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Improved Method for Piezo-Raman Stress Measurements

IP.com Disclosure Number: IPCOM000107917D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 1 page(s) / 73K

Publishing Venue

IBM

Related People

Needham, C: AUTHOR

Abstract

The described invention covers a design for improving the accuracy and resolution of stress gradient measurements on silicon microcircuit devices by the piezo-Raman effect. An argon ion laser operating in the all-line mode is used to create a bichromatic beam of wavelengths 488.0 and 514.5 nm, by dispersing the lines with a prism, using a blocking mask to pass only these two lines, and recombining the lines with a second prism. The bichromatic beam is focused onto the device through a microscope, and the Raman scattered radiation is focused by the objective lens, through a beam splitter, and into a monochromator, using the usual microprobe optics.

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Improved Method for Piezo-Raman Stress Measurements

      The described invention covers a design for improving the
accuracy and resolution of stress gradient measurements on silicon
microcircuit devices by the piezo-Raman effect.  An argon ion laser
operating in the all-line mode is used to create a bichromatic beam
of wavelengths 488.0 and 514.5 nm, by dispersing the lines with a
prism, using a blocking mask to pass only these two lines, and
recombining the lines with a second prism.  The bichromatic beam is
focused onto the device through a microscope, and the Raman scattered
radiation is focused by the objective lens, through a beam splitter,
and into a monochromator, using the usual microprobe optics.

      The Stokes line of the silicon phonon band from the 488.0 nm
laser line, and the anti-Stokes line from the 514.5 laser line, lie
very close together at about 500 nm. Compressive strain in the
silicon lattice will cause these lines to move closer together;
tensile strain will move them apart.  Since both lines shift, the
sensitivity of the measured stress is doubled over that of the
conventional experiment where one line moves relative to a fixed
external standard.  In this invention, the external standard is not
needed, since the experiment is self-calibrating, thus improving the
accuracy.  Further improvement in accuracy results from the curve
fitting algorithm for locating the band centers.  Since the intensity
ratio of the bands is now constant and independent of  t...