U.S. patent application number 11/437994 was filed with the patent office on 2008-01-10 for system and method of monitoring contamination.
Invention is credited to William M. Goodwin, Anatoly Grayfer, Devon Kinkead, Oleg P. Kishkovich.
Application Number | 20080009099 11/437994 |
Document ID | / |
Family ID | 32872679 |
Filed Date | 2008-01-10 |
United States Patent
Application |
20080009099 |
Kind Code |
A1 |
Kishkovich; Oleg P. ; et
al. |
January 10, 2008 |
System and method of monitoring contamination
Abstract
The present invention provides passive sampling systems and
methods for monitoring contaminants in a semiconductor processing
system. In one embodiment, that passive sampling system comprises a
collection device in fluid communication with a sample line that
provides a flow of gas from a semiconductor processing system. The
collection device is configured to sample by diffusion one or more
contaminants in the flow of gas.
Inventors: |
Kishkovich; Oleg P.;
(Greenville, RI) ; Grayfer; Anatoly; (Newton,
MA) ; Goodwin; William M.; (Medway, MA) ;
Kinkead; Devon; (Holliston, MA) |
Correspondence
Address: |
WEINGARTEN, SCHURGIN, GAGNEBIN & LEBOVICI LLP
TEN POST OFFICE SQUARE
BOSTON
MA
02109
US
|
Family ID: |
32872679 |
Appl. No.: |
11/437994 |
Filed: |
May 19, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10662892 |
Sep 15, 2003 |
7092077 |
|
|
11437994 |
May 19, 2006 |
|
|
|
10395834 |
Mar 24, 2003 |
|
|
|
10662892 |
Sep 15, 2003 |
|
|
|
10253401 |
Sep 24, 2002 |
6759254 |
|
|
10395834 |
Mar 24, 2003 |
|
|
|
09961802 |
Sep 24, 2001 |
6620630 |
|
|
10253401 |
Sep 24, 2002 |
|
|
|
Current U.S.
Class: |
438/115 ; 356/36;
438/14; 438/16 |
Current CPC
Class: |
G01N 1/2205 20130101;
B01D 53/22 20130101; G01N 1/2247 20130101; G01N 1/405 20130101;
H01L 21/67253 20130101 |
Class at
Publication: |
438/115 ;
356/036; 438/014; 438/016 |
International
Class: |
H01L 21/00 20060101
H01L021/00; G01N 1/00 20060101 G01N001/00; H01L 21/66 20060101
H01L021/66 |
Claims
1. A method for sampling a contaminant in a semiconductor
processing system, comprising the steps of: delivering a gas stream
from the semiconductor processing system to a collection device,
the processing system having an optical system; and collecting a
contaminant from the gas stream in the collection device for a
duration exceeding a saturation capacity of the collection
device.
2. The method of claim 1 further comprising determining a
contaminant concentration in the semiconductor processing system
from a sample collected with the collection device.
3. The method of claim 1 further comprising collecting a sample
from a photolithography tool.
4. The method of claim 1 further comprising collecting a lower
molecular weight contaminant and a higher molecular weight
contaminant and continuing to collect the higher molecular weight
contaminant the saturation capacity for the lower molecular weight
contaminant.
5. The method of claim 1 further comprising collecting a sample in
the collection device with an adsorptive material.
6. The method of claim 5 further comprising providing an adsorptive
material including Tenax.
7. A method for monitoring and removing a contaminant in a
photolithography system having an optical path, comprising the
steps of: delivering a gas stream from a photolithography system to
a collection device; collecting a contaminant from the gas stream
with the collection device; analyzing a collected sample of the
contaminant; and actuating a membrane to remove the contaminant
from the optical path.
8. The method of claim 7, wherein collecting a contaminant
comprises collecting at least one of refractory compounds, high
molecular weight compounds and low molecular weight compounds.
9. The method of claim 7 further comprising collecting a low
molecular weight compound and a high molecular weight compound past
a saturation capacity of the device.
10. The method of claim 7 further comprising analyzing the
collected sample to determine a contaminant concentrate.
11. The method of claim 7 further comprising flowing the gas stream
through a contaminant removal device including the membrane.
12. A method for cleaning a contaminated surface in a semiconductor
processing system, comprising the steps of: delivering a gas stream
to the contaminated surface in the processing system in the
presence of light, the gas stream having an additive gas and the
gas stream combining with a contaminant on the contaminated surface
to form a volatile product; and removing the volatile product from
the processing system.
13. The method for cleaning of claim 12, wherein the step of
removing the volatile product includes using a purge gas.
14. The method of cleaning of claim 12, wherein steps of delivering
a gas stream to the contaminated surface further comprises
delivering a gas stream to an optical system surface.
15. The method of claim 13 wherein the step of removing further
comprising filtering the volatile product from the gas stream with
a filter.
16. The method of claim 13 further comprising monitoring a
concentration of the volatile product.
17. The method of claim 12 further comprising removing the volatile
product from a photolithography tool.
18. The method of claim 12 further comprising removing an organic
compound.
19. The method of claim 12 further comprising removing an inorganic
compound.
20. The method of claim 12 further comprising removing a refractory
compound.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional application of U.S.
patent application Ser. No. 10/662,892 filed Sep. 15, 2003, which
is a continuation-in-part of U.S. patent application Ser. No.
10/395,834 filed Mar. 24, 2003, which is continuation-in-part of
U.S. patent application Ser. No. 10/253,401 filed Sep. 24, 2002,
now U.S. Pat. No. 6,759,254, which is a continuation-in-part of
U.S. patent application Ser. No. 09/961,802, filed Sep. 24, 2001,
now U.S. Pat. No. 6,620,630. The entire contents of the above
patents and applications are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] Semiconductor manufacturers continue to measure and control
the level of contamination in the processing environment,
especially during the critical steps of the photolithography
processes. The typical means of determining the quality and
quantity of contamination in gas samples in cleanroom manufacturing
environments involves sampling air and purge gases, such as, for
example, filtered and unfiltered air, clean dry air, and nitrogen,
with sampling tubes or traps, typically containing adsorptive
medium such as, the polymer Tenax.RTM. This sampling process is
followed by analysis using thermal desorption, gas chromatography
and mass spectrometry (TD/GC/MS). The combination of TD/GC/MS
provides identification of sample components and a determination of
the concentration of these components. The most abundant
contaminants in these manufacturing environments are low molecular
weight components such as acetone and-isopropyl alcohol. The
current sampling time for existing traps typically varies between
0.5 and 6 hours with total accumulated sample volumes ranging
typically between 20 and 50 liters.
[0003] Further, in applications that are directed to the
manufacturing of or use of optical elements such as, for example,
photolithography, the detection and quantification of compounds
having a higher molecular weight such as, for example, siloxanes is
of primary concern. These compounds having a higher molecular
weight are, however, typically in much lower concentrations as
compared with the low molecular weight species. Further, the
compounds having a high molecular weight can also be defined as
condensable compounds with a boiling point typically greater than
approximately 150 degrees C. The current methods for determining
contamination have the limitation of the sample volume being based
on the total trap capacity of the lighter or lower molecular weight
components, for example, compounds having typically less than six
carbon atoms. As the heavier components are usually present at much
lower concentrations, the collection of a significant mass of these
higher molecular weight species is limited.
[0004] In addition, polluting or contaminating substances may
adhere onto the optical elements and reduce the transmission of
light. Currently airborne contamination is addressed in cleanroom
environments with little regard for contaminants that may be
adsorbed onto the surfaces of optical elements. The adsorbed
contamination reduces the transmission of light through the optical
elements and system.
[0005] Thus, contamination of optical systems is emerging as a
significant risk to photolithography and other semiconductor
manufacturing processes as shorter wavelengths of the
electromagnetic spectrum are exploited. However, molecular films on
optical surfaces physically absorb and scatter incoming light.
Scattered or absorbed light in photolithography optical surfaces
causes distortion of the spherical quality of wavefronts. When the
information contained in the spherical wavefront is distorted, the
resulting image is also misformed or abberated. Image distortions,
or in the case of photolithography, the inability to accurately
reproduce the circuit pattern on the reticle, cause a loss of
critical dimension control and process yield.
[0006] Typically, filter systems are used to remove molecular
contamination in semiconductor processing environments. Systems are
in place to measure the performance of such filter systems.
However, typical monitoring of filter performance includes
measurement of filter breakthrough either by process failure or by
detection of the target filtered gas at the discharge of the filter
system. However, these measurement means detect breakthrough after
it has occurred.
[0007] A need still exists for determining, accurately and
efficiently, the presence and quantity of contaminants that can
alter and degrade the optical systems in semiconductor processing
instruments. There further remains a need to monitor the
performance of gas phase filter systems prior to a breakthrough
failure.
SUMMARY OF THE INVENTION
[0008] The preferred embodiments of the system of the present
invention provide an accurate and efficient system of determining
and/or controlling the quality and/or quantity of contamination
within a gas sample which can reduce the performance of optical
elements used in semiconductor processing instruments, such as, for
example, within the light path of a deep ultraviolet
photolithography exposure tool. In a preferred embodiment of the
present invention, the contamination may be gaseous as well as
contamination adsorbed onto optical surfaces. Optical performance
can be evaluated without limitation as the level of transmitted or
reflected light through an optical system. The embodiments of the
system and method of the present invention are predicated on the
recognition that compounds having both high and low molecular
weights can contribute to the contamination of optical systems but
can operate at different rates. As such, the contaminants that
negatively impact the performance of optical elements can be
described in terms of different orders, such as, for example,
first, second and third order effects.
[0009] First and second order contaminating effects have a greater
impact on contamination of optical systems than third or fourth
order contaminants. The first order contaminants may comprise high
molecular weight organics such as, for example, C.sub.6 siloxanes
and C.sub.6 iodates with an inorganic component which is not
volatilized through combination with oxygen. Second order
contaminants may comprise high molecular weight organics, such as,
for example, compounds including carbon atoms within the range of
approximately six to thirty carbon atoms (C.sub.6-C.sub.30). Third
order effects can arise due to the contaminating effects of
organics such as C.sub.3-C.sub.6 that have approximately three to
six carbon atoms. Fourth order contaminants include organics such
as, for example, methane, that have approximately one to five
carbon atoms. In many applications, the first and second order
contamination can have a much lower concentration than the third
and/or fourth order contamination, yet have a significantly greater
effect on the operation of the system.
[0010] A preferred embodiment in accordance with the present
invention of a method for detecting and monitoring, and preferably
removing contamination in a semiconductor processing system
includes delivering a gas sample from the processing system to a
collection device. The method further includes collecting
contamination which comprises refractory compounds, and high and
low molecular weight compounds, from the gas in the collection
device by sampling the gas for a duration exceeding the saturation
capacity of the collection device for high molecular weight
compounds. The compounds having a high molecular weight are
condensable with a boiling point typically greater than
approximately 150 degrees C.
[0011] A preferred embodiment of the system and method of the
present invention for determining contamination includes the
detection of refractory compounds such as, for example, siloxanes,
silanes and iodates, and high molecular weight organics. The
preferred embodiment includes the removal of refractory compounds,
high molecular weight organics and low molecular weight organics,
all of which contribute to the contamination of optical systems,
but which can operate at different contamination rates.
[0012] The system of the present invention for determining
contamination can use different types of sample collecting media.
In a preferred embodiment, the sample collecting media can emulate
the environment of the optical surfaces of interest such as, for
example, the absorptive or reactive properties of the optical
surfaces. A measure of contamination adsorbed onto optical surfaces
enables the minimization and preferably the removal of the
contaminants. In another preferred embodiment, a polymer that has a
high capacity for absorbing the compounds with a high boiling point
is used in a collection device such as, for example, Tenax.RTM. a
polymer based on 2-6 diphenyl p-phenylene. The operation of the
system in accordance with a preferred embodiment of the present
invention includes quantitatively measuring the concentration of
both low and high boiling point compounds in the same sample
wherein the collection device has been driven beyond the
breakthrough volume or saturation capacity of the collection media
to capture the low molecular weight compounds. The breakthrough
volume of the collection device is defined in a preferred
embodiment as the quantity of gas needed to go beyond the
adsorption capacity of the device.
[0013] In accordance with a preferred embodiment of the present
invention, the method for detecting contamination includes a
sampling time extended by, for example, a number of hours, days or
weeks to enable collection of an appropriate mass of contaminants
which are present in relatively low concentration. In a preferred
embodiment, the sampling time is typically beyond the breakthrough
capacity of the collection device for low molecular weight
components, is at least six hours long and preferably within a
range of six to twenty-four hours for a sampling tube system. The
extended time allows for the collection of higher masses of
refractory compounds and higher molecular weight compounds that may
interfere with the performance of optical components even more than
low molecular weight compounds. The higher molecular weight
compounds include, but are not limited to, for example, siloxanes
and silanes.
[0014] In accordance with another preferred embodiment of the
present invention, a semiconductor processing instrument, for
example, a photolithography cluster, includes a filtering system to
remove contaminants. The filtering system includes a selective
membrane to filter organic compounds from a gas stream.
[0015] A preferred embodiment includes a method for monitoring the
performance of a filter positioned in an airstream in a
semiconductor processing system. The method includes sampling the
airstream at a location upstream of the filter to detect the
molecular contaminants present in the airstream, identifying a
target species in the contaminants upstream of the filter,
selecting a non-polluting species of a contaminant having a
concentration greater than a concentration of the target species,
measuring the non-polluting species in the airstream at a plurality
of locations, and determining the performance of the filter with
respect to the target species from measurements of the
non-polluting species. The plurality of locations includes, but is
not limited to, a location downstream of the filter and at a
location within the filter. Further, the method for monitoring
includes generating a numerical representation of a chromatogram of
the airstream sampled at a location upstream of the filter. The
method for monitoring includes the non-polluting species having a
molecular weight that is lower than that of the target species. A
correlation is established between the low and high molecular
weight compounds. In addition, in the method for monitoring, the
step of sampling includes collecting refractory compounds, high
molecular weight compounds and low molecular weight compounds. The
filter comprises absorptive material.
[0016] A preferred embodiment includes a system for determining and
monitoring contamination in a photolithography instrument, having
at least one collection device in fluid communication with a gas
flow extending through an optical system of the tool, the
collection device having a material analogous to optical elements,
and a light source providing high energy light to the collection
device such that at least one contaminant in the gas flow reacts
with the light to create a deposition layer on the material.
Further, the system includes at least one photodetector coupled to
the collection device to detect the presence of the deposition
layer on the material by monitoring either the spectral or
transmission differences. The material in the system comprises
glass spheres having predetermined surface properties for
adsorption of contaminants. The material is at least one of glass
and coated glass material. The contamination includes at least one
of refractory compounds, high molecular weight compounds and low
molecular weight compounds.
[0017] In accordance with another aspect of the present invention,
an apparatus for determining contamination in a semiconductor
processing system includes a filter system having a plurality of
filter traps for collecting contaminants from a gas stream for a
duration, and an interface module coupled to the filter system in
fluid communication with a gas flow extending through the
processing system and directing a portion of the gas flow into and
out of the filter system.
[0018] The contaminants include at least one of refractory
compounds, high molecular weight compounds and low molecular weight
compounds. A vacuum source can be coupled to the filter system to
increase a pressure gradient across the filter traps. The filter
traps can have a permeable membrane that filter contaminants such
as at least one of a refractory compound, a high molecular weight
compound and a low molecular weight compound from the gas flow.
[0019] In preferred embodiments, the interface module further
comprises a pressure regulation device, a controller,
electronically controlled valves to impose a duty cycle for
sampling, a timer device to determine a sampling duration and a
cooling device such as a thermoelectric cooling device. Further,
the filter traps have an absorptive material such as a polymer, for
example, Tenax.RTM..
[0020] The foregoing and other features and advantages of the
system and method for determining and controlling contamination
will be apparent from the following more particular description of
preferred embodiments of the system and method as illustrated in
the accompanying drawings in which like reference characters refer
to the same parts throughout the different views. The drawings are
not necessarily to scale, emphasis instead being placed upon
illustrating the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Preferred embodiments of the present invention are described
with reference to the following drawings, wherein:
[0022] FIG. 1 is a graphical representation of contamination
coefficient versus molecular weight;
[0023] FIG. 2 is a graphical representation illustrating a
comparison of a preferred embodiment of the system for determining
contamination with respect to sample mass in a trap and sampling
time in accordance with the present invention and the prior
art;
[0024] FIG. 3 is a graphical representation illustrating analyzed
spectral comparisons of the system and method of determining
contamination in accordance with a preferred embodiment of the
present invention and the prior art;
[0025] FIG. 4 is a graphical representation illustrating surface
coverage as a function of contamination level in accordance with a
preferred embodiment of the present invention;
[0026] FIG. 5 is a preferred embodiment of a system of determining
contamination in accordance with the present invention;
[0027] FIG. 6 is a preferred embodiment of a refractory trap system
in accordance with the present invention;
[0028] FIG. 7 shows a flow chart of a method of detecting
contamination in accordance with a preferred embodiment of the
present invention;
[0029] FIG. 8 is a diagram illustrating a preferred embodiment of a
filtering system in accordance with the present invention;
[0030] FIGS. 9A and 9B illustrate a schematic block diagram of a
filter device having a bed showing the retention of different
species in the bed and a graphical representation of the efficiency
of the filter bed with respect to time by measuring the different
species, respectively, in accordance with a preferred embodiment of
the present invention;
[0031] FIG. 10 is a flowchart of a method for monitoring the
performance of a gas phase filter system in accordance with a
preferred embodiment of the present invention;
[0032] FIG. 11 is a schematic diagram of a system that includes a
filter system in accordance with a preferred embodiment of the
present invention;
[0033] FIGS. 12A-12C are graphical illustrations of chromatograms
of a gas sample including an average ion scan of the spectra end
(FIG. 12C) in accordance with a preferred embodiment of the present
invention;
[0034] FIGS. 13A and 13B are chromatograms of a second gas sample
in accordance with a preferred embodiment of the present
invention;
[0035] FIG. 14 is a graphical illustration of a chromatogram of a
sample of oil free air sampled at a location prior to a filter in
accordance with a preferred embodiment of the present
invention;
[0036] FIG. 15 is a graphical illustration of a chromatogram of a
sample of oil free air sampled at a location after the filter in
accordance with a preferred embodiment of the present
invention;
[0037] FIG. 16 is a graphical illustration of a chromatogram of a
sample of nitrogen gas sampled at a location prior to a filter bed
in accordance with a preferred embodiment of the present
invention;
[0038] FIGS. 17A and 17B graphically illustrate a chromatogram of a
sample of nitrogen gas sampled after the filter system and an
average ion scan of the end of the spectra, respectively, in
accordance with a preferred embodiment of the present
invention;
[0039] FIG. 18 graphically illustrates a chromatogram of a empty
sampling tube in accordance with a preferred embodiment of the
present invention;
[0040] FIG. 19 is a flow chart of a method for on-line, real-time
monitoring of the performance of a filter system in accordance with
a preferred embodiment of the present invention;
[0041] FIG. 20 illustrates a schematic block diagram of a system
using a system for determining and monitoring contaminants and
performance of a filter system in accordance with a preferred
embodiment of the present invention;
[0042] FIG. 21 illustrates a schematic diagram of system modules in
accordance with a preferred embodiment of the system for
determining and monitoring contaminants and the performance of a
filter system of the present invention;
[0043] FIG. 22 illustrates a schematic diagram of a module having a
plurality of filter traps of the system shown in FIG. 20 in
accordance with a preferred embodiment of the present
invention;
[0044] FIG. 23 illustrates an alternate view of the module having a
plurality of filter traps as shown in FIG. 21;
[0045] FIG. 24 illustrates a detailed view of the module having a
plurality of filter traps as shown in FIG. 21 along with the
plumbing in the manifolds in accordance with a preferred embodiment
of the present invention;
[0046] FIGS. 25A-25C illustrate schematic diagrams of a device that
functions as a concentrator in a filter system in accordance with a
preferred embodiment of the present invention;
[0047] FIGS. 26A and 26B illustrate schematic block diagrams of a
detection system that emulates and detects a deposition process on
optical elements in accordance with a preferred embodiment of the
present invention;
[0048] FIG. 27 is a schematic illustration of a passive sampling
system in accordance with various embodiments of the present
invention;
[0049] FIG. 28 is a flow chart of methods for passive monitoring of
contaminants in a semiconductor processing system in accordance
with various embodiments of the present invention;
[0050] FIGS. 29A-29B are schematic diagrams illustrating one
embodiment of a system for detecting airstream backflow in a
semiconductor processing system in accordance with a preferred
embodiment of the present invention;
[0051] FIGS. 30A-30E illustrate schematic diagrams of a device that
functions as a concentrator in a filter system in accordance with a
preferred embodiment of the present invention; and
[0052] FIGS. 31A-31E illustrate a schematic diagram of a system
using a device for monitoring contaminants and performance of a
filter system in accordance with a various embodiments of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0053] The present invention is directed to a system and method for
determining and controlling contamination. Preferred embodiments of
the present invention address gaseous contamination as well as the
contaminants adsorbed on surfaces, for example, an optical surface.
The latter is more critical to the performance of the optical
elements.
[0054] Table 1 illustrates various species in a cleanroom
environment, such as, for example, a fabrication environment using
photolithography systems. The low molecular weight species, such as
acetone, isopropyl alcohol and low molecular weight siloxanes are
the most prevalent in manufacturing environments. Compounds that
are most likely to reduce the performance of optics are compounds
having a high contamination coefficient or a high molecular weight
examples can include, but are not limited to, methoxytrimethyl
silane, trimethyl silane and trimethyl silanol. These compounds
appear in italics in Table 1 have a higher molecular weight, higher
contamination coefficient and an inorganic component. Compounds
that negatively impact optical systems may also be described and
include refractory compounds such as silanes, siloxanes and
iodates, in particular hexamethyldisiloxane (C.sub.6-siloxane).
TABLE-US-00001 TABLE 1 Typical concentration, Compound (in clean
rooms) ppbV Isopropyl Alcohol 610.0 Acetone 330.0 Ethanol 134.0
Silane,Methoxytrimethy/- 35.0 Heptane,Hexadecafluoro- 28.0
2-Pentanone 17.0 2-Butanone (MEK) 9.8 Hexane,Tetradecafluoro- 8.9
Butanoic Acid,Heptafluoro- 5.2 Tetrahydrofuran 3.3 3-Buten-2-one
2.5 4-Methyl-2-pentanone (MIBK) 1.9
Silane,Trimethy/(1-Methy/ethoxy)- 1.7 n-Pentane 1.4
Silanol,Trimethy/- 1.4
[0055] Optics design also affects the relative sensitivity of the
system to contamination. For example, light transmission is
important in transmissive optical systems, like windshields,
wherein reflectance approaches zero. High reflectivity systems,
where transmission approaches zero, are inherently twice as
contamination sensitive as transmissive optical systems because
photons pass through any contaminating film twice, whereas light
energy is only absorbed or scattered once in transmissive
systems.
[0056] Describing the effect of molecular films on optical surface
properties in terms of mathematics yields equation 1, for
reflectance, and equation 2 for transmission.
.rho.x(.lamda.)=.rho.(.lamda.)exp[-2.alpha.c(.lamda.)x] Equation 1
.tau.x(.lamda.)=.tau.(.lamda.)exp[-.alpha.c(.lamda.)x] Equation 2
Where: [0057] P=reflectance [0058] .alpha.=absorbance [0059]
.tau.=transmittance [0060] .lamda.=wavelength [0061]
.alpha.c=absorbance of a contaminating film, empirically
determined
[0062] Both transmitted and reflected energy, which is information
used in lithography instruments and tools in semiconductor
fabrication systems, drop exponentially with the accumulation of
molecular films on optical surfaces. In lithography processes, the
first order effect of molecular films on lenses is typically a
reduction in light intensity due to energy absorbance by the
contaminating film. These transmission losses reduce the number of
wafers processed per hour, and consequently reduce productivity.
This is analogous to the power reductions in spacecraft solar
arrays, caused by accumulating molecular films. Secondary effects,
in lithography processes, involve a reduction in image uniformity,
which reduces critical dimension uniformity and yield.
[0063] Photochemical decomposition reactions occur when high-energy
photons interact with organic vapors. These reactions form
extremely reactive free radicals from otherwise neutral and
relatively inert organic molecules. Irrespective of where radical
formation occurs, in the gas phase or on the surface of optical
elements, the resulting free radicals may react to form much larger
organic compounds, which can contaminate optical elements. In
severe cases, a polymer layer may be formed on the optical surface.
The relationship between the chemical nature of the organic species
and wavelength of light it absorbs can affect the nature and
severity of optics contamination. For example, I-line or 365 nm
wavelength light is energetic enough to break down only a few
iodated components, which are not commonly found in clean room air.
248 nm wavelength light, typically used in deep ultraviolet (DUV)
lithography for fabricating 250 to 150 nm linewidth devices, is
more efficient and reacts with most halogenated organics and may
even interact with some common hydrocarbons. 193 nm light, required
for less than 130 nm geometries, reacts very efficiently with a
wide range of airborne or gaseous molecular organic contaminants.
157 nm optical elements are even more sensitive to environmental
conditions than 193 nm optics because this wavelength of light is
efficiently absorbed or interacts with nearly all organic species
plus oxygen and atmospheric moisture, requiring the exposure area,
the area between the final optical element and the wafer, commonly
called the free working area, to be purged with an inert, clean,
dry, oxygen-free gas.
[0064] As the wavelength of light used in the lithography exposure
tool decreases, the energy per unit photon increases. These
progressively higher energy photons stand a better chance of
breaking the bonds of a number of commonly present molecular
species, ultimately rendering them into reactive species that stick
to optical surfaces. The overall structure of a molecule plays a
significant role in the ability of a photon to break any specific
bond. Table 2 summarizes optics contamination as the lower
wavelengths of electromagnetic spectrum are used to provide for the
fabrication of smaller features.
[0065] Atmospheric pressure, low K1 factor optical lithography for
less than 150 nm critical dimension on 300 mm wafer substrate
device production may be the basis of advanced Integrated Circuit
(IC) production in the near term. In these technology nodes,
lithography-induced critical dimension variations have a
particularly acute affect on device characteristics. For example,
the standard deviation of propagation delay times for CMOS based
ring-oscillators increases from 1% for 300 nm devices to 20% in 250
nm devices. Variations in gate oxide, impurity, and gate lengths
were the primary causes of variations in device delay times. Below
200 nm gate length, however, the impact of gate length variation
accounts for a remarkable 80% of the effect. The criticality of
dimension variation in 150 nm lithography, for example, has lead to
a critical dimension control budget of 15 mn, post-etch, 3 sigma.
Since exposure dose and image resolution are compromised by optics
contamination in proportion to the location and thickness of the
contaminating film, contamination needs to be prevented before it
occurs. TABLE-US-00002 TABLE 2 Issue .lamda. = 248 nm .lamda. = 193
nm .lamda. = 157 nm Comments Propensity to Low Moderate Nearly
Assumes form vapor photo- concentration deposits the low ppb
nitrogen range (<10 ppb O2) Ability to Low Moderate High Based
on photoclean absorption surfaces in- coefficients using active
organic layer oxygen absorbance Interactions Aromatics Aromatics
Nearly all Interaction hydro- moderate very hydro- determines
carbons absorbance other weakly carbons allowable absorb of before
lens performance suffers
[0066] Existing methods of contamination control in lithography
involves the use of activated carbon filters and/or some
combination of adsorptive and chemisorptive media to adsorb or
chemisorb the contaminants in air and gas streams that come in
contact with the lens surfaces. In some cases, periodic
regeneration of the adsorptive beds by thermal desorption
occurs.
[0067] Passive adsorption is unable to practically capture and
retain the lighter hydrocarbons, oxygen, and water that interfere
with imaging using 193 nm and 157 nm light. The propensity to form
photodeposits, ability to photoclean, and interaction of
hydrocarbons is tabulated relative to different wavelengths of
light in Table 2.
[0068] Filter systems for contamination control are described in
U.S. application Ser. No.: 10/205,703, filed on Jul. 26, 2002
entitled "Filters Employing Porous Strongly Acidic Polymers and
Physical Adsorption Media", now U.S. Pat. No. 6,761,753, U.S.
application Ser. No.: 09/969,116, filed on Oct. 1, 2001 entitled
"Protection of Semiconductor Fabrication and Similar Sensitive
Processes", and U.S. application Ser. No. 09/783,232, filed on Feb.
14, 2001 entitled "Detection of Base Contaminants In Gas Samples",
now U.S. Pat. No. 6,855,557, the entire teachings of the above
referenced patents and applications being incorporated herein by
reference in their entirety.
[0069] FIG. 1 is a graphical representation 20 of contamination
coefficient 22 versus a molecular weight 24. Note that a higher
contamination coefficient means that it is more likely to
contaminate system optics. The nearer term 193 nm wavelengths show
some correlation between the contaminants molecular weight and its
ability to contaminate the lens. Consequently, while the higher
molecular weight species are of greater immediate concern for lens
contamination, the lower boiling point materials, which are
typically in higher concentration in semiconductor cleanrooms as
shown in Table 1, can become a concern due to their much higher
concentration and ability to adsorb photon energy at progressively
shorter wavelengths. Moreover, particularly at 157 nm, oxygen and
water need to be removed from the light path because they also
absorb photon energy.
[0070] Existing systems have many disadvantages including passive
adsorption systems that do not effectively remove low molecular
weight organic materials; the removal efficiency and capacity of
passive adsorption systems are proportional to the concentration of
the impurities. In this application, the inlet concentrations are
very low, making efficiency and capacity correspondingly low; and
on-site regeneration of passive adsorption beds requires periodic
temperature increases to regenerate the beds. Since most advanced
lithography systems must maintain air and gas temperature stability
at typically less than 100 milliKelvin, to avoid heating or cooling
the optics, which change their optical characteristics, this
strategy is impractical in advanced lithography.
[0071] FIG. 2 is a graphical representation 30 illustrating a
comparison of a preferred embodiment of the system for determining
contamination with respect to sample mass in a collection device or
contamination trap and sampling time in accordance with the present
invention and the prior art. An extended duration sample time,
sample time 40, is used wherein the gas sample volume is not
limited by the low molecular weight breakthrough volume, as is the
case with the prior art method using sample time 38. In a preferred
embodiment, the sampling time is at least six hours long and is
preferably in a range of six hours to twenty-four hours. Higher
capacity traps yielding longer collection times may be necessary
for certain applications.
[0072] The extended time sampling method in accordance with a
preferred embodiment of the present invention, collects higher
masses of higher molecular weight compounds, which contribute to
the contamination in the gas supply and which reduce the
performance of optical elements more so than lower molecular weight
compounds. Both high and low molecular weight compounds contribute
to the contamination level but are operative at different rates.
The high molecular weight compounds contribute to first order
contaminating effects as they cause more damage to the optical
systems even if present at low concentrations than low molecular
weight compounds which contribute to third and fourth order
effects. The collection device in accordance with a preferred
embodiment is driven beyond saturation or breakthrough capacity to
quantitatively measure the equilibrium concentration of low
molecular weight compounds. The breakthrough volume is the amount
of gas sample volume required to go beyond the absorbent capacity
of the collection device. It should be noted that contaminates may
be inorganic materials which may be carried by organics to the
optical element. This extended time sampling method can also use
different types of sample collecting media including those with
adsorptive properties close to that of the optical surfaces of
interest.
[0073] A preferred embodiment of the present invention includes
"glass" or "coated glass" based adsorptive contamination traps.
These contamination traps have not been used in the past due to
their limited ability to collect and retain lower molecular weight
species. These materials have surface properties identical or
similar to properties of the optical elements used in the optical
systems of photolithography tools. Other materials that emulate the
surface properties of these optical elements that generate
contamination can also be used.
[0074] In a preferred embodiment, the extended time sampling method
may be extended from a few hours to several days and even weeks.
The amounts of analyte collected represents the average value over
time for compounds that have not reached their breakthrough time as
illustrated by line 36 at sample time 2, line 40, and an average
equilibrium concentration for those species that have already
reached their breakthrough volume as illustrated by line 34 at
sample time 2, line 40.
[0075] With respect to higher molecular weight species, the
internal surface of the sampling lines and/or manifolds are kept at
equilibrium with the gas phase sample, and therefore do not
interfere with the sample collection process. In a preferred
embodiment, between sampling sessions, flow through the sampling
lines and/or manifolds is maintained.
[0076] FIG. 3 is a graphical representation 50 illustrating
spectral analysis comparisons of the system and method of
determining contamination in accordance with a preferred embodiment
of the present invention and the prior art. The extended time
sampling method of the present invention offers better sensitivity
for components having high boiling points as illustrated by lines
52, 56. The results of the extended time sampling method in
accordance with a preferred embodiment of the present invention
better represent contamination on the optical surface, given the
improved high molecular weight sample collection method of the
present invention. A preferred embodiment of the system of the
present invention provides the ability to use the actual optical
surface of interest as the collection medium which in turn allows
alignment of sampling surface properties and optical surface
properties thereby making the analysis results more meaningful to
the prediction of optics contamination.
[0077] The extended time sampling method in accordance with a
preferred embodiment may reduce and preferably eliminate the
uncertainties of sample loss on sample lines and/or manifolds. The
extended time sampling method's simplicity minimizes the effect of
uncontrolled contamination by personnel deploying the traps.
Consequently, less training and experience are required to collect
samples.
[0078] FIG. 4 illustrates graphically surface coverage as a
function of contamination level showing greater surface mass
coverage per unit concentration in accordance with a preferred
embodiment of the present invention. FIG. 4 illustrates this
relationship for higher molecular weight components at the upper
left with the lower molecular components towards the lower right of
the graph. For a given concentration, the higher molecular weight
compounds collect on surfaces more readily than do lower molecular
weight species. One of the problems with the prior art method is
that due to the shorter sampling times, much of what little sample
is available for collection collects on the sample tube walls and
manifold surfaces, all upstream of the collection trap, and never
reaches the trap. This phenomenon causes a further loss of high
molecular weight sample mass. Moreover, heated sampling lines
and/or manifolds, which could ameliorate the problem, are not
practical in the production cleanroom environment.
[0079] FIG. 5 is a diagram of a preferred embodiment of a system
100 for determining contamination in accordance with the present
invention. The preferred embodiment of the apparatus includes a
tubular collection device 102 having an inlet port 104 and an
outlet port 106. In a preferred embodiment, the collection device
includes, absorptive materials 108 such as, for example, glass
spheres of a given size. In a preferred embodiment, crushed glass
spheres are used. In another preferred embodiment, the absorptive
material 108 is the polymer Tenax.RTM. supplied by, for example,
Supelco. Tenax.RTM. has a high capacity for high boiling point
compounds and operating Tenax.RTM. past low molecular weight
breakthrough capacity allows the capture of a meaningful and
analyzable mass of high molecular weight compounds. To collect a
sample, an end cap in the inlet post is removed, allowing gas from
a gas source to pass through the inlet port 104. Laser light may be
directed through the sampling tube in a preferred embodiment of the
present invention. The free radicals of the contaminants present in
the gas sample may bond with the absorptive media 108 in the
collection device 102.
[0080] In a preferred embodiment of the system for controlling
contamination, multiple sample tubes and blank collection devices
may be used. The collection device or refractory trap is applicable
to both high pressure sampling, for example, purge gas, venting to
the atmosphere assuming sufficient pressure and filter sampling,
wherein the traps are connected to a vacuum source. The flow is
controlled by an easily changeable critical orifice.
[0081] In a preferred embodiment, the trap contains three sample
tubes, one blank and two active sample devices. Chemical analysis
of the data may be correlated to transmission or image uniformity
loss of the lithography tool, for example, using a regression
analysis which weights first, second, third and fourth order
effects: Uniformity or Intensity=a
[C.sub.6-siloxane]+b[C.sub.6-C.sub.30]+c[C.sub.3-C.sub.6]+d[C.sub.1-C.sub-
.5] herein the parenthetic expressions are indicative of the
concentration of species. First and second order contaminating
effects have a greater impact on contamination of optical systems
than third or fourth order contaminants and typically show a
greater contamination coefficient (e.g. a>b>c>d). The
first order contaminants may comprise high molecular weight
refractory organics such as, for example, C.sub.6 siloxanes and
C.sub.6 iodide with an inorganic component which is not volatilized
through combination with oxygen. Second order contaminants may
comprise high molecular weight organics, such as, for example,
compounds including carbon atoms within the range of approximately
six to thirty carbon atoms (C.sub.6-C.sub.30). Third order effects
can arise due to the contaminating effects of organics such as
C.sub.3-C.sub.6 that have approximately three to six carbon atoms.
Further, fourth order contaminants Include organics such as, for
example, methane, that have approximately one to five carbon
atoms.
[0082] In preferred embodiments of the system in accordance with
the present invention, a refractory trap may be used both upstream
and downstream of any in-line filtration system. FIG. 6 is a
preferred embodiment of a refractory trap system 120 in accordance
with the present invention. As described herein before refractory
compounds include at least siloxanes such as, for example,
hexamethyldisiloxane (C.sub.6), silanes such as, for example,
C.sub.3-silane, silanes such as, for example, C.sub.3 and iodates.
The refractory trap system 120 includes a conduit 121 in
communication with a gas source and through which a gas sample is
carried with pressures ranging between approximately 1 to 120 psi.
The gas sample is carried downstream to a pressure cavity 122. A
pressure relief valve 123 allows the continuous flow of gas to
ensure that the pressure cavity walls are in equilibrium with the
gas phase of the gas sample. The refractory trap system 120
includes active sampling traps or collection devices 124 and a
blank trap 125 in the trap cavity 126. The active sampling trap
elements 124 may include an absorptive medium such as, for example,
the polymer Tenax.RTM.. The gas sample flow in active elements is
approximately 0.11 lpm. The blank trap 125 is not in communication
with the gas source or pressure cavity and as such is not removing
any contaminants. The outflow gas stream from the active collection
devices 124 flows downstream into a manifold 127 which is in fluid
communication with a vacuum line 130, via an orifice 129. A
pressure/vacuum regulator valve 108 is disposed between the
manifold and the orifice 129 to regulate pressure. The refractory
trap system 120 provides for both a low pressure application or a
high pressure application using a single design.
[0083] In a preferred embodiment, the gas supply may include a
particular constituent such as hydrogen gas which may be used to
clean the surfaces of the collection devices or, surfaces of
optical systems that have been contaminated by a surface
contaminant, for example, SiX. The gas additive combines with the
surface contaminant to form a volatile compound that is then purged
from the system. For example, SiX combines with hydrogen gas to
form silane (SiH.sub.4) which is volatile and is purged. The purge
gas, is preferably in the ultra high purity gas level allowing the
collection device to be placed upstream and downstream of typical
in-line filters.
[0084] A sample report derived from a collection device may
comprise the following information: [0085] Contact information:
Name, address, phone, email of person sending the sample [0086]
Tool #: [0087] Gas sampled: N2 Air [0088] Sample location: [0089]
Upstream of filter [0090] Downstream of filter [0091] Interstack
[0092] Sample start date: [0093] Sample end date: [0094] Date
received: [0095] Report date: [0096] Upstream Sample: [0097] C2-C5:
X ppb*(*equilibrium concentration) [0098] C.sub.6-C.sub.30: Y ppb
[0099] Total siloxanes: z ppb [0100] Total sulfur compounds: [0101]
Past history on this sample location:
[0102] In another preferred embodiment the collection device is
located directly in contact with the airstream, thereby avoiding
sample line contamination and using either passive diffusion or an
active flow to collect the sample.
[0103] FIG. 7 is a flow chart of the method 150 of detecting and
removing contamination in accordance with a preferred embodiment of
the present invention. The method includes the step 152 of
delivering a gas sample to a collection device. In a preferred
embodiment, the collection device is as described with respect to
FIG. 5 and/or FIG. 6. The method further includes the step 154 of
absorbing contaminants contained in the gas sample in the
collection device. The collection device is configured to emulate
the environment of surfaces of optical elements. The method 150
includes the step 156 of maintaining the gas sample in the
collection device for an extended duration sampling time which
represents operation of the collection device past the saturation
or breakthrough capacity of the device, for at least the lower
molecular weight species. As described herein before the extended
duration sampling time enables the collection of an equilibrium
concentration of low and preferably high molecular weight
compounds.
[0104] The internal surfaces of the sampling lines and manifolds
are in equilibrium with the gas phase sample in order to not
interfere with the sample collection process. In a preferred
embodiment, the method 150 includes maintaining the flow of the gas
sample through the sampling lines and manifolds.
[0105] In accordance with another preferred embodiment, the system
of the present invention comprises a photolithography cluster tool,
for example, an exposure tool, used in manufacturing semiconductor
devices, that is sensitive to molecular contamination and a
filtering system which removes the molecular contamination which
may include volatile and semi-volatile or condensable organic
substances, causing contamination of optical elements via series of
homogeneous and/or heterogeneous ultraviolet (UV) induced
processes. These optical elements are contained typically within a
light path of a photolithography tool. In accordance with a
preferred embodiment of the present invention, the filtering system
for the ultra-purification of compressed fluids, for example,
nitrogen, air or other suitable gases for purging of optical
elements, with organic constituents comprises a membrane module,
which separates the components of a given gas mixture by means of
their different transport rates through the membrane. High removal
efficiency of organic contaminants, in particular of first and
second order contaminants may be obtained due to selective
permeation on glassy polymers such as, for example, polyetherimide
or rubbery polymers such as, for example, silicone rubber and also
on porous ceramic membranes which generally have extended
temperature limits up to approximately 300.degree. C. Water and
oxygen are preferably also removed using the membrane as they can
degrade light transmission along the optical path in the
system.
[0106] Membranes are generally available in two morphologies:
homogeneous or composite. In the latter, thin polymeric
permselective "skin" is deposited on a preformed porous substrate,
which need not be the same polymer and may or may not interact with
permeate. Polymeric membranes may be cast into various shapes: flat
sheets for plate and frame and spiral wound modules, in the latter
sheets and separating screens are wound into sandwich like
structure by rolling around central permeate tube and
self-supporting fibers, for example, hollow fibers and capillary
membranes.
[0107] In a preferred embodiment as illustrated in FIG. 8 the
filtering system 170 comprises a filtration module based on a
selectively permeable membrane 186 to filter organic compounds from
a gas stream such as, for example, a nitrogen stream. The
selectively permeable membrane may be of the type such as supplied
by, for example, Membrane Technology & Research, Inc. In this
preferred embodiment, the feed flow 174 is nitrogen that contains
some amount of organic contamination. The feed flow may comprise
99-100% nitrogen with any balance in organic contaminants as well
as water and oxygen. Assuming 90% removal efficiency of the
membrane, the composition of the residue is purified by a factor of
10. The composition of the permeate stream can be enriched with
organic contaminants. The filtering system 170, in accordance with
a preferred embodiment of the present invention preferably removes
contamination effects of first through fourth order
contributors.
[0108] In another preferred embodiment the filtering system 170
comprises a filtration module based on a selective membrane 186 to
filter organic compounds from a gas stream 174 wherein the
collection device or pipe 172 is connected to a vacuum source to
increase the pressure gradient across the membrane 186 to increase
membrane efficiency. In this embodiment the feed flow 174 is
nitrogen that contains some amount of organic contamination. In a
particular embodiment the feed flow, 174 can include nitrogen with
organic contaminants as indicated above. Assuming a 99% removal
efficiency of the membrane, the composition of the residue 176 is
again improved by a factor of 10 for nitrogen and the balance in
organic contaminants. The composition of the permeate stream 178 is
further enriched with organic contaminants.
[0109] In another preferred embodiment, the filtering system 170
comprises a filtration module based on a selective membrane 186 to
filter organic compounds from a gas stream. In this particular
embodiment the feed flow is nitrogen that contains some amount of
organic contamination. The feed flow 174 comprises 99-100% nitrogen
with the balance being organic contaminants. Assuming 90% removal
efficiency of the membrane, the composition of the residue 176 is
99-100% nitrogen and the balance in organic contaminants. The
composition of the permeate stream 178 may be enriched with organic
contaminants. The organic contaminant enriched airstream 178 is
then directed to a regenerative adsorption device for purification.
The permeate stream 178, which has been purified by an adsorption
bed system, is then returned to the feed flow. This filtering
system in accordance with a preferred embodiment of the present
invention reduces the loss of feed flow volume.
[0110] In another preferred embodiment, the filtration module
consists of a composite membrane, a support of which is pretreated
with a solid electrolyte washcoat and an oxide catalyst to promote
electrochemical decomposition of the permeate 178 within the
support at relatively low temperature.
[0111] In another preferred embodiment, the filtering system 170
comprises a filtration module based on a selective membrane 182 to
filter organic compounds from a gas stream. In this embodiment, the
feed flow 174 is nitrogen that contains some amount of organic
contamination. The feed flow comprises 99-100% nitrogen with the
balance being organic contaminants, oxygen, and water. Assuming 90%
removal efficiency of the membrane, the composition of the residue
is again improved by a factor of 10 for nitrogen with the balance
being organic contaminants, but the membrane may not be selective
enough to remove oxygen and water. Accordingly, the residue 176 of
the filter system 170 is then directed to a second filter system,
of similar mechanical construction to the first, which contains a
different membrane specifically selected to allow oxygen and water
to traverse the membrane, but is, again, less permeable to
nitrogen. The residue of this second filter system may now be
substantially free of organics, water, and oxygen which are all
hazards to advanced lithography processes. Again, the composition
of the permeate stream may be enriched with organic contaminants,
water, and oxygen.
[0112] This filtering system can be used to purify nitrogen,
synthetic air, clean dry air, all gas streams used in advanced
photolithography, or any other compressed gas used in semiconductor
processing. It may be, however, advantageous to filter synthetic
air prior to mixing, for example, filter oxygen and nitrogen
separately, before mixing them together to make synthetic air.
[0113] The filtering system may be constructed without limitation
in a number of ways such as, for example, rolled-up supported
membrane, rolled up self-supporting membrane, membrane disposed on
a prefabricated porous supporting structure, a cylindrical pleated
air filter, or comprise hollow fiber bundles through which the feed
flow is directed.
[0114] The preferred embodiments of the filter system of the
present invention remove both high and low molecular weight organic
compounds and other unwanted contaminants such as water vapor,
oxygen, inorganic impurities, effectively, and with a low
concentration feed flow. In addition, the filter systems of the
present invention operate continuously without filter replacement
or pressure, flow, or temperature change or disruption. The
preferred embodiments of the present invention address the problems
of the prior art filters which have a limited capacity for low
molecular weight hydrocarbons and rely on regenerative thermal
cycles, which cause instability of the output gas temperature. The
preferred embodiments of the filtering systems of the present
invention provide an unlimited capacity for removing low molecular
weight hydrocarbons and other contaminating species, independent of
feed flow concentration, produce no sudden changes in the output
flow conditions, and are easy and inexpensive to maintain.
[0115] FIG. 9A illustrates a schematic block diagram of a filter
device having a bed showing the retention of different species in
the bed in accordance with a preferred embodiment of the present
invention. This preferred embodiment takes advantage of the
inherent property of physioadsorbants to show different retention
times for different species. For example, lower molecular weight
species move through the carbon bed 252 more rapidly than do higher
molecular weight species. As described hereinbefore, certain higher
molecular weight species may be more contaminating to a process
than lower molecular weight species. Accordingly, measurements are
taken at a location upstream, in the middle of the chemical filter
bed 252 or in an alternate preferred embodiment between two
in-series filters, and at the discharge of relatively fast moving
(moving through the filter bed) species, hereinafter referred to as
leading indicator gases as indicators of the imminent breakthrough
of the more slow moving species.
[0116] FIG. 9B graphically illustrates the efficiency of the filter
bed with respect to time by measuring the different species in
accordance with a preferred embodiment. In a preferred embodiment,
the target gas is an C.sub.6 organic contaminant which may, or may
not, contain an inorganic atom, and the leading tracer gas is a
C.sub.5 organic species. The detector system in a preferred
embodiment includes a thermal desorption preconcentrator coupled to
a gas chromatograph with flame ionization detection. This system
achieves the sensitivity the system requires to perform reliable
low concentration work. Samples of the leading tracer gas are taken
at various locations in the filter, before or after the filter or
between two filters, for example, filter 1 and 2. The performance
of the filter can be illustrated on a graphical user interface
included in the system.
[0117] FIG. 10 is a flowchart 290 of a method for monitoring the
performance of a gas phase filter system in accordance with a
preferred embodiment of the present invention. The method includes
the generation of a numerical representation of the chromatogram of
the gas flow upstream of the filter per step 292. Per step 294 the
target polluting species are selected as the target is present at a
detectable level upstream. In step 296 the non-polluting species
that are the leading indicators are selected that are closest in
elution (removing of absorbed material from adsorbent) time and
greater than and equal to the concentration of target species of
interest. The leading indicator tracer gas travels faster than the
target pollutant through the filter bed. The method includes
measuring the non-polluting species in different locations, for
example, at a location prior to the filter bed, at a location in
the middle of the filter bed and at a location at the discharge of
the filter bed. The breakthrough of the target pollutant is then
assessed and determined by the measurement of the leading indicator
(tracer gas) as detected by a detector system per step 300.
[0118] A method for monitoring the performance of a gas-phase
filter positioned in an air stream, which may be subject to
molecular contamination, and useful for removing molecular
contamination therefrom includes sampling the airstream at a
location upstream of the air filter so that a variety of upstream
molecular contaminants are detected and a target pollutant and a
tracer gas are identified. The tracer gas travels faster than the
target pollutant of interest in the filter. Further, the method
includes sampling the airstream at a location downstream of the air
filter so that the tracer gas is detected over time. The method
includes determining the performance of the filter with respect to
the target pollutant using a method that establishes a correlation
between the low molecular weight compounds and the high molecular
weight compounds and thus determining the performance of the air.
In a preferred embodiment, the method includes sampling the
airstream at a location in the middle of the filter bed.
[0119] FIG. 11 is a schematic diagram of a system 320 that includes
a filter system in accordance with a preferred embodiment of the
present invention. The gas flow or airstream 322 input into the
filter 324 is sampled by a detector system. The filter bed includes
a physioadsorbent to chemically adsorb contaminants. The air flow
in the middle of the filter bed is also sampled and analyzed using
a sampling port 326 that provides the sample to the detection
system. The location of the sampling port 326 with respect to the
outlet is proportional to the propagation rate of the leading
indicator gas, for example, if the propagation rate of the tracer
gas is high then the distance of the sampling port 326 from the
outlet is raised. The discharge flow 328 at the outlet of the
filter 324 is also sampled. A position selectable valve 336
disposed in the inlet of the detection system provides sampling
capability for more than one stream. Thus, the sampled flow from
the inlet of the filter bed, the middle of the filter bed or the
outlet of the filter bed can be selected as input into the
detection system. A valve 338 allows for the selection of the flow
into a preconcentrator 340 or into a bypass 342. A pump 346 for the
preconcentrator provides adequate flow therein. The discharge of
the bypass or the preconcentrator is then selected by the valve to
then form an input into a chromatographic column 350. A heater 348
is disposed around the chromatographic column 350. The outlet of
the column forms the input of the detector 352 having a flame
ionization detection system. The spectrum illustrating the
abundance of the constituents detected with respect to time is
displayed on a graphical user interface 358.
[0120] The preferred embodiment uses detection technology which is
inherently sensitive to, and can identify and quantify organic
species at very low concentrations, for example, below 1 ppb (V)
using, for example, gas chromatograph/flame ionization detection
(GCFID). The preferred embodiments of the present invention provide
advanced warning of filter failure without actually jeopardizing
the process by allowing the actual species of interest to
breakthrough. The preferred embodiment does so at a low enough
concentration to be meaningful to highly sensitive processes, like
optics systems.
[0121] In a preferred embodiment the filter includes a bed of the
polymer pellets exposed to the airstream using a traditional media
tray and rack system. In an alternative preferred embodiment the
filter includes a honeycomb configuration with the polymer pellets
held in a partially filled or completely filled honeycomb
structure. Other embodiments include filter construction including,
but not limited to, a monolithic porous or honeycomb structure
formed from polymer, a mat of polymer fiber, either woven or
nonwoven, pleated and arranged in a traditional air filter, a bed
of the activated carbon pellets exposed to the airstream using a
traditional media tray and rack system, a honeycomb configuration
wherein the activated carbon pellets are held in a partially filled
or completely filled honeycomb structure, a monolithic porous or
honeycomb structure formed from the activated carbon, a mat of
activated carbon fiber, either woven or nonwoven, pleated and
arranged in a traditional air filter and a carbon based composite
filter constructed of woven or nonwovens support structures.
[0122] In preferred embodiment the detection system may include any
system that is capable of measuring organic compounds at very low
concentrations including, but not limited to a GCFID with, or
without a preconcentrator, a GCMS with, or without a
preconcentrator, a photoacoustic detector with, or without a
preconcentrator, and IMNS with, or without a preconcentrator, or
any combination thereof.
[0123] In a preferred embodiment reactive inorganic materials,
including molecular bases and molecular acids are included in the
airstream. These compounds may react to form nonvolatile salt
particles. Molecular condensable high boiling point organic
materials which may be adsorbed on the optical elements and undergo
DUV light induced radical condensation or polymerization. Resulting
polymer films in some cases may be removed by active oxygen
treatment species. Refractory materials are compounds containing
atoms forming nonvolatile or reactive oxides, for example, but not
limited to, P, Si, S, B, Sn, Al. These contaminants may be exposed
to DUV light and may form refractory compounds resistant to active
oxygen treatment.
[0124] In a preferred embodiment molecular bases and molecular acid
samples are collected using impingers filled with distilled water
(10 cc). An air (gas) sample is drawn through the impinger at 1
L/min for 240 minutes using a programmable sample pump. The total
sample volume in a preferred embodiment, without limitation is 240
L.
[0125] Further, in a preferred embodiment, molecular condensable
high boiling point organic materials and refractory material
samples are collected using Thermodesorbtion Samplers (TDS) filled
with porous medium, for example, Tenax.RTM. T.A. An air (gas)
sample is drawn through the collection media at a flow of the 0.15
L/min for 240 minutes, using a programmable sampling pump with low
flow adapter. Total sample volume is approximately 36 L. In
preferred embodiments, the flow rate can vary in a range 50 cc/min
to 250 cc/min. The temperature can also vary from approximately
room temperature to approximately -100.degree. C. Field blank or
empty samples are collected for each type of sample. The field
blank is a sample device (impinger of TDS), which is handled in the
field the same way as an actual sample having zero sample volume
drawn through. The purpose of the field blank is to detect possible
uncontrolled contamination events during sample handling and
transportation. Field blanks are analyzed in the same manner as
actual samples.
[0126] In a preferred embodiment, analyses of molecular bases and
molecular acids samples includes using Ion Chromatography methods.
Compounds are identified by retention time and quantified using
individual calibration standards and a 10-point calibration
procedure. Low Detection Limit (LDL) of the corresponding methods
is 0.1 ug/m.sup.3 per individual component. In a preferred
embodiment, molecular bases and refractory material samples are
analyzed using a Gas Chromatograph (GC) equipped with a Mass
selective Detector and Thermal Desorption System (TD). The total
analytical system (TD/GC/MS) is optimized to separate and quantify
analytes with a boiling temperature of hexane and higher with LDL
of -0.1 ug/m.sup.3 per individual component. Individual components
are identified by a MS library search and chromatographic peak
position. Individual component are quantified against two
analytical standards, for example, toluene and hexadecane.
Analytical results are listed in the Tables 3-9. TABLE-US-00003
TABLE 3 N2- N2- Concentration, ug/m3 facilities facilities Oil free
Air Oil free Air before after before after Fab ambient Sub Fab
Ammonia (as NH3) 0.4 <0.1 0.4 <0.1 4.2 6.4 Other inorganic
<0.1 <0.1 <0.1 <0.1 <0.1 <0.1 acids Nitrous acid
(as <0.1 <0.1 0.8 <0.1 0.8 1 NO2) Nitric acid (as NO2)
<0.1 <0.1 <0.1 <0.1 <0.1 <0.1 C.sub.6 + Organic
-1.1 -0.9 -.0.8 -.2.3 -213 H Compounds (as toluene)
[0127] TABLE-US-00004 TABLE 4 Concentration, ug/m3 Compound as
toluene as hexadecane Benzene (78) 0.4 0.2 Silane,Dimethoxydimethyl
(59) 2.7 1.2 Hexane,3-Methvl (26) 0.4 0.2 2-Heptane (47) 0.5 0.2
Silane,Trimethoxymethyl (45) 0.4 0.2 Hexane,2,5-Dimethyl (33) 0.3
0.1 Toluene (82) 1 2.9 1.3 Propanoic acid,2-hydroxy-ethyl ester
(59) 2 1.5 0.7 PGMEA (92) 3 2.2 1 Ethylbenzene (59) 4 3.2 1.3
n-Propylbenzene (56) 0.3 0.1 Cyclohexane (84) 9.5 0.2 Xylenes (48)
5 15.2 6.1 Styrene (59) 0.3 0.1 1,2,3Trimethylbenzene (72) 1.8 0.7
1,3,5Trimethylbenzene (60) 0.6 0.2 Cyclohexanone (77) 6 0.6 0.2
3-Heptanone (47) 0.4 0.2 Unknown 0.5 0.2 Unknown 0.7 0.3
Octane,2,6-Dimethyl (59) 7 0.3 0.1 Cyclohexane,(1-Methylethyl) (40)
0.4 0.2 Nonane (59) 0.4 4.1 Octane,2,5,6-Trimethyl (53) 4.3 1.7
Octane,2,2,7,7-Tetramethyl (53) 1.8 0.7 Octane,2,2,6-Trimethyl (64)
1.4 0.6 Benzene,1-Ethyl,3-Methyl (93) 8 3.1 1.2 Decane,2-Methyl
(77) 1.2 0.5 Benzene,1-Ethyl,2-Methyl (77) 0.9 0.4 Benzaldehyde
(48) 9 2.8 1.1 Carbamic acid,methyl-phenyl ester (25) 2.1 0.8
Propylene cabonate (86) 10 3.5 1.4 Heptane,2,2,4,6,6-Pentamethyl
(64) 2.6 1 Decane,2,2''Dimethyl 64) 11 5.7 4 Decane2,2,9-Trimethyl
(77) 12 10.1 2.3 Nonane,3,7-Dimethyl (67) 13 17 0.2
Decane,5,6-Dimethyl (50) 1.7 0.7 Decane,2,3-Dimethyl (40) 1.9 0.8
Nonane,3-Methyl-5-propyl (64) 3 1.6 Decane,2,6,7-Trimethyl (47) 14
1 6 Heptane,4-Ethyl-2,2,6,6-Tetramethyl (72) 15 14 0.2
Undecane,2,5-Dimethyl (59) 1 0.2 Undecane,4,6-Dimethyl (59) 16 1
4.8 Undecane,3,5-Dimethyl (53) 1 0.7 Undecane,4-methyl (83) 2 1
Nonane,3-methyl-5-propyl (64) 17 5 2.3 Undecane,5,7-Dimethyl (43) 1
0.7 Undecane,3,8-Dimethyl (38) 2 1 Dodecane,2,5-Dimethyl (36) 3 1.4
Heptane,2,2,3,4,6,6-Hexamethyl (72) 1 0.6 Dodecane,2,6,10-Trimethyl
(72) 2. 0.9 Tridecane,5-Methyl (64) 0. 0.3 Tridecane,4-Methyl (64)
0. 0.2 Dodecane (50) 0. 0.2 Benzoic acid (66) 18 9. 4
Cyclotetrasiloxane,Hexamethyl (39) 0. 0.2
Cyclotetrasiloxane,Octamethyl (54) 0. 0.2
2,5Cyclohexadiene-1,4-dione,2,5,-diphenyl (97) 2 10.1 Total 21
73
[0128] FIGS. 12A-12C are graphical illustrations of chromatograms
of a gas sample including an average ion scan of the spectra end
(FIG. 12C) in accordance with a preferred embodiment of the present
invention. The gas sample is fabricated ambient air.
[0129] The mass spectrometry (MS) results for sub-fabricated air
are listed in Table 5. TABLE-US-00005 TABLE 5 Concentration, ug/m3
Compound as toluene as hexadecane Hexane (78) 0.4 0.2 Benzene (84)
0.5 0.2 3-Pentanone,2,4-Dimethvl (72) 0.2 0.1 Hexanal (64) 0.3 0.1
Propanoc acid,2-hydroxy,propyl ester (56) 0.4 0.2 Propanoc
acid,2-oxo-ethyl ester (29) 0.1 0.05 Toluene (79) 1 3.3 1.4
3-Pentanone,2,4-Dimethyl (36) 0.2 0.1 2,3-Dimethyl Pentane (21) 0.4
0.2 Propanoic acid,2-hydroxy,propyl ester (57) 0.4 0.2 Propanoic
acid,2-oxo-ethyl ester (27) 0.1 0.05 PGMEA (59) 0.8 0.3 Ethyl
Benzene (61) 4 7 4.9 Styrene (39) 0.3 0.1 Xylenes (35) 5 35 17.5
1,2,4-Trimethylbenzene (67) 1.4 0.6 Nonane (61) 0.7 0.3
2-Furanol,tetrahydro-2-Methyl (56) 1.1 0.5 Cyclohexanone (73) 6 92
40 Octane,2,5,6-Trimethyl (50) 7 1.7 0.7 Benzene,1-Ethyl-3-methyl
(91) 8 2.2 0.9 Decane,3,4-Dimethyl (59) 0.4 0.2
Benzene,1-Ethyl-2-methyl (72) 0.5 0.2 Alpha-methylstyrene (96) 1.1
0.4 Heptane-2,2,4,6,6-Pentamethyl (42) 0.8 0.3 Benzaldehyde (96) 9
0.9 0.4 Decane,2,2-Dimethyl (64) 11 1.7 0.7 Decane,2,2,9-Trimethyl
(53) 12 4.2 1.7 Nonane,3,7-Dimethyl (47) 13 4.7 1.9
Benzene,1,3,5-Trimethyl (91) 0.6 0.2 Undecane,3,6-Dimethyl (38) 1
0.4 Decane,2,6,7-Trimethyl(53) 14 4.2 1.7 1-Hexanol,2-Ethyl (47)
1.2 0.5 Undecane,3,8-Dimethyl (43) 3.4 1.4 Undecane,4,6-Dimethyl
(59) 16 0.5 0.2 Nonane,3-methYI-5-propyl (53) 17 0.7 0.3
Nonane,5-Butyl (59) 1 0.4 Undecane (90) 1 0.4 Undecane,4-Methyl
(72) 1 0.4 Benzene,1-Ethyl-2,3-dimethyl (38) 0.5 0.2
Benzene,-4-Ethyl,1,2-dimethyl (72) 0.3 0.1 Dodecane,2,5-Dimethyl
(40) 1.1 0.4 Acetophenone (47) 0.7 0.3 1-Octanol,2-Butyl (78) 0.4
0.2 Benzene,1-Ethyl,2,4-dimethyl (47) 0.3 0.1
Dodecane,2,7,10-Trimethyl (59) 0.8 0.3 Undecane,2,7,10-Dimethyl
(53) 0.3 0.1 Benzoic acid (41) 18 8.9 3.6 Dodecane (87) 0.5 0.2
Phenyl maleic anhydride (23) 0.4 0.2 Trimethyl,1,3-Pentadiol
diisobutyrate (42) 19 2.9 1.2 Benzophenone (42) 0.1 0.05
2,5-Cyclohexadiene-1,4-dione-2,5-diphenvl (89) 20 12.1 4.8 Total
216 96
[0130] FIGS. 13A and 13B are chromatograms of another gas sample in
accordance with a preferred embodiment of the present invention.
The gas sample is a sub-fabricated ambient air sample.
[0131] Table 6 lists the mass spectrometry results for oil free air
upstream of the filter. TABLE-US-00006 TABLE 6 Concentration, ug/m3
(as Compound toluene) as hexadecane Silane,Dimethoxydimethyl 0.5
0.2 Toluene 0.3 0.1 Total /0.8 0.3
[0132] FIG. 14 is a graphical illustration of a chromatogram of a
sample of oil free air before a filter in accordance with a
preferred embodiment of the present invention.
[0133] Table 7 lists the mass spectrometry results for oil free air
sampled downstream of the filter. TABLE-US-00007 TABLE 7
Concentration, ug/m3 (as Compound toluene) as hexadecane
Silane,Dimethoxydimethyl 2.3 0.9 Silane,Trimethoxymethyl 1.3 0.5
Total 3.6 1.4
[0134] FIG. 15 is a graphical illustration of a chromatogram of a
sample of oil free air downstream of the filter in accordance with
a preferred embodiment of the present invention.
[0135] Table 8 lists the mass spectrometry results for nitrogen
facilities upstream of the filter. TABLE-US-00008 TABLE 8
Concentration, ug/m3 (as Compound toluene as hexadecane
Silane,Dimethoxydimethyl 0.8 0.3 Silane,Trimethoxymethyl 0.3 0.1
Total 1.1 0.4
[0136] FIG. 16 is a graphical illustration of a chromatogram of a
sample of nitrogen gas upstream of a filter in accordance with a
preferred embodiment of the present invention.
[0137] Table 9 lists the mass spectrometry results for nitrogen
downstream of the filter. TABLE-US-00009 TABLE 9 Concentration,
ug/m3 (as Compound toluene) as hexadecane Silane,Dimethoxydimethyl
0.9 0.4 Total 0.9 0.4
[0138] FIGS. 17A and 17B graphically illustrate a chromatogram of a
sample of nitrogen gas downstream the filter system and an average
ion scan of the end of the spectra, respectively, in accordance
with a preferred embodiment of the present invention.
[0139] FIG. 18 graphically illustrates a chromatogram of a blank
sampling tube in accordance with a preferred embodiment of the
present invention.
[0140] FIG. 19 is a flow chart of a method 600 for on-line
monitoring of the performance of a filter system in accordance with
a preferred embodiment of the present invention. The real-time
monitoring system for the performance of the filter system includes
taking a sample of the airstream upstream of the filter system per
step 602. The spectrum, for example, a chromatogram of the
airstream is generated and stored per step 604. A threshold target
range, in terms of, but not limited to, compounds and quantity, for
example, C.sub.5, 32 ppb, is determined. In step 606, all
contaminants below the target filteration range, location and
quantity are identified. In step 608, it is determined if the
contaminants match those present in the upstream sampling location.
If it is determined that there is no match, then another sample is
taken at the location and the process iterated. However, if the
contaminant level matches the threshold range upstream of the
filter then an alarm is set per step 618, indicating a breakthrough
condition for the particular compound.
[0141] Per step 610, for contaminants within the threshold target
filtration range, location and quantity, for example, C.sub.7, 12
ppb are identified from the spectrum. The total challenge for each
location is updated in step 612 and the remaining filter life is
calculated in step 614.
[0142] The remaining filter life is compared to a predetermined
warning limit in step 616. If the filter life is not greater than
the warning limit then the alarm is set per step 618. However, if
the filter life is greater than the warning limit then the process
is iterated again by taking a sample in step 602 and progressing
through the method described herein.
[0143] These steps in accordance with the method are iterated for
samples taken at different locations such as, but not limited to, a
location downstream of the filter, at locations in the filter bed
or within an interstack filter configuration including filter beds
in a series configuration.
[0144] The target range in preferred embodiments can include
variables such as amplitude of the peaks in a spectrum indicative
of the concentration of the compounds, or fast moving compounds
through the filter system indicative typically of low molecular
weight compounds. In an alternate embodiment a mixture of species
may be used as a determinant to monitor filter life and performance
or combinations of variables to analyze the efficacy of the
filteration system based on a parametric analysis.
[0145] FIG. 20 illustrates a schematic block diagram of a system
for determining and monitoring contaminants and the performance of
a filter system in accordance with a preferred embodiment of the
present invention. The system 650 includes a clean dry air filter
652 upstream of the system, a base module 654 and a module 682
having a plurality of filters or refractory traps. The base module
provides an interface to the filter module 682 and includes a
pressure regulation device 656 proximate to the inlet interface
674. The outlet interface 678 is in communication with the outlet
interface of the filter module 682 and the exhaust of the system
672. The exhaust interface 672 can also, in alternate embodiments,
be coupled to a vacuum system if evacuation of the system for
determining contamination is required. All the inlet and outlet
interfaces have sealed surfaces for environmental isolation. The
base module 654 further includes a controller/processor 658 such as
a proportional integral controller and a control module 670 in
preferred embodiments. A preferred embodiment includes
electronically controlled valves to impose a duty cycle for
sampling per filter cartridge. The duty cycle can be programmable.
The electronically controlled valves assist in embodiments having
high concentrations of impurities as they can address the potential
of overload.
[0146] The filter module 682 includes a plurality of filter traps
or cartridges 686 and an adequate valving arrangement in the
interfaces between the cartridges to allow accurate directional
flow between filters and post-collection sampling and analysis at a
plurality of sites. The post-collection analysis provides
quantitative and qualitative measures of the contamination present
in an airstream in the semiconductor processing environment.
Analysis tools such as, for example, GCMS or GCFID can be used to
detect the contaminants. It may also provide for monitoring of the
performance of the filter system.
[0147] In a preferred embodiment, the filter module can also
include a timer device, for example, a battery powered clock to
determine a sampling duration commensurate with predetermined
control parameters. A manifold 688 in the filter module provides
for flow between the plurality of filters. The manifolds have
mechanical interfaces such as adequate beveling to help in the
insertion of the filter cartridges. In a preferred embodiment the
channels in the filter module can accommodate filter blanks or trap
blanks which eliminate measurement errors.
[0148] In alternate embodiments the analysis system can be cooled
using a thermoelectric cooling device. Organics can be condensed
and collected using the low temperature embodiment. A fewer number
of traps are required for the low temperature embodiment since the
organics can be collected post condensation. An embodiment of the
low temperature system can include heat sinks to dissipate the heat
energy generated.
[0149] Alternate embodiments include safety devices coupled to
external interface connections in the event pressure is lost. This
obviates sampling inaccuracies.
[0150] FIG. 21 illustrates a schematic diagram of the modules in
accordance with a preferred embodiment of the system for detecting
and monitoring contaminants and the performance of a filter system
of the present invention. A cover 702 is placed over the base
module 704 and the filter module 706. The filter module 706
includes a plurality of filter cartridges 708 as described with
respect to FIG. 20.
[0151] FIG. 22 illustrates a schematic diagram of a module having a
plurality of filter traps of the detection system in accordance
with a preferred embodiment of the present invention. The base
module 704 is illustrated as being coupled to the filter module 706
as discussed with respect to FIG. 20.
[0152] FIG. 23 illustrates an alternate view of the module having a
plurality of filter traps as shown in FIG. 21.
[0153] FIG. 24 illustrates a detailed view of the module having a
plurality of filter traps as shown in FIG. 21 along with the
plumbing in the manifolds in accordance with a preferred embodiment
of the present invention.
[0154] FIGS. 25A-25C illustrate schematic diagrams of a device that
functions as a concentrator in a contaminant and filter monitoring
system as it increases the sensitivity of collection in accordance
with a preferred embodiment of the present invention. The
concentrator device 804 has a cover 802 and is inserted in a
manifold, for example, manifold 806 that has the inlet and outlet
interfaces. The filter system including a filter monitoring
functionality can be reduced in size using a coupling device such
as, for example, the concentrator 804. A greater volume can be
collected in the filter system if the temperature is reduced, for
example, to 0.degree. C. or below. The sensitivity of data
collection is also increased by the use of the concentrator device
that includes absorptive materials such as, for example, Tenax.RTM.
T.A. High boilers, such as, for example, organics having six carbon
atoms or more are absorbed by Tenax.RTM. T.A. In the alternative,
absorptive materials such as, for example, carbon traps such as
supplied by, for example, Supelco can be used in embodiments
including low boilers. Alternate embodiments include a combination
of the filters for high and low boilers which can be arranged in
parallel and/or in series.
[0155] FIGS. 26A and 26B illustrate schematic block diagrams of a
system that emulates and detects a deposition process on optical
elements in accordance with a preferred embodiment of the present
invention. As described hereinbefore, photochemical deposition
reactions occur when high-energy photons interact with organic
vapors. These reactions form extremely reactive free radicals which
may form larger organic compounds can contaminate optical elements.
A polymer layer may be formed on the optical surfaces and
contaminate the optical elements. A preferred embodiment includes a
detection system that emulates the deposition process of organic
compounds on optical surfaces. A filter cartridge 902 filled with a
glass pack such as, for example, glass beads 912 emulates the
optical materials. Compressed, clean dry air 910 is passed through
the filter cartridge. A light source 906 provides light, for
example, a laser providing laser light energy to the cartridge to
cause the formation of a polymer film on the surfaces of the glass
beads as high energy photons react with organic vapors in the
trap.
[0156] The photodetector includes a photocell 904 to measure the
energy level of light, which is altered based on the deposition of
contaminants on the surfaces of the multitude of glass beads. The
glass beads provide for a larger surface area for deposition. The
spectral and transmission differences are monitored to determine
the level of contamination. This embodiment provides a prospective
method to determine damage that can occur on the optical elements
such as, for example, the optics in the stepper. Measures can then
be taken to counter the potential damage to valuable optics.
[0157] It should be understood that the programs, processes,
methods and systems described herein are not related or limited to
any particular type of collection media, or computer or network
system (hardware or software), unless indicated otherwise. Various
types of general purpose or specialized computer systems may be
used with or perform operations in accordance with the teachings
described herein.
[0158] In view of the wide variety of embodiments to which the
principles of the present invention can be applied, it should be
understood that the illustrated embodiments are exemplary only, and
should not be taken as limiting the scope of the present invention.
For example, the steps of the flow diagrams may be taken in
sequences other than those described, and more or fewer elements
may be used in the block diagrams. While various elements of the
preferred embodiments have been described as being implemented in
software, other embodiments in hardware or firmware implementations
may be used, and vice-versa.
[0159] It will be apparent to those of ordinary skill in the art
that methods involved in the system and method for determining and
controlling contamination may be embodied in a computer program
product that includes a computer usable medium. For example, such a
computer usable medium can include a readable memory device, such
as, a hard drive device, a CD-ROM, a DVD-ROM, or a computer
diskette, having computer readable program code segments stored
thereon. The computer readable medium can also include a
communications or transmission medium, such as, a bus or a
communications link, either optical, wired, or wireless having
program code segments carried thereon as digital or analog data
signals.
[0160] In another aspect, the present invention provides systems,
apparatuses and methods for passive monitoring of contamination in
a semiconductor processing system using passive samplers and
sampling instead of active sampling. As used herein, "active
sampling" refers to the use of air moving device which utilizes an
external source of energy coupled to the sampling system to deliver
a gas sample to a collection material of a collection device of the
sampling system. In comparison, passive sampling uses the energy of
the gas sample itself to deliver a gas sample to a collection
material of a collection device, for example, by diffusion.
[0161] Typically, passive sampling has been considered inadequate
for monitoring contamination in a semiconductor processing system
because of the generally very low sample delivery rates associated
with passive sampling. For example, for a system which may have a
sample delivery rate of 0.1 liters/min. with active sampling, can
have a sample delivery rate of only 0.0001 to 0.001 liters/min. In
another example, for active sampling using a hand held pump to pull
air through a Tenax.RTM. TA tube at a flow rate of 0.150
liters/min., the diffusive flow rate is 0.0003 liters/min for
passive sampling. As a result, passive sampling at a flow rate of
0.0003 liters/min. typically needs to be conducted for over 83 days
to achieve the same total sampling volume of active sampling at a
flow rate of 0.150 liters/min for 4 hours. Accordingly, passive
sampling has generally been viewed as inadequate for monitoring
trace contaminants (for example, contaminants with a concentration
less than about 10 ppb) because of the long sampling duration
needed to sample a volume of contaminant comparable to that
collected by active sampling.
[0162] Active sampling, however, has several disadvantages. Active
sampling requires an external source of energy for the active
sampling system, which may limit the number and placement of such
active systems in, for example, a semiconductor processing facility
or system. In addition, by requiring a source of power active
systems are susceptible to failure due to power outages or
breakdown of the external source of energy, such as, for example, a
pump. In comparison, a passive sampling system, in accordance with
a preferred embodiment of the present invention, is typically
unaffected by power outages and there is no external source of
energy for the sampling system which can breakdown.
[0163] Other disadvantages of typical prior art active sampling
approaches, which use a pump as an active source of energy,
include, for example: calibration of multiple devices (such as, for
example, the pump, flow meters, and timers); pump vibration; and
the need for trained system operators.
[0164] In comparison, in a passive sampling system, in accordance
with a preferred embodiment of the present invention, only one
parameter, the flow rate, is calibrated. In another embodiment, of
the present invention, a sampling duration time is calibrated, but
no flow parameters are calibrated. In addition, in accordance with
a preferred embodiment of the passive sampling system of the
present invention, the passive system substantially operates on its
own without the need for constant operator oversight.
[0165] In one aspect, the present invention provides passive
sampling systems for monitoring contaminants in a semiconductor
processing system. Referring to FIG. 27, in one embodiment, that
passive sampling system 2700, comprises a collection device 2701 in
fluid communication with a sample line 2705 which in turn is in
fluid communication with a semiconductor processing system 2703. A
flow regulator 2707 can be disposed in the sample line 2705 to
regulate a flow of gas 2709 out of the semiconductor processing
system 2703. In one embodiment, the semiconductor processing system
comprises a photolithography instrument. The flow of gas 2709 can
arise for example, from semiconductor processing system over
pressure.
[0166] In accordance with a preferred embodiment, the semiconductor
processing system comprises a photolithography cluster tool, such
as for example, an exposure tool, used in manufacturing
semiconductor devices, that is sensitive to molecular contamination
and a filtering system which removes the molecular contamination
which may include volatile and semi-volatile or condensable organic
substances, which, if present, can cause contamination of optical
elements via series of homogeneous and/or heterogeneous ultraviolet
(UV) induced processes.
[0167] The collection device 2701 contains an absorptive material
2711 to collect one or more contaminants from the flow of gas 2709.
The collection device 2701 is sealed at the end distal 2713 to the
sample line 2705. The proximal end 2715 of the collection device
2701 is in fluid communication with the sample line 2705 such that
the absorptive material 2711 is capable of receiving one or more
contaminants from the flow of gas 2709 by a passive transport
process, such as, for example, diffusion. In a preferred
embodiment, one or more contaminants reach the absorptive material
substantially by diffusion from the flow of gas. For example, in
one embodiment, the collection device comprises a 1/4'' diameter by
3'' long Tenax.RTM.) tube, which is connected to he sample line by
a Swagelok.RTM. fitting. The 1/4'' diameter by 31/2'' long
Tenax.RTM. tube contains about 150 milligrams (mg) of adsorptive
material.
[0168] In accordance with preferred embodiments, the collection
device 2701 includes an amount of adsorptive material with an
adsorption capacity equivalent to an amount of Tenax T.A. in the
range from about 0.05 g to about 1.0 g.
[0169] In another embodiment, the sample line is positioned such
that the flow of gas comprises gas from a location downstream of a
filter or filter system. In another embodiment, the sample line is
positioned such that the flow of gas comprises gas from a location
upstream of a filter or filter system. In another embodiment, the
sample line is positioned such that the flow of gas comprises gas
from a location inside a filter or filter system. In one version of
these embodiments, the passive sampling system is configured to
monitor the condition of the filter or filter system. For example,
the passive sampling system, which can comprise one or more
collection devices, sampling lines etc., can be configured to
sample a gas flow from a location upstream and a location
downstream of a filter to assess breakthrough of a target
contaminant.
[0170] In various embodiments, the passive sampling systems of the
present invention further comprise a monitor system 2717 positioned
to measure the temperature, the pressure, or both, of the flow of
gas. Preferably, the monitor system 2717 measures the temperature
and pressure of a region adjacent the proximal end 2715 of the
collection device 2701. In one embodiment, the monitor system 2717
measures the temperature and pressure of a region adjacent to the
flow regulator 2707, inside the flow regulator 2707, or both.
[0171] In various embodiments, the passive sampling systems of the
present invention further comprise a regulator system 2721
positioned to regulate the temperature, the pressure, or both, of
the flow of gas. Preferably, the regulator system 2721 regulates
the temperature, the pressure, or both, of the flow of gas at least
in a region adjacent the proximal end 2715 of the collection device
2701. In one embodiment, the regulator system 2721 regulates the
temperature and pressure of a region adjacent to the flow regulator
2707, inside the flow regulator 2707, or both.
[0172] The regulator system 2721 can comprise, for example, a
heating/cooling device 2123 proximate to or in contact with, for
example, the sample line 2705. Examples, of suitable
heating/cooling devices include, but are not limited to,
thermoelectric devices.
[0173] In various embodiments, the regulator system regulates
temperature, pressure, or both, based at least in part on
measurements provided by a monitoring system. For example, a
regulator system 2721 can send a signal to a heating/cooling device
2123 based on a temperature measured by the monitor system 2717 to
bring the temperature of the gas flow in a region of the sample
line 2705 into a selected temperature range. In addition, the
regulator system 2721 can send a signal to a flow regulator 2707
(such as, for example, a mass flow controller) based on a pressure
measured by the monitor system 2717 to bring the pressure of the
gas flow in a region of the sample line 2705 into a selected
pressure range.
[0174] In various embodiments, the passive sampling systems of the
present invention further comprise a backflow prevention device
2725 positioned in the sample line 2705 such that it is capable of
substantially preventing gas flow from the sample line 2705 into
the semiconductor processing system 2703. Preferably, the backflow
prevention device 2725 comprises a filter positioned in the sample
line such that it is capable of substantially preventing gas flow
from the sample line into the semiconductor processing system.
Examples of suitable backflow prevention devices include, but are
not limited to, checkvalves with or without activated filter is in
series.
[0175] The collection device includes absorptive material such as,
for example, a refractory absorptive material. In one embodiment,
glass spheres of a given size are used. In a preferred embodiment,
crushed glass spheres are used. In another preferred embodiment,
the absorptive material is the polymer Tenax.RTM.. For example,
Tenax.RTM.. has a high capacity for high boiling point compounds
and operating Tenax.RTM.. past low molecular weight breakthrough
capacity allows the capture of high molecular weight compounds.
Preferably, the absorptive material of the collection device is a
material capable of collecting one or more contaminants in a
molecular weight range of interest. In a preferred embodiment, the
absorptive material is capable of collecting C.sub.6-C.sub.30
containing contaminants. In another embodiment, the absorptive
material is capable of collecting molecular bases or/and molecular
acids, and comprises, for example, a reagent treated glass fiber
non-woven media.
[0176] The sample line may comprise any material suitable for
conveying a gas flow from the semiconductor processing system.
Suitable materials can be selected, for example, based on the known
or predicted reactivity of the sample line material with known or
suspected constituents in the gas flow. Suitable materials include,
but are limited to, PFA, stainless steel, Ni, quartz,
polytetrafluoroethylene (PTFE). Preferably, the sample line
comprises a PFA tube.
[0177] It is further preferred that the internal surface of the
sample line, at least in the portion between the semiconductor
processing system and the collection device, is equilibrated with
the flow of gas. The internal surface of the sampling line is
preferably in equilibrium with the gas phase sample in order to not
interfere with the contaminant collection process. For example, it
is preferred that the concentration of contaminants of interest on
an internal surface of the sample line are such that the internal
surface of the sample line does not significantly uptake the
contaminants of interest from the flow of gas. A sample line may be
equilibrated, for example, by inputting a gas flow until the
concentrations of one or more contaminants of interest at the input
to the sample line are substantially the same as the concentrations
at the output of the sample line. In another example, an
approximately twenty foot long sampling line was found to be
substantially equilibrated with hexadecane contaminants in typical
clean room air after approximately 24-48 hours using a gas flow
rate of 0.15 liter/min. of the clean room air. Although sample line
equilibration tests were conducted with an approximately twenty
foot line, it is preferred that the sampling line be as short as
possible. In practical applications, it is believed that sample
lines in the range from about one to five feet may be practical and
will have correspondingly shorter equilibration times than a twenty
foot line.
[0178] In addition, it is preferred that in operation the
absorptive material of the passive sampling systems of the present
invention is exposed to a substantially continual flow of gas from
the semiconductor processing system such that the collection device
samples a fresh sample of the gas. In one embodiment, the gas flow
rate is in the range from about 0.3 liters/min. to about 3
liters/min. In a preferred embodiment, the gas flow rate is greater
than about 1 liter/min.
[0179] The flow regulator may be any device or structure suitable
for regulating the flow of gas from the semiconductor processing
system. For example, the flow regulator can be a valve, a series of
valves, a critical orifice or series of critical orifices, a
voltage sensitive orifice or series of voltage sensitive orifices,
a mass flow controller (MFC), a temperature regulated flow
controller, or combinations thereof. In a preferred embodiment, the
flow regulator is adapted to regulate the flow of gas to a flow
rate in the range from about 0.3 liters/min. to about 5
liters/min.
[0180] In another aspect, the present invention provides passive
sampling apparatus for monitoring contaminants in a semiconductor
processing system. In one embodiment, referring to FIG. 27, the
apparatus comprises a sample line 2705 having a portion 2730
adapted to be placed into fluid communication with a semiconductor
processing system.
[0181] In accordance with a preferred embodiment, the adapted
portion 2730 of the sample line is adapted to be placed into fluid
communication with the semiconductor processing system comprising a
photolithography cluster tool, such as for example an exposure
tool, used in manufacturing semiconductor devices, that is
sensitive to molecular contamination and a filtering system which
removes the molecular contamination which may include volatile and
semi-volatile or condensable organic substances, and/or inorganic
compounds, which, if present, can cause contamination of optical
elements via series of homogeneous and/or heterogeneous ultraviolet
(UV) induced processes.
[0182] Suitable sample lines, collection devices, absorptive
materials, flow regulators, backflow prevention devices, monitor
systems, and regulator systems, for the passive sampling
apparatuses of the present invention, include, but are not limited
to, those discussed in the context of FIG. 27 and the passive
sampling systems for monitoring contaminants in a semiconductor
processing system of the present invention.
[0183] In another aspect, the present invention provides methods
for passive monitoring of contaminants in a semiconductor
processing system. In one embodiment, the method monitors
contaminants in a filter or filter system of a semiconductor
processing system.
[0184] Referring to FIG. 28, various embodiments of methods for
passive monitoring of contaminants in a semiconductor processing
system 2800 are shown. The methods provide a collection device
containing an absorptive material 2810. Suitable collection devices
and absorptive materials for the methods of the present invention
include, but are not limited to, those discussed in the context of
the passive sampling systems for monitoring contaminants in a
semiconductor processing system. The methods proceed with sampling
one or more contaminants by diffusion of the contaminants to the
collection device 2820 from a gas or gas flow, and at least a
portion of these contaminants are collected by the absorptive
material 2830. In a preferred embodiment, one or more contaminants
reach the absorptive material substantially by diffusion from the
flow of gas. An appropriate analytical technique is then used to
identify at least one of the contaminants collected by the
absorptive material 2840.
[0185] In preferred embodiments of the methods for passive
monitoring of contaminants in a semiconductor processing system of
the present invention, the collection device is exposed to a
substantially continual supply of gas to be sampled during the step
of sampling 2820 and, preferably, during the step of collecting
2830. In various embodiments, the collection device is exposed to a
substantially continual flow of gas from the semiconductor
processing system such that the collection device samples a fresh
sample of the gas. In other embodiments, the collection device is
placed inside the semiconductor processing system and exposed to a
substantially continual flow of gas through the semiconductor
processing system such that the collection device samples a fresh
sample of the gas. In one embodiment, the gas flow rate is in the
range from about 0.3 liters/min. to about 3 liters/min. In a
preferred embodiment, the gas flow rate is greater than about 1
liter/min.
[0186] The provision of a fresh sample allows the absorptive
material to collect a greater contaminant sample volume in a given
time period, for example, by maintaining a contaminant
concentration gradient between a sampling volume (for example, a
volume of gas in a sample line or volume of gas in a semiconductor
processing system) and the volume adjacent the absorptive material
of the collection device. It is to be understood that the
concentration gradient drives, in part, the rate of first order
diffusion of a gas.
[0187] In various embodiments, the methods for passive monitoring
of contaminants in a semiconductor processing system of the present
invention further comprise a step of providing a sample line having
a portion adapted to be placed into fluid communication with the
semiconductor processing system. In these embodiments, it is
preferred that the methods for passive monitoring of contaminants
in a semiconductor processing system further comprise a step of
conditioning the sample line to equilibrate the internal surface of
the sample line, at least in the portion between the semiconductor
processing system and the collection device, with the flow of gas.
The internal surface of the sampling line is preferably in
equilibrium with the gas phase sample in order to not interfere
with the contaminant collection process.
[0188] For example, it is preferred that the concentration of
contaminants of interest on an internal surface of the sample line
are such that the internal surface of the sample line does not
significantly uptake the contaminants of interest from the flow of
gas. A sample line may be equilibrated, for example, by inputting a
gas flow until the concentrations of one or more contaminants of
interest at the input to the sample line are substantially the same
as the concentrations at the output of the sample line. In another
example, an approximately twenty foot long sampling line was found
to be substantially equilibrated with typical organic contaminants
in typical clean room air after approximately 24 hours using a gas
flow rate of 1 liter/min. of the clean room air.
[0189] In one embodiment, the method samples by diffusion 2820,
from a gas flow to a collection device, one or more contaminants in
the gas flow; and at least a portion of these sampled contaminants
are collected by the absorptive material 2830 of the collection
device. Structures, collection devices, and absorptive materials
suitable for sampling and collecting in accordance with these
embodiments of the present invention include, but are not limited
to, those discussed in the context of FIG. 27.
[0190] In another embodiment, the method samples by diffusion 2820,
from a gas in the semiconductor processing system to an adsorptive
material of a collection device, one or more contaminants; and at
least a portion of these contaminants are collected by the
absorptive material 2830. Collection devices and absorptive
materials suitable for sampling and collecting in accordance with
these embodiments of the present invention include, but are not
limited to, those discussed in the context of FIG. 27. In one
embodiment, the collection device has a shape adapted to be placed
into a semiconductor wafer carrier. For example, the collection
device can comprise a 200-300 mm diameter thick wafer with
absorptive material disposed (for example, deposited, or grown) on
one or both sides of the wafer. This wafer collection device can
then be placed into a semiconductor processing system, together
with actual semiconductor wafers or by itself, to provide an in
situ monitor of contaminants in the semiconductor processing
system. In another embodiment, the collection device or at least a
portion of the absorptive material is positioned in the
semiconductor processing system through a port in the processing
system.
[0191] In various embodiments, the step of sampling contaminants
2820 comprises sampling for a sample duration. The sample duration
can be chosen, for example, based on required lower detection limit
of the procedure. In one embodiment, the sample duration is chosen
such that a contaminant with an uptake rate of 1.5 ng per ppb per
minute on the absorptive material is detectable, to a selected
degree of uncertainty, by the analyzer technique and
instrumentation employed in identifying the contaminant. In another
embodiment, the sample duration is chose such that a contaminant
with an uptake rate in the range from about 1.9 to about 4.2 ng per
ppb per minute on the absorptive material is detectable, to a
selected degree of uncertainty, by the analyzer technique and
instrumentation employed in identifying the contaminant.
[0192] In a preferred embodiment, the analyzer comprises a mass
spectrometry instrument, which is tuned to transmit only a single
narrow mass-to-charge ratio range of interest to increase detection
sensitivity and thereby decrease the sample duration required to
detect a contaminant of interest to a selected degree of
uncertainty. Preferably, the sample duration is in the range from
about 5 min to about 50 min for an aromatic contaminant, such as,
for example, toluene with an uptake rate of 1.9-4.2 ng/ppb/min and
an adsorptive material with a surface area in the range from about
620 cm.sup.2 to about 1440 cm.sup.2 using a GCMS instrument to
identify the toluene contaminant, where the mass spectrometer is
tuned to transmit ions with a mass-to-charge ratio in the range
from about 91 to about 93. In another embodiment, for example,
using a 1/4'' Tenax.RTM.. tube and a gas flow rate in the range
from about 0.3 liters/min. to about 3 liters/min, the sample
duration is in the range from about 2 months to about 4 months.
[0193] Preferably, the analyzer uses a detection technology that is
inherently sensitive to, and can identify and quantify organic
species at very low concentrations, for example, below 1 ppb (V).
Suitable approaches for detecting contaminants using a analyzer
2840 include, for example, gas chromatograph/flame ionization
detection (GCFID), and combination chromatography-mass spectrometry
techniques and instrumentation. The analyzer may include any system
that is capable of measuring organic compounds at very low
concentrations including, but not limited to a GCFID with, or
without a preconcentrator, a gas chromatography-mass spectrometry
(GCMS) with, or without a preconcentrator, a photoacoustic detector
with, or without a preconcentrator, and TMS with, or without a
preconcentrator, or any combination thereof.
[0194] Combination chromatography-mass spectrometry techniques and
instrumentation include, but are not limited to, gas
chromatography-mass spectrometry (GCMS), liquid chromatography-mass
spectrometry, and high performance liquid chromatography-mass
spectrometry (HPLC-MS). In addition, techniques, such as tuning the
mass spectrometry instrument to transmit only a narrow
mass-to-charge ratio range of interest, can be used to increase
detection sensitivity. For example, for a typical radio-frequency
multipole mass spectrometer, the signal-to-noise (SN) for a given
charge-to-mass ration is proportional to the square root of the
time the mass spectrometer is transmitting that mass-to-charge
ratio. As a result, tuning a mass spectrometer to transmit only a
narrow mass-to-charge ratio range can improve, in some cases, the
SN for that ratio range by two orders of magnitude versus broader
scanning of the mass spectrometer.
[0195] In a preferred embodiment, analyses of molecular bases and
molecular acids samples includes using ion chromatography methods.
Contaminants are identified by retention time and quantified using,
for example, individual calibration standards and a 10-point
calibration procedure. The Low Detection Limit (LDL) of these
chromatographic methods is approximately 0.1 ug/m.sup.3 per
individual component. In a preferred embodiment, molecular bases
and refractory material samples are analyzed using a gas
chromatograph (GC) equipped with a mass selective detector (such
as, for example, a mass spectrometer) and Thermal Desorption System
(TD). The total analytical system (TD/GC/MS) is optimized to
separate and quantify analytes with a boiling temperature of hexane
and higher with LDL of approximately 0.1 ug/m.sup.3 per individual
component. Individual components, and thereby contaminants, are
identified by a mass spectrometry library search and
chromatographic peak position. In one embodiment, contaminant
concentrations are quantified against two analytical standards, for
example, toluene and hexadecane.
[0196] It is to be understood that techniques and instrumentation
can be chosen based on the semiconductor processing system and
process to which the methods of the present invention are applied.
For example, in one embodiment of passive monitoring of
contaminants in a filter or filter system, the step of identifying
targets a low boiling point contaminant propagated through the
filter. This targeted contaminant can serve, for example, as a
leading indicator gas. In these embodiments, the analyzer
techniques and instrumentation need only be capable of identifying
the target contaminant.
[0197] In other embodiments, identification of a range of
contaminant masses is desired. For example, in monitoring first,
second, third, and fourth order contamination effects in a
photolithography tool, the target contaminants can comprise high
molecular weight refractory organics and compounds including carbon
atoms within the range of approximately one to thirty carbon atoms
C.sub.1-C.sub.30. The first order contaminants may comprise high
molecular weight refractory organics such as, for example, C.sub.6
siloxanes and C.sub.6 iodide with an inorganic component which is
not volatilized through combination with oxygen. Second order
contaminants may comprise high molecular weight organics, such as,
for example, compounds including carbon atoms within the range of
approximately six to thirty carbon atoms (C.sub.6-C.sub.30). Third
order effects can arise due to the contaminating effects of
organics such as C.sub.3-C.sub.6 that have approximately three to
six carbon atoms. Fourth order contaminants include organics such
as, for example, methane, that have approximately one~to five
carbon atoms.
[0198] In other embodiments, target contaminants can comprise only
first and second order contaminants because first and second order
contaminating effects have a greater impact on the contamination of
optical systems than third or fourth order contaminants. In these
embodiments, the analyzer techniques and instrumentation need only
be capable of identifying these target contaminants.
[0199] Referring again to FIG. 28, in various embodiments, the
methods for passive monitoring of contaminants in a semiconductor
processing system of the present invention further comprise a step
of evaluating the condition of a filter 2850 of the semiconductor
processing system based at least in part on one or more
contaminants identified by the analyzer. The filter may be a single
filter, multiple filters or a filter system. In one embodiment, the
step of evaluating evaluates the condition of a filter based on the
concentration of a low boiling point target contaminant propagated
through the filter. This targeted contaminant can serve, for
example, as a leading indicator gas. Preferably, the targeted
contaminant travels faster in the filter than other target
contaminants. These methods including a step of evaluating
preferably establish a correlation between one or more low
molecular weight compounds and one or more high molecular weight
compounds to determine the condition of the filter with respect to
a one or more contaminants of interest.
[0200] Further, the methods for passive monitoring of contaminants
in a semiconductor processing system including a step of evaluating
the condition of a filter preferably include sampling a gas flow at
a multiple locations, such as, for example, upstream, downstream
and inside of the filter.
[0201] In one embodiment, the methods for passive monitoring of
contaminants in a semiconductor processing system of the present
invention further comprise a step of measuring at least one of
temperature, pressure or flow rate of a gas flow 2860. In another
embodiment, the methods for passive monitoring of contaminants in a
semiconductor processing system of the present invention further
comprise a step of monitoring at least one of temperature and
pressure of a gas in the semiconductor processing system 2860.
These measurements can be used to provide increased accuracy in the
quantitative determination of one or more contaminant
concentrations in the semiconductor processing system. For example,
an average contaminant concentration in a semiconductor processing
system can be determined from a contaminant concentration
determined in the identifying step using the gas flow rate,
temperature and pressure, assuming a sufficiently equilibrated
sampling line. In addition, the temperature, pressure and flow rate
measurements can be used in embodiments comprising a step of
evaluating the condition of a filter to evaluate the condition of a
filter or filter system.
[0202] Structures and monitor systems suitable for the step of
measuring include, but are not limited to, those discussed in the
context of FIG. 27. Preferably, the step of measuring 2860 measures
the temperature, pressure, and flow rate in a region adjacent the
proximal end of the collection device. In one embodiment, the step
of measuring 2860 measures the temperature, pressure and flow rate
in a region adjacent to a flow regulator, inside the flow
regulator, or both.
[0203] In one embodiment, the methods for passive monitoring of
contaminants in a semiconductor processing system of the present
invention further comprise a step of regulating at least one of
temperature, pressure or flow rate of a gas flow 2870. In another
embodiment, the methods for passive monitoring of contaminants in a
semiconductor processing system of the present invention further
comprise a step of regulating at least one of temperature, pressure
of a gas in the semiconductor processing system 2870. In various
embodiments, the step of regulating regulates temperature,
pressure, or both, based at least in part on measurements provided
by a monitoring system.
[0204] The step of regulating can be used to provide increased
accuracy in the quantitative determination of one or more
contaminant concentrations in the semiconductor processing system.
Structures and regulator systems suitable for the step of
regulating include, but are not limited to, those discussed in the
context of FIG. 27. Preferably, the step of regulating 2860
regulates the temperature, the pressure, or both, of the flow of
gas at least in a region adjacent the proximal end of a collection
device. In one embodiment, the step of regulating 2860 regulates
the temperature and pressure of a region adjacent to a flow
regulator, inside the flow regulator, or both.
[0205] In another aspect, the present invention provides systems
and methods for detecting airstream backflow in a semiconductor
processing system using a differential pressure monitor.
[0206] In semiconductor processing, the direction of airstream flow
can be critical to controlling system contamination. One area of
particular concern is the backflow of an airstream from the track
into the stepper. Typically, the airstream flows from the stepper
to the track. In certain situations, however, this airstream may be
misdirected causing air to backflow into the stepper. Such
misdirection can occur, for example, when a processing tool is
stopped, a processing tool door is opened, or a system air filter
fails.
[0207] Misdirected airstream flow can have serious consequences.
For example, during backflow -contaminants in the track can be
forced into the stepper and potentially onto to the optics of the
photolithography tools connected to the stepper.
[0208] In one aspect, the present invention provides a system for
detecting airstream backflow using a differential pressure monitor.
In preferred embodiments, the present invention provides a system
for detecting backflow from the track into the stepper. Referring
to FIG. 29A, the system detects backflow in a semiconductor
processing system comprising an airstream source 2901 (such as, for
example, a track) and a delivery region 2903 (such as, for example,
a stepper). The system comprises a differential pressure monitor
2905 comprising a first pressure measurement device 2907 positioned
at the airstream source 2901, and a second pressure measurement
device 2909 positioned at the delivery region 2903. In desired
operation of the semiconductor processing system, the pressure,
P.sub.1, in the source airstream 2901 is greater than in the
pressure, P.sub.2, in the delivery region 2903; and the airstream
2911 flows from the source 2901 to the delivery region 2903. This
situation is illustrated in FIG. 29A.
[0209] The differential pressure monitor 2905 monitors the
difference in pressure between the pressure, P.sub.1, in the source
airstream 2901 and the pressure, P.sub.2, in the delivery region
2903. When P.sub.1 is greater than P.sub.2, the differential
pressure monitor 2905 provides, for example, no signal, or a signal
indicating normal airflow.
[0210] When the pressure, P.sub.2, in the delivery region 2903 is
greater than the pressure, P.sub.1, in the source airstream 2901,
conditions may exist for airstream backflow 2915. This situation is
illustrated in FIG. 29B. When the differential pressure monitor
2905 detects that P.sub.2 is greater than P.sub.1, the differential
pressure monitor 2905 provides a warning signal indicating
potential backflow in the semiconductor processing system.
[0211] FIGS. 30A-30E illustrate schematic diagrams of another
embodiment of a device that can function as a concentrator in a
contaminant and filter monitoring system in accordance with a
preferred embodiment of the present invention. FIG. 30A is an
illustration of one embodiment of the concentrator device 3050,
with a cover 3026 in place, and showing one embodiment of an inlet
interface 3054 and an outlet interface 3056. FIG. 30B is an
exploded assembly drawing of a concentrator 3057, FIG. 30C is an
assembly drawing of a concentrator device 3050, and FIG. 30D is an
assembly drawing of the concentrator 3057 inserted into a manifold
3059 having an inlet interface 3054 and an outlet interface 3056
where, in one embodiment, the components and mounting hardware of
FIGS. 30B-30D are as follows: [0212] 4-40.times.1/4'' Phillips Head
Screw 3001; [0213] 1/4'' Comp. Teflon Elbow Union 3002; [0214]
1/8'' SS Tubing 3003 (FIG. 30E is a scale drawing of one embodiment
of a 1/8'' SS Tubing 3003); [0215] 1/4''38 .times.1/4'' Straight
Teflon Union 3006; [0216] 1/4'' FPT -1/4'' Comp. Stainless Steel
(SS) Adapter 3007; [0217] 1/8'' FPT .times.1/8'' Comp. SS Elbow
3008; [0218] 25 Micron Particle Filter 3009; [0219] 1/8'' NPT Male
2E Orifice 3010; [0220] 1/8'' SS Comp. Tee 3011; [0221] 1/4''
Teflon Tubing 3012; [0222] 1/4'' Teflon Comp. Tee 3013; [0223]
Rubber Multi-Tube Holder 3014; [0224] Refractory Trap Tube Holder
Plate 3015; [0225] 6-32.times.1/4'' Phillips Screws 3016; [0226]
1/4''.times.1/8'' SS Bulkhead Union 3019; [0227] 6-32.times.1/4''
Button Head Screw 3021; [0228] Locking Plate for Bulkhead 3023;
[0229] 1/4''.times.1/4'' SS Bulkhead Union 3024; [0230] Bulkhead
3025; [0231] Cover 3026; [0232] 1/4''.times.31/2'' Tenax Tube
containing about 150 mg of adsorptive material 3027; [0233] 1/8''
Teflon Tubing 3028; and [0234] 1/4'' SS Comp. Tee 3029.
[0235] The filter system including a filter monitoring
functionality can be reduced in size using a device such as, for
example, the concentrator 3057. A greater volume of contaminants
can be collected in the filter system over an interval of time if
the temperature is reduced to, for example, 0.degree. C. or lower.
Using a concentrator device that includes absorptive materials such
as, for example, Tenax.RTM. T.A, in a collection device 3027 can
also increase the volume of material collected. High boilers
(compounds with boiling points greater than about 150.degree. C.),
such as, for example, organics having or more six carbon atoms are
generally absorbed by Tenax.RTM. T.A. Preferably, the total mass of
adsorptive materials, such as, for example, Tenax.RTM. T.A. is
greater than about 0.05 grams (g). In another embodiment, the total
mass of adsorptive material is in the range from about 0.05 g to
about 1 g.
[0236] In another embodiment, absorptive materials for use in the
collection device 3027 include, for example, carbon traps such as
supplied by, for example, Supelco can be used in embodiments
including low boilers. Other embodiments include a combination of
the collection devices 3027 for high and low boilers, which can be
arranged in parallel and/or in series. In addition, the collection
device 3027 can be a single device instead of multiple devices
arranged in parallel and/or series.
[0237] In preferred embodiments, the concentrator 3057 includes two
series of collection devices 3027 in parallel. A series of
collection devices enables one to better resolve differences in
contaminant uptake along a length of adsorption material because
the collection device corresponding to a given location along the
length of adsorptive material can be analyzed separately from the
others. In comparison, such resolution is lost when a single
collection device, of equal length to the series, is used because
length dependence information is lost due to contaminants desorbing
from the single collection device independent of their position
along the length of adsorptive material.
[0238] Having two substantially identical series of collection
devices in parallel is preferred because the redundancy inherent in
this configuration increases the reliability of the contaminant
analysis by providing a measure of the variation in collection
properties between collection devices and provide a measure of
variance for the data. An example of one preferred embodiment of
two substantially identical series of collection devices 3027 in
parallel is illustrated in FIGS. 303B and 30D.
[0239] FIGS. 31A-31E illustrate a schematic diagram of a system for
monitoring contaminants and the performance of a filter system in
accordance with a various embodiments of the present invention. In
various embodiments, the system 3100 includes a plurality of
concentrator devices 3110 (such as, for example, illustrated in
FIGS. 25A-25C and/ or 30A-30E) for monitoring contaminants and the
performance of a filter system. The filter system includes an inlet
interface 3120, a filter module 3140 having a plurality of filters
3192 (schematically illustrated in FIG. 31E), a HEPA filter module
3150 having a HEPA filter, an output interface 3130, and a
compressed air inlet 3172 for actuation of system pneumatics. The
outlet interface 3130 can also, in other embodiments, be coupled to
a vacuum system if evacuation of the system for determining
contamination is required. The inlet and outlet interfaces
preferably have sealed surfaces for environmental isolation.
[0240] The system 3100 includes interstack sampling ports 3162,
3164, 3166 for sampling the gas stream between filters 3192 or
after the filters 3192. The system also includes an inlet sample
port 3168 for sampling the input gas stream prior to filtration and
an outlet sample port 3170 for sampling the gas stream after the
HEPA filter module 3150 but prior to return through the output
interface 3130. Preferably, the system also includes a pressure
regulation device proximate to the inlet interface 3120 and a
pressure gauge 3180 to measure pressure in the system.
[0241] In one embodiment, the filter module 3140 includes an
adequate valving arrangement to allow accurate sampling of the
various sampling ports 3162, 3164, 3166, 3168, 3170 by the
concentrator devices 3110. A single concentrator device 3110 or
multiple concentrator devices 3110 can be used to monitor the
output of a sampling port and collect a sample for post-collection
analysis. For example, in one embodiment, one concentrator device
3110 is connected to each of the five sampling ports. In another
embodiment, multiple concentrator devices 3110 can be connected to
a single sampling port, for example, where contamination
concentration is anticipated to be low, such as at the outlet
sampling port 3170.
[0242] The system can further include a controller/processor, such
as a proportional integral controller and a- control module, A
preferred embodiment includes electronically controlled valves to
impose a duty cycle for sampling per concentrator device. The duty
cycle can be programmable. The electronically controlled valves can
assist in embodiments having high concentrations of impurities as
they can address the potential of overload. Preferably, the
controlled valves are pneumatically actuated with compressed clean
dry air.
[0243] The post-collection analysis of the material collected by a
concentrator device can provide quantitative and qualitative
measures of the contamination present in a gas stream in the
semiconductor processing environment. Analysis tools such as, for
example, GCMS or GCFID can be used to detect the contaminants. It
may also provide for monitoring of the performance of the filter
system.
[0244] In some embodiments the concentrator devices can be cooled
using a thermoelectric cooling device. Organics can be more readily
condensed and collected using the low temperature embodiment. A
fewer number of traps are required for the low temperature
embodiment since the organics can be collected post condensation.
An embodiment of the low temperature system can further include
heat sinks to dissipate the heat energy generated.
[0245] The claims should not be read as limited to the described
order or elements unless stated to that effect. Therefore, all
embodiments that come within the scope and spirit of the following
claims and equivalents thereto are claimed as the invention.
* * * * *