Spatial frequency analysis of resolution enhancement technology

As two of the most important resolution enhancement technology (RET), off-axis illumination (OAI) and attenuated phase-shift mask (AttPSM) can not only improve image quality, but also improve the depth of focus (DOF) to get a better process window which make a great contribution to the realization of 65-32 nm technological mode. A consistent frequency-space analysis of the off-axis illumination and attenuated phase-shift mask is presented here to explain its influence to the transmission cross coefficient (TCC) and image frequency distribution. Study on the optical mechanism of these resolution enhancement technology can benefit the design of projection lens optical system, optimization of resolution enhancement technology and the parameter setting of lithographic tool. It shows resolution enhancement technology can adjust image frequency distribution to enhance the lithographic resolution and image quality. As for 65 nm node pattern, off-axis illumination and phase-shift mask can improve image contrast to 0.948, process window to depth of focus 0.51 μm while exposure latitude is 5%.