Fabrication of low leakage-current backside illuminated photodiodes
Ultra-low leakage current backside-illuminated semiconductor photodiode arrays are fabricated using a method of formation of a transparent, conducting bias electrode layer that avoids high-temperature processing of the substrate after the wafer has been gettered. As a consequence, the component of the reverse-bias leakage current associated with strain, crystallographic defects or impurities introduced during elevated temperature processing subsequent to gettering can be kept extremely low. An optically transparent, conductive bias electrode layer, serving as both an optical window and an ohmic backside equipotential contact surface for the photodiodes, is fabricated by etching through the polysilicon gettering layer and a portion of the thickness of heavily-doped crystalline silicon layer formed within, and near the back of, the substrate during the gettering process.
1 . A backside illuminated diode comprising:
a single continuous piece of substantially optically transparent semiconductor material, having a rear conductive surface, and a front surface with at least one PN junction adjacent thereto.
2 . A diode as in claim 1 , further comprising an anti-reflection coating, coated on said rear surface.
3 . A diode as in claim 2 , wherein said anti-reflection coating is formed of a dielectric material.
4 . A diode as in claim 3 , wherein said anti-reflection coating is formed of multiple layers of dielectric materials.
5 . A diode as in claim 1 , wherein said semiconductor material is of an N conductivity type.
6 . A backside illuminated diode comprising:
a single continuous piece of substantially optically transparent semiconductor material, having a rear conductive surface adapted for receiving illumination, and a front surface with at least one PN junction adjacent thereto, which PN junction receives photons from a back side and produces a signal indicative of photocurrent generated by said photons.
7 . A diode as in claim 6 , further comprising an anti-reflective coating, coated over said back side.
8 . A diode as in claim 7 , further comprising a readout structure layer, having readout circuits formed therein, formed on a front surface.
9 . A diode as in claim 7 , wherein said anti-reflective coating is formed of a material other than Indium Tin Oxide.
10 . A diode as in claim 7 , wherein said anti-reflective coating is formed of multiple separate layers of dielectric material.