Wafer-scale MEMS Package by means of room temperature bonding

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A sequential plasma activation process is proposed to bond wafers of silicon and glasses at low temperature. The method is composed by oxygen plasma activation followed by nitrogen plasma activation. The effect of the surface activation on the bond strength and the bonding mechanism were investigated by using surface characterization. The bond strength increases with increasing the bonding temperature and the contents of OH group in the glasses does not affect the bond strength. The dependence of the bond strength on the plasma activation conditions was investigated quantitatively. The results of the characterization of the bonded interfaces using HRTEM show that there is an amorphous layer at the bonded interface which is induced by nitrogen radical irradiation, forming a kind of silicon oxynitride.As a new application of the proposed process, sapphire wafers were bonded to silicon at a temperature annealing as low as 300℃. No other method is known other than our proposal method for low temperature sapphire wafer bonding so far.Also the feasibility of low temperature wafer bonding of Lithium tantarate was demonstrated using the sequential plasma activation process at low temperature. The results show that a reliability enough high for industrial application such as SAW filters is achieved by bonding at low temperature in air, which fill the requirement of dicing the bonded wafers into 1 mm by 1mm pieces without delamination.Finally, a structure with microcavities was constructed by using the wafer bonding technique we propose in the present study. The tight sealing characteristic of the bonded interface was confirmed by a vacuum leak test.