Fabrication of low leakage-current backside illuminated photodiodes

• US 6,734,416 B2
• Filed: 11/15/2002
• Issued: 05/11/2004
• Est. Priority Date: 04/20/2000
• Status: Expired due to Term

• Current Assignee: Digirad Corporation
• Original Assignee: Digirad Corporation
• Inventors: Sheridan, John, Mollet, Alan, Carlson, Lars S., Zhao, Shulai
• Primary Examiner(s): Porta, David
• Assistant Examiner(s): Meyer, David C.
• Application Number:
  US10/295,285
• Publication Number:
  US 20030059630A1
• Time in Patent Office: 543 Days
• Field of Search: 250/208.1, 250/208.2, 250/214.1, 250/214.R, 257/431, 257/447, 257/460
• US Class Current: 250/214.1
• CPC Class Codes: H01L 27/1446 in a repetitive configuration
• CPC Class Codes: H01L 27/14609 Pixel-elements with integrated switching, control, storage or amplification elements scanning details of imagers (circuitry of solid-state image sensors H04N25/00); circuitry of imagers H04N25/70
• CPC Class Codes: H01L 27/1462 Coatings
• CPC Class Codes: H01L 27/1464 Back illuminated imager structures
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers
• CPC Class Codes: H01L 27/14687 Wafer level processing
• CPC Class Codes: H01L 31/02161 for devices characterised by at least one potential jump barrier or surface barrier
• CPC Class Codes: H01L 31/022408 for devices characterised by at least one potential jump barrier or surface barrier
• CPC Class Codes: H01L 31/022466 made of transparent conductive layers, e.g. TCO, ITO layers
• CPC Class Codes: H01L 31/103 the potential barrier being of the PN homojunction type
• CPC Class Codes: H01L 31/186 Particular post-treatment for the devices, e.g. annealing, impurity gettering, short-circuit elimination, recrystallisation
• CPC Class Codes: H01L 31/1884 Manufacture of transparent electrodes, e.g. TCO, ITO
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product
• CPC Class Codes: Y10T 428/31663 As siloxane, silicone or silane

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.

Claims

1. A low-leakage current photodiode array comprising:

a substrate having a front side and a back side;

a plurality of gate regions formed near the front side of the substrate;

a backside layer formed within the substrate, near the back side of the substrate, the backside layer having a thickness of approximately 0.25 to 1.0 micrometers and having a sheet resistivity of approximately 50 to 1000 Ω

per square.

2. The photodiode array of claim 1, wherein the backside layer is thinned by etching.

3. The photodiode array of claim 1, wherein the backside layer is a crystalline silicon layer.

4. The photodiode array of claim 1, wherein the backside layer is formed during a final high-temperature process of forming the photodiode.

5. The photodiode array of claim 1, wherein the backside layer is thinned after final high-temperature process of forming the photodiode array.

6. The photodiode array of claim 1, further comprising additional layers formed over the back side to decrease the backside reflectivity of the photodiode.