MICROMACHINING THROUGH SILICON SUBSTRATES BY ULTRAFAST LASER AT 1552 nm

摘要

Micromachining of silicon (Si) using lasers isattracting much interest in the field of modernmicrofabrications. Because Si absorbs majority ofindustrial lasers in near-IR to uv region, laserprocessing of Si is usually performed using linearabsorption processes of the laser radiation.Micromachining by non-linear absorption processesinduced by short pulse lasers has many unique featuresand has been applied to transparent materials in manyfields. The application of these non-linear processes tothe micromachining of Si would be very advantageous.In this study, ultrafast pulses from a fiber-basedinfrared laser at 1552.5 nm were irradiated throughsilicon substrates such that they were focused at thefront or the rare surfaces of the substrates under aninfrared microscope. Focused outputs of the laser madesharp and deep trenches on the front surface. When thelaser was focused on a gold (Au) film on the surface ofthe second substrate placed at the back of the first Sisubstrate, the Au film was ablated by irradiationthrough the Si substrate. This was applied successfullyto an up-conversion of the frequency of crystaloscillator in a Si package. When the focus was placedat rear surface of a Si substrate and aberration of thelaser light caused by large refractive index of Si wascompensated, an Au film on the rear surface wasablated and deposited on another substrate placed atthe back of the substrate.