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Publication Detail
Non-destructive assessment of semiconductor carrier lifetime using photothermal radiometry
  • Publication Type:
    Journal article
  • Publication Sub Type:
    Conference Proceeding
  • Authors:
    Amirhaghi S, Kenyon AJ, Federighi M, Pitt CW
  • Publication date:
  • Pagination:
    455, 460
  • Journal:
    Materials Research Society Symposium - Proceedings
  • Volume:
  • Status:
  • Print ISSN:
Of crucial importance to all areas of the microelectronics industry is the characterization of silicon wafer quality. An important indicator of this is carrier lifetime, and a convenient non-destructive method for its measurement is Photothermal 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 ir-radiation detected from the photo-excited region is inversely proportional to the optically induced career 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 frequency scans of free-carrier absorption. From these, it is possible to obtain information on surface recombination velocity and diffusion length.
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