Plasma ashing devices

We used two plasma ashing devices International Plasma Corporation, Model 1003B-248AN and LFE Corporation, Low Temperatures Asher, No. LTA-600.) Since the plasma combustion temperature does not exceed 50°C we avoid the possibility of mineral decomposition (especially of carbonates) encountered during high temperature combustion. 

In integrated circuit fabrication, novolac-based photoresist is used as a mask to define selectivity areas to be ion implanted. The implanted photoresist does not remain a part of the device structure and must be removed. Removal of implanted photoresist is extremely difficult because of its high degree of chemical resistance and is accomplished by harsh chemical treatment, such as with sulfuric peroxide, or by plasma ashing [23]. The toughness of implanted polymers presents a problem in this application, but it is just this chemical resistance that enables their photolithographic processing. 

Polymer ashing is another process related method. This process is fairly complex and involves patterning of a polymer layer during the release. First, structures are partially released by a timed etch. Next, a polymer film is deposited onto the partially released structures. This film is patterned into support posts that hold the structure in position as the remainder of the sacrificial layer is etched away. Because the polymer support structures hold the devices in place, there is no concern for special drying techniques. Finally, the polymer supports are burned away, typically by ashing in an oxygen plasma.This leaves behind fully released and free-standing microstructures. 

Particulate matter in a measured volume of air can be collected on a cellulose-acetate-membrane filter (e.g., Millipore ). The filter is dry ashed in a low-temperature asher. (This device uses oxygen radicals in a radio-frequency plasma for ashing at below 100°C, thus minimizing losses due to volatility of the test element and retention on crucible walls.) The ash is taken up in dilute HCl and aspirated directly, or the filter can be digested with a mixture of nitric and perchloric acids. For beryllium determination, a nitrous oxide-acetylene flame is used. Results are reported as Mg/m of air. 

Almost all modern fusion devices rely on the divertor concept and all planned devices comprise a divertor. The divertor was initially a separate chamber to which the boundary plasma was diverted by additional divertor coils. In the divertor, the plasma is guided onto target plates. The dominant and most important process at the target plate is neutralization. The impinging plasma ions are neutralized and reemitted into the gas phase. Therefore, the neutral gas pressure in the divertor is substantially higher than in the main chamber. The pump ducts to the vacuum pumps are located underneath the divertor to pump the neutral gas. Naturally, the pumped gas is dominantly composed of fuel species, but in addition, the helium ash and other volatile impurities will be removed in this way. The pumped fuel will be recycled in the gas handling facility and pumped impurities will be permanently removed. The other important function of the divertor is to handle the arriving power flux. This will be discussed further below. 

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