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1. (WO1999006841) OPTICAL METHOD FOR THE DETERMINATION OF STRESS IN THIN FILMS

Pub. No.:    WO/1999/006841    International Application No.:    PCT/US1998/013742
Publication Date: Fri Feb 12 00:59:59 CET 1999 International Filing Date: Fri Jul 03 01:59:59 CEST 1998
IPC: G01L 1/24
Applicants: BROWN UNIVERSITY RESEARCH FOUNDATION
Inventors: MARIS, Humphrey, J.
Title: OPTICAL METHOD FOR THE DETERMINATION OF STRESS IN THIN FILMS
Abstract:
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 (P1) 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 (P1), applying at least one optical probe pulse (P2), the optical probe pulses (P2) being applied with different time delays after the application of the corresponding optical probe pulses (P2); (B) detecting variations in an intensity of a reflection of portions of the optical probe pulses (P2), 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 (P2), while in another embodiment the step of detecting measures a change in intensity of the reflection of portions of the optical probe pulses (P2) and determines a time at which the propagating strain pulse (S1) reflects from a boundary of the film layer.