Nitridation of Si(111)

The surface of Si(1 1 1) exposed to NH3 or NO is analyzed with scanning tunneling microscopy, low-energy electron diffraction (LEED), Auger electron spectroscopy. and transmission electron microscopy. Crystalline silicon nitride thin films are formed on Si(l 1 1) after nitridation at T > 1075 K. Corresponding to the 8 x 8 LEED pattern, a 30.7-Angstrom periodic superstructure is observed. The film thickness is saturated at 20 Angstrom. Among all known Si3N4 phases, the nitride film on Si(l 1 1) probably is beta -Si3N4, then the 30.7-Angstrom superstructure is the 4 x 4 reconstruction on Si3N4(0 0 0 1). The possibility that the film is a new silicon nitride phase also exists. An 8/3 x 8/3 quasi-periodic structure is formed at T less than or equal to 1075 K or when the gas purity is degraded. The quadruplet LEED spots are related to carbon contamination. Etching happens during nitridation, which limits the nitride film thickness. Impurities in the nitridant enhance etching. The effectiveness of different nitridants is discussed. (C) 2001 Published by Elsevier Science B.V.