Wafer bonding using low temperature melting glass

Summary form only given. The two bonding substances investigated were BPSG TEOS and PSG glasses used in semiconductor manufacturing. Both substances can be deposited in an LPCVD furnace on either bare silicon or wafers covered by previously grown thermal oxides. BPSG TEOS (3% phosphorous, 3% boron) softens at 850°C, and usable bonded wafers were achieved by bonding wafers at 950°C, in oxygen or nitrogen, using a ramp-up/ramp-down procedure. PSG, formed by the reduction of POCl₃ gas, softens at a temperature of 900°C, and usable bonded wafers were achieved by bonding wafers at 950°C using times as short as one hour (no shorter times were tried). Wafers were assembled for bonding within 24 hours of deposition to avoid the creation of circular nonbonded areas caused by outgassing of moisture or dopant in the film. Spin on glass could be used to alleviate the outgassing problem, but in that case the minimum bonding temperature increases to 1100°C. Bond quality was evaluated by destructive wafer separation and physical inspection of the bonded oxide and by grinding back the bonded wafer and assessing the strength of the bond with sonic treatment. Heat stressing was used to determine whether BPSG TEOS could be used to make bonded wafers capable of withstanding the rigors of the standard manufacturing process line. Bond reliability, dopant diffusion, induced bow, and wafer crystal slip were measured on bonded wafers