Novel method for formation and characterization of self-assembling block copolymer nanostructures
Lithographic processes capable of achieving feature sizes on the order of nanometers are required to facilitate further developments in nanotechnology. For devices where a repeating pattern is desired, it is possible to create a nanoscale template by applying a diblock copolymer to a wafer surface. The periodic pattern that forms in the copolymer can be aligned to step edge features etched into the substrate. Further advances in nanoscale device design can be made if self-assembly is accomplished at a specific location on a surface. This research focuses on obtaining a straight step edge to align a lattice of spherical microdomains formed in a thin layer of the diblock copolymer polystyrene-poly(ethylene-alt-propylene) as a method to aid with finding the optimal process parameters by varying the step height and the thickness of the polymer layer applied over a relatively large test pattern comprised of said step edges. This work develops a combinatorial method to aid with finding the optimal process parameters by varying the step height and the thickness of the polymer layer applied over a relatively large test pattern comprised of said step edges. Resulting nanostructure formations form at these step edges, giving a means of locating the features for more reliable and predictable pattern transfer processes. The key feature of the step edge is edge straightness, and this work also describes the fabrication experiments that result in lithographically defined straight edges using optimized microlithography techniques.
The results of this work show that extremely straight step edges of less than 2 nm RMS wiggle can be accomplished with process parameters of fresh Futurrex PR 1-1000A positive photoresist applied at 1000 rpm for 40 seconds, soft baked at 120° C for 2 minutes, contact exposed with a dose of 5.6 mW/cm2 for 2 seconds, developed for 2 minutes, and a post develop baked at 140° C for 1 minute. Additionally, the combinatorial optimization of locating self-assembly along a step edge shows that self assembled features in polystyrene-poly(ethylene-alt-propylene) can be located along step edges with heights of roughly 8.5 nm to 38 nm and a diblock polymer thickness of 12 nm to 35 nm. This demonstrates the effectiveness of the combinatorial approach determining optimal process parameters and also demonstrates that self-assembled structures in diblock copolymer films can be located along step edges of appropriate straightness and height.
0794: Materials science
0795: Materials science