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Nanoscale patterning and selective chemistry of silicon surfaces by ultrahigh-vacuum scanning tunneling microscopy

Nanometer scale patterning of the monohydride surface has been achieved by using an ultrahigh-vacuum (UHV) scanning tunneling microscope (STM) to selectively desorb the hydrogen. After preparing high-quality H-passivated surfaces in the UHV chamber, patterning is achieved by operating the STM in field emission. The field-emitted electrons stimulate the desorption of molecular hydrogen, restoring clean in the patterned area. This depassivation mechanism seems to be related to the electron kinetic energy for patterning at higher voltages and electron current for low-voltage patterning. The patterned linewidth varies linearly with tip bias, achieving a minimum of less than 10 Å at -4.5 V. The linewidth dependence on electron dose is also studied. For positive tip biases up to 10 V no patterning occurs. The selective chemical reactivity of the patterned surface has been explored by oxygen and ammonia dosing. For the oxygen case, initial oxidation of the patterned area is observed. Ammonia dosing, on the other hand, repassivates the surface in a manner different from that of atomic hydrogen. In both cases the pattern resolution is retained and the surrounding H-passivated areas remain unaffected by the dosing.