Challenges with hyper-NA (NA>1.0) polarized light lithography for sub lambda/4 resolution

Abstract

The use of immersion technology will extend the lifetime of 193nm and 157nm lithography by enabling numerical apertures (NA) much greater than 1.0. This paper explores the effects that will occur when the high NA systems are augmented with polarization.. Specifically we show that there are strong interactions between the polarization induced by the reticle and polarization in the optics. This has a direct impact on the across-field specification of the polarization of the optical system as it causes a large variation in the imaging impact in photoresist. The impact of lens and reticle birefringence on the imaging is also analyzed. We show that reticle birefringence should not be a major concern when the birefringence is maintained to 2nm/cm -4nm/cm levels. The lens can be modeled by a Jones matrix approach, where multiple pupils must be defined for each polarization state. We show the impact of the optical components by using a rigorous photoresist simulation on the process window of sub-50nm features using NA>1.3. The simulator uses a full Maxwell equation solver for the mask, polarized illumination, a Jones matrix approach for the pupil, and a photoresist simulation with calibrated model. The photoresist process is also shown to interact with polarization. Different photoresist will show varying degrees of sensitivity to polarization variation.

The impact of mask birefringence on hyper-NA (NA>1.0) polarized imaging

“…A combination of linear polarized light in the right direction with a background of unpolarized light, or linear polarization in a slightly different direction, or elliptically polarized light, or a combination of all these effects can give the same IPS value. It has been shown that the specific way a certain IPS value is obtained has no impact on imaging (6) . The simulation results in Figure 3 show that the details of IPS "formation" have no impact on the resulting CD change.…”

“…A detailed analysis of how mask birefringence can alter the effective IPS can be found in Ref. (6). This section will reassess the impact of mask birefringence using the concept of Stokes parameters and Mueller matrices rather than the Jones representation.…”

“…In Ref. (6) it was shown, that the impact of mask birefringence depends on the specific polarization properties of the light. This shall be illustrated for the case of light with an IPS value of 0.9.…”

Characterization and mitigation of 3D mask effects in extreme ultraviolet lithography

“…Nevertheless, some characteristic phenomena such as mask-induced polarization effects [3][4][5], mask-induced wave aberrations and best-focus (BF) shifts [6][7][8], and an impact on the obtained OPC models [9,10] can be observed. These so-called 'three-dimensional (3D) mask effects' or 'mask topography effects' depend on the 3D geometrical shape of the mask and on the optical properties, specifically the extinction value k and the refractive index n, of the mask materials.…”

Novel apodization and pellicle optical models for accurate optical proximity correction modeling at 45 and <inline-formula><math altimg="none" display="inline" overflow="scroll"><mrow><mn>32</mn><mspace width="0.3em" /><mi>nm</mi></mrow></math></inline-formula>

“…To model these hyper-NA systems, current state-of-the-art OPC modeling engines are already capable of modeling thin-film energy coupling, vector diffraction, polarization illumination, and immersion, imaging. [1][2][3] However, current OPC simulators * do not consider the loss of spatial frequency content due to pupil apodization or pellicle film effects. Both of these effects cause a loss of critical high-spatial-frequency information in the imaging process.…”