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The quality of masks is the crucial key to reliable and cost-efficient lithography. For conventional optical masks focused ion beam (FIB) has become popular as an approved tool for repairing defects detected in mask inspection. However, the repair of phase shift masks by FIB technology remains critical due to the lack of local deposition processes for materials issuing both, a sufficient optical transparency and an etching rate comparable to quartz glass. A focused ion beam tool utilizing a gallium ion beam with a tunable acceleration voltage of 5-50 kV is used to investigate a siloxane based deposition process of silicon oxides on quartz glass substrates. Tetramethyltetracyclosiloxan together with oxygen is decomposed by the ion beam on a silicon substrate and on a quartz glass surface. A chemical investigation of deposited dielectric layers is performed by Auger spectroscopy (AES) and Secondary Ion Mass (SIMS) spectroscopy. Optical quality of FIB-deposited silicon oxide is investigated by measuring the transmission at 248 nm. The etching selectivity of “as deposited layers” versus pure silicondioxide are determined in in-situ sputter etch experiments. We found a significant influence of process parameters such as precursor gas composition ratios, exposure times, and scan rates on the chemical composition of the deposited layers. Moreover, for optical transmission as well as for etch-rate selectivity the parameters of the deposition process are found to be decisive factors. A model explaining the correlation between process parameter, related chemical composition of dielectrics and resulting etch selectivity and optical transmittance is proposed. In summary, proper control of FIB CVD process parameters in combination with appropriate precursor gas system design are prerequisites for a promising approach in phase mask repair. Keywords: focused ion beam; phase-shift mask; mask repair; silicondioxide, SiO2, CVD
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