A scanning tunneling microscopy study of PH_3 adsorption on Si(111)-7 × 7 surfaces, P-segregation and thermal desorption

摘要

PH_3 adsorption on Si(111)-7 × 7 was studied after various exposures between 0.3 and 60 L at room temperature by means of scanning tunneling microscopy (STM). PH_3-, PH_2-, H-reacted, and unreacted adatoms can be identified by analyzing empty-state STM images at different sample biases. PH_χ-reacted rest-atoms can be observed in empty-state STM images if neighboring adatoms are hydrogen terminated. Most of the PH_3 adsorbs dissociatively on the surface, generating H- and PH_2-adsorbed rest-atom and adatom sites. Dangling-bonds at rest-atom sites are more reactive than adatom sites and the faulted half of the 7 × 7 unit cell is more reactive than the unfaulted half. Center adatoms are overwhelmingly preferred over corner adatoms for PH_2 adsorption. The saturation P coverage is ～0.18 ML. Annealing of PH_3-reacted 7 × 7 surfaces at 900 K generates disordered, partially P-covered surfaces, but dosing PH_3 at 900 K forms P/ Si(111)-63~(1/2) surfaces. Si deposition at 510 K leaves disordered clusters on the surface, which cannot be reordered by annealing up to 800 K. However, annealing above 900 K recreates P/Si(111)-63~(1/2) surfaces. Surface morphologies formed by sequential rapid thermal annealing are also presented.