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Cymer runs rings round its laser for 45nm semiconductor immersion litho |
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Jul 06, 2006 at 11:01 AM |
 Cymer claims the world's first argon fluoride (ArF) laser
light source for 45nm production immersion photolithography with its XLR 500i deep
ultraviolet (DUV) laser light source for semiconductor manufacturing. The XLR
enables a 1.5× improvement in energy stability performance and a greater than
20 percent reduction in Cost of Ownership (CoO) compared to the company's previous
generation ArF products.
Cymer based the new source on its proven dual-chamber platform, but the
new XLR 500i architecture adds a "Recirculating Ring" technology to the
conventional power amplifier stage. This is claimed to deliver a
step-function improvement in pulse energy stability for both yield and
productivity enhancements.Dual-chamber lasers separate the linewidth
control (master oscillator) and light power amplification (PA)
functions.
A key challenge in such a set-up is the limited lifetime of the master
oscillator (MO) module. Current technology requires a MO pulse energy
of around 1mJ per pulse, that inherently limits the use of the latest,
long lived chamber designs. Dual chamber ArF light sources running on
leading edge applications in memory and logic today see very high pulse
count usage. Some tools run in excess of 30 billion pulses/year.
Seeking the meaning of "Recirculating Ring", a Cymer white paper
(available on the company web site) offers the paragraph: "The key to
this new design is the use of Orthogonal Injection Seeding (OIS) of the
pulse from the MO into the Recirculating Ring via an Output Coupler
(OC). The low reflectivity OC allows the majority of the light from the
MO to pass into the Ring with very low transmission loss, and
orthogonal (90 degrees) to the final laser output beam. A non-Ring
cavity such as a conventional linear Power Oscillator (PO) requires
that the seed pulse from the MO be injected through the rear High
Reflector (HR) with resultant high pulse-energy loss that results in
non optimal optical architecture leading to lifetime limitations."
Comparing the schematics of the previous dual-chamber "MOPA" system and
the new one with "Recirculating Ring" reveals the main difference to be
in the coupling between the chambers and the outside world. The MOPA
system has two blocks in front of the PA chamber labelled Bandwidth
Analysis Module (BAM) and PA WEB. The first seems to contain one
optical element and the second three. The new system reverses the order
of the BAM and PA WEB functions with the BAM only processing output
light. The PA WEB module now apparently contains six optical elements
with a somewhat more complicated light path.
Improved dose performance can also reduce the number of pulses consumed
during wafer exposure reducing CoO on a per wafer basis. The Ring
Technology has the additional advantage of doubling the lifetime of two
key modules within the MOPA-based ArF laser light source. Together, the
reduced pulses from better dose control and improved module lifetimes,
result in a greater than 20 percent reduction in the CoO, says Cymer.
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