LIGHTSOURCE
35
Laser treatment
Applications for laser in the semiconductor
market have undergone several performance
enhancements within the last decades.
Coherent describes why this led lasers to be
an important part of PV as well.
L
aser sources have played an increasingly
prominent role within the PV value chain
over the past few years, in particular for
c-Si cell and thin film panel manufacturing.
Typically, lasers are integrated into turnkey
production line equipment, sometimes referred to
simply as ‘laser scribers’. Laser tools perform
scribing, ablating, cutting, and melting
applications on the various material layers that
make up c-Si and thin film cells. The processes
already adopted with laser equipment include laser
edge isolation on c-Si cells and interconnection /
isolation (or patterning) on thin film panels.
Almost all laser sources used within the
photovoltaic industry are of the type diode pumped (ii) the availability of sub nanosecond pulse duration
solid state (or DPSS) lasers. These lasers are ideal lasers, typically around the 10 ps mark, for high
for the PV industry. They are turnkey solutions, finesse material ablation and patterning with
with long lived components of tens of thousands of significantly reduced thermal effects / bulk c-Si
hours, do not require any external gas or water damage; (iii) faster pulsing operation at greater than
consumables, and have special beam properties 100 kHz to keep up with c-Si and thin film production
overlapping with manufacturing requirements. line capacity increases.
DPSS lasers can operate with outputs in the IR
(around 1064 nm), in the visible spectral region Two new laser sources from Coherent meet these
(normally at 532 nm), or in the UV (355 nm), and roadmap objectives for PV manufacturers. First, the
possess high quality beams which can be focused new AVIATM-355-28 provides powers at 28 W, with
down to micron size resolution. excellent beam quality, at the UV wavelength of 355
nm. This laser is already the industry standard for UV
During the past decade, DPSS lasers have laser Edge Isolation, and can also be used for Wrap
undergone considerable performance Though via drilling for back contact cells and dielectric
enhancements, driven primarily by the ablation on front and back cell surfaces.
microelectronics and flat panel display industries.
The applications for lasers in these markets have Second, the new Talisker family of short pulse pico
provided an ideal platform for PV implementation, second lasers actually combines all three requirements
with extensive applications development for laser for next generation laser based tooling for PV,
tools in micro machining silicon based materials picosecond operation, wavelength options at each of
and large glass panel substrates. 1064, 532, and 355 nm, and fast operation well in
excess of 100 kHz.
New demands from the PV industry on DPSS
lasers have resulted in a few additional product The next few years will continue to see further
improvements: (i) a continuous increase in output optimisation of DPSS lasers’ performance
power levels (or processing speed for increased characteristics, driven by specific c-Si and thin film
wafers/hour) at short wavelengths at 532 and 355 production line adoption. Choice of wavelength, pulse
nm where both c-Si and their dielectric passivation width, speed, and cost of ownership will remain the key
layers have increased absorption characteristics; drivers here for lasers in PV.
October 2008 www.euroasiasemiconductor.com
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