Synthesis of silicon carbonitride dielectric films with improved optical and mechanical properties from tetramethyldisilazane

Films of silicon carbonitride have been obtained by the plasma chemical decomposition of a gaseous mixture of helium and a volatile organic silicon compound 1,1,3,3-tetramethyldisilazane (TMDS) in the temperature range of 373–973 K. The modeling of the processes of deposition from a gaseous mixture (TMDS + He) in the temperature range of 300–1300 K and pressures of P _total ⁰ = 10^?2–10 Torr has shown that it is possible to vary the equilibrium composition of the condensed phase depending on the synthesis temperature and the initial gaseous mixture composition. The chemical and phase compositions, as well as physicochemical and functional properties, of the films obtained in the range of 373–973 K have been studied using a complex of modern techniques, including Fourier transformed infrared (FTIR) Raman, X-ray photoelectron (XPS) and energy-dispersive spectroscopy (EDS), scanning electron (SEM) and atomic-force microscopy (AFM), X-ray diffraction using synchrotron radiation (XRD-SR), ellipsometry, and spectrophotometry. The electrophysical parameters are determined using the C-V and I-V characteristics, and the microhardness and Young’s modulus are determined by the nanoindentation method. It is established that the chemical composition of low-temperature (373–673 K) films of silicon carbonitride corresponds to a gross formula of SiC _x N _y O _z : H, while that of high-temperature films corresponds to SiC _x N _y . The presence of nanocrystals with the phase composition close to the standard phase α-Si₃N₄ is detected in the films. It is shown that all of the films are perfect dielectrics (k = 3.8–6.4, ρ = 2.2 × 10¹⁰?1.3 × 10¹¹ Ohm · cm), possess high transparency (～98%) in a wide spectral range of 280–2500 nm, and have a high microhardness (3.8–36 GPa) and Young’s momentum (125–190 GPa).     

Films based on phases in a Si–C–N system. Part II. plasma chemical synthesis of SiC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>:Н films from the mixture of bis(trimethylsilyl)ethylamine and hydrogen

Thin silicon carbonitride SiC_xN_y films are synthesized by means of plasma enhanced chemical vapor deposition using an organosilicon compound such as bis(trimethylsilyl)ethylamine EtN(SiMe₃)₂ as the precursor in a mixture with hydrogen. The chemical composition and properties of the films are characterized by a set of modern research methods such as IR, Raman, and energy dispersive spectroscopy; ellipsometry; scanning electron microscopy; and spectrophotometry. The growth rate, chemical composition, and optical properties of the films have been studied depending on the synthesis temperature in the range from 373 to 1073 K. It is found that the substrate temperature exerts a significant effect on the growth kinetics, surface morphology, physicochemical properties, and functional characteristics of the films. Low temperature SiC_xN_y films have high transparency in the visible and infrared regions of the spectrum. Varying the parameter of synthesis allows one to obtain layers with different values of the refractive index (1.50–2.50).     

Synthesis and Physicochemical Properties of Nanocrystalline Silicon Carbonitride Films Deposited by Microwave Plasma from Organoelement Compounds

Nanocrystalline films of a ternary compound, namely, silicon carbonitride SiC_xN_y, are prepared by plasma-enhanced chemical vapor deposition at temperatures of 473–1173 K with the use of a complex gaseous mixture of hexamethyldisilazane Si₂NH(CH₃)₆, ammonia, and helium. The chemical and phase compositions and the physicochemical properties of the films are investigated using IR, Auger electron, and X-ray photoelectron spectroscopy; ellipsometry; synchrotron X-ray powder diffraction; electron and atomic-force microscopy; microhardness measurements with a nanoindenter; and electrical measurements. Correlations of the composition of the initial gas phase and the synthesis temperature with a number of functional properties of the SiC_xN_y silicon carbonitride films are revealed.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Fainer, Kosinova, Rumyantsev, Maksimovskii, Kuznetsov, Kesler, Kirienko, Han Bao-Shan, Lu Cheng.     

<Emphasis Type="Italic">N</Emphasis>-bromohexamethyldisilazane: Investigation of properties and thermodynamic simulation of precipitation of thin-layer structures from the vapor phase

N-Bromohexamethyldisilazane has been characterized using an elemental analysis and IR, UV, ¹H NMR, ¹³C NMR, and ²⁹Si NMR spectroscopy. The spectral characteristics of the compound have been determined and the saturated vapor pressure has been measured. The thermodynamic simulation of the chemical vapor deposition (CVD) of silicon carbonitride films in the Si-C-N-Br-H system has been performed at low pressures (13.30 and 1.33 Pa) over a wide temperature range (from 400 to 1200 K) with the use of initial gas mixtures of N-bromohexamethyldisilazane with hydrogen and ammonia. The possibility of preparing films of different compositions has been demonstrated and the optimum conditions for deposition of silicon carbonitride coatings of the general composition SiC _x N _y have been established.     

Study of chemical bonds and element composition of silicon oxycarbonitride films by the methods of XP-, IR-, and energy-dispersive spectroscopy

The element composition and chemical bonds of nanocomposite films of hydrogenated silicon oxycarbonitride fabricated through high-frequency plasma-chemical deposition from initial gas mixtures of 1,1,3,3-tetramethyldisilazane with nitrogen and oxygen in the temperature range 373–973 K depending on the synthesis conditions is studied. The effect of changes in the temperature and chemical composition of the initial gas mixtures on the element composition and types of chemical bonds in SiC _x N _y O _z :H films is investigated.     

Bonding characterization and nano-indentation study of the amorphous SiCxNy films with and without hydrogen incorporation

The hardness and effective modulus of hydrogen-containing and hydrogen-free amorphous SiC_xN_y films were studied by nano-indentation. Amorphous SiC_xN_y films with and without hydrogen were deposited by electron cyclotron resonance plasma chemical vapor deposition (ECR-CVD) using a SiH₄–CH₃NH₂–N₂–H₂ gas mixture and hydrogen-free ion-beam sputtering deposition (IBSD), respectively. Fourier-transform infrared spectroscopy (FTIR) studies were used to investigate the bonding states of the SiC_xN_y materials. SiH, CH and NH bonds were detected by FTIR in ECR-CVD, but not in IBSD, films. The incorporation of hydrogen led to a reduction in both the hardness and modulus of the amorphous SiC_xN_y films. From nano-indentation measurements, the hardness and effective modulus of the IBSD coated, hydrogen-free amorphous SiC_xN_y films were 27–30 and 211–258 GPa, respectively. The corresponding values for the ECR-CVD coated, hydrogen-containing amorphous SiC_xN_y were 22–26 and 115–144 GPa, respectively.     

Films of hydrogenated silicon oxycarbonitride. Part I. Chemical and phase composition

The method of preparation of hydrogenated silicon oxycarbonitride films with variable composition SiC _x N _y O _z : H by the plasma chemical vapor decomposition of a volatile organosilicon compound, 1,1,1,3,3,3-hexamethyldisilazane (enhanced to IUPAC, bis(trimethylsilyl)amine) in a gas phase containing nitrogen and oxygen in the temperature range of 373–973 K has been developed. It has been shown that nitrogen and oxygen provide the decrease in carbon content in films due to gas-phase reaction giving volatile products (CN)₂, CH₄, CO, and H₂(H). The obtained SiC _x N _y O _z : H films are nanocomposite, in the amorphous part of which the nanocrystals are distributed, which belong to the determined phases of the Si-C-N system, namely, α-Si₃N₄, α-Si_{3 ? x} C _x N₄, and graphite.     

Synthesis and Properties of Thin Films Formed by Vapor Deposition from Tetramethylsilane in a Radio-Frequency Inductively Coupled Plasma Discharge

Thin films of hydrogenated silicon carbide (SiC_x:H) and carbonitride (SiC_xN_y:H) are synthesized in a reactor with inductively coupled RF plasma with the introduction of tetramethylsilane vapors and additive gases—argon and/or nitrogen. The process is carried out at different synthesis temperatures, plasma power, and partial pressure of tetramethylsilane and additive gases in the reactor. The dependences on the synthesis conditions of the films’ growth rate, chemical composition, and properties such as the light transmission coefficient, refractive index, optical band gap, and dielectric constant are obtained. The weak dependence of the films’ composition and properties on the preset synthesis conditions is a characteristic feature of the studied process within the investigated range of conditions. The possible reasons of this phenomenon and the results of in situ studies of the gas phase composition in the plasma are examined.     

Mechanical Properties and Microstructural Characterization of Amorphous SiCxNy Thin Films After Annealing Beyond 1100°C

The effect of thermal annealing on structure and mechanical properties of amorphous SiC_xN_y (y ≥ 0) thin films was investigated up to 1500°C in air and Ar. The SiC_xN_y films (2.2–3.4 μm) were deposited by reactive DC magnetron sputtering on Si, Al₂O₃ and α‐SiC substrates without intentional heating and at 600°C. The SiC target with small excess of carbon was sputtered at various N₂/Ar gas flow ratios (0–0.48). The nitrogen content in the films changes in the range 0–43 at.%. Hardness and elastic modulus (nanoindentation), change in film thickness, film composition, and structure (Raman spectroscopy, XRD) were investigated in dependence on annealing temperature and nitrogen content. All SiC_xN_y films preserve their amorphous structure up to 1500°C. The hardness of all as‐deposited and both air‐ and Ar‐annealed SiC_xN_y films decreases with growth of nitrogen content. The annealing in Ar at temperatures of 1100°C–1300°C results in noticeable hardness growth despite the ordering of graphite‐like structure in carbon clusters in nitrogen free films. Unlike the SiC, this graphitization leads to hardness saturation of SiCN films starting above 900°C, especially for films with higher nitrogen content (deposited at higher N₂/Ar). This indicates the practical hardness limit achievable by thermal treatment for SiC_xN_y films deposited on unheated substrates. The ordering in carbon phase is facilitated by the presence of nitrogen in the films and its extent is controlled by the N/C atomic ratio. The suppression of graphitization was observed for N/C ranging between 0.5–0.7. Films deposited at 600°C show higher hardness and oxidation resistance after annealing in comparison with those deposited on unheated substrates. Hardness reaches 40 GPa for SiC and ~28 GPa for SiC_xN_y (35 at.% of nitrogen). Such a high hardness of SiC film stems from its partial crystallization. Annealing of SiC_xN_y film (35 at.% of N) in Ar at 1400°C is accompanied by formation of numerous hillocks (indicating heterogeneous structure of amorphous films) and redistribution of film material.     

Plasma enhanced chemical deposition of nanocrystalline silicon carbonitride films from trimethyl(phenylamino)silane

Synthetic process for nanocrystalline silicon carbonitride films was developed using plasma-chemical decomposition of a new organosilicon reagent, namely, trimethyl(phenylamino)silane Me₃SiNHPh. Synthesis was carried out from the gaseous mixtures, such as Me₃SiNHPh + He, Me₃SiNHPh + N₂, and Me₃SiNHPh + NH₃, in a reactor in the wide temperature range (473–973 K) under the low pressure (4–5 × 10⁻² Torr). Polished wafers of Si(100), Ge(111), and silica glass were used as substrates. Dependences of the chemical and phase compositions, the surface morphology, and the silicon carbonitride optical properties on the process temperature were studied using FTIR and Raman spectroscopy, energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), scanning electron microscopy (SEM), ellipsometry, and spectrophotometry.     

Thermal diffusivity in diamond,SiCxNy and BCxNy

Thermal diffusivity (α) of free standing diamond, amorphous silicon carbon nitride (a-SiC_xN_y) and boron carbon nitride (a-BC_xN_y) thin films on crystalline silicon, has been studied using the travelling wave technique. Thermal diffusivity in all of them was found to depend on the microstructure. For a-SiC_xN_y and a-BC_xN_y thin films two distinct regimes of high and low carbon contents were observed in which the microstructure changed considerably and that has a profound effect on the thermal diffusivity. The defective C(sp)N phase plays a key role in determining the film properties.     

Tris(diethylamino)silane—A new precursor compound for obtaining layers of silicon carbonitride

Silicon carbonitride layers have been obtained by chemical deposition from the gas phase with thermal (LPCVD) and plasma (PECVD) activation of the gas mixture of helium with the new volatile siliconorganic compound tris(diethylamino)silane (Et ₂N)₃SiH (TDEAS) in the temperature region 373–1173 K. Thermodynamic simulation of the deposition processes from the gas mixture (TDEAS + He) in the temperature interval 300–1300 K and pressure interval P _tot⁰ from 1 × 10⁻² to 10 mm Hg has revealed the possibility of varying the equilibrium composition of the condensed phase depending on the synthesis temperature and the composition of the initial gas mixture. Physicochemical and functional properties of obtained layers were studied by complex of modern methods. It has been established that the chemical composition of the silicon carbonitride layers obtained by the PECVD method, depending on the deposition conditions, approaches that of silicon oxynitride or nitride, and the composition of those obtained by the LPCVD method approaches that of silicon carbide. The presence of nanocrystals with a phase composition close to the standard α-S_i3N₄ phase and of carbon inclusions has been found in the layers.     

Nitrogenated amorphous carbon films synthesized by electron cyclotron resonance plasma enhanced chemical vapor deposition

Nitrogenated amorphous carbon (a-CN_x:H) films were investigated as protective overcoats for industrial applications. Thin a-CN_x:H films have been deposited on silicon by electron cyclotron resonance plasma-enhanced chemical vapor deposition. The substrate bias was found to play an important role in determining the chemical compositions and mechanical properties of the films. The surface roughness and hardness of the films can reach 1.4 Å and 20 GPa, respectively. The influence of mechanical properties by hydrogen was studied. A correlation exists between the background slope of Raman spectra and the hydrogen content as determined by elastic recoil detection analysis.     

Controlled nitrogen content synthesis of hafnium carbonitride powders by carbonizing hafnium nitride for enhanced ablation properties

In this study, a new method of carbonizing hafnium nitride was proposed to synthesize ultrahigh-temperature hafnium carbonitride (HfC_xN_y) powders. The new method helps to maintain both the purity of phases and control the content of nitrogen in the HfC_xN_y. The results show that the as-prepared HfC_xN_y powders have a single phase, with an average particle size of approximately 2 $\mu m$, and Hf, C and N are evenly distributed. Moreover, the microstructures, phase compositions, ablation properties and mechanism of the HfC_0.62N_0.38 composites under a plasma ablation environment were studied in detail. The results show that the HfC_0.62N_0.38 composites exhibited excellent ablation resistance at 3073 K for 60 s and the ablation mechanism of HfC_0.62N_0.38 can be identified as HfC_0.62N_0.38→HfC_xO_y→HfO₂. The mass ablation rate of the HfC_0.62N_0.38 composite is evaluated to be 1.36 mg/cm²∙s, which is lower than that of HfC ceramics. Our work is intended to provide new insight regarding the development of ultrahigh-temperature ceramics and widen their applications.     

Product of carbonitriding of leucoxene concentrate

The grain, phase, and chemical compositions and the microstructure of tusin (a mixture of titanium carbonitride TiC_1-xN_x (x ≈ 0.4 - 0.5) and silicon carbide SiC), used as the base of a new kind of refractory that is the product of carbonitriding of leucoxene concentrate, are presented. It is shown that titanium carbonitride and silicon carbide intergrow finely, which hampers phase separation. Chemical treatment of tusin yields technical silicon carbide. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 1, pp. 25–27, January, 2000. RF Patent No. 2100317.     

Compositional and optical properties of SiO x films and (SiO x /SiO y ) junctions deposited by HFCVD

In this work, non-stoichiometric silicon oxide (SiO _x ) films and (SiO _x /SiO _y ) junctions, as-grown and after further annealing, are characterized by different techniques. The SiO _x films and (SiO _x /SiO _y ) junctions are obtained by hot filament chemical vapor deposition technique in the range of temperatures from 900°C to 1,150°C. Transmittance spectra of the SiO _x films showed a wavelength shift of the absorption edge thus indicating an increase in the optical energy band gap, when the growth temperature decreases; a similar behavior is observed in the (SiO _x /SiO _y ) structures, which in turn indicates a decrease in the Si excess, as Fourier transform infrared spectroscopy (FTIR) reveals, so that, the film and junction composition changes with the growth temperature. The analysis of the photoluminescence (PL) results using the quantum confinement model suggests the presence of silicon nanocrystal (Si-nc) embedded in a SiO _x matrix. For the case of the as-grown SiO _x films, the absorption and emission properties are correlated with quantum effects in Si-nc and defects. For the case of the as-grown (SiO _x /SiO _y ) junctions, only the emission mechanism related to some kinds of defects was considered, but silicon nanocrystal embedded in a SiO _x matrix is present. After thermal annealing, a phase separation into Si and SiO₂ occurs, as the FTIR spectra illustrates, which has repercussions in the absorption and emission properties of the films and junctions, as shown by the change in the A and B band positions on the PL spectra. These results lead to good possibilities for proposed novel applications in optoelectronic devices.

PACS

61.05.-a; 68.37.Og; 61.05.cp; 78.55.-m; 68.37.Ps; 81.15.Gh     

Novel synthesis method for quaternary Cd(Cu,Zn)Se thin films and its characterizations

Nowadays, the search for novel compounds by chemical synthesis is in trend. Herein, we report the deposition of Cd_1-x-yZn_xCu_ySe (0.025 ≤ x = y ≤ 0.15) films by facile, industry-oriented chemical synthesis. The Cd_1-x-yZn_xCu_ySe thin films were deposited at the optimized growth conditions (temperature = 70 ± 0.1 °C, pH = 10.3 ± 0.1, substrate rotation speed = 70 ± 2 rpm and time = 100 min). As-synthesized thin films were characterized for physical, chemical, topographical and electrical attributes. The study of vibrational modes in Cd_1-x-yZn_xCu_ySe thin films was done with the help of Raman spectroscopy. Improvement in surface topography with the integration of Cu²⁺ and Zn²⁺ into the CdSe lattice has been noticed by the atomic force microscopy (AFM). The electrochemical impedance spectroscopy revealed lower values of R_s and R_ct for x = y = 0.05 composition. Chemical deposition of Cd_1-x-yZn_xCu_ySe thin films may offer an excellent way to fabricate quaternary chalcogenide-based absorber materials for solar cells.     

Improving electrical conductivity and wear resistance of hafnium nitride films via tantalum incorporation

Transition metal nitrides are being widely applied, as durable sensors, semiconductor and superconductor devices, their electrical conductivity and wear resistance having a significant influence on these applications. However, there are few reports about how to improve above properties. In this paper, tantalum was incorporated into hafnium nitride films through Hf_1-xTa_xN_y [x=Ta/(Hf+Ta), y=N/(Hf+Ta)] solid solution. The electrical conductivity and wear resistance of the films were significantly improved, due to the increase of the electron concentration (tantalum has one more valence electron than hafnium) and the increase in H/E and H³/E² ratios caused by the effect of solid solution hardening, respectively. The highest electrical conductivity of Hf_1-xTa_xN_y films is 8.3×10⁵ S m⁻¹, which is 1.7 times and 5.2 times of that of hafnium nitride and tantalum nitride films, respectively. In addition, the lowest wear rate of films is 1.2×10⁻⁶ mm³/N m, which is only 10% and 48% of that of hafnium nitride and tantalum nitride films, respectively. These results indicate that alloying with another transition metal is an effective method to improve electrical conductivity and wear resistance of transition metal nitrides.     

Tantalum (oxy)nitrides prepared using reactive sputtering for new nonplatinum cathodes of polymer electrolyte fuel cell

Tantalum (oxy)nitrides (TaO_xN_y) have been investigated as new cathodes for polymer electrolyte fuel cells without platinum. TaO_xN_y films were prepared using a radio frequency magnetron sputtering under Ar + O₂ + N₂ atmosphere at substrate temperatures from 50 to 800 °C. The effect of the substrate temperature on the catalytic activity for the oxygen reduction reaction (ORR) and properties of the TaO_xN_y films were examined. The catalytic activity of the TaO_xN_y for the ORR increased with the increasing substrate temperature. The ORR current density at 0.4 V vs. RHE on TaO_xN_y prepared at 800 °C was approximately 20 times larger than that on TaO_xN_y prepared at 50 °C. The onset potential of the TaO_xN_y for the ORR was obtained at the ORR current density of −0.2 μA cm⁻². The onset potential of the TaO_xN_y prepared at 800 °C was ca. 0.75 V vs. RHE. The X-ray diffraction patterns revealed that Ta₃N₅ structure grew as the substrate temperature increased. While, the ionization potentials of all specimens were lower than that of Ta₃N₅, and decreased with the increasing substrate temperature. The TaO_xN_y which had Ta₃N₅ structure and lower ionization potential might have a definite catalytic activity for the ORR.     

Tribological study of boron nitride films

Boron nitride (BN) films with different cubic and hexagonal phase compositions were deposited on silicon substrates via diamond interlayers by magnetron sputtering and electron cyclotron resonance microwave plasma chemical vapor deposition. The tribological behaviors of the BN films were investigated systematically using a ball-on-disc tribometer with silicon nitride as the counterpart. Comparison studies were also performed on sintered cubic and hexagonal BN compacts. The influence of phase compositions and surface roughness of BN coatings on their tribological characteristics was studied. The cubic BN (cBN) films showed excellent wear resistance against silicon nitride. The wear rate of the cBN films was estimated to be about 1.0 × 10^?7 mm³/N m by measuring the cross-sectional area of the wear track after the sliding test over a distance of 12 km.