Papers by Keyword: LPCVD

Abstract: A simple theoretical model and resistor fabrication for calculating the resistance of a polycrystalline silicon thin film is presented. The resistance value for poly-resistor is perfomed in terms of polysilicon thickness and its total area. The KrF excimer laser micromachine is used in assisting the resistor formation for a low pressure chemical vapor deposition (LPCVD) based polysilicon. Laser micromachine with three main parameters is used to aid the fabrication of the poly-resistor; namely as the pulse rate (i.e. number of laser pulses per second), laser beam size and laser energy. These parameters have been investigated to create the isolation between materials and also to achieve the desired poly-resistor shape. Preliminary results show that the 35 um beam size and 15 mJ of energy level is the most effective parameter to produce the pattern. Poly-resistor formation with 12 and 21 number of squares shows the total average resistance of 303.52 Ω and 210.14 Ω respectively. The laser micromachine process also significantly reduce the total time and number of process steps that are required for resistor fabrication.

Abstract: Uncoated SiC fibres in SiC/SiC composites manufactured by the liquid-silicon infiltration (LSI) process show a strong degradation as a result of silicon attack. The goal of this research is the development of a SiN_x-based fibre coating, which acts as a barrier against the liquid silicon. The coating is applied by means of low-pressure chemical vapour deposition (LPCVD) utilising the gaseous precursors silane (SiH₄) and ammonia (NH₃) on a commercial SiC multifilament yarn. The result is an amorphous fibre coating with an increasing coating thickness and a variable chemical composition from the middle of the yarn to the edges. The coated fibres exhibit a reduced characteristic Weibull strength in comparison to the uncoated fibres. In order to examine the stability of the films, the coated fibres undergo a heat treatment at 1450 °C in different environments (vacuum, argon and nitrogen). In all environments, the amorphous SiN_x coatings crystallise to the trigonal Si₃N₄. Depending on the coating thickness cracks and defects develop. However, the best results and the lowest amount of damaging occurs during the treatment in nitrogen.

Abstract: In the fabrication of SiC high-temperature sensors, the phosphosilicate glass film (PSG) is deposited on the SiC wafer as the intermediate layer, achieving the bonding of two SiC wafers. The ease of bonding is affected by the PSG film thickness uniformity. In this paper, the flow field distribution in the LPCVD tube is simulated under different deposition conditions,obtaining the wafer surface uniformity of gas flow distribution, which was verified by the experiment, The aim of this work is to study the impact of several deposition conditions such as the location of SiC wafers, wafer inclination and wafer spacing on the thickness uniformity of PSG film. Experimental results show that SiC wafer position in the tube and its own inclination and wafer spacing affect gas flow field on the SiC wafer surface,leading to uneven distribution of gas flow, thus affect the thickness uniformity of PSG.

Abstract: One of the advantages of silicon substrate over other semiconductor substrate is the high temperature process capability of the silicon. In this work, silicon wafer is used for thermal processing which involves many high temperature processes such as oxidation and deposition. Thin films on the wafer surface are investigated for its thickness and uniformity. Silicon dioxide (SiO₂) is initially grown using wet oxidation method and characterized for its thickness using FilmetricsSpectrometer. The thickness of SiO₂ achieved is less than 300nm. Silicon Nitride (Si₃N₄) is then deposited by sputter method and its thickness is measured at 210 nm. For the electrode, polysilicon (PolySi) is deposited using Low Pressure Chemical Vapor Deposition (LPCVD) process. Silane (SiH₄) is used as the source forPolySi deposition and the thickness is measured at 160nm. Standard deviation is calculated based on the layer thickness and the uniformity is checked across 5 points on the wafer. Hence, it is very important to have a uniform layer across the wafer surface for a defect free device and at the same time it protects the sensitivity of the sensor.

Abstract: Preparation and characteristics of amorphous silicon nitride (a-SiNx) thin films deposited by low pressure chemical vapor deposition (LPCVD) are investigated. Free gaseous radicals of trichlorosilane (TCS) and ammonia (NH3) are produced by passing each of the precursor gases separately over Pt-Ir/Al2O3 catalyst at the temperature of 600 C. Kinetics studies of the LPCVD are carried out in different total pressures, NH3/TCS flow rate ratios and temperatures. Surface topography, chemical concentrations, growth rate and thickness are studied by Ellipsometry, x-ray photo-electron spectroscopy (XPS), atomic force microscopy (AFM) and auger depth profiling (ADP). Analysis of experiments indicates that at the temperatures between 730 C and 830 C, the growth rate of thin films follows an Arrhenius behavior with activation energy of 166.3 KJ.mol-1. The measured hydrogen contamination in a-SiNx ultra thin films is 1.05 at% which is 17 times lower than the corresponding contamination in the films produced by (PECVD) and 3.4 times lower than the contamination in the LPCVD thin films with silane (SiH4) or dichlorosilane (DCS) and Ammonia. The surface topography of the prepared films is smooth and uniform and the thickness varies between 23 and 101 nanometers.

Abstract: ~50 μm single crystal graphene with hexagonal flower shape was synthesized on copper foils by low pressure chemical vapor deposition (LPCVD). The strong influence of Cu foils annealing on suppressing the nucleation of graphene was observed. Scanning electron microscopy (SEM), Optical microscopy (OM), and Raman spectrum showed that single crystal graphene as grown was monolayer with high quality. Suppressing nucleation through an annealing procedure offers an promising way to grow large-scale single crystal graphene controllably.

Abstract: In this paper, we report the fabrication and characteristics of the top-gated thin film transistors (TFTs) with nanopolysilicon as active layers. The nanopolysilicon thin films were deposited on SiO₂ layers by LPCVD and the SiO₂ layers were grown on the single silicon substrates. Then the nanopolysilicon thin film transistors with different thin film thicknesses and different channel width length radios were fabricated by CMOS technology, in which the thicknesses of channel layers were 90nm and 120nm, and the channel width length radios were 160μm/160μm, 320μm/160μm and 640μm/160μm, respectively. The experiment results show that drain current is in proportion to channel width length radio. In addition, when the thickness of the nanopolysilicon thin film is 90nm and the channel width length radio is 640μm/160μm, the on/off current radio reaches 10⁶.

Abstract: In order to improve the anti-oxidation of C/C composites, a C/SiC functionally graded coating for C/C composites was prepared by low pressure chemical vapor deposition (LPCVD) using methyltrichlorosilane (MTS, CH3SiCl3) and H2 as precursors. The relative amount of C and SiC in coatings was varied by controlling the input ratio of H2 to MTS. The phase composition and morphology were examined by scanning electron microscope (SEM) and X-ray diffraction (XRD), and the content distribution of C and SiC phases were investigated by energy dispersive spectroscopy (EDS). The isothermal oxidation test was evaluated at 900 °C and 1500 °C respectively. The results showed that the as-obtained coatings were possessed of a dense and uniform structure, and the SiC content in coatings increased with an increment of the molar ratio of H2 to MTS. The C/SiC coating had a good oxidation resistance.

Abstract: The growth of continuous silicon monocrystalline thin films on 3C-SiC epilayers deposited on silicon substrates is presented in this study. Such heterostructures can be beneficial for the fabrication of Micro Electro Mechanical Systems or electronic applications. The elaboration of these heterostructures was carried out using Low Pressure Chemical Vapor Deposition. X-ray Diffraction, Fourier Transformed Infra-Red spectroscopy and Scanning Electron Microscopy have been used to investigate the structural properties of Si epilayers and their dependence on growth conditions. Monocrystalline Si (110) films are obtained on 3CSiC(100)/Si (100) substrates, only when using growth temperatures close to 850°C. The strong influence of the underlying 3C-SiC film on the final structural properties of Si epilayer is evidenced.

Abstract: Using AlN as a buffer layer, 3C-SiC film has been grown on Si substrate by low pressure chemical vapor deposition (LPCVD). Firstly growth of AlN thin films on Si substrates under varied V/III ratios at 1100oC was investigated and the (002) preferred orientational growth with good crystallinity was obtained at the V/III ratio of 10000. Annealing at 1300oC indicated the surface morphology and crystallinity stability of AlN film. Secondly the 3C-SiC film was grown on Si substrate with AlN buffer layer. Compared to that without AlN buffer layer, the crystal quality of the 3C-SiC film was improved on the AlN/Si substrate, characterized by X-ray diffraction (XRD) and Raman measurements.