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Non-Destructive Assessment Of Semiconductor Carrier Lifetime Using Photothermal Radiometry

Published online by Cambridge University Press:  15 February 2011

S. Amirhaghi
Affiliation:
Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WCIE 7JE, UK
A. J. Kenyon
Affiliation:
Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WCIE 7JE, UK
M. Federighi
Affiliation:
Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WCIE 7JE, UK
C. W. Pitt
Affiliation:
Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WCIE 7JE, UK
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Abstract

Of crucial importance to all areas of the microelectronics industry is the characterisation of silicon wafer quality. An important indicator of this is carrier lifetime, and a convenient non-destructive method for its measurement is Pholothermal Radiometry. This involves the photo-generation within a semiconductor sample of electron-hole pairs. Periodic generation of carriers leads to modulation of free-carrier absorption of mid-ir radiation provided by a black body source. The fr-radiation detected from the photo-excited region is inversely proportional to the optically induced carrier density. As the modulation frequency is increased, a point is reached at which the photo-generated carriers no longer have sufficient time to decay between pulses. This frequency is dependent on the carrier lifetime. We present a description of the Photothermal Radiometric lifetime scanning instrument built at UCL. This instrument offers an accurate method for producing detailed maps of carrier lifetime across whole or part wafers. The problem of surface-state effects has been addressed by employing a broad-band uv source to optically fill the surface states of the sample under investigation. The instrument is capable of producing maps of lifetime variation with 0.5 mm resolution. Alternatively, for selected points on a wafer, the instrument can generate detailed frequercy scans of free-carrier absorption. From these, it is possible to obtain information on surface recombination velocity and diffusion length.

Type
Research Article
Copyright
Copyright © Materials Research Society 1996

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