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Title: Optical method for the determination of stress in thin films

Patent ·
OSTI ID:872118
 [1]
  1. Barrington, RI
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A method and optical system is disclosed for measuring an amount of stress in a film layer disposed over a substrate. The method includes steps of: (A) applying a sequence of optical pump pulses to the film layer, individual ones of said optical pump pulses inducing a propagating strain pulse in the film layer, and for each of the optical pump pulses, applying at least one optical probe pulse, the optical probe pulses being applied with different time delays after the application of the corresponding optical probe pulses; (B) detecting variations in an intensity of a reflection of portions of the optical probe pulses, the variations being due at least in part to the propagation of the strain pulse in the film layer; (C) determining, from the detected intensity variations, a sound velocity in the film layer; and (D) calculating, using the determined sound velocity, the amount of stress in the film layer. In one embodiment of this invention the step of detecting measures a period of an oscillation in the intensity of the reflection of portions of the optical probe pulses, while in another embodiment the step of detecting measures a change in intensity of the reflection of portions of the optical probe pulses and determines a time at which the propagating strain pulse reflects from a boundary of the film layer.

Research Organization:
Brown Univ., Providence, RI (United States)
DOE Contract Number:
FG02-86ER45267
Assignee:
Brown University Research Foundation (Providence, RI)
Patent Number(s):
US 5864393
OSTI ID:
872118
Country of Publication:
United States
Language:
English

References (14)

Picosecond transient grating studies of polymeric thin films journal February 1986
Physics of ultrafast phenomena in solid state plasmas journal January 1978
Ion implant monitoring with thermal wave technology journal September 1985
Third order nonlinear optical interactions in thin films of poly‐ p ‐phenylenebenzobisthiazole polymer investigated by picosecond and subpicosecond degenerate four wave mixing journal May 1986
Detection of thermal waves through optical reflectance journal June 1985
Picosecond Ellipsometry of Transient Electron-Hole Plasmas in Germanium journal May 1974
Thermal and plasma wave depth profiling in silicon journal September 1985
Thin‐film thickness measurements with thermal waves journal July 1983
Carrier lifetime versus ion‐implantation dose in silicon on sapphire journal February 1987
Picosecond spectroscopy of semiconductors journal January 1978
Analysis of lattice defects induced by ion implantation with photo‐acoustic displacement measurements journal November 1994
Measurements of the Kapitza conductance between diamond and several metals journal March 1992
Kapitza conductance and heat flow between solids at temperatures from 50 to 300 K journal December 1993
A New Method of Photothermal Displacement Measurement by Laser Interferometric Probe -Its Mechanism and Applications to Evaluation of Lattice Damage in Semiconductors journal November 1992

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optical
method
determination
stress
films
disclosed
measuring
amount
film
layer
disposed
substrate
steps
applying
sequence
pump
pulses
individual
ones
inducing
propagating
strain
pulse
probe
applied
time
delays
application
corresponding
detecting
variations
intensity
reflection
portions
due
propagation
determining
detected
sound
velocity
calculating
determined
embodiment
step
measures
period
oscillation
change
determines
reflects
boundary
layer disposed
probe pulse
time delays
optical method
optical pump
intensity variations
pump pulse
time delay
optical probe
film layer
sound velocity
individual ones
responding optical
detecting variations
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