Resist Processes for High Resolution Mask and Direct Write Applications Using the Latest Vistec VSB Electron Column

Abstract

Summary form given only. High resolution variable shaped beam (VSB) electron lithography becomes more and more important for chip and mask making. The use for direct write of critical layers, at least one node ahead of the current production level, enables early device and technology development as well as fast prototyping. Aggressive OPC features of advanced photomasks require a resolution capability of the chrome patterning process clearly below 80 nm. Finally, the nanoimprint lithography has been discussed as a future option for device making and template structuring demands minimum feature sizes corresponding to the considered node. These three addressed pattern generator applications require both, high resolution and a cost-effective throughput for complex pattern and therefore we evaluated a VSB system in combination with latest chemically amplified resist (CAR) samples for these purposes. The used Vistec VSB writer is equipped with Vistec's most recent 3050 column [1], operating at 50 kV, a current density of 20A/cm2 with an improved edge acuity focussed on a resolution of 35 nm and below. In a test using HSQ lines with 30 nm half pitch could be obtained proving the high resolution capability of this new column. For the considered applications we evaluated e-beam sensitive pCARs and nCARs of different vendors in combination with the new Vistec column. The evaluation of all CARs was accomplished according to an identical method focussed on the determination of resolution, line edge roughness, sensitivity, vacuum stability, bake sensitivity and etch stability After these basic tests first optimized processes have been developed executing DoEs with bake and developer conditions as input parameters. Many CARs suffer from limited resolution and severe line edge roughness. One resist vendor provided CARs based on the same polymer but with different PAG and quencher concentrations resulting in different e-beam sensitivities. On the basis of these materials we investigated the dependency between the sensitivity on one hand and resolution and line edge roughness on the other hand. Finally, we will demonstrate the application of selected CARs for nanoimprint template and photomask patterning. Sub-50 nm pillars on a template have been generated using a negative-tone resist while a pCAR has been applied for structuring of 50 nm features in an 80 nm thick hardmask / chrome stack of a binary photomask.