Evaluating Interface Effect On Stresses In Thin Films By A Local Curvature Metrology With High Accuracy And Resolution

Abstract

Novel local curvature test structures combined with a sub-nanometer optical interferometry measuring setup have been developed to detect stresses in nanometer-scale films as well as ultra low stresses in thin films. Stress difference as small as 1.5 MPa within a 30 nm film can be resolved with this metrology, which is among the best in the present reports. Residual stresses in thermal SiO2 and LPCVD Si3N4 thin films are measured with repeatability better than 1%, which are in good agreement with those extracted by other methods. In addition, residual stresses in Si3 N4 thin films with different types of substrates are evaluated. Taking the advantage of the high accuracy and high resolution of this metrology, interface effect on stresses in Si3N4 films has been experimentally revealed, which is acute in nanometer-scale film but relaxes with the increase of film thickness. Stress differences as high as 42% suggest that Si3N4 deposited on oxide has a much higher residual stress than that grown on silicon, which is crucial for stringent MEMS/NEMS design