This disclosure relates to an active pixel cell including a shallow trench isolation (STI) structure. The active pixel cell further includes a photodiode neighboring the STI structure, where a first stress resulted from substrate processing prior to deposition of a pre-metal dielectric layer increases dark current and white cell counts of a photodiode of the active pixel cell. The active pixel cell further includes a transistor, where the transistor controls the operation of the active pixel cell. The active pixel cell further includes a stress layer over the photodiode, the STI structure, and the transistor, and the stress layer has a second stress that counters the first stress exerted on the substrate, and the second stress reduces the dark current and the white cell counts caused by the first stress.