In recent low-k1 lithography, the size of a mask pattern is becoming close to the wavelength of the light source. In a sub-100-nm pattern at wafer scale of 4× masks, transverse electric (TE) polarization light had higher transmittance of the zeroth order than TM polarization for a Cr mask according to rigorous model simulation of a finite difference time domain method. On the other hand, transverse magnetic (TM) polarization light had higher transmittance than TE polarization light for a MoSi mask. From the results of lithography simulation for a 45-nm pattern on the MoSi mask, TE polarization was better for wide exposure latitude, but TM polarization was better for large depth of field. The performance of a current MoSi mask is inferior to that of a Cr mask. However, a lower transmittance MoSi mask has better performance in the exposure defocus window under the dipole illumination. Also, rigorous simulation showed transmittance dependency of the light incident angle to the MoSi mask. The dependency was larger for TM polarization than for TE polarization.
