Semiconductor devices with single-photon avalanche diodes and isolation structures

Abstract

An imaging device may include single-photon avalanche diodes (SPADs). To mitigate crosstalk, isolation structures may be formed around each SPAD. The isolation structures may include front side deep trench isolation structures that extend partially or fully through a semiconductor substrate for the SPADs. The isolation structures may include a metal filler such as tungsten that absorbs photons. The isolation structures may include a p-type doped semiconductor liner to mitigate dark current. The isolation structures may include a buffer layer such as silicon dioxide that is interposed between the metal filler and the p-type doped semiconductor liner. The isolation structures may have a tapered portion or may be formed in two steps such that the isolation structures have different portions with different properties. An additional filler such as polysilicon or borophosphosilicate glass may be included in some of the isolation structures in addition to the metal filler.