Improvement of SPAD Photon Detection Efficiency with Diffraction Window Layer

A new structure is proposed for single photon avalanche diodes (SPADs) to improve photon detection efficiency (PDE) in 180 nm CMOS process. This structure is achieved with a diffraction window layer which is manufactured in the first intermetallic dielectric (IMD1) layer. The diffraction window design features interlaced silicon nitride and oxide regions, aiming to modify the photon path and distribution in the device. TCAD simulation and computation results indicate a maximum PDE gain of 22.5% at 825 nm wavelength and a general enhancement at near-infrared short wavelengths. Crucially, this method does not damage the active region of the SPAD device, thus ensures good performance of dark count rate (DCR).