LithoWare brings PROLITH to design

by M. David Levenson, Senior Technical Editor

PROLITH, the lithography simulator originally created by Chris Mack, has long been the most popular tool for optimizing lithography processes before exposure. Its library of calibrated resist and other material parameters has enabled accurate simulations on small circuit regions for years. However, running under Windows on a PC, it has always seemed too slow to help wavefront engineers optimize entire chip designs.

To address this, KLA-Tencor has introduced LithoWare, a new Linux-based product enabling semiconductor circuit designers to run PROLITH on large server farms, accelerating development of resolution-enhancement techniques (RET) and optical proximity correction (OPC) processes. Customers can now co-optimize the RET and the process conditions simultaneously, while minimizing calibration data collection, according to Dale Legband, senior program director at KLA-Tencor.

Edward Charrier, GM of KLA-Tencor’s process analysis division (the former Finle Technologies), explained in a statement that LithoWare’s predictive capabilities lets RET engineers “optimize their OPC at the same time they explore lithography conditions such as illumination, the latest photoresists, post-exposure bake, and more,” to more quickly create an RET recipe and ensure that it works across the entire process window.

Most EDA products run on a Linux/Unix environment, and LithoWare provides full compatibility with these products without leaving the Linux environment, reported Legband. LithoWare lets users load GDSII files, select multiple simulation regions, conduct OPC decoration interactively by changing illuminations on the fly, and output an OPC-decorated mask clip as a GDSII file.

The company cited recent estimates that the number of lithography simulations required for 32nm development will be in the hundreds of millions, noting that operating in a Linux environment allows LithoWare to distribute huge volumes of simulations across a large number of computers.

LithoWare is already being used at IC companies in both the US and Japan, to enhance their RET development productivity, KLA-Tencor said.

Standard RET/OPC production models have limited illumination predictability and don’t support process changes on the fly, and thus they require an expensive sequence of mask fabrication, wafer printing, measurement, and model calibration that can take days, weeks, or even months, stated Charrier. “LithoWare allows engineers to get it right the first time by providing a unique ‘what-if’ exploration capability that can optimize large numbers of process and RET variables on the fly,” he said.

Wavefront engineers also would not need to wait for their process engineers or foundry partners to provide proprietary process information and results before laying out the circuit geometries and OPC decorations. The physics and chemistry-based models in PROLITH make it possible to predict resist dimensions, wall slopes, and other yield-important parameters even before the production tools are delivered, just so long as their parameters are known, according to Legband. Still, the realities of model complexity and computer speed mean that only design clips in the vicinity of hotspots can be simulated using the full power of PROLITH. Larger regions require the approximate Lumped Parameter Model, even using large numbers of CPUs. Calibrating faster OPC models may prove to be the most important use of LithoWare. — M.D.L.

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