Methods of stress engineering to reduce dark current of cmos image sensors

Abstract

A method of preparing an active pixel cell on a substrate includes exerting a first stress on the substrate by forming a shallow trench isolation (STI) structure in the substrate. The method further includes testing the stressed substrate using Raman spectroscopy at a plurality of locations on the stress substrate. The method further includes depositing a stress layer having a second stress on the substrate. The stress layer covers devices of the active pixel cell that are on the substrate and the devices include a photodiode next to the STI and a transistor, and the deposition of the stress layer results in the second stress being exerted on the substrate, the second stress countering the first stress.