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Utilizing the transparency of semiconductors via "backside" machining with a nanosecond 2 μm Tm:fiber laser

: Gehlich, N.; Bonhoff, T.; Sisken, L.; Ramme, M.; Gaida, C.; Gebhardt, M.; Mingareev, I.; Shah, L.; Richardson, M.C.

Preprint urn:nbn:de:0011-n-2833574 (2.4 MByte PDF)
MD5 Fingerprint: 7ec5dcafd95f9bdfcecd015317c7496c
Created on: 28.3.2014

Klotzbach, U. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Laser-based Micro- and Nanoprocessing VIII : February 2014, San Francisco, California, United States
Bellingham, WA: SPIE, 2014 (SPIE Proceedings 8968)
ISBN: 978-0-8194-9881-6
Paper 89680W
Conference "Laser-Based Micro- and Nanoprocessing" <8, 2014, San Francisco/Calif.>
Conference Paper, Electronic Publication
Fraunhofer ILT ()

Semiconductors such as Si and GaAs are transparent to infrared laser radiation with wavelengths >1.2 μm. Focusing laser light at the back surface of a semiconductor wafer enables a novel processing regime that utilizes this transparency. However, in previous experiments with ultrashort laser pulses we have found that nonlinear absorption makes it impossible to achieve sufficient optical intensity to induce material modification far below the front surface. Using a recently developed Tm:fiber laser system producing pulses as short as 7 ns with peak powers exceeding 100 kW, we have demonstrated it is possible to ablate the “backside” surface of 500-600 μm thick Si and GaAs wafers. We studied laser-induced morphology changes at front and back surfaces of wafers and obtained modification thresholds for multipulse irradiation and surface processing in trenches. A significantly higher back surface modification threshold in Si compared to front surface is possibly attributed to nonlinear absorption and light propagation effects. This unique processing regime has the potential to enable novel applications such as semiconductor welding for microelectronics, photovoltaic, and consumer electronics.