Ultraviolet exposure enhanced silicon direct bonding

Abstract

Ultraviolet (UV) exposure, as an additional technique following the traditional wet chemical activation processes, is applied to enhance hydrophilic silicon direct bonding. The effects of UV exposure on silicon wafers' nano-topography and bonding strength are studied. It is found that the surface roughness of silicon wafers initially decreases and then increases with UV exposure time, and the bonding strength increases and then decreases accordingly. The correlations of annealing temperature and annealing time vs. bonding strength are experimentally explored. Results indicate that the bonding strength increases sharply then gently with increasing annealing temperature and annealing time using UV exposure. Besides, the reliability of silicon direct bonding with UV exposure enhancement after the high/low temperature cycle test, constant temperature and humidity test, vibration test and shock test is investigated. It follows from the results that the bonding strength of silicon wafer pairs with UV exposure decreases after the environmental tests, whereas the residual strength is still higher than that without UV exposure, and the variation trends of bonding strength vs. UV exposure time, annealing temperature and annealing time remain unchanged. Therefore, following the traditional wet chemical activation processes, appropriate UV exposure (about three minutes in this study) is effective and promising to enhance silicon direct bonding.

A review: wafer bonding of Si-based semiconductors

“…Shi et al and Kub et al [119][120][121][122][123] systematically studied the effect of UV irradiation on Si/Si wafer bonding. The effect of UV irradiation time on the RMS of the Si surface and on bonding strength was investigated, as shown in figure 18.…”