The optical reflectivity of a GaAs wafer is found to decrease from about 45% down to about 5% for both the g-line and i-line by oxidation in low-power oxygen plasma at 300°C for 4 hours. The oxide layer on the GaAs top surface used as an in situ antireflection layer for optical microlithography is demonstrated to be effective.

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To distinguish between a mechanism in which thionyl chloride oxidizes a methylene group from one in which thionyl chlorides oxidizes a methyl group while converting monosubstituted acetones into 3-thietanones, a series of 4-aryl-2-butanones was subjected to oxidation conditions (thionyl chloride, 25-85O, 5 min-3 hr). Butanones. with the following ring substitution gave only 3-thietanones as products: 3-NO2, 3-F, 4-N02,4-C1,4-CH30. However, 4-(3-hydroxyphenyl)-2-butanone gave only 2-acetyl-5-hydroxybenzo [ b] thiophene, and 4-( 3-methoxypheny1)-2-butanone gave both 2-(3-methoxybenzylidene)-3-thietanone and 2-acetyl-5-methoxybenzo[b]thiophene as products. The results are consistent only with thionyl chloride oxidation proceeding exclusively at the methylene position.A few years ago we reported the oxidative conversion of @-aryl carboxylic acids and certain ketones to benzo[ blthiophenes2 and of methyl ketones to 3-thietan0nes.~ The unusual nature of these products and the generality of the reactions prompted us to examine the mechanism by which these products were being formed. The results of our investigation of the benzothiophene case have been reported.2The key to the mechanism was the intermediacy of sulfenyl chlorides by oxidation of a methylene group adjacent to the carbonyl function.On the reasonable assumption that the 3-thietanones were being formed through the intermediacy of a structurally similar sulfenyl chloride, we proposed3 a mechanism for 3-thietanone formation (eq 1). However, this mechanism did not seem to account for the lack of benzothiophene formation in those cases where Ar (in eq 1) is an aromatic ring. If for some reason oxidation of the methyl ke-0 CI ArCH,

An accurate method for measuring defocus, which is an application of phase shifting mask technology for higher resolution microlithography, reveals the impacts of reticle topography on optical microlithography. On the topographic reticles, there exist many focus monitors besides overlay marks. These reticles include almost flat and convex to concave topography with a maximum altitude difference of 2 m. Contrary to our expectation, the experimental results showed that reticle topography has little impact on the field curvature, but has a significant impact on overlay errors. The lithography tool used in this experiment presses topographic reticles flatly against the face of a reticle stage to plane the field curvature, with generating magnification errors only in the slit direction.