Nanotech 2010

Silicon nanopillar arrays on 4” wafers using self-assembly derived sub-50nm scale lithographic masks and investigation of the means of exercising fine-control over their optical properties

S. Krishnamoorthy and F.L. Yap
Institute of Materials Research and Engineering (IMRE), SG

Keywords: silicon nanopillar, self-assembly, anti-reflection, copolymer micelle, scattering


We demonstrate nanolithography on 4” silicon wafers to create sub-50nm scale silicon pillars using self-assembled copolymer micelle masks for dry etching. We further investigate their optical properties, and present results that demonstrate a fine degree of control over reflection and scattering behavior of these surfaces. Under sufficiently optimized conditions, the copolymer micelle coatings exhibiting a Gaussian sigma <15% for feature size, <5% for spacing and < 10% for variation in size or spacing from centre to edge of a wafer can be routinely obtained. Challenges pertaining to controlling the organization of copolymer micelles on surfaces and the influence of micelle preparation and coating conditions on the resulting distributions and uniformity would be discussed. The reflection behavior of the silicon pillar arrays as investigated through microspectrometry in visible-near IR wavelength range reveal distinct anti-reflection capability that substantially depends on the profile of the pillars and their densities. Systematic control over the geometric characteristics of the pillar arrays in the sub-100nm regime through control over self-assembly as well as pattern-transfer conditions is explored as means of achieving surfaces with engineered reflectivity and broad band anti-reflection. The high surface roughness and therefore high surface areas of the pillar arrays contribute to enhanced scattering that we further investigate through micro-Raman spectroscopy.
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