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In recent low-k1 lithography, the size of a mask pattern is becoming close to wavelength of the light source. The light intensity through the mask pattern is depending on polarization. TM polarization light is higher transmission than TE polarization light for a MoSi mask. This effect influences not only the zeroth-order light but the first-order light. On the other hand, TE polarization imaging makes higher contrast than TM polarization in two beam interference. Effects of polarization to resolution are not simple. Since an attenuated phase shift mask is used in order to obtain high contrast, it is necessary to take into consideration the influence of that. It is also taken into consideration that illumination light is not perpendicular incidence but oblique incidence for an ArF hyper-NA tool. We will perform a rigorous simulation in consideration of the above conditions. Hereby influence of the to the utmost resolution will be clarified by the rigorous simulation.

In the 45 nm half pitch node, a mask induced polarization effect appears. Because of this effect, intensity of diffracted light depends on a pattern size and a diffraction order. This is pronounced in an attenuated phase shift mask (attPSM). A mask topography effect has to be considered for rigorous simulation. A small window attributable to diffraction efficiency is generated, because of an insufficient ratio of 1st order and 0th order diffracted light from the attPSM. Two approaches to produce a sufficient ratio, namely, a low transmittance layer attPSM and a biased pattern attPSM, were investigated by simulation. A mask bias of more than 10 nm on both sides is required to generate an optimal diffraction efficiency ratio for the 0th and 1st orders. The low transmittance (around 1%) attPSM had higher contrast at 45 nm half pitch in the resist image than the biased attPSM. It was also shown that a phase difference between diffraction orders caused lower contrast imaging.

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