1. Field of the Invention
This invention relates to a method for testing the quality of a silicon wafer. More particularly, this invention relates to a method for testing a semiconductor silicon single crystal bar grown from molten silicon by the Czochralski (CZ) method or the float zone (FZ) method to determine the presence or absence therein of a D defect which is one form of the point defect.
2. Description of the Prior Art
As a measure to test the quality of a semiconductor silicon single crystal bar which has been grown by the Czochralski method or the float zone method, the procedure which comprises preparing a polished wafer (PW wafer) as a sample from the bar, oxidizing the surface of the silicon wafer with steam at a temperature in the range of from 1,100.degree. C. to 1,200.degree. C., cooling the oxidized silicon wafer to normal room temperature, stripping the oxidized silicon wafer of the oxide film with hydrofluoric acid, and selectively etching the wafer surface for about two minutes with a mixture of K.sub.2 Cr.sub.2 O.sub.7, hydrofluoric acid, and water has been prevailing. This method represents a substantially perfect simulation of the heat treatment to be performed in the formation of a device on the silicon wafer. Because of its ability to determine the presence or absence of an oxidation-induced stacking fault within the wafer during the formation of the device, this method has been heretofore accepted as an important testing technique.
It has been known that an aggregate of point defects are introduced into a silicon single crystal bar while the growth thereof is in progress [(1) Takao Abe, "Applied Physics," 59 (1990), p. 272]. Among other defects, the A defect which is suspected to be an aggregate of interstitial silicon atoms and the D defect which is suspected to be an aggregate of vacancy type lattice defects are particularly popular. The aggregate of point defects is suspected to cause an oxidation-induced stacking fault (OSF) during the formation of the device. A need has been felt for a method capable of testing a silicon wafer to determine the presence or absence therein of the aggregate of point defects. The test of crystallinity which involves the heat treatment described above is problematic in that the test is impracticable unless the target of detection is an oxidation-induced stacking fault, that the test is incapable of directly detecting an aggregate of point defects to be formed during the growth of a crystal, that the test as a process spends a large amount of time, and that the apparatus required for the test is expensive. As a means of test for the detection of an aggregate of point defects, the copper decoration method has been adopted to date. This method comprises preparatorily applying an aqueous solution of nitric acid to the surface of a silicon wafer and then heating the coated silicon wafer at 1,000.degree. C. for several hours thereby decorating an aggregate of point defects with copper.
The test by the copper decoration method mentioned above for the detection of an aggregate of point defects is problematic in that the test necessitates a heat treatment, that the treatment has the possibility of altering lattice defects themselves and, therefore, constitutes itself a destructive testing and consumes a long time, and that the apparatus required for the test is expensive.