AVS 45th International Symposium
    Electronic Materials and Processing Division Wednesday Sessions
       Session EM1-WeA

Paper EM1-WeA6
Silicon Epoxide: Fundamental Intermediate in Si(100) Oxidation

Wednesday, November 4, 1998, 3:40 pm, Room 314/315

Session: Si Surface Chemistry
Presenter: Y.J. Chabal, Bell Laboratories, Lucent Technologies
Authors: A.B. Gurevich, Columbia University
M.K. Weldon, Bell Laboratories, Lucent Technologies
Y.J. Chabal, Bell Laboratories, Lucent Technologies
B.B. Stefanov, Bell Laboratories, Lucent Technologies
K. Raghavachari, Bell Laboratories, Lucent Technologies
Correspondent: Click to Email
Understanding the growth and formation of thin oxides is critical to the development of high quality gate oxides. However, obtaining a detailed structural picture of interfacial SiO@sub 2@ poses a formidable scientific challenge due to the lack of long-range order and the critical dependence on processing parameters. We have therefore investigated with infrared absorption spectroscopy the water-induced oxidation of Si(100)-(2x1) under ultra-high vacuum conditions, as a prototypical silicon-oxide system: the water is initially dissociated into H and OH on each surface dimer; as the temperature is increased to 675K, the Si-Si dimer becomes the first target for oxygen insertion into the surface, facilitating in turn the subsequent incorporation of O into the Si backbonds.@footnote 1@ We show here that, upon dehydrogenation at higher temperatures (900K), a surprising structure is formed. The combination of high resoluton IR spectroscopy and density functional cluster calculations can, for the first time, identify this triangular SiOSi sub-unit, termed silicon epoxide, based on subtantially lower Si-O stretch frequencies (780-990 cm@super -1@) and smaller isotopic shifts (20-30 cm@super -1@) compared to those of known oxide structures. These silicon epoxides are similar to COC structures well-known in organic chemistry and characterized by a shorter Si-Si bond (2.4Å). We demonstrate that epoxides are the thermodynamically favored product upon dehydrogenation when three or more oxygen atoms are agglomerated. These epoxide structures are stable at intermediate annealing temperatures (800-1000K) and are observed upon pure oxygen exposure as well. They therefore constitute a metastable intermediate in the growth of thermal gate oxides, and are expected to be preferentially formed both in small molecules and at silica interfaces. @FootnoteText@ @footnote 1@ M.K. Weldon, B.B. Stefanov, K. Raghavachari and Y.J. Chabal, Phys. Rev. Lett. 79, 2851 (1997).