In this paper, we describe the use of ozone microbubbles
in photoresist
removal from silicon wafers. Ozonized water has attracted much attention
as an environmental friendly cleaning method in semiconductor manufacturing.
However, it would be desirable to enhance the oxidative ability of
ozonized water for practical application. The existence of microbubbles
in ozonized water has been shown to significantly enhance the photoresist
removal rate due to an elevated dissolved ozone concentration (approximately
2.5 times that of ordinary ozone bubbling) and a direct effect of
the microbubbles (removal rate is approximately 1.3 times faster than
water with the same concentration of dissolved ozone without microbubbles).
Additionally, the ozone microbubble solution was able to effectively
remove a high-dose ion-implanted photoresist, which is extremely resistant
to removal by ozonized water and other wet chemicals because of its
amorphous carbon-like layer, or “crust”. Electron spin
resonance experiments were also performed without the influence of
serious metal contamination and indicated the presence of hydroxyl
radicals, which are thought to be formed by interaction of ozone with
hydroxide ions adsorbed at the gas–water interface upon collapse
of the microbubbles. The hydroxyl radicals play an important role
in photoresist removal by the ozone microbubble treatment.
Liquefied products with high wood content were prepared by pretreating wood with ozone before liquefaction. As a result, the ratio of wood to polyhydric alcohol (W/P ratio) used as solvent could be increased to 2:1. Resin blends were prepared by mixing liquefied products with ethylene glycol diglycidyl ether (EGDGE, water-soluble) and diglycidyl ether of bisphenol A (DGEBA, oily consistency). The wood content of the resin blend could be increased to 53%. The resins were cured by citric acid or triethylene tetramine (TETA), and their mechanical properties were evaluated. Dynamic mechanical measurements revealed that the former had higher glass transition temperatures than the latter. It was found that the resin with DGEBA cured by citric acid had almost the same level of tensile strength as commercial plastics.
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