Comparison of EBR-900 M1 and ZEP 7000 with plasma-etch processing for MEBES 4500S

Abstract

Advanced photomask fabrication specifications for 180 nm generation devices require large-scale improvements to resolution, critical dimension (CD) control, and CD linearity. These requirements mandate the adoption of zero bias processes. The approximately 200 nm of bias required with widely used wet-etch processes cannot meet these advanced specifications. Plasma-etch processing provides an alternative to wet etching and has been shown to have little or no undercutting. However, some of the standard resists used with electron-beam (e-beam) exposure of photomasks have very poor dry-etch characteristics. In this paper, EBR-900 M1 and ZEP 7000 resist processes, in conjunction with inductively coupled plasma (ICP) etching, are described. EBR-900 is a DNQ-novolac i-line resist. The exposure dose and the development process were investigated using a caustic-based developer optimized for e-beam exposure. ZEP 7000 is a polymer of methylstyrene and chloromethyl acrylate, which uses a solvent-based developer. Spray and puddle processes were both investigated for their influence on resist sensitivity, edge slope, resist loss, and CD uniformity. While EBR-900 and ZEP 7000 are less sensitive than PBS, the higher current delivery of newer e- beam systems combined with multipass gray (MPG) writing strategies result in improvements to the lithographic performance without incurring any throughput limitations. MEBES 4500S is the target platform for these processes. It has the gun brightness and writing strategy (MPG) needed to expose these resists while maintaining high throughput.