Abstract
Despite thermal silicon oxide desorption is a basic operation in semiconductor nanotechnology, its detailed chemical analysis has not been yet realized via time-resolved photoemission. Using an advanced acquisition system and synchrotron radiation, heating schedules with velocities as high as 100 K.s−1 were implemented and highly resolved Si 2p spectra in the tens of millisecond range were obtained. Starting from a Si(111)-7 × 7 surface oxidized in O2 at room temperature (1.4 monolayer of oxygen), changes in the Si 2p spectral shape enabled a detailed chemical analysis of the oxygen redistribution at the surface and of the nucleation, growth and reconstruction of the clean silicon areas. As desorption is an inhomogeneous surface process, the Avrami formalism was adapted to oxide desorption via an original mathematical analysis. The extracted kinetic parameters (the Avrami exponent equal to ~2, the activation energy of ~4.1 eV and a characteristic frequency) were found remarkably stable within a wide (~110 K) desorption temperature window, showing that the Avrami analysis is robust. Both the chemical and kinetic information collected from this experiment can find useful applications when desorption of the oxide layer is a fundamental step in nanofabrication processes on silicon surfaces.
Highlights
The photoemission intensity versus kinetic energy spectra measured at the start and at the end of the heating process are presented in the panels (a) and (d), respectively
Our result suggests that the clean areas of the vav = 10 K.s−1 ramp are composed of less ordered 7 × 7 dimer-adatom-stacking fault (DAS) surface cells that transit to “1 × 1” below their expected thermodynamic phase transition temperature of ~1130 K
The combination of the synchrotron radiation high flux and a fast acquisition system synchronized to the temperature measurement and to a controlled heating program, lead to the recording of “chemically meaningful” spectra with a time resolution of 50 ms
Summary
Since the earlier experimental works of D’Evelyn et al.[1] and Engstrom et al.[2] the study of the thermal decomposition of silicon oxide layers on silicon has remained an active field of research, both at experimental[3,4,5,6,7,8,9,10,11,12,13,14,15,16,17] and theoretical[18,19,20,21] levels. Most thermally programmed desorption (TPD) studies[1,2,7] were based on the monitoring of the oxygen surface density via the measurement of the volatile SiOg signal. Kinefuchi et al.[7] took explicitly the inhomogeneous nature of the desorption process into account by considering the Avrami model, which is widely used to analyze the kinetics of phase transition[34,35,36,37,38]. Core-level X-ray photoelectron spectroscopy (XPS) is in principle the ideal technique to study surface kinetics, as it allows an analysis both qualitative (via the binding energy shifts) and quantitative (via the photoemission intensity) of the species present on the surface at a given time, especially when the synchrotron radiation is used, as the high photon flux combined to a fast detection system[39] enables the real-time monitoring of reactions with high time resolution. Spectroscopic information on the clean areas can be provided independently of the SiOg desorption event
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