Surface structures of silicon nitride thin films on Si(111)

After exposing Si(111) to NH 3 at about 1075 K, a 10.2-Å surface periodic structure (the ‘8/3×8/3’ reconstruction) is observed in scanning tunneling microscopy images. When the nitridation temperature is above 1125 K, a silicon nitride film with a surface superstructure with a period of 30.7 Å and a minimum step height of 2.9 Å is obtained. Our systematic analyses suggest that the 30.7-Å superstructure is the 4×4 reconstruction on the Si 3N 4(0001) surface of the crystalline silicon nitride ( β-Si 3N 4) thin film formed on Si(111), while the 10.2-Å periodic structure is an incomplete nitridation phase on Si(111) surface. The surface structure has been found to be sensitive to the impurities in NH 3.