Polariscope stress measurement tool and method of use
AssigneeGeorgia Tech Research Corporation
InventorsSteven Danyluk, Fang Li
Life of this patent
Estimating the term…
Abstract
The present invention provides a tool for and method of using an infrared transmission technique to extract the full stress components of the in-plane residual stresses in thin, multi crystalline silicon wafers including in situ measurement of residual stress for large cast wafers. The shear difference method is used to obtain full stress components by integrating the shear stress map from the boundaries. System ambiguity at the boundaries is resolved completely by introducing a new analytical function. A new anisotropic stress optic law is provided, and stress optic coefficients are calibrated for different crystal grain orientations and stress orientations.
Claims19
A polariscope for measuring a sample, comprising:
- a light source;
- a first lens;
- a second lens;
- a sample stage for retaining the sample to be measured;
- and
- a camera;
- wherein:
- said light source, said first lens, said second lens, and said camera are positioned such that light emitting from said light source defines a light path that passes through said first lens and said second lens and into said camera;
- and
- said sample stage is positioned such that when the sample is positioned thereon the sample is within said light path intermediate said first and second lenses, with no polariscope components interrupting said light path between the sample and said first and second lenses.
A method of determining the amount of residual stress present in a silicon wafer sample, comprising:
- providing a polariscope including a light source, a first lens, a second lens, and a camera positioned such that light emitting from said light source defines a light path that passes through said first and second lenses and into said camera;
- placing the sample intermediate said first lens and said second lens within said light path;
- causing light to emit from said light source through said first lens, the sample, and said second lens and into said camera;
- capturing an image of said light after passing through the sample;
- determining a maximum shear stress within the sample based on said image;
- and
- determining full residual stress components within the sample based on said maximum shear stress.
Dependencies are inferred from the claim text.