Filter-protected photodiodes for high-throughput enzymatic analysis

This paper relates to the use of a thin film of re-crystallized (polycrystalline) silicon as a low-pass rejection filter in the ultraviolet light range and, more particularly, to the use of this layer as a protective layer for semiconductor diodes. The polycrystalline silicon filters were fabricated by laser annealing a thin film of amorphous silicon deposited by an LPCVD process. A standard component of the polysilicon-gate CMOS process is the boron phosphor silicate glass (BPSG) planarization layer. Since this layer is always applied, the possibility of using it as the isolator between the diode and the filter (and, thereby, omit one SiO₂ layer) is considered. Using scanning electron microscopy, we compared the crystallization process of the LPCVD silicon film deposited on a glass substrate and on a BPSG layer. The fabrication and the characterization of the filter-protected photodiodes are described in the paper.