Lateral and Vertical Quantification of Spin-Coated Polymer Films on Silicon by TOF-SIMS, XPS, and AFM

Abstract

PMMA and PVC were spin coated on silicon wafers using a range of polymer concentrations. This resulted in a corresponding range of film thicknesses and, for ultrathin film layers, various degrees of surface coverage. The thickness was determined by AFM profilometry and was used to correlate the time scale of a dynamic TOF-SIMS depth profile analysis to a depth scale. The degree of surface coverage was determined from AFM imaging and was used to correlate polymer secondary-ion yields of a static TOF-SIMS analysis to the degree of surface coverage. TOF-SIMS imaging was found to be inferior to AFM imaging with regard to determining the degree of surface coverage of polymers on silicon surfaces. PVC and PMMA both form separated domains on silicon when using spin-coating solutions with a polymer concentration below a material-dependent threshold. In the intermediate concentration range between domain formation and complete surface coverage, networks form. At low concentrations, the deposited polymer material was heterogeneously distributed in the plane of the film as well as vertically to the substrate, resulting in relatively thick hillocks distributed over a limited surface area. At higher concentrations, where network formation is observed, the polymer is heterogeneously distributed in the plane of the film with a large degree of surface coverage, and the average small thickness of the polymer network is fairly constant. A linear correlation was observed between the secondary-ion yield and the degree of surface coverage for both PVC and PMMA, which constitutes the calibration curves for the lateral quantification.