Photoemission study of ammonia dissociation on Si(100) below 700 K

Ultraviolet and x-ray photoelectron spectroscopies (UPS and XPS) have been used to study the initial NH₃ adsorption stage on the S(100)-2×{}1 surface between room temperature (RT) and 700 K. Our results are markedly different from recently reported data, showing complete NH₃ dissociation and surface dangling-bond (DB) saturation with H adatoms even below RT. While UPS features relevant to Si---H bonds (in dihydride at RT and monohydride near 600 K) are actually observed, other coadsorbed species labeled NHₓ are clearly identified in our photoemission experiments and contribute to the surface passivation. Thus only partial dissociation of NH₃ occurs on Si(100) at least up to 550 K, and the initial thermal nitridation is not just rate limited by surface DB saturation with H. The present findings allow new insights into the mechanism of electron-beam-assisted nitridation at low temperature.