Tungsten removal

The coefficient of friction and acoustic emission signal can be effectively utilized for functional testing of consumables. An example of such a utility is illustrated in Fig. 4.26. For a quantitative, fast, and inexpensive estimate of the functional properties of two different products from a manufacturer, the slurry samples were tested on a CMP tester equipped with capability for continuous acquisition of the frictional and acoustic signals. The collected signals allow the determination of three important functional parameters, namely, time of complete tungsten removal, time of complete underlayer removal, and intensity of polishing (characterized by the level of acoustic signal). 

FIGURE 5.29 Correlation of relative blanket tungsten removal rate (W-RR) and PECVD-TEOS coating time [86]. 

Comparison of particulate levels for after tungsten removal by RIE and CMP. (From Ref. (6).)... 

O Tungsten removal rate. Aymin (Ox 5X) O" Tungsten removal rate. A/min (Ox 3X) Tungsten removal rate. A/min Ox IX)... 

Electrochemical interaction between the oxidizer and the metal is believed to play a key role in material removal in tungsten CMP. In this study, we use X-ray Photoelectron Spectroscopy (XPS) in conjunction with electrochemical measurements in both in-situ polishing conditions as well as in static solutions, to identify the passivation and dissolution modes of tungsten. Dissolution of tungsten oxides was found to be the primary non-mechanical tungsten removal mechanism in CMP. 

Fig. 4 Tungsten removal rate as a function of solids loading for different particle sizes...

This inverse dependence of tungsten removal rate on particle size and the fact that the roughness of the polished sur ce is independent of particle size indicates tiiat tiie polishing process is not... 

Since detailed chemical structure information is not usually required from isotope ratio measurements, it is possible to vaporize samples by simply pyrolyzing them. For this purpose, the sample can be placed on a tungsten, rhenium, or platinum wire and heated strongly in vacuum by passing an electric current through the wire. This is thermal or surface ionization (TI). Alternatively, a small electric furnace can be used when removal of solvent from a dilute solution is desirable before vaporization of residual solute. Again, a wide variety of mass analyzers can be used to measure m/z values of atomic ions and their relative abundances. 

Weldments subjected to corrosive attack over a period of time may crack adjacent to the weld seams if the residual stresses are not removed. Gas—tungsten arc welding and gas—metal arc welding ate recommended for joining magnesium, the former for thinner materials and the latter for thicker materials. Maintaining a protective atmosphere is a critical issue in welding these alloys. 

Phthalocyanines are excellent lubricants at temperatures of 149—343°C (191). Combinations with other lubricants, like grease, molybdenum, or tungsten sulfides, have found appHcations in the automotive industry or professional drilling equipment (192—195). Further uses include indicators for iron(Il), molybdenum(V), and uranium(IV) (196) or redox reactions (197), medical appHcations like hemoglobin replacements (198) or sterilisation indicators (199), or uses like in gas filters for the removal of nitrogen oxides from cigarette smoke (200). 

The tert-huty hydroperoxide is then mixed with a catalyst solution to react with propylene. Some TBHP decomposes to TBA during this process step. The catalyst is typically an organometaHic that is soluble in the reaction mixture. The metal can be tungsten, vanadium, or molybdenum. Molybdenum complexes with naphthenates or carboxylates provide the best combination of selectivity and reactivity. Catalyst concentrations of 200—500 ppm in a solution of 55% TBHP and 45% TBA are typically used when water content is less than 0.5 wt %. The homogeneous metal catalyst must be removed from solution for disposal or recycle (137,157). Although heterogeneous catalysts can be employed, elution of some of the metal, particularly molybdenum, from the support surface occurs (158). References 159 and 160 discuss possible mechanisms for the catalytic epoxidation of olefins by hydroperoxides. 

For the production of lamp-filament wire, aluminum, potassium, and siHcon dopants are added to the blue oxide. Some dopants are trapped in the tungsten particles upon reduction. Excess dopants are then removed by washing the powder in hydroflouric acid. Eor welding electrodes and some other appHcations, thorium nitrate is added to the blue oxide. After reduction, the thorium is present as a finely dispersed thorium oxide. 

Heating and Cooling. Heat must be appHed to form the molten zones, and this heat much be removed from the adjacent sohd material (4,70). In principle, any heat source can be used, including direct flames. However, the most common method is to place electrical resistance heaters around the container. In air, nichrome wine is useflil to ca 1000°C, Kanthal to ca 1300°C, and platinum-rhodium alloys to ca 1700°C. In an inert atmosphere or vacuum, molybdenum, tungsten, and graphite can be used to well over 2000°C. 

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