Pressure Aided Low Temperature Direct Bonding of Silicon Wafers with High Surface Roughness

It has been widely accepted that the threshold of surface roughness for low temperature hydrophilic wafer bonding is 0.5nm. However, we have proven that wafers with higher surface roughness can be bonded. By the aid of proper contact pressure, we have bonded the wafers with roughness of 1.0nm successfully and found that thinner wafers were easier to be bonded than thick ones whereas wafers with thickness of 525mum couldn't be bonded and maximum bonding strength has been obtained for wafers with thickness of 300mum in our tensile test. In a word, low temperature hydrophilic bonding can be realized for wafers with high surface roughness if thickness and contact pressure are chosen properly