The growth and physical properties of low pressure chemically vapour-deposited films of tantalum silicide on n+-type polycrystalline silicon

Bilayer films of tantalum silicide on n⁺-type polycrystalline silicon prepared by low pressure chemical vapour deposition (LPCVD) were fabricated from SiH₄ and TaCl₅ in a single standard hot-wall LPCVD reactor. The main advantages over conventional co-sputtered films are reduced wafer handling, improved conformal deposition, increased wafer throughput and the use of only one piece of process equipment. Both films of the bilayer structure are deposited at 575°C and annealing is carried out in the deposition reactor at 900°C. The amorphous deposited silicon films were doped in situ with PH₃. The stoichiometry of the as-deposited tantalumrich Ta₅Si₃ films is shifted to the desired low resistivity TaSi₂ during the annealing process, in which the additional silicon required is supplied from the underlying polycrystalline silicon. The resistivity of annealed LPCVD tantalum silicide films is 60–70μΩ cm which is comparable with that of films prepared by co-sputtering. The peak-to-valley surface roughness of 30 nm is at present typically a factor of 2 larger than that for co-sputtered films. Wet oxidation experiments indicate that there is no large difference in the thermal SiO₂ formation between LPCVD and co-sputtered tantalum silicide.     

Evidence for a solid state reaction at the a-SiSnOx interface: An x-ray photoelectron spectroscopy study

X-ray photoelectron spectroscopy together with argon ion sputtering were used to investigate the depth distribution of tin and silicon suboxides formed during thermal annealing of an amorphous silicon (a-Si) film vacuum evaporated onto a conducting tin oxide surface. The presence of multicomponent silicon suboxides together with free tin was observed at the a-SiSnO_x interface. The presence of these components is attributed to a solid state reaction between silicon and SnO_x.     

Gas pressure dependence of composition in Ta–Ti–N films prepared by pulsed high energy density plasma

Tantalum titanium nitride (Ta–Ti–N) films were deposited on silicon wafer substrates by pulsed high energy density plasma (PHEDP), under different intake gas pressures, ranging from 0.1 to 0.4 MPa. The films were investigated by X-ray photoelectron spectroscopy. Results were analyzed in detail, which reveals that the contents of the metallic elements (Ta and Ti) tend to decrease with pressure, while that of nitrogen increases as expected. With increasing pressure, the films can be denoted as TaTi_3.9N_2.8, TaTi_4.7N_6.0, TaTi_2.2N_8.4 and TaTi_3.1N1_3.5, respectively. The bonding state of tantalum, titanium, as well as nitrogen was fitted and discussed. Our results demonstrate that almost all the titanium bonded with nitrogen. The Ta–N and Ti–N bonds have equal shares under low gas intake pressure, while the Ti–N bonds prevail under high pressure. The preferential sputtering between the coaxial electrodes should be responsible for this phenomenon. Under low nitrogen pressure, the preferential sputtering is quite significant; while it could be neglected under high pressure.     

Electrical characterization of high-pressure reactive sputtered ScOx films on silicon

Al/ScO_x/SiN_x/n-Si and Al/ScO_x/SiO_x/n-Si metal-insulator-semiconductor capacitors have been electrically characterized. Scandium oxide was grown by high-pressure sputtering on different substrates to study the dielectric/insulator interface quality. The substrates were silicon nitride and native silicon oxide. The use of a silicon nitride interfacial layer between the silicon substrate and the scandium oxide layer improves interface quality, as interfacial state density and defect density inside the insulator are decreased.     

Stress evolution in magnetron sputtered Ti-Zr-N and Ti-Ta-N films studied by in situ wafer curvature: Role of energetic particles

Stress evolution during reactive magnetron sputtering of binary TiN, ZrN and TaN thin films as well as ternary Ti-Zr-N and Ti-Ta-N solid-solutions was studied using real-time wafer curvature measurements. The energy of the incoming particles (sputtered atoms, backscattered Ar, ions) was tuned by changing either the metal target (M_Ti = 47.9, M_Zr = 91.2 and M_Ta = 180.9 g/mol), the plasma conditions (effect of pressure, substrate bias or magnetron configuration) for a given target or by combining different metal targets during co-sputtering. Experimental results were discussed using the average energy of the incoming species, as calculated using Monte-Carlo simulations (SRIM code). In the early stage of growth, a rapid evolution to compressive stress states is noticed for all films. A reversal towards tensile stress is observed with increasing thickness at low energetic deposition conditions, revealing the presence of stress gradients. The tensile stress is ascribed to the development of a ‘zone T’ columnar growth with intercolumnar voids and rough surface. At higher energetic deposition conditions, the atomic peening mechanism is predominant: the stress remains largely compressive and dense films with more globular microstructure and smooth surface are obtained.     

The film growth process in the bias sputtering of superconducting Nb3Ge

Metastable A15 Nb₃Ge films were sputter deposited onto sapphire substrates under thermalizing conditions. Simultaneously the configuration of the electric potential was varied by the application of a negative bias to the tantalum substrate holder or to both the holder and the growing Nb-Ge film. Films deposited with no bias showed an initial nucleation with disordered crystallites of low super-conducting transition temperature T_c and a subsequent “homoepitaxial” growth process towards a well-ordered state of high T_c. In contrast, bias sputtering led to well-ordered A15 crystallites at an earlier growth stage, which was then succeeded by a non-homoepitaxial growth process. These results will be discussed in the context of ion bombardment of the growing film surface and of the tantalum holder.     

Dependence of hydrogen and oxygen incorporation on deposition parameters in photochemical vapor deposited mercury free silicon nitride films

Silicon nitride films have been deposited on p-type Si (100) by mercury-sensitized photo-chemical vapor deposition (photo-CVD) method varying deposition pressure and substrate temperature. Energy dispersive X-ray fluorescence spectra of the samples show that the incorporation of mercury in the films, if any, is below 20 ppm. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy studies show the incorporation of oxygen and hydrogen in all the films, which is a function of the deposition parameters. Higher substrate temperature favors the formation of SiH bonds and reverse is the case for the formation of SiNH bonds. The sample deposited at low temperature (170 °C) shows the presence of less unreacted silicon (4%) in comparison to the sample (12.5% unreacted silicon) deposited at higher deposition temperature (250 °C), but the variation of pressure shows no significant change in terms of the unreacted silicon. The incorporated hydrogen and oxygen passivate surface defects thereby influencing interface electronic state densities (D_it) and fixed insulating charges (Q_ss).     

Stress induced crystallization of hydrogenated amorphous silicon

Hydrogenated amorphous silicon films were grown on to thermally oxidized silicon wafers by Radio Frequency magnetron sputtering, and SiN_x and Al₂O₃ capping layers were used to control the residual thermal stress. After annealing, a comparison of the silicon films with and without capping layers indicates that tensile stress induced by the capping layer enhances the crystallinity of the annealed amorphous silicon film. The stress is due to the mismatch between the coefficients of thermal expansion for the capping layer and amorphous silicon film. These results highlight the potential of thermal stress as a means to alter the crystallization in thin film architectures and suggest that even larger effects can be obtained with suitable choices of capping layer chemistry.     

Copper diffusivity in boron-doped silicon wafer measured by dynamic secondary ion mass spectrometry

The effective copper diffusivity (D_eff) in boron-doped silicon wafer was measured using a Dynamic Secondary Ion Mass Spectrometry (D-SIMS) that was incorporated with an out-drift technique. By this technique, positive interstitial copper ions (Cu_I⁺) migrated to the surface region when a continuous charge of electrons showered on the oxidized silicon wafer, which was also bombarded by primary O₂⁺ ions. The Cu_I⁺ ions at the surface region diffused back to the bulk when the electron showering stopped. The D-SIMS recorded the real-time distribution of Cu_I⁺ ions, generating depth profiles for in-diffusion of copper for silicon-wafer samples with different boron concentrations. These were curve-fitted using the standard diffusion expressions to obtain different D_eff values, and compared with other measurement techniques.     

Improvement and characteristics of conical silicon emitters employing wet-dry etching

A number of new technologies require conical and sharp tips to serve as electron emitters in the vacuum microelectronics. In this paper, we improved radius of curvature, height and cone angle of emitters in order to reach the enhancement result of field enhancement factor (β). We developed a fabrication process to improve geometry of emitter by employing isotropic dry etching in pure SF₆ and a mixture of SF₆ and O₂ followed by thermal oxidation technique. We successfully achieved excellent conical emitters with 5–10 nm radius of curvature, 4.4 μm height, and 30° cone angle. The conical silicon emitters current–voltage characteristics shows that E_to = 4.8 V/μm (turn-on electric field) with current density of 10 μA/cm², and maximum current density J = 60.4 μA/cm² at E = 8.14 V/μm. This study may provide a practical guideline for design and fabrication of a high-performance silicon emitter used in various industrial applications.     

Residual stresses and Raman shift relation in anatase TiO2 thin film

Anatase TiO₂ film (100-1000 nm thick) grown on glass, sapphire (0001), and Si (100) substrates by pulsed dc-magnetron reactive sputtering were evaluated for stress and strain analysis using Raman spectroscopy and curvature measurement techniques. The X-ray analysis revealed that films prepared for this study were purely anatase, and the measurements indicate that the film exhibit that (101) is the preferred growth orientation of the crystallites, especially for the film thicker than 100 nm. Curvature measurements and Raman spectroscopy, with 514.5 nm excitation wavelength, phonon line shift were used for stress analysis. A comparison between Raman lineshapes and peak shifts yields information on the strain distribution as a function of film thickness. The measurements of residual stresses for crystalline anatase TiO₂ thin film showed that all thin film were under compressive stress. A correlation between Raman shifts and the measured stress from the curvature measurements was established. The behavior of the anatase film on three different substrates shows that the strain in film on glass has a higher value compared to the strain on sapphire and on silicon substrates. The dominant 144 cm^− 1E_g mode in anatase TiO₂ clearly shifts to a higher value by 0.45-5.7 cm^− 1 depending on the type of substrate and film thickness. The measurement of the full width at half maximum values of 0.59-0.80 (2θ°) for the anatase (101) peaks revealed that these values are greater than anatase powder 0.119 (2θ°) and this exhibits strong crystal anisotropy with thermal expansion.     

The effect of ribbon curvature on the magnetic properties of Fe-based amorphous cores

Coercivity and losses properties of Fe₈₀Si₉B₁₁ (at.%) amorphous cores with different radius of curvature have been studied. It shows that coercivity and core loss of the Fe₈₀Si₉B₁₁ amorphous alloy increases with the decrement of the winding radius. The domain structure of the ribbons is different for different radius of curvature R. The domain width increases with the decrease of the radius of curvature, since the stress within the ribbon with lower radius of curvature is much stronger. Magnetic-elastic anisotropy energy has also been studied.     

Structure and tribological properties of reactively sputtered Zr-Si-N films

Zr-Si-N films were deposited on silicon and steel substrates by magnetron sputtering of a Zr-Si composite target in Ar-N₂ reactive mixtures. The silicon concentration in the films was adjusted in the 0-7.6 at.% range by varying the surface of Si chips located on the erosion zone of the target. The films were characterised by X-ray diffraction, electron probe microanalysis, atomic force microscopy and wear tests. The structure and the tribological properties of Zr-Si-N films were compared to those of ZrN coatings. Depending on the silicon concentration, the films were either nanocomposites (nc-ZrN/a-SiN_x) or amorphous. Introduction of silicon into the zirconium nitride coatings induced a change in the preferential orientation of the ZrN grains: [111] for ZrN films and [100] for Zr-Si-N ones. This texture modification was also observed for a ZrN film deposited on an amorphous SiN_x layer. Thus, within our deposition conditions, the occurrence of a-SiN_x enhanced the [100] preferred orientation. Friction and wear behaviour of the films were carried out against spheres of alumina or 100 Cr6 steel by using a ball-on-disc tribometer. The results showed that addition of silicon into ZrN-based coating induced a strong decrease in the friction coefficient and in the wear rate compared to those of ZrN films. These results were discussed as a function of the films structure and composition.     

Advanced key technologies for magnetron sputtering and PECVD of inorganic and hybrid transparent coatings

Besides classical multilayer systems with alternating low and high refractive indices, reactive pulse magnetron sputtering processes offer various possibilities of depositing gradient films with continuously varying refractive index. Using nanoscale film growth control it is possible to achieve optical filter systems with a defined dependency of refractive index on film thickness, e.g. by sputtering a silicon target in a time variant mixture of oxygen and nitrogen. Also reactive co-sputtering of different target materials such as silicon and tantalum in oxygen is suitable as well. Rugate filters made from SiO_xN_y or Si_xTa_yO_z gradient refractive index profiles find their application in spectroscopy, laser optics and solar concentrator systems.Furthermore polymer substrates are increasingly relevant for the application of optical coatings due to their mechanical and economical advantages. Magnetron PECVD (magPECVD) using HMDSO as precursor allows to deposit carbon containing films with polymer-like properties. Results show the suitability of these coatings as hard coatings or matching layers. Multifunctional coatings with antireflective and scratch-resistant properties were deposited on polymer substrates using a combined magPECVD and sputter deposition process.     

The influence of pressure on the structure and the self-cleaning properties of sputter deposited TiO2 layers

TiO₂-layers for self-cleaning applications were deposited on glass and silicon wafer by reactive dc-sputtering at various oxygen and argon pressures in the range from 0.18 Pa to 3.0 Pa. With an increasing sputtering pressure the microstructure of the resulting films is significantly modified. The deposited crystal phases change from rutile to anatase and the density and the refractive index decrease by a factor of about 1.3. The microstructure of the layers is strongly influenced by the sputtering pressure. An improvement of the hydrophilicity as well as of the photocatalytic activity can be observed, due to the changes in the structure of the layers.     

Characterization of interface states at Au/SnO2/n-Si (MOS) structures

The purpose of this paper is to characterize the interface states in Au/SnO₂/n-Si (MOS) structures. The characteristic parameters of the interface states are derived from capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements as a function of frequency. The C-V and G/ω-V measurements have been carried out in the frequency range of 1 kHz to 1 MHz at room temperature. At each frequency, the measured capacitance and conductance decrease with increasing frequency due to a continuous distribution of the interface states. The frequency dispersion in capacitance and conductance can be interpreted in terms of the interface state density (N_ss) and series resistance (R_s). Especially at low frequencies, the interface states can follow the ac signal and yield an excess capacitance. Due to a continuous density distribution of interface states, the C and G/ω values decrease in depletion region with increasing frequencies. At high frequencies, the effect of series resistance on the capacitance is found appreciable due to the interface state capacitance decreasing with increasing frequency. Experimental results show that the locations of interface states between SnO₂/Si and series resistance have a significant effect on electrical characteristics of MOS structures.     

The Mode I elastic stress distribution in the immediate vicinity of an intrusion-type notch

The representation of the elastic stress distribution in the immediate vicinity of a notch root is a key element in the development of a fracture mechanics methodology for blunt notches. Earlier work has shown that, for Mode III deformation, the stress at a distance x ≪ ρ (notch root radius of curvature) ahead of the root is unique in that it only depends on x, ρ and the peak stress σ_p irrespective of the notch shape and the loading characteristics. However with Mode I deformation, it has been shown that the local stress does not exhibit this uniqueness characteristic. This conclusion is underpinned by this paper’s quantification of the Mode I elastic stress distribution in the immediate vicinity of an intrusion-type notch.     

Residual compressive stress in sputter-deposited TiC films on steel substrates

Polycrystalline TiC films with thickness between 0.1 and 2.8 microm were deposited by r.f. sputtering onto 1010 steel and borosilicate glass substrates at 200°C. All films were found to be in a state of compression. For a film grown under a given set of deposition conditions, the incremental compressive stress, i.e. the average stress in the uppermost deposited layer, was generally found to be largest near the film-substrate interface and to become constant with film thickness t_f for t_f ? 0.3 microm. However, for a given t_f the incremental stress increased with a decrease in the argon sputtering pressure P_Ar. Experimental results showed that the incremental compressive stress in bulk films could be directly related to the trapped argon concentration. Argon incorporation is due to the burial of energetic species incident on the growing film surface from two primary sources: energetic neutrals produced by Ar⁺ ions scattered off the target in binary collisions and Ar⁺ ions accelerated to the substrate owing to its induced negative potential with respect to the positive space charge region in the r.f. discharge. The trapped argon concentration from both contributions increased with decreasing P_Ar. All films grown on steel substrates exhibited good adhesion as indicated by indentation and diamond stylus scratch tests. The residual compressive stress in the films was found to be beneficial for wear-related applications in which the film was subjected to a large tensile stress.     

Intrinsic stress of magnetron-sputtered niobium films

The stresses in niobium films were studied and the following preliminary results were obtained. (1) Niobium films can be prepared in any stress state (tensile, stress free or compressive) by varying the argon sputtering pressure. (2) As the bias voltage increases, more argon is incorporated into the film; both T_c and R/R₀ decrease; and the stress becomes more compressive and seems to saturate at about 1.5 × 10¹⁰ dyn cm^?2 at higher bias voltages (at an argon sputtering pressure of 1.9 Pa). (3) The lattice parameters show a close relation to the film stresses. (4) Lowering the sputtering rate results in a higher argon content in the bias-sputtered films. (5) The as-deposited film surface is smoother when deposited at lower pressures; the film has a columnar structure and intercolumnar gaps at higher pressures. (6) The film prepared at a higher bias voltage has a smoother as-deposited surface and a much smaller column size.From this study of the behavior of the stresses in niobium films, it appears that the stress is determined mainly by the microstructure and the energetic particle bombardment. Energetic particle bombardment may promote compressive stress by the incorporation of argon, by the formation of a more dense microstructure and by a “shot-peening” action.     

Improved efficiency of p-type quasi-mono silicon blanket emitter solar cell by ion implantation and backside rounding

A novel type of silicon material, p-type quasi-mono wafer, has been produced using a seed directional solidification technique. This material is a promising alternative to traditional high-cost Czochralski (CZ) and float-zone (FZ) materials. This study evaluates the application of an advanced solar cell process that features a novel method of ion-implantation and backside rounding process on p-type quasi-mono silicon wafer. The ion implantation process substituted for thermal POCl₃ diffusion leads to better R _sheet uniformity (<3 %). After screen-printing, the interface of Al and back surface field (BSF) layers was analyzed for the as prepared samples and the samples etched to three different depth. SEM showed that increased etch depth improved both BSF layer and Al-Si layer. The IQE result also showed that the samples with higher etching depth had better performance at long wavelength. The I–V cell tester showed that the sample with the etching depth of 6 μm ± 0.1 μm had the greatest efficiency, due to the highest V _oc and I _sc . The solar cell fabricated in this innovative process on 156 × 156mm p-type quasi-mono silicon wafer achieved 18.82 % efficiency.