Coating processes – Measuring – testing – or indicating
Reexamination Certificate
2001-07-11
2004-01-20
Beck, Shrive P. (Department: 1762)
Coating processes
Measuring, testing, or indicating
C427S240000, C427S425000, C118S052000, C118S320000, C118S710000, C118S713000, C438S758000, C438S780000, C438S782000
Reexamination Certificate
active
06680078
ABSTRACT:
BACKGROUND
The present invention relates generally to methods for dispensing flowable substances on microelectronic substrates, for example, methods for controlling a flow of a liquid photoresist onto a semiconductor wafer. Microelectronic features are typically formed in semiconductor wafers by selectively removing material from the wafer and filling in the resulting openings with insulative, semiconductive, or conductive materials. One typical process includes depositing a layer of light-sensitive photoresist material on the wafer, then covering the photoresist layer with a patterned mask, and then exposing the masked photoresist to a selected radiation. The mask is then removed and the entire photoresist layer is exposed to a solvent. In one case, the portions of the photoresist layer exposed to the radiation through patterned openings in the mask become resistant to the solvent. Alternatively, the portions covered by the mask become resistant to the solvent. In either case, the portions of the photoresist layer remaining on the wafer after being exposed to the solvent can protect the underlying structure when the wafer is subsequently exposed to an etchant. The etchant then creates a pattern of openings (such as grooves, channels, or holes) in the wafer material or in materials deposited on the wafer. These openings can be filled with insulative, conductive, or semiconductive materials to build layers of microelectronic features on the wafer.
One conventional arrangement for depositing photoresist on a semiconductor wafer is shown in FIG.
1
A. An apparatus
10
(such as a DNS SK2000, available from Dai Nippon Screen of Kyoto, Japan) includes a substrate support
11
that supports a wafer
12
. A dispense nozzle
43
is positioned above the wafer
12
to dispense a liquid photoresist
33
on a central portion of the wafer
12
. The wafer
12
spins (as indicated by arrow “A”) to distribute the photoresist
33
over the upward facing surface of the wafer
12
.
The apparatus
10
also includes a delivery system
40
that provides a regulated quantity of liquid photoresist to the dispense nozzle
43
. The delivery system
40
includes a resist reservoir
41
coupled to a pump
42
to propel the photoresist to the dispense nozzle
43
. A valve assembly
30
between the reservoir
41
and the dispense nozzle
43
regulates the flow of the photoresist to the dispense nozzle
43
. The valve assembly
30
includes a dispense valve
31
that opens to allow the photoresist to flow to the dispense nozzle
43
and closes to prevent the flow of the photoresist. The valve assembly
30
further includes a suckback valve
32
that withdraws at least some of the liquid photoresist from the dispense nozzle
43
when the dispense valve
31
is closed, thereby reducing the likelihood for extraneous drops of photoresist to drip from the dispense nozzle
43
. For example, as shown in
FIG. 1B
, the suckback valve
32
can operate to keep the photoresist
33
flush with the end of the dispense nozzle
43
or, (as shown in
FIG. 1C
) recessed from the end of the dispense nozzle
43
after the dispense valve
31
is closed. In either case, the suckback valve
32
is configured to prevent the photoresist
33
from extending beyond the end of the dispense nozzle
43
(as shown in
FIG. 1D
) when the dispense valve
31
is closed.
The dispense valve
31
and the suckback valve
32
are operated by air from a pressurized air supply
44
. The flow of pressurized air to the valves
31
and
32
is controlled by electrically-operated solenoids
45
a
and
45
b
, respectively.
A computer-based controller
20
controls the operation of the solenoids
45
a
and
45
b
, and also controls the spin motion of the substrate support
11
. Accordingly, the controller
20
includes a valve controller
23
operatively coupled to the solenoids
45
a
and
45
b
, and a spin speed controller
22
operatively coupled to a motor that rotates the substrate support
11
.
The apparatus
10
can further include a video camera
21
operatively coupled to the spin speed controller
22
. In operation, the video camera
21
can detect when a certain portion of the wafer
12
is covered with the photoresist
33
. The speed controller
22
can then alter the speed with which the substrate support
11
spins, based on the image received from the video camera
21
, to control the coverage of the photoresist
33
over the surface of the wafer
12
.
One drawback with the conventional arrangement shown in
FIG. 1A
is that it can be difficult to accurately control the amount of photoresist
33
dispensed on the wafer
12
. For example, dispensing even one additional drop of photoresist on a wafer can dramatically increase the amount of photoresist required to process a large number of wafers. Conversely, dispensing too little photoresist on the wafer can produce an ineffective photoresist layer.
One approach to addressing the foregoing drawback is to calibrate the apparatus
10
. Calibration can both improve the uniformity with which a given apparatus dispenses the photoresist, and improve the consistency of results obtained from one apparatus to the next. One approach to performing the calibration is to open and close the dispense valve
131
over a period of 0.1 second while monitoring the dispense nozzle
43
by eye, and reducing the rate at which the dispense valve
131
opens if more than one drop of photoresist exits the dispense nozzle
43
. The process is repeated until only a single drop exits the dispense nozzle
43
. The resulting rate at which the dispense valve
131
opens is then used when dispensing the full amount of photoresist on the surface of the wafer
12
.
One drawback with the foregoing approach is that it is typically not repeatable. For example, different calibration runs can produce single drops having different sizes, and the drop size can vary from one apparatus to the next. Accordingly, the existing methods for calibrating the apparatus
10
are not sufficiently accurate because they can produce photoresist layers having thicknesses that vary by up to 100 angstroms depending on which apparatus dispenses the photoresist.
SUMMARY
The present invention is directed toward methods for dispensing a flowable substance on a microelectronic substrate. In one aspect of the invention, the method can include dispensing a portion of the flowable substance on a surface of the microelectronic substrate and receiving an image of at least some of the flowable substance on the surface of the microelectronic substrate. The method can further include comparing a characteristic of the image with a pre-selected characteristic, or comparing a time required to dispense the flowable substance with a pre-selected time by reference to the image, or both comparing the image and the time. The method can still further include adjusting a characteristic of the dispense process when the image differs from the pre-selected image by a least a predetermined amount, or when the time differs from the pre-selected time by at least a predetermined amount, or both.
In another aspect of the invention, the method can further include selecting the flowable substance to include a photoresist material. Comparing the image or the time and adjusting a characteristic of the dispense process can be performed by digital computer. Adjusting a characteristic of the dispense process can include adjusting a rate at which a valve, positioned along a flow path of the flowable substance, changes from a closed state to an open state.
In still a further aspect of the invention, the method can include receiving an image of a field that includes at least some of the flowable substance on the surface of the microelectronic substrate. Based on the image, the method can further include determining an elapsed time between a first point in time and a second point in time, the second point in time corresponding to a point at which a selected fraction of the field is at least approximately covered with the flowable substance. The method can further include determining an e
Davlin John T.
Montanino Greg
Beck Shrive P.
Jolley Kirsten Crockford
Perkins Coie LLP
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