Effect of Pulse Interval on TSV Process using a Picosecond Laser

Abstract

The advantage of using lasers for through silicon via (TSV) drilling is that they allow higher flexibility during manufacturing because vacuums, lithography, and masks are not required; furthermore, lasers can be applied to metal and dielectric layers other than silicon. However, conventional nanosecond lasers have disadvantages including that they can cause heat affection around the target area. In contrast, picosecond lasers enable the precise generation of TSVs with a smaller heat affected zone. In this study, a comparison of the thermal effects around laser drilled holes when using a picosecond laser (8 ps, 515 nm) with fluence and repetition rate was conducted. Furthermore, the laser drilling mechanism of silicon was examined through a two-temperature model (TTM) approach to resolve problems related to the heat affection that can be caused by the photo-thermal effect. Notably, the lower fluence and repetition rate of the picosecond laser process reduced the experimentally recast layer, surface debris, and melts around the hole better than the high fluence and short pulse interval condition process. These findings suggest that even the picosecond laser has a heat accumulation effect under high fluence and short pulse interval conditions. However, the long pulse interval due to the low repetition rate can eliminate the heat accumulation effect in the TSV process.