Development of a sub-100-nm integrated imaging system using chromeless phase-shifting imaging with very high NA KrF exposure and off-axis illumination

Examining features of varying pitch imaged using phase-shifting masks shows a pitch dependence on the transmission best suited for optimum imaging. The reason for this deals with the relative magnitude of the zero and higher diffraction orders that are formed as the exposing wavelength passes through the plurality of zero and 180-degree phase-shifted regions. Subsequently, some of the diffraction orders are collected and projected to form the image of the object. Chromeless Phase-Shift Lithography (CPL) deals with using halftoning structures to manipulate these relative magnitudes of these diffraction orders to ultimately construct the desired projected image. A key feature of CPL is that with the ability to manipulate the diffraction orders, a single weak phase-shifting mask can be made to emulate any weak phase-shifting mask and therefore the optimal imaging condition of any pattern can be placed on a single mask regardless of the type of weak phase-shifter that produces that result. In addition, these structures are used to render the plurality of size, shape and pitch such that the formed images produce their respective desired size and shape with sufficient image process tolerance. These images are typically made under identical exposure conditions, but not limited to single exposure condition. These halftoning structures can be used exterior, as assist features, or interior to the primary feature. These structures can range in transmission from 0% to 100% and they can be phase-shifted relative to the primary features or not. Thus CPL deals with the design, layout, and utilization of transparent and semi-transparent phase-shift masks and their use in an integrated imaging solution of exposure tool, mask and the photoresist recording media. This paper describes the method of diffraction matching, provides an example and reviews some experimental data using high numerical aperture KrF exposure.