U.S. patent application number 11/414132 was filed with the patent office on 2007-11-29 for chemical dispense system.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Y. Sean Lin.
Application Number | 20070272327 11/414132 |
Document ID | / |
Family ID | 38748430 |
Filed Date | 2007-11-29 |
United States Patent
Application |
20070272327 |
Kind Code |
A1 |
Lin; Y. Sean |
November 29, 2007 |
Chemical dispense system
Abstract
The performance of photolithography chemical dispense apparatus
is improved by placing the chemical filter before the dispense pump
and providing a separate pressure control for the filter. This
approach allows the system to utilize both an optimal dispense rate
and an optimal filtration rate. A chemical source can have a first
pressure source applied, and a second pressure source applied where
necessary to control the filtration rate. The pressures can be
optimized during calibration, and optimal pressures can be
maintained using pressure sensors that monitor the pressures. A
controller can model the behavior of at least the dispense pressure
during a dispense cycle and can calculate an adjustment function to
be applied to the dispense pump during a subsequent dispense cycle
in order to optimize the dispense pressure (and hence flow rate)
during each cycle.
Inventors: |
Lin; Y. Sean; (Irvine,
CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Applied Materials, Inc.
Santa Clara
CA
|
Family ID: |
38748430 |
Appl. No.: |
11/414132 |
Filed: |
April 27, 2006 |
Current U.S.
Class: |
141/286 |
Current CPC
Class: |
G03F 7/70991 20130101;
G03F 7/162 20130101 |
Class at
Publication: |
141/286 |
International
Class: |
B65B 1/04 20060101
B65B001/04 |
Claims
1. A method of dispensing a flow of photolithography chemical onto
a substrate, comprising: directing a flow of photolithography
chemical into a buffer vessel for providing a continuous source of
the photolithography chemical for a dispense cycle; applying a flow
of pressurized fluid to the buffer vessel in order to push the
photolithography chemical out of the buffer vessel to a chemical
filter; directing the photolithography chemical through a chemical
filter at substantially a predetermined flow rate; directing the
filtered photolithography chemical to a dispense pump operable to
direct the filtered photolithography chemical out of the dispense
pump at a controlled flow rate using a selected flow rate function;
and dispensing the photolithography chemical onto the substrate at
substantially the controlled flow rate.
2. A method according to claim 1, wherein: directing the
photolithography chemical through a chemical filter includes
suctioning the photolithography chemical through the filter using
the dispense pump.
3. A method according to claim 1, wherein: the controled flow rate
is substantially an optimal dispense flow rate.
4. A method according to claim 1, wherein: the photolithography
chemical is at least one of a bottom anti-reflective coating
(BARC), top antireflective coating (TARC), spin on dielectric
(SOD), spin on polymer (SOP), and top coat (TC).
5. A method of dispensing a selected flow of photolithography
chemical onto a substrate, comprising: directing a flow of the
photolithography chemical through a chemical filter at a
preselected flow rate; directing the filtered flow of the
photolithography chemical through a dispense pump in order to
direct the filtered flow of the photolithography chemical to a
dispense nozzle at a controlled flow rate using a selected flow
rate function; monitoring a variation in pressure of the
photolithography chemical adjacent the dispense nozzle while
dispensing the photolithography chemical onto the substrate;
determining dispense adjustments for at least two values of the
monitored pressure variation; and adjusting the operation of the
dispense pump for a subsequent substrate according to the
determined dispense adjustments.
6. A method according to claim 5, wherein: directing a flow of the
photolithography chemical through a chemical filter directs the
flow at substantially an optimal filtration rate.
7. A method according to claim 5, wherein: directing the filtered
flow of the photolithography chemical through a dispense pump
directs the photolithography chemical out of the dispense pump at a
controlled flow rate that is substantially an optimal dispense flow
rate function.
8. A system for dispensing a flow of photolithography chemical onto
a substrate, comprising: a buffer vessel configured to receive a
flow of photolithography chemical and provide a continuous source
of photolithography chemical during a dispense process; a pressure
source operable to apply a flow of pressurized fluid to the buffer
vessel in order to provide the photolithography chemical at a
controlled pressure; a chemical filter configured to receive and
filter the photolithography chemical at substantially a preselected
flow rate; a dispense pump operable to receive the filtered
photolithography chemical at substantially the preselected flow
rate and direct the filtered photolithography chemical out of the
dispense pump at a controlled flow rate using a selected flow rate
function; and a nozzle for receiving the filtered photolithography
chemical and dispensing the filtered photolithography chemical onto
the substrate at substantially the controlled flow rate.
9. A system according to claim 8, wherein: the preselected flow
rate is substantially an optimal filtration rate.
10. A system according to claim 8, wherein: the controlled flow
rate is substantially an optimal dispense flow rate.
11. A system according to claim 8, further comprising: a chemical
source for supplying the photolithography chemical.
12. A system according to claim 11, further comprising: an
additional pressure source operable to apply an additional flow of
pressurized fluid to the chemical source in order to push the
photolithography chemical out of the chemical source.
13. A system for dispensing a flow of photolithography chemical
onto a substrate, comprising: a pressure source operable to apply a
flow of pressurized fluid in order to provide photolithography
chemical at a controlled pressure; a chemical filter configured to
receive and filter the photolithography chemical at substantially a
preselected flow rate; a dispense pump operable to receive the
filtered photolithography chemical at substantially the preselected
flow rate and direct a flow of filtered photolithography chemical
out of the dispense pump at a controlled flow rate using a selected
flow rate function; a nozzle for receiving the filtered
photolithography chemical and dispensing the filtered
photolithography chemical onto the substrate at substantially the
controlled flow rate; and a system controller operable to monitor a
variation in pressure of the filtered photolithography chemical
near the nozzle while dispensing the photolithography chemical onto
the substrate, the system controller being further operable to
determine dispense adjustments for at least two values of the
monitored pressure variation and adjust the operation of the
dispense pump for a subsequent substrate according to the
determined dispense adjustments.
14. A system according to claim 13, wherein: the preselected flow
rate is substantially an optimal filtration rate.
15. A system according to claim 13, wherein: the controlled flow
rate is substantially an optimal dispense rate.
16. A system according to claim 13, further comprising: a chemical
source for supplying the photolithography chemical.
17. A system according to claim 16, further comprising: an
additional pressure source operable to apply an additional flow of
pressurized fluid to the chemical source in order to push the
photolithography chemical out of the chemical source.
18. A system according to claim 17, further comprising: a buffer
vessel configured to receive the flow of photolithography chemical
from the chemical source and provide a continuous source of the
photolithography chemical for a dispense process.
19. A system according to claim 13, wherein: the system controller
is further operable to determine an adjustment function from the
determined dispense adjustments and adjust the operation of the
dispense pump for a subsequent substrate according to the
adjustment function.
20. A computer program product stored on a computer-readable
storage medium for dispensing a flow of photolithography chemical
onto a substrate, the computer program product comprising: computer
program code for directing a flow of the photolithography chemical
through a chemical filter at a preselected flow rate; computer
program code for directing the filtered flow of the
photolithography chemical received from the filter from a dispense
pump to a dispense nozzle at a controlled flow rate using a
selected flow rate function; computer program code for monitoring a
variation in pressure of the photolithography chemical near the
dispense nozzle while dispensing the photolithography chemical onto
the substrate; computer program code for determining dispense
adjustments for at least two values of the monitored pressure
variation; and computer program code for adjusting the operation of
the dispense pump for a subsequent substrate according to the
determined dispense adjustments.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to the field of
substrate processing equipment. More particularly, the present
invention relates to a method and apparatus for providing separate
optimized pressure sources to control filtration and dispensation
flow rates in a chemical dispense system.
[0002] Modern integrated circuits contain millions of individual
elements that are formed by patterning the materials making up the
integrated circuit to sizes that are small fractions of a
micrometer. A technique typically used throughout the industry for
forming such patterns is photolithography. A photolithography
process sequence generally includes the deposition of one or more
uniform photoresist (resist) layers on the surface of a substrate,
followed by the drying and curing of the deposited layers,
patterning of the substrate by exposing the photoresist layer to
electromagnetic radiation suitable for modifying the exposed layer,
and developing the patterned photoresist layer.
[0003] It is common in the semiconductor industry for many of the
steps associated with the photolithography process to be performed
in a multi-chamber processing system (e.g., a cluster tool) that
has the capability to sequentially process semiconductor wafers in
a controlled manner. One example of a cluster tool that is used to
deposit (i.e., coat) and develop a photoresist material is commonly
referred to as a track lithography tool.
[0004] Track lithography tools typically include a mainframe that
houses multiple chambers (sometimes referred to as stations)
dedicated to performing various tasks associated with pre- and
post-lithography processing. There typically are both wet and dry
processing chambers within track lithography tools. Wet chambers
typically include coat and/or develop bowls, while dry chambers
typically include thermal control units that house bake and/or
chill plates. Track lithography tools also frequently include one
or more pod/cassette mounting devices, such as an industry standard
FOUP (front opening unified pod), to receive substrates from and
return substrates to the clean room, multiple substrate transfer
robots to transfer substrates between the various chambers/stations
of the track tool, and an interface that allows the tool to be
operatively coupled to a lithography exposure tool in order to
transfer substrates into the exposure tool and receive substrates
from the exposure tool after the substrates are processed within
the exposure tool.
[0005] Over the years there has been a strong push within the
semiconductor industry to shrink the size of semiconductor devices
produced by such tools. The reduced feature sizes have caused the
industry's tolerance to process variability to shrink, which in
turn, has resulted in semiconductor manufacturing specifications
having more stringent requirements for process uniformity and
repeatability. Processing variables that may later affect tool
performance are controlled so that all substrates in a lot or batch
are processed the same way. During a photolithography process, for
example, a substrate such as a semiconductor wafer is rotated on a
spin chuck at a predetermined speed(s) while liquids and gases such
as solvents, photoresist (resist), developer, and the like are
dispensed onto the surface of the substrate. Typical
photolithography chemicals include bottom an anti-reflective
coating (BARC), a top antireflective coating (TARC), a spin on
dielectric (SOD), a spin on polymer (SOP), a and top coat (TC).
[0006] As an example, an inadequate volume of photoresist dispensed
during a coating operation will generally impact the uniformity and
thickness of coatings formed on the substrate. Additionally, the
dispense rate of the photoresist will generally impact film
properties, including the lateral spreading of the resist in the
plane of the substrate. Therefore, it is desirable to control both
the volume and dispense rate of the photoresist applied to the
substrate with respect to both the accuracy (e.g., total volume per
dispense event) and repeatability (e.g., difference in volume per
dispense over a series of dispense events) of the dispense
process.
SUMMARY OF THE INVENTION
[0007] Systems and methods in accordance with embodiments of the
present invention provide for separate control and optimization of
the filtration and dispense rates in a photolithography chemical
dispense apparatus. By placing the filter before the dispense pump,
the filtration rate can be controlled separately from the dispense
rate, allowing the dispense pump to dispense the chemical at an
optimal dispense rate while the chemical is filtered at an optimal
filtration rate.
[0008] In one embodiment, a feed pump is used with the dispense
pump to push photolithography chemical through a chemical filter at
a selected flow rate, such as near the optimal filtration rate. The
feed pump can receive the chemical from a chemical source and/or a
buffer vessel. The filtered chemical then is directed to a dispense
pump, either directly or indirectly, which can direct the filtered
chemical to a dispense nozzle at a second flow rate, such as near
an optimal dispense flow rate. The chemical then can be dispensed
onto the substrate at near the optimal dispense flow rate. The
second flow rate can be a constant flow rate, or can be any other
controlled flow rate, such as may correspond to a selected or
determined dispense flow rate function that provides an optimal
controlled dispense flow.
[0009] In another embodiment, a bottle-in-bottle (BIB) chemical
source is used with the dispense pump to direct photolithography
chemical through a chemical filter at a selected flow rate, such as
near the optimal filtration rate. A source of pressurized fluid is
applied to an outer chamber of the chemical source in order to push
the chemical out of the inner chamber at the selected flow rate. No
buffer vessel is needed, although one can be used if desired. The
filtered chemical then is directed to a dispense pump, either
directly or indirectly, which can direct the filtered chemical to a
dispense nozzle at a controlled flow rate, such as near an optimal
dispense flow rate, using a controlled dispense flow rate function.
The chemical then can be dispensed onto the substrate using the
controlled flow rate.
[0010] In another embodiment, a buffer vessel receives a flow of
photolithography chemical from a chemical source and temporarily
stores the photolithography chemical, acting as a continuous source
of photolithography chemical for a lithography cycle or process. A
pressure source applies a flow of pressurized fluid to the buffer
vessel in order to push the photolithography chemical out of the
buffer vessel. A chemical filter then receives and filters the
photolithography chemical at a selected flow rate, such as an
optimal flow rate, as controlled by the dispense pump and the
pressure source. After exiting the filter, the filtered
photolithography chemical is directed to a dispense pump, which
applies pressure to the filtered photolithography chemical in order
to direct the filtered photolithography chemical out of the
dispense pump at a controlled flow rate, such as near an optimal
dispense rate, using a controlled flow rate function. A dispense
nozzle then dispenses the filtered photolithography chemical onto
the substrate at substantially the controlled flow rate.
[0011] In another embodiment, a pressure source applies a flow of
pressurized fluid in order to push the photolithography chemical at
a controlled pressure. A chemical filter receives and filters the
photolithography chemical at substantially a preselected flow rate.
A dispense pump receives the filtered photolithography chemical and
directs the filtered photolithography chemical out of the dispense
pump at a controlled flow rate, such as near an optimal dispense
rate, using a controlled flow rate function. A nozzle then
dispenses the filtered photolithography chemical onto the substrate
at substantially the controlled flow rate. A system controller
monitors a variation in pressure of the filtered photolithography
chemical near the nozzle while dispensing the photolithography
chemical onto the substrate. The system controller then determines
dispense adjustments for at least two values of the monitored
pressure variation and adjusts the operation of the dispense pump
for a subsequent substrate according to the determined dispense
adjustments.
[0012] In one embodiment, a flow of photolithography chemical is
directed into a buffer vessel for temporarily storing the
photolithography chemical. A flow of pressurized fluid is applied
to the buffer vessel in order to push the photolithography chemical
out of the buffer vessel at a controlled pressure. The
photolithography chemical is directed through a chemical filter at
substantially a preselected flow rate as controlled by the flow of
pressurized fluid and dispense pump. The filtered photolithography
chemical then is directed to the dispense pump operable to direct
the filtered photolithography chemical out of the dispense pump at
a controlled flow rate, such as by using a controlled flow rate
function. The photolithography chemical then is dispensed onto the
substrate at substantially the controlled flow rate.
[0013] In one embodiment, a flow of the photolithography chemical
is directed through a chemical filter at a first flow rate. The
filtered flow of the photolithography chemical is directed through
a dispense pump in order to direct the filtered flow of the
photolithography chemical to a dispense nozzle at a second flow
rate. A variation in pressure of the photolithography chemical is
monitored near the dispense nozzle while dispensing the
photolithography chemical onto the substrate. Dispense adjustments
are determined for at least two values of the monitored pressure
variation. The operation of the dispense pump then is adjusted for
a subsequent substrate according to the determined dispense
adjustments.
[0014] Other embodiments will be obvious to one of ordinary skill
in the art in light of the description and figures contained
herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Various embodiments in accordance with the present invention
will be described with reference to the drawings, in which:
[0016] FIG. 1 illustrates a photolithography chemical dispense
apparatus that can be used in accordance with one embodiment of the
present invention;
[0017] FIG. 2 illustrates a photolithography chemical dispense
apparatus that can be used in accordance with one embodiment of the
present invention;
[0018] FIG. 3 illustrates a photolithography chemical dispense
apparatus that can be used in accordance with one embodiment of the
present invention;
[0019] FIG. 4 illustrates a photolithography chemical dispense
apparatus that can be used in accordance with one embodiment of the
present invention;
[0020] FIG. 5 illustrates steps of a method that can be used in
accordance with one embodiment of the present invention;
[0021] FIG. 6 illustrates a plot of the behavior of the dispense
pressure with pump speed in accordance with one embodiment of the
present invention;
[0022] FIG. 7 illustrates a plot of the behavior of the dispense
pressure with pump speed in accordance with one embodiment of the
present invention;
[0023] FIG. 8 illustrates a photolithography chemical dispense
apparatus that can be used in accordance with one embodiment of the
present invention;
[0024] FIG. 9 illustrates steps of a dispense rate adjustment
method that can be used in accordance with one embodiment of the
present invention; and
[0025] FIG. 10 is a simplified plan view of an embodiment of a
track lithography tool according to an embodiment of the present
invention.
DETAILED DESCRIPTION
[0026] Systems and methods in accordance with various embodiments
of the present invention overcome the afore-mentioned and other
deficiencies in existing dispense systems by changing the way in
which pressure is applied and/or controlled throughout a dispense
system. Separate pressure controls can be used for the filtration
rate and the dispense flow rate. These separate pressures can be
monitored and adjusted in order to reduce the error in the dispense
pressure, and hence the dispense flow rate, in order to improve the
accuracy of the overall dispense process for each cycle. Further,
the separate pressure sources allow the filtration rate to be
optimized, and also can allow for the monitoring and adjustment of
the filtration rate. These optimizations provide for precise
volumes and dispense rates for chemicals applied to substrates of a
lot or batch.
[0027] As described above, track lithography tools dispense precise
amounts of expensive lithography chemicals onto substrates to form
thin, uniform coatings. For modern lithography processes, the
volumes of lithography chemicals such as photoresist that are
dispensed per event are small, with volumes typically ranging from
about 0.5 ml to about 5.0 ml. The volume of chemical dispensed and
the flow rate during a dispense operation, among other variables,
are controlled during the process of dispensing the lithography
chemicals. Control of the dispense operations in a track
lithography tool typically should provide actual dispensed volumes
with an accuracy of .+-.0.02 milliliters (ml) and repeatability
from dispense event to dispense event of 3.sigma.<0.02 ml.
[0028] A wide variety of photolithography chemicals are utilized in
such track lithography tools. For example, photoresist, bottom
anti-reflective coating (BARC), top anti-reflective coating (TARC),
top coat (TC), Safier, and the like are dispensed onto the
substrate. After the selected chemical is dispensed, the substrate
sometimes is spun to create a uniform thin coat on an upper surface
of the substrate. Generally, to provide the levels of uniformity
desired of many photolithography processes, dispense events start
with a solid column of chemical. The flow rate is generally set at
a predetermined rate as appropriate to a particular chemical
deliver process. For example, the flow rate of the fluids is
selected to be greater than a first rate in order to prevent the
fluids from drying out prior to dispense. At the same time, the
flow rate is selected to be less than a second rate in order to
maintain the impact of the fluid striking the substrate below a
threshold value.
[0029] As the dispense event is terminated, the fluid is typically
drawn back into the dispense line, sometimes referred to as a
suck-back process utilizing a suck-back valve. In some track
lithography tools, the fluid is brought back into the dispense line
about 1-2 mm from the end of the dispense nozzle, forming a reverse
meniscus. This suck-back process prevents the lithography chemicals
from dripping onto the substrate and prevents the chemicals from
drying out inside the nozzle.
[0030] There are many dispense systems available for use with such
a track lithography tool, which typically utilize a dispense pump
for applying the lithography chemical at the specified flow rate
and a filter for filtering any impurities and/or particulates from
the lithography chemical before dispense. Typically, the filter is
placed downstream of the pump, or between the dispense pump and the
nozzle. This is an advantageous configuration since it is necessary
to have enough pressure to push the lithography chemical through
the filter to meet the necessary flow criteria. This configuration
is not optimal, however, as the optimum dispense rate generally is
not the same as the optimum filtration rate for a given system or
chemical. The optimum rates can vary depend on various factors,
such as chemical type, filter type, and pore size. Placing the
filter after the dispense pump causes the dispense and filtration
rates to be substantially identical, such that at most one of these
flow rates can be optimized.
[0031] FIG. 1 shows a simplified schematic illustration of a
photolithography chemical dispense apparatus 100 in accordance with
an embodiment that places the chemical filter before the dispense
pump (following along the process flow), allowing for the
filtration rate to be different than the dispense rate. This is
done through the addition of a feed pump used to control the
filtration rate of chemical through the filter before reaching the
dispense pump.
[0032] In the system of FIG. 1, a pressure valve 102 used to apply
a flow of pressurized gas is coupled to a chemical source bottle
104 containing the photolithography chemical to be dispensed onto
the surface of a substrate 146. In one embodiment, the source
bottle is a NOWPak.RTM. container available from ATMI, Inc., of
Danbury, Conn. The container includes a softpack for use with a
nitrogen push source, such that the nitrogen does not contact the
chemical. The gas source applies pressure to the softpack, pushing
chemical out of the chemical source. The output line from the
source bottle 104 is coupled to a flow control valve 108 in order
to regulate the flow of the photolithography chemical in the fluid
line 106. A buffer vessel 112 for receiving and temporarily storing
the chemical includes an input port 110, coupled to the fluid line
106, and an output port 120, as well as a venting line 122. The
buffer vessel also includes level sensor LS1 (114) and level sensor
LS2 (116) for regulating the volume of photolithography chemical
present in the buffer vessel 112.
[0033] The vent line 122 from the buffer vessel 112 is coupled to a
vent valve 124 and a level sensor LS3 (126). The level sensor LS3
(126) serves to monitor the level of fluid passing through the vent
valve 124. The output port 120 of the buffer vessel is coupled to
input port of the feed pump 128. The feed pump receives in a flow
of fluid, such as nitrogen (N.sub.2) gas, and has an output to
vacuum. The feed pump 128 provides pressure to push a flow of
chemical through a control valve to the input port 132 of the
chemical filter 134. A flow of filtered chemical then is directed
into the dispense pump 136, which is capable of providing a more
accurate flow control than the feed pump 128. A filling cycle of
the dispense pump, such as where a piston is retracted at a
selected rate to draw chemical into the pump, can cause the
filtered chemical to flow through the filter at a desired or
preselected flow rate. During a dispense cycle, the piston can push
gas out of the dispense pump at a controlled dispense flow rate
that is approximately the optimal dispense flow rate for the given
system and chemical. Typically, the preselected filter rate and
controlled dispense rate will not be the same. Further, the
preselected filter rate typically will be substantially constant,
while the controlled dispense rate can correspond to any
appropriate control function, such as a constant, linear, step, or
non-linear function as described further below.
[0034] The application of pressure from the feed pump can prevent a
negative pressure in the system, which can draw particles or
contaminants back into the chemical. A vent port 138 and an output
port 154 can be provided on the dispense pump 136 if desired, with
a vent valve 140 being coupled to the vent port 138. A shut
off/suck-back valve 142 is coupled to the fluid line running from
the output port 154 of the dispense pump. From the suck-back valve
142, the photolithography chemical is delivered to the substrate
146 through an appropriately sized dispense nozzle 144. As will be
apparent to one of skill in the art, apparatus adapted to chuck and
spin the substrate are not illustrated for purposes of clarity.
Furthermore, additional dispense systems adapted to provide
photolithography chemicals, e.g., multi-nozzle systems, are not
illustrated for purposes of clarity and simplicity of
understanding.
[0035] While the system of FIG. 1 allows for separate control of
the filtration and dispense flow rates, experimental use has shown
that this configuration does not provide improved results for all
cases. This is due in part to the fact that the feed pump is less
accurate than the dispense pump, such that the actual filtration
rate is not controlled as precisely. Further, the additional
components and piping provide additional locations for expansion,
compression, or other sources of pressure and volume variation.
[0036] In order to reduce the number of components, and thus
potential sources of pressure and volume variation, as well as to
provide at least a similar level of control over a separate
filtration rate, FIG. 2 shows a simplified schematic illustration
of a photolithography chemical dispense apparatus 200 in accordance
with an embodiment that eliminates both the buffer valve and the
feed pump. In this embodiment, the chemical source 204 is a
bottle-in-bottle design that has a flexible inner chamber for
containing the chemical and a rigid outer chamber for receiving a
flow of pressurized fluid, such as a flow of N.sub.2 fluid. A
pressure regulator 202 can be used to apply a specific amount of
pressure to the outer chamber of the chemical source 204, in order
to compress the inner chamber and push a flow of chemical from an
output port of the chemical source 204.
[0037] The flow of nitrogen gas into the outer chamber can be
controlled in order to pass a flow of chemical to the filter 212 at
a controlled pressure, such that when the dispense pump is in a
fill cycle the chemical will pass through the filter at near an
optimal filtration rate, as can be determined through calibration
and/or experimentation. A control valve 208 also can be used to
control the flow of chemical into the filter 212. The filter can
have a vent line 216 with a vent valve 214, as well as an output
fluid line 218 for passing the filtered liquid to the dispense pump
220. The outlet of the dispense pump 220, at near a controlled
and/or optimal dispense rate, is passed through a suck-back valve
228 and onto the surface of the substrate 232 through the dispense
nozzle 230. In some embodiments, a pressure sensor 224 can receive
an input flow 232 from the dispense pump and output an output flow
226 to the suck-back valve 228 in order to monitor the dispense
pressure.
[0038] While the system of FIG. 2 reduces the number of components,
and thereby the amount of potential expansion or compression in the
system, there is no buffer valve ensuring that there is enough
chemical to finish a lot of substrates even if the chemical source
runs empty. In some embodiments, multiple chemical sources can be
used to supply a flow of chemical, such that an operator (or the
system itself) simply switches to another source when the current
source runs empty. Since the heads for chemical source bottles, for
example, are relatively expensive, this might not be an appropriate
solution for all applications. In other embodiments, the source is
monitored and simply replaced when the source is running low. This
results in a waste of chemical, however, as some chemical will be
discarded with each source bottle.
[0039] FIG. 3 shows a simplified schematic illustration of a
photolithography chemical dispense apparatus 300 in accordance with
an embodiment that utilizes a buffer vessel, and utilizes the
chemical source as a pressure source for the filter, placed before
the dispense pump. Reference numbers are carried over from FIG. 2
where appropriate for simplicity, but this should not be read as a
limitation on the various embodiments. In this embodiment, a flow
of fluid 304 from the chemical source 204 is directed through the
control valve 208 into the buffer vessel 302. The buffer vessel
includes two level sensors LS2 (306) and LS3 (308) for ensuring a
proper amount of chemical in the buffer vessel 302. An output flow
310 from the buffer vessel flows into the filter 212, and is
processed as in FIG. 2 above. This embodiment provides a buffer
vessel to ensure availability of enough chemical to finish a given
lot or batch of substrates, but utilizes the chemical source as a
pump source for the filter. A problem can arise with such a system,
however, as many chemical sources are not able to provide enough
flow, or at least a stable or accurate enough flow, to accurately
control and maintain the optimal filtration rate and prevent
negative pressure in the system.
[0040] FIG. 4 shows a simplified schematic illustration of a
photolithography chemical dispense apparatus 400 in accordance with
an embodiment that utilizes a three-way valve 402 to provide a
separate flow of pressurized fluid, such as nitrogen gas, to the
buffer vessel, although such an assembly could be provided
elsewhere in a dispense system as would be apparent to one of
ordinary skill in the art. During a dispense process, the three-way
valve 402 is opened to direct the additional flow of nitrogen into
the filter 212. A pressure regulator 404 can be used to ensure that
the proper amount of pressure is being used to push the chemical
through the filter at near the optimal filtration rate (or another
appropriate rate) during a fill or suction cycle of the dispense
pump. Since the chemical source may not provide a sufficient source
of pressure, and since one chemical source might be connected to
multiple lines, it might not otherwise be possible to get a
consistent, accurate filtration rate using just the chemical source
and dispense pump to push and/or suction chemical through the
filter. This additional flow through the three-way valve allows
additional pressure to be added to the filter, in order to push the
chemical through this particular line at near the desired flow
rate. The three-way valve 402 then can be opened in another
direction in order to vent the filter, and another pressure valve
406 can be used to monitor the pressure in the line 2.
[0041] FIG. 5 illustrates steps of an exemplary method 500 that can
be used with a system such as the system shown in FIG. 4. In this
embodiment, a first flow of pressurized fluid is applied to a
chemical source in order to push a flow of chemical through the
system 502. The chemical flow is fed into a buffer vessel 504, the
amount of flow being regulated by a control valve or other such
component where appropriate. The chemical typically is supplied to
the buffer vessel such that at least a minimum amount of chemical
is always in the buffer vessel during operation, ensuring that
enough chemical is present to finish any given lot or batch of
substrates being processed by the system. A separate flow of
pressurized fluid is applied to the buffer vessel to ensure that a
sufficient amount of pressure is applied to the buffer vessel to
pass the chemical out of the buffer vessel 506 and through the
filter at a selected filter flow rate during a fill or suction
cycle of the dispense pump, wherein the pump is the primary control
of the rate of flow through the filter 508. The amount of pressure
applied by the separate fluid flow can be regulated to ensure a
proper first flow rate. The chemical from the buffer vessel passes
through the filter in order to remote contaminants and/or
particulates from the chemical. In this example, the pressures
applied in steps 502 and 506 can be calibrated and controlled such
that the flow rate of chemical through the filter is at or near the
optimal filtration rate for the system, chemical, and operating
conditions.
[0042] The filtered flow of chemical from the filter then is
directed into a dispense pump 510. The dispense pump in one
embodiment suctions in the chemical during a suction phase, then
pushes the chemical out at a controlled rate, such as a constant
rate or a variable rate as determined using a selected flow
function, to a nozzle of the system in order to dispense the
chemical onto the surface of a substrate 512. The dispense pump can
be calibrated and controlled such that the flow rate of chemical
from the dispense pump is maintained at or near an optimal dispense
rate for the system, chemical, and operating conditions, where the
optimal dispense rate can be constant or can vary over time. The
chemical from the dispense pump can be passed through a suck-back
valve in order to prevent excess chemical from dripping or
otherwise passing onto the surface of the substrate after a
sufficient volume is applied to the substrate.
[0043] While such a method provides for separate, controllable
filtration and dispense rates, there still may not be an accurate
dispense rate for any given substrate, cycle, or process. For
example, FIG. 6 illustrates a speed of the dispense pump and a
corresponding behavior of the dispense pressure, which is
correlated with the dispense flow rate. It should be understood
that these plots are merely for explanation, and are not meant to
be to scale or to accurately model the precise behavior of these
parameters. When an optimal or desirable constant dispense rate is
calculated for the system in this example, the dispense pump
typically is set to a constant speed (or other pressure setting),
such that the pump speed is substantially constant during a
dispense operation as shown by the speed plot over time 602. As
indicated by experimental use, however, the actual pressure during
the dispense process and, correspondingly, the flow rate are not
constant over time. It should be understood that the desired flow
rate may not be constant, but may follow a flow function that steps
or otherwise varies over time, either linearly or non-linearly. The
effects of increasing pressure can be handled in a similar fashion
for these non-constant flows.
[0044] For example, consider a positive displacement pump. If a
piston (or other mechanism) of the pump is moved at a constant
speed such that the displacement changes at a constant rate, it
would be expected that a constant volume of chemical is pushed out
of the pump. Unfortunately, there are a number of components in the
system, including the tubing used to direct the flow of chemical,
which are not 100% incompressible or 100% non-expandable. As such,
the amount of chemical that is actually dispensed (per unit time)
at the beginning of a dispense process is less than the amount of
chemical dispensed (per unit time) at the end of a dispense
process, as some components will expand or compress upon the
initial application of pressure, such that the volume of the system
downstream of the pump will slightly increase near the beginning of
the dispense cycle. There may be an initial spike at startup, as
shown the by plot 604, but otherwise the actual dispense rate will
increase from the beginning of the dispense cycle until the end of
the cycle. Once the actual components are substantially compressed
or expanded, such that the volume does not substantially change,
the pressure and corresponding dispense rate then should be
substantially constant. Unfortunately, the pressure can change
between each dispense cycle, such that the dispense rate will again
start at a lower value at the next cycle.
[0045] Because the physical displacement of the pump therefore is
not accurate enough to describe the dispense flow rate (using the
cross-section of the pump cylinder and the piston speed, for
example), and to account for these small errors, it can be
desirable to monitor the dispense rate in order to adjust the
behavior of the system during a dispense cycle. It is desirable for
many applications to have a dispense flow rate that is relatively
constant during the dispense cycle. If another flow rate is
desired, it still could benefit from a more accurate control
model.
[0046] A first approach to improving flow rate performance in
accordance with one embodiment is to utilize a pressure sensor
(such as the pressure sensor 224 in FIG. 4) between the dispense
pump (220) and the dispense nozzle (230). Pressure can build up in
the system before opening the nozzle. By viewing the pressure near
the nozzle before the beginning of the dispense process, a
necessary pressure adjustment can be determined, such as by
comparing the actual pressure to a reference or calibrated
pressure. An adjustment then can be calculated for the dispense
pump, such as an increase or decrease in piston speed, in order to
ensure that the dispense process starts near the reference pressure
(within an allowable amount of error, such as 0.02 ml). This
process can be repeated before each dispense cycle. The reading,
calculation, and adjustment can be done manually, or can be done
automatically using processes such as are discussed below with
respect to FIG. 8. In another embodiment, the pressure inside the
pump is read at the beginning of the dispense cycle, before the
beginning of the actual dispensing of chemical, such that the pump
(or a controller in electronic communication with the pump) can
adjust the pressure automatically before the nozzle is opened. This
also can ensure that the actual pressure, at least inside the
dispense pump, is near the reference pressure before dispensing
starts.
[0047] In order to obtain optimal performance for the dispense
system, however, an advanced control system can be used to monitor
and adjust the performance of the system in order to maintain near
optimal filtration and/or dispense rates within much less than the
allowable error. An exemplary system 800 in accordance with one
embodiment is shown in FIG. 8. Reference numbers are again carried
over where appropriate for simplicity, but should not be read as a
limitation on any of the respective embodiments. As illustrated,
the system 800 includes a system controller 802, which can include
a processor 804 and memory 806 as known in the art, as well as at
least one system interface 808 for communicating with a component
of the system, such as a pressure sensor, pump, etc. The controller
also can have a user interface component 810, which can include a
control panel, display, interface signal, or any other appropriate
device or component allowing a user or external device to access
functionality of the controller 802.
[0048] As shown, the controller 802 in one embodiment is in
communication with a pressure sensor 224 between the dispense pump
and the dispense nozzle, as well as in communication with the
dispense pump 220. The controller is configured to monitor the
behavior of the pressure as measured by the pressure sensor 224
during a dispense cycle. Once the controller determines a typical
behavior of the pressure during a dispense cycle, such as is shown
by plot 604 in FIG. 6, the controller can compute a controlled flow
rate function to be applied to the dispense pump in order to obtain
a relatively constant pressure (and dispense flow rate) during a
cycle, or to substantially follow a desired pressure function or
variation for the dispense process. For example, if the pressure
increases during a dispense cycle as shown in FIG. 6, the
controller can calculate a decreasing speed control function for
the dispense pump, as shown by the plot 702 in FIG. 7. Because the
controller has access to calibration information for the dispense
pump, which can be stored in accessible memory 806, the controller
can compute an adjustment to be made to the pump speed for any
point along the dispense pressure curve in order to bring the
actual pressure to the reference pressure. In one example, the
controller can look at the minimum pressure at the beginning of the
cycle (after any initial spike) and the maximum pressure at the end
of the cycle, and can calculate a monotonically decreasing pump
speed function, such as shown by the plot 702 of FIG. 7, which will
cause the pressure curve 704 to be more constant during the
dispense cycle where a constant pressure is desired. For many
systems, this first order adjustment can be sufficient to reduce
the amount of dispense error to well within specification.
[0049] In order to further reduce error, determinations of
adjustment can be made at a plurality of points along the pressure
curve, in order to calculate a number of necessary pump adjustments
over time. Because the pressure does not monotonically increase
over the dispense cycle, a more complex function can more
accurately adjust for the behavior of the system over time. This
also can help to account for an initial spike by starting the
process at a lower pressure and quickly increasing the pressure.
The function can be a step function, whereby if five measurements
are taken during a cycle, for example, there will be five different
pressure (pump speed) settings over a given dispense cycle. A curve
can be fit to the data in another embodiment, in order to compute a
smooth speed adjustment function to be applied to the dispense
pump. The smooth function can more accurately track the behavior of
the system and reduce the likelihood of pressure spikes due to
sudden changes in pump speed.
[0050] Such an approach also can be used to optimize the filtration
rate of the system, although the filtration rate is typically less
critical. A pressure sensor 812 can be placed between the filter
212 and the dispense pump 220 (or at another appropriate location)
in order to monitor the behavior of the pressure (and hence the
flow rate) corresponding to the filtration rate. The controller can
calculate adjustments to be applied to a pressure regulator 404
directing a flow of gas into the buffer vessel 302 and/or a
pressure regulator 202 directing a flow of gas into the chemical
source 204. There can be many other appropriate locations for
measuring and/or adjusting pressure as would be apparent to one of
ordinary skill in the art in light of the disclosure and teachings
contained herein.
[0051] FIG. 9 illustrates an exemplary method 900 for controlling a
dispense flow rate using a system such as that illustrated in FIG.
8. In this embodiment, the dispense pressure during an initial
dispense process is monitored 902. Using the behavior of the
dispense pressure, an adjustment function is calculated to be
applied to the dispense pump during a dispense cycle 904. An
initial pressure is built up inside the dispense system before the
next dispense cycle 906. The pressure is measured near the dispense
nozzle 908, and an adjustment is made to the dispense pump in order
to bring the system pressure to substantially a reference pressure
before the chemical is dispensed 910. Once the pressure is
substantially at the reference pressure, the dispense cycle begins
and the adjustment function is used to drive the dispense pump in
order to control the pressure (and dispense flow rate) during the
dispense cycle 912. The dispense pressure is measured during the
dispense process 914. Adjustments are made to the adjustment
function to be used for subsequent dispense cycles 916. These
adjustments in one embodiment are made in real time, during the
dispense process, in order to attempt to reduce the error in a
given cycle. In another embodiment, these adjustments are instead
tracked during the dispense cycle then used to calculate a new
adjustment function to be used for the next dispense cycle. In one
embodiment, the adjustment function is reevaluated after each
dispense cycle, such that the behavior of the pump can be different
for any or all dispense cycles, which can account for changes in
system behavior, atmospheric conditions, or any other such
potentially influencing factor. In other embodiments, the
adjustment function is only reevaluated periodically, after each
lot, or when the error reaches a given threshold (less than or
equal to the allowable error).
[0052] The above sequences of steps provide methods for controlling
and/or adjusting the dispensing of a photolithography chemical onto
a substrate positioned in a track lithography tool in accordance
with various embodiments. As shown, the methods use certain
combinations of steps, although other sequences of steps may also
be performed according to alternative embodiments. For example,
alternative embodiments of the present invention may perform the
steps outlined above in a different order.
[0053] Moreover, the individual steps may include multiple
sub-steps that may be performed in various sequences as appropriate
to the individual step. Furthermore, other alternatives can also be
provided where steps are added, one or more steps are removed, or
one or more steps are provided in a different sequence without
departing from the scope of the claims herein. One of ordinary
skill in the art would recognize many variations, modifications,
and alternatives.
Track Lithography Tool
[0054] FIG. 10 is a plan view of an exemplary track lithography
tool 1000 which can be used with various embodiments in accordance
with the present invention. As illustrated in FIG. 10, the track
lithography tool 1000 contains a front end module 1006 (sometimes
referred to as a factory interface or FI) and a process module
1008. In other embodiments, the track lithography tool 1000
includes a rear module (not shown), which is sometimes referred to
as a scanner interface. Front end module 1006 generally contains
one or more pod assemblies or FOUPS (e.g., items 1002A-D) and a
front end robot assembly 1010 including a horizontal motion
assembly 1066 and a front end robot 1012. The front end module 1006
may also include front end processing racks (not shown). The one or
more pod assemblies 1002A-D are generally adapted to accept one or
more cassettes 1004 that may contain one or more substrates or
wafers that are to be processed in the track lithography tool 1000.
The front end module 1006 may also contain one or more pass-through
positions (not shown) to link the front end module 1006 and the
process module 1008.
[0055] The process module 1008 generally includes a number of
processing racks 1014A, 1014B, 1030, and 1040. As illustrated in
FIG. 10, some processing racks 1014A and 1014B in this embodiment
each include a coater/developer module with a shared dispense 122.
A coater/developer module with this shared dispense 1022 includes
two coat bowls 1016 positioned on opposing sides of a shared
dispense bank 1018, which contains a number of nozzles 1020
providing processing fluids (e.g., bottom anti-reflection coating
(BARC) liquid, resist, developer, and the like) to a wafer mounted
on a substrate support 1028 located in the coat bowl 1016. In the
embodiment illustrated in FIG. 10, a dispense arm 1024 sliding
along a track 1026 is able to pick up a nozzle 1020 from the shared
dispense bank 1018 and position the selected nozzle over the wafer
for dispense operations. Of course, coat bowls with dedicated
dispense banks are provided in alternative embodiments.
[0056] Processing rack 1030 includes an integrated thermal unit
1038 including a bake plate 1032, a chill plate 1034, and a shuttle
1036. The bake plate 1032 and the chill plate 1034 are utilized in
heat treatment operations including post exposure bake (PEB),
post-resist bake, and the like. In some embodiments, the shuttle
1036, which moves wafers in the x-direction between the bake plate
1032 and the chill plate 1034, is chilled to provide for initial
cooling of a wafer after removal from the bake plate 1032 and prior
to placement on the chill plate 1034. Moreover, in other
embodiments, the shuttle 1036 is adapted to move in the
z-direction, enabling the use of bake and chill plates at different
z-heights. Processing rack 1040 includes an integrated bake and
chill unit 1046, with two bake plates 1042A and 1042B served by a
single chill plate 1044.
[0057] One or more robot assemblies (robots) 1048A, 1048B are
adapted to access the front-end module 1006, the various processing
modules or chambers retained in the processing racks 1014A, 1014B,
1030, and 1040, and the scanner 1062. By transferring substrates
between these various components, a desired processing sequence can
be performed on the substrates. The two robots 1048A, 1048B
illustrated in FIG. 10 are configured in a parallel processing
configuration and travel in the x-direction along horizontal motion
assembly 1050A, 1050B. Utilizing a mast structure (not shown), the
robots 1048A, 1048B are also adapted to move in a vertical
(z-direction) and horizontal directions, i.e., transfer direction
(x-direction) and a direction orthogonal to the transfer direction
(y-direction). Utilizing one or more of these three directional
motion capabilities, the robots 1048A, 1048B are able to place
wafers in and transfer wafers between the various processing
chambers retained in the processing racks that are aligned along
the transfer direction.
[0058] The first robot assembly 1048A and the second robot assembly
1048B here are adapted to transfer substrates to the various
processing chambers contained in the processing racks 1014A, 1014B,
1030, and 1040. In one embodiment, to perform the process of
transferring substrates in the track lithography tool 1000, robot
assembly 1048A and robot assembly 1048B are similarly configured
and include at least one horizontal motion assembly 1050A, 1005B,
at least one vertical motion assembly 1054A, 1054B, and robot
hardware assemblies 1052A, 1052B supporting robot blades 1056A,
1056B. Robot assemblies 1048A, 1048B are in communication with a
system controller 1066. In the embodiment illustrated in FIG. 10, a
rear robot assembly 1060 is also provided.
[0059] The scanner 1062, which in one embodiment may be purchased
from Canon USA, Inc. of San Jose, Calif., Nikon Precision Inc. of
Belmont, Calif., or ASML US, Inc. of Tempe Ariz., is a lithographic
projection apparatus used, for example, in the manufacture of
integrated circuits (ICs). The scanner 1062 exposes a
photosensitive material (resist), deposited on the substrate in the
cluster tool, to some form of electromagnetic radiation to generate
a circuit pattern corresponding to an individual layer of the
integrated circuit (IC) device to be formed on the substrate
surface.
[0060] Each of the processing racks 1014A, 1014B, 1030, and 1040
can contain multiple processing modules in a vertically stacked
arrangement. That is, each of the processing racks may contain
multiple stacked coater/developer modules with shared dispense
1022, multiple stacked integrated thermal units 1038, multiple
stacked integrated bake and chill units 1046, or other modules that
are adapted to perform the various processing steps required of a
track photolithography tool. As examples, coater/developer modules
with shared dispense 1022 may be used to deposit a bottom
antireflective coating (BARC) and/or deposit and/or develop
photoresist layers. Integrated thermal units 1038 and integrated
bake and chill units 1046 may perform bake and chill operations
associated with hardening BARC and/or photoresist layers after
application or exposure.
[0061] In one embodiment, a system controller 1066 is used to
control all of the components and processes performed in the
cluster tool 1000. The controller 1066 is generally adapted to
communicate with the scanner 1062, monitor and control aspects of
the processes performed in the cluster tool 1000, and is adapted to
control all aspects of the complete substrate processing sequence.
The controller 1066, which is typically a microprocessor-based
controller, is configured to receive inputs from a user and/or
various sensors in one of the processing chambers and appropriately
control the processing chamber components in accordance with the
various inputs and software instructions retained in the
controller's memory. The controller 1066 generally contains memory
and a CPU (not shown) which are utilized by the controller to
retain various programs, process the programs, and execute the
programs when necessary. The memory (not shown) is connected to the
CPU, and may be one or more of a readily available memory, such as
random access memory (RAM), read only memory (ROM), floppy disk,
hard disk, or any other form of digital storage, local or remote.
Software instructions and data can be coded and stored within the
memory for instructing the CPU. The support circuits (not shown)
are also connected to the CPU for supporting the processor in a
conventional manner. The support circuits may include cache, power
supplies, clock circuits, input/output circuitry, subsystems, and
the like all well known in the art. A program (or computer
instructions) readable by the controller 166 determines which tasks
are performable in the processing chamber(s). Preferably, the
program is software readable by the controller 166 and includes
instructions to monitor and control the process based on defined
rules and input data.
[0062] It is to be understood that embodiments of the invention are
not limited to use with a track lithography tool such as that
depicted in FIG. 10. Instead, embodiments of the invention may be
used in any track lithography tool including the many different
tool configurations described in U.S. patent application Ser. No.
11/315,984, entitled "Cartesian Robot Cluster Tool Architecture"
filed on Dec. 22, 2005, which is hereby incorporated by reference
for all purposes and including configurations not described in the
above referenced application.
[0063] A particle detection apparatus 1064 also can be provided as
a module in the track lithography tool 1000. This particle
detection apparatus 1064 is serviced by one or both of the robot
assemblies 1048A, 1048B and is utilized, as described more fully
throughout the present specification, to detect particles present
on the backside of a wafer or substrate. The use of the particle
detection apparatus may occur before or after several of the wafer
processes performed within the track lithography tool 1000. These
wafer processing include coat, develop, bake, chill, exposure, and
the like. In a particular embodiment, the substrate is scanned for
particles prior to processing by the scanner. In alternative
embodiments, the particle detection apparatus 1064 is located
external to the track lithography tool 1000 in a separate
stand-alone test module. One of ordinary skill in the art would
recognize many variations, modifications, and alternatives.
[0064] The examples and embodiments described herein are for
illustrative purposes only. Various modifications or changes in
light thereof will be suggested to persons skilled in the art and
are to be included within the spirit and purview of this
application and scope of the appended claims. It is not intended
that the invention be limited, except as indicated by the appended
claims.
* * * * *