Effect of substrate material on the rate of growth and the optical parameters of a-C:H layers

a-C:H layers were grown by dc magnetron reactive sputtering of a graphite target in Ar + H₂ plasma. Ellipsometric measurements were carried out and analyzed at a wavelength of 6328Å for three sets of a-C:H layers with different thicknesses (different sputtering times) on silicon, fused quartz, and glass-ceramic substrates. It was shown that the substrate material had a substantial effect upon a-C:H growth: a-C:H layers on Si substrates were uniform up to ～ 7000Å thickness; for thin layers (<1000 Å) the growth rate was greater on quartz than on Si; the refractive index values of a-C:H were slightly different on quartz and Si substrates (1.60–1.65 and 1.65–1.72, respectively); a-C:H layers on glass-ceramic substrates were not uniform and had variable refractive index.     

Vibration modes of carbon in hydrogenated amorphous carbon modified with copper

Activation in IR absorption of quasi-Raman vibration modes of graphene planes was studied in a-C:H modified with copper; these modes are forbidden in the absence of copper. Parameters of the quasi-Raman bands G and D in optical absorption in the region of carbon-carbon mode vibrational frequencies and the parameters of true Raman bands are compared in the Raman spectra of pure a-C:H and in that modified with copper. It is stated that the close coincidence of the frequencies of the true Raman bands in a-C:H and quasi-Raman bands in a-C:H(Cu) indicates that the interaction of copper atoms with the carbon matrix leaves the graphene rings practically intact and can be regarded as intercalation. To identify the observed quasi-Raman and the satellite bands, correlations between their parameters are considered. The sizes of graphite-like clusters and their dependence on the copper content in the film were evaluated from the ratios between the integrated intensities of D and G bands.     

Photosensitivity of a-C:H/c-Si heterojunctions

Layers of a-C:H were grown on c-Si wafers by the glow discharge method in a CH₄ + Ar gaseous mixture. The electrical and photoelectric properties of a-C:H/c-Si heterojunctions were studied. It was found that the heterojunctions display rectification and broad-band photovoltaic effects. It is shown that the polarization sensitivity in these structures occurs at an oblique incidence of linearly polarized light under the illumination of the surface coated with a-C:H layers. The observed oscillations in the spectrum of the coefficient of induced photopleochroism are attributed to the interference of light in these layers.     

Plasma chemistries for high density plasma etching of SiC

A variety of different plasma chemistries, including SF₆, Cl₂, ICl, and IBr, have been examined for dry etching of 6H-SiC in high ion density plasma tools (inductively coupled plasma and electron cyclotron resonance). Rates up to 4500?-min⁻¹ were obtained for SF₆ plasmas, while much lower rates (≤800?·min⁻¹) were achieved with Cl₂, ICl, and IBr. The F₂-based chemistries have poor selectivity for SiC over photoresist masks (typically 0.4–0.5), but Ni masks are more robust, and allow etch depths ≥10 μm in the SiC. A micromachining process (sequential etch/deposition steps) designed for Si produces relatively low etch rates (<2,000?-min⁻¹) for SiC.     

Scanning tunneling spectroscopy of a-C:H and a-C:(H, Cu) films prepared by magnetron sputtering

Scanning tunneling spectroscopy was used to study a-C:H and a-C:(H, Cu) films under atmospheric conditions; these films were formed on semiconductor (Si) and metallic (Cr/Si) substrates using dc magnetron sputtering of graphite or graphite/copper targets. The local density of electron states was determined from normalized differential tunneling conductance with the aim of probing the individual sp ²-phase clusters. The well-defined valence-band edge and the varying (i.e., dependent on the scanning coordinate) shape of the distribution of the density of electron states within the conduction band are characteristic of the a-C:H films; also, the largest experimental value of the band gap in these films is ～3 eV; finally, the tendency towards the stable position of the Fermi level at a level of ～1 eV above the valence-band top is observed in a-C:H films. The a-C:(H, Cu) films are homogeneous with respect to the local density of electron states, which is accounted for by the formation of a homogeneous surface layer in the course of growth.     

Investigation of surface morphology of copper-modified amorphous carbon films

A study of the surface morphology of copper-modified amorphous hydrogenated carbon films a-C:H(Cu) by scanning tunnel microscopy (STM) is reported. An algorithm is presented for the digital analysis of STM images to obtain the size distribution function for the longitudinal component of the surface relief. a-C:H(Cu) films were deposited by magnetron co-sputtering of graphite and copper onto two types of substrates: (100) n-Si with a heavily doped surface layer, and Si covered with a chromium layer. A mesoscopic surface structure of crystalline silicon, a chromium layer, and a-C:H(Cu) film has been revealed. A correlation between the structural elements of the film and the substrate is considered and a conclusion is made that inherent grains with characteristic size of 6–8 nm are formed in the film.     

Raman spectroscopy study of the carbon structure of <Emphasis Type="Italic">a</Emphasis>-C:(H,Cu) and <Emphasis Type="Italic">a</Emphasis>-C:(H,Co) composite films

The main changes induced in the Raman spectrum of a-C:H films in the 1200-to 1700-cm^?1 frequency region by modification with Cu and Co are ascertained. A comparison of the results obtained with the available data on various carbon structures reveals that the introduction of metals in concentrations comparable to the carbon content stimulates growth and ordering of graphite-like nanoclusters in the sp² carbon bonding system. It is found that, while similar structural rearrangements occur under thermal annealing of both a-C:H and composite a-C:(H, Cu) and a-C:(H, Co) films, the presence of metals interferes with thermally stimulated graphitization. The size of the graphite-like nanoclusters in annealed and unannealed films of all types is estimated, and Co is shown to produce a more efficient graphitizing effect than Cu.     

Formation technology of through metallized holes to sources of high-power GaN/SiC high electron mobility transistors

The technology of through metallized holes to sources of high-power GaN/SiC high electron mobility transistors is studied. The dependences of the reactive ion etch rate of SiC in the inductively coupled plasma discharge on the pressure of the SF₆/O₂/Ar gas mixture (5–40 mTorr), the high-frequency power applied to the bottom electrode (200–300 W), the working gas flow ratio (5 : 1 : (0–10)), and the bottom electrode temperatures (5–50°C) are studied. Based on these dependences, the hole etching process on 76-mm-diameter SiC substrates 50 and 100 μm thick is developed. The process features smooth etched-surface morphology, a high rate (1 μm/min), and low high-frequency power deposited into the inductively coupled plasma discharge (1000 W). The developed process of hole etching in SiC substrates is characterized by the selectivity coefficient S = 12 and the anisotropy coefficient A = 13. Films based on NiB are recommended as masks for etching through holes into SiC substrates. The processes of through-hole metallization by the electrochemical deposition of Ni and Au layers are developed.     

Density of states in amorphous carbon and its modification by annealing

The effect of annealing on the electron density of states in amorphous carbon a-C and amorphous hydrogenated carbon a-C:H has been studied. a-C and a-C:H layers were grown by magnetron sputtering of a graphite target in, respectively, argon and argon-hydrogen plasmas. Optical transmission spectra were studied experimentally in the range 1.5–5.6 eV, and ellipsometric parameters were measured at the He-Ne laser wavelength. The spectral dependence of the imaginary part of the dielectric function was reconstructed. A model describing the optical response of amorphous carbon was developed on the basis of the hypothesis that there are fluctuations of the sp² fragment sizes in the allotropic composition of amorphous carbon. The optical gap E_g in both types of material is accounted for by the presence of fragments of critical size. Experimental data were used to reconstruct, with the use of model parameters, the energy dependence of the density of states in the ground and excited bands, and the plasma frequencies for electrons involved in optical transitions are found. It is shown that the bands of both the ground and excited states are inhomogeneously broadened sets of levels, which are symmetrical about the Fermi level. The behavior of the model parameters E_g and E_G (energy corresponding to the peak of the Gaussian distribution) and the plasma frequency with annealing temperature shows, for materials of both types, a substantial rise in the size and number of critical fluctuations with increasing temperature.     

Growth of a-C:H and a-C:H〈Cu〉 films produced by magnetron sputtering

Growth behavior of a-C:H and a-C:H〈Cu〉 films produced by the magnetron sputtering of a composite target consisting of graphite and copper plates in an argon-hydrogen atmosphere was studied by infrared spectroscopy, scanning electron microscopy, and ellipsometry. The introduction of copper into amorphous hydrogenated carbon films was shown to cause no marked changes in the carbon-hydrogen bonds in the matrix. In the a-C:H〈Cu〉 films ～2 µm thick, a thin uniform layer (～1000 Å) was found to adjoin the substrate; closer to the free surface, the layer acquires a columnar texture with columns oriented from the substrate to the surface. The results of ellipsometry measurements were analyzed in terms of a two-layer film model.     

Dry etching process for bulk finFET manufacturing

This paper describes a method to manufacture bulk fins for finFET. The bulk fins consist of two parts: the straight top of 125 nm height which is used as a fin and a sloped bottom of 200 nm one that facilitates the trench filling. The method is based on a conventional shallow trench isolation (STI) process flow with an additional α-C hard mask of 90 nm (with antireflective SiOC coating of 35 nm) on top of the STI stack (70 nm nitride on top of 8 nm oxide). The nitride layer and the top straight part of the fin is patterned using CH₂F₂/SF₆/N₂ chemistry and α-C as a mask, while the bottom sloped part is patterned using Cl₂/O₂/N₂ chemistry and the nitride layer as a mask. After the etching, the STI process flow remains almost unchanged.     

Isotropic Plasma Etching of SiO2 Films

The isotropic etching of SiO₂ with an SF₆–O₂ plasma is studied experimentally. It is shown that the key factors in the process are the total and partial pressures of SF₆ and O₂ and the RF power. A smoothed-down edge profile of contact windows is obtained if SF₆ and O₂ are mixed in a ratio of 1 : 10 to 1 : 5. The maximum etch rate is achieved at total pressures of 250 to 450 Pa.     

添加气体对TE N2激光器输出的影响

本文给出了在纯N2中添加SF6和He气对TEN2激光器3371Å输出影响的实验结果。实验结果表明,在纯N2中添加少量SF6,可使激光输出增加一倍,而添加2～3倍He气,可提高输出功率30%～7倍。本文研究艺了添加He气对混合气体电子温度、电子密度和电子能量分布的影响,从而合理地解释了加He气可以提高输出功率这一实验结果。     

Deep dry etching of borosilicate glass using SF6 and SF6/Ar inductively coupled plasmas

Deep reactive ion etching (DRIE) of borosilicate glass was carried out using SF₆ and SF₆/Ar plasmas in an inductively coupled plasma (ICP) reactor. Electroplated Ni on Cu (≅50 nm)/Cr (≅100 nm)/glass structure using patterned SU-8 photoresist mask with a line spacing of 12-15 μm was used as a hard-mask for plasma etching. Plasma etching of borosilicate glass was performed by varying the various process parameters such as the gas chemistry, the gas flow ratio, the top electrode power, and the dc self-bias voltage (V_dc). In the case of using SF₆ gas only, the profiles of the etched channel showed the undercut below the Ni hard-mask due to a chemical etching and the microtrenching at the bottom of the etched channel. An optimized process using the SF₆ plasmas showed the glass etch rate of ≅750 nm/min. The addition of the Ar gas to the SF₆ gas removed the undercut and microtrenching but decreased the etch rate to ≅540 nm/min. The increasing and decreasing time-dependent etch rates with the etch depth in the SF₆ (200 sccm) and SF₆(60%)/Ar(40%) plasmas, respectively, were ascribed to the different ion-to-neutral flux ratios leading to the different etch process regime.     

A preliminary study of SF6 based inductively coupled plasma etching techniques for beta gallium trioxide thin film

Beta phase Gallium trioxide (β-Ga₂O₃) thin film was grown by metal organic chemical vapor deposition technology. Mixture gases of SF₆ and Ar were used for dry etching of β-Ga₂O₃ thin film by inductively coupled plasma (ICP). The effect of SF₆/Ar (etching gas) ratio on etch rate and film etching damage was studied. The etching rate and surface roughness were measured using F20-UN thin film analyzer and atomic force microscopy showing that the etching rate in the range between 30 nm/min and 35 nm/min with an improved surface roughness was obtained when the reactive mixed gas of SF₆/Ar was used. The analysis of X-ray diffraction and transmission spectra further confirmed the non-destructive crystal quality. This work demonstrates that the properly proportioned mixture gases of SF₆/Ar is suitable for the dry etching of β-Ga₂O₃ thin film by ICP and can serve as a guide for future β-Ga₂O₃ device processing.     

Possibility of the use of intermediate carbidsiliconoxide nanolayers on polydiamond substrates for gallium nitride layers epitaxy

The results of using carbidsiliconoxide (a-C:SiO1_.5) films with a thickness of 30–60 nm, produced by the pyrolysis annealing of oligomethylsilseskvioksana (CH₃–SiO_1.5)_n with cyclolinear (staircased) molecular structure, as intermediate films in the hydride vapor phase epitaxy of gallium nitride on polycrystalline CVD-diamond substrates are presented. In the pyrolysis annealing of (CH₃–SiO_1.5)_n films in an atmosphere of nitrogen at a temperature of 1060°C, methyl radicals are carbonized to yield carbon atoms chemically bound to silicon. In turn, these atoms form a SiC monolayer on the surface of a-C:SiO_1.5 films via covalent bonding with silicon. It is shown that GaN islands grow on such an intermediate layer on CVD-polydiamond substrates in the process of hydride vapor phase epitaxy in a vertical reactor from the GaCl–NH₃–N₂ gas mixture.     

a-SiOx:H passivation layers for Cz-Si wafer deposited by hot wire chemical vapor deposition

In order to get the high photoelectric conversion efficiency a-Si:H/c-Si solar cells, high quality intrinsic hydrogenated passivation layer between the a-Si:H emitter layer and the c-Si wafer is necessary. In this work, hot wire chemical vapor deposition (HWCVD) is used to deposite intrinsic oxygen-doped hydrogenated amorphous silicon (a-SiO_x:H) and hydrogenated amorphous silicon (a-Si:H) films as the intrinsic passivation layer for a-Si:H/c-Si solar cells. The passivation effect of the films on the c-Si surface is shown by the effective lifetime of the samples that bifacial covered by the films with same deposition parameters, tested by QSSPC method. The imaginary part of dielectric constant (ε₂) and bonds structure of the layers are analyzed by Spectroscopic Ellipsometry(SE) and Fourier Transfom Infrared Spectroscopy(FTIR). It is concluded that: (1) HWCVD method can be used to make a-SiO_x:H films as the passivation layer for a-Si:H/c-Si cells and the oxidation of the filament can be overcome by optimizing the deposition parameters. In our experiments, the lowest surface recombination velocity of the c-Si wafer is 3.0 cm/s after a-SiO_x:H films passivation. (2) Oxygen-doping in the amorphous silicon layers can increase H content and the band-gap of films, similar as the phenomenon of the films deposited by PECVD.     

Effect of thermal treatment on structure and properties of a-Si:H films obtained by cyclic deposition

The effect of thermal treatment in a vacuum on the structure and properties of amorphous hydrogenated silicon (a-Si:H) films obtained by cyclic deposition with intermediate annealing in hydrogen plasma was studied. a-Si:H films deposited under optimal conditions are characterized by the nonuniform distribution of the nanocrystalline phase (<1 vol %) across the film thickness and have the optical gap E _g=1.85 eV, the activation energy of conductivity E _a =0.91 eV, and a high photosensitivity (σ_ph/σ_d≈10⁷ under illumination of 100 mW/cm² in the visible spectral range). Transmission electron microscopy studies demonstrated that thermal treatment in a vacuum leads to blurring of the initial layered structure of a-Si:H films and to a somewhat higher amount of nanocrystalline inclusions in the amorphous phase matrix. Thermal treatment above 350°C causes a dramatic increase in the dark conductivity, as well as the resulting decrease in the photosensitivity, of a-Si:H films.     

Properties of periodic α-Si:H/a-SiNx:H structures obtained by nitridization of amorphoussilicon layers

The kinetics of nitridization of a-Si:H layers, the properties of the structures that are formed and a-Si:H in them have been investigated. The changes occurring in the resistance of the a-Si:H layers in the course of nitridization are described in terms of the competition between doping, transport, and change in the thickness of the remaining a-Si:H layer. The experimental data on the band spectrum of superlattices with a-Si:H and a-SiN_x:H layer thicknesses ～35 Å and ～5 Å, respectively, are in agreement with calculations in a model of interacting quantum wells with m*=(0.36±0.1)m ₀. Comparison of the properties of superlattices obtained by deposition of successive layers and nitridization of the a-Si:H layers showed that the latter can have a higher “structural perfection.”     

Structure and properties of a-Si:H films grown by cyclic deposition

Amorphous hydrogenated silicon films obtained by cyclic deposition with intermediate annealing in hydrogen plasma were studied. a-Si:H films deposited under optimal conditions are photosensitive (photoconductivity to dark conductivity ratio σ_ph/σ_d is as high as 10⁷ under 20 mW cm^?2 illumination in the visible region of the spectrum) and have an optical gap (E _g ) and activation energy of conductivity (E _a ) of 1.85 and 0.91 eV, respectively. Electron microscopy studies revealed a clearly pronounced layered structure of a-Si:H films and the presence of nanocrystalline inclusions in the amorphous matrix.