We exposed PMMA positive electron-beam resist using a scanning probe. Lithography was performed in the hybrid AFM / STM mode. Continuous features as small as 26-nm-wide were successfully patterned and transferred into the silicon substrate using lift-off. The lift-off technique is particularly useful for achieving good pattern transfer fidelity when using thin resists. Here the PMMA thickness was only 50 nm. For lift-off, 10 nm of chrome was evaporated onto the samples after resist development. The chrome was lifted off in acetone with ultrasonic agitation. The chrome pattern was then transferred into the silicon substrate using an anisotropic NF3 dry etch. Since chrome serves as a robust etch mask, high aspect ratio silicon features were created.

AFM image of the PMMA resist on silicon after scanning probe exposure and subsequent resist development. Since PMMA is a positive resist, the region that was exposed by the AFM was removed during development.

Chrome was evaporated onto the developed PMMA sample and the resist was lifted off. Shown here is the resulting chrome feature on top of silicon. The chrome serves as a robust etch mask for subsequent pattern transfer into the silicon.

exposure of SAL601..

...........latent image formation

 

home | micromachining | imaging | lithography | biosensors | other work

Questions? Comments? Mail : QuateWebmaster