Fine particle removal by a negatively-charged fine particle collector in silane plasma

To suppress inclusion of fine particles in amorphous silicon films, a negatively-charged fine particle (NFP) collector has been successfully installed in a silane plasma. Two modes of operation of the NFP collector biasing were examined: (i) turning on after the appearance of fine particles; and (ii) turning on from the very beginning of the plasma operation. While the former proved the effectiveness of the NFP collector in the removal of fine particles, apparently very small particles (<100 nm) removal in the latter reduced the degradation of the photo conductivity in deposited a-Si:H films by light soaking. This effect is accompanied by the increased density of SiH bonding, which can be related to the possible modification in the silicon networks in the amorphous film.     

Improve silane utilization for silicon thin film deposition at high rate

In order to investigate the silane utilization during silicon thin film deposition, one quadrupole mass spectrometer was used to monitor the partial pressure of silane during high pressure and high power deposition process. Relationship of silane consumption with silane concentration, excitation power and reaction pressure was investigated. The results show that increasing silane concentration leads to lower silane consumption. Increasing excitation power can improve the silane utilization, which is proved by higher deposition rate. However, when the power is higher than a certain value, much more power will consume by the transmission line and matching network. The power coupled into the plasma saturates to a certain value and then no more silane decomposes any more. In addition, the silane consumption decreased and then increased with increasing reaction pressure, which is related with the voltage of electrodes. These results could help to improve silane utilization for low cost production and better quality of film.     

Deposits obtained by photolysis of hexamethyldisilane by ArF excimer laser (SiC thin film preparation by ArF excimer laser chemical vapor deposition, Part 2)

Thin films have been prepared by decomposition of hexamethyldisilane (HMDS) by ArF excimer laser at the fixed laser fluence of 800 J m⁻² and the substrate temperatures from 300 to 673 K and have been characterized using X-ray diffraction (XRD), scanning electron microscope observation, IR reflection spectroscopy and X-ray photoelectron spectroscopy. The XRD patterns showed the formation of 3C-SiC films but it is suggested that the films obtained at lower substrate temperature include organic functional groups, which might be derived from gaseous reaction products. Hydrogen existing in the form of Si-CH₂-Si could be decreased by decreasing the partial pressures of HMDS.     

Epitaxy of In0.01Ga0.99As on Ge/offcut Si (001) virtual substrate

In_0.01Ga_0.99As thin films free of anti-phase domains were grown on 7° offcut Si (001) substrates using Ge as buffer layers. The Ge layers were grown by ultrahigh vacuum chemical vapor deposition using ‘low/high temperature’ two-step strategy, while the In_0.01Ga_0.99As layers were grown by metal-organic chemical vapor deposition. The etch-pit counting, cross-section and plane-view transmission electron microscopy, room temperature photoluminescence measurements are performed to study the dependence of In_0.01Ga_0.99As quality on the thickness of Ge buffer. The threading dislocation density of Ge layer was found to be inversely proportional to the square root of its thickness. The threading dislocation density of In_0.01Ga_0.99As on 300 nm thick Ge/offcut Si was about 4 × 10⁸ cm^− 2. Higher quality In_0.01Ga_0.99As can be obtained on thicker Ge/offcut Si virtual substrate. We found that the threading dislocations acted as non-radiative recombination centers and deteriorated the luminescence of In_0.01Ga_0.99As remarkably. Secondary ion mass spectrometry measurement indicated as low as 10¹⁶ cm^− 3 Ge unintended doping in In_0.01Ga_0.99As.     

Growth of 3C-SiC on 150-mm Si(100) substrates by alternating supply epitaxy at 1000 °C

To lower deposition temperature and reduce thermal mismatch induced stress, heteroepitaxial growth of single-crystalline 3C-SiC on 150 mm Si wafers was investigated at 1000 °C using alternating supply epitaxy. The growth was performed in a hot-wall low-pressure chemical vapor deposition reactor, with silane and acetylene being employed as precursors. To avoid contamination of Si substrate, the reactor was filled in with oxygen to grow silicon dioxide, and then this thin oxide layer was etched away by silane, followed by a carbonization step performed at 750 °C before the temperature was ramped up to 1000 °C to start the growth of SiC. Microstructure analyses demonstrated that single-crystalline 3C-SiC is epitaxially grown on Si substrate and the film quality is improved as thickness increases. The growth rate varied from 0.44 to 0.76 ± 0.02 nm/cycle by adjusting the supply volume of SiH₄ and C₂H₂. The thickness nonuniformity across wafer was controlled with ± 1%. For a prime grade 150 mm virgin Si(100) wafer, the bow increased from 2.1 to 3.1 μm after 960 nm SiC film was deposited. The SiC films are naturally n type conductivity as characterized by the hot-probe technique.     

超长单晶硅纳米丝的化学气相沉积法制备

采用化学气相沉积法在镀金硅片上制备出了大量直径均匀、长度大于100肿的单晶纳米硅丝。采用场发射扫描电镜（FESEM）、能谱分析（EDX）、透射电镜（TEM）和拉曼光谱（Rarnan）对样品进行了表征和分析，并对超长纳米硅丝的生长机理进行了讨论。     

Effect of layer thickness on structural quality of Ge epilayers grown directly on Si(001)

A study of Ge epilayer growth directly on a Si(001) substrate is presented, following the two temperature Ge layer method. In an attempt to minimize the overall thickness while maintaining a good quality Ge epilayer, we have investigated the effect of varying the thickness of both the low and high temperature Ge layers, grown at 400 °C and 670 °C, respectively, by reduced pressure chemical vapor deposition. We find that the surface of the low temperature (LT) seed layer has a threading dislocation density (TDD) to the order of 10¹¹ cm^− 2. On increasing the LT layer thickness from 30 nm to 150 nm this TDD decreases by a factor of 2, while its roughness doubles and degree of relaxation increases from 82% to 96%. Growth of the high temperature (HT) layer reduces the TDD level to around 10⁸ cm^− 2, which is also shown to decrease with increasing layer thickness. Both the surface roughness and degree of relaxation reach stable values for which increasing the thickness beyond about 700 nm has no effect. Finally, annealing the HT layer is shown to reduce the TDD, without affecting the degree of relaxation. However, unless a thick structure is used the surface roughness increases significantly on annealing.     

AlGaN/GaN-heterostructures on (111) 3C-SiC/Si pseudo substrates for high frequency applications

We present the realization of high electron mobility transistors (HEMTs) based on AlGaN/GaN heterostructures, which were grown on silicon substrates using an ultrathin SiC transition layer. The growth of AlGaN/GaN heterostructures on 3C-SiC(111)/Si(111) was performed using metalorganic chemical vapour deposition (MOCVD). The 3C-SiC(111) transition layer was realized by low pressure CVD and prevented Ga-induced meltback etching and Si-outdiffusion in the subsequent MOCVD growth. The two-dimensional electron gas (2DEG) formed at the AlGaN/GaN interface showed an electron sheet density of 1.5 × 10¹³ cm^− 3 and a mobility of 870 cm²/Vs. The HEMTs DC and RF characteristics were analysed and showed a peak cut-off frequency as high as 29 GHz for a 250 nm gate length.     

Adsorption of Ni on Si(1 0 0) surface

The chemisorption of one monolayer Ni atoms on ideal Si(1 0 0) surface is studied by using the self-consistent tight binding linear muffin-tin orbital method. Energies of adsorption systems of Ni atoms on different sites are calculated. It is found that Ni atoms can adsorb at fourfold site above the surface and bridge site below the surface. The adsorption of Ni atoms can readily diffuse and penetrate into the subsurface. A Ni, Si mixed layer might exist at the Ni-Si(1 0 0) interface. The layer projected density states are calculated and compared with that of the clean surface. The charge transfers are also investigated.     

Growth of 3C-SiC on Si(111) using the four-step non-cooling process

A modified four-step method was applied to grow a 3C-SiC thin film of high quality on the off-axis 1.5° Si(111) substrate in a mixed gas of C₃H₈, SiH₄ and H₂ using low pressure chemical vapor deposition. The modified four-step method adds a diffusion step after the carburization step and removes the cooling from the traditional three-step method (clean, carburization, and growth). The X-ray intensity of the 3C-SiC(111) peak is enhanced from 5 × 10⁴ counts/s (the modified three steps) to 1.1 × 10⁵ counts/s (the modified four steps). The better crystal quality of 3C-SiC is confirmed by the X-ray rocking curves of 3C-SiC(111). 3C-SiC is epitaxially grown on Si(111) supported by the selected area electron diffraction patterns taken at the 3C-SiC/Si(111) interface. Some {111} stacking faults and twins appear inside the 3C-SiC, which may result from the stress induced in the 3C-SiC thin film due to lattice mismatch. The diffusion step plays roles in enhancing the formation of Si-C bonds and in reducing the void density at the 3C-SiC/Si(111) interface.     

Fluidized bed micro-machining and HFCVD of diamond films onto Co-cemented tungsten carbide (WC-Co) hardmetal slabs

The effect of fluidized bed (FB) treatment upon hot filament chemical vapor deposition (HFCVD) of polycrystalline diamond films onto WC-Co hardmetal substrates was investigated. Several scenarios to make the substrates ready for HFCVD were, comparatively, evaluated and the resulting diamond films were examined in terms of their morphology and adhesion. The diamond grain density was measured by scanning electron microscopy. The adhesion of continuous diamond film to substrate was evaluated by the reciprocal of the slope of crack radius-indentation load functions. Surface binder dissolution followed by FB treatment (PF pretreatment) allowed very high diamond nucleation density and smaller grain size. The adhesion of films grown on PF pretreated substrates was found to be very close to that of films deposited on hardmetal slabs pretreated by Murakami's reagent followed by Co etching with Caro's acid and seeded with diamond suspension in an ultrasonic vessel (MPS pretreatment). However, diamond coatings on MPS pretreated samples exhibited a rougher surface morphology as a result of both lower diamond nucleation density and larger substrate surface roughening by Murakami's etching. Based upon experimental findings, our newly developed PF pretreatment was found to be a very promising technique in substrates conditioning as well as in promoting adherent, uniform and smooth diamond coatings onto hardmetal tools and wear parts.     

Faceting and nanostructure effects in Si and SiGe epitaxy

Epitaxy in Si technologies has to be integrated in the flow of fabrication; in most cases, it has to be selective and deposition takes place in extremely small patterns.In a first part, Si or SiGe epitaxy faceting is presented and discussed. Today, the global view is that, at first order, faceting is a kinetic phenomenon, controlled by deposition kinetic anisotropies. On the contrary, in a second part we show that highly faceted structures tend to decrease their surface energy by thermal rounding and that this phenomenon is very important when considering very small (20-40 nm) patterns.The main part reports on the combination of faceting with small size effects. Experiments consist in depositing Si_0.72Ge_0.28 selectively in very narrow (35-80 nm) lines oriented either along < 110 > or < 100 > crystal axis on (100) Si wafers. Preliminary observations clearly demonstrate an important {100} faceting that is often not observed or reported in literature. Our results also evaluate the lateral overgrowth of selective epitaxies. < 110 >-oriented lines lead to a certain lateral epitaxial overgrowth that is limited by {111} facets whereas epitaxies in < 100 > lines present a much larger (> 2 times) overgrowth bordered by {100} facets.Finally, we demonstrate that the edge effects have to be taken into account. Firstly, the amount of epitaxial material deposited in narrow lines depends on the line orientation, and then we propose the concept of “anisotropic loading effect”. Secondly, we found that deposition rates in small patterns are not constant with time. This corresponds to “time-nonlinear loading effects” that were never conceptualized in literature.     

Ge组分渐变的Si1-x-yGexCy薄膜的制备

用化学气相淀积方法在Si（100）衬底上外延生长了Ge组分最高约0．40的组分渐变的Si1-x-yGexCy合金薄膜,研究了生长温度等工艺参数的影响．结果表明,生长温度和C2H4分压的提高均导致薄膜中碳组分的增加和合金薄膜晶格常数的减小,这表明外延薄膜中的C主要以替位式存在．C掺入量的变化可有效地调节薄膜的禁带宽度,而提高生长温度有助于改善Si1-x-yGexCy薄膜的的晶体质量．组分渐变的Si1-x-yGexCy合金薄膜包括由因衬底中Si原子扩散至表面与GeH4．C2H4反应而生成的Ni1-x-yGexCy外延层和由Ni1-x-yGexCy外延层中Ge原子向衬底方向扩散而形成的Ni1-xGex层．     

Growth of long aligned carbon nanotubes on amorphous hydrogenated silicon nitride by thermal chemical vapor deposition

Vertically aligned long carbon nanotubes in the range of 80-100 µm have been synthesized on amorphous hydrogenated silicon nitride (a-SiN_x:H) coated silicon substrate by thermal chemical vapor deposition of ferrocene and xylene. It is observed that high temperature annealing in oxygen ambient results in formation of crystalline silicon dioxide in the matrix of amorphous silicon nitride due to out diffusion of hydrogen. It is suggested that active sites created on silicon dioxide and a-SiN_x:H clusters provide mechanical support for the alignment of long carbon nanotubes. It is proposed that a thin layer of a-SiN_x:H prevents silicide formation between the catalyst (Fe) and silicon thus lengthening the catalyst life.     

Preparation and room temperature photoluminescence characterization of PbS/Si(100) thin films

PbS nanoparticles and smooth nanocrystalline thin films (nc-PbS) were prepared by chemical precipitation from aqueous solutions. Polyethylene oxide and isopropyl alcohol were used as additives in the aqueous solution, which results in the enhancement of the blue luminescence of PbS thin films. The introduction of isopropyl reduced the grain size and increases the optical gap of the PbS particles. The size of PbS particles was estimated to be ~ 3.5 nm. The broad emission bands exhibited were composed by a multiple overlapping peaks. The photoluminescence (PL) intensity was significantly influenced by the excitation wavelength. Indeed, intense blue luminescence was obtained under 230 nm compared to that obtained under 325 nm excitation wavelength. The PL emission from PbS nanoparticles was less intense than the luminescence of PbS thin films. The high PL intensity of the thin films was attributed to the lower density of defects introduced in the thin films during the chemical bath deposition growth process compared the defects density of PbS powder.     

Mechanism of immersion deposition of Ni-P films on Si(100) in an aqueous alkaline solution containing sodium hypophosphite

The immersion deposition of Ni-P films on Si(100) surface without prior activation by metallic catalytic was carried out in an aqueous alkaline solution containing sodium hypophosphite. The deposition mechanism was investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Two stages of deposition were observed when the Si substrate was immersed in the deposition solution at an appropriate pH value. In the first stage, crystalline Ni nanoparticles were formed through a galvanic displacement reaction, which accompanied the oxidation of Si substrate without involving the reducing agent, NaH₂PO₂. Experimental results indicate that the oxidation states of Si⁴⁺ and Si³⁺ exist in the oxide layer. The amount of suboxide, Si³⁺, increased with deposition time, and the oxide layer became activated. In the second stage, amorphous Ni-P was deposited on this activation oxide layer in a process involving the reducing agent. The microscopic structure of the deposition film, observed by TEM cross-sectional analysis, verifies the mechanism of deposition suggested in this study.