Through-pellicle defect inspection of EUV masks using an ArF-based inspection tool
The use of EUV photomasks in a semiconductor manufacturing environment requires their periodic inspection to ensure they are continually free of defects that could impact device yield. Defects typically occur from fall-on particles or from surface degradation such as "haze". The proposed use of a polycrystalline-based EUV pellicle to prevent fall-on particles would preclude periodic through-pellicle mask defect inspection using e-beam, as well as, DUV inspection tools (the pellicle is opaque at DUV wavelengths). Thus, to use these types of defect inspection tools would require removal of the EUV pellicle before inspection. After inspection, the pellicle would need to be re-attached and the mask re-qualified using a test wafer, thus causing expense and delays. While EUV-wavelength inspection tools could inspect through such a pellicle precluding the need to remove the pellicle, these tools are not likely to be available in the commercial marketplace for many years. An alternate EUV pellicle material has been developed that is semi-transparent to 193nm wavelengths, thus allowing through-pellicle inspection using existing ArF-based, or other 193nm wavelength mask inspection tools. This eliminates the requirement to remove the pellicle for defect inspection and the associated time and expense. In this work, we will conduct an initial evaluation of through-pellicle EUV mask defect inspection using an existing 193nm mask inspection tool. This initial evaluation will include durability of the pellicle to defect inspection, and impact of the pellicle on inspection tool performance.