Real-time coverage monitoring of initial oxidation processes on Si(001) by means of surface differential reflectance

Abstract

Initial oxidation processes on Si(001) have been studied by means of surface differential reflectance (SDR). The time courses of the SDR spectra measured during thermal oxidation at 820 and 920 K allowed two different growth modes, Langmuir-type adsorption and two-dimensional island growth, to be distinguished. No photon energy dependence was observed in the time course of the SDR intensity at either temperature. On the other hand, different uptake curves were observed at different photon energies for oxidation at 300 K. The difference between the oxidation mechanisms at 300 K and at high temperatures was qualitatively apparent from SDR results, because significant photon energy dependence was observed only at 300 K. Possible assignments of the spectral components in the SDR spectra are discussed.

Monolayer oxidation onSi(001)−(2×1)studied by means of reflectance difference spectroscopy

“…8 Our results may indicate that this trend is also the case for the transition temperature between Langmuir-type adsorption and two-dimensional island growth. In our previous study with SDR, we demonstrated that the SDR signal is proportional to the total oxygen coverage above 820 K. 9 The transition temperature obtained with SDR at the same oxidation pressure of 1.0ϫ 10 −5 Pa is between 820 and 920 K and consistent with the present results.…”

“…6 This transition of the monolayer regime has been further studied with AES both at 2.7ϫ 10 −5 and at 3.7ϫ 10 −4 Pa. 6 Our recent study at the relatively low pressure of 1.0ϫ 10 −5 Pa with real-time SDR showed that the two growth modes, Langmuir-type adsorption and two-dimensional island growth, can be distinguished from the uptake curves for monolayer oxidation with this technique, as with other spectroscopic methods. 9 This result confirmed the feasibility of using such an optical method to estimate the coverage of adsorbates with the same precision as AES.…”

“…9 On the other hand, such different line shapes were not observed with RD measurements across the transition temperature, as shown in Fig. 2.…”

“…The line shape obtained with RD measurements below 823 K is consistent with the AES study of O͑KLL͒ intensity, 5 as well as our previous SDR results. 9 At temperatures of 630-882 K, a recent UPS study clearly showed a single exponential increase of O͑2p͒ intensity. 21 In a recent study, change of RD intensity was postulated to be proportional to the coverage of adsorbates for various molecules at room temperature.…”

“…It is recognized that SDR excels at precise measurement of the coverage of adsorbates, 9,10 while RDS is more sensitive to the surface anisotropy. 11 A theoretical study indicated that layer-by-layer oxidation on Si͑001͒ should be detectable with RDS.…”