Capturing properties of a threefold coordinated silicon atom in silicon nitride: Positive correlation energy model

Abstract

Electronic structure and capturing properties of three-fold coordinated silicon atom (≡ Si·) and the Si-Si bond in silicon nitride (Si 3 N 4 ) were studied using the ab initio density functional theory. The results show that the previously proposed negative correlation energy (NCE) model is not applicable to Si 3 N 4 . The NCE model was proposed for interpreting the absence of the ESR signal for three-fold coordinated silicon defects and suggested that an electron can transfer between two silicon defects. We proposed that the absence of this ESR signal is due to the creation of neutral diamagnetic Si-Si defects in Si 3 N 4 . This model offers the most fundamental theory for explaining the hole localization (memory) effect in silicon nitride.This work is partially supported by research project N 7001134 of City U.Carrier capturing in localized states or localization of electrons or holes is a fundamental process that governs the electronic properties of many amorphous solids, such as amorphous silicon, amorphous chalcogenides (a-Se, a-As 2 S 3 ) and silicon nitride (Si 4 N 4 ) films [1-4]. Particularly, amorphous Si 3 N 4 is the most common material for observing this phenomenon as it has a gigantic cross-section (5 × 10 −13 cm) for carrier capturing. An electron or a hole, being injected into the Si 3 N 4 film, can be captured by a deep trap with a lifetime in the localized state of more than 10 years at room temperature [4]. This localization property is treated as memory effect from the application point of view. Its practical application is the use of amorphous Si 3 N 4 as a gate dielectric in the SONOS (silicon-oxide-nitrideoxide-semiconductor) field effect transistors. Although this memory effect has been discovered for more than thirty years and is widely used in modern silicon devices [2,[4][5][6][7][8], the exact nature and the kind of defects responsible for the carrier localization in the nitride film is still controversial. However, we already had a consensus that the localization of electrons and holes in the Si 3 N 4 film is related to the intrinsic defects created by the excess silicon atoms [2,4,8,9].The intrinsic defects in amorphous solids are believed to be due to the dangling bonds. However, most of the defects could not be detected with the electron spin resonance (ESR) measurement in a number of amorphous semiconductors and wide-gap polar dielectrics such as amorphous SiO 2 and Si 3 N 4 films [1-4,10]. The signal for N 3 Si· defect in silicon nitride, a three-fold coordinated silicon atom with unpaired electron, could be detected with ESR only after ultraviolet irradiation [11]. For freshly synthesized nitride film, no related ESR signal can be detected. This observation was explained with the negative correlation energy (NCE) model [12,13]. This model suggested that two diamagnetic defects: a positively charged N 3 Si + and a negatively charged N 3 Si − :, can be formed from a N 3 Si· (paramagnetic neutral defects in Si 3 N 4 ) pair via the following reaction,In the NCE model, the repulsive...

Density functional theory study of deep traps in silicon nitride memories

“…11,12 The simulations results explain the trapping of electrons by neutral dangling bonds but had difficulties in interpreting the trapping of holes. First to mention is a structural model that assumes dangling Si and N bonds, labeled K 0 ͑N 3 Si•͒ and N 0 ͑Si 2 N•͒, respectively.…”

“…12 Evidence of limited amounts of low activation energy holes in cycled NROMs 15 can be attributed to these types of defects. In particular, Si-Si bonds ͑without H͒ are plausible candidates for hole traps in the silicon nitride strongly enriched with silicon.…”

Characterization of oxygen impurity in silicon nitride storage layer: A first-principles investigation

“…Owing to the smaller module size and simpler integration processes, Si 3 N 4 -based charge trapping memory (CTM) with siliconoxide-nitride-oxide-silicon structure (SONOS) [2], as shown in Fig. 1, has attracted much attention [3][4][5][6][7]. CTM stores charges in silicon nitride storage layer at atomic scale, making the charges spatially separated.…”