Polymer masks on semiconductors: a novel way to nanostructures

We have successfully used self-assembling diblock copolymers on semiconductors as nanolithographic masks in dry etching processes. Quantum structures in the range of only a few nanometers have been fabricated, far beyond the limits of conventional optical lithography processes. In a first step, diblock-copolymers in solution are used to generate micelles. These micelles are loaded by a noble metal salt. After dipping of a semiconductor wafer into this solution, a monolayer of ordered micelles is generated over an area of up to 3 x 3 cm 2 . Exposure of the surface to a hydrogen plasma removes all the organic components and only the small metal clusters remain, each 15 nm in diameter and 50-130 nm apart. These clusters can be used as a direct mask for dry etching of semiconductor quantum wells to fabricate quantum dots. With the anisotropic etching of these structures in a reactive ion-beam chlorine plasma, it is possible to create cylinders in GaAs of up to 80 nm height. After annealing and overgrowing these structures by molecular beam epitaxy it should be possible to create quantum dots embedded in barrier material with higher energy gap and to detect photoluminescece light from these quantum structures at low temperatures.