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Determining Epitaxial Layer Quality

IP.com Disclosure Number: IPCOM000076475D
Original Publication Date: 1972-Mar-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 21K

Publishing Venue

IBM

Related People

Schumann, PA: AUTHOR [+2]

Abstract

Emitter-collector leakage is a common and high yield loss problem in bipolar devices. Although pipes or, more generally, emitter-collector leakage has been related to crystallographic defects such as dislocation, slip and stacking faults, it is not always possible to trace the problem directly to any particular fault in epitaxial layer. Generally, the absence of such faults is grouped together in a term, the epitaxial quality. It is believed that a pipe is primarily caused by the interaction of a crystallographic defect with an anomalous impurity. During a heating step, anomalous impurities in the epitaxial layer may be expected to be precipitated at a crystallographic defect. Such anomalous impurities can affect the minority carrier lifetime of the epitaxial layer.

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Determining Epitaxial Layer Quality

Emitter-collector leakage is a common and high yield loss problem in bipolar devices. Although pipes or, more generally, emitter-collector leakage has been related to crystallographic defects such as dislocation, slip and stacking faults, it is not always possible to trace the problem directly to any particular fault in epitaxial layer. Generally, the absence of such faults is grouped together in a term, the epitaxial quality. It is believed that a pipe is primarily caused by the interaction of a crystallographic defect with an anomalous impurity. During a heating step, anomalous impurities in the epitaxial layer may be expected to be precipitated at a crystallographic defect. Such anomalous impurities can affect the minority carrier lifetime of the epitaxial layer. Therefore, it would appear that the epitaxial layer with the highest minority carrier lifetime should have the lowest emitter-collector leakage if all other factors are equal.

While the measurement of the minority carrier lifetime in the epitaxial layer is extremely difficult, this lifetime may be directly related to the diffusion length. Diffusion length is directly related to minority carrier lifetime via the diffusion coefficient in accordance with the following formula: L = square root of D Lambda where L = diffusion length D = diffusion coefficient

Lambda = minority carrier lifetime.

Diffusion length may be determined using a scanning-light spot in accordance w...