NANOSCALE PATTERNING AND SELECTIVE CHEMISTRY OF SILICON SURFACES BY ULTRAHIGH-VACUUM SCANNING-TUNNELING-MICROSCOPY

Nanometer scale patterning of the Si(100)2 x 1:H monohydride surface h as 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 a chieved by operating the STM in field emission. The field-emitted elec trons stimulate the desorption of molecular hydrogen, restoring clean Si(100)2 x 1 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 pattern ed linewidth varies linearly with tip bias, achieving a minimum of les s than 10 Angstrom at -4.5 V. The linewidth dependence on electron dos e is also studied. For positive tip biases up to 10 V no patterning oc curs. The selective chemical reactivity of the patterned surface has b een explored by oxygen and ammonia dosing. For the oxygen case, initia l oxidation of the patterned area is observed. Ammonia dosing, on the other hand, repassivates the surface in a manner different from that o f atomic hydrogen. In both cases the pattern resolution is retained an d the surrounding H-passivated areas remain unaffected by the dosing.