Lithography-free fabrication of sub-100 nm structures by self-aligned plasma etching of silicon dioxide layers and silicon

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A general scheme for the fabrication of silicon and silicon dioxide structures with lateral dimensions of less than 100 nm is introduced that avoids high-resolution lithography processes. For the self-aligned formation of extreme small openings in silicon dioxide layers at sharpened surface structures the angle dependent etch rate distribution of silicon dioxide against plasma etching with a fluorocarbon gas (CHF3) was exploited. Subsequent anisotropic plasma etching of the silicon substrate material through the perforated silicon dioxide masking layer results in high aspect ratio trenches of approximately the same lateral dimensions. The latter can be reduced and precisely adjusted between 0 and 200 nm by thermal oxidation of the silicon structures owing to the volume expansion of silicon during oxidation.