Preparation of n-type nanocrystalline 3C-SiC films by hot-wire CVD using N2 as doping gas

N-type nanocrystalline 3C-SiC films were prepared by hot-wire chemical vapor deposition from SiH₄/CH₄/H₂ and N₂ as a doping gas and the structural and electrical properties were investigated. The gas flow rates of SiH₄, CH₄ and H₂ were 1, 1 and 200 sccm, respectively. As the N₂ gas flow rate was increased from 0 to 10 sccm, the conductivity and the activation energy improved from 0.05 to 0.3 S/cm and from 45 to 28 meV, respectively. The Hall Effect measurement proved that the improvement of the electrical properties was caused by the increase in the carrier concentration. On the other hand, in the N₂ gas flow rate between 10 and 50 sccm, the conductivity and the activation energy remained unchanged. The crystallinity deteriorated with increasing N₂ gas flow rate. This gave rise to the unchanged electronic properties in spite of the increase in the intake of N atoms.     

Polycrystalline silicon film growth in a SiF4/SiH4/H2 plasma

The growth of polycrystalline silicon (polysilicon) films from SiF₄/SiH₄/H₂ gas mixtures is reported. The polysilicon films have been deposited in a multi process reactor by a PECVD process. The effect of r.f. power, chamber temperature and gas flow ratios on grain size and deposition rate have been determined. The fluorine concentration and the grain sizes of the films have been determined by SIMS and atomic force microscopy (AFM), respectively. Grain sizes in excess of 900 Å are reported for layers deposited at 300°C.     

CVD growth and characterization of 3C-SiC thin films

Cubic silicon carbide (3C-SiC) thin films were grown on (100) and (111) Si substrates by CVD technique using hexamethyldisilane (HMDS) as the source material in a resistance heated furnace. HMDS was used as the single source for both Si and C though propane was available for the preliminary carbonization. For selective epitaxial growth, patterned Si (100) substrates were used. The effect of different growth parameters such as substrate orientation, growth temperature, precursor concentration, etc on growth was examined to improve the film quality. The surface morphology, microstructure and crystallinity of grown films were studied using optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and X-ray photoelectron spectroscopy (XPS).     

Synthesis and characterization of nano-crystalline CVD diamond film on pure titanium using Ar/CH4/H2 gas mixture

Titanium and Ti alloys have poor tribological properties and deposition of a well adherent diamond coating is a promising way to solve this problem. But diamond film deposition on pure titanium and Ti alloys is always difficult due to the high diffusion coefficient of carbon in Ti, the large mismatch in their thermal expansion coefficients, the complex nature of the interlayer formed during diamond deposition, and the difficulty of achieving very high nucleation density. A nano-crystalline diamond (NCD) film can resolve Ti and Ti alloys weak tribological performance due to its smooth surface. A well-adhered NCD film was successfully deposited on pure Ti substrate by using a microwave plasma assisted chemical vapor deposition (MWPCVD) system in the environment of Ar, CH₄ and H₂ gases at a moderate temperature. Detailed experimental results on the preparation, characterization and successful deposition of the NCD film on pure Ti are discussed.     

Hydrogen dependent surface morphology study of plasma deposited SiN(x):H films for two gas systems SiH4/NH3 and SiH4/N2

Partially amorphous silicon nitride thin films were deposited using plasma enhanced chemical vapor deposition technique using the two gas systems: SiH4/NH3 and SiH4/N2. Fourier Transform infrared spectroscopy was employed to derive the relative changes in the bonded hydrogen content with increasing flow rates of NH3 and N2. Surface morphology was monitored using atomic force microscopy. Root mean square surface roughness was found to be dependent on the NH3 and N2 flow rates, unlike silicon nitride films deposited by rf magnetron sputtering with variation in (N2/Ar) (Li et al. Thin Solid Films 334 (1998) 140). The discrepancy has been explained in the light of bonded hydrogen content in these films. The X-ray diffraction technique has also been used to observe the phases of the nitride films which showed the presence of silicon nitride grains oriented in (200), (400) and (221) directions in the predominantly amorphous as-deposited SiN(x):H films.     

Development of TiSiN CVD process using TiCl4/SiH4/NH3 chemistry for ULSI anti-oxidation barrier applications

CVD-TiSiN may be promising material for O₂ diffusion-barrier films in ultra-large scale integrated (ULSI) circuit applications, especially for dynamic random-access memory (DRAM) capacitors. We developed a method for introducing Si into TiN, which is a common material used for diffusion-barrier films. TiSiN films were deposited by reacting TiCl₄, SiH₄, and NH₃ in a hot-wall CVD reactor. We measured TiSiN film deposition rates, composition, crystal structure, and resistivity as a function of SiH₄ partial pressure. Adding Si to TiN converts the TiN film structure from columnar grains to columnar-free structure films, thereby effectively removing the diffusion paths for O₂. The resistivity of TiSiN films was increased by adding SiH₄ to the reactant gas. With an increase in SiH₄ partial pressure up to P_siH4 = 0.8 Torr, the resistivity gradually increased, but for P_siH4 = 1.2 Torr, the phase present in the film was almost SiN and its resistivity jumped up. TiSiN film rapid thermal annealing was performed to evaluate the anti-oxidation performance at the temperature range from 400 to 600 °C in 100 Torr of O₂. For an increase the Si concentration up to 4.4 at.% improved anti-oxidation performance of TiSiN films. Flow modulation chemical vapor deposition (FMCVD) was used to create TiSiN films with low Cl concentration and improved anti-oxidation performance.     

Room temperature PL characterization of micro and nanocrystalline diamond grown by MPCVD from Ar/H2/CH4 mixtures

A photoluminescence (PL) study at room temperature was accomplished as a complement to well-established structural and morphological characterization techniques such as μ-Raman, FTIR, XRD, XPS or SEM. Considering the wide electronic band gap of pure diamond (5.45 eV), the near ultraviolet excitation (325 nm) from an HeCd laser source was selected. The observed nanocrystalline diamond (NCD) and microcrystalline CVD diamond (MCD) samples were obtained by microwave plasma (MPCVD) from hydrogen poor Ar/H₂/CH₄ mixtures. The PL spectrum of both NCD and MCD samples is dominated by the 1.681 eV emission with significant intensity and energy variations. The well-known 1.681 eV band related to the Si-vacancy colour centre is much more pronounced in MCD. In addition, for NCD, the band shifts to higher energies with thickness, suggesting two mechanisms for the silicon incorporation: co-deposition from the plasma and diffusion from the substrate. The samples were further characterized by μ-Raman spectroscopy, X-ray diffraction and scanning electron microscopy, structurally and morphologically.     

压力对热丝化学气相沉积的CH4/H2/Ar气氛中的纳米金刚石薄膜生长的影响

在热丝化学气相沉积体系中,系统研究了气压对CH4/H2/Ar气氛中纳米金刚石薄膜生长的影响.研究发现,体系气压对纳米金刚石的生长有很大的影响.在40torr的气压下,在CH4/H2/Ar气氛中的Ar气含量需高达90%才能保证纳米金刚石薄膜的生长,但降低气压至5torr时,50%的Ar气含量即可保证纳米金刚石薄膜的生长.压力对薄膜生长表面的气体浓度的影响是这个转变的主要原因.在同样的Ar含量下,在5torr下的C2活性基团的浓度高于40 torr的浓度,因而低的Ar含量会保证纳米金刚石薄膜的生长.     

Dry sol-gel condensation of p-X-C6H4SiH3 (X = H, CH3, CH3O, F, Cl) to organosilica p-X-C6H4SiO3 using nickelocene

The dry sol-gel reaction at toluene in ambient air atmosphere of p-X-C6H4SiH3 (X = H, CH3, CH3O, F, Cl) to p-C6H4SiO3 in high yield, catalyzed by nickelocene, is reported. The highest yield, molecular weight, polydispersity index, and TGA residue yield were obtained for p-Cl-C6H4SiH3. Some degree of unreacted Si-H bonds still remained in the gel because of steric reason. All the insoluble gels adopt an amorphous structure with a smooth surface. A plausible mechanism for the dry sol-gel reaction was suggested.     

Preparation of SiC ultrafine particles from SiH2Cl2 and C2H4 gas mixtures by a CO2 laser

Preparation of SiC ultrafine particles from SiH₂Cl₂-C₂H₄ mixtures by a CO₂ laser was investigated. The powders with specific surface area in the 8–150 m² g^–1 range were obtained by irradiating SiH₂Cl₂-C₂H₄ gas mixtures with a CO₂ laser at atmospheric pressure. X-ray diffraction of the products showed that silicon, SiC and free carbon were produced and the composition of the powders depended on the C₂H₄/SiH₂Cl₂ ratio. The reaction flame temperature changed from less than 1273 K to more than 3073 K with the laser power density and C₂H₄/SiH₂Cl₂ ratio. When SiH₂Cl₂ was irradiated with the CO₂ laser, the reaction temperature was less than 1273 K and silicon particles were formed. When the SiH₂Cl₂-C₂H₄ mixture was irradiated with a CO₂ laser, the reaction temperature was low (<1273 K) at low power density and low C₂H₄/SiH₂Cl₂ ratio, but it increased rapidly to around 3000 K at high laser power density and high C₂H₄/SiH₂Cl₂ ratio (>0.3). SiC was formed at both high and low reaction flame temperatures. It was considered that the rapid increase in the reaction flame temperature was caused by the initiation of exothermic reactions and the increase in laser absorption which was caused mainly by carbon particle formation. Hysteresis was observed between the reaction flame temperature and the power density of the laser beam. It was found that SiH₂Cl₂ underwent a disproportionation reaction on irradiation with the CO₂ laser, and silicon and SiC particles were formed through the various products of the disproportionation reaction. In particular, at low reaction flame temperature, the reactive species, such as SiH₄ and SiH₃Cl, produced by the disproportionation of SiH₂Cl₂ were considered to play an important role in the formation of silicon and SiC particles.     

Preparation of SnO2 thin films at low temperatures with H2 gas by the hot-wire CVD method

H₂ additional effect for crystallization of SnO₂ films prepared by the hot-wire CVD method was investigated. The crystallization of SnO₂ films starts at 170 °C. The selectivity enhancement of the solar cell substrate will contribute to reduce the cost of silicon thin film solar cells. The atomic hydrogen assisted nano-crystallization exists for the depositions of SnO₂ films by the hot-wire CVD method. Furthermore, the addition of H₂ gas improved the electrical conductivity up to 5.3 × 10⁰ S/cm. However, these effects are limited in the deposition condition of a small amount of hydrogen. Addition of much higher hydrogen concentration starts an etching effect of oxygen atoms.     

Influence of gas pressure on low-temperature preparation and film properties of nanocrystalline 3C-SiC thin films by HW-CVD using SiH4/CH4/H2 system

We investigated an influence of gas pressure on low-temperature preparation of nanocrystalline cubic silicon carbide (nc-3C-SiC) films by hot-wire chemical vapour deposition (HW-CVD) using SiH₄/CH₄/H₂ system. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra revealed that the films prepared below 1.5 Torr were Si-nanocrystallite-embedded hydrogenated amorphous SiC. On the other hand, nc-3C-SiC films were successfully prepared at gas pressure above 2 Torr. The high gas pressure plays two important roles in low-temperature preparation of nc-3C-SiC films: (1) leading to sufficient decomposition of CH₄ molecules through a gas phase reaction and an increase in the incorporation of carbon atoms into film and (2) promoting a creation of H radicals on the heated filament, allowing the sufficient coverage of growing film surface and a selective etching of amorphous network structure and/or crystalline-Si phase. It was found that total gas pressure is a key parameter for low-temperature preparation of nc-3C-SiC films.     

Ultra-smooth nanostructured diamond films deposited from He/H2/CH4/N2 microwave plasmas

Addition of He to a high CH4 content (10.7 vol%) H2/CH4/N2 feedgas mixture for microwave plasma chemical vapor deposition produced hard (58-72 GPa), ultra-smooth nanostructured diamond films on Ti-6AI-4V alloy substrates. Upon increase in He content up to 71 vol%, root mean squared (RMS) surface roughness of the film decreased to 9-10 nm and average diamond grain size to 5-6 nm. Our studies show that increased nanocrystallinity with He addition in plasma is related to plasma dilution, enhanced fragmentation of carbon containing species, and enhanced formation of CN radical.     

Oxidation kinetics of SiC deposited from CH3SiCl3/H2 under CVI conditions

Oxidation tests were performed on SiC deposits prepared from CH₃SiCl₃/H₂ under chemical vapour infiltration conditions, at temperatures ranging from 900–1500 °C under a flow of pure oxygen at 100 kPa (passive oxidation regime). The kinetics of growth of the silica layer were established from thickness measurements performed by spectroreflectometry. They obey classical parabolic laws from which rate constants are calculated. Within 1000–1400 °C, the oxidation process is thermally activated with an apparent activation energy of 128 kJ mol^–1. Above 1400 °C and below 1000 °C, an increase in the activation energy is observed which is thought to be related to a change in the mechanism of the oxygen transport across the silica layer forT>1400 °C and tentatively to stress effects forT<1000 °C. The kinetics data are compared to those measured on silicon single crystals (used as a standard) and to other reported data on SiC.     

Mass spectrometric study of gas-phase chemistry in the hot-wire CVD processes of SiH4/NH3 mixtures

The gas-phase reaction products of SiH₄, NH₃ and their mixtures from a hot-wire CVD chamber were investigated using laser ionization time-of-flight mass spectrometry. Both vacuum ultraviolet laser single photon ionization and laser-induced electron impact ionization were used. The main products observed from a 50% NH₃/He sample were H₂ and N₂. The study of an NH₃/SiH₄ mixture (P_NH3:P_SiH4 = 100:1) has shown that the NH₃ dissociation on the filament was suppressed by the presence of SiH₄ in the system. Signals from Si(NH₂)₄ and Si(NH₂)₃ species were identified as products from the 100:1 NH₃/SiH₄ mixture. The spectrum for a 1:1 NH₃/SiH₄ mixture was dominated by mass peaks characteristic of SiH₄ chemistry in the reactor, i.e. H₂, Si₂H₆, and Si₃H₈, at low temperatures. The extent to which the decomposition of NH₃ is suppressed is enhanced with more SiH₄ molecules in the system.     

脉冲调制射频容性耦合SiH/C2H4/Ar放电的发射光谱诊断

本文采用发射光谱法诊断了低气压下氩气(Ar)、硅烷(SiH4)及乙烯(C2H4)混合气体(SiH4/C2H4/Ar)脉冲调制射频放电等离子体特性,利用了Ar发射光谱中的五条谱线通过Boltzmann斜率法计算了电子激发温度,研究了占空比、调制频率、功率及气压等对电子激发温度和谱线相对强度的影响.     

直流热阴极PCVD法CH_4:N_2:H_2气氛下制备纳米金刚石膜

采用直流热阴极等离子体化学气相沉积(PCVD)技术,在CH4:H2中加入N2改变等离子体能量分布状态,提高二次形核比例,制备纳米金刚石膜。在CH4:H2气体中,在不同压力和温度下,改变通入N2的比例,分析直流热阴极等离子体放电下N2对金刚石膜生长的影响。采用拉曼光谱仪、扫描电镜(SEM)和X射线衍射分析仪(XRD)对样品进行了表征,结果表明,直流热阴极PCVD系统中,CH4:N2:H2气氛下,N2流量小于气体总流量的50%时,在6×103 Pa、850℃条件下,制备的金刚石膜样品的晶粒小于100nm、金刚石1332 cm-1特征峰展宽且强度较高、金刚石的XRD衍射峰强度也较高,具备纳米金刚石膜的基本特征。因此,利用直流热阴极PCVD方法,在较低温度和气压下,CH4:H2中加入少量N2,可以制备出纳米金刚石膜。     

Amorphous Si1−xCx:H films prepared by hot-wire CVD using SiH3CH3 and SiH4 mixture gas and its application to window layer for silicon thin film solar cells

B-doped hydrogenated amorphous silicon carbon (a-Si_1−xC_x:H) films have been prepared by hot-wire CVD (HWCVD) using SiH₃CH₃ as the carbon source gas. The optical bandgap energy and dark conductivity of the film are about 1.94 eV and 2 × 10^− 9 S/cm, respectively. Using this film as a window layer, we have demonstrated the fabrication of solar cells having a structure of the textured SnO₂(Asahi-U)/a-Si_1−xC_x:H(p)/a-Si_1−xC_x:H(buffer)/a-Si:H(i)/μc-Si:H(n)/Al. The conversion efficiency of the cell is found to be 7.0%.