Since laser has high power density, it is useful in MEMS packaging application such as silicon-glass bonding and silicon-silicon bonding. Irradiating laser on Si-Au-Si layer, Si layers bond by Au-Si eutectic bonding around 400℃. Shape of upper silicon, absorption coefficient and reflectivity determines power absorption. Suggest reflection-absorption method and transmission method to get fast bonding and localized heating effect with various upper silicon shape using Nd:YAG laser and $CO_2$ laser. As to power absorption transmission method using Nd:YAG laser is good and control power absorption by upper silicon groove depth. For localized heating transmission method using Nd:YAG laser with large depth of upper silicon groove is more effective rather than reflection-absorption method. As absorption coefficient of Nd:YAG laser is larger than $CO_2$ laser, silicon absorbs Nd:YAG laser power more and absorbed power density of silicon surface is higher than other parts of silicon. High absorbed power density of upper silicon surface and groove thickness with Nd:YAG laser affect Si-Au-Si bonding with localized heating. Irradiating laser as a spot has the limited effect on localized heating but increasing laser power with changing laser spot to line has the possibility of local heating.
