Resolution enhancement technologies
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Resolution enhancement technologies are methods used to modify photomasks for integrated circuits (ICs) to compensate for limitations in the lithographic processes used to manufacture the chips.
Traditionally, after an IC design has been converted into a physical layout, the timing verified, and the polygons certified to be DRC-clean, the IC was ready for fabrication. The data files representing the various layers were shipped to a mask shop, which used mask-writing equipment to convert each data layer into a corresponding mask, and the masks were shipped to the fab where they were used to repeatedly manufacture the designs in silicon. In the past, the creation of the IC layout was the end of the involvement of electronic design automation.
However, as Moore’s law has driven features to ever-smaller dimensions, new physical effects that could be effectively ignored in the past are now having an impact on the features that are formed on the silicon wafer. So even though the final layout may represent what is desired in silicon, the layout can still undergo dramatic alteration through several EDA tools before the masks are fabricated and shipped. These alterations are required not to make any change in the device as designed, but to simply allow the manufacturing equipment, often purchased and optimized for making ICs one or two generations behind, to deliver the new devices. The intent of these alterations is to precompensate for known manufacturing distortions that are inherent in the manufacturing process. These distortions can arise in almost any processing step: photolithography, etching, planarization, and deposition, all of which introduce distortions of some kind. Fortunately, when these distortions are measured and quantified, an algorithm for their compensation can often be determined.
These lithographic compensations are usually grouped under the heading resolution enhancement techniques (RET). This is closely related to, and a part of, the more general category of design for manufacturability (IC) or DFM.
After RET, the next step in an EDA flow is usually mask data preparation.
[edit] References
- Electronic Design Automation For Integrated Circuits Handbook, by Lavagno, Martin, and Scheffer, ISBN 0-8493-3096-3 A survey of the field, from which this summary was derived, with permission.
