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Electrochemical Method to Locate High Leakage Paths in NPN Transistor Structures

IP.com Disclosure Number: IPCOM000076642D
Original Publication Date: 1972-Apr-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Hasson, JC: AUTHOR [+2]

Abstract

Shown is a testing scheme for mapping of both big and small transistors optically for pipes and leakage currents.

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Electrochemical Method to Locate High Leakage Paths in NPN Transistor Structures

Shown is a testing scheme for mapping of both big and small transistors optically for pipes and leakage currents.

In operation, the oxide on the surface of silicon wafers containing transistor structures is stripped followed by coating of the back side and all of the edges with black wax 5, in which condition the substrate wafer is made an anode of an electrolytic cell containing either 5 to 25% HF solution or an aqueous solution of an inert electrolyte 7. A large platinum foil 8 serves as the cathode.

When HF solution is used as the electrolyte, the P+ isolation diffusion area dissolves at a relatively high rate of approximately one micron per minute at a current density of 0.025 amp/cm/2/. The N epitaxial region 4 of the collector region undergoes relatively no change. However, the N+ region on the collector produces, in 10 minutes, a colored surface (brown, violet or green) as a result of anodic oxidation reactions. If the transistor structure has no high leakage (emitter-collector) path, both the N+ emitter 1 and P base regions 2 do not undergo any electrochemical reaction.

In the case of the pipe or leakage path, the emitter region shows colored spots or areas, which are believed to represent natural locations of the leakage path on the surface.

A close correlation has been found between the colored areas on emitter and a leakage current on those transistors large enough to be e...