Recent applications of spectroscopie phase modulated ellipsometry, from 0.25 to 11 μm, to study the growth of plasma deposited thin film semiconductors like amorphous (a-Si:H) silicon are reviewed. The high sensitivity of this technique is emphasized. In the infrared (IR), the hydrogen incorporation during a-Si:H growth can be precisely investigated. Photoelectronic quality a-Si:H films grow beneath a hydrogen rich overlayer (a few monolayers thick) containing SiH2. the hydrogen being bonded as SiH in the bulk material. In the ultraviolet (UV) range, the ability of kinetic ellipsometry, with fast time resolution, to study interfaces formation is illustrated. Examples of sharp interfaces are presented. In the case of amorphous silicon-silicon nitride structures, it is shown that an inversion of the deposition sequence of the various layers can lead to a graded transition. A detailed analysis of a growth process involving a chemical reaction with the substrate is illustrated in the case the a-Si:H / Pd interface.

The use of plasma excitation frequencies f in the VHF band (30–300 MHz), and particularly of f=70 MHz, for the high-rate deposition of amorphous hydrogenated silicon (a-Si:H) is described. Deposition rates, using monosilane (SiH4) as source gas, are thereby increased roughly five fold to over 10 Å/s as compared with the conventional case of RF plasma enhanced chemical vapour deposition with f=13.56 MHz. This may possibly be attributed to an enhancement in the high-energy tail of the electron energy distribution function (EEDF) of the plasma. Thereby, no noticeable deterioration in film properties is found.

Characteristics of VHF-deposited a-Si:H films are extensively reported, including properties like microstructure, hydrogen effusion behaviour and its low internal mechanical stress. High quality hydrogenated microcrystalline silicon (μc-Si:H) can be deposited at low substrate temperature and low plasma power densities thanks to VHF glow discharge. This can be linked to a reduction in sheath potential and to the energy of the ions arriving at the growing surface. Thereafter, use of VHF plasma in applications such as 100 μm thick a-Si:H layer for particle detectors and powder-free deposition of solar cells with efficiencies over 8% are reported.

We have applied real time spectroscopie ellipsometry (2.5≤hv≤4.5 eV) to investigate in situ hydrogenation of thin film a-Si:H prepared by plasma-enhanced CVD. When a-Si:H is exposed to atomic H generated by a tungsten filament heated in H2, as many as ∼5×1021 Si-Si bonds/cm3 can be converted to Si-H bonds in the top ∼200 Å of the film. We have determined the spectroscopie characteristics of Si-H bonds from optical to near-uv photon energies through an analysis of the changes in the dielectric function of the near-surface of the film upon hydrogenation. The conversion of Si-Si bonds to Si-H bonds is identified as reaction-limited to a depth of ∼500 Å. We find that a surface oxide a few monolayers in thickness acts as an effective diffusion barrier to H-incorporation.

Using a “macro-trench” technique, the surface reaction probabilities β of the a-Si:H growth precursors for remote hollow cathode silane discharge (HC) and reactive magnetron sputter deposition (RMS) are measured. Both deposition methods produce state of the art photo-electronic quality a-Si:H. For the HC case, β= 0.28 ± 0.05, whereas for RMS deposition β ≈ 0.97 ± 0.05. We conclude that β is not universally correlated with film quality, and discuss mitigating factors present in RMS deposition that permit high quality film to be deposited despite the high film precursor reactivity.

The idea of surface mobility of growth precursors determined material quality has been exploited by raising the substrate temperature above the conventional 250°C and the ensuing thermal depletion of the surface hydrogen coverage compensated by increasing the precursor flux (deposition rate) to prepare ultra low defect density hydrogenated amorphous silicon.

A-Si films with a constant optical band gap were prepared by plasma CVD from silane at deposition rates up to 17 Å/s under controllably varied conditons and characterized by a number of techniques. Photodegradation under AM1 simulator has been done for 50 hours and for 4–17 hours under 2 Watt/cm2 dye laser illumination at a wavelength corresponding to an absorption coefficient of about 104 cm-1 up to saturation. Samples with different initial value of σ(d) and σ(ph) show different rates of photodegra-dation, but they reach very similar saturation values. The fast photode-gradation with the dye laser is equivalent to a long term (several thousand hours) photodegradation under AM1. The AMI photodegradation for 50 to 100 hours does not yield any reliable measure of the stability of the films. The best films, which were prepared at a high deposition temperature show a low saturation defect density of about 5·1016 cm-3 (CPM-data).

We have studied the effect of RF power on the properties of Si thin films prepared by a conventional plasma and remote plasma(RP)- CVD. The structure of the Si film changes from amorphous to crystalline with increasing RF power in RP-CVD. However, the structure of Si film deposited by P-CVD remains amorphous with increasing RF power. The relaxation of Si atoms by means of chemical annealing of He metastable atoms gives rise to the formation of macrocrystalline structure at the high RF powers.

We have studied a-Si:H prepared by alternating plasma deposition with atomic H treatments performed with a heated W filament. Real time spectroscopie ellipsometry provides the evolution of film thickness, optical gap, and a measure of the fraction of Si-Si bonds broken in the near-surface (200 Å) during H-exposure of single films. This information guided us to the desired parameters for the H-treatments. Here, we concentrate on a weak hydrogenation regime characterized by minimal etching, a higher H content by 2 at.%, and a larger optical gap by 0.02 eV for the growth/hydrogenation structures in comparison to continuously deposited control samples. This new material has shown an improvement in the defect density in the light-soaked state in comparison to the control samples. This may result from stabilization of the Si structure due to an increase in the H chemical potential in the a-Si:H.

Hydrogenated amorphous silicon (a-Si:H) with Tauc's optical bandgap (Eopt) between 1.7 and 2.1 eV was deposited at room-temperature by concentric-electrode plasma-enhanced chemical vapor deposition (CE-PECVD). The variation of Eopt was achieved by varying the flow of silane, without hydrogen dilution. The increase in Eopt results from an increase in the hydrogen concentration in the film from 7 to 15%. The photoconductivity shows a monotonie decrease with increasing Eopt and is 10'-7 Scnr-1 for the 2.1 eV sample. The Urbach energy (Eu) is observed to increase sharply with increasing Eopt, while the subgap defect (Ns) density remains approximately constant.

It was found that hydrogen dilution in the SiH4/H2 mixture tend to show a sharp line-shape in the NMR spectra as the substrate temperature is higher than 300 °C. The hydrogen-atom-treatment method also produces the same effect at a lower substrate temperature about 250°C. The Raman scattering spectra show that the hydrogen-atom-treatment creates the microcrystalline structure at a temperature higher than 250°C while hydrogen dilution produces mixed phases containing amorphous phase and a small quantity of micro-crystalline phase. Together with the optical bandgap narrowing, the increase of the dark conductivity and the reduction of photo-to-dark conductivity ratio, these samples indicate that with more hydrogen incorporation during deposition and plasma hydrogen treatment, these films possess a much compact structure, and the degree of crystallinity of hydrogenated silicon film was found to be systematically changed.

In the present work the change of the opto-electronic properties of intrinsic a-Si:H films as a function of their deposition temperature is investigated by transient photoconductivity measurements with the contactless Time Resolved Microwave Conductivity (TRMC) technique. As well in-situ as ex-situ TRMC-measurements will be presented. It is concluded that the electron drift mobility for a-Si:H films deposited in the temperature range between 200° C and 300° C does not depend on the deposition temperature. For temperatures below 200° C the electron drift mobility decreases with decreasing deposition temperature. Annealing of opto-electronic properties of intrinsic a-Si:H films deposited at lower temperatures is observed.

In this study, amorphous silicon and polycrystalline silicon films were implanted with arsenic and subjected to varied low temperature (<900°C) anneal conditions and characterized using TEM. The microstructure is of interest for later correlation with electrical measurements. The amorphous deposition produces larger, more irregular grains with more strain than does the polysilicon deposition for a single-step rapid thermal anneal (RTA) cycle. This can be explained by the number of critical nucleii and the rate of grain growth. The sheet resistivity, as measured by four-point probe, correlates to the deposition conditions. A two-stage anneal makes the grains less irregular by reducing the roughness of the grains and decreasing the strain in the grains. For a given deposition condition, the final microstructure is most strongly influenced by the first anneal. The second anneal produces no clear change in grain size. 800°C anneals result in larger grains than 900°C anneals. This is explained by the presence of less critical nucleii for 800°C anneals. In comparing short and long durations of RTA, the short duration produced slightly larger grains than the long duration RTA due to greater nucleation in the longer RTA wafers. In the case of RTA versus furnace anneals, RTA produces larger, more irregular grains, with more strain in the grains. A model in terms of the size of critical nucleii is used to explain the difference.

The results of the investigation of doping by B and P ion implantation into LPCVD amorphous silicon films in the range from 2*1015 to 2*1021 atoms/cm3 are presented. The room temperature conductivity increases to 10-2 Ω-1 cm-1 and to 10-2 Ω-1 cm-1 for the highest B and P doping, respectively. The subsequent hydrogenation (2.5 and 5 at%) by ion implantation increases the doping efficiency for P doping. For B doping efficiency increases at the low and decreases for the high doping range. The results of conductivity measurements vs temperature of doped and hydrogenated films are presented.

Ion implantation of boron and phosphorus in device quality a-SixC1-x:H films deposited by Ultra High Vacuum Plasma Enhanced Chemical Vapor Deposition (UHV PECVD) has been performed. The effects of damage and of damage recovering after annealing were investigated by optical absorption, electrical conductivity and infrared (IR) spectroscopy measurements. It is found that samples doped by phosphorus implantation can have dark conductivities as high as those obtained on samples doped with boron, either by ion implantation or gas phase.

Fabrication of SiGe heterojunction bipolar transistors (HBTs) requires a low thermal budget to avoid relaxation of the strained SiGe base layer. Ion implantation is one of the most widely used techniques to achieve contacts. However, due to thermal budget constraints, low temperature rapid thermal annealing (RTA) cycles to activate these implants are insufficient to anneal out all of the implant damage. Polysilicon contacts provide an alternative to ion implantation, but are typically annealed at high temperatures (>950°C) to achieve low sheet resistivity. In this study, amorphous silicon and polycrystalline silicon films were implanted with boron, arsenic, or phosphorus and RTA'd at temperatures from 800°C to 950°C and compared to single crystal silicon with identical implants and RTA cycles. The films were characterized using four-point probe, Hall measurements, TEM (transmission electron microscopy), and SIMS (secondary-ion mass-spectrometry). TEM analysis shows that the amorphous deposition produces larger grains upon RTA due to more rapid grain growth than the polycrystalline deposition. The sheet resistance for the amorphous deposited films is much lower than that of the polycrystalline deposition for all implant conditions. Activations of the implants indicate that the arsenic and phosphorus segregate to the grain boundaries, while the boron does not. The segregation is more significant for the polycrystalline films than for the amorphous films and can be explained by the grain boundary area. For contacts to the SiGe HBT, which requires a low thermal budget, an amorphous deposited silicon film is advantageous over a polycrystalline film at low annealing temperatures because it has lower sheet resistance, less segregation to the grain boundaries, and produces larger grains.

The conductivity control of amorphous hydrogenated silicon (a-Si:H) by incorporation of electron donors or acceptors is prerequisite for the application of these layers in devices. The doping sources B2H6 and PH3 which are usually highly toxic are substituted by not dangerous boron and phosphorus liquid sources based on hydro-carbons. The avoidance of gas cylinders and expensive safety measure techniques is another advantage of these liquids.

In this paper we have studied the influence of boron, phosphorus and carbon on the electrical, photoelectrical and optical properties. The layers were produced in a capacitively coupled reactor in a silan-doping gas mixture. The maximum of the dark conductivities (300K) of the p- and n-type a-SiC.,:H layers was 10-5 and 103 (Ωcm)-1, respectively, the activation energys decreases to 0.4 and 0.2 eV respectively. With a high quantity within the range of doping gas in the mixture, the carbon determines the layer properties. At a gas mixture ratio of 1:1 ( silan: doping gas) the optical gap expands to 2.7 eV and the dark conductivity decreases below 10∼13 (Ωcm)-1.

Explosive crystallization of amorphous silicon (a-Si) during pulsed laser annealing occurs at an intermediate laser energy fluence above the threshold for surface melting. Mediated by a molten silicon layer which is undercooled with respect to crystalline silicon and above the melting point of a-Si, the crystallization interface drives down into the sample, sustaining itself due to the difference in the latent heats of the crystalline and amorphous silicon. Explosive crystallization has been the subject of numerous studies which have for the most part been restricted to ion implanted amorphized layers in silicon bulk samples. In this study we examine the crystallization kinetics of vapor deposited thin films of hydrogenated a-Si for films of differing hydrogen content and substrate temperature. We reevaluate current models of interface and nucleation kinetics qualitatively in light of these results. The fundamental physical mechanisms in these non-equilibrium phase transitions during pulsed laser annealing are discussed.

Pulsed laser-induced melting followed by crystallization and amorphization were studied on silicon-germanium alloy (SiGe) films. Although amorphization was achieved on SiGe films, it was not observed in pure Ge films. Crystalline nucleation density in homogeneous solidification increased as Ge concentration increased. It was 1×1024m-3for Si0.22Ge0.78 films, while it was 4×1022m-3 for pUre si films. Electrical conductivity of laser polycrystallized films increased as Ge concentration increased. It had a maximum of 1 S/cm when Ge concentration was 0.78. This high electrical conductivity would be brought about by the increase of carrier mobility as well as the reduction of the band gap.

A recent report on pulsed laser crystallization of a-Si thin films concluded that substrate bias temperatures up to 400°C in combination with laser fluences below 500 mJ/cm2 had little effect on grain size and transport properties. The current report describes the effects of substrate bias temperature up to 500°C and laser fluence up to 540 mJ/cm2 on grain size, mobility and Si (111) x-ray peak intensities. Results indicate that substrate bias temperatures above 400°C, in combination with high laser shot densities and large laser beam spot energies (> 500 mJ/cm2), are a factor in Improving these film properties.

The Au-induced crystallization of a-Si:H has been studied by evaporating Au films of different thicknesses onto intrinsic glow discharge deposited a-Si:H layers. The presence of a sharp peak in the Raman spectra (FWHM≈9 cm-1, ω516 cm-1) of samples with a Au thickness larger than 2 nm, which have been annealed in vacuum at 400K≤T≤600K, indicate that the crystallites have approximately the same size (6nm) regardless of the annealing conditions. An investigation of crystallization versus Au-film thickness revealed, that the total crystallized volume is increasing with Au thickness, and furthermore a saturation of the crystallized volume takes place, most probably due to an exhaustion of the Au reservoir. The increase of crystallization rate with temperature follows an Arrhenius-like dependence with an activation energy of 1.1 eV. Changes in hydrogen content as a consequence of the crystallization have been monitored by H-effusion measurements: Au-coated a-Si:H samples show a strong H2 evolution at temperatures substantially lower than uncoated ones.