180-nm mask fabrication process using ZEP 7000, multipass gray, GHOST, and dry etch for MEBES 5000

Abstract

Advanced reticle specifications for resolution, critical dimension (CD) control and CD linearity of 180-nm generation devices require large-scale improvements to maskmaking processes. The approximately 200 nm of bias required with widely used wet etch processes will not meet these specifications. A solution to the high bias requirement of wet etch processing is to implement a plasma or dry etch process. Plasma etch processing 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 poor dry etch characteristics. ZEP 7000 is an e-beam resist that has good dry etch resistance while exhibiting superior lithographic quality. In this paper, processes using ZEP 7000 resist and inductively coupled plasma (ICP) etching are described. The combination of these operations can result in zero bias or near zero bias process with e-beam exposure of photomasks. While the required dose for ZEP 7000 is higher than that of PBS, the higher beam current capability of newer e-beam systems, together with multipass writing strategies, enables the use of these slower resists without throughput penalty. Optimization of the development process was done using a two-component solvent developer. A puddle process was investigated for optimizing sensitivity, edge slope, resist loss, mean-to-target control, and CD uniformity. Dry etching with ICP has been shown to etch chromium films with good selectivity to the resist, give a highly anisotropic etch, and, most significantly, show insensitivity to loading effects. The net result of this effort is the development of a process that gives excellent CD control when meeting MEBES 5000 system requirements for 180-nm maskmaking. Data on resolution, CD control, and defects are presented using this process.