Dependence of power trench metal-oxide-semiconductor field-effect transistor processes on wafer thickness

Abstract

The dependence of trench metal-oxide-semiconductor field-effect transistor processes on wafer thickness has been studied. In the photolithography process, it was found that the photoresist thickness decreased with the decrease of wafer thicknesses. This is due to the fact that thinner wafer has less thermal mass and hence less dissipation time. Unless compensated for, this change in resist thickness adds to critical dimension and trench depth variations. After the rapid thermal processing, the thinner wafers exhibited a lower resistivity and higher silicide stress (i.e., 3.23E+10dyn∕cm2 for 508μm wafers and 4.60E+09dyn∕cm2 for 675μm wafers). Also, the stress is more uniform across the thinner wafers, possibly due to uniform Si-rich TixSiy (x<y) phase. Both Z-contrast transmission electron microscopy imaging and energy dispersive x-ray profiling on the silicide layers of the thicker wafers revealed a Ti-rich layer (possibly TiSi) on the top of TixSiy (x<y) layer and at the Si-silicide interface; whereas only scattered regions of Ti-enriched regions were observed in thinner wafers. Higher temperature in thinner wafers seems to assist in the removal of this Ti-rich layer.