Localized back-side heating for low-temperature wafer-level bonding

A new wafer-level method has been developed for localized heating of the bond region between two wafers. Using this method, one of the two wafers to be bonded is heated from the backside, and the other is cooled from the backside, so that heat flows through the bond regions while the device regions stay relatively cool. In this work, integrated temperature sensors were used to measure the temperature at different distances from the bond region during Si to glass and Si to Si (with a -7 mum SiO2) bonds in order to verify the utility of this bonding technique. The temperature was measured to be only 25% and 37% of the bond ring temperature at 650 mum away from the bond ring for a Si to glass bond and 250 mum away from the bond ring for a Si to Si (with a ~7 mum oxide) bond respectively for bond ring temperatures up to 410degC and 200degC. Furthermore a successful Au-Si eutectic bond was demonstrated using this technique.