SiOxNy Films deposited with SiCl4 by remote plasma enhanced CVD

Silicon oxynitride films have been deposited with SiCl₄ by remote-plasma enhanced chemical vapor deposition (PECVD) at a substrate temperature of 250°C. Different mixtures of O₂ and NH₃ were used to obtain different oxynitride compositions ranging from SiO₂ to an stoichiometry close to that of silicon nitride. Rutherford backscattering spectrometry was used to determine the chemical composition of the SiO_xN_y films. The behavior of the IR absorption spectra as well as the refractive index measured by ellipsometry were used to estimate the effect of the different deposition parameters. It was found that the IR spectra show a shift of the characteristic peak associated with the stretching vibration mode of the Si-O-Si bonds towards lower wavenumbers as the relative concentration of ammonia was increased with respect oxygen. No double peaks associated with silicon oxide and silicon nitride were observed, indicating the formation of an homogeneous alloy. The IR spectra did not show any presence of water or hydrogen related impurities in the film. Also the effect of a hydrogen flow added during the deposition process on the structural characteristics of the deposited films was studied using dielectric spectroscopy and atomic force microscopy measurements showing that the hydrogen flow added during deposition results in a reduction of the film roughness and a planarization effect, which is very interesting for the application of these films in microelectronics devices.     

Silicon nitride films prepared by reactive plasma sputtering

Silicon nitride films were prepared by reactive plasma sputtering in nitrogen at a pressure of 2×10^-4 Torr. The residual gas in the reactor during film sputtering was analysed. The chemical composition of the films was determined from infrared absorption spectra in the wavelength region 2.0–15.0 μm and by the elastic scattering of ³He particles.The best quality silicon nitride films were obtained in pure nitrogen at the minimum residual gas pressures. An absorption minimum at 11.0 μm in the infrared spectra, corresponding to the Si-N chemical bond in the Si₃N₄ molecule, was observed in our films, indicating that their composition was close to stoichiometric.With a residual hydrogen pressure above 10% or a residual oxygen pressure above 2% the generation of new chemical bonds Si-H, N-H and Si-O respectively was observed in the silicon nitride films.     

The influence of CH4 addition on composition, structure and optical characteristics of SiCN thin films deposited in a CH4/N2/Ar/hexamethyldisilazane microwave plasma

Amorphous silicon carbonitride (a-SiCN) thin films were synthesized in a microwave plasma assisted chemical vapor deposition system using N₂, Ar, CH₄ and hexamethyldisilazane vapor (HMDSN). Composition, morphology and optical constants of the layers have been studied as a function of CH₄ rate in the range 0 to 9%. It was found that films are mainly composed of silicon nitride like compound whatever the CH₄ rate. However, CH₄ addition leads to less hydrogenated and denser films. In addition, a refractive index augmentation from 1.7 to 2.0 and a Tauc gap decrease from 5.2 eV to 4.8 eV is measured with CH₄ rate increase. It is believed that the refractive index augmentation is due to higher thin film density whereas hydrogen bonds decrease is assumed to contribute to the band gap narrowing. Besides, CH₄ addition to the gaseous mixture increases thin film oxidation resistance. These results show the ability of varying composition, structure and optical constants of a-SiCN films by modifying CH₄ rate in a N₂/Ar/HMDSN plasma.     

Effects of bombardment on optical properties during the deposition of silicon nitride by reactive ion-beam sputtering

Thin silicon nitride (Si(1_x)N(x)) films were synthesized without substrate heating by means of reactive argon-ion sputtering of either silicon or a silicon nitride target in the 1000-1500-eV energy range at a nitrogen partial pressure of 1.3 × 10(-2) Pa and with simultaneous nitrogen ion-assisted bombardment in the 300-500-eV low energy range. The extinction coefficient and refractive index of the films were directly dependent on the N(+) ion-to-atom arrival ratio, assisted ion energy, film growth rate, and indicated a correlation with film stoichiometry and disorder. Si(3)N(4) films were obtained for N(+) ion/Si atom arrival ratios from 0.6 to 1.7 and for different Si:N atom arrival rates and had a refractive index as high as 2.04 (633 nm) and a low hydrogen content as indicated by IR spectra.     

Optical properties of amorphous silicon nitride thin-films prepared by VHF-PECVD using silane and nitrogen

Hydrogenated amorphous silicon nitride (a-Si_1-x N _x :H) thin-films with x between 0.42 and 0.58 were deposited from silane diluted in nitrogen gas by VHF PE-CVD using a novel method for impedance matching. We determine the refractive index dispersion relations and the optical absorption edge information from the transmission spectra and report on the changes in the optical properties as the composition is varied. The optical properties of these films are similar to those of silicon nitride deposited using the more conventional silane-ammonia mixtures.     

Optical properties of hydrogenated hard carbon thin films

Hydrogenated amorphous carbon (a-C:H) films were deposited onto glass, silicon and germanium substrates. The films are transparent in the IR and are extremely hard (Mohs' hardness of about 8). The a-C:H coatings were prepared in an r.f.-excited discharge sustained by various hydrocarbon gases.The thickness, density, refractive index (at 0.3 μm and 2–10 μm) and relative hydrogen content were determined. Variations in the IR refractive index and the relative hydrogen content could be correlated with the deposition conditions. With a refractive index of approximately 2 a-C:H is an ideal antireflection coating for germanium (n = 4).Laser calorimetric measurements of optical absorption at 10.6 μm give a loss as low as 3% for a coating 1.3 μm thick on germanium (λ/4 for n = 2 at 10.6 μm).     

Optische und mechanische Eigenschaften von RLVIP HfO2‐Schichten

Optical and mechanical properties of RLVIP HfO₂ films In this paper HfO₂‐films were deposited on unheated fused silica, borosilicate glass, and silicon wafer substrates by reactive low voltage ion plating (RLVIP). Optical film properties, i. e. refractive index and absorption as well as mechanical properties, particularly film stress, were investigated. Their dependence on deposition parameters, i. e. arc current and oxygen partial pressure was studied. The film refractive index was calculated from spectrophotometric measurements. The low absorption was determined by photothermal deflection spectrometry. Stress measurements were performed by bending disc method with uncoated and coated silicon wafer substrates.     

用ECRCVD方法制备优质氮化硅钝化膜

利用电子回旋共振等离子体化学气相沉积(ECR—CVD)技术，以SiH4和N2为反应气体进行了氮化硅钝化薄膜的低温沉积技术的研究。采用原子力显微镜、傅立叶变换红外光谱和椭圆偏振光检测等技术对薄膜的表面形貌、结构、厚度和折射率等性质进行了测量。结果表明，采用ECR—CVD技术能够在较低的衬底温度条件下以较高的沉积速率制备厚度均匀的氮化硅薄膜，薄膜中H含量很低。薄膜沉积速率随微波功率和混合气体中硅烷比例的增加而增大。折射率随微波功率的增大而减小，随混合气体中硅炕比例的增大而增大。在相同气体混合比和微波功率条件下，较高衬底温度条件下制备的薄膜折射率较大。     

Annealing optimization of silicon nitride film for solar cell application

Hydrogenated films of silicon nitride (SiNx:H) is commonly used as an antireflection coating as well as passivation layer in crystalline silicon solar cell. SiNx:H films deposited at different conditions in Plasma Enhanced Chemical Vapor Deposition (PECVD) reactor were investigated by varying annealing condition in infrared (IR) heated belt furnace to find the optimized condition for the application in silicon solar cells. By varying the gases ratio (R = NH₃/SiH₄ + NH₃) during deposition, the SiNx:H films of refractive indices 1.85-2.45 were obtained. Despite the poor deposition rate, the silicon wafer with SiNx:H film deposited at 450 °C showed the best effective minority carrier lifetime. The film deposited with the gases ratio of 0.57 shows the best peak of carrier lifetime at the annealing temperature of 800 °C. The single crystalline silicon solar cells fabricated in conventional industrial production line applying the optimized film deposition and annealing conditions on large area substrates (125 mm × 125 mm) were found to have the conversion efficiencies as high as 17.05 %. Low cost and high efficiency single crystalline silicon solar cells fabrication sequence employed in this study has also been reported in this paper.     

Plasma etching of virtually stress-free stacked silicon nitride films

Stacked silicon nitride films for use in manufacturing of surface micromachined membranes were deposited using custom made plasma-enhanced chemical vapor deposition instrument with silane (SiH₄) and ammonia (NH₃) gas mixture as deposition precursor. Deposition conditions were adjusted by varying substrate temperature and SiH₄ to NH₃ flow ratio and temperature to obtain the required stress related and electrical properties of the membranes. Transmission Fourier transformed infrared spectroscopy and scanning electron microscopy were used to investigate the chemical composition and morphology of the stacked film components. An increase in the SiH₄ to NH₃ flow ratio and a decrease in temperature resulted in a silicon-rich silicon nitride film, as well as an increased silicon oxide concentration. To avoid underetch and sidewall defects, the plasma power density during the plasma etching was changed from 0.5 W/cm² during the etching of both top and bottom layers in a stacked film, to 1.0 W/cm² during the etching of the middle both silicon and silicon oxide rich film. This resulted in an improved overall stacked film sidewall quality and reduced the unwanted underetch.     

Optical and dielectric properties of thin SiOx films of variable composition

The effect of the composition of amorphous SiO_x films produced by the vacuum evaporation of SiO, on their optical and dielectric properties was investigated. The variation in the composition of the films was achieved by changing the deposition rate and the pressure of the residual gases.The optical band gap was observed to increase from 2.2 to 3.1 eV as the deposition rate was decreased from 50 to 5 Å s^-1 and simultaneously the refractive index, the permittiviity and the dielectric loss factor were found to decrease. The composition and structure of the films were determined from the optical absorption and IR spectroscopy.The experimental results revealed that SiO_x films produced by vacuum evaporation do not comprise a simple mixture of silicon and SiO₂ phases but they have a single-phase structure.     

Composition and optical properties of silicon nitride films grown on SiO2-glass and R-Al2O3 substrates by reactive RF magnetron sputtering

We have grown silicon nitride (Si₃N₄) films on SiO₂-glass and R-Al₂O₃ substrates by using reactive RF magnetron sputtering deposition methods with N₂ pure gas and N₂ + Ar mixture gas. The film composition, thickness and impurities have been examined by ion beam analysis. It is shown that the films have stoichiometric composition and are free from Ar contamination, when N₂ gas was used for the film deposition. Effects of impurities on the film properties, e.g., optical properties will be discussed.     

Silicon nitride and oxynitride films prepared by ion beam reactive sputtering

The composition of particles sputtered from a silicon target during bombardment by nitrogen and oxygen ions was measured. Elementary processes on both the substrate and the target were examined. A model of silicon nitride film formation was proposed, in which the main idea is the interaction of silicon on the substrate with the atomic nitrogen sputtered from the target. The dependence of the film properties on the oxygen concentration in N₂O₂ mixtures was investigated. The relationship between the nitrogen and silicon concentrations in silicon nitride films, the nitrogen ion beam incidence angle and the ejection angle of the sputtered particles was revealed experimentally. In the proposed model this relationship is interpreted as a result of the difference between the angular distribution of silicon and nitrogen atoms sputtered from the target.     

Plasma-enhanced deposition of silicon oxynitride films

Optical, mechanical and chemical properties of plasma-enhanced chemically vapor-deposited silicon oxynitride films were investigated for the SiH₄ (10% in helium), NH₃ and N₂O system at 13.56 MHz. The film composition was varied by changing the ratio of N₂O to NH₃ in the gas phase. The deposition rate, refractive index and stress were observed to be linear functions of the mole fraction of N₂O in the feed gases. The ratio of oxygen to nitrogen in the film, determined by Rutherford backscattering spectrometry, was found to be a linear function of the ratio of N₂O to NH₃. The relative hydrogen content of the films was found to decrease as the N₂O concentration increased. Film structure and composition were also varied by changing the total pressure.     

Optical properties of LPCVD silicon oxynitride

Low pressure chemical vapour deposition (LPCVD) silicon oxynitride films of various compositions (from pure SiO₂ to pure Si₃N₄) were deposited by changing the relative gas flow ratio. The effects of oxygen on the physical properties of the films were studied by spectroellipsometry (using Bruggeman approximation and Wemple Di Domenico model) and infrared spectroscopy. Refractive index measured by spectroellipsometry method is studied as a function of some deposition parameters: temperature of deposition, gases fluxes ratio. The high value of deposition temperature means low values in refractive index. More oxygen into films decreases the refractive index. The refractive index dispersion is studied by single-oscillator Wemple Di Domenico model. The optical band gap varies monotonically from 5 eV for silicon nitride, to 9eV for HTO LPCVD silicon dioxide and for the studied silicon oxynitride was found to be between 5 and 6 eV.     

Hydrogen etching of Si3N4 layers with plasma assisted hot wire CVD

In order to develop sustainable processes for clean manufacturing environment for thin film or other solar cell production, we studied the hydrogen etching of silicon nitride (Si₃N₄) films on flat crystalline silicon (c-Silicon) substrates. With an arrangement primarily constructed for hot wire CVD (HWCVD) deposition of thin silicon films also cleaning processes with atomic hydrogen were studied with a simplified three wire assembly. The three filaments could be biased independently by different potential. A variation of hydrogen pressure and flow was performed to find out conditions of high etching rates for the Si₃N₄ layers. The etching rate was simply determined by measuring the time for total removal of the film, since this could be easily detected by the change of the anti-reflection property. Etching rates of 0.1 nm/s have been obtained under 15 Pa and a flow of 50 sccm. An intensive study was carried out of the direct current (DC) plasma hot wire CVD conditions.     

Mechanical properties optimization of tungsten nitride thin films grown by reactive sputtering and laser ablation

Transition metal nitrides coatings are used as protective coatings against wear and corrosion. Their mechanical properties can be tailored by tuning the nitrogen content during film synthesis. The relationship between thin film preparation conditions and mechanical properties for tungsten nitride films is not as well understood as other transition metal nitrides, like titanium nitride. We report the synthesis of tungsten nitride films grown by reactive sputtering and laser ablation in the ambient of N₂ or N₂/Ar mixture at various pressures on stainless steel substrates at 400  C. The composition of the films was determined by XPS. The optimal mechanical properties were found by nanoindentation based on the determination of the proper deposition conditions. As nitrogen pressure was increased during processing, the stoichiometry and hardness changed from W₉N to W₄N and 30.8-38.7 GPa, respectively, for films deposited by reactive sputtering, and from W₆N to W₂N and 19.5-27.7 GPa, respectively, for those deposited by laser ablation.     

Infrared spectra of the hydrogenated amorphous silicon layers on metallic substrates of solar absorbers

Infrared absorption spectra were investigated in hydrogenated amorphous silicon (a-Si(H)) films deposited both by d.c. reactive sputtering (RS) and by r.f. glow discharge (GD) of silane. The films were deposited onto polished niobium and tungsten solar test disks to form spectrally selective absorbers for comparative photothermal and photovoltaic studies. Spectra were observed from the normal spectral reflectance from 400 to 3900 cm^-1 with a Fourier transform spectrometer. Hydrogen, alloyed typically at 10–35 at.% in these a-Si films, significantly reduces the gap state density and produces IR spectra characteristic of Si-H bonding complexes depending on the deposition method and the substrate temperature T_D. Comparison between RS and GD films revealed significant differences in their IR spectra. RS films show a strong Si-O-Si bonding absorption from atmospheric oxygen. GD films have a marked Si-H wagging mode absorption resolved into three components. This band is very sensitive to the deposition conditions and decays with increasing T_D. The SiH₃ rocking mode was identified at 500 cm^-1 in the GD films. The hydrogen concentration from the IR stretching mode absorption was correlated with the H₂ evolution results of McMillan and Peterson on identical films. The transition with increasing T_D could be traced from the room temperature state with polymeric complexes of hydrogen to the high temperature state with the single monohydride complex.     

Hydrogen-related mechanical stress in amorphous silicon and plasma-deposited silicon nitride

Hydrogen concentrations in amorphous silicon (a-Si) prepared by electron beam evaporation or plasma deposition as well as in plasma-deposited silicon nitride were measured as a function of annealing conditions using the photon-proton scattering method. Comparison with IR evaluations of SiH bonds shows the existence of “quasi-free” (IR inactive) hydrogen in a-Si. The amount of this component can be altered by annealing. The dependence of the mechanical stress on the annealing conditions was determined interferometrically, and the intrinsic contribution was separated in the case of plasma-deposited silicon nitride. As the hydrogen content decreases monotonically with increasing annealing temperature, the initial compressive stress of plasma-deposited a-Si or silicon nitride films changes to a tensile stress. For these films a linear correlation between the amount of mechanical stress and the number of SiH or NH bonds is shown. Evaporated a-Si films show a totally different stress behaviour from that of plasma-deposited a-Si. No correlation of stress with the hydrogen concentration was found for the evaporated a-Si films.     

IR and x-ray studies of ion-beam-synthesized aluminium nitride films

IR transmission spectroscopy in conjunction with X-ray diffraction was used to characterize the phase composition of aluminium films after nitrogen ion implantation. Aluminium films deposited onto single-crystal silicon and implanted with 30 keV nitrogen ions (¹⁴N₂⁺) to a dose of 10¹⁷-10¹⁸ ions cm^-2 were subsequently characterized for aluminium nitride (AIN) formation by IR spectroscopy. The formation of a stoichiometric AIN layer was evident from the IR absorption band observed at 648 cm^-1. Furthermore, X-ray diffraction of an aluminium foil after nitrogen implantation at 110 keV to a dose of 5.0 × 10¹⁷ ions cm^-2 on each side revealed the presence of a polycrystalline AIN phase. A thermal treatment at 700°C did not yield any new crystalline phases.