Thermodynamic study of photomask plasma etching

Banqiu Wu

doi:10.1117/12.584205

6 December 2004 Thermodynamic study of photomask plasma etching

Banqiu Wu

Proceedings Volume 5567, 24th Annual BACUS Symposium on Photomask Technology; (2004) https://doi.org/10.1117/12.584205
Event: Photomask Technology, 2004, Monterey, California, United States

Abstract

Photomask plasma etch reactions were studied using Gibbs energy minimization method. The equilibrium compositions were analyzed at practical photomask plasma etch conditions of temperatures, pressures, and reactant inputs. The thermodynamic calculations were based on common gaseous systems used in photomask plasma etching such as Cl_2-O_2-He, SF_6-O_2-He, and CF_4-O_2-He, as well as alternative gases. For Cr etch, the thermodynamically calculated results showed that volatile CrO₂Cl₂ was the moderate equilibrium composition in the predetermined system only when the temperature was higher than 400°C, indicating that temperatures of heavy particles in practical plasma conditions might be higher than this temperature. The effects of assistant chemicals on equilibrium compositions were investigated. For MoSi etch, the thermodynamic calculation showed that the main volatile etch products were MoF₆ and SiF₄. The comparison of MoSi etch using SF₆ and CF₄ was made and gaseous input condition for obtaining all volatile products was found, which would be helpful for defectivity and passivation controls. The calculation also showed that the addition of oxygen in SF₆ and CF₄ systems could increase the equilibrium composition of atomic fluorine, resulting in the etch rate increase. This result agreed with previous hypothesis on the oxygen effects on etch rate. For quartz etch, the calculation showed that the main volatile etch product was SiF₄. For Ta or TaN absorber EUV mask etch, the volatile Ta-containing product was found to be TaCl₅.

Citation Download Citation

Banqiu Wu "Thermodynamic study of photomask plasma etching", Proc. SPIE 5567, 24th Annual BACUS Symposium on Photomask Technology, (6 December 2004); https://doi.org/10.1117/12.584205

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