Effect of wafer size on the film internal stress measurement by wafer curvature method

Abstract

Wafer curvature method has been applied to determine the internal stress in the films using Stoney’s equation. During the film deposition, the wafer fixation on the sample holder will restrict the deformation of the rectangle-shaped wafer, which may result in the stress datum difference along length and width direction. In this paper, the effect of wafer size and the wafer fixation on the TiN film internal stress measured by wafer curvature method was discussed. The rectangle-shaped wafers with different length/width ratios (L/W=1:1, 2:1, 3:1 and 4:1) were fixed as a cantilever beam. After the TiN films deposition, the profiles of the film/wafer were measured using a stylus profilometer and then the internal stress was calculated using the Stoney equation in the film. The results showed that the fixed end of the wafers limited to some degree the curvature of the wafers along the width direction. For film internal stress measured by wafer curvature method, the wafer profile should be scanned along the length direction and the scan distance should be greater than or equal to half of wafer length. When the length/width ratio of the wafer reached 3:1, the wafer curvature and the calculated stress were basically the same at different positions along the length direction. For film internal stress measured by wafer curvature method, it was recommended that the length/width ratio of wafer should be considered to be greater than or equal to 3:1, and the deformed profile was scanned along the length direction.