Measuring stress in Si ingots using linear birefringence

We report near infrared (NIR) linear birefringence measurements on shaped and surface finished Czochralski (CZ) grown silicon ingots. The linear birefringence was measured using a commercially available NIR system. All measurements were done with the NIR beam configured parallel to one of the < 100 > directions of silicon. Stress-optic coefficient values of silicon were used to calculate the residual stress from phase retardation values. Two-dimensional scans were performed along flat surface, i.e. the crystallographic [001] and [010] directions. Examples of both, higher and lower stressed Si ingots are presented. Due to the large diameter of silicon ingots, stress resolution and stress detection limits are much enhanced for ingots than for silicon wafer. Phase retardation measurements for most ingots showed only low stress distribution of < 30kPa. However, some ingot sections show stress as high as nearly 1.0MPa. (C) The Authors. Published by Elsevier Ltd.