Atomic structure of Si(001)-c(4 x 4) formed by heating processes after wet cleaning and its first-principles study

In order to yield an atomically flat Si(001) reconstructed surface at as low a temperature as possible, 2-step heating processes after wet cleaning are proposed based on thermal desorption spectroscopy (TDS) spectra. They are pre-annealing at 300degreesC for 60 min, and subsequent flashing at 650degreesC. The pre-annealing desorbs one hydrogen atom at each-dihydride on the surface, and the flashing desorbs the rest of the hydrogen atoms. Furthermore, for practical device processes, it is proposed that the 2-step heating processes should be performed in a hydrogen ambient to prevent the surface from adsorbing contaminations. Scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) observations reveal that an atomically flat Si(001)-c(4 x 4) surface is obtained by flashing at 650degreesC in not only ultrahigh vacuum, but also in hydrogen ambient. STM images and first-principles simulations demonstrate that the Si(001)-c(4 x 4) structure is explained by a missing-dimer model.