2 μm wavelength nanosecond laser welding of silicon

We investigate direct laser welding of silicon-to-silicon, without the requirement of any interlayers, using 40 ns pulses at 2.1 μm wavelength and 1kHz repetition rate. A parameter study was conducted over pulse energies from 20–50.2μJ, scan speeds from 1 mm/s – 0.015 mm/s for various depths of focus. Successful bonding was achieved through individual melt features within the weld track, analyzed with a bespoke IR transmission microscope, with slower scan speeds and higher pulse energies increasing the number of these features. For 1090 μmthick silicon samples, the optimum focal plane for a 50μJ pulse energy was found to be approximately 200 μm below the interface. Scanning electron microscope analysis confirms material redistribution between the top and bottom samples, thus providing evidence of silicon-to-silicon laser welding.