Fluoride etch masks for high-resolution pattern transfer

We use thermally evaporated fluoride films as dry etch masks to fabricate sub-100 nm wide features into III–V heterostructures. Fluorides are compatible with lift-off processing and display excellent resistance to halide etch gas mixtures. Among the advantages which these materials offer over conventional metal masks are their thermal stability, good adhesion, high resistivity, the avoidance of ‘‘flags’’ arising from angle evaporation, and the ease with which they can be removed from the surface. By adjusting the composition of these fluorides and thereby controlling their grain size, we can optimize the resolution and erosion rates of our masks and fabricate structures with lateral sizes below 20 nm.