Hot-wall Furnace Research Articles

Nanoparticles generated by combining hot wall and microwave plasma chemical vapor synthesis

ABSTRACTControlling the oxidation state of iron and the crystal structure of iron containing compounds is the key to improved materials such as iron oxide nanoparticles for cancer treatment or heterogeneous catalysis. Iron oxides contain iron in different oxidation states and form different phases for one valence state (α-Fe3+2O2-3, β- Fe3+2O-32, etc.). Chemical vapor synthesis (CVS) allows the reproducible production of pure nanocrystals with narrow size distribution where particle formation and growth take place in the gas phase. Through the controlled variation of synthesis parameters CVS enables the synthesis of diverse iron oxide phases. In this study the energy for the CVS process is supplied by a hot wall furnace and a microwave plasma. The advantage of an plasma reactor as the first CVS stage is the fast and complete precursor decomposition at low temperatures. This results in a larger process window for the hot wall reactor in the second stage. The nanoparticles are examined regarding their structure, surface and valence by XRD and TEM.

Highly sensitive photosensor based on in situ synthesized CdS nanowires

In this work, CdS nanowires were synthesized in situ on the finger electrodes of interdigitated Au-electrodes via pulsed-laser deposition (PLD, KrF excimer laser excited at 248nm) using a sintered CdS target at the center of a quartz tube in a hot-wall furnace. The photo-response characteristics of the in situ synthesized CdS nanowires such as sensitivity, reproducibility, and response according to the wavelength of the incident light were analyzed and compared to those of a CdS thin-film electrode. Photosensitivity enhancement was investigated following the deposition of a parylene film with anti-reflecting properties on the CdS nanowires.

Structural and optical properties of MoS2 layers grown by successive two-step chemical vapor deposition method

We have studied a successive two-step chemical vapor deposition (CVD) method to prepare large-scale MoS2 thin films using a horizontal hot wall furnace. The CVD growth was followed by evaporation of the MoO3 precursor on ~2.5×2.5cm2 SiO2/Si substrates in the first step and a temperature ramp for sulfurization as a second step. Synthesized films were systematically analyzed by various structural and optical measurements. Crystallinity of the synthesized MoS2 tri-layer films exhibited a typical 2H-MoS2 structure and uniformly covered the whole substrate. MoS2 field effect transistors were fabricated by using the obtained CVD-MoS2, and these showed n-type behavior with an on/off ratio of about 103.

Honeycomb arrays of carbon nanotubes in alumina templates for field emission based devices and electron sources

Field Emission (FE) properties of vertically aligned Carbon Nanotubes (CNTs) grown in a nanoporous anodic aluminium oxide (AAO) template have been investigated. A 50-μm-thick AAO template was fabricated by electrochemical techniques. The nanotubes were synthesized in a CVD quartz hot wall furnace using C 2H 2/N 2 mixtures as feeding gas. I–V measurements have been performed on samples after the nanotubes growth (type I samples) and after a partial Al 2O 3 removal (type II samples) in order to obtain segments of nanotubes protruding from the nanopores. The effects of the conditioning process and adsorbates release have been investigated. The emission curves have been analysed in the framework of the Fowler–Nordheim model. For the β factor enhancement, a different dependence on time has been evidenced for two types of investigated samples and has been tentatively correlated with materials modifications occurring under the HV polarisation (in case of type I samples) and with the damage induced by chemical etching (in case of type II samples). The values of emitted current density (up to 40 mA/cm 2) and the emission properties indicate that the proposed preparation methodology is suitable for the realization of robust and efficient CNT-based field emission devices and electron sources.

Optimization of GaN nucleation layer deposition conditions on sapphire substrates in HVPE system

The influence of deposition conditions of nucleation GaN layer on the properties of high-temperature GaN layer, grown on sapphire substrates, was investigated. The hydride vapor phase epitaxy (HVPE) three-section horizontal hot-wall furnace technique was applied. Various temperatures, HCl flows and time intervals of nucleation layer growth were utilized. Based on previous studies the following experimental conditions were selected: temperature was kept at 450 or 570 °C, and HCl flows were 8 or 10 sccm/min. The duration of nucleation layer deposition was 5, 7 and 9 min. The scanning electron microscopy technique was applied for the investigation of nucleation layer morphology after migration. Thick GaN layers were deposited during the three-step growth process at 1060 °C. Samples with various surface morphologies were obtained. Photoluminescence spectra and X-ray measurements were performed, which permitted clarifications of the influence of growth conditions of the nucleation layer on the properties of high-temperature layers.

In Vitro Bioactivity of Atomic Layer Deposited Titanium Dioxide on Titanium and Silicon Substrates

A non-bioactive implant device can easily be changed to in vitro bioactive with a thin coating of crystalline TiO2. This crystalline coating can be deposited very thin with great step coverage at a low temperature with Atomic Layer Deposition (ALD). An anatase TiO2 coating was built up atomic layer by atomic layer using TiI4 and H2O as precursors in a hot wall furnace. Several hundreds of cycles resulted in a 10-30nm well defined TiO2 of anatase phase on both Si and Ti substrates. These coatings were shown to be bioactive when immersed in simulated body fluid in vitro, as hydroxyapatite (HA) formed on the surface. The surface roughness of the substrates affected the adhesion of the HA. The adhesion was low on the smooth Si but much better on the 100 times rougher Ti. The ALD technique is promising for coating substrates of all shapes with bioactive crystalline TiO2 at a low temperature.

Role of the Si∕SiO2 interface during dopant diffusion in thin silicon on insulator layers

We found that As and B diffusion in 90nm thick Si on SiO2, silicon on insulator, samples is reduced, by ∼20%, with respect to that of bulk Si for thermal processing in a lamp-based system. In contrast, when annealing is performed in a hot-wall furnace system and sample heating is determined by conduction diffusion length in Si–SiO2–Si samples is very similar to that occurring in bulk-Si reference samples. We demonstrate that diffusion in Si–SiO2–Si multilayer structures is primarily determined by an increased sample reflectivity, generated by the presence of the buried Si∕SiO2 interface that reduces the amount of heat absorbed by the sample, rather than by the enhanced recombination of point defects at this interface. The latter phenomenon is not ruled out but plays a less relevant role in determining the measured reduction of diffusion.

Metallo-organic low-pressure chemical vapor deposition of Ta2O5 using TaC12H30O5N as precursor for batch fabrication of microsystems

Ta2O5 thin films were produced by metallo-organic low pressure chemical vapor deposition using Tantalum(V) Tetraethoxydimethylaminoethoxide (TaC12H30O5N) as precursor. This liquid precursor at room temperature makes it possible to deposit thin films of Ta2O5 on wafer batches of up to 35 wafers. In this communication, we report on the processing and equipment development to achieve batch fabrication, and on the optimization of the deposited thin films properties for their application in microsystems. An evaporator was linked to a horizontal hot wall furnace. The deposition of Ta2O5 was performed at 425 °C and the influence of a post-annealing at higher temperatures on the chemical, electrical and optical properties of the films was evaluated. Annealing treatments in oxygen were found to reduce the amount of residual carbon and hydrogen in the films. An annealing in oxygen followed by an annealing in forming gas was used to improve the charge levels and hysteresis. The optical properties of the amorphous Ta2O5 films varied slightly with the annealing treatment. Annealing the films at a temperature of 700 °C and higher caused their crystallization, leading to a decrease of their optical bandgap. The processed films have found applications in microsystems as chemical resistant coatings, optical coatings for wave guides, and chemical sensitive layers for Ion-Sensitive Field-Effect Transistors.

Batch process for atomic layer deposition of hafnium silicate thin films on 300-mm-diameter silicon substrates

Atomic layer deposition (ALD) of hafnium silicate HfxSi1−xO2 thin films from tetrakis(ethylmethylamino)hafnium, tetrakis(ethylmethylamino)silicon, and ozone was accomplished onto 300-mm-diam Si substrates using a hot-wall furnace system with a 50-wafer batch configuration. For 23-nm-thick hafnium silicate, excellent film thickness uniformity with a mean within-wafer uniformity of 0.84% (1σ∕mean) and a wafer-to-wafer thickness uniformity of 0.80% (1σ∕mean) was achieved over the top, middle, and bottom wafers in the full batch process. Over three times enhancement in wafer-per-hour throughput per chamber was observed as compared with a single-wafer ALD module.

Effects of aluminum content and substrate temperature on the structural and electrical properties of aluminum-doped ZnO films prepared by ultrasonic spray pyrolysis

Transparent conductive aluminum-doped zinc oxide (AZO) films were prepared by an ultrasonic spray pyrolysis method. A vertical type hot wall furnace was used as a reactor in the deposition system Zinc acetate dissolved in methanol was selected as a precursor. The substrate temperature was varied from 180 °C to 240 °C. Aluminum (Al) was doped into ZnO films by incorporating anhydrous aluminum chloride AlCl3 in the zinc acetate CH3CO2)2Zn solution. The proportion of the Al in the starting solution was varied from 0 wt % to 3.0 wt %. The crystallographic properties and surface morphologies of the films were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The resistivity of the films was measured by the Van der Pauw method, and the mobility and carrier concentration were obtained through Hall effect measurements. Transmittance was measured in the visible region. The effects of substrate temperature and aluminum content in the starting solution on the structural and electrical properties of the AZO films are discussed.

Low pressure r.f. nitriding of austenitic stainless steel in an industrial-style heat-treatment furnace

The nitriding efficiency of a low pressure r.f. plasma is investigated in an industrial style hot-wall furnace in which the component is heated by thermal radiation from the walls of the vacuum chamber. The role of degassed impurities is also addressed. Samples of AISI 316 stainless steel were treated at a relatively low temperature of 400°C to avoid loss of corrosion resistance. The results are compared with treatments under similar conditions of plasma (sample bias, gas pressure, process temperature and treatment time), in cold wall experimental reactors, including a fully UHV compatible apparatus. Process conditions can be found for which the hot-wall furnace gives the best results, despite a high rate of impurity evolution. The apparently higher activity of the low pressure r.f. plasma in this environment can be exploited for low temperature plasma assisted nitriding.

Rapid Thermal Oxidation of Silicon in Mixtures of Oxygen and Nitrous Oxide

AbstractOxidation in nitrous oxide by conventional hot wall furnace processing and by rapid thermnal oxidation (RTO) has been a subject of much interest in recent years. RTO is a fundamentally different process than furnace oxidation, however, and the full effects of this type of processing on the oxidation kinetics are not well understood. Oxidation of silicon by RTO at a variety of pressures, temperatures, and oxidation gas mixtures has been studied. Although at lower temperatures (<850°C) the atmospheric pressure oxidation rate in nitrous oxide is very close to that in oxygen, at higher temperatures the oxidation rate in nitrous oxide is much lower than that in oxygen. At lower pressures in a RTO process, the oxidation rate in nitrous oxide is higher than that in oxygen. The effect of the nitrogen incorporated in the oxide acting as a diffusion barrier has been proposed as the mechanism of temperature dependence for atmospheric pressure oxidation in nitrous oxide. This does not explain the effects seen at lower pressures, however. We propose that some of the intermediate species produced in the decomposition of nitrous oxide into molecular nitrogen, molecular oxygen, and nitric oxide play a role in the initial stages of oxidation by RTO in nitrous oxide.

Applicability of furnace analysis in determination of the performance characteristics of a hot wall furnace fired with sorbent-loaded coal-water fuel

A hot-wall furnace of 40 ft 3 fired with sorbent-loaded coal-water fuels at 1 MMBtu/h was found to generate firing and efficiency (performance) curves in functional agreement with the equations developed in furnace analysis. (In the FPS system, M = 1000 and MM = 1000000. It is based on the Latin prefix, M, as abbreviation for mille.) The present study includes a theoretical correction for the dependence of the firing parameters on excess air due to water in the fuel, and this correction is shown to be supported by test against the experimental results. The complete results show the variation with output of: thermal input (firing curve), thermal (operational) efficiency, heat utilization factor, specific gas enthalpy, and wall loss

Silicon deposited by low pressure chemical vapour deposition from Si 2H 6: experiments, modelling and properties

This paper describes the study of low pressure chemical vapour deposition of silicon from disilane (Si 2H 6) in a horizontal hot-wall furnace. Special attention is devoted to the kinetic phenomena, and in particular to the thickness distribution across the wafers and across the load. Examples are given, which show that acceptable uniformities can be obtained. A simulation of these processes is also presented. For that, a two-dimensional model taking into account, in every region of the furnace, mass transport, fluid dynamics and chemical reactions in the gas phase and on the solid surfaces has been used. In particular, it shows that the much lower deposition rate obtained when silane (Si 2H 4) is the source gas is due to a much lower silylene (SiH 2) contribution. The SiH content measurements by Fourier transform IR spectroscopy show that, for similar deposition conditions (temperature and pressure), the SiH content of “SiH 4 films” is much higher than that of “Si 2H 6 films”, thus confirming than the ultimate silicon precursor is different for the two gases. The study of the crystallization properties of the amorphous films made on SiO 2 shows that they are dependent not only on the SiH content, but also on the deposition growth rate and pressure.

Silicon nitride elaborated by low pressure chemical vapour deposition from Si 2H 6 and NH 3 at low temperature

For the elaboration of silicon nitride at a temperature of up to 600°C, plasma-enhanced chemical vapour deposition is generally used and the resulting films present a large amount of electrical defects. In addition, this technique is expensive and is not very well suited for mass production. We present a study of the low pressure chemical vapour deposition of silicon nitride in a horizontal hot-wall furnace. Preliminary experiments at 600°C were carried out, in which we tested the SiH 2Cl 2-NH 3 system. We show that it leads to an unsatisfactory thickness homogeneity and to a poor chemical quality of the film. A second attempt was made using SiH 4 and NH 3. The kinetic results compared with those for Si deposition from SiH 4 showed that, similarly to the case of the addition of PH 3 to SiH 4, NH 3 addition causes an important reduction of the Si supply to the film with poor thickness homogeneity on the wafer. Consequently, we tested the Si 2H 6-NH 3 system at temperatures between 555 and 645°C, with the pressure lower than 200 mTorr. The resulting kinetic data were evaluated, taking into account their variation along the wafer and along the load. The material properties were systematically assessed by ellipsometry measurements, and some samples were characterized by Fourier transform IR spectroscopy. In addition, the passivation capability and the insulating properties were tested by buffer HF etching and I–V measurements respectively. The first general result is that the films are Si rich, with only the lowest Si 2H 6/NH 3 ratio giving stoichiometric Si 3N 4, and that the deposition rate can reach high values (20 Å min −1 or more) for high values of the ratio (according to what can be obtained in the case of Si deposition from Si 2H 6) but with a high Si content in the resulting film. The buffer HF etching rate is low, with a minimum when the Si content is at a maximum, despite the fact that the density of Si-bonds can be quite high (about 5%). The I–V characteristics of the different films show that the stoichiometric films present a breakdown field of about 7 MV cm −1 and that the Si-rich films have a semi-resistive behaviour.

Rapid Thermal Annealing of Implanted Layers in Silicon Nitride Encapsulated Gallium Arsenide

The rapid thermal annealing (RTA) of implanted layers in semi‐insulating gallium arsenide encapsulated with silicon nitride has been investigated and compared with conventional hot wall furnace annealing. The evaluation was based on comparisons of the electrical characteristics of MESFET's including channel sheet resistance, pinchoff voltage, saturation drain current, and isolation sheet resistance. The results show that a high degree of uniformity and reproducibility of device characteristics over full 2 and 3 in. wafers can be obtained using rapid thermal annealing. Moreover, the rapid thermal annealing process has resulted in reduced damage to the silicon nitride encapsulating dielectric, and increased carrier mobility in the active layers, making it a desirable alternative for the production of gallium arsenide integrated circuits.

The electrical properties of Hg-sensitized “photox”-oxide layers deposited at 80°C

This paper deals with the electrical properties of low-pressure CVD SiO 2 deposited at 80°C. The deposition rate is enhanced by UV radiation in the presence of Hg vapor. The photo-enhanced low-pressure chemical-vapor-deposited oxide, known also as “photox,” offers a good quality oxide deposited at temperatures as low as 80°C. The films are deposited in a batch-load “photox” barrel reactor and subsequently annealed at 950°C for 30 min in a conventional hot-wall furnace. Cold-sputtered aluminum-gate guard-ring capacitors are fabricated on the oxide films. High-frequency and quasi-static capacitance measurements indicate the interfacial properties of “photox” are comparable to those of thermal oxide. Fast interface states density are less than 2 × 10 10 cm −2 eV −1 and a light negative interfacial charge could just be detected. The dielectric breakdown field is typically 4–5 MV/cm. Deep-depletion transient-capacitance measurements were performed at temperatures between 20 and 100°C to investigate the possible impact of “photox” processing on the generation lifetime. The Hg in particular might be suspected as a heavy-metal contaminant. Typical recovery times observed at 20°C were in the range of 10–15 min. The generation lifetime derived from such measurements ranges from 140 to 200 μs which is comparable to values for control samples made with standard thermal oxide. The magnitude and temperature dependence of the generation lifetime suggest that the same G-R centers are present in both “photox” and thermal oxide devices. The only apparent electrical effect of the Hg vapors used in the deposition process is a small negative fixed interface charge, 2 × 10 10 cm −2.

A High Production System for the Deposition of Silicon Nitride

Amorphous silicon nitride is well known as a barrier to the penetration of alkali metal contaminants into junctions of semiconductor devices and as a gate dielectric for MIS devices. This paper discusses the operating characteristics of a production system for the deposition of silicon nitride by the ammonolysis of silicon tetrachloride in a hot wall furnace, and the characteristics of the resulting films.The protective film (1700–2500Aå) for bipolar devices can be deposited at a rate of 120 wafers/hr. For MIS work, where film thickness directly affects device threshold voltage, better uniformity can be achieved by modifying the wafer placement and operating procedures. The nitride films are amorphous with an index of refraction of approximately 1.95; the surface‐state density is in the order of 1012; and the etch rate in buffered hydrofluoric acid is .