Mechanism of backside etching of transparent materials with nanosecond UV-lasers

摘要

In consequence of high interest in micro- and nanomachining of transparent materials by laser irradiation, studies on the mechanism of laser-induced backside wet etching (LIBWE) are presented. To reveal the role of the surface modification due to LIBWE the backside ablation (BSA) of LIBWE-modified fused silica (mFS) surfaces at 248 nm was investigated. The threshold fluence and the etch rate of BSA are similar to that of LIBWE and amount ～250 mJ/cm~2 and 30 nm for 1 J/cm~2, respectively. The sample transmission after backside ablation of mFS increases and proves the decreasing thickness of the absorbing layer. Time-resolved reflection studies at LIBWE and BSA of mFS show similar patterns in the backside reflection that can be assigned an ablation process as the comparison to thin polymer films demonstrates. By fitting the BSA data to an exponential decay absorption model a modification depth and a surface absorption of about 38 nm and α~S ～ 1.3 × 10~7 m~(-1) were calculated, respectively. In conclusion of the results a new model for LIBWE is proposed.