Defect compensation at the interface between directly bonded silicon wafers

Abstract

In smart power applications, the Si/Si bonded interface must be electrically transparent for the high voltage bipolar transistor. The bonded interface resistance variation (measured by spreading resistance analysis) is consistent with a potential barrier due to positively charged interface states, whatever the semiconductor type. With a proper preimplanted boron dose, the potential barrier can be reduced and even removed, probably by defect compensation. For a p/p bonded interface, a 7 × 10¹¹ at cm⁻² boron preimplantation leads to no resistance variation near the interface. The ion dose must be adjusted depending upon the substrate type, its resistivity, its flatness and the quality of the prebonding etching. Comparing the spreading resistance results and SUPREM simulations, the interface states density is calculated to be roughly 5 × 10¹⁰ cm⁻² and it does not drastically affect the boron diffusion length.