Defect Generation Mechanism In Sputtered Au Films On PMMA Substrates

Polymer metallization is widely used for integrating various metal components on polymer micro and nano devices.Deposition of a metal film is one of the essential processes of polymer metallization.Magnetron sputtering is widely used for depositing metal films on inorganic materials,while some defects can be generated in the sputtered metal film on polymer substrates due to large differences in mechanical and thermal properties between inorganic materials and polymer.In this work,the defect characteristics were examined and the defect generation mechanism in sputtered Au films on a polymethylmethacrylate(PMMA)substrate was investigated.Firstly,the characteristics of defects in the Au film were examined by an optical microscope,a confocal microscope and a scanning electron microscope(SEM).The result shows that,the morphology of the defect presented an irregular,snowflake-like structure under the optical microscope.The Au film in the middle of the snowflake-like structure was broken,and a microscale hole appeared.Secondly,the thermal properties and mechanical properties of PMMA substrate were studied by a DSC differential thermal analyzer,a nanoindenter and a quadrupole mass spectrometer.The characteristics of defects on the PMMA surface were examined by an optical microscope,and a confocal microscope.The chemical structure of PMMA substrates was studied by a laser confocal microscope Raman spectrometer.Finally,detailed characterization results indicate that at the beginning of sputtering,the bombardment of the ejected metal atoms randomly caused tiny damage to the PMMA surface due to the low hardness of PMMA.With the sputtering time,the temperature of the PMMA surface increased,the hardness of PMMA was further decreased,and the damage gradually increased and formed a snowflake-like defect.At the same time,the ejected metal atoms nucleated and grew 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.In addition,the effects of sputtering parameters on the defects were studied.The experimental results show that the amount of defects in the Au film reduced with the decrease of the sputtering power or the sputtering pressure.