NPGS: Wheel Pattern #5

This is an AFM image of the very same "wheel" pattern as the other diagnostic images! The image was acquired after exposure, development, evaporation, and liftoff.

This exposure was done with a line dose of about 14 nC/cm in PMMA, which is about ten times higher than the dose normally used to produce fine lines. This very high dose, the large features, and the fact that the pattern is only exposed where the spokes meet the rim and in the center where they are close together indicates that the beam was extremely out of focus during the pattern writing. The diameter of this structure is ~10 microns.

In PMMA, fine lines (50 nm or less) are typically obtained at a line dose of about 1.3 nC/cm. If the pattern only shows features where lines cross or come close together and the dose is much higher than the expected dose, it is the classic sign of not having the beam focused well on the surface of the resist.

Also see the general SEM Optimization Guide and the SEM Lithography Setup Guide.