Silicon wafer bonding through RF dielectric heating

Abstract This paper presents a new silicon wafer bonding process based on radio-frequency (RF) heating of an intermediate dielectric layer. The method uses a capacitive RF field to heat a dielectric interlayer up to its glass transition temperature and permanently join two wafers. A 500 W 14 MHz source was used to deliver RF power to the substrates. A 5 cm diameter 300 μm thick silicon wafers with 2–20 μm thick polyimide intermediate layers were successfully bonded (>95% bond area) in less than 7 min. The results of the pull tests indicate a bond strength of >1.5 MPa for cured polymers, which is greater than the strength of other low-temperature adhesive bonds, e.g. bonds with a photoresist layer used as an adhesive. Steady-state heat transfer equations were solved to estimate the dielectric junction temperature (T0∼300 °C comparable to the glass transition temperature of polyimide).