An effective method to improve the sensitivity of deep submicrometer CMOS image sensors

An effective method has been successfully developed to improve the sensitivity of deep sub-micrometer CMOS image sensors (CIS). In advanced CIS technology, the shallow trench isolation (STI) SiO₂ on the photodiode and the SiON film are used for silicide blocking and as a contact etching-stop layer, respectively. However, the dielectric structure, which is composed of an interlayer dielectric/SiON/STI_SiO₂/Si, causes a destructive interference and thus degrades quantum efficiency (QE), especially at short wavelengths. In this paper, an effective method for improving CIS sensitivity has been proposed, based on both theoretical analysis and simulation results, by removing the STI from the photodiode area and then forming a deposition of SiON. Experimental results show that a 40% QE improvement can be achieved under the irradiance of light at a wavelength of 450 nm.