AVS 49th International Symposium
    Surface Science Wednesday Sessions
       Session SS-WeP

Paper SS-WeP1
Study of Polymethylmethacrylate Removers for Electron Beam Lithography through Quantitative Surface Roughness Characterization by AFM

Wednesday, November 6, 2002, 11:00 am, Room Exhibit Hall B2

Session: Surface Science Poster Session
Presenter: Q. Hang, University of Notre Dame
Authors: Q. Hang, University of Notre Dame
D. Hill, University of Notre Dame
G.H. Bernstein, University of Notre Dame
Correspondent: Click to Email
As nanotechnology approaches molecular scales,issues of surface contamination by unremoved resists will play an important role in device fabrication. Electron beam lithography (EBL) of polymethylmethacrylate (PMMA) resist is still among the most widely used nanofabrication techniques, so it is relevant to study its residual contamination on both exposed and unexposed surfaces using a variety of resist removers. Besides preventing good metal adhesion, the resulting contaminant-induced surface roughness reduces the ability to characterize deposited molecular patterns by atomic force microscopy (AFM). We are aware of no systematic, quantitative study of surface roughness after removal of PMMA by different solvents toward determining the least amount of residual resist. The ideal stripper exhibits high affinity for both the polymer (as quantified by the lowest Flory-Huggins interaction parameter) and the substrate, the latter aimed at reducing the solid-liquid surface energy. We characterized the effectiveness of several different strippers: acetone, dichloromethane (DCM), a mixture of acetone and DCM (volume ratio 1:1), 1,2-dichloroethane (DCE), a mixture of acetone and DCE (volume ratio 1:1), and the commercial PMMA remover Nano@super TM@ Acryl Strip (MicroChem), on two different molecular weights of PMMA. Environmental AFM was used to investigate SiO@sub 2@ surfaces before and after PMMA was applied and removed by those strippers. The effects of electron beam exposure of the PMMA will also be presented. Power spectral density and root mean square surface roughness analyses showed that DCM and DEC are the best PMMA removers, and can produce the same surface roughness as the original SiO@sub 2@ surface (i.e. no contamination). Estimates of the polymer-solvent, Flory-Huggins, interaction parameters and surface-solvent interfacial energy (from contact angle measurements) satisfactorily predict the effectiveness of the solvents.