Hot-wire Chemical Vapor Deposition System Research Articles

Structure and properties of Si3N4-based diamond/MoS2-TiN composite films

This study aims to optimize the performance of silicon nitride (Si3N4) ceramic bearings in high-temperature and heavy-duty environments and to address the issues of insufficient lubrication and heat generation in vacuum environments. To this end, we prepared diamond and MoS2-TiN composite films on silicon nitride ceramic substrates using a hot-wire chemical vapor deposition system and a physical vapor deposition system. The experimental results show that increasing the deposition time of the diamond films can significantly improve their hardness and elastic modulus, enhance the bonding of the films with the substrate, reduce the friction coefficient, and increase the thermal conductivity. Furthermore, by appropriately reducing the sputtering power of the MoS2 film, we can effectively minimize damage to the diamond film and further enhance the overall performance of the composite film. This study offers valuable insights for addressing lubrication and heat dissipation challenges in vacuum environments.

Influence of filament-to-substrate distance on the spectroscopic, structural and optical properties of silicon carbide thin films deposited by HWCVD technique

Silicon carbide (SiC) thin films were deposited using hot wire chemical vapor deposition (HWCVD) technique from pure silane and methane gas mixture. The effect of filament distance to the substrate on the structural and optical properties of the films was investigated. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman scattering spectroscopy and UV–Vis–NIR spectroscopy were carried out to characterize SiC films. XRD patterns of the films indicated that the film deposited under highest filament-to-substrate distance were amorphous in structure, while the decrease in distance led to formation and subsequent enhancement of crystallinity. The Si–C bond density in the film structure obtained from FTIR data, showed significant increment with transition from amorphous to nano-crystalline structure. However, it remained almost unchanged with further improvement in crystalline volume fraction. From Raman data it was observed that the presence of amorphous silicon phase and sp 2 bonded carbon clusters increased with the decrease in distance. This reflected in deterioration of structural order and narrowing the optical band gap of SiC films. It was found that filament-to-substrate distance is a key parameter in HWCVD system which influences on the reactions kinetics as well as structural and optical properties of the deposited films.

In-line deposition of silicon-based films by hot-wire chemical vapor deposition

Silicon-based films such as hydrogenated amorphous silicon (a-Si:H), nanocrystalline silicon (nc-Si:H), and hydrogenated amorphous silicon nitride (a-SiNx:H) can be deposited by hot-wire chemical vapor deposition (HW-CVD). The HW-CVD technology differs from conventional plasma-enhanced (PE)-CVD in a number of technological aspects, such as soft activation, high growth rates, and low system costs. To evaluate the HW-CVD technology for thin film deposition in solar industry an in-line hot-wire CVD system was used to deposit a-Si:H films for passivation of crystalline silicon solar cells as well as for the fabrication of thin film silicon solar cells. The HW-CVD system consists of seven vacuum chambers including three hot-wire systems with maximum deposition areas of 500mm by 600mm for each hot-wire activation source. The deposition processes were investigated by applying design of experiment to identify the effects and interactions of the process parameters on the deposition characteristics and film properties. The process parameters investigated were silane flow, deposition pressure, substrate temperature, film thickness, as well as temperature, diameter and number of wires, respectively. Growth rates up to 2.5nm/s were achieved for a-Si:H films. Intrinsic a-Si:H films for passivation of different crystalline solar cell types yielded carrier lifetimes of more than 1000μs for film thickness values below 20nm. For n-doped a-Si:H films prepared with PH3 as dopant gas, electrical resistivity is in the range of 102Ωcm. P-doped a-Si:H films prepared with B2H6 as dopant gas show electrical resistivity of about 105Ωcm. Crystalline silicon heterojunction solar cells with intrinsic thin layer (HIT cells) exhibit energy conversion efficiencies of more than 17% when fabricated with intrinsic HW-CVD amorphous silicon films as passivation layers.

Optimization of process parameters in a large-area hot-wire CVD reactor for the deposition of amorphous silicon (a-Si:H) for solar cell application with highly uniform material quality

Abstract Scale-up of a-Si:H-based thin film applications such as solar cells, entirely or partly prepared by hot-wire chemical vapor deposition (HWCVD), requires research on the deposition process in a large-area HWCVD system. The influence of gas supply and filament geometry on thickness uniformity has already been reported, but their influence on material quality is systematically studied for the first time. The optimization of deposition parameters for obtaining best material quality in our large-area HWCVD system resulted in an optimum filament temperature, T fil ≈1600°C, pressure, p =8 mTorr and silane flow, F(SiH 4 )=100 sccm, keeping the substrate temperature at T S =200°C. A special gas supply (gas shower with tiny holes of uniform size) and a filament grid, consisting of six filaments with an interfilament distance, d fil =4 cm were used. The optimum filament-to-substrate distance was found to be d fil–S =8.4 cm. While studying the influence of different d fil and gas supply configurations on the material quality, the above-mentioned setup and parameters yield best results for both uniformity and material quality. With the setup mentioned, we could achieve device quality a-Si:H films with a thickness uniformity of ±2.5% on a circular area of 20 cm in diameter. The material, grown at a deposition rate of r d ≈4 A/s, was characterized on nine positions of the 30 cm×30 cm substrate area, and revealed reasonable uniformity of the opto-electronic properties, e.g photosensitivity, σ Ph / σ D =(2.46±0.7)×10 5 , microstructure factor, R =0.17±0.05, defect densities, N d(PDS) =(2.06±0.6)×10 17 cm −3 and N d(CPM) =(2.05±0.5)×10 16 cm −3 (film properties are given as mean values and standard deviations). Finally, we fabricated pin solar cells, with the i-layer deposited on small-area p-substrates distributed over an area of 20 cm×20 cm in this large-area deposition system, and achieved high uniformity of the cell parameters with initial efficiencies of η =(6.1±0.2)% on the 20 cm×20 cm area.