X-Ray Determination of Stresses in Thin Films and Substrates by Automatic Bragg Angle Control

Abstract

A modification of a scanning x‐ray topographic camera is described which automatically plots the lattice curvature of single crystal substrates strained by thin films or surface treatments such as diffusion and ion implantation. Film and substrate stresses are calculated from the radius of curvature. The unit operates as an electromechanical feedback system which maintains the orientation of a wafer such that the diffracted x‐ray intensity remains within preset limits while a finely collimated x‐ray beam traverses the wafer. An x‐y recorder continuously plots the changes in orientation as a function of position yielding a trace whose slope is proportional to the radius of curvature of the substrate lattice. The sensitivity of the apparatus is such that radii of curvature of 2000 m can be measured. In addition, the lateral spatial resolution is such that the local substrate lattice curvature can be determined under alternating and overlapping 2.5 mm wide stripes of metal and oxide films. It is also shown that both the curvature and uniformly exposed x‐ray topographs can be obtained simultaneously even though the wafers are severely warped due to the processing steps.