FAST DIRECT NITRIDATION OF SILICON WITH NITROGEN PLASMA AND ITS EFFECT ON THE SHIFT OF FLAT-BAND POTENTIAL

Silicon nitride films are produced by the reaction of crystalline silicon with nitrogen plasma, and the nitride films are studied by means of Auger electron spectroscopy, X-ray photoelectron spectroscopy, and work function measurements. The growth rate of the nitride film is very high at the initial stage; a 2-nm-thick Si nitride film is formed in 20 s by the reaction at 700-degrees-C. The work function of the Si (100) surface increases slightly at the very initial nitridation stage and decreases by further nitridation. The work function of the (111) surface, on the other hand, decreases from the initial nitridation stage. The work function decrease is attributed to the nitrogen atoms below the surface. The change in the work function of the Si (100) surface is much larger than that for the Si (111) surface, because the (100) surface has an open structure. The Si electrode coated with a 2-nm-thick nitride layer shows a large anodic shift (maximum 1.5 V) in the flat-band potential after sweeping the electrode potential in an acetonitrile solution of LiClO4. This shift is caused by Li+ ions included in the oxynitride layer formed from the nitride film by the reaction with a small amount of water in the solution.