Photoelectron Emission Technique for the Surface Analysis of Silicon Wafer Covered with Oxide Film
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E9.34.1
Photoelectron Emission Technique for the Surface Analysis of Silicon Wafer Covered with Oxide Film Takao Sakurai, Yoshihiro Momose1, Masanori Kudou1, and Keiji Nakayama2 Division of General Education, Ashikaga Institute of Technology, Tochigi 326-8558, Japan, 1 Department of Materials Science, Ibaraki University, Hitachi 316-8511, Japan, 2 National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8564, Japan ABSTRACT A new analysis method using the photoelectron emission yield spectra near threshold has been developed to characterize solid surfaces exposed to ambient air. The application of the analysis method to the yield spectra for a Si (100) wafer surface covered with a native oxide film revealed that three emission peaks are cumulated on the basic yield spectrum line for the silicon. It was indicated that these peaks have a Gaussian-shaped density distribution and the energy levels are located at 5.37, 5.68, and 6.02 eV below the vacuum level, respectively. INTRODUCTION The development of process monitors capable of examining surfaces and interphases in ambient production environments is one of the crucially needed areas of research [1]. Greber reviewed the history and mechanism of the emission of electrons, ions and photons in gas surface reactions [2]. The application of electron emission phenomena to examine real surfaces is considered to be very attractive [1]. Since the pioneering work by Gobeli and Allen who measured the photoelectric yield for a cleaved Si (111) surface [3], the photoelectric yield measurement technique was refined by Fisher [4] and then it has been established as ultraviolet photoelectron spectroscopy (UPS) for the analysis of surface electronic states of semiconductors. In recent years angle-resolved photoelectron spectroscopy (ARPES) has become the most important tool for the characterization of surface electronic states [5]. The work function is a very important quantity to control the physical/chemical property of a solid surface. The photoelectron emission near the threshold from semiconductors is theoretically represented by the following equation of a power law [6]: I ph = Cn ( hv − ϕ )
n
(1)
where hν is incident photon, ϕ is the threshold value, Cn is a constant, and n is exponent. The values of n and ϕ are dependent on the excitation and emission mechanisms involved. The theoretical study for the volume process predicted the following value of n: n =1 for the direct transition threshold without scattered process at the surface, n = 2 for the direct transition with scattered process, and n = 5/2 for the indirect transition [6]. On the other hand the experimental value of n = 3 ± 1/2 was reported [3,7], and this value was in agreement with the predicted value within an experimental accuracy. The experimental photoelectric threshold ϕ for Si (111) surfaces cleaved in UHV was 5.15 eV [3]. This corresponds to the energy difference between the vacuum level and the top edge of valence band at the surface. This value may be modified by band bending at th
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