In general, semiconductor wafer defects (structural or chemical abnormalities that impair the ideal crystal structure of the surface layer of the semiconductor wafer) are classified in terms of the effect that they have on a semiconductor device that is formed on the wafer into slight defects, which are allowable, and fatal defects. Fatal defects are called “killer defects” and result in a lowering of the yield of semiconductor devices. In particular in the case of epitaxial wafers, the main defects are stacking faults (SF) of the epitaxial layer; usually, these appear as protuberances or concavities of the surface of the semiconductor wafer. Most killer defects are part of such an SF. Killer defects are caused for example by the height being such as to generate a defocusing fault in the process of manufacturing a device, or by a defect termed a large area defect (LAD), having a wide area, that affects several devices. For convenience, defects including surface defects of epitaxial wafers will herein be referred to as ELDs (EP layer defects). Techniques for detecting “killer defects” on the surface of semiconductor wafers are extremely important in semiconductor manufacture.
An abnormality inspection device employing an optical scattering method is widely employed for surface inspection of semiconductor wafers. Using such an abnormality inspection device, the surface of a semiconductor wafer is scanned with a laser beam of minute size and scattered light from laser light scatterers (defects or particles) on the surface of the semiconductor wafer is detected; the size (value corresponding to the size of standard particles (PLS; polystyrene latex)) of laser light scatterers present on the wafer surface is measured from the intensity of this scattered light. Whereas it is impossible to permanently remove defects from semiconductor wafers, particles can be removed by subsequent processing and are not therefore fatal as regards the semiconductor device. Consequently, in surface inspection using an optical, scattering method, it is important to be able to distinguish whether the individual laser light scatterers that are detected are defects or particles.
Laid-open Japanese Patent Application No. 2001-176943 discloses a method for detecting stacking faults of epitaxial wafers using an optical scattering method. In this method, using an abnormality detection device employing an optical scattering method (for example a Surfscan 6200 (Trade Mark) manufactured by KLA-Tencor Ltd), the size of laser light scatterers present on the surface of an epitaxial wafer is measured and these laser light scatterers are classified into bodies whose size is no more than 1.6 μm and bodies that exceed this value; laser light scatterers exceeding 1.6 μm are identified as being stacking faults, while laser light scatterers of no more than 1.6 μm are identified as pits other than stacking faults.