In this article, we discuss the phantom exposure of chemically amplified resists in x-ray lithography, which is attributable to acids in environmental air induced by x-ray irradiation. Since the acids generated in the air diffuse into the resist film from the top to the bottom like so many catalytic acids, they cause cross linking in a negative resist and decomposition in a positive resist. The phantom exposure in flood exposures of a 20 mm square increases as the exposure dose increases, and expands more than 10 mm outside the exposure field when the exposure dose is ten times greater than the optimum exposure dose for patterning. Dependence of the phantom exposure on the exposure dose and resist material are evaluated.

The patterning characteristics of synchrotron radiation lithography for hole patterns using a low-contrast mask (contrast: 3.5) are investigated. A resolution of 110 nm provides a large exposure dose latitude of more than 10% when the proximity gap is less than 15 µm, and the replicated minimum hole size is 70 nm with a 10-µm gap. Resist pattern sizes from 110 to 360 nm are kept within ±10% with proximity gaps of less than 20 µm. However, the exposure dose margin to guarantee mask linearity decreases to several percent because of the different optimum exposure dose for each pattern. Pattern size correction using mask bias to improve the mask linearity and exposure dose margin is proposed.

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