Wafer fragments can be examined. A line from 2 to 5 mm high can be scanned across the entire wafer for curvature, while the entire wafer can be scanned in a topograph. The material must be single crystal, usually silicon or gallium arsenide. For topography a square area of up to 150mm on a side can be examined. Contrast is determined from the diffracted beam intensity, which is increased by local strain fields in the crystal lattice.
Topographical information is provided.