Wafer mapping

Mapping of crystal orientation and other properties of wafers

The homogeneity of crystal wafers is mapped in order to get information on the as-grown quality of the crystalline material as well as on the influence of surface preparation steps.

The Wafer Mapping Machine is based on the Omega Scan Method. The in-plane shift of the specimen is realized by one translation and one rotation (shift according to polar coordinates). The points of the specimen to be measured are brought into the rotation axis of a turntable which bears the shift mechanism. The machine is equipped with an automatic feeding mechanism allowing the reproducible positioning of the wafer. There are three loading positions from which the three wafers in turn can be measured fully automatically.

Specifications of the machine:

• Materials: silicon, silicon carbide, sapphire and quartz*
• Possible wafer sizes:
  Round, diameters 0.5” – 4” (12.7 – 101.6 mm), with and without flat;
  Rectangular, 12x12 mm² - 75x75 mm².
• Diameter of the measuring area for a single measurement: 1 mm.
• Shift accuracy: 0.1 mm.
• Measuring time per measured point (at 3 overlays): 9 seconds.
• Measuring time of a wafer with 40´20 measuring points (at 3 overlays): 2 hours.
• Reproducibility of the cutting angle of AT-cut quartz (at 3 overlays): 3 arc seconds.

*) other crystal types and orientations on request. Other parameters to be mapped: intensity, lattice parameters, surface shape, rocking-curve widths, …

Distribution of the AT-cutting angle over the surface of a quartz wafer 40x20 mm² (spread of measuring values: 2 arc minutes)

Bending of the same wafer (determined only by laser-scan evaluation: spread of measuring values: 10 arc minutes)

Wafer on measurement support.

Total view of the Wafer Mapping Machine

Further information:

• Prospect of the wafer mapping machine
• Principle of the Omega-Scan method