Effects of Thermocapillary Convection on the Growth Process in Industrial 8-inch Silicon Czochralski Growth

Czochralski (CZ) crystal growth process is a widely used technique in manufacturing of silicon crystals and other semiconductor materials. The ultimate goal of the IC industry is to have the highest quality substrates, which are free of point defect, impurities and micro defect clusters. The scale up of silicon wafer size from 200 mm to 300 mm requires large crucible size and more heat power. Transport phenomena in crystal growth processes are quite complex due to melt and gas flows that may be oscillatory and/or turbulent, coupled convection and radiation, impurities and dopant distributions, unsteady kinetics of the growth process, melt crystal interface dynamics, free surface and meniscus, stoichiometry in the case of compound materials. A global model has been developed to simulate the temperature distribution and melt flow in an 8-inch system. The present program features the fluid convection, magnetohydrodynamics, and radiation models. A multi-zone method is used to divide the Cz system into different zones, e.g., the melt, the crystal and the hot zone. For calculation of temperature distribution, the whole system inside the stainless chamber is considered. For the convective flow, only the melt is considered. The widely used zonal method divides the surface of the radiation enclosure into a number of zones, which has a uniform distribution of temperature, radiative properties and composition. The integro-differential equations for the radiative heat transfer are solved using the matrix inversion technique. The zonal method for radiative heat transfer is used in the growth chamber, which is confined by crystal surface, melt surface, heat shield, and pull chamber. Free surface and crystal/melt interface are tracked using adaptive grid generation. The competition between the thermocapillary convection induced by non-uniform temperature distributions on the free surface and the forced convection by the rotation of the crystal determines the interface shape, dopant distribution, and striation pattern. The temperature gradients on the free surface are influenced by the effects of the thermocapillary force on the free surface and the rotation of the crystal and the crucible.

The mechanism of PEO process on Al–Si alloys with the bulk primary silicon

This study focuses on mechanism of ceramic coating on Al-Si alloys with bulk primary Si using plasma electrolytic oxidation (PEO) technology. Al-Si alloys with 27-32% Si in weight were used as substrates. The morphologies, composition and microstructure of PEO coatings were investigated by scanning electron microscopy (SEM) with energy dispersive X-ray system (EDX). Results showed that the PEO process had four different stages. The effect of bulk Si is greatly on the morphology and composition of coatings at first three stages. Anodic oxide films formed on Al and Si phases, respectively. When the voltage exceeded 40 V, glow appeared and concentrated on the localized zone of interface of Al and Si phase. Al-Si-O compounds formed and covered on the dendrite Si phase surface, and the coating on bulk Si, which was silicon oxide, was rougher than that on other phase. If the treatment time was long enough, the coatings with uniform surface morphologies and elements distribution will be obtained but the microstructure of inner layer is looser due to the bulk Si.

EPITAXIAL LATERAL OVERGROWTH OF GaN ON SILICON-ON-INSULATOR

From a single process, GaN layers were laterally overgrown on maskless stripe-patterned (111) silicon-on-insulator (SOI) substrates by metalorganic chemical vapor deposition. The influence of stress on the behavior of dislocations at the coalescence during growth was observed using transmission electron microscopy (TEM). Improvement of the crystallin equality of the GaN layer was demonstrated by TEM and micro-Raman spectroscopy. Furthermore, the benefits of SOI substrates for GaN growth are also discussed.

Room temperature photoluminescence of tensile-strained Ge/Si0.13Ge0.87 quantum wells grown on silicon-based germanium virtual substrate

We report a room temperature study of the direct band gap photoluminescence of tensile-strained Ge/Si0.13Ge0.87 multiple quantum wells grown on Si-based germanium virtual substrates by ultrahigh vacuum chemical vapor deposition. Blueshifts of the luminescence peak energy from the Ge quantum wells in comparison with the Ge virtual substrate are in good agreement with the theoretical prediction when we attribute the luminescence from the quantum well to the c Gamma 1-HH1 direct band transition. The reduction in direct band gap in the tensile strained Ge epilayer and the quantum confinement effect in the Ge/Si0.13Ge0.87 quantum wells are directly demonstrated by room temperature photoluminescence.

Bulge testing and fracture properties of plasma-enhanced chemical vapor deposited silicon nitride thin films

The mechanical properties and fracture behavior of silicon nitride (SiNx) thin film fabricated by plasma-enhanced chemical vapor deposition is reported. Plane-strain moduli, prestresses, and fracture strengths of silicon nitride thin film; deposited both oil a bare Si substrate and oil a thermally oxidized Si substrate were extracted using bulge testing combined with a refined load-deflection model of long rectangular membranes. The plane-strain modu i and prestresses of SiNx thin films have little dependence on the substrates, that is, for the bare Si substrate, they are 133 +/- 19 GPa and 178 +/- 22 MPa, respectively, while for the thermally oxidized substrate, they are 140 +/- 26 Gila and 194 +/- 34 MPa, respectively. However, the fracture strength values of SiNx films grown on the two substrates are quite different, i.e., 1.53 +/- 0.33 Gila and 3.08 +/- 0.79 GPa for the bare Si substrate a A the oxidized Si substrate, respectively. The reference stresses were computed by integrating the local stress of the membrane at the fracture over the edge, Surface, and volume of the specimens and fitted with the Weibull distribution function. For SiNx thin film produced oil the bare Si Substrate, the Volume integration gave a significantly better agreement between data and model, implying that the volume flaws re the dominant fracture origin. For SiNx thin film grown on the oxidized Si substrate, the fit quality of surface and edge integration was significantly better than the Volume integration, and the dominant surface and edge flaws could be caused by buffered HF attacking the SiNx layer during SiO2 removal. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.

Novel room temperature photoluminescence of Ge/Si islands in multilayer structure grown on silicon-on-insulator substrate

Novel room temperature photoluminescence (PL) of the Ge/Si islands in multilayer structure grown on silicon-on-insulator substrates is investigated. The cavity formed by the mirrors at the surface and the buried SiO2 interface has a strong effect on the PL emission. The peak position is consistent with the theoretical calculation and independent of the exciting power, which is the evidence of cavity effect on the room temperature photoluminescence. (C) 2004 Elsevier B.V. All rights reserved.

Quasi-aligned ZnO nanotubes grown on Si substrates

Quasi-aligned ZnO nanotubes have been grown on silicon substrates by metalorganic chemical vapor deposition without using any catalyst. Two kinds of ZnO nanotubular structures were found: Nanotubes with single walls and nanotubes with double walls. The nanotubes were grown along the [001] direction. Room-temperature photoluminescence measurements of the ZnO nanotubes indicate strong ultraviolet emission and weak green emission. A new growth mode for these ZnO nanotubes is proposed, which can be used to prepare other nanotubular structures. (c) 2005 American Institute of Physics.

Stress reduction in GaN films on (111) silicon-on-insulator substrate grown by metal-organic chemical vapor deposition

The GaN film was grown on the (111) silicon-on-insulator (SOI) substrate by metal-organic chemical vapor deposition and then annealed in the deposition chamber. A multiple beam optical stress sensor was used for the in-situ stress measurement, and X-ray diffraction (XRD) and Raman spectroscopy were used for the characterization of GaN film. Comparing the characterization results of the GaN films on the bulk silicon and SOI substrates, we can see that the Raman spectra show the 3.0 cm(-1) frequency shift of E-2(TO), and the full width at half maximum of XRD rocking curves for GaN (0002) decrease from 954 arc see to 472 are sec. The results show that the SOI substrates can reduce the tensile stress in the GaN film and improve the crystalline quality. The annealing process is helpful for the stress reduction of the GaN film. The SOI substrate with the thin top silicon film is more effective than the thick top silicon film SOI substrate for the stress reduction. (C) 2007 Elsevier B.V. All rights reserved.

Stress evolution influenced by oxide charges on GaN metal-organic chemical vapor deposition on silicon-on-insulator substrate

GaN epilayers have been deposited on silicon-on-insulator (SOI) and bulk silicon substrates. The stress transition thickness and the initial compressive stress of a GaN epilayer on the SOI substrate are larger than those on the bulk silicon substrate, as shown in in situ stress measurement results. It is mainly due to the difference of the three-dimensional island density and the threading dislocation density in the GaN layer. It can increase the compressive stress in the initial stage of growth of the GaN layer, and helps to offset the tensile stress generated by the lattice mismatch.

Reduction of dislocations in GaN epilayer grown on Si (111) substrates using a GaN intermedial layer

GaN intermedial layers grown under different pressures are inserted between GaN epilayers and AlN/Si(111) substrates. In situ optical reflectivity measurements show that a transition from the three-dimensional (3D) mode to the 2D one occurs during the GaN epilayer growth when a higher growth pressure is used during the preceding GaN intermedial layer growth, and an improvement of the crystalline quality of GaN epilayer will be made. Combining the in situ reflectivity and transmission electron microscopy (TEM) measurements, it is suggested that the lateral growth at the transition of growth mode is favourable for bending of dislocation lines, thus reducing the density of threading dislocations in the epilayer.

Temperature dependence of the formation of nano-scale indium clusters in InAlGaN alloys on Si(111) substrates

The temperature dependence of the formation of nano-scale indium clusters in InAlGaN quaternary alloys, which are grown by metalorganic chemical vapour deposition on GaN/Si(111) epilayers, is investigated. Firm evidence is provided to support the existence of phase separation, or nano-scale In-rich clusters, by the combined results of high-resolution transmission electron microscopy (HRTEM), high-resolution x-ray diffraction (HRXRD) and micro-Raman spectra. The results of HRXRD and Raman spectra indicate that the degree of phase separation is strong and the number of In clusters in the InAlGaN layers on silicon substrate is higher at lower growth temperatures than that at higher growth temperatures, which limits the In and Al incorporated into the InAlGaN quaternary alloys. The detailed mechanism of luminescence in this system is studied by low temperature photoluminescence (LT-PL). We conclude that the ultraviolet (UV) emission observed in the quaternary InAlGaN alloys arises from the matrix of a random alloy, and the second emission peak in the blue-green region results from the nano-scale indium clusters.

Influence of the cavity on the low-temperature photoluminescence of SiGe/Si multiquantum wells grown on a silicon-on-insulator substrate

The influences of the cavity on the low-temperature photoluminescence of Si0.59Ge0.41/Si multiquantum wells grown on silicon-on-insulator substrates are discussed. The positions of the modulated photoluminescence (PL) peaks not only relate to the nature of SiGe/Si multiquantum wells, but also relate to the characteristic of the cavity. With increasing temperature, a redshift of the modulated PL peak originating from the thermo-optical effect of the cavity is observed.

Electrical properties of B-doped polycrystalline silicon thin films prepared by rapid thermal chemical vapour deposition

In this paper, about 30 mu m thick B-doped polycrystalline silicon (poly-Si) thin films were deposited on quartz substrates, n-type single crystalline silicon wafers and p(++)-type poly-Si ribbons by a rapid thermal chemical vapour deposition system in a temperature range from 1000 to 1150 degrees C. Activation energy measurement and room temperature/temperature dependent Hall effect measurement were performed on the poly-Si thin films prepared on the former two kinds of substrates, respectively. It seems that the electrical properties of as-prepared poly-Si thin films could be qualitatively explained by Seto's grain boundary (GB) trapping theory although there is a big difference between our samples and Seto's in gain size and film thickness etc. The experimental results reconfirm that GB itself is a kind of most effective recombination center with trapping level near the midgap and trapping state density in the order of 1012 cm(-2) magnitude. Electron beam induced current measurements on the poly-Si thin films prepared on the poly-Si ribbons also show that severe recombination occurs at the positions of GBs. (c) 2005 Elsevier B.V All rights reserved.

Heteroepitaxial growth and annealing of gamma-Al2O3 thin films on silicon

The gamma-Al2O3 films were grown on Si (100) substrates using the sources of TMA (Al (CH3)(3)) and O-2 by very low-pressure chemical vapor deposition (VLP-CVD). It has been found that the gamma-Al2O3 film has a mirror-like surface and the RMS was about 2.5nm. And the orientation relationship was gamma-Al2O3(100)/Si(100). The thickness uniformity of gamma-Al2O3 films for 2-inch epi-wafer was less than 5%. The X-ray diffraction (XRD) and reflection high-energy electron diffraction (RHEED) results show that the crystalline quality of the film was improved after the film was annealed at 1000degreesC in O-2 atmosphere. The high-frequency C-V and leakage current of Al/gamma-Al2O3/Si capacitor were also measured to verify the annealing effect of the film. The results show that the dielectric constant increased from 4 to 7 and the breakdown voltage for 65-nm-thick gamma-Al2O3 film on silicon increases from 17V to 53V.

Structural properties of polycrystalline silicon films formed by pulsed rapid thermal processing

A novel pulsed rapid thermal processing (PRTP) method has been used for realizing solid-phese crystallization of amorphous silicon films prepared by plasma-enhanced chemical vapour deposit ion. The microstructure and surface morphology of the crystallized films were investigated using x-ray diffraction and atomic Force microscopy. The results indicate that PRTP is a suitable post-crystallization technique for fabricating large-area polycrystalline silicon films with good structural quality, such as large grain size, small lattice microstrain and smooth surface morphology on low-cost glass substrates.