DC Reactive Sputtering Method Research Articles

The protection of MgO film against hydration by using Al 2O 3 capping layer deposited by magnetron sputtering method

Al 2O 3 capping layer was deposited by DC reactive sputtering method on MgO protective layer deposited by RF magnetron sputtering method. Thickness of capping layer, Al 2O 3, was varied from 1 to 15 nm. Deposited MgO thin films were hydrated in the ambience of 80% humidity and at room temperature. Surface morphology and rms roughness were observed by SEM and AMF, respectively. Chemical shift of electron binding energy was observed by XPS. And the composition and concentration of hydrogen were observed by RBS and ERD. From these analyses, it was found that Mg atoms diffused into Al 2O 3 layer and reacted with moisture at surface, forming Mg(OH) 2 phase during hydration reaction. At the thin capping layer region (1–5 nm thickness), as thickness of Al 2O 3 increased, total amount of hydration decreased. But, beyond 5 nm thickness, the tendency became reverse. Although Al 2O 3-capped MgO thin film was hydrated to some extent, total amount of hydration is much less than uncapped MgO single layer. Therefore, it can be concluded that Al 2O 3 might be suitable for protecting MgO layer against hydration.

Study on Raman spectra of electrochromic c-WO 3 films and their infrared emittance modulation characteristics

Polycrystalline tungsten oxide films with good electrochemical stability were prepared by dc reactive sputtering method. The Raman spectra of these films show that the W 6+ ions were reduced to W 5+ with the co-intercalation of Li + ions and electrons. Intercalated electrons entered extended states of crystalline tungsten oxide and caused infrared reflectance variation, therefore, the emissivity of WO 3/ITO/glass can be reversible modulated between 0.261 and 0.589.

Ti ion valence variation induced by ionizing radiation at TiO 2/Si interface

Titanium oxide films are prepared on silicon substrates by the DC reactive sputtering method. The TiO 2/Si structures with different TiO 2 film thickness are irradiated by electron beams and γ-rays. It is found after irradiation that the shift of flat-band voltage Δ V FB of MOS structures is very small. There is no evident distortion in the HF C– V curves in comparison with pre irradiation cases. By the XPS analysis, it is found that, after irradiation, the valence of the Ti ion varies; the Ti 3+ ion increases and the Ti 4+ ion clearly decreases at the TiO 2/Si interface. The variation comes mainly from the transition layer between the titanium oxide film and silicon substrate. The mechanism has been discussed in detail.

Sensing characteristics of dc reactive sputtered WO 3 thin films as an NO x gas sensor

In order to apply WO 3 thin films to the NO x gas sensor, WO 3 thin films (3000 Å) were fabricated by using dc reactive sputtering method on alumina substrate and assembled as a unit of an NO x gas sensor by adopting a patterned heater on the back side of substrate. The deposition temperatures of WO 3 thin film were changed from 200°C to 500°C, and then post-annealed for the crystallization for 4 h at 600°C. There were no WO 3 phases at the substrate temperature of 200°C, but the crystalline phases of WO 3 thin film were appeared with the increase of substrate temperature from 200°C to 500°C. The post-annealing of as-deposited WO 3 thin films at 600°C resulted in the enhancements of crystallinity, but it was observed that the quality of the final phases severely depends on the initial formation of phase during deposition. From the SEM images, crack free morphologies were found, which was different from the room temperature growth films. The sensitivity ( R gas/ R air) of as-deposited thin films was ranged from 4 to 10 for the 5 ppm NO test gas at the measuring temperature of 200°C. However, after post-annealing process at the temperature of 600°C, the sensitivities were increased around the values of 70–180 at the same test condition. These results show the WO 3 thin films need to be processed at least at the temperature of 600°C for the well-improved sensitivity against NO x gas. It was also observed that the recovery rate of a sensing signal after measuring sensitivity was faster in the in-situ sputtered films than in the evaporated films or room temperature sputtered films.

Bendable and temperable solar control glass

Bendable and temperable solar control glass with a basic layer construction of SnO 2/SiN x /CrN x /SiN x /SnO 2 was produced by the dc reactive sputtering method. For protection of the CrN x layer from oxidation during heat treatment processes, thin buffer layers of SiN x were inserted between the CrN x layer and oxygen sources such as air and SnO 2 layers. It was found that the stoichiometric Si 3N 4 with a minimum of impurities is a good buffer layer. The SnO 2 layer deposited on the transition mode indicated the lower oxygen diffusion coefficient and oxygen release property than one deposited on an oxide mode. The transition mode SnO 2 has, therefore, been proved to be suitable for the bendable and temperable solar control glass.

Adhesion and structural changes of multi-layered and multi-doped a-C:H films during annealing

High residual stress in hydrogenated amorphous carbon (a-C:H) films makes them rather difficult to integrate to substrates whose reactivity for carbide formation is low at the deposition temperature. Additionally, when exposed to thermal cycling, a-C:H films not only soften (i.e., graphitization), but also peel off because of thermal stresses. To improve adhesion and reduce the graphitization at high temperatures, we studied multi-element doped a-C:H films with multi-layered buffer structures on austenitic stainless steel substrates. A multi-layered structure was deposited in the order of TiC/ TiCN/TiN/Ti/stainless steel prior to depositing multi-element doped a-C:H films using dc reactive sputtering and plasma-enhanced CVD methods. The a-C:H films were doped with Ti and Si. Chemical analyses of the multi-layer structure was performed using X-ray photoelectron spectroscopy. Adhesion of the films with the multi-layered buffers was better than those without buffer layers at high temperatures ( T = 600 ° C). The critical scratching load was maximum at around 400 °C on (Si:Ti)-a-C:H films. Similarly, as observed by Raman spectroscopy Si:Ti doped films had higher resistance to the graphitization than undoped films.

Two Stages High Rate Reactive Sputtering, Divided Sputter Process and Oxidation Process.

For optical thin film production by a sputtering method, it is common to use RF or DC reactive sputtering. Since during deposition sputtering and reactive processes are operated simultaneously, a substrate temperature rise is caused. Also the deposition rate is very low because metal atoms sputtered need enough time for sufficient oxidation. For solving these problems, we separated the deposition process into two stages, i.e., sputtering and reactive processes. As result of these two successively separated processes, the deposition rate for metal oxides can be as similar to that of pure metals with no substrate temperature rise. This is completely different from that during RF sputtering. This new type DC reactive sputtering method is called Two Stages High Rate Sputtering, Divided Sputtering Prosess and Reactive process (TSH Sputtering Method). This paper describes the deposition principle and reports the improvements of refractive index, deposition rate and substrate temperature rise. Finally the antireflection coatings produced by the TSH sputtering method as an example of multilayer, and their spectral characteristics and reproducibility are represented.

Properties of W–N and Mo–N films prepared by reactive sputtering

The structure and properties of W–N films up to 22 μm thick prepared by a reactive dc magnetron sputtering process are reported. It has been found that the properties of the deposited films not only depend on the nitrogen partial pressure in the argon–nitrogen gas mixtures but also on total gas pressure and input power during sputtering. The rate of deposition decreased with increase of nitrogen partial pressure, but was higher at higher total pressure and input power. The resistivity increased with nitrogen partial pressure but was lower at lower total gas pressure and higher input power. The hardness of W–N films could be varied from 600 to 3000 kg/mm2 depending on sputtering conditions. The hardness, in general, increased with nitrogen partial pressure with higher value at higher total pressure and input power. X-ray diffraction did not indicate presence of nitride phases when the content of nitrogen in the argon–nitrogen gas mixtures during sputtering was below 10%, and the total gas pressure was <40 mTorr. W2N was observed when the nitrogen content was over 30% and also when the nitrogen content was over 10% and total gas pressure was over 40 mTorr. These results are consistent with composition determined by the microprobe measurements. Similar studies on Mo–N films made by dc and rf magnetron reactive sputtering methods are reported. Hardness values for the Mo–N films of more than 2200 kg/mm2 have been observed.

Fabrication of NbN Films by dc Bias Sputtering and Their Application to Superconducting Bridges

NbN thin films have been prepared by double cathode dc reactive sputtering method. The effect of the substrate bias and the nitrogen partial pressure on the films' resistivity and superconducting transition temperature were investigated. A high critical temperature of around 16 K was obtained for 300 nm films made at about -80 V substrate bias voltage and suitable nitrogen partial pressure. The thickness dependence of the films' critical temperature was determined for film thickness down to 5 nm. NbN variable thickness bridges with length of about 0.2 µm were fabricated and shown to be feasible for use as Josephson devices. Microwave induced steps were observed over the bridges' I-V characteristics over rather narrow temperature ranges.

Characteristics of Silicon Silicon-Dioxide Structures Formed by DC Reactive Sputtering

The C-V characteristics of silicon silicon-dioxide structures fabricated using DC reactive sputtering method were investigated. The fast interface states were able to be eliminated by subjecting the sample to high temperature treatment in inert gas flow and subsequent Al-treatment. The surface state charge Qss was of the order of 1010 q·cm-2 in the sample treated in nitric acid prior to oxide deposition. The substitution of a hydrofillic pretreatment for the nitric pretreatment resulted in a negative Qss of approximately -5×1011 q cm-2. This small Qss was stable under bias-temperature stressing at 300°C even without additional processing, and, on the other hand, the negative Qss could be stabilized with comparable ease by forming the usual phosphate glass layer on the oxide. This stable negative Qss is of interest from the viewpoint of practical application such as making normally off n-channel MOS transistors.