In a particle counter apparatus, it is possible to perform not only particle measurement but also haze measurement. Here, the particle counter apparatus is an apparatus which checks the number or positions of particles by generating intensive scattering light when incident light strikes on a wafer and the particles are present there.
When a haze (roughness on a surface) is present on a silicon wafer surface, weak scattering light is generated by applying the light to the wafer, and hence the haze can be measured by using the particle counter apparatus.
The haze is an important quality item, and it is managed as a haze value by the particle counter apparatus. A high haze value means large roughness on a surface, and a low haze value means small roughness on the surface.
To enhance a measurement accuracy, the particle counter apparatus usually calibrates a particle size with a standard wafer (a standard sample) having standard particles (made of polystyrene or SiO2) applied thereto.
Since laser intensity or sensitivity of a photomultiplier (a photomultiplier tube) slightly differs depending on each apparatus, intensity of scattering light from particles of a given fixed size is supposed to be the same with respect to the incident light, but perfectly equalizing detector sensitivity and the like is difficult, and a difference between apparatuses is filled by, in reality, placing the standard particles of a given fixed size on a wafer and treating intensity of scattering light generated from this wafer (which differs depending on each apparatus) as intensity of scattering light relative to particles of a fixed size, which is an inherent value of each apparatus.
Although the haze value should be likewise calibrated on the standard wafer (the standard sample), what are required for the standard wafer for a haze are as follows.
1) Roughness is fixed without a radial distribution, and it is fixed as seen from all directions (although an atomic step is inappropriate since a step can be seen from a given direction but no step can be seen from another direction).
2) No contamination must be produced during measurement (the haze value changes when contamination is produced).
3) No contamination or no tarnish must be produced during storage (the haze value changes when the tarnish is produced).
Patent Document 1 discloses that a standard wafer for a haze is formed by forming cylindrical irregularities on a silicon wafer surface in terms of roughness which is fixed as seen from all directions.