The measurement of thin film stress using phase shifting interferometry

A new technique for determining the stress of thin films is described. This technique combines digital phase shifting interferometry with image-proces sing software. A circular disc polished on one side is used as the coated s ubstrate during film deposition. The average stress in thin films can be de rived by comparing the deflection of the substrate before and after him dep osition. The deflection of the substrate by the deposited film is obtained by the phase map. Using the Zernike polynomial fitting algorithm, a three-d imensional contour map is generated from the polynomial coefficients to vis ualize the deformation of the thin film and to examine the tensile or compr essive stress after film deposition. Four oxide films prepared by ion-beam sputter deposition are investigated for their film stresses. The experiment al results show that the stress values are concordant with measurements usi ng other methods.