Shear Stress in Wafers

Shear stress has become a more and more important issue, as the device geometries keep getting smaller, making the devices sensitive to the quality of the substrate material. Small defects in the crystal structure lead to devices not meeting their specs or in worst case cause the wafer to break in one of the production systems of the wafer fab.

The stress measurement is based on the physical effect that a polarized light will be depolarized, if it is transmitted through a substrate under mechanical stress. The SIRD and SIRIS systems use IR as silicon is transparent for infra-red light.

The most common application for this technique is monitoring of epitaxial reactors with special attention to the wafer edge. Other applications include monitoring of abrasive or high temperature process steps in the manufacturing of silicon wafers, solar cells or special material for opto-electronic devices.

The inspection using our SIRD and SIRIS systems does not only include the measurement but also special analysis programs. The results will be presented in detailed maps and in numeric values for statistical process control applications. The analytical package allows post measurement analysis for global stress fields, localized defects, analysis of a small area and many more. It can be used on monitor wafers as well as on product wafers.

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