P.L.F. Hemment

Visible photoluminescence at room temperature from microcrystalline silicon precipitates in SiO2 formed by ion implantation

We have investigated the photoluminescence of microcrystalline silicon formed in SiO2 layers by ion beam synthesis. 28Si+ ions over the dose range 1 × 1017 to 6 × 1017 cm−2 at energies of 150 keV and 200 keV were implanted into thermal oxide. Samples were annealed in a halogen lamp furnace at temperatures of 900°C, 1100°C and 1300°C for times between 15 and 120 min. The implanted layers were analysed by Rutherford Backscattering Spectroscopy (RBS), Cross-Sectional Transmission Electron Microscope (XTEM) and Photoluminescence (PL) (80 K to 300 K) using an Ar laser of 488 nm wavelength. Room temperature (300 K) visible photoluminescence has been observed from all the samples. XTEM confirms the existence of Si microcrystals (within the SiO2 layers), which typically have a diameter within the range of 2–15 nm. The luminescence peak wavelength was about 600 nm or 800 nm, depending upon processing. Changes in the peak wavelength and intensity from these samples and other samples in which the crystallites were reduced in size by thermal oxidation, show trends which are generally consistent with quantum confinement, however, other mechanisms cannot be ruled out.

Oxygen distributions in synthesized SiO2 layers formed by high dose O+ implantation into silicon

Abstract Oxygen depth distributions have been determined, in silicon on insulator (SOI) structures formed by implantation of 200 keV oxygen ions into (100) silicon wafers. The implanted layers have been studied by RBS, SIMS and cross-sectional TEM and a computer model has been developed which enables the evolution of the oxygen distribution to be followed. Processing conditions, to form SOI substrates for fabrication of VLSI devices in the top silicon layer, are implantation energy 200 keV, dose 1.8 × 10 18 O cm −2 and implantation temperature 500°C. An anneal at 1150°C for 2 h is required to form a thin single crystal layer, which is depleted of oxygen. The dielectric properties of the stoichiometric SiO 2 are improved by this thermal processing.

An investigation of as‐implanted material formed by high dose 40 keV oxygen implantation into silicon at 550 °C

Device grade 〈100〉 single crystal silicon wafers have been implanted with 40 keV oxygen ions (16O+) over the dose range of 1×1017–8×1017/cm2 at a temperature of 550±10 °C. Transmission electron microscopy, ion channeling, and secondary ion mass spectroscopy studies show that during implantation the critical dose required to form a buried oxygen‐rich amorphous (SiOx, x<2) layer is lower than 1×1017 O+/cm2. As the dose increases from 1×1017 to 4×1017/cm2 the thickness of the buried SiOx layer increases and there is a corresponding decrease in the thickness of the single crystal silicon top layer, with the oxygen concentration and residual radiation damage playing important roles in determining its position and thickness. A dose of 5×1017/cm2 results in a continuous surface amorphous layer, with a buried SiO2 sublayer being formed in the region corresponding to the implanted oxygen peak. With further increasing dose, the buried SiO2 sublayer grows primarily towards the surface. The results for the sample imp...

SIC BURIED LAYER FORMATION BY ION BEAM SYNTHESIS AT 950 C

Carbon implantation into Si at a temperature of 950 °C and at doses in the range of 0.2×1018 to 1×1018 cm−2 at 200 keV results in the formation of β‐SiC buried layers having the same orientation as the Si matrix. Under these conditions redistribution of the implanted species occurs enabling the formation of a buried layer of β‐SiC with an overlayer of high quality single crystal Si which is free of structural defects. The quality of the Si overlayer and the β‐SiC buried layer was investigated by Rutherford backscattering and transmission electron microscopy. A mechanism for the formation of the β‐SiC without the generation of defects in the Si matrix is proposed.

The role of implantation temperature and dose in the control of the microstructure of SIMOX structures

Abstract Single-crystal ⇇100↩ silicon wafers have been implanted with 200 keV oxygen ions over a dose range of 0.1×10 18 O + cm -2 to 1.4×10 18 O + cm -2 and a temperature range of ≈250°C to 550°C. The specimens have been analyzed, both before and after high-temperature annealing, using a variety of techniques, such as cross-sectional and planar Transmission Electron Microscopy (TEM), Rutherford backscattering (RBS), and ion channelling, Secondary Ion Mass Spectroscopy (SIMS), Infra-red Spectroscopy (IR), and Raman Spectroscopy. This has enabled us to evaluate the development of the SIMOX structure both with respect to implantation temperature and dose and also with respect to annealing temperature and time.

High quality silicon on insulator structures formed by the thermal redistribution of implanted nitrogen

Silicon wafers have been implanted with 200‐keV 14N+ ions to doses between 0.25 and 1.4×1018 N+ cm−2 at a temperature of 500 °C and have been annealed at 1200 °C for 2 and 8 h. Rapid redistribution of the implanted nitrogen occurs, against the macroscopic concentration gradient, in samples implanted with doses below that required to directly synthesize stoichiometric Si3N4. This leads to the formation of a continuous buried layer of either amorphous or polycrystalline Si3N4. The surface layer is high quality single crystal silicon (χmin =0.043) containing no polycrystalline material nor precipitates. The Si‐Si3N4 interfaces are extremely abrupt but with an irregularity of ∼100 and ∼50 A at the upper and lower interfaces, respectively.

Formation of buried insulating layers in silicon by the implantation of high doses of oxygen

Abstract Silicon wafers have been implanted with 200 keV oxygen to dosss of up to 2.4 × 10 18 O + /cm 2 at implantation temperatures of 325°C to 600°C. Rutherford backscattering and SIMS show the oxygen depth distribution is insensitive to the implantation temperature but is modified by subsequent high-temperature processing. Multiple laser irradiations produced a single crystal layer at the surface by LPE regrowth but better crystallinity is observed in samples which have been furnace annealed, when a layer of 1000 A thickness is formed which is denuded of oxygen. Preferred conditions to form a silicon on insulator structure (SOI) suitable for VLSI device technology are implantation temperature 400–500°C followed by furnace annealing at 1150°C for 2–4 h with an SiO 2 cap.

Ion beam synthesis of thin buried layers of SiO2 in silicon

New experiments are reported which explore the possibility of using ion implantation to form thin (<2000 A) buried layers of stoichiometric SiO2 in single crystal silicon, Silicon (100) wafers have been implanted with O+ ions within the dose range 0.1×1018–1.8×1018O+ cm−2 at a particle energy of 200 keV and a substrate temperature of 500°C. Both (100) channelled and non-channelled implants have been carried out. Samples were subsequently annealed at temperatures of up to 1405°C, which causes the oxygen to segregate near the peak of the implanted oxygen distribution. The high dose samples have a continuous buried oxide layer whose thickness scales with the implanted dose, whilst in samples implanted with 0.1×1018O cm−2, discrete, strain free polyhedral precipitates, of diameter 500–1600 A, grow within the single crystal silicon matrix, by a mechanism which is qualitatively similar to oxygen precipitation in C-Z bulk silicon.

Mechanism of buried β-SiC formation by implanted carbon in silicon

Abstract The structure of silicon implanted with high doses of carbon ions in the range (0.35–1.3) × 10 18 C + cm −2 at implantation temperatures from 500 to 700 °C is studied by transmission electron microscopy. At an implantation temperature of 700 °C, cubiv (β-SiC) and hexagonal coherent or semicoherent precipitates are formed in the silicon overlayer. Only the cubic form is stable during high temperature annealing. At high implantation temperatures a thin discrete buried layer of β-SiC, with an epitaxial relationship to the silicon substrate, is formed. The quality of this layer is greatly improved after a high temperature annealing as revealed by the translation-type (111) Moire pattern. The β-SiC epitaxial layer consists of adjoined grains on {111} and {100} planes without appreciable coalescence of these adjoining grains. The stability of the β-SiC precipitates is discussed and it is compared with the stability of SiO 2 precipitates which are formed in silicon implanted with oxygen.

Reduction of parasitic capacitance in vertical MOSFETs by spacer local oxidation

Application of double gate or surround-gate vertical metal oxide semiconductor field effect transistors (MOSFETs) is hindered by the parasitic overlap capacitance associated with their layout, which is considerably larger than for a lateral MOSFET on the same technology node. A simple self-aligned process has been developed to reduce the parasitic overlap capacitance in vertical MOSFETs using nitride spacers on the sidewalls of the trench or pillar and a local oxidation. This will result in an oxide layer on all exposed planar surfaces, but no oxide layer on the protected vertical channel area of the pillar. The encroachment of the oxide on the side of the pillar is studied by transmission electron microscopy (TEM) which is used to calibrate the nitride viscosity in the process simulations. Surround gate vertical transistors incorporating the spacer oxidation have been fabricated, and these transistors show the integrity of the process and excellent subthreshold slope and drive current. The reduction in intrinsic capacitance is calculated to be a factor of three. Pillar capacitors with a more advanced process have been fabricated and the total measured capacitance is reduced by a factor of five compared with structures without the spacer oxidation. Device simulations confirm the measured reduction in capacitance.