Analysis of debris generated during UV laser micro-machining of silicon

The generation of debris is critical in the future application of laser technology in IC, MEMS, MOEMS manufacture. Re-deposition of debris is also critical in optimising throughput of multi-pass laser ablative processes. In this study, the debris formed in laser micromachining of wafer grade silicon is investigated. Details of the laser workstation, based on a UV DPSS laser, will be presented and the development of real time diagnostic capabilities and off-line techniques will then be described. A real time imaging capability has been used to monitor plasma and shock front propagation with nanosecond resolution. The detection system is also used to monitor spectral emission of debris and micron-sized particulate emission from the silicon surface. Emission spectroscopy of the laser ablated silicon in the plasma show spectral features that are characteristic of atomic and molecular species on timescales of nanoseconds and microseconds, respectively, after the laser pulse. Off-line characterisation techniques have focused on investigating the distribution and chemical composition of entrapped particulate. A number of novel experimental configurations for particulate entrapment, both adjacent to and remote from the laser-ablated surface, will be described. EDX results indicate that debris generated in air is composed principally of oxygen and silicon. Additional SEM results indicate that the particulate size grows through aggregation and depends on the environment in which it is generated.