Selective etching of polylactic acid in poly(styrene)‐block‐poly(d,l)lactide diblock copolymer for nanoscale patterning

Self‐assembled thin films of a lamellar forming polystyrene‐block‐poly(d,l )lactide (PS‐b‐PLA) block copolymer (BCP) contain a “reactive” block that can be readily removed to provide a template for substrate pattern formation. Various methods of PLA removal were studied here with a view to develop the system as an on‐chip etch mask for substrate patterning. Solvo‐microwave annealing was used to induce microphase separation in PS‐b‐PLA BCP with a periodicity of 34 nm (L_o) on silicon and silicon on insulator (SOI) substrates. Wet etches based on alkaline and enzymatic solutions were studied in depth. Fourier transform‐infrared (FT‐IR) analysis showed that basic hydrolysis using sodium hydroxide (NaOH) or ammonium hydroxide (NH₄OH) solutions resulted in greater PLA removal in comparison to an enzymatic approach using Proteinase K in a Tris‐HCl buffer solution. However, in the enzymatic approach, the characteristic self‐assembled fingerprint patterns were retained with less damage. Comparison to a dry etch procedure using a reactive ion etch (RIE) technique was made. A detailed study of the etch rate of PS and PLA homopolymer and PS‐b‐PLA shows depending on DC bias, the etch selectivity of PLA and PS can be almost doubled from 1.7 at DC bias 145 V to 3 at DC bias 270 V. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40798. Together with Krebs et al., J. Appl. Polym. Sci. (2014) 131 , 40795, doi: 10.1002/app.40795 , this article is part of a Special Issue on Polymers for Microelectronics. The remaining articles appear in J. Appl. Polym. Sci. (2014) volume 131 , issue 24. This note was added on 1st July 2014.