Stress engineering to reduce dark current of cmos image sensors

Abstract

The active pixel cell structures and methods of preparing such structures described above enable reduction of dark current and white cell counts for active pixel cells. The process of preparing active pixel cell structures introduces stress on the substrate, which could lead to increased dark current and white cell counts of active pixel cells. By depositing a stress layer as part of a pre-metal dielectric layer with a stress that counters the stress induced, both the dark current and the white cell counts can be reduced. If the transistors of the active pixel cells are NMOS, the carrier mobility can also be increased by a tensile stress layer. Raman Spectroscopy can be used to measure the stress exerted on the substrate prior to the deposition of the stress layer.