Characteristics of SiO_2 as a High-Resolution Electron Beam Resist

概要

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Characteristics of thermally grown SiO_2, which is a candidate for high-resolution electron beam resists, are studied. In order to improve the selectivity (the etch rate ratio of electron-irradiated area to unirradiated area) which defines the profile of developed patterns, the etching property of electron-irradiated SiO_2 is investigated for various solutions. To eliminate the effect of contamination resulting from electron irradiation, oxygen plasma ashing is used after the irradiation. The saturated selectivity at a dose of about 2 C/cm^2 is 1.6 to 3.3 for HF-based solution while it is almost unity for aqueous KOH. Although tire etch rate of unirradiated SiO_2 follows the linear combination of [HF] and [HF^-_2], that of electron irradiated SiO_2 does not follow such a relation. The saturated selectivity of a mixture of HF and NH_4F takes a maximum at the composition of [HF] and [HF^-_2] of nearly equal quantities. The profile of the etched groove is well calculated by using a string model. A 20 nm line is fabricated onto SiO_2 of an initial thickness of 120 nm by this process.
社団法人応用物理学会の論文
1993-12-30