The fate of optical-based lithography hinges on the ability to deploy viable resolution enhancement techniques (RET). One such solution is double patterning (DP). Like the double-exposure technique, double patterning is a decomposition of the design to relax the pitch that requires dual masks, but unlike double-exposure techniques, double patterning requires an additional develop and etch step, which eliminates the resolution degradation due to the cross-coupling that occurs in the latent images of multiple exposures. This additional etch step is worth the effort for those looking for an optical extension [1]. The theoretical k1 for a double-patterning technique of a 32nm half-pitch (HP) design for a 1.35NA 193nm imaging system is 0.44 whereas the k1 for a single-exposure technique of this same design would be 0.22 [2], which is sub-resolution. There are other benefits to the DP technique such as the ability to add sub-resolution assist features (SRAF) in the relaxed pitch areas, the reduction of forbidden pitches, and the ability to apply mask biases and OPC without encountering mask constraints. Similarly to AltPSM and SRAF techniques one of the major barriers to widespread deployment of double patterning to random logic circuits is design compliance with split layout synthesis requirements [3]. Successful implementation of DP requires the evolution and adoption of design restrictions by specifically tailored design rules. The deployment of double patterning does spawn a couple of issues that would need addressing before proceeding into a production environment. As with any dual-mask RET application, there are the classical overlay requirements between the two exposure steps and there are the complexities of decomposing the designs to minimize the stitching but to maximize the depth of focus (DoF). In addition, the location of the design stitching would require careful consideration. For example, a stitch in a field region or wider lines is preferred over a transistor region or narrower lines. The EDA industry will be consulted for these sound automated solutions to resolve double-patterning sensitivities and to go beyond this with the coupling of their model-based and process-window applications. This work documented the resolution limitations of single exposure, and double-patterning with the latest hyper-NA immersion tools and with fully optimized source conditions. It demonstrated the best known methods to improve design decomposition in an effort to minimize the impact of mask-to-mask registration and process variance. These EDA solutions were further analyzed and quantified utilizing a verification flow.
[1]
George E. Bailey,et al.
Effective multicutline QUASAR illumination optimization for SRAM and logic
,
2003,
SPIE Advanced Lithography.
[2]
Travis Brist,et al.
Illumination optimization effects on OPC and MDP
,
2004,
SPIE Advanced Lithography.
[3]
Lars W. Liebmann,et al.
Layout Methodology Impact of Resolution Enhancement Techniques
,
2007
.
[4]
Robert Boone,et al.
Reticle enhancement verification for the 65nm and 45nm nodes
,
2006,
SPIE Advanced Lithography.
[5]
Vincent Wiaux,et al.
Application challenges with double patterning technology (DPT) beyond 45 nm
,
2006,
SPIE Photomask Technology.
[6]
Vincent Wiaux,et al.
Manufacturability issues with double patterning for 50-nm half-pitch single damascene applications using RELACS shrink and corresponding OPC
,
2007,
SPIE Advanced Lithography.
[7]
John Sturtevant,et al.
Impact of process variation on 65nm across-chip linewidth variation
,
2006,
SPIE Advanced Lithography.
[8]
Eric Hendrickx,et al.
Source polarization and OPC effects on illumination optimization
,
2005,
SPIE Photomask Technology.
[9]
M. Van Hove,et al.
Double patterning scheme for sub-0.25 k1 single damascene structures at NA=0.75, λ=193nm
,
2004,
SPIE Advanced Lithography.