Measuring small-area Si/SiO2 interface stress with SEM

Abstract

A method for measuring small-area Si/SiO2 interface stress with the scanning electron microscope (SEM) has been developed. The method consists of cleaving a Si wafer (chip) through the desired area and selectively etching the Si back from the broken edge. The compressive stress in the remaining SiO2 shelf is thus released. When viewed on edge by a SEM, the sample conveniently shows the resulting sinusoidal shape of SiO2. Direct measurement of the arc length and its corresponding straight-line distance can then be used to calculate the Si/SiO2 stress. The technique is particularly suited for measuring stress in local areas of thin SiO2. Stress calculations obtained from SiO2 films 500–700 Å thick at local regions only 4 μ wide have shown the compressive stress to be as high as 5.1×1010 dyn/cm2. The lower limit of film thickness to which this technique may be applied is governed by the resolving power of the SEM or the ability of the thin film to support itself. The upper limit of film thickness is dependent upon the length and thickness of the strut and the actual compressive stress, all of which affect the critical value that will cause the unsupported film to buckle.