Investigations of SU-8 removal from metallic high aspect ratio microstructures with a novel plasma technique

First promising investigations of SU-8 removal experiments with a novel plasma etching technique are presented. The basic idea of this technique is to separate the highly effective generation of chemical radicals (e.g. oxygen radicals) using a traveling wave reactor (TWR) microwave source with water cooled plasma zone from the chemical reaction with the resist polymer. The etching tool operates in a remote and downstream mode with very high radical density allowing precise thermal management of the substrates on the chuck giving controlled process conditions without deviation in temperature, and generally preventing ion bombardment, at least resulting in gentle processing without jeopardizing the integrity of the metal structures. Very good removal of SU-8 with very few residues and very high etching rates up to 10 μm per minute are observed in first experiments which are offering chances to get even more than 20 μm per minute. The etching process is isotropic, and the rate stays stable during the whole removing process even for very thick films of 1 mm and more. First application examples of SU-8 removal are demonstrating the great potential of the presented microwave plasma based technique not only for the cleaning of metallic microparts but also for other more sensitive materials which is demonstrated by SU-8 removal from graphite X-ray mask substrates.