Coating apparatus – Projection or spray type
Reexamination Certificate
1999-12-02
2002-03-05
Crispino, Richard (Department: 1734)
Coating apparatus
Projection or spray type
C118S052000, C118S623000, C118S625000, C118S730000, C427S096400, C427S240000, C427S425000, C427S458000, C438S758000, C239S690000
Reexamination Certificate
active
06352589
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus for spin-coating a semiconductor substrate, and a method of spin-coating a semiconductor substrate.
2. Description of the Related Art
There are many methods of coating a semiconductor substrate such as a silicon wafer and a mask substrate with chemical such as photoresist. A typical one among such methods is spin-coating.
In spin-coating, as illustrated in
FIG. 1
, a semiconductor substrate
1
is fixed on a rotary table
2
by means of a vacuum wafer chuck
3
. Chemical
5
is dropped onto a center
1
a of the semiconductor substrate
1
from an application nozzle
4
having a vertical axis A.
Then, a spindle shaft
6
is rotated to thereby rotate the rotary table
2
and accordingly the semiconductor substrate
1
in a direction indicated with an arrow B. As a result, there is generated centrifugal force exerts on the chemical
5
. The chemical
5
is uniformly spread over the semiconductor substrate
1
, and thus, there is formed a chemical coating layer
5
a
having a uniform thickness.
A thickness of the chemical coating layer
5
a
is dependent on various factors, in particular, on a viscosity of the chemical
5
.
The above-mentioned spin-coating is accompanied with a problem that the chemical coating layer
5
a
has a locally increased thickness at the center
1
a
and a periphery
1
b
of the semiconductor substrate
1
. The reason is as follows. The centrifugal force is equal to almost zero in the vicinity of the center
1
a
of the semiconductor substrate
1
. Hence, the centrifugal force does not exert on the chemical around the center
1
a
of the semiconductor substrate
1
, resulting in an increase in a thickness of the chemical coating layer
5
at the center l
a
. Since a peripheral speed of the semiconductor substrate
1
in the vicinity of the periphery
1
b
is relatively high, solvent contained in the chemical
5
is facilitated to volatilize, resulting in an increase in a thickness of the chemical coating layer
5
at the periphery
1
b.
As mentioned above, spin-coating cannot always provide a uniform thickness in a chemical coating layer. In order to solve this problem, many attempts have been suggested.
FIG. 2
illustrates one of apparatuses for spin-coating a semiconductor substrate having been suggested in order to solve the problem.
With reference to
FIG. 2
, in a chamber
11
of the spin-coating apparatus, there is installed a chuck designed to be rotatably driven by a motor
12
. Above the chuck
13
is situated a nozzle
15
through which chemical is dropped onto a wafer
14
fixed on the chuck
13
.
The chamber
11
is formed with a drain
11
a
through which residual chemical not used for coating is discharged and a discharge port
11
b
through which chemical scattering in the chamber
11
is discharged.
An electrode
16
is embedded in the chuck
13
. The electrode
16
is electrically connected to a negative terminal of a dc power source
17
.
The spin-coating apparatus illustrated in
FIG. 2
operates as follows.
First, the wafer
14
onto which chemical is to be applied is fixed on the chuck
13
, and then, chemical
18
is dropped onto a center of the wafer
14
through the nozzle
15
.
Then, the wafer
14
is rotated at 1000 rpm to thereby uniformly spread the chemical
18
over the wafer
14
. Thus, there is formed a chemical coating layer having a uniform thickness.
In accordance with the above-mentioned spin-coating apparatus, it is possible to apply the chemical onto the wafer
14
such that spaces between projections formed on a surface of the wafer
14
are filled with the chemical, if such spaces are relatively long, for instance, if such spaces are equal to or longer than 0.5 &mgr;m.
However, when such spaces are relatively small, for instance, if such spaces are equal to or smaller than 0.1 &mgr;m, it was impossible to fill the chemical in the spaces formed between projections, due to surface tension of the chemical
18
and/or resistance of air sealed between the spaces.
Hence, the spin-coating apparatus illustrated in
FIG. 2
is accompanied with a problem that a resultant photoresist has a pattern different from a designed pattern.
In order to solve this problem, Japanese Unexamined Patent Publication No. 4-135667 has suggested such an apparatus for spin-coating a semiconductor substrate as illustrated in FIG.
3
. Parts or elements that correspond to those of the spin-coating apparatus illustrated in
FIG. 2
have been provided with the same reference numerals.
The illustrated spin-coating apparatus is designed to include a second electrode
19
embedded in the nozzle
15
as well as the electrode
16
embedded in the chuck
13
. The second electrode
19
is electrically connected to a positive terminal of a dc power source
20
.
In the spin-coating apparatus illustrated in
FIG. 3
, dc voltages having opposite polarities are applied to the electrode
16
embedded in the chuck
13
and the second electrode
19
embedded in the nozzle
15
. Hence, there is generated Coulomb force between electric charges existing on a surface of the chemical
18
having been dropped from the nozzle
15
and electric charges existing on a surface of the wafer
14
placed on the chuck
13
. Thus, it is possible to fill the chemical
18
in small spaces formed between projections formed on the wafer
14
, which ensures to avoid formation of a photoresist having a pattern different from a designed pattern.
Japanese Unexamined Patent Publication No. 5-259053 has suggested an apparatus for spin-coating a semiconductor substrate, in order to solve the problem that a resultant photoresist has a pattern different from a designed pattern.
FIG. 4
illustrates the suggested spin-coating apparatus. The illustrated spin-coating apparatus is comprised of a rotary table
22
fixed to a spindle shaft
21
for rotation, an electrode table
24
facing the rotary table
22
and designed to raise and lower relative to the rotary table
22
by means of a support shaft
23
, and a nozzle
27
for dropping chemical
26
onto a wafer
25
, situated above the rotary table
22
and designed to be vertically movable.
A plurality of lower electrodes
28
are coaxially arranged and equally spaced in the rotary table
22
. The lower electrodes
28
are electrically connected to a power source (not illustrated) through wirings
29
arranged in the spindle shaft
21
.
A plurality of upper electrodes
30
are coaxially arranged and equally spaced in the electrode table
24
. The upper electrodes
30
are electrically connected to a power source (not illustrated) through wirings
31
arranged in the support shaft
23
.
The spin-coating apparatus illustrated in
FIG. 4
operates as follows.
After chemical
26
has been dropped onto the wafer
25
from the nozzle
27
, the nozzle
27
is raised. Then, the electrode table
24
is lowered to a certain position.
Then, the rotary table
22
is rotated to thereby spread the chemical
26
over the wafer
25
. During the rotary table
22
is being rotated, predetermined voltages are applied to both the lower electrodes
28
and the upper electrodes
30
. The application of the voltages makes it possible to uniformly spread the chemical
26
over the wafer
25
, ensuring photoresist having a desired pattern.
However, the spin-coating apparatuses illustrated in
FIGS. 3 and 4
are accompanied with such a problem as mentioned below.
In the spin-coating apparatus illustrated in
FIG. 3
, since the second electrode
19
faces only a central region of the electrode
16
, an electric field formed between the electrode
16
and the second electrode
19
has an intensity which is great only in a central region, and hence, an electric field formed around the electrode
16
can have a small intensity.
As a result, the chemical
18
tends to be concentrated to a central region of the wafer
14
rather than a periphery of the wafer
14
. Thus, the spin-coating apparatus illustrated in
FIG. 3
cannot always provide a uniform thickness in a chemical coating
Crispino Richard
Hutchins, Wheeler & Dittmar
Lorengo J. A.
NEC Corporation
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