The reaction of Si(100) 2×1 with NO and NH3: The role of surface dangling bonds

Abstract

We present the results of a detailed study of the reactions of Si(100) 2×1 with NO and NH3. We use several electron spectroscopies and ion scattering to study the reactivity of the surface and to determine the nature of the rate limiting steps of the above reactions over a wide temperature range (90–1200 K). We find that the Si(100) 2×1 surface is quite reactive and can dissociate NO or NH3 even at 90 K. The reactions are, however, self-limiting. The released O or H atoms tie up the surface dangling bonds and passivate the surface. The N atoms, on the other hand, occupy mostly subsurface sites. Sustained reactivity and thin film growth occurs only at temperatures sufficiently high enough to desorb the surface oxygen or hydrogen and regenerate the surface dangling bonds. We find, however, that electron-stimulated desorption of the hydrogen can be used to nonthermally regenerate the surface dangling bonds and allow silicon nitride thin film growth even at 90 K. Because of the crucial role the top layer plays in the film growth mechanism we investigate its nature using the new technique of scanning tunneling microscopy (STM). This is the first in situ study of a surface chemical reaction by STM. The STM topographs indicate that the 2×1 reconstruction is preserved after exposure of the Si(100) 2×1 surface to NH3. The topographs and the tunneling current versus voltage curves suggest the formation of a Si(100) 2×1 monohydride-like surface layer.