September 2011 - I-Micronews

I S S U E 1 3 S E P T E M B E R 2 0 1 1
is said to cleanly remove the oxide without
damaging the glass. Work on the P1 scribe for CdTe
thin film shows potential to reduce process steps
by leaving intact a barrier layer which prevents
sodium from the soda-line glass diffusing into
the scribe and poisoning the CdTe. Typically the
CdTe P1 scribe removes the barrier layer and must
therefore be backfilled with a planarizing filler to
avoid sodium diffusion. The tailored pulse laser,
however, can etch precisely through only the TCO
on the architectural glass substrate, leaving the
underlying SiO 2
barrier layer intact.
Other work with the Fraunhofer Institute in
Michigan found that the shaped beam laser was
much faster than conventional lasers for drilling
the thousands of hole per second across the
wafer needed for emitter wrap through solutions.
Practical mass production of EWT will likely need
drilling some 10,000 holes across the wafer at
one wafer per second without too much damage,
while a conventional 100W laser can only do about
4,300 holes per second. ESI’s 25W tailored-pulse
laser drilled 6,800 holes per second in the tests
in the Fraunhofer lab. Murison says ESI has since
made considerably more improvement in its own
lab as it has learned more about how light actually
interacts with silicon. The solution turns out to be
tailoring the pulse to first heat up the silicon before
hitting it hard, which enables the material to use
the available energy more efficiently. Typically
a laser drills quickly down through the first part
of the hole as the silicon melts, but then about
halfway through the process slows down as the
silicon starts to boil and vaporize, filling the hole
with silicon plasma that absorbs the laser light.
The relatively low 25W power of the ESI pulseshaped
laser currently limits the throughput of
removal processes, and so limits use for a number
of c-Si solar laser applications. The company
is currently working on the tricky business of
developing a higher power version, as pulsetailoring
is typically only possible at relatively
low power. Unlike a standard Q-switching laser,
where the energy is stored up then all released
in one flash that can’t be precisely controlled, the
fiber laser’s low power continuous beam can be
shaped by an optical modulator. The PyroPhotonics
technology controls the modulator by changes in
voltage, for faster response rate than changing
the current. The beam must then be amplified to
be most useful. The founders say their approach
allows very precise control of the shape at low
power, so the beam remains tailored even through
the distortions created by amplification.
www.esi.com
Richard Murison, CTO and Director
of Product Marketing,
PyroPhotonics Lasers
Richard Murison received his BSc in
Physics from Loughborough University of
Technology, UK and is Chief Technology
Officer and Director of Product Marketing
at PyroPhotonics Lasers, a subsidiary of
ESI, Inc.
Tullio Panarello, General Manager
of the Laser Business Unit, ESI
Tullio Panarello serves as the General
Manager of the ESI’s Laser Business Unit.
Mr. Panarello joined ESI in September
2010 following the acquisition of
PyroPhotonics Lasers, Inc. He co-founded
PyroPhotonics in 2003 and served as the
company’s CEO.
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Additional webcast topics:
• Sept. 28:
Benefits and perspectives
of Cu-Pillar bumping
• Oct. 18:
Thin wafer handling
& processing
•Nov.8:
Glass emergence
into the semiconductor
wafer-processing world
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