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Phosphorous Diffusion Gettering

IP.com Disclosure Number: IPCOM000084628D
Original Publication Date: 1975-Dec-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Pak, MS: AUTHOR [+2]

Abstract

Metallic impurities are commonly gettered using the phosphorus diffusion technique, which requires forming a phosphorus diffusion layer. For example, phosphosilicate glass (PSG) formed during POCl(3) diffusion acts as a phosphorus source for this layer.

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Phosphorous Diffusion Gettering

Metallic impurities are commonly gettered using the phosphorus diffusion technique, which requires forming a phosphorus diffusion layer. For example, phosphosilicate glass (PSG) formed during POCl(3) diffusion acts as a phosphorus source for this layer.

The efficiency of phosphorous diffusion gettering is related to the amount of integrated phosphorus doping, Q i.e., gettering efficiency increases with Q. To maximize Q, it is desirable to leave intact the PSG layer, because it acts as a dopant source during subsequent heat treatments. However, this glass is normally stripped off during processing.

The emitter diffusion cycle is the largest contribution to Q with resistor reoxidation second. Therefore, it is desirable to retain the PSG layer on the back of the wafer until after the emitter diffusion cycle.

The figure shows the various diffusions and films that are typically on the back of a wafer after POCl(3) diffusion. The thin PSG layer 2 is normally stripped prior to resistor diffusion drive-in.

In order to retain the PSG until after the emitter cycle, a layer of pyrolytic oxide 4 is deposited on the PSG layer 2; then a layer of Si(3)N(4) 6 is deposited on the pyrolytic oxide 4. The Si(3)N(4), which prevents etching of the oxide layers is etched later in the process, which requires back-coating the wafer during the emitter photoresist process. Also shown is N+ phosphorus diffused layer 8.

The front of the wafer is not damaged du...