Spin coating bowl

Details Spin coating bowl Spin coating bowl

1998-09-03

2001-01-02

Edwards, Laura (Department: 1734)

Coating apparatus

With means to centrifuge work

C118S056000, C118S319000, C118S320000, C134S153000, C134S902000, C427S246000

Utility Patent

active

06168660

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to containers and methods for use in dispensing process liquids onto a surface. More particularly, the present invention relates to a bowl and method for use in a spin coating apparatus for the coating of wafer shaped semiconductor material.
2. Description of the Invention Background
Integrated circuits are typically constructed by depositing a series of individual layers of predetermined materials on a wafer shaped semiconductor substrate, or “wafer”. The individual layers of the integrated circuit are in turn produced by a series of manufacturing steps. For example, in forming an individual circuit layer on a wafer containing a previously formed circuit layer, an oxide, such as silicon dioxide, is deposited over the previously formed circuit layer to provide an insulating layer for the circuit. A pattern for the next circuit layer is then formed on the wafer using a radiation alterable material, known as photoresist. Photoresist materials are generally composed of a mixture of organic resins, sensitizers and solvents. Sensitizers are compounds, such as diazonapthaquinones, that undergo a chemical change upon exposure to radiant energy, such as visible and ultraviolet light resulting in an irradiated material having differing salvation characteristics with respect to various solvents than the nonirradiated material. Resins are used to provide mechanical strength to the photoresist and the solvents serve to lower the viscosity of the photoresist so that it can be uniformly applied to the surface of the wafers. After a photoresist layer is applied to the wafer surface, the solvents are evaporated and the photoresist layer is hardened, usually by heat treating the wafer. The photoresist layer is then selectively irradiated by placing a radiation opaque mask containing a transparent portion defining the pattern for the next circuit layer over the photoresist layer and then exposing the photoresist layer to radiation. The photoresist layer is then exposed to a chemical, known as developer, in which either the irradiated or the nonirradiated photoresist is soluble and the photoresist is removed in the pattern defined by the mask, selectively exposing portions of the underlying insulating layer. The exposed portions of the insulating layer are then selectively removed using an etchant to expose-corresponding sections of the underlying circuit layer. The photoresist must be resistant to the etchant, so as to limit the attack of the etchant to only the exposed portions of the insulating layer. Alternatively, the exposed underlying layer(s) may be implanted with ions which do not penetrate the photoresist layer thereby selectively penetrating only those portions of the underlying layer not covered by the photoresist. The remaining photoresist is then stripped using either a solvent, or a strong oxidizer in the form of a liquid or a gas in the plasma state. The next layer is then deposited and the process is repeated until fabrication of the semiconductor device is complete.
Photoresist and developer materials are typically applied to the wafer using a spin coating technique in which the photoresist is dispensed on the surface of the wafer as the wafer is spun on a rotating chuck. The spinning of the wafer distributes the photoresist over the surface of the material and exerts a shearing force that separates the excess photoresist from the wafer thereby providing a thin layer of photoresist on the surface of the wafer. Spin coating operations are performed in a clean room environment, and it is necessary to contain not only the excess coating material that is separated from the wafer, but also the vapor resulting from the evaporation of the solvent. In addition, photoresist materials are generally very expensive, ranging from $500 to $2300/gallon, therefore, reducing the amount of coating material used in the process can significantly reduce the overall cost of producing semiconductor devices. Also, a build up of excess coating material in the bowl requires additional downtime to remove and clean the bowl that further increases production costs.
FIG. 1
shows a side view of a typical bowl
200
and a porous wafer support chuck
202
of the prior art, such as is disclosed in U.S. Pat. No. 5,289,222 issued Feb. 22, 1994 to Hurtig. The wafer support chuck
202
is supported by a shaft
204
that passes through a hole
206
in the bowl
200
and attaches to a spin motor
208
in a motor compartment
209
. A wafer
210
having a top and a bottom surface,
212
and
214
respectively, is placed on the wafer support chuck
202
and is secured using a vacuum (not shown). The wafer
210
is spun and coating material, such as photoresist or developer, is dispensed onto the top surface
212
of the wafer
210
. The rotation of the wafer
210
causes the coating material to distribute over the top surface
212
and exerts a shear force on the coating material that separates excess coating material from the surface
212
.
Some of the solvent in the excess coating material vaporizes upon leaving the surface producing dry aerosol particles of the coating mixed with the liquid drops which accumulate over time on wall
216
of the bowl
200
. Also, the excess coating material has a tendency to creep around the edge of the wafer
210
and contaminate the bottom surface
214
. If the coating material on the bottom surface
214
migrates to the chuck
202
a loss of vacuum could occur and the wafer
210
will be released, possibly damaging the wafer. A solvent spray nozzle
218
is attached to the bowl
200
and is directed toward the edge of the wafer
210
to rinse the bottom surface
214
, thereby preventing a buildup of coating material. Solvent spray holes (not shown) are also provided in the bottom
217
of the bowl
200
to rinse the coating solution from the bottom surface.
The excess liquid coating and liquid solvent are drained from the bowl
200
using drain line
220
and the solvent vapors are purged from the bowl
200
with air through air purge line
222
. Solvent vapors are exhausted from the motor compartment
209
through a safety exhaust line
224
. The drain line
220
, the air purge line
222
and the safety exhaust line
224
are connected to an exhaust manifold and the vapor and liquid are separated and either reclaimed or disposed accordingly.
One problem that exists with the prior art design shown in
FIG. 1
is that in the region between the bottom surface
214
of the wafer
210
and the bottom of the bowl
217
a low pressure zone is created that results in a recirculation zone being formed that increases the amount of contamination that reaches the bottom surface
214
of the wafer
210
, the bottom of the bowl
217
, the chuck
202
, and the motor
208
. The recirculation zone results in a lower production yield due to contamination of the wafers and an increase in the overall processing time due to the increased downtime required to clean the bowl
200
.
One prior art effort to eliminate the recirculation zone, shown in
FIG. 2
, employs a bowl
200
having a bottom
217
that is in close proximity to the bottom surface
214
. While this design does eliminate the recirculation zone beneath the bottom surface
214
, the pressure differential between the edge of the wafer and the axis of rotation and the proximity of the bottom
217
to the bottom surface
214
produces a wicking effect that draws coating material in toward the center of the bowl
200
. The proximity of the bottom surface
214
to the bottom
217
of the bowl
200
also makes it more difficult to rinse the coating material off the bottom surface
214
using the solvent spray nozzle
218
.
Another problem is that proior art bowls are generally segregated, such as by divider
226
, to prevent the excess coating material from getting splashed or drawn onto the bottom surface
214
of the wafer
210
. While this design is effective for that purpose, the solvent is also segregated from the excess coating material that is r

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