Excimer laser photochemistry of silane-ammonia mixtures at 193 nm

Directed Gas-Phase Formation of Aminosilylene (HSiNH2; 1A'): The Simplest Silicon Analogue of an Aminocarbene, under Single-Collision Conditions

The aminosilylene molecule (HSiNH₂, X¹A')-the simplest representative of an unsaturated nitrogen-silylene-has been formed under single collision conditions via the gas phase elementary reaction involving the silylidyne radical (SiH) and ammonia (NH₃). The reaction is initiated by the barrierless addition of the silylidyne radical to the nonbonding electron pair of nitrogen forming an HSiNH₃ collision complex, which then undergoes unimolecular decomposition to aminosilylene (HSiNH₂) via atomic hydrogen loss from the nitrogen atom. Compared to the isovalent aminomethylene carbene (HCNH₂, X¹A'), by replacing a single carbon atom with silicon, a profound effect on the stability and chemical bonding of the isovalent methanimine (H₂CNH)-aminomethylene (HNCH₂) and aminosilylene (HSiNH₂)-silanimine (H₂SiNH) isomer pairs is shown; i.e., thermodynamical stabilities of the carbene versus silylene are reversed by 220 kJ mol^-1. Hence, the isovalency of the main group XIV element silicon was found to exhibit little similarities with the atomic carbon revealing a remarkable effect not only on the reactivity but also on the thermochemistry and chemical bonding.

Role of a 193 nm ArF Excimer Laser in Laser-Assisted Plasma-Enhanced Chemical Vapor Deposition of SiNx for Low Temperature Thin Film Encapsulation

In this study, silicon nitride thin films are deposited on organic polyethylene-naphthalate (PEN) substrates by laser assisted plasma enhanced chemical vapor deposition (LAPECVD) at a low temperature (150 °C) for the purpose of evaluating the encapsulation performance. A plasma generator is placed above the sample stage as conventional plasma enhanced chemical vapor deposition (PECVD) configuration, and the excimer laser beam of 193 nm wavelength illuminated in parallel to the sample surface is coupled to the reaction zone between the sample and plasma source. Major roles of the laser illumination in LAPECVD process are to compete with or complement the plasma decomposition of reactant gases. While a laser mainly decomposes ammonia molecules in the plasma, it also contributes to the photolysis of silane in the plasma state, possibly through the resulting hydrogen radicals and the excitation of intermediate disilane products. It will also be shown that the LAPECVD with coupled laser illumination of 193 nm wavelength improves the deposition rate of silicon nitride thin film, and the encapsulation performance evaluated via the measurement of water vapor transmission rate (WVTR).

Reactions in silicon-nitrogen plasma

Reaction mechanisms that lead to creation of silicon-nitrogen bonds are studied in detail. These reactions are of fundamental importance for silicon nitride synthesis by plasma enhanced chemical vapour deposition from the gas mixture of silane (SiH₄) and ammonia (NH₃). All reactions in SiH₄-NH₃ plasma can be categorised as some of the basic types of reactions: bond dissociation, neutral nucleophilic substitution, radical neutralisation, neutral-radical addition, silylene addition, silylene rearrangement, radical nucleophilic addition or hydrogen abstraction reaction. Energetics of these reactions is analysed in detail for a great number of reactions belonging to these categories, by using theoretical modelling. Geometry optimisations are carried out with the MP2/aug-cc-pVTZ level of theory and energetics is further determined with high level ab initio calculations at the CASPT2/aug-cc-pVTZ level, which enabled confirmation of relevance of several mechanisms as reactions that lead to silicon nitride growth from plasma enhanced chemical vapour deposition, as well as introduction of new, energetically favourable mechanisms. Besides amine radical assisted eliminative addition and proton transfer reactions, silylene addition reactions are thermodynamically and kinetically favourable since they lack energy barriers. A new reaction pathway for synthesis of silicon nitride from plasma is proposed. This pathway is enabled by the ability of silylene to create two weak dative bonds, which enables silylene-amine complexes to stick to the silicon nitride surface. Upon dissociation of amine from the surface-bound complex, silylene remains on the surface, available for reaction with other reactive species from plasma.

Rapid synthesis of nc-Si/a-SiNx:H QD thin films by plasma processing for their cost effective applications in photonic and photovoltaic devices

A rapid and single step synthesis of nc-Si/a-SiN_x:H QD thin films has been made possible from a (SiH₄ + NH₃) gas mixture, with the advent of high density low pressure planar inductively coupled plasma processing.

Low temperature plasma processing of nc-Si/a-SiNx:H QD thin films with high carrier mobility and preferred (220) crystal orientation: a promising material for third generation solar cells

The nc-Si-QDs/a-SiN_x:H (∼5.7–1.3 nm) thin-films grown by low-temperature Inductively-coupled plasma, possess high carrier-mobility, electrical-conductivity, photosensitivity and preferred (220) crystal orientation, suitable for third-generation solar cells.