Phase-shift lithography for sub-wavelength patterns of varying aspect ratios

• We developed a low-cost mask making process for phase-shift lithography.
• Multiple exposures can be used to obtain sub-150 nm elliptical features.
• Aspect ratio of features is controlled by changing mask angles between exposures.
• O2 reactive ion etching can be used to further reduce size of features.
• This cost-effective alternative allows researchers to pattern nanoscale features.

A technique for creating phase shift photolithography masks for use with a stepper or mask aligner, as well as how to achieve sub-150 nm features of different aspect ratios is described. The mask utilizes two different regions, one transparent region of only the mask material, and another transparent region of SiO2, which are overlapped to create the pattern. Patterning was done by use of a Canon Stepper. By adjusting the angle between the two mask regions, the aspect ratio, which is defined as the length:width, of features was controlled. Features below 100 nm were patterned, and aspect ratios were controllably tuned between 1.1 and 2.6. The feature size was also shown to be able to be reduced by 25–30 nm with the use of reactive ion etching.

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