Block copolymer lithography for growth of wide band gap nanostructures: Process control and optimization

Block copolymer lithography offers a promising route for fabricating wide band gap semiconductor quantum dots. A PS-PMMA block copolymer is self-assembled over a random copolymer brush to allow for perpendicular orientation of PMMA cylinders. The substrate consists of GaAs, SiO$_{2}$ and the brush layer. The block copolymer pattern is transferred to the SiO$_{2}$ by reactive ion etching. In the next step, growth of InAs quantum dots in the holes of the template is achieved by MBE. The quantum dots are further characterized by TEM and photoluminescence. The copolymer molecular weight is a critical parameter in determining density and size of the dots. Although use of lower molecular weight polymers can result in higher density of dots, it also leads to more processing challenges. We demonstrate the process optimizations involved in templating with lower molecular weight polymers, and in particular address the challenges in RIE.