In EUV lithography, the short wavelength of the light makes the topography of the mask stand out as three dimensional objects rather than thin masks. This generally requires use of a rigorous scattering simulator to calculate the diffracted orders of a mask in order to explain experimental results. In contrast, for optical proximity correction we cannot afford such detailed calculations and we would like to replace such detailed simulations with faster methods that give similar results.In this paper, we discuss observations we made during our printing experiments on a 0.33 NA EUV projection system. In order to extend the process window for non-nested trenches we introduced clear assist features. We observed strong tilt of Bossung curves and best focus shifts for certain pitches. These shifts can be explained by a phase difference between main and assist feature. This effect is very similar for both horizontal and vertical trenches, and it depends strongly on the illumination of the mask. We find that the best focus shift can be minimized for certain assist pitches and illumination conditions, but a general solution for random pitches appears not obvious.

Several methods are evaluated to improve the accuracy of extreme ultraviolet (EUV) lithography OPC models by including additional physical effects which are not commonly used in deep ultraviolet (DUV) OPC. The primary additions to the model in this work are model based corrections for flare and two different corrections for mask shadowing effects, commonly referred to as HV bias. The quantitative, incremental, improvement from each of these additions is reported, and the resulting changes in tape-out flow and OPC runtime are discussed

The first use of extreme ultraviolet (EUV) lithography in logic manufacturing is targeted for the 14 nm node, with possible earlier application to 20-nm node logic device back-end layers to demonstrate the technology. Use of EUV lithography to pattern the via-levels will allow the use of dark-field EUV masks with low pattern densities and will postpone the day when completely defect-free EUV mask blanks are needed. The quality of the imaging at the 14 nm node with EUV lithography is considerably higher than with double-dipole or double-exposure double-etch 193-nm immersion lithography, particularly for 2-dimensional patterns such as vias, because the Rayleigh k1-value when printing with 0.25 numerical aperture (NA) EUV lithography is so much higher than with 1.35 NA 193-nm immersion lithography and the process windows with EUV lithography are huge. In this paper, the status of EUV lithography technology as seen from an end-user perspective is summarized and the current values of the most important metrics for each of the critical elements of the technology are compared to the values needed for the insertion of EUVL into production at the 14 nm technology node.

Although the k1 factor is large for extreme ultraviolet (EUV) lithography compared to deep ultraviolet (DUV) lithography, OPC is still needed to print the intended patterns on the wafer. This is primarily because of new non-idealities, related to the inability of materials to absorb, reflect, or refract light well at 13.5nm, which must be corrected by OPC. So, for EUV, OPC is much more than conventional optical proximity correction. This work will focus on EUV OPC error sources in the context of an EUV OPC specific error budget for future technology nodes. The three error sources considered in this paper are flare, horizontal and vertical print differences, and mask writing errors. The OPC flow and computation requirements of EUV OPC are analyzed as well and compared to DUV. Conventional optical proximity correction is simpler and faster for EUV compared to DUV because of the larger k1 factor. But, flare and H-V biasing make exploitation of design hierarchy more difficult.

To avoid expensive immersion lithography and to further use existing dry tools for critical contact layer lithography at 4Xnm DRAM nodes the application of altPSM is investigated and compared to attPSM. Simulations and experiments with several test masks showed that by use of altPSM with suitable 0°/180° coloring and assist placement 30nm smaller contacts can be resolved through pitch with sufficient process windows (PW). This holds for arrays of contacts with variable lengths through short and long side pitches. A further benefit is the lower mask error enhancement factor (MEEF). Nevertheless 3D mask errors (ME) consume benefits in the PW and the assist placement and coloring of the main features (MF) put some constraints on the chip design. An altPSM compatible 4Xnm full-chip layout was realized without loss of chip area. Mask making showed very convincing results with respect to CDU, etch depth uniformity and defectiveness. The printed intra-field CD uniformity was comparable to attPSM despite the smaller target CDs. Room for improvement is identified in OPC accuracy and in automatic assist placement and sizing.

Modular OPC modeling, describing mask, optics, resist and etch processes separately is an approach to keep efforts for OPC manageable. By exchanging single modules of a modular OPC model, a fast response to process changes during process development is possible. At the same time efforts can be reduced, since only single modular process steps have to be re-characterized as input for OPC modeling as the process is adjusted and optimized. Commercially available OPC tools for full chip processing typically make use of semi-empirical models. The goal of our work is to investigate to what extent these OPC tools can be applied for modeling of single process steps as separate modules. For an advanced gate level process we analyze the modeling accuracy over different process conditions (focus and dose) when combining models for each process step - optics, resist and etch - for differing single processes to a model describing the total process.

High NA scanners with adjustable polarization are becoming commercially available. Linear polarization has been shown to significantly improve imaging performance of preferentially oriented fines.' Azimuthal and tangential polarization are now becoming commercially available. The latter has less asymmetry in its imaging and can resolve critical features oriented in multiple directions at the same time. Linear y-oriented or vertical polarization was used, since at the time of this work, azimuthal and tangential polarization were not available. Such x- and y-oriented linear polarization could be used in double exposure imaging, for example. Just as for unpolarized imaging, OPC models are required for polarized imaging that are accurate in (a) fitting and predicting experimental CD values, (b) fragmenting layout, and (c) correcting the fragmented layout to target. This paper describes the results of such a first OPC verification loop. Experimental proximity data in X- and Y-orientation were measured. Source polarization and wafer stack thin film effects were included in the empirically fit OPC simulation model. A parallel investigation was undertaken using an unpolarized source. It served as the reference case. Simple test patterns as well product-like 2D layout was treated with the vertically polarized and unpolarized OPC models. A test mask was written and wafer printing results obtained. They demonstrated the validity of the approach and pointed to further OPC model improvements.