THICKNESS CONSIDERATIONS IN DIRECT SILICON-WAFER BONDING

A simple approximate analytical expression based on an elastic deflect ion principle is suggested as a design guideline for direct bonding of blank or patterned Si or dissimilar materials of various thicknesses. To achieve the high flatness requirement of the mating surfaces for t hick wafer bonding, optical polishing must be employed. With a surface flatness variation of 0.1 wavelength (similar to 630 Angstrom), two 2 0 mm thick Si pieces of 100 mm in diam were spontaneously bonded at ro om temperature. On the other hand, the gaps designed to be formed by p atterned surfaces may collapse during the bonding process if the patte rn dimensions are not properly selected.