Study on Intrinsic Void Defects at the Bonding Interface of 200mm Soi Wafers

Abstract

In this research, the intrinsic void defects at the interface of bonded wafers have been investigated in terms of the mechanism of occurrence and improvements for elimination of such intrinsic void defects have been verified by several methods. The intrinsic void defects at the edge of the wafers are caused by saturated humid vapor that easily nuclei into tiny water droplets due to the Joule-Thomson effect. Influence on bonding voids by downforce pressure during bonding process and different pre-bond treatments has been studied and the density of intrinsic bonding void defects can be decreased by applying either lower downforce pressure or hydrophobic surface before bonding, however, neither of these methods can eliminate the intrinsic voids completely. Vacuum condition during bonding has been verified as an effective way to improve the intrinsic voids and with bonding chamber pressure lower, the intrinsic void defects density gets lower, and as long as pressure lower than 1E3 pa during bonding that can make intrinsic void defects free. The bonding strength of bonded wafers after annealing has also been studied and with chamber pressure gets lower, the bonding strength gets slightly higher than ambient condition and once below 1E3 pa, the strength will keep consistent that can be explained by the fact of that bonding strength more determined by annealing process given the qualified top wafer and handle wafer.

Keywords: Key words: Bonding, Intrinsic void, substrate, interface, surface defects