Temporary glass carrier
Spin on polymer
Silicon deposition - LTPS -
excimer beam for LLO
separated from glass carrier
www.industrial-lasers.com JANUARY/FEBRUARY 2017 Industrial Laser Solutions 17
recently introduced TriV YPER laser system yields 3.6k W, enabling
it to process the next generation of glass panels. It’s important to
note that the multiple beams are not simply stitched end-to-end to
produce the final line. Rather, the beams are combined first, and
then shaped to their final line profile.
This beam-combining approach was taken because, in addition
to simply scaling up power, it also enabled improvements in pulse-to-pulse stability, as well as allowed greater flexibility in terms of
temporal pulse shaping. This is possible because the two oscillators contained in each V YPER are arranged in a master and slave
configuration. Synchronization and feedback circuitry accurately
controls the time delay between the pulses of these two oscillators, enabling long-term temporal stability to an accuracy of about
2ns. The arrangement allows the overall pulse length of the laser to
be varied to provide pulses ranging from the standard pulse width
up to essentially twice this value. This permits the manufacturer
to explore the exact effects of pulse duration on the crystal structure, and to optimize the results in terms of the effects on the bulk
electronic properties of the silicon.
Other high-power UV applications
The unmatched ability of excimer lasers to produce high-energy
UV pulses is also benefiting other applications in displays and
microelectronics manufacturing. For example, excimer lasers
are used in mask-based direct patterning of microcircuits for
cost-sensitive applications like medical disposables. Here, the
excimer laser is used to pattern a very high volume of disposable sensor circuits in thin metal on a flex substrate in a reel-to-reel process.
Laser Lift-Off (LLO) is another important application enabling
the next generation of flexible displays. A major obstacle in fabri-
cating flexible displays is that the thin plastic substrates employed
are too delicate to be handled with traditional tooling, and will typi-
cally lose their limited rigidity at the high temperatures experienced
in some production steps.
To overcome this problem, a glass substrate is used as a temporary carrier for handling purposes during fabrication (FIGURE 3).
It is first coated with polymer layer and then display circuitry is
created on top of this polymer layer. Finally, a high-power excimer laser beam, such as the specially designed UVblade series,
is directed through the glass carrier (which is sufficiently transparent in the UV). The laser light is strongly absorbed by the polymer
layer, which vaporizes and thus releases the completed flexible
display from the carrier.
Excimer lasers continue evolve as the only practical source of very
high-power UV laser light. Their unique characteristics have made
them an enabling technology in a number of high-precision processing tasks, especially in display manufacturing, microelectronics, and medical device fabrication. Continuing improvement in the
quality, reliability, and output characteristics of excimer lasers, necessary to meet today’s demanding applications, promises to keep
this powerful UV technology relevant for some time to come. ✺
RAINER PÄTZEL and RALPH DELMDAHL ( email@example.com) are with
Coherent, Santa Clara, CA; www.coherent.com.
FIGURE 3. The main steps in the excimer Laser Lift-Off process.