Temperature Dependence of Oxidation-Induced Changes of Work Function on Si(001)2×1 Surface Studied by Real-Time Ultraviolet Photoelectron Spectroscopy

Abstract

At the initial stage of oxidation on a Si(001)2×1 surface, real-time ultraviolet photoelectron spectroscopy revealed that the O2 dosage dependences of band bending and work function due to a surface dipole layer show a distinct change with increasing temperature from 300 to 600°C in a Langmuir-type adsorption region, while oxygen uptake curves are almost the same at all temperatures examined. In constant to a dual-oxide-species (DOS) model in which the surface migration of adsorbed oxygen is not considered for Langmuir-type adsorption, the observed changes in work function due to the surface dipole layer mean that adsorbed oxygen can migrate on the surface more frequently with increasing temperature, leading to a decrease in the number of adsorbed oxygen atoms bonded at dimer backbond centers and furthermore a significant structural change of the oxide layer.

Experimental estimation of oxidation-induced Si atoms emission on Si(001) surfaces

“…(1), which is constructed based on an oxidation reaction model of Langmuir-type adsorption. 8,9,12,14 …”

“…11,12 In particular, in Langmuir-type adsorption regions of passive oxidation where only oxide growth occurs, it has been proven both theoretically 13 as well as experimentally, 14 that oxygen can diffuse easily into Si dimer back-bonds. Diffusion of oxygen into dimer back-bonds causes a large strain.…”

Simultaneous observation of oxygen uptake curves and electronic states during room-temperature oxidation on Si(0 0 1) surfaces by real-time ultraviolet photoelectron spectroscopy

“…As a consequence of the large oxidation-induced strain, Si atoms are significantly emitted as observed as isolated dimers at RT by STM [9]. Therefore, it is necessary to investigate the O 2 adsorption reaction mechanism on Si surfaces from the viewpoint of the behavior of adsorbed O atoms and the adsorbed-oxygen-induced generation of point defects (emitted Si atoms + vacancies) [10] as well as from the conventional viewpoint of the reaction order and reaction rate [2,3]. Changes in work function, D/, are very sensitive to the lattice site and h O of adsorbed O atoms, especially with respect to the diffusion of adsorbed O atoms to the subsurface [10,11].…”

“…Therefore, it is necessary to investigate the O 2 adsorption reaction mechanism on Si surfaces from the viewpoint of the behavior of adsorbed O atoms and the adsorbed-oxygen-induced generation of point defects (emitted Si atoms + vacancies) [10] as well as from the conventional viewpoint of the reaction order and reaction rate [2,3]. Changes in work function, D/, are very sensitive to the lattice site and h O of adsorbed O atoms, especially with respect to the diffusion of adsorbed O atoms to the subsurface [10,11]. Two chemically shifted components of O 1s photoelectron spectra are also available to discern between the on-top site (Si-O) and the bridge site (Si-O-Si) of adsorbed O atoms [6,12].…”

“…Compared with the Kelvin probe method, ultraviolet photoelectron spectroscopy (UPS) has the advantage of being able to measure both D/ and h O from secondary electron spectra neat the low-energy cutoff due to the vacuum level, VL, and the O 2p photoelectron spectra, respectively. In addition, changes in band bending, DBB, are also measurable by UPS to trace the oxidation-induced peak shift of the dimer dangling bond derived surface states (SS) on Si(0 0 1) surface [10]. Since DBB is caused by the defect-related midgap state at the SiO 2 /Si interface [14], therefore, UPS enables us to obtain the information on the point defect generation as well as on the behavior of adsorbed O atoms.…”