There has conventionally known an epitaxial silicon wafer having a substrate of a silicon single crystal and an epitaxial layer formed on a surface of the substrate.
Since contamination of metal impurities of the epitaxial layer of the epitaxial silicon wafer deteriorates device characteristics, the contamination of the metal impurities of the epitaxial layer is removed by gettering.
Specifically, the substrate is doped with nitrogen to form oxygen deposited nuclei inside the substrate, into which the metal impurities are captured to be gettered.
As shown in FIG. 4A, COP (Crystal Originated Particle), which is minute fault, exists not only on the surface of the nitrogen-doped substrate 11 but also inside the nitrogen-doped substrate 11. The COP 111 exposed to the surface of the substrate 11 (the COP opened to the substrate surface) becomes a cause of generating a SF (a stacking fault) in the epitaxial layer 12. Incidentally, the numeral 13 denotes the oxide film.
Heat treatment is one of the ways for removing the COP 111 exposed to the surface of the substrate 11. However, as shown in FIGS. 4B and 4C, in the nitrogen-doped substrate 11, due to inner wall oxide film 112 remaining inside the COP 111, the shape of the COP 111 tends to remain unchanged, so that the COP 111 can not be removed only by heat treatment. Thus, as shown in FIG. 4D, the stacking fault 121 is generated in the epitaxial layer 12.
In order to remove the inner wall oxide film 112 inside the COP 111, it is proposed that the substrate 11 is cleaned with a hydrofluoric acid solution to remove the inner wall oxide film 112 inside the COP 111 (see, for example, Patent Document 1).
With this method, after the surface of the substrate 11 is cleaned with the hydrofluoric acid solution, particles are apt to adhere on the surface of the substrate 11. To prevent the particles from adhering on the surface of the substrate 11, an oxide film is formed by cleaning the surface of the substrate 11 with SC-1 (ammonia aqueous hydrogen peroxide) after being cleaned with the hydrofluoric acid solution.
[Patent Document 1] Japanese Patent Laid-Open Publication No. 2002-20200 (Page 2 to Page 5)