Tungsten oxides, deposition

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

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Vapor deposition techniques have been extensively studied for the fabrication of metal and metal oxide structures. Indeed, the first reported tungsten oxide nanorods were essentially grown by this method. This groundbreaking synthesis of W02.72 leaves room for improvement, however, as it requires a reaction temperature of 1600°C in an argon atmosphere. Additionally, the researchers found the reaction product to be commingling WO2.72 nanorods and WO3 platelets rather than pure nanorods. Later,... 

The silicon detectors were made of n-typed single crystal of 1 mm thick. They have a MOS structure of gold, tungsten oxide, n-typed silicon and aluminum back contact. Since these layers can be deposited on the silicon wafer by evaporation techniques, the fabrication process is so simple as to be applicable to fabrication of the detectors for a special use. No surface treatment for passivation is given to them so that their performance is affected by ambient gases. For example, some good detectors show a leakage current of half micro-ampere at room temperature in the atmosphere, but a few micro-ampere in vacuum. So, in order to stabilize their performance, the silicon detectors were operated at the dry ice temterature. 

Yamada-Takamura, Y. et al.. Hydrogen permeation barrier performance characterization of vapor deposited amorphous aluminum oxide films using coloration of tungsten oxide. Surface and Coatings Technology, 153, 114 (2002). 

HYDROGEN BEHAVIOR AND COLORATION OF TUNGSTEN OXIDE FILMS PREPARED BY MAGNETRON SPUTTERING AND PULSED LASER DEPOSITION ... 

Figure 2. The X-ray diffraction patterns from the deposited films prepared by pulsed laser deposition using tungsten oxide (WO3) target with different partial pressure of oxygen.

The structure and composition of tungsten oxide films prepared by RF magnetron sputtering and by pulsed laser deposition was examined using X-ray diffraction and ion beam analysis techniques. The correlation of the hydrogen in the film with the optical absorption characteristics was investigated to clarify the gasochromic mechanism. 

Hydrogen Behavior and Coloration of Tungsten Oxide Films Prepared by Magnetron Sputtering and Pulsed Laser Deposition... 

Unlike W plasma etch back process, the typical W CMP process usually removes the adhesion layer such as Ti/TiN or TiN during the primary polish. As a result, during the over polish step there is some oxide loss. Since the oxide deposition, planarization CMP (oxide CMP), and tungsten CMP steps are subsequent to each other, the oxide thickness profile could become worse further into the process flow. Therefore, the across-wafer non-uniformity of the oxide loss during W CMP process is one of the very important process parameters needs to be optimized. To determine the effect of the process and hardware parameters on the polish rate and the across-wafer uniformity, designed experiments were run and trends were determined using analysis of variance techniques. Table speed, wafer carrier speed, down force, back pressure, blocked hole pattern, and carrier types were examined for their effects on polish rate and across-wafer uniformity. The variable ranges encompassed by the experiments used in this study are summarized in Table I. 

Molybdenum and tungsten oxides are generally similarly prepared, but even though the lower oxidation state compounds should be interesting, the trioxides receive most of the attention. Electrodeposition from a hydrogen peroxide solution yields films that are crystalline as deposited higher temperature preparation techniques often result in amorphous films. The peroxide would be expected to result in fully oxidized material as deposited, but subsequent heat treatment is needed to achieve this state. 

A similar approach, but now for interconnect applications, was followed by Black et al.192 to convert laser written poly-Si lines partially into tungsten. The poly-Si lines were exposed for 6 minutes to a WF /Ar mixture at 0.625 Torr. At 475°C, 0.4/im thick doped poly-Si lines exhibited a conductivity improvement of up to a factor of 20. RBS and SEM analysis showed that about 100 nm of tungsten was deposited on the poly-Si and that the resistivity of the tungsten film was about 10 /iftcm. The results here, as in the poly-Si plug conversion case, were rather dependent how exactly the poly-Si was pretreated in terms of residual oxide thickness. 

Nano-particulate tungsten oxide films were also synthesized by pulsed electrodeposition in libraries. Particle sizes between 45 330 nm were achieved by varying pulse duration from 5 ms to 500 ms. Films prepared by continuous electrodeposition had an average particle size of approximately 375 nm. As the pulse time decreased, particle size decreased as well. For a 5 msec pulsed deposition, the average particle size was approximately 45 nm. We checked the particle size with respect to deposition time (30 sec to 30 min, that is 3,000 to 180,000 pulses) and found that particle size was independent of total number of pulses the total number of pulses seemed to affect only film thickness and not the final particle size. 

In addition to innovative coatings for the protection of the hydrogen dissociation catalyst, mesoporous metal oxide layers for enhanced performance of the sensor elements were investigated. The results demonstrated the suitability of an electrodeposited tungsten oxide (WO3) as a chemochromic layer for hydrogen detection, providing a valuable alternative to vacuum deposition. 

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