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Isolation of Device Components

IP.com Disclosure Number: IPCOM000084470D
Original Publication Date: 1975-Nov-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Galyon, GT: AUTHOR

Abstract

Recessed oxide isolation has been developed previously, in order to isolate bipolar transistors in integrated circuits. To achieve high densities of bipolar transistors in integrated circuits, it is desirable to have the emitter and base overlap the silicon dioxide isolation. Unfortunately, boron from the base diffuses into the silicon dioxide isolation and creates an inversion which produces leakage between the emitter and collector.

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Isolation of Device Components

Recessed oxide isolation has been developed previously, in order to isolate bipolar transistors in integrated circuits. To achieve high densities of bipolar transistors in integrated circuits, it is desirable to have the emitter and base overlap the silicon dioxide isolation. Unfortunately, boron from the base diffuses into the silicon dioxide isolation and creates an inversion which produces leakage between the emitter and collector.

By doping the transistor silicon dioxide interface with boron, a boron (P- type) skin is made which reduces leakage between the emitter and collector. Three techniques have been devised to accomplish this result.

Figs. 1A-1C show a method where the surface of the silicon dioxide trench is lightly doped with boron. Since it is difficult to control small concentrations of dopant, a layer of silicon dioxide 1 is first placed inside the empty silicon dioxide trench and boron is allowed to diffuse through the silicon dioxide. The silicon dioxide acts as a sieve, so that the boron that diffuses into the silicon is of low concentration.

It is necessary to produce a very lightly doped p skin 2, since leakage between the base and P+ isolation region would result otherwise. It would be desirable to reduce this leakage by applying the boron skin only to the upper sidewall of the silicon dioxide trench that adjoins the base and emitter; the methods described below achieve this result.

As is shown in Fig. 2A, a lay...