CD requirements for advanced photomasks are getting very demanding for the 100 nm-node and below; the ITRS roadmap requires CD uniformities below 10 nm for the most critical layers. To reach this goal, statistical as well as systematic CD contributions must be minimized. Here, we focus on the reduction of systematic CD variations across the masks that may be caused by process effects, e.g. dry etch loading.
As the industry accelerates the reduction in sub-wavelength device feature sizes, it is necessary that the traditional barriers between design, mask data preparation (MDP), and the lithography process be broken down or eliminated. These processes, which now possess increased levels of complexity and interconnectivity, can no longer work independently but must be linked and all applicable information about the processes propagated upstream.
Options associated with phase shift masks, optical proximity correction, increasing constraints for the minimum defect size requirements, improving yield and throughput, etc. have been key to the increased demands placed on the photomask manufacturers. Knowledge of the lithographic performance of a selected option prior to mask build is key to reducing mask cost, improving turn around time and staying on the aggressive path established by the mask user.
Integrating CD and lithographic process window analysis with MDP provides a convenient means of helping the mask makers to predict the performance of a mask within the wafer fab. This paper will discuss the integration of CD and lithographic process window analysis tools with CATS mask data preparation software. The benefits of implementing this methodology will be explored and illustrated with data.
Within the past decades data file sizes and the related computing power for mask data preparation grew linearly following Moore’s law. However, within the last two years the balance between rising data complexity and computing equipment became unstable due to the massive introduction of OPC and the broad rollout of complex variable shaped beam (VSB) data formats. The disturbance of the former linear coherence led to exploding data conversion times (exceeding 100 hours for a single layer) accompanied by heavily escalating data volumes. A very promising way out of that dilemma is the recently announced introduction of distributed job processing within the mask data processing flow. This way was initially introduced to fracture flat jobs. Building on our first promising results last year we now implemented a fully automated design flow with an integrated Linux based cluster for distributed processing. The cluster solution is built in an automated environment in coexistence with our conventional SUN servers. We implemented a highly reliable DP flow on a large scale base which became as stable as our former Solaris SUN system. In the meanwhile we reached a job first time success rate exceeding 99%. After reaching a very stable state we recently started to extend our flat processing conversion steps by investigating hierarchical distributed processing in CATS version 23. We also report on benchmark results comparing new promising hardware configurations to further improve the cluster performance.
CD requirements for advanced photomasks are getting very demanding for the 100 nm-node and below; the ITRS roadmap requires CD uniformities below 10 nm for the most critical layers. To reach this goal, statistical as well as systematic CD contributions must be minimized. Here, we focus on the reduction of systematic CD variations across the masks that may be caused by process effects, e.g. dry etch loading. We address this topic by compensating such effects via design data correction analogous to proximity correction. Dry etch loading is modeled by gaussian convolution of pattern densities. Data correction is done geometrically by edge shifting. As the effect amplitude has an order of magnitude of 10 nm this can only be done on e-beam writers with small address grids to reduce big CD steps in the design data. We present modeling and correction results for special mask patterns with very strong pattern density variations showing that the compensation method is able to reduce CD uniformity by 50-70% depending on pattern details. The data correction itself is done with a new module developed especially to compensate long-range effects and fits nicely into the common data flow environment.
In the paper given by these authors this spring at Photomask Japan, investigations into the advances in the CATS tool that combine hierarchical fracturing and distributed processing were begun. In addition to the beneficial reduction in processing times, various shortcomings of the software were detailed.
For this study, the next version of the CATS software tool has been made available and those shortcomings are remedied. Difficult model OPC (MOPC) fractures and complicated de-slivering fractures for variable shaped beam machines are analyzed. Timing results, exclusive-OR operations, and the implications of Amdahl’s Law are also considered. Further intricacies of Linux cluster computing are also addressed.
In previous papers, [BACUS 2000 4186-13 and BACUS 2001 4562-20], developments in hierarchical fracturing and in distributed processing in the CATSTM tool were studied. This study investigates the advances in the CATSTM tool that combine hierarchical fracturing and distributed processing. Time-consuming processes such as PSM, OPC and de-slivering logic for shaped beam machines are addressed. The attendant hierarchical fracturing commands are reviewed and commands associated with distributed processing are introduced. Hierarchical and flat data fracture times are compared, as well as threaded fracture and distributed fracture times. The resulting benefits are tabulated.
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