Defect generation mechanism in magnetron sputtered metal films on PMMA substrates

Polymer metallization is widely used in a variety of micro and nano system technologies, and magnetron sputtering of a metal film is one of the essential processes of polymer metallization. However, some defects are likely generated in sputtered metal films on a polymer substrate. In this work, the defect generation mechanism in the sputtered Au film on a polymethylmethacrylate (PMMA) substrate was investigated for the first time. The characteristics of defects on the PMMA surface and in the Au film were examined by an optical microscope, a scanning electron microscope (SEM) and a confocal microscope. Detailed characterization results indicate that the ejected Au atoms bombard the PMMA substrate and cause snowflake-like defects on the PMMA surface because of the low hardness of PMMA, then Au atoms nucleate and grow at PMMA defect sites and form a partially suspended metal film, subsequently dropping the photoresist makes the suspended metal film conformally adhere to the PMMA defect, and the snowflake-like morphology is replicated to the metal film. The effects of sputtering parameters on the defects were studied, and the amount of defects in the Au film reduced with the decrease of the sputtering power or the sputtering pressure.