Coating processes – Spraying – Moving the base
Reexamination Certificate
1999-08-31
2001-06-26
Beck, Shrive (Department: 1762)
Coating processes
Spraying
Moving the base
C427S240000, C427S385500
Reexamination Certificate
active
06251487
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coating method and a resist coater for coating a resist film on a wafer. More particularly, the invention relates to a coating method and a resist coater for coating a resist film having a thickness of 5500 Å or less on a wafer having a large diameter of 8 inches or more by a spin coating process, wherein the resist film is free from unevenness in the coating of the resist film and favorable in an in-plane evenness in film thickness and film quality. Incidentally, the resist film in this specification refers to a wide concept including a photoresist film.
2. Description of the Related Art
In a manufacturing process of a semiconductor device, when patterning is performed by etching, a resist film mask having a desired pattern Is formed on a layer to be etched, and the layer is etched by the use of the mask.
A resist film for forming a mask is normally formed on a layer to be etched by coating a resist on a wafer using a resist coater and baking the resist.
By the way, according to a higher integration of a semiconductor device, each elements in the semiconductor device including wirings is made more and more fine. In the generation of the fine pattern rule of 0.35 &mgr;m or less, the thickness of a resist film which is coated on a wafer is made thinner and thinner for reasons in the etching processing. In particular, in an resist coating process which requires a coating of a reflection preventing film, in order to secure evenness in film thickness and prevent generation of unevenness in reflection as can be seen in pin holes, it is required to set the thickness of the reflection preventing film to 2000 Å or more.
On the other hand, in order to improve precision in dry etching for a resist resolution pattern, and in order to prevent the neighboring resist patterns from being connected, it is required to set the total thickness of the reflection preventing film and the resist film to 7000 Å or less. Consequently, it is inevitably required to set the thickness of the resist film to 5500 Å or less.
Before explaining a conventional coating method, a resist coater for coating a resist on a wafer will first be explained with reference to FIG.
1
.
FIG. 1
is a sectional view showing a structure of a conventional resist coater of a spin coat type.
As shown in
FIG. 1
, a resist coater
10
has a wafer holding table
12
for rotating a wafer W around an axis which is perpendicular to the wafer W while holding the wafer W with a wafer surface thereof directed upwardly. A resist supply nozzle
14
supplies resist to the wafer W which is held on the wafer holding table
12
. A coater cup
16
surrounds the wafer holding table
12
and the resist supplying nozzle
14
.
The wafer holding table
12
is attached on an upper end of a rotation shaft
18
which penetrates a bottom portion of the coater cup
16
and which is rotated with a rotation device (not shown). The wafer holding table
12
is provided on its wafer holding surface with a chuck mechanism for vacuum-sucking the wafer W, and it is rotated together with the rotation shaft
18
around an axis which is perpendicular to the wafer holding surface.
The coater cup
16
is provided for trapping resist particle which are scattered from the wafer W by a centrifugal force due to rotation of the wafer W, and the coater cup
16
has an outer cup
20
for trapping resist particles which are scattered in a sidewise and an upward directions, and an inner cup
22
for guiding resist particles which are scattered in a downward direction from the wafer W to a bottom portion of the outer cup
20
.
The outer cup
20
has at an upper portion thereof an opening
24
for introducing the resist supply nozzle
14
or the like, and for taking in and taking out the wafer W. Furthermore, the inner cup
22
is provided on a lower portion of the outer cup
20
, and the inner cup
22
has a cylindrical portion
22
a
, and an umbrella portion
22
b
which spreads toward the inside of the coater cup
16
from an upper opening thereof.
The resist supply nozzle
14
is lowered from the above via the opening
24
of the coater cup
16
, and is arranged at a position facing a resist coating surface of the wafer W. Also, in order to clean an edge to the back surface of the wafer W, a first cleaning nozzle
26
for spraying rinse agent is provided to be directed toward the edge of the back surface of the wafer W through the bottom portion of the coater cup
16
. Furthermore, in order to clean an edge of the surface of the wafer W, a second cleaning nozzle
28
for spraying rinse agent is provided to be directed toward the edge of the wafer W via the upper opening
24
of the coater cup
16
.
Exhaust pipes
30
connected to an exhaust device (not shown) for exhausting the inside of the coater cup
16
, and a drain pipe
32
for exhausting the resist trapped in the coater cup
16
are connected to the bottom portion of the coater cup
16
.
Following, a conventional method for coating a resist film by the use of the above-mentioned resist coater
10
will be explained by giving an example of forming a resist film having a thickness of 5500 Å on an 8 inch wafer.
FIG. 2
is a graph showing a rotating speed of a wafer of each step in the conventional method.
When a resist film having a thickness of 5500 Å or less, for example, 5000 Å, is coated on an 8 inch wafer, the coating process is conventionally performed in the following procedure.
Resist having, for example, a relatively low viscosity on the order of 7 cp is used for a resist film. The wafer is held on the wafer holding table
12
and the resist is first dripped on a wafer from the resist supply nozzle
14
while rotating the wafer at a low rotation speed of 1000 rpm, and the resist is spread on the whole surface of the resist coating surface of the wafer for 4 seconds.
Next, the dripping of resist is suspended, and the wafer is rotated for 19 seconds at a rotation speed of 5000 rpm, so that a resist film having a desired thickness, i.e., of 5000 Å is formed.
Subsequently, rinse agent is sprayed from the first cleaning nozzle
26
for 20 seconds, and the back surface edge of the wafer is cleaned. Also, rinse agent is sprayed from the second rise nozzle
28
, and the surface edge of the wafer is cleaned. Thus, the coating step is terminated.
Subsequently, the process proceeds to the following baking step, where the residual solution in the resist is completely removed.
However, in the case where a resist film having a thickness of 5500 Å or less on a 8 inch or more wafer in accordance with the conventional coating method, an in-plane unevenness regarding film thickness and film quality are not favorable, so that variations occur in film thickness and film quality. For example, when a high speed rotational coating is performed on an 8 inch or more wafer, variations in the resist film thickness occur in the in-plane of the wafer in a range of 90 Å or more.
As a consequence, problems are caused in a photolithography stop and an etching step which follow the coating step. For example, there arise a problem that unevenness occurs in wiring width which is obtained in the etching, which results in difficulty in improvement in product yield.
Specifically, on a wafer having a large diameter of 8 inches or more, when the wafer is rotated for 20 seconds or more at a rotation speed of 5000 rpm after dripping the resist agent, a coating unevenness occurs and generated at a constant cycle on a peripheral portion of the wafer having a width of 20 mm from an outer periphery thereof inwardly. For example, in an example according to the method described above, the coating unevenness occurs on the peripheral portion of the wafer, and a variation in the resist film thickness is caused between a central portion of the wafer and the peripheral portion thereof due to the coating unevenness. Thus, as shown in
FIG. 3
, variations in the fill thickness exceeding 100 Å are generated wit
Beck Shrive
Calcagni Jennifer
Hayes Soloway Hennessey Grossman & Hage PC
NEC Corporation
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