Abstract
A high-resolution technique has been developed for the fabrication of photomasks for 10nm logic nodes and beyond. Current mask manufacturing techniques use a chemically amplified resist (CAR) material that has a complex mechanism of acid generation; this complicates the criteria for selecting the polymer and the quencher for industrial purposes. It is therefore important to validate non-CAR materials as alternative solutions for mask fabrication. In this research, we used diluted ZEP520A as a non-CAR material in conjunction with a JBX9000 variable-shaped electron-beam (VSB) lithography tool. Additionally, a post-exposure bake (PEB), routinely used in mask fabrication, was also applied. We investigated the effects of the PEB temperature on the fabrication of masks from non-CAR resists, and we demonstrated the feasibility of using a PEB as a high-resolution technique. The critical dimensions (CDs) for 1:1 line-and-space, isolated space, and isolated line patterns on a diluted ZEP520A resist were measured and showed a shrinkage, an extension effect, and retention of the integrity of the shape after the PEB process, respectively. Furthermore, the line-edge roughness (LER) of the 1:1 line-and-space and isolated space CDs was improved by approximately 40% by optimizing the PEB temperature. We investigated the process characteristics of this PEB annealing effect by examining the hardness of the cured resist with and without exposure to PEB at various temperatures, with the aim of elucidating the underlying mechanism. Optimizing the PEB temperature of the non-CAR increased the resist contrast, annealing the resist and improving the LER. This permitted us to demonstrate an advanced fabrication technique capable of high resolutions of the order of 20nm. The insights gained from the optimization of the PEB process might be useful in advanced methods of fabricating masks of the next generation.
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