(A) study on improved nanolithography process in PS-b-PMMA block copolymer system

Abstract

Microdevice is important in the future industries such as semiconductor, energy, medicine and so on. Microdevices are composed of two or three dimensional (3D) nanostructure of metal, ceramic or polymer materials. Nanopatterning techniques are very important to build these nanostructures integrated with various materials. Although the photolithographic process is mainly used as the nanopatterning technique, there is a limitation in reducing pattern size to 50 nm or less due to the resolution limit in its single process. The bottom-up approach has been extensively studied in that it can be combined with a top-down approach to form controlled nanostructures. Among them, block copolymer (BCP) self-assembly can be used to overcome the resolution limitations of the photolithographic process and to form a large-area, well-ordered nanoscale surface pattern having a dimension below 30 nm in a cost effective manner. Significantly, BCP self-assembly can be integrated with a mass-produced photolithography, to direct the spatial registration and lateral ordering of nanoscale domains, which is generally referred as directed self-assembly (DSA).

In this dissertation, DSA process improvement in poly(styrene-block-methyl metacrylate) (PS-b-PMMA) BCP system is studied. DSA process is generally divisible by four stages. First step is neutral layer formation with hydroxyl terminated random copolymer, poly(styrene-random-methyl methacrylate) (PS-r-PMMA), to provide nonpreferential wetting to either PS or PMMA blocks. Second step is pattern formation that BCP self-assembly could generate sphere, cylinder, lamellar and gyroid structure. Third, selective removal of one block should be done for making lithographic mask. Lastly, inorganic components are deposited by evaporation process from perforated BCP template, which is referred to as pattern transfer process. For the improved DSA nanolithography process, four new methods are discussed here. The method includes a new non-destructive surface energy test, a new BCP pattern with modified pattern symmetry, a PS-b-PMMA lamellar pattern with a high aspect ratio that allows wet etching, and finally a highly reactive three dimensional heterogeneous material.