Integrated circuits suffer from serious layout printability issues associated to the lithography manufacturing process. Regular layout designs are emerging as alternative solutions to help reducing these systematic sub-wavelength lithography variations. From CAD point of view, regular layouts can be treated as repeated patterns that are arranged in arrays. In most modern mask synthesis and verification tools, cell based hierarchical processing has been able to identify repeating cells by analyzing the design’s cell placement; however, there are some routing levels which are not inside the cell and yet they create an array-like structure because of the underlying topologies which could be exploited by detecting repeated patterns in layout thus reducing simulation run-time by simulating only the representing cells and then restore all the simulation results in their corresponding arrays. The challenge is to make the array detection and restoration of the results a very lightweight operation to fully realize the benefits of the approach. A novel methodology for detecting repeated patterns in a layout is proposed. The main idea is based on translating the layout patterns into string of symbols and construct a “Symbolic Layout”. By finding repetitions in the symbolic layout, repeated patterns in the drawn layout are detected. A flow for layout reduction based on arrays-detection followed by pattern-matching is discussed. Run time saving comes from doing all litho simulations on the base-patterns only. The pattern matching is then used to restore all the simulation results over the arrays. The proposed flow shows 1.4x to 2x run time enhancement over the regular litho simulation flow. An evaluation for the proposed flow in terms of coverage and run-time is drafted.
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.
Rapidly decreasing critical dimension is demanding new RET technologies like PSMgate, customized strong off-axis, and Double Exposure. Among them, Double Exposure is becoming a stronger candidate as throughput issue is getting better because of exposure tool's enhancement. Indeed, immersion is not fully ready and many semiconductor manufacturing companies want to extend their exposure tools for sub 55nm process. So, Double Exposure has been studied for a long time and suggested by many lithographers for sub 55nm process. For Logic device, it has many challenges to make Double Exposure work like need for model based layer decomposition. But for Memory device such as DRAM and FLASH, there is a good way to make Double Exposure flow robust because its design is not that random like Logic Device. In this paper, we will investigate and show how to implement robotic Double Exposure using two typical Double Exposure illumination combinations, Dipole-Ann and Double Dipole.
This paper investigates variability across multiple lithographic domains, as experienced in typical manufacturing environments, and assesses the impact on achievable post-OPC image fidelity and CD control. Across scanner field and tool-tool effects are considered, and a distinction is made between systematic phenomena, which typically manifest within chip, and random fluctuations, which predominantly impact chip-to-chip mean distributions. The paper will outline which lithographic parameters can effectively be accounted for in OPC models, and over what temporal/spatial extents. The non-correctable phenomena assessed include misalignment, projection optic aberrations, illumination source profile, mask CD, focus and exposure dose variation, and flare. Specific analyses are applied to the case of gate edge placement error (EPE) control as a function of these manufacturing variables. Recommendations are made for "field-aware" metrology sample plans during model creation, such that globally optimized models can be realized. With knowledge of manufacturing input parameter variation, CalibreTM enables a detailed understanding of realistic post-OPC CD control, and can guide judicious product metrology sampling and specifications. It is highlighted that even for the case of a "perfect" OPC model, the post-OPC CD variation within chip can still be substantial, due to manufacturing variability.
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