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NON-DESTRUCTIVE HIGH RESOLUTION MAPPING OF DEFECTS IN GaAs

IP.com Disclosure Number: IPCOM000035909D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 113K

Publishing Venue

IBM

Related People

Albert, M: AUTHOR [+4]

Abstract

To date, near band-edge photo-luminescence (PL) imaging of GaAs wafers affords the only non-contact and non-destructive characterization of microscopic material inhomogeneity within a depth of less than one micrometer. Material inhomogeneity refers to spatial variations in the distribution of dopants, and native defects which usually occur unintentionally, and can cause considerable variations in transistor characteristics over a wafer surface. The major source of this material inhomogeneity is associated with the accumulation or depletion of these point defects around dislocation sites during boule formation and cooling. Therefore, dislocation density and distribution have been of primary importance in measuring material inhomogeneity.

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NON-DESTRUCTIVE HIGH RESOLUTION MAPPING OF DEFECTS IN GaAs

To date, near band-edge photo-luminescence (PL) imaging of GaAs wafers affords the only non-contact and non-destructive characterization of microscopic material inhomogeneity within a depth of less than one micrometer. Material inhomogeneity refers to spatial variations in the distribution of dopants, and native defects which usually occur unintentionally, and can cause considerable variations in transistor characteristics over a wafer surface. The major source of this material inhomogeneity is associated with the accumulation or depletion of these point defects around dislocation sites during boule formation and cooling. Therefore, dislocation density and distribution have been of primary importance in measuring material inhomogeneity.

Photo-luminescence emission in GaAs at room temperature arises from direct electron-hole (e-h) recombination and consists of a broad, asymmetric emission spectrum which peaks at 1.37 eV and has a FWHM of 35 meV. Impurities in GaAs generally provide additional channels for e-h recombination that may either be non-radiative, or result in radiation at wavelengths beyond the range of our detector. As a result,

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the near band-edge PL emission efficiency is greatly reduced in the presence of electronically active impurities. Dislocations become "visible" because they act as intrinsic gettering centers (during boule formation and cooling) for non- radiative recombination centers which provide competitive e-h recombination channels and reduce PL emission efficiency.

We describe a scanning technique which, in 20 minutes, produces a digital PL image of a full GaAs wafer consisting of 1024 by 1024 picture elements, and has an effective spatial resolution of 50 mm over a wafer 51 mm in diameter. Scanning can also be conducted at high resolution and can be used to obtain more detailed PL images of single dislocations in low dislocation density...