Principles and applications of trans-wafer processing using a 2-μm thulium fiber laser
- 141 Downloads
A self-developed nanosecond-pulsed thulium fiber laser operating at the wavelength λ = 2 μm was used to selectively modify the front and the back surfaces of various uncoated and metal-coated silicon and gallium arsenide wafers utilizing transparency of semiconductors at this wavelength. This novel processing regime was studied in terms of the process parameter variations, i.e., pulse energy and pulse duration, and the corresponding modification fluence thresholds were determined. The results revealed nearly debris-free back surface processing of wafers, in which modifications could be induced without affecting the front surfaces. The back surface modification threshold of Si was significantly higher than at the front surface due to non-linear absorption and aberration effects observed in experiments. A qualitative study of the underlying physical mechanisms responsible for material modification was performed, including basic analytical modeling and z-scan measurements. Multi-photon absorption, surface-enhanced absorption at nano- and microscopic defect sites, and damage accumulation effects are considered the main physical mechanisms accountable for consistent surface modifications. Applications of trans-wafer processing in removal of thin single- and multi-material layers from the back surface of Si wafers, both in single tracks and large areas, are presented.
KeywordsInfrared lasers Laser materials processing Semiconductors
Unable to display preview. Download preview PDF.
- 2.Ohmura E, Fukuyo F, Fukumitsu K, Morita H (2006) Internal modified-layer formation mechanism into silicon with nanosecond laser. J Achiev Mater Manuf Eng 17(1-2):381–384Google Scholar
- 3.Bärsch N, Körber K, Ostendorf A, Tönshoff KH (2003) Ablation and cutting of planar silicon devices using femtosecond laser pulses. Appl Phys A 77:237–242Google Scholar
- 5.Brown WL (1983) Laser processing of semiconductors. In: Bass M (ed) Laser materials processing. Elsevier, vol. 3, pp. 337--406Google Scholar
- 31.Kruusing A (2010) Handbook of liquids-assisted laser processing. ElsevierGoogle Scholar