Experimental analysis on the anodic bonding with an evaporated glass layer

We performed a silicon-to-silicon anodic bonding process using a glass layer deposited by electron beam evaporation. Corning No 7740 Pyrex glass was used as the source material of electron evaporation. The effects on the bonding process were investigated as a function of the thickness of the glass layer and the concentration of sodium ions in the glass layer. The surface roughness of the glass layer decreased with increasing thickness of the glass layer. It was observed that the deposited glass layers of more than 1.5 μm thickness had very small surface roughness. The depth profile of sodium ions showed that the glass layer deposited by electron beam evaporation contained many more sodium ions than the glass layer deposited by sputtering. The silicon-to-silicon bonding process was performed at temperatures in the range of 135-240 °C with an electrostatic voltage in the range of 35-100 V_DC. A pull test revealed that the tensile strength of bonded specimens was in the region of 1-8 MPa. The role of sodium ions in anodic bonding was studied by investigating the theoretical bonding mechanism and examining the results of secondary-ion mass spectroscopy (SIMS) analysis on the glass layer before and after the bonding process.