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Speaker calls for mask design rule standard

Posted: 07 Oct 2005 ?? ?Print Version ?Bookmark and Share

Keywords:mask? mask design? foundry? eda? bacus photomask?

A proliferation of mask design rules from different sources calls out for a standard "lexicon" so that IDMs, foundries, mask makers and EDA providers can all speak the same language, according to a paper presented at the Bacus Photomask Technology symposium here Tuesday (Oct. 5).

Co-authored by representatives from Texas Instruments, Photronics, and HPL Technologies, the paper was presented by Mark Mason, director of resolution enhancement technology (RET) at Texas Instruments. Mason said that a standard for mask rule checks (MRCs) would provide a strong step towards enabling design for manufacturability (DFM).

Mason said that DFM is "a process that you use to make sure you can build the stuff that designers draw." The industry has always had a lithography DFM effort, he said, but today RET is becoming more complex, and traditional rule-based layout checks can't detect all of the potential manufacturing problems.

Mask rule checks are increasingly necessary, Mason said, because mask errors can cause a host of problems, including catastrophic shorts and opens and missing patterns. Mask inspection tools have difficulty inspecting patterns and may be misled by false defects. An example of a mask problem is chrome peeling in the undercut created by a phase-shift mask (PSM).

There are many complicated geometries to check, Mason said, and they need to be specified by commonly-understood rules. "You can say you can't have an anti-serif of more than 60nm, but what does this mean? Is there a clear definition that can be implemented in code?" Mason asked.

MRCs come from many sources, Mason noted, and are represented differently in different tools. For example, a rule designed to avoid chrome slivers would come from the mask maker, while minimum feature spacing would be defined by the foundry. "We need a standard common language so the tools we use can talk to each other," he said.

What the paper's authors are proposing is a standard mask design rule "lexicon," with the goal of creating a standard such that various companies can discuss, negotiate, specify, test and enforce mask design rules unambiguously. Additionally, Mason said, the standard should be machine readable.

A standard would allow the creation of standard test structures to predict and project MRCs, Mason said, and would enable foundries and mask suppliers to agree on rule sets. The standard would be a "baby step to a fully integrated DFM environment," Mason said.

Given the length of time it took the industry to come up with the Oasis layout format standard, an audience member asked, isn't it already too late?

"Maybe it's too late for 45nm," Mason said. "But 32nm is looking really hairy. If we can get something like this together with strong application at the 32nm node, it's not too late."

- Richard Goering

EE Times

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