Sequential Plasma-Activated Bonding Mechanism of Silicon/Silicon Wafers

To investigate the sequentially plasma-activated bonding (SPAB) mechanism of silicon/silicon wafers, the surface hydrophilicity, and the interface voids, nanostructures and chemical compositions that control the bonding quality, such as bonding strength, have been observed. Although the sequentially plasma-activated surfaces are hydrophilic, the SPAB mechanism is not identical to the hydrophilic bonding. SPAB shows high bonding strength at room temperature and water rearrangement below 150 °C, which removes the water from the interface to the bulk. This results in a thinner amorphous silicon oxide layer at the interface. Further heating of the bonded wafers desorbs water from the bulk. The heating at 225 °C starts producing hillocks at the interface, which turn into voids at temperatures above 400 °C for absorbing the hydrogen gas produced from the desorbed water at the interface. The new and bigger voids are due to the hydrogen gas at 600 °C and start accumulating at 800 °C, resulting in bubbles caused by the accumulation of voids at the preferential sites. No nitrogen exists either in silicon or in the amorphous $\hbox{SiO}_{2}$ layer at the interface. The $\hbox{Si-L}_{2, 3}$ edges from the amorphous silicon oxide at the bonded interface are identical to those of the standard $\hbox{SiO}_{2}$. $\hfill$[2009-0253]