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This study takes an integrated approach utilizing a combination of high NA 193 nm lithography, a sidewall chrome alternating aperture (SCAA) phase shift mask, optical proximity correction (OPC) and customized illumination in an attempt to demonstrate the feasibility of using 193 nm lithography to support the 65 nm node. A SCAA mask was designed and built with line/space patterns ranging in pitch from 300 nm down to 140 nm. A range of mask biases were applied to the zero and pi spaces in order to examine to response of the lithography to a combination of the SCAA approach and asymmetric biasing. In combination to the asymmetric biasing, overlay bracketing was applied in order to measure the chrome overlay tolerances of the mask. Simulations suggested that an unconventionally small sigma of 0.15 would be the optimum coherence for a high 193 nm optical system. A custom 0.15 sigma partial coherence illuminator was, therefore, built and installed in the experimental ASML Micrascan V 0.75 NA 193 nm scanner. Wafers were exposed using 190 nm of 193 nm resist and an organic BARC. The 70 nm 1:1 line/space patterns resolved with a depth of focus of about 0.2 μm. The 75 nm 1:1 line/space patterns showed a 0.3-0.4 μm depth of focus. Both of these process windows were limited by pattern collapse. Addressing the pattern collapse may improve the depth of focus. Comparing mask measurements to wafer measurements show that little or no asymmetric biasing in necessary to balance the pitch. Moreover, the measured pitch was stable over a focus range of at least 0.4 microns demonstrating that any phase imbalance present was not significantly affecting the observed lithography.

Each generation of semiconductor device technology drive new and interesting resolution enhancement technology (RET’s). The race to smaller and smaller geometry’s has forced device manufacturers to k1’s approaching 0.40. The authors have been investigating the use of Chromeless phase-shifting masks (CLM) exposed with ArF, high numerical aperture (NA), and off-axis illumination (OAI) has been shown to produce production worthy sub-100nm resist patterns with acceptable overlapped process window across feature pitch. There have been a number of authors who have investigated CLM in the past but the technology has never received mainstream attention due to constraints such as wet quartz etch during mask fabrication, limited approach to optical proximity correction (OPC), and exposure tool limitations such as on-axis illumination and too low of NA. With novel binary halftone OPC and a capable modern mask making process, it has become possible to achieve global and local pattern optimization of the phase shifter for a given layout especially for patterning features with dimension at sub-half-exposure wavelength. The authors have built a number of test structures that require superior 2D control for SRAM gate structures. In this paper the authors will focus on image process integration for the 65nm node. Emphasis on pattern layout, mask fabrication and image processing will be discussed. Furthermore, the authors will discuss defect printing, inspection and repair, mask error enhancement factor (MEEF) of 2D structures coupled with phase error, layout, and mask fabrication specifications.

In this paper the concept of chromeless phase lithography (CPL) is introduced and experimental results on an ASML PAS 5500/800 are presented. CPL is a single exposure technique and is capable of resolution enhancement on all device layers (bright and dark field masks). Line space structures through pitch are measured with cross section and have O.35jim depth of focus (DOF) at 10% exposure latitude without forbidden pitches. CPL experimental results for a k1 of 0.38 (½ pitch) are presented for three DRAM device layers, isolation brick wall, storage capacitor, and honeycomb contact. Each of these layers have a DOF of O.35jim at 10% exposure latitude. CPL experimental results are presented for a SRAM gate and contact with lOOnm feature size (k1=O.32) and have a DOF of O.35jim at 10% exposure latitude.

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.

The remaining difficulties in applying dual exposure dark-field strong-PSM technology can be overcome using the Sidewall Chrome Alternating Aperture (SCAA) mask structure, first proposed in 1992 and now fabricated. With all silica sidewalls covered and all chrome supported, the SCAA mask is largely immune to the phase and amplitude anomalies that cause spacewidth alternation as well as the design, fabrication and cleaning difficulties that plague other structures. Maxwell's equation solvers predict that the optical phase will be essentially independent of aperture size. Chips designed with their fmest features on a pre-defined regular grid can employ generic SCAA mask substrates in which the topography has been pre-patterned using wafer fab techniques. Guaranteed defect-free SCAA mask substrates will be manufactured in large quantity and low cost if the design grids become standardized. Fabricating strong-PSMs using these Phase Phirst mask substrates will prove no more difficult for mask-makers than COG masks, and the reduced MEEF will permit loosened CD specifications, among other advantages. The Phase Phirst Paradigm promises to reduce optical lithography costs —even for ASIC manufactures — and to delay the need for NGL technologies.