We characterized a-Si:H films deposited by the electron cyclotron resonance (ECR) microwave plasma-enhanced CVD technique with the purpose of comparing ECR film quality widi that of films deposited by the rf plasma-enhanced CVD method. These ECR films were deposited in the 1–10 mT pressure region under a variety of growth conditions. Our investigations reveal the following typical properties for intrinsic ECR-deposited a-Si:H: (1) high photosensitivity as indicated by a light-to-dark DC conductivity ratio of up to 2×106, (2) a Tauc gap in the range of 1.75–1.85 eV, (3) an Urbach slope of 45–60 meV as determined by CPM and (4) an integrated deep defect density of 0.5–2×1016 cm-3 with Ec - Ef = 0.74–0.87 eV as determined by drive level profiling and junction capacitance vs. temperature scans. Variations of these quantities with deposition temperature, hydrogen dilution and magnetic field profile are discussed. Our results indicate that ECR-deposited a-Si:H is of comparable quality to a-Si:H deposited by the rf plasma glow discharge technique. ECR deposition conditions for a highly conductive type of a-Si:H film also are discussed. This material, while only slightly photosensitive and possessing an Urbach slope of over 100 meV, has a light DC conductivity of 3×10-4 (Ωcm)-1. Boron doping of this material produces a conductivity of 5×10-2 (Ωcm)-1.

Optical, electronic and structural properties of a-Si:H samples grown by Low Pressure Chemical Vapor Deposition have been investigated by means of IR spectroscopy, Raman scattering and Photothermal Deflection Spectros-copy.

Samples grown at different positions along the tube show very different properties that can be related to the amount of H and to the nature of the Si-H bonds.

The most important parameters governing the thermally excited growth of a-Si:H are presented and discussed.

A-SiGe: H film properties with a low impurity concentration were investigated using a super chamber in the range of Ge content of 0% to 36%. These a-SiGe films can maintain a high photosensitivity of about 106 for Ge content up to 13%, which is comparable to high-quality a~Si films. It was found that impurity incorporation deteriorates optoelectronic properties in the range of a small amount of Ge content, and film rigidity in the range of a large amount of Ge content. Using high-quality a-SiGe films with a low impurity concentration in solar cells, the highest conversion efficiency of 3.15% was obtained for an a-SiGe single-junction cell under red light (AM-1.5, 100mW/cm2 light through the optical filter, in which the wavelength of transmitted light is longer than 650nm). A stacked cell of a-Si/a-Si/a-SiGe has a conversion efficiency of 11.9%.

The uses of liquid sources such as tertiarybutylphosphine (TBP) for n-type doping in hydrogenated amorphous silicon (a-Si:H) and ditertiarybutylsilane (DTBS) and n-butylsilane (NBS) for hydrogenated amorphous silicon-carbon alloys (a-SiC:H) are described. A rf glow discharge process is employed to produce the doped a-Si:H and a-SiC:H thin films. Tertiarybutylphosphine (TBP) may ultimately be preferred over phosphine because TBP is less toxic, less pyrophoric and safer to implement. The gross doping properties of a-Si:H doped with TBP are the same as those obtained with phosphine, but there are some differences. N-butylsilane (NBS) and DTBS have been used to produce wide band gap (E04 3 ≈ eV) a-SiC:H.

Gas-phase chemical reactions of interest for the deposition of amorphous silicon carbide in a remote hydrogen plasma reactor have been quantitatively characterized with electron spin resonance, and the deposition of a-SiC:H from silane and acetylene is demonstrated.

We use in situ multi-wavelength ellipsometry to study growth of hydrogenated amorphous silicon and crystalline silicon deposited by reactive DC magnetron sputtering. Crystal silicon covered with native oxide and oxide free crystal silicon are used as substrates. Deposition on c-Si/ox over a wide range of conditions yields amorphous films, and the growth proceeds with formation of small islands, regardless of hydrogen partial pressure. Growth on oxide free c-Si, on the other hand, is hydrogen dependent. Even at a low hydrogen pressure, a layer with mixed phase of c-Si and a-Si:H begin to appear near the c-Si substrate. This layer thickness and its c-Si fraction increase with hydrogen pressure. Bombardment of growing surface by energetic particles, both silicon and hydrogen species, appears to lead to the crystallization.

The effects of deposition conditions on the intrinsic stress in a-Si:H films deposited in a remote hydrogen plasma reactor are reported. The intrinsic stress is calculated from the change in substrate curvature induced by the a-Si:H film, as measured by the optical lever technique, and the results are compared with those for rf glow discharge deposited a-Si:H films.

We report here the first phase of our attempt to deposit “device-quality” a-Si:H films by glow discharge near room temperature (50 °C). We have found that, at a low rf power density (40 mW/cm2) and high hydrogen/silane ratios (≥ 2), film quality is not uniquely determined by the substrate temperature, Ts. The microstructure of our low hydrogen content films as revealed by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies is similar to that of “device-quality” films deposited at standard Ts. The next phase of our work is to ascertain whether or not similar IR and NMR characteristics between our low Ts films and the standard Ts films imply also similar opto-electronic properties.

Amorphous silicon selenium alloy films were prepared by plasma enhanced chemical vapor deposition with hydrogen dilution. The flow rate ratio of hydrogen to silane was about 8:1. Amorphous silicon selenium alloy was found to have an optical bandgap ranging from 1.7 eV to 2.0 eV depending on the selenium concentration in the films. The light to dark conductivity ratios of the alloy films are ∼ 104. The optical and electrical properties, Urbach tail energy and sub-bandgap photo response spectroscopy of the alloy film were investigated. The film quality of the alloy deposited with hydrogen dilution is greatly improved comparing to that of the alloy film deposited without hydrogen dilution. The electron spin resonance experiment shows that selenium atom is a good dangling bond terminator.

Thin films of an amorphous silicon-boron alloy with boron content 1–50 at.% have been deposited by low pressure chemical vapor deposition (LPCVD). The boron content and film thickness of the samples were controlled by regulating the ratio of diborane and silane gases during the deposition. It was observed that the crystallization of the amorphous alloy took place at higher temperatures as boron concentration was increased. After a thermal oxidation was performed, the stoichiometry of die resulting oxide layers on various samples was determined by the secondary ion mass spectrometry and Auger depth profile methods. While the threshold temperature for thermal oxidation was determined to be inversely proportional to the boron concentration, the oxidation rate showed a dramatic increase with boron content. In particular, an alloy containing 30% boron was readily oxidized at 500°C. Mechanisms for the enhancement of oxidation consistent with stoichiometric and spectroscopic properties of the oxide layers are discussed.

Doping of amorphous silicon (a-Si or a-Si:H) coated by a spin-on oxide film containing the dopant (phosphorus or boron) using an ArF excimer laser has been investigated as a function of laser fluence, number of pulses and dopant film thickness. From these results, it is found that the surface concentration and the junction depth vary with the number of pulses, and that the doping process is rate limiting. Sheet resistance lower than 10 kΩ/□ have been obtained. It is also shown that for a-Si:H films, laser irradiation produces exodiffusion of hydrogen from the molten layer resulting in rough surface. This one-step process seems suitable for polycrystalline silicon thin film transistors (TFT's) fabrication.

We present evidence that an independently applied dc bias voltage has a significant effect on the plasma deposition of amorphous hydrogenated silicon carbide. Deposition rates increase with either positive or negative dc voltages applied to the powered rf electrode. The microstructure of the films (as determined by infrared absorption) can be reduced by increasing the plasma potential (positive dc bias voltages). Negative dc biases, or excessively high positive biases, result in increased amounts of film microstructure. Film carbon content is increased when positive biases are applied, but the optical band gaps decrease suggesting increased amounts of graphitic bonding configurations. Negative biases do not change the carbon content of the films, but do increase both deposition rate and microstructure.

We have extended the remote PECVD process to the deposition of intrinsic and doped, amorphous and microcrystalline silicon, carbon alloy films, a-Si,C:H and μc-Si,C, respectively. The electrical and optical properties of a-Si,C:H deposited by remote PECVD are comparable to those of films deposited by the glow discharge or GD process. The degree of crystallinity in the μc-Si,C alloys, as determined from the relative intensities of crystalline and amorphous features in the Raman spectra, is lower than that of μc-Si films deposited under comparable deposition conditions. The Raman spectra indicate that the crystallites in the μc-Si,C alloys are Si, while the infrared measurements establish that the intervening amorphous component is an a-Si,C:H alloy.

High hydrogen content of ammonia/silane deposited silicon nitride films has been linked to instability in electronic devices such as MOSFET's MNOSFET's and TFT's. Fluorine has been proposed to help reduce the hydrogen content of these films. In this work, NF3 was used as a fluorinating agent. Optical and electrical properties were studied as a function of NF3 flow rate. A maximum optical gap of 5.3 eV was obtained with NF3 as compared to 3.2 eV without. The dielectric strength improved from 4 to 10 MV/cm with the addition of NF3. FTIR data show that the Si-N peak shifts to higher wave numbers and the Si-H peak drops below the detection limit with the addition of NF3. Also, the broad Si-N peak at 850 cm-1 is composed of many individual peaks which become discernable when a stainless steel screen is placed in front of the substrate. As the NF3 concentration is increased, a new peak at 1030–1060 cm-1 appears. This may be associated with a N-F vibration (1030 cm-1).

Amorphous hydrogenated silicon carbide has been studied extensively because of its properties as a wide bandgap material. However, a large amount of methane is needed to deposit the material. Also, the high carbon content of these films poses some problems. The addition of NF3 to the gas stream results in wide bandgap films with a substantial reduction in the required CH4 flow for deposition. Amorphous SiCx Ny :H:F films were prepared using rf glow discharge decomposition of silane, methane, and nitrogen trifluoride in a parallel-plate stainless steel reactor. Gas flow rate and power density were varied. For a gas mixture containing 6% NF3 and 78% CH4, FTIR measurements reveal a reduction in C-H peak heights at 2960 cm-1 and 2880 cm-1 with respect to the Si-H peak at 2080 cm-1 indicating a smaller carbon content in the film. The C-H peaks shift to higher wavenumbers with increasing NF3. The use of NF3 increases the bandgap from 2.6 to 3.14 eV while reducing the refractive index from 2.12. to 1.87. A maximum deposition rate of 625 A/min was achieved. This should be compared to the very low deposition rate of 18 A/min for comparable bandgap Si-C films deposited using 97% methane in silane. Increasing the deposition power density resulted in a larger bandgap and a smaller refractive index.

We have studied methods of improving glow-discharge-deposited a-Si1−x Gex :H alloys deposited using silane and germane gas mixtures. Material processing methods studied include (1) varying the substrate temperature from 170° to 280°C, (2) varying the process gas composition and pressure, (3) dilution of the feed gas by hydrogen, argon, or helium, (4) enhancing etching during deposition by adding small amounts of XeF2 vapor into the process gas, and (5) postdeposition annealing and/or hydrogenation.

We studied the layer by layer deposition technique of a-Si:H film, where the hydrogen radicals are exposed between the deposition of each layer. The effects of each layer thickness and hydrogen radical exposure time on the electrical and optical properties were studied. With the decrease of the each layer thickness, more hydrogen is involved in the network if the structure is still amorphous, but the hydrogen content is very small for microcrystal Si formed by long exposure to hydrogen radicals in between the depositions of thin layers.

The electronic and optical properties of device quality hydrogenated amorphous silicon (a-Si:H) films grown by electron cyclotron resonance (ECR) plasma deposition were studied together with in-situ plasma characteristics. Hydrogen and helium plasmas, excited by 50–250 watts of 2.45 GHz microwave power under ECR conditions, were used to decompose silane at 6 to 20 mtorr pressures during the deposition of a-Si:H films at a 297 C substrate temperature. Both the electron temperature and density, and ion flux are measured near the deposition surface using plane and cylindrical Langmuir probes. An attempt is made to correlate these plasma properties with the light and dark photoconductivity, optical gap, refractive index, and subband gap photoconductivity.

Amorphous silicon nitride films deposited from a gas mixture of SiH4 and N2 with a large flow of He have shown many interesting characteristics. The films show a wide variety of electrical, optical, and mechanical properties with varying amounts of SiH4 and N2. The effect of N2 flow rate on film composition in N2-SiH4 processes is quite different from that of NH3 flow in NH3-SiH4 processes. The films were characterized by measurements of (1) Si-H and N-H bond density and bonded hydrogen content, both from infrared absorption, (2) Si/N ratio, (3) refractive index, (4) film stress, and (5) wet chemical etch rate and (6) electrical properties including current-voltage (I-V) and capacitance-voltage (C-V). We find that adding helium to the PECVD process enhances the incorporation of nitrogen in the film and an optimized flow of SiH4 improves the electrical properties. Films with optimum electrical properties with minimum charge trapping are obtained with N/Si ratio close to 1.33. These films have a small amount of Si-H and N-H bonds, and a low etch rate (> 100 A/min) in aqueous HF solution. The properties of these low temperature (250°C) PECVD nitrides have many similarities with LPCVD nitrides. Compared with films deposited from SiH4, NH3 mixture, these films exhibit very low wet etch rates and much lower H contents, but greater hysteresis in C-V characteristics.

Boron doped a-SiC:H samples have been obtained both by gas phase doping during film growth and by using ion implantation. All the implanted samples were annealed under vacuum to remove the damage introduced by ion implantation and to produce a dopant diffusion. Physical properties deduced by optical, electrical and structural characterization of the two sets of samples have been compared. Ion implantation technique allows a better control of the dopant dose but increases the compositional disorder and the obtained conductivity values are one order of magnitude lower than those of gas doped samples.