Coating apparatus – With means to centrifuge work
Reexamination Certificate
2001-05-16
2003-06-10
Crispino, Richard (Department: 1734)
Coating apparatus
With means to centrifuge work
C118S056000, C118S064000, C118S070000
Reexamination Certificate
active
06576055
ABSTRACT:
TECHNICAL FIELD
The present invention is directed toward methods and apparatuses for controlling the movement of air over a spinning microelectronic substrate, for example during application of a liquid to the microelectronic substrate.
BACKGROUND OF THE INVENTION
During the manufacture of microelectronic devices, such as memory chips, processor chips and field emission displays, etching processes are often used to form features on a microelectronic substrate or substrate assembly that forms the foundation of the device. A typical etching technique includes depositing a layer of a photoresist material on the substrate, masking selected portions of the layer and exposing the unmasked portions to a selected radiation. The selected radiation changes the solubility of the unmasked portions to become either soluble (in the case of a positive photoresist) or insoluble (in the case of a negative photoresist) when exposed to a selected solvent. The photoresist layer is then washed with the selected solvent to remove either the exposed or unexposed photoresist material, exposing a portion of the substrate beneath. The substrate is washed with an etchant that removes material from the exposed portions of the substrate while leaving intact the portions of the substrate covered by the photoresist material.
It is often important to control the uniformity of the thickness to which the photoresist material is deposited on the substrate. For example, if the photoresist material is deposited to a non-uniform thickness, certain portions of the photoresist material may he overexposed to the radiation while other portions may be underexposed. Where the photoresist material is overexposed, the edges between the masked and unmasked regions can become blurred, making the process unsuitable for forming very small features. Where the photoresist material is underexposed, it may not have sufficient exposure time to change solubility. Furthermore, it may be desirable to keep the overall thickness of the photoresistant layer relatively small to increase the resolution of the features formed with this technique.
The photoresist material is typically deposited on the substrate or substrate assembly by disposing the material in liquid form at the center of the substrate and spinning the substrate about its center to spread the material outwardly by centrifugal force. One drawback with this technique is that the liquid photoresist material can interact with the adjacent air mass, creating waves or other disturbances in the photoresist material that affect the uniformity of the layer thickness. This problem can become more acute when the velocity of the substrate increases, for example, when the substrate is rotated at a high angular velocity and/or when the substrate has a large radius so that at even moderate angular velocities, the linear speed toward the edge of the substrate is high.
Another drawback with this technique is that the convective heat transfer rate can vary over the surface of the substrate because the relative linear velocity between the substrate and the adjacent air mass varies with the distance from the substrate center. The variation in heat transfer rates can cause the surface temperature of the substrate to vary, in turn causing the evaporation rate of the fluid (and therefore the thickness of the fluid) to vary over surface of the substrate.
Yet another drawback with this technique is that the viscosity selected for the liquid photoresist material must account for the diameter and rotation speed of the substrate. For example, a relatively viscous liquid may be selected for large substrates to prevent the liquid from flying off the edges of the substrate before accumulating to the desired thickness. Such a liquid may be too viscous for smaller substrates. Accordingly, conventional techniques typically use liquids with different viscosities to form layers having different thicknesses. For example, less viscous liquids can be used to form thinner layers and more viscous liquids can be used to form thicker layers. One problem with this approach is that it requires controlling and/or adjusting the viscosity of the liquid and/or providing multiple sources of the liquid, each having a different viscosity. Furthermore, while the angular velocity of the substrate can be used to control the thickness of the liquid layer (for example, by increasing the angular velocity to reduce the layer thickness), this technique is limited because at high angular velocities, the liquid can form waves or other disturbances, as discussed above.
FIG. 1
is a partially schematic, partially cutaway side elevation view of a conventional device
10
that can address some of the foregoing problems for rectangular substrates. The device
10
includes a motor
30
having a shaft
32
connected to a chuck
33
and a bowl
20
. A substrate
12
having a rectangular planform shape is releasably mounted to the chuck
33
and both the substrate
12
and the bowl
20
spin as the shaft
32
rotates. Accordingly, the air adjacent to the substrate
12
is partially contained within the spinning bowl
20
so that at least a portion of the air will spin at the same rate as the substrate
12
. A fluid supply conduit
23
disposes a liquid onto the substrate
12
through an aperture
24
and the liquid spreads out over the surface of the substrate
12
as the substrate
12
spins. Excess liquid is collected in the bowl
20
as it runs over the edges of the substrate
12
and can be removed from the bowl via a drain
21
. Air can be exhausted from the bowl
20
through an exhaust port
22
.
One potential drawback with the device
10
shown in
FIG. 1
is that the bowl
20
can be heavy and difficult to spin smoothly at high rates of speed. Furthermore, the drain
21
and the exhaust port
22
may be coupled to a drain line
23
a
and an exhaust line
23
b
, respectively, which must be secured to the bowl
20
with fluid-tight rotating couplings. Still further, the bowl
20
is partially open so that it may be time consuming to bring the air mass adjacent to the substrate
12
up to the same rotational speed as the substrate
12
, particularly where the substrate
12
rotates at high speed.
FIG. 2
is a partially schematic, partially cutaway side elevation view of another conventional device
10
a
that includes a motor
30
a
coupled with a shaft
32
a
to a chuck
33
a.
The chuck
33
a
includes a rectangular recess
36
for receiving the rectangular substrate
12
. A cover
40
is releasably placed on the chuck
33
a
to rotate with the chuck
33
a
and the substrate
12
. The cover
40
includes an aperture
41
that allows fluid to pass from the fluid supply conduit
23
to the surface of the substrate
12
. The apparatus
10
a
can further include a collection vessel
20
a
fixed relative to the motor
30
a
and having a drain
21
and an exhaust port
22
for removing liquid and gas from the region adjacent to the substrate
12
.
One problem with the device
10
a
shown in
FIG. 2
is that the liquid disposed on the substrate
12
can become trapped between the lower surface of the substrate
12
and the walls of the recess
36
into which the substrate
12
is placed. A further drawback is that the recess
36
is sized for rectangular substrates
12
, making it unsuitable for or unusable with round substrates, particularly where the diameter of the round substrate exceeds the width of the recess
36
.
SUMMARY OF THE INVENTION
The present invention is directed toward methods and apparatuses for uniformly distributing a liquid over a surface of a spinning microelectronic substrate. An apparatus in accordance with one aspect of the invention can include a support having an engaging portion for engaging the microelectronic substrate and rotating the microelectronic substrate at a first rate. The microelectronic substrate can have a first surface that receives the liquid and a second surface facing opposite the first surface with the engaging portion configured to engage less than the entire second surface. A rotating barrier
Crispino Richard
Dorsey & Whitney LLP
Koch, III George R.
Micro)n Technology, Inc.
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