Browse Prior Art Database

Nondestructive Electrolytic Localization of Pipe Sites in Bipolar transistors

IP.com Disclosure Number: IPCOM000089354D
Original Publication Date: 1977-Jul-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 109K

Publishing Venue

IBM

Related People

Das, G: AUTHOR

Abstract

The use of anodization techniques for the detection of pipes in bipolar devices is known and described in U. S. Patent 3,846,259 and by M. V. Kulkarni et al. in IEEE Transactions ED-19, 1098 (1972).

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Nondestructive Electrolytic Localization of Pipe Sites in Bipolar transistors

The use of anodization techniques for the detection of pipes in bipolar devices is known and described in U. S. Patent 3,846,259 and by M. V. Kulkarni et al. in IEEE Transactions ED-19, 1098 (1972).

Disclosed herein is a novel and simplified technique for nondestructive electrolytic location of pipe sites in the emitter region of bipolar silicon devices.

In NPN transistors, localized regions between the collector and emitter, through the base, are usually defined as "pipes". In a suitable electrolyte, when a wafer-containing device or transistor is made, an anode (plus (+V)) current should flow only between the collector and the cathode. If, however, a "pipe" or "pipes" exist between the emitter and collector through the base, the emitter region will also conduct current. The extent of this conducting region normally depends on the size of the pipe, the conductivity of the electrolyte, and the conductivity of the conductor metallurgy (if a suitable conductor metallurgy has been fabricated for interconnection purposes). Thus, by suitably choosing a conductor metallurgy and an electrolyte capable of "electro-polishing" (anodically oxidizing the conductor metallurgy in conducting regions and dissolving the oxidized product in the electrolyte), pipes or pipe sites can be revealed.

In principle, many combinations of high conductivity metallurgy (such as evaporated thin films of aluminum, copper, gold, silver, etc.) and suitable electrolytes can be used to reveal the "pipe sites"; "pipe sites" are acting as conducting regions only. However, lack of good adhesion of vapor-deposited copper, gold, silver films on silicon and possible contamination (such as plating back onto the silicon) from the electrolytes narrows down a preferred choice to aluminum as the metallurgy. Two electrolytes were found particularly useful, as identified below, with the first preferred because of its efficient localized attacks at the pipe site(...