Current particle counting techniques employ common technologies: lasers, detectors, and optics. The theory of light
scattering and particles is well known, and is standard in most particle counters. However, the need to detect smaller
particles (nanoparticles) challenges the technological limits of traditional light-scattering techniques.
Counting nanoparticles in liquids offers unique problems because of the intensity of scattered light from the particles
relative to the light scattered by the fluid and flow cell. Consequently, the particle may be lost in the background noise.
New technologies employ sophisticated detection elements and high-powered lasers to provide three-dimensional
particle signatures and real-time videos as the particle passes through the laser.
Aerosol nanoparticle counting offers the challenge of light scatter in an open sample chamber. Simply, the nanoparticles
are too small to be effectively illuminated by lasers, so a new technique employs dynamic mobility to classify specific
particle sizes. This technique can provide particle counting—and accurate particle size classification—down to 5 nm.
Employing traditional optical particle counting technology is not efficient for detecting nanoparticles, but new
technologies can meet these challenges. When combined with other support equipment (e.g. WiFi, software, etc.), new
technologies provide innovative techniques for monitoring nanoparticles and managing nano-contamination in clean
environments.
While photomask prices continue to increase and their lifetime continues to be shortened due to molecular
contamination, it is a key issue to understand the chemical mechanism of the mask damage caused by haze problem to
save fabrication cost. We show a unique method for in-situ Airborne Molecular Contamination, or AMC, measurement
in the mask carrier mini-environment as well as the small volume confined under the pellicle protective film.
Additionally, an ultimate solution to decontaminate the photomask and surrounding environment with a vacuum purging
system shows preliminary positive results on the extension of photomask life time by elimination of the haze problem
cause.
Monitoring and controlling Airborne Molecular Contamination (AMC) has become essential in deep ultraviolet (DUV)
photolithography for both optimizing yields and protecting tool optics. A variety of technologies have been employed
for both real-time and grab-sample monitoring. Real-time monitoring has the advantage of quickly identifying "spikes"
and upset conditions, while 2 - 24 hour plus grab sampling allows for extremely low detection limits by concentrating
the mass of the target contaminant over a period of time. Employing a combination of both monitoring techniques
affords the highest degree of control, lowest detection limits, and the most detailed data possible in terms of speciation.
As happens with many technologies, there can be concern regarding the accuracy and agreement between real-time and
grab-sample methods. This study utilizes side by side comparisons of two different real-time monitors operating in
parallel with both liquid impingers and dry sorbent tubes to measure NIST traceable gas standards as well as real world
samples. By measuring in parallel, a truly valid comparison is made between methods while verifying the results against
a certified standard. The final outcome for this investigation is that a dry sorbent tube grab-sample technique produced
results that agreed in terms of accuracy with NIST traceable standards as well as the two real-time techniques Ion
Mobility Spectrometry (IMS) and Pulsed Fluorescence Detection (PFD) while a traditional liquid impinger technique
showed discrepancies.
A new approach to monitoring molecular contamination in lithography is presented. Recent technical advances have
made it feasible to perform continuous real-time monitoring with significant advances in sensitivity and stability while
minimizing sample tubing effects. These improvements are realized by using a small, low-cost monitor that is dedicated
to monitoring a single location. A dedicated, point-of-use monitor offers the following advantages over a conventional
multipoint sampling system: continuous monitoring, no missed contamination events, sample tubing lengths reduced
from 20 - 30 meters to 2 - 3 meters, and 5 - 10x better sensitivity. Improvements in sensitivity and stability are realized
through a dedicated monitor approach to molecular contamination monitoring. Because the monitor is continuously
sampling the same environment, sample averaging can be used in a highly effective manner to reduce the detection limit.
This is particularly useful in chemically filtered environments where the concentrations are usually low and stable. An
automated monitoring software package can simultaneously plot individual one minute data points and a long-term
running average. The one minute samples are used to immediately detect the onset of a contamination event while the
long term running average is used to monitor background contamination at the lowest levels.
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