Fabrication of low leakage-current backside illuminated photodiodes

US6670258B2 · kind B2 · utility

Assignee

• Digirad Corporation · US

Inventors

• Lars Carlson · Del Mar, US
• Shulai Zhao · Encinitas, US
• John Sheridan · San Diego, US
• Alan Mollet · Oceanside, US

Key dates

• Filing date: Apr 20, 2001
• Grant date: Dec 30, 2003
• Expiry date: Oct 9, 2021

Classification

• Technology area (CPC Y): Emerging Cross-Sectional Technologies
• CPC primary: Y10T428/31663

Abstract

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.