Depth Dependence of Dopant Induced Features on The Si(100)2x1:H Surface and Its Application for Three Dimensional Dopant
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Depth Dependence of Dopant Induced Features on The Si(100)2x1:H Surface and Its Application for Three Dimensional Dopant Profiling Lequn Liu1, Jixin Yu2, and Joseph W. Lyding2 Beckman Institute, University of Illinois, Urbana, IL 61801. 1 Department of Materials Science and Engineering, University of Illinois, Urbana, IL 61801 2 Department of Electrical and Computer Engineering, University of Illinois, Urbana, IL 61801 ABSTRACT The lack of surface states within the band gap of the perfect Si(100)2x1:H surface opens the way to scanning tunneling microscopy studies of dopant atom sites in Si(100). In this paper, Boron and Arsenic induced features are studied by ultrahigh vacuum scanning tunneling microscopy. The values of their amplitudes naturally group such that several subsurface layers can be identified. This technique for producing atom-resolved three-dimensional maps of electrically active dopants in silicon may be a useful metric for characterizing dopant profiles in ultra-small electronic device structures. INTRODUCTION With the development of advanced fabrication technology, semiconductor device features have shrunk into the nanometer-scale size region, with the concomitant need to measure dopant profiles with spatial resolution better than 100Å. Scanned probe microscopy (SPM) techniques, with their inherent spatial resolution and electronic sensitivity, show considerable promise for profiling dopants on the nanometer scale. Among them, scanning tunneling microscopy (STM) is the only one that can measure the electron density of states at the atomic scale and detect individual dopants [1]. Since the hydrogen passivated Si(100)2x1 surface has an unpinned Fermi level, it was used as the substrate to investigate individual dopants by STM [2]. In this paper, we report the first study on both Boron and Arsenic induced features. Their amplitudes show a strong depth dependence, which is used to distinguish the position of the subsurface dopants and obtain real space three-dimensional dopant profiles. EXPERIMENTAL DETAILS High quality Si(100)2x1:H surfaces were prepared by an in situ high temperature procedure. The P-type Si samples were Boron doped with 0.01-0.03 ohm-cm bulk resistivity. The N-type Arsenic doped Si sample has a bulk resistivity smaller than 0.005 ohm-cm. After RCA cleaning, Si(100) samples were transferred into the preparation chamber with a base pressure of 7×10-11 Torr and thoroughly degassed at 600°C. This was followed by flash at 1200°C for 15 seconds and finally by passivation with atomic hydrogen at 377°C for 10 minutes. A hot W filament placed nearby the sample was used to crack molecular hydrogen that was introduced into the preparation chamber by the leak valve at a hydrogen pressure of 10–6 Torr. The samples were then transferred into STM chamber with a base pressure of 6×10-11 Torr. A well-ordered Si(100)2x1:H surface resulted from this procedure has unpinned Fermi level and is suitable for subsurface dopant investigations by STM [1].
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DISCUSSION Boron induced features on the Si(1
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