Using TaN as extreme ultra-violet lithography (EUVL) mask absorber has been previously explored in wafer format 1-2 . Due to substrate material difference between the square mask format and Si wafer format, e.g., electrical conductivity and thermal conductivity difference, etc., the etch process does not behave the same when mask substrate switches from the Si wafer to the square quartz substrates. With low thermal conductivity on quartz material and no backside cooling, mask etch prefers low power as compared to the Si wafer etch. In the study, we found that for a given source and bias power, the cooling of the substrate plays a role in TaN etch rate and selectivity to the buffer oxide layer.In this paper, we will present detailed study and comparison of TaN EUVL mask absorber etch characteristics for both the Si substrate and the square quartz substrate cases. The effect of source power, bias power, and backside cooling will also be discussed. The etchers used in study to etch TaN film on the wafer substrate and on the square format mask substrate have the similar configuration. With the optimized etch process, we have achieved good TaN etch profile with high etch selectivity to SiO 2 buffer layer on the square quartz mask substrate.
As mask specifications continually tighten with the ever-present progression of Moore's law, mask manufacturing specifications have become increasingly difficult to achieve. Global process optimization from coat to etch is critical for achieving the required mask performance. As an Applied Materials company, Etec is in a unique position within the maskmaking industry to introduce mask manufacturing solutions that are optimized across a number of process steps. Working with the Applied Materials photomask etch team, Etec's laser mask-patterning product group characterized and implemented an integrated process recipe for the deep ultraviolet (DUV), raster-scan, continuouswave, laser mask-patterning ALTA® 4000 system and the Applied Materials TetraTM Photomask Etch System. Using a photomask recipe already developed by Etec, commercially manufactured DX1 loop photoresist-coated masks were patterned on the ALTA 4000 system, the latest optical pattern generator released by Etec Systems, and were subsequently used for integrating a dry-etch process with the Centura Photomask Etch system. The newly developed photomask process solution includes an anti-reflective resist top coat (patent pending), post-exposure bake (PEB), develop, dry etch, and resist sthp steps. The areas investigated to optimize dry etch included partial pressure and flow rates of reactant gases, chamber pressure, overetch, and focus ring geometry. The characterization primarily focused on those parameters directly affecting the productive yield of the maskmaker, including critical dimension (CD) mean error, CD uniformity, process bias, selectivity, and micro-loading. This paper documents the results of Etec's implementation and characterization of an integrated mask manufacturing process, which is optimized across many process steps, creating a Total SolutionsTM concept for maskmaking.
In this paper we describe the development of a chrome dry etch process on a new type of mask etch tool. One crucial goal was to minimize the CD etch bias. To meet this goal, a procedure for the direct characterization of CD etch bias was developed. The common methods for measuring the CD etch bias as resist-to-chrome CD difference, such as confocal optical microscope or SEM measurement, only give correct results, if the sidewalls are identical to the calibration standard. This is normally not the case as, due to the differing step height of resist and chrome, and the fact that during process development, in particular, the sidewall shapes and angles can vary significantly. Thus, it is very important to use a CD measurement method which takes the sidewall shapes (slope, foot) into account. One novel method is the use of a Scanning Nano Profiler (SNP) which was derived from the AFM principle. In contrast to AFM the use of a special high aspect ratio tip with 90° sidewall angle, in combination with pixelwise scanning of the substrate surface, provides information about the true sidewall shape and CD.
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