Three - University of Arkansas Physics Department

Proceedings of the SPIE , v 3134, p 475-85.1997
STRESS MEASUREMENT OF DEPOSITED Si02 FILMS ON SILICON WAFER
USING DIMENSIONAL STABILITY HOLOGRAPHIC INTERFEROMETRY
TEST
G. E. Dovgalenko, M. S. Haque, A. V. Kniazkov,Y. I. Onischenko,
G.J. Salamo, H. A. Naseem
University of Arkansas, Fayetteville, AR, 7270 1, USA
ABSTRACT
In quality control nondestructive techniques gain more and more importance.
Holographic interferometry has the advantage of being very sensitive and can be used
contactless for inspection of technical components. The interferogram contains fnnges,
whose pattern holds information about the surface deformation of a part subjected to the
load he he load in case of deposited silicone oxide film is cased by stress produced
different thermal expansion temperature coefficients film and silicone substrate. Change
in stress in thin silicon dioxide films was observed using a high stability portable
holographic interferometer using dimension stability test. Pattern recognition algorithm
for synthesis of stress analyses map is reported. A stress relaxation phenomenon in this
film thickness of 0.5 pm on Si wafer has been observed. Correlation of differential stress
with initial flatness deviation of Si wafer has been discovered. The advantages of the
proposed measuring technique and results are discussed.
Key words: holographic interferometry, pattern recognition, stress analysis, thin film,
portability.
1. INTRODUCTION
Thin films deposited on hot substrates get a stress component in them because of the
difference in the thermal expansion coefficients of the film and the substrate. Due to
presence of defects and impurities, along with the film microstructure give rise to another
component of stress called the intrinsic stress. Chemical vapor deposited silicon &oxide
films have moisture related silanol (Si-OH) impurities. With increase in agng in
atmospheric ambient, the film absorbs moisture and the film stress becomes more
compressive 2,3. Thus the intrinsic stress of chemical vapor deposited silicon dioxide
films changes during shelf storage. Observing the film stress continuously at room
temperature can give an idea abou the quality of the film. Traditionally bending plate
deflection technique is used to measure thin film stress. The bow of the bare substrate is
measured before film deposition. After film deposition, measuring the bow of the
substrate at any time and using the change in bow, film and substrate thickness, and
Young's modulus and Poisson's ratio of the substrate, the film stress at that time can be
estimated 4. In most of the commercial devices, a laser deflection technique is used to
measure the bow (or radius of curvature). A good reflectivity of the substrate material
requirement limits its application. Also this device operates in quasi-real time. The
SPIE Vol. 3134 7 0277-786X1971510.00