Chenglu Lin

Molecular beam epitaxy of GaAs on Si‐on‐insulator

Epitaxial GaAs films have been grown by molecular beam epitaxy (MBE) on Si‐on‐insulator (SOI) formed by ion beam synthesis. Rutherford backscattering and channeling, x‐ray double‐crystal diffraction, and infrared reflection measurements have been used to characterize the epitaxial GaAs films. Experimental results show that the crystal quality of the GaAs films improves markedly towards the GaAs surface for thicker films where the minimum channeling yield drops to 10%. Infrared reflection spectra prove that crystalline GaAs films have been deposited on the SOI structures. Refractive index profiles of the GaAs films on SOI structures can be obtained by computer fitting the interference spectra. The results indicate that the crystal quality of these GaAs films is comparable to similar GaAs films deposited directly on Si by MBE.

Investigation of buried AlN layers formed by nitrogen implantation into Al

Abstract The composition and microstructure of buried layers of AlN formed by high energy N+ ion implantation into polycrystalline Al have been determined. Both bulk and evaporated thin films of Al have been implanted with 100 and 200 keV N+ ions to doses of up to 1.8 × 1018/cm2. The layers have been characterised using SIMS, XTEM, X-ray diffraction, FTIR, RBS and in terms of their microhardness. It is found that, for doses greater than the critical dose, buried, polycrystalline AlN layers are formed with preferred (100) or (002) orientations, which are sample specific. With increasing dose the nitrogen concentration saturates at the value for stoichiometric AlN although the synthesised compound is found to be rich in oxygen.

Auger electron and IR spectroscopic studies of SOI structure formed by oxygen and nitrogen implantation

The chemical composition and structure of silicon on insulator (SOI) formed by the combination of O+ (200 keV, 1.8*1018 cm-2) and N+ (180 keV, 4*1017 cm-2) implanted into silicon has been investigated by Auger electron, IR absorption and reflection spectroscopic measurements. After annealing at 1200 degrees C for 2 h, the in-depth composition profiles of the SOI structure show that the nitrogen segregates to the wings of the buried silicon oxide layer where it forms an oxynitride. The characteristic Auger spectrum for the buried oxide layer identified a chemical state of silicon whose major transition at 85 eV is different from that of bulk silicon or silicon in SiO2 and the ratio of the amplitude of the Si peak at 85 eV to the Si peak at 76 eV remains unchanged in the buried oxide layer. Infrared (IR) absorption and reflection spectra in the wavenumber range 800-5000 cm-1 were measured for the SOI structure. 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 SOI structure were obtained.

Insulator structures obtained by high dose nitrogen implantation into aluminium on silicon

Abstract Aluminium films with various thicknesses from 4500 to 15000 A were deposited on single crystal 〈100〉 Si wafers and 200 keV nitrogen ions, with doses ranging from 5 × 1017 to 1.8 × 1018 N/cm2, were implanted into the deposited layers. The synthesi structures have been evaluated by RBS and channelling, FTIR, X-ray diffraction and spreading resistance methods. The formation of a buried insulating layer of thickness 3000 A consisting of stoichiometric A1N has been achieved and the evolution of the implanted nitrogen has been successfully modelled for samples implanted with 1.68 × 1018 N/cm2 and annealed above 400°C for one hour.

STUDIES ON SI+(+)B+ DUAL IMPLANTATIONS INTO THE TOP SILICON LAYER OF SIMNI MATERIAL

Abstract SIMNI material was formed by N + implantation into crystalline silicon wafers at 170 keV with a dose of 1.8 × 10 18 cm −2 and annealing at 1200° C for 2 h. The top silicon of these SIMNI wafers was amorphized at different depths by Si + implantation at three conditions: (1) 25 keV, 5 × 10 15 cm −2 ; (2) 140 keV, 5 × 10 15 cm −2 ; (3) 25 keV, 5 × 10 15 cm −2 + 80 keV, 5 × 10 15 cm −2 + 140 keV, 5 × 10 15 cm −2 . Then the three groups of SIMNI wafers and another group with no implantation by Si + were implanted by B + at 25 keV with a dose of 1 × 10 15 cm −2 , and annealed at a series of temperatures for 30 min. Glancing RBS/C measurement shows that an epitaxial regrowth toward the surface or the inner part of the top silicon exists for the samples in group (1) and (2), respectively, with increasing annealing temperature. No epitaxial regrowth exists for the samples in group (3). Raman measurement shows that a phase transformation from amorphized silicon to polysilicon exists for the top silicon of samples in group (3) when the annealing temperature is increased from 500° C to 600° C. SRP measurement shows that Si + + B + dual implantations are able to increase the activation rate of boron in the top silicon of SIMNI material.

Optical characteristics of multi-layer structures formed by ion beam synthesis and their computer simulation

Abstract Layered structures such as silicon on insulator (SOI), and Si 3 N 4 on silicon have been synthesized by different ion beam techniques and investigated by infrared (IR) reflection and absorption. Auger electron spectroscopy (AES) and cross-sectional transmission electron microscopy (XTEM). Buried SiO 2 , Si 3 N 4 and SiO x N y layers in silicon have been formed by oxygen (200 keV 1.8 × 10 18 O + /cm 2 ) or nitrogen (190 keV, 1.8 × 10 18 N + /cm 2 ) implantation and by dual implantation of oxygen (200 keV, 1.8 × 10 18 O + /cm 2 ) and nitrogen (180 keV, 4 × 10 17 N + /cm 2 ) into silicon and annealing at different temperatures. Silicon nitride films with a stoichiometric ratio of Si 3 N 4 have been synthesized by ion beam enhanced deposition (IBED). Infrared reflection spectra in the wavenumber range 1700–5000 cm −1 were measured for the SOI structures and Si 3 N 4 films on silicon. Refractive index profiles of the SOI structures and Si 3 N 4 films on silicon were obtained by computer simulation of the IR reflection interference spectra. In-depth composition profiles of the Si 3 N 4 film on silicon have been correlated with its refractive index profiles using the Lorentz-Lorenz equation. The results of IR analysis are in agreement with AES and XTEM results.

TI SILICIDE FORMATION ON THIN-FILM SILICON ON INSULATOR

In this letter the formation of Ti silicide on thin‐film silicon on insulator has been investigated. The experimental results indicated that uniform TiSi2 layers with a low sheet resistance of 4.0–4.5 Ω/⧠ can be formed on thin‐film silicon on insulator with a high carrier concentration of 2×1020/cm3. So a structure of Ti/n+‐Si/SiO2/Si can be obtained. Secondary‐ion mass spectrometer profiles of the As showed that a relatively homogeneous redistribution of the As in the TiSi2 layer is revealed and the As pileup at Si/SiO2 interface is noticeable when the thickness of the silicon overlayer after the TiSi2 formation is less than 520 A.

Slow Positron Annihilation in Silicide Films Formed by Solid State Interaction of Co/Ti/Si and Co/Si

Slow positron beam was used to investigate the solid state reaction of Co/Si and Co/Ti/Si. Variable-energy (0-20 keV) positrons were implanted into samples at different depths. The Doppler broadening of the annihilation γ-ray energy spectra measured at a number of different incident positron energies is characterized by a line-shape parameter, S. It was found that the measured S parameters are sensitive to thin film reaction and crystalline characteristics. In particular, the S parameter of epitaxial CoSi2 formed by the ternary reaction is quite different from that of the polycrystalline CoSi2 formed by direct reaction of Co with Si.