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Room Temperature Photoluminescence Measurement of Stress in Silicon

IP.com Disclosure Number: IPCOM000100490D
Original Publication Date: 1990-Apr-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 3 page(s) / 106K

Publishing Venue

IBM

Related People

Guidotti, D: AUTHOR [+2]

Abstract

There are three aspects of the interaction between photo-generated carriers and an applied stress that are well known in silicon at low temperature. I. When a uniform, uniaxial stress is applied to a Si sample, both shear and hydrostatic components of the stress cause shifts in the intrinsic band edge proportional to the magnitude of the stress. A tensile stress causes a widening of the intrinsic band edges and results in a blue shift of intrinsic recombination radiation (RR), while a compressive stress causes a red shift (1). II. Shear components of an applied uniaxial stress separate some of the degenerate states at critical points in the band structure and result in polarization selection rules for RR with respect to the direction of applied stress (2). III.

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Room Temperature Photoluminescence Measurement of Stress in Silicon

       There are three aspects of the interaction between
photo-generated carriers and an applied stress that are well known in
silicon at low temperature.  I. When a uniform, uniaxial stress is
applied to a Si sample, both shear and hydrostatic components of the
stress cause shifts in the intrinsic band edge proportional to the
magnitude of the stress.  A tensile stress causes a widening of the
intrinsic band edges and results in a blue shift of intrinsic
recombination radiation (RR), while a compressive stress causes a red
shift (1).  II. Shear components of an applied uniaxial stress
separate some of the degenerate states at critical points in the band
structure and result in polarization selection rules for RR with
respect to the direction of applied stress (2).  III. Photo-generated
electron-hole (e-h) pairs (free excitons, at low temperatures)
diffuse under the influence of a strain gradient.  In a non-uniform
strain field, excitons diffuse toward maximum compressive strain
because this corresponds to a minimum band energy. A local region of
maximum compressive strain acts as a local potential well in which
excitons can diffuse and become trapped (3-5).  In addition, a strain
potential well can be selectively photo-excited by using sub-bandgap
illumination thereby causing photo-excitation of carriers only within
regions of maximum compressive strain (6).  Lasers that can be
conveniently used for this purpose exist with output at wavelengths
1.0644 mm (Nd:YAG) and 1.0796 mm (Nd:YA103). Conversely, excitons
diffuse away from regions of high tensile strain.

      A simple experiment was designed to show that room temperature
RR in Si, though broad, is nevertheless usefully sensitive to stress
and can, therefore, be contemplated as a potentially practical
technique for measuring some properties of local stress in Si wafers.
 In the figure RR spectra are shown, which were taken at room
temperature and for various applied stresses.  A sketch of the
experiment is shown in the insert.  A bearing ball 1 inch in diameter
was used to apply a high, local, non-uniform stress to a 5 inch Si
wafer which was clamped on its periphery.  The elastic restoring
force of the wafer itself was used to appl...