STM MODIFICATION OF HYDROGEN PASSIVATED SI(100) SURFACE BY A VERY-LOWVOLTAGE-MODE IN AIR

We report on the modification of hydrogen passivated silicon(100) surf ace by STM in a low voltage mode (Vs=-0.7 - -2.0 volt, I set=1.0 nA) i n air. We observed that the scanned area can be oxidized in a low volt age mode and the depth profiles of oxide squares are not same for scan ning direction (x-direction) and non-scanning direction (y-direction). The depth profile of x-direction changed gradually at edge region whe reas the depth profile of y-direction changed abruptly at edge region. The different depth profiles of oxide squares could be explained by n on-uniform concentration of hydrogen atoms at edge region due to the m ovement of tip. It was also suggested that the oxide formation was enh anced by strong electric field strength between tip and sample rather than bias voltage itself allowing the water and oxygen ions to further attack silicon atoms to result in the formation of oxide bridge betwe en two silicon atoms.