Liu Xianghuai

Synthesis of silicon nitride films by ion-beam-enhanced deposition and their protective properties against oxidation☆

Abstract Silicon nitride films were synthesized on cold-rolled nickel coupons by concurrent electron beam evaporation of silicon and bombardment with nitrogen ions (ion-beam-enhanced deposition). IR, Rutherford backscattering, Auger electron spectroscopy, transmission electron spectroscopy, scanning electron microscopy, energy dispersive ellipsometry and spreading resistance measurements were performed for investigating the properties, composition, and structure of the films. Isothermal and cyclic oxidation tests were carried out on the uncoated nickel coupons and those coated with films of thicknesses up to 10 000 A at 1300 K in a flow of pure oxygen at atmospheric pressure. The films decrease the isothermal oxidation rates, the thicker films having a larger effect. However, films of thicknesses up to 3000 A are not effective for cyclic oxidation. The scanning electron microscopy observation and energy dispersive X-ray analysis revealed that thin films rich in silicon remained in the NiO scale near the scale-substrate interface after both isothermal and cyclic oxidation. Further, much thinner films containing silicon were present on the outer surface of the NiO scales formed on the specimens coated with nitride films of thickness 10 000 A. The oxidation mode initially follows an approximately linear law and approaches a parabolic law later.

SYNTHESIS OF SILICON-NITRIDE FILMS BY ION-BEAM ENHANCED DEPOSITION

Abstract Silicon nitride films with stoichiometric ratio of Si3N4 have been synthesized by concurrent electron beam evaporation of silicon and bombardment with nitrogen ions. The results show that the component ratio of nitrogen to silicon in IBED silicon nitride films can be controlled and predicted by the atomic arrival rate ratio of nitrogen to silicon. IR measurement shows that the characteristic absorption peak of IBED Si3N4 is located at a wavenumber of 840 cm−1. The refractive index ranges from 2.2 to 2.6. RBS, AES, TEM, SEM, ED and spreading resistance measurement were used for investigation of the depth profiles of composition and structure of silicon nitride films synthesized by IBED. An intermixed layer is formed at the interface by the knock on effect, and a silicon enriched layer is observed at the surface region of the film. Normally the films were found to be amorphous, but electron diffraction patterns taken from deposited layer showed a certain crystallinity. The silicon nitride films prepared by IBED have dramatically less oxygen content than that formed by non-ion-assisted deposition.

Properties and structure of silicon nitride films synthesized by ion-beam-enhanced deposition

Abstract Silicon nitride films with a stoichiometric ratio of Si 3 N 4 were synthesized by ion-beam- enhanced deposition (IBED). It was observed that a silicon nitride film formed by IBED is composed of a thin silicon-enriched top layer, a stoichiometric Si 3 N 4 layer and a smooth transition layer at the interface next to the substrate. By detailed theoretical analysis and computer simulation of IR reflection interference spectra, refractive index profiles of the films were obtained. Composition profiles and refractive index profiles were correlated using the Lorentz-Lorenz equation. The fatigue and high temperature oxidation behaviour of metals can be improved using Si 3 N 4 coatings made by means of IBED, and the mechanisms of these are discussed.

OPTICAL-PROPERTIES AND MICROSTRUCTURE OF SILICON-NITRIDE FILM SYNTHESIZED BY ION-BEAM ENHANCED DEPOSITION

Abstract Silicon nitride films with a stoichiometric ratio of Si3N4 have been synthesized by concurrent electron beam evaporation of silicon and bombardment with nitrogen ions. Infrared reflection spectra in the wavenumber range 1500–5000 cm−1 were measured for the silicon nitride films. Interference fringes were observed in the IR spectra. By detailed theoretical analysis and computer simulation of the IR reflection interference spectra, refractive index profiles of the films were obtained. The chemical composition and interface structure of the IBED Si3N4 films have been investigated using Auger electron spectroscopy (AES) in conjunction with in-situ sputtering. The characteristic Auger spectrum for Si3N4 was measured. In-depth composition profiles and refractive index profiles have been correlated using the Lorentz-Lorenz equation. The results show that the refractive index profile determined by the IR reflection is consistent with that obtained from AES.

Computer simulation of ion beam enhanced deposition of silicon nitride films

Abstract A Monte Carlo computer simulation code SIBL has been developed to describe the growth of silicon nitride films by ion beam enhanced deposition (IBED). A successive and alternate process of deposition of silicon atoms and implantation of nitrogen ions is applied to replace the actual continuous and synchronous process of IBED. The change of the composition and density profiles during film growth is taken into account. The obtained composition profile and the relationship between the film composition and the atomic arrival ratio N/Si are in agreement with the experimental measurements.

Protective behaviour against high temperature oxidation of silicon nitride films synthesized by ion-beam-assisted deposition

Abstract Silicon nitride films were synthesized on the surface of nickel-based alloys by concurrent electron beam evaporation of silicon and bombardment with 25 keV nitrogen ions (ion-beam-assisted deposition, IBAD). Analyses of X-ray photoelectron and IR spectra reveal that stoichiometric Si 3 N 4 films are formed by IBAD. Transmission electron microscopy observations show that IBAD Si 3 N 4 films normally have amorphous structure; selected area diffraction, however, reveals some crystallinity. An analysis of Auger electron spectroscopy profiles shows that the Si 3 N 4 film consists of a silicon-enriched layer on the outer surface, an Si 3 N 4 layer with uniform composition, and a mixed layer at the film-substrate interface. Isothermal oxidation tests were carried out on the uncoated nickel-based alloy specimens and those coated with films of thicknesses up to 1 μm at 1173 K, 1373 K in air for 8–20 h. The oxidation mode initially follows an approximately linear trend and later approaches a parabolic trend. The films of Si 3 N 4 decrease the thermal oxidation rates considerably. X-ray diffraction analysis of the oxidation products shows that there exist five phases,. Cr 2 O 3 , SiO 2 , NiCr 2 O 4 , Al 2 O 3 and Ni 3 Si.

SIFN-IMPLANTED GAAS AND SHALLOW JUNCTIONS

Abstract The characteristics of SiF n -implanted GaAs ( n = 1, 2, 3) have been measured by C – V and SIMS measurements. The experimental results show that SiF implantation into GaAs is, compared to Si implantation, a promising method for forming thinner active layers of GaAs MESFETs without degrading the activation efficiency. The SIMS measurements indicate that fluorine will be outdiffused under high temperature annealing, and the RBS channeling shows that the SiF 3 implanted wafers are damaged heavily, but the damage can be greatly reduced by a two step annealing method, i.e., first low temperature annealing for a long time followed by a high temperature RTA. By this method a shallow junction can be made.

Improvement of secondary electron emission characteristics by ion implantation

Abstract Improvements of the secondary electron emission coefficient and oxidation resistance of copper grid by Cr ion implantation have been investigated. In comparison with the copper grid coated with carbon, ion implantation is a prospective and practical method for improving the secondary electron emission characteristics.

Characteristics of the nitrogen ion implanted intermetallic compound TiAl

Abstract Experiments were conducted to investigate the characteristics of the nitrogen ion implanted intermetallic compound TiAl. RBS and AES analysis indicated that the Al concentration at the nitrogen ion implanted layer was very low compared with unimplanted TiAl specimens. It was found, by X-ray diffraction, that the Ti 2 N phase was formed after ion implantation. The corrosion behavior of TiAl specimens implanted with nitrogen ions has been characterized by multisweep cyclic voltammetry. The result revealed that the corrosion resistance of TiAl specimens in a solution of IN sulphuric acid had been improved after nitrogen ion implantation. An isothermal oxidation test, which was carried out at 1100 and 1300 K in a flow of pure oxygen at atmospheric pressure, showed that the oxidation rate of nitrogen ion implanted specimens was higher than of unimplanted ones. The corrosion and oxidation behavior has been explained having in view the composition and structural changes of the specimens after nitrogen ion implantation.

Ion implantation in China

Abstract Ion implantation in silicon has been widely used in the production of semiconductor devices and integrated circuits in China. Research of low energy ion implantation, high energy ion implantation and the SOI technology is in progress. Fully Si-implanted planar GaAs dual-gate MESFETs, high linear GaAs Hall effect sensors, light emitting diodes, laser devices, and infrared detectors made of HgCdTe have been fabricated by ion implantation and have been applied in telecommunication, transportation, medicine, and in a ground satellite station. The research of ion implantation in metals began in 1978 in China. Ion implantation for improving wear, corrosion, oxidation, fatigue-resistance and secondary electron emission characteristics has progressed. The artificial joints treated by ion implantation have been used in trial medical treatment. Thin films of high T c superconductors of Y 1 Ba 2 Cu 3 O 7 zero resistance temperature of 86 K have been worked out with reactive ion beam coating. Recently, ion beam enhanced deposition has been used to synthesize Si 3 N 4 and other compound films. The process of ion beam enhanced deposition has been studied by a dynamic ion implantation model and Monte Carlo computer simulation. It was at the end of the 1960s that China began to work on ion implantation. China now has more than 80 units involved in the field of research and application of ion implantation, including scientific research institutes, universities and factories.