505-gritsenko-prl-1998-1054 - VOLUME 81 NUMBER 5 PHYSICAL...

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V OLUME 81, N UMBER 5 P H Y S I C A L R E V I E W L E T T E R S 3 A UGUST 1998 Short Range Order and the Nature of Defects and Traps in Amorphous Silicon Oxynitride Governed by the Mott Rule V. A. Gritsenko, 1,2, * J. B. Xu, 2,3, ² R. W. M. Kwok, 2,4 Y. H. Ng, 2,4 and I. H. Wilson 2,3 1 Institute of Semiconductor Physics, 630090, Novosibirsk, Russia 2 Materials Science and Technology Research Centre, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong 3 Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin, New Territory, Hong Kong 4 Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territory, Hong Kong ( Received 4 May 1998 ) Using valence band and Si 2 p core level photoelectron spectroscopy, it is shown that the short range order in amorphous silicon oxynitride s a - SiO x N y d is governed by the Mott rule. According to this rule, each Si atom is coordinated by four O and/or N atoms, each O atom (as in SiO 2 ) is coordinated by two Si atoms, and each N atom (as in Si 3 N 4 ) is coordinated by three Si atoms. The nature of the removal of Si-Si bonds (hole traps) at the interface of SiO 2 y Si by nitridation and the origin of Si-Si bond creation near the top surface of gate oxynitride in metal-oxide-semiconductor devices are understood for the first time by the Mott rule. [S0031-9007(98)06731-3] PACS numbers: 61.43.Dq, 61.72.Ww, 71.23.–k Short range order in tetrahedral solids such as Si, SiO 2 , crystalline a - Si 3 N 4 and b - Si 3 N 4 , amorphous silicon ni- tride a - Si 3 N 4 , and crystalline silicon oxynitride c - Si 2 N 2 O is described by the Mott rule as N C 8 2 n , (1) where N C is the coordination number and n is the number of valence electrons [1–3]. The Si atom has four valence electrons s 3 s 2 3 p 2 d , and according to Eq. (1), its N C is equal to 4. The O atom has six valence electrons s 2 s 2 2 p 4 d . Therefore, in SiO 2 and c - Si 2 N 2 O, each O atom is coordinated by two Si atoms. Similarly, the N atom has five valence electrons s 2 s 2 2 p 3 d , and in Si 3 N 4 and c - Si 2 N 2 O, each N atom is threefold coordinated by Si atoms. The amorphous silicon oxynitride s a - SiO x N y d of different compositions (from SiO 2 to Si 3 N 4 ) consists of Si-O and Si-N bonds and involves five types of tetrahedra SiO y N 4 2y for y 0 , 1, 2, 3, 4. The distribution of a particular tetrahedron SiO y N 4 2y with y configuration for composition s x , y d is given by random statistics w s y , x , y d μ 2 x 2 x 1 3 y y μ 3 y 2 x 1 3 y 4 2y 4! y ! s 4 2 y d ! . (2) Previous studies showed that the short range order in a - SiO x N y is generally governed by the Mott rule. But at some composition of a - SiO x N y a deviation from the Mott rule by up to 5 at. % was observed [1]. The nature of this deviation is still unclear, so the validity of the Mott rule is under question. More fundamentally, the defect creation in solids is an important chemical and physical process, the understanding of which is basic to our knowledge of solid states. A relevant example is the defect creation in a - SiO x N y .
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