating process. A large starting volume of solution also
translates into a large amount of wasted solution. The increased
amount of solution used also means an increase in the cost of
production for semiconductor wafers. Approximately 30%-90% of the
process solution used in the spin coating process is wasted in the
form of excess solution that is thrown off of the wafer substrate.
The excess solution is deposited to assure a thin uniform layer in
the end product.
[0011] There have been a number of inventions proposed to alleviate
these problems. U.S. Pat. No. 5,395,649 to Ikeda, employs a plate
positioned above the wafer to change the air turbulence and fluid
behavior on the wafer for improved layer uniformity.
[0012] In U.S. Pat. No. 5,405,813 to Rodrigues, a plurality of
rotational speeds are used to increase layer uniformity and
decrease the amount of starting solution required.
[0013] A number of patents use different types of nozzle
mechanisms. U.S. Pat. No. 5,405,443 to Akimoto et al., discloses a
nozzle that dispenses a fixed quantity of solution without
entrainment of bubbles and particles utilizing a negative pressure
system. U.S. Pat. No. 4,267,212 to Shinichi, includes moving the
conventional spin coat nozzle across the radius of the wafer during
solution application while rotating the wafer at a first and second
speed. U.S. Pat. No. 5,403,617 to Haaland, enlists a computer
controlled droplet generator to select droplet size and velocity to
cause impact with the wafer without splashing. There is still a
demand in the semiconductor wafer manufacturing industry for more
economical means of solution application to the wafer that improves
the uniformity of the process layers on the wafers and uses less
chemicals.
[0014] The other major process used to deposit dielectrics on to
wafer substrates is a spray coat process. The spray coating process
permits much more efficient use of the process solution because the
large starting excess needed for the spin coating process is not
needed for the spray coating process. The problem with conventional
spray coat processes are that they require thorough and
comprehensive optimization of the process to obtain the quality of
uniform layer thickness that is more easily obtained with the spin
coat process. With the spray coat process the size and shape of the
wafer have little effect on the end result. The uniformity of
thickness of dielectric coating obtained using the spray process is
determined by the sweeping motion of the spray nozzle.
[0015] An alternative to using either the spin coat or spray coat
processes and their inherent problems is to coat the wafers using
chemical vapor deposition (CVD). The CVD process includes the
following basic steps: a) a known composition of reactant and inert
gases is introduced into a reaction chamber; b) the gas species
move to the substrate; c) the reactants are decomposed and
chemically reacted at a heated surface of the substrate; e) the
gaseous by-products are desorbed and removed from the reaction
chamber. With the CVD process high purity films can be formed and
deposited and a greater variety of starting compounds can be used.
There are certain compositions that cannot be adequately applied to
the wafer by any other process. The CVD process also had certain
disadvantages. It increases both the cost of wafer production and
increases the complexity of manufacturing the wafer. There are also
often defects in the uniformity of the layers deposited on the
wafer using the CVD process. Because of the increased cost and
complexity of the CVD process it is still used far less that either
spin or spray coating of the dielectrics onto semiconductor
wafers.
SUMMARY OF THE INVENTION
[0016] The present invention is a method for coating dielectrics on
to the surface of a wafer substrate by rotating the substrate at a
speed sufficient to cause a liquid, through centrifugal effect, to
flow outwardly toward the perimeter of the surface and form a
substantially uniform thickness liquid coating thereon and starting
at the central region of the wafer surface and moving radially
outward therefrom, spraying a fine mist of the liquid dielectric to
the surface of the wafer,
[0017] An advantage of the invention is that the amount of liquid
that is wasted as excess is reduced from as much as 90% to 10%.
Another advantage of the present invention is that less organic
solvent is used because less total material is required to coat the
wafer satisfactorily. Decreased use of organic solvent improves the
indoor air quality of the workplace as well as the safety and
overall improvement of the environment, over which there is
increasing concern and stricter regulation. The decrease in organic
solvents also decreases the risk of flammability and the problems
associated with proper disposal of organic solvents. The process of
the invention still allows for the decreased amount of material
associated with a spray coating process while still yielding the
layer uniformity achieved with a spin coating process. This process
also does not require the comprehensive fine tuning required in the
conventional spray coating process.
[0018] Additional objects, advantages and novel features of the
invention will be set forth in part in the description that
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 objects and advantages of the invention may
be realized and attained by means of the instrumentalities and
combinations particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE FIGURES
[0019] FIG. 1A is a representation of a prior art spin coating
device showing a coating liquid pooled at the center of a
wafer;
[0020] FIG. 1B is a representation of the wafer of FIG. 1A with the
wafer spinning to form a thin coat on top of the wafer;
[0021] FIG. 2 is a representation of the prior art spray coating
process; and
[0022] FIG. 3 is a representation of the spray/spin coating process
and apparatus according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0023] FIGS. 1 and 2 are schematic representations of the prior
art. FIG. 3 schematically represents the wafer coating method of
the present invention. A spin chuck 12, holds wafer 20 by vacuum to
allow spinning of wafer 20. In the preferred embodiment, wafer 20
is rotated at a speed ranging between 500 and 1500 rpm in an 50%
relative humidity environment at 72.degree. F., depending on the
solution that is going to be applied to wafer 20. Spin chuck 12
holding wafer 20 is enclosed by bowl 30 inside a housing. Bowl 30
can be moved up or down to surround wafer 20. Drain and exhaust
pipes are connected to the underside of bowl 30. The spatial
relationships and operation of spin chuck 12, wafer 20, bowl 30 and
the housing are omitted as they are known in the art.
[0024] While wafer 20 is being rotated within the proscribed speed
range nozzle 40 is positioned over the center point of wafer 20 and
dispensing of solution from nozzle 40 over already rotating wafer
20 is initiated. Nozzle 40 moves radially away from the central
point of wafer 20 while continuously dispensing the selected
solution. The radial speed of nozzle 40 as it moves radially away
from the center point of wafer 20 is constant. Dispensing of
solution by nozzle 40 is discontinued at a predetermined position,
here when nozzle 40 is within 1 cm of the outer edge of wafer 20.
It is also possible that the direction of nozzle 40 could be
reversed and start dispensing at the outside edge of wafer 20 and
discontinue dispensing at the center point of wafer 20. The nozzle
can be halted at the center by fixing a nozzle-stopper in a
position above the center of the chuck 12 and co-planar with the
nozzle 40. In another embodiment nozzle 20 can begin dispensing at
the outside edge of wafer 20, and dispense solution across a
diameter of wafer 20 and discontinue at the opposite outside edge
of wafer 20.
[0025] Nozzle 40 dispenses solution in the form of a fine mist in a
dispersed and divergent pattern. Examples of appropriate nozzles
include atomizing nozzles, airless spray nozzles, and the like.
Nozzle 40 is supplied from a separate pressurized reservoir.
[0026] The fine mist spray dispensing of solution of this invention
allows the wafer to be spun at a moderate speed. This more moderate
speed allows less of the coating solution to be thrown off of the
surface of wafer 20. This method allows up to a 90% efficiency in
usage of coating solution in the process. This greatly increases
the economy of semiconductor wafer production. One of the greatest
expenses in the production of semiconductor wafers is the cost of
the materials that wafer 20 must be coated with. With this method a
satisfactorily uniform coating can still be applied but with a
significantly smaller consumption of coating materials. This
process works well for polymer dielectrics, but can also be used
equally well for coating any solution onto the surface of
semiconductor wafers including polysiloxanes, photo resists,
developers, adhesives, protective coatings and the like.
[0027] It will therefore be understood that modifications and
variations are possible without departing from the scope of the
invention as expressed in the following claims.
* * * * *