Journal of Micro/Nanolithography, MEMS, and MOEMSMoSi etch of phase-shift masks
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Studies on MoSi etch processes were carried out using a design-of-experiments (DOE) methodology. Data was gathered using profilometers and optical critical dimension (CD) measurement systems. MoSi etch chemical kinetics was studied and a kinetic equation was developed showing that MoSi etch rate has a linear relationship with inductively coupled plasma (ICP) power, and an exponential relationship with the negative inverse of the DC bias electrode voltage. The reaction orders of the MoSi etch were 0.2 to SF6 concentration (molar fraction) and 0.5 to O2 concentration, and the activation energy was found to be 1350 kJ/mol. A dimensionless number method was used for results analysis and a calculable dimensionless number was defined. This number was found to be proportional to the isolated/dense etch bias. Etcher performance was also analyzed using a matrix transformation method and it was found that matrix-analysis-calculated etch results agreed with those obtained by experimental measurement. The optimal MoSi etch process window was expressed graphically.