D2I Project Reduces Mask Inspection Time

Kenji Tsuda, Asia Contributing Editor -- Semiconductor International, 4/21/2008 8:33:00 AM

Japan’s mask inspection research project, Mask D2I (design, drawing and inspection), has developed a method to reduce mask inspection times by as much as 40% by learning to discriminate between defects on critical and non-critical patterns.

The Mask D2I project has achieved two major improvements: shortening the review of repetitive patterns and simplifying defect decisions based on a prioritization technique.

The time it takes to inspect a mask depends on the review and checking time. The research team did not focus on the mask checking time, which depends on the hardware used to scan the mask. The Mask D2I team sought to reduce review time by specifying defects and significantly simplifying the defect definition process.

When a defect in a repetitive pattern is found, similar patterns are observed to look for the same defect. To search for similar defects, a design pattern may be overlaid on the observed pattern. The exact alignment of the design pattern may lead to the exact alignment of the similar patterns. By searching locations near the defective pattern, similar defects can easily be found. The review time is reduced by grouping detected defects.

Japan’s Mask D2I project has improved the time required to review mask defects, significantly cutting mask inspection time.

The threshold to determine a defect or normal pattern is simplified, thus speeding up the search time. The tool puts a priority on the threshold to decide on a defect, lowering the threshold for critical defects on smaller lines and creating a higher threshold for non-critical defects on wider patterns. The research tool used colors to discriminate between the critical and non-critical patterns. Even when critical and non-critical patterns have the same defects, the defects in the wider patterns may not cause failures or affect reliability. Faults in the wider lines are not identified as defects.

In the case of a complex mask represented by >200 GB of data, the tool can operate on a cluster of 16 PCs operating in parallel. A review of a 105 GB data file required ~10 minutes to perform a defect view.

The steps to convert from mask data rank (MDR) to a data management (DM) format were reduced. Previously, conversion to the variable shaped beam (VSB) format required adhering to a data expansion format, as well as the DM format.

The Mask D2I project is part of the Association of Super-Advanced Electronics Technologies (ASET, Tokyo), a consortium of 37 semiconductor-related companies partly supported by New Energy and Industrial Technology Development Organization (NEDO, Kanagawa, Japan) under the Ministry of Economy, Trade and Industry (METI). The three-year project ends in March 2010.

The project team leader comes from Nuflare Technology Inc. (Tokyo), a subsidiary of Toshiba Corp. (Tokyo). The completed technology developed by the project will be transferred to NuFlare, which makes electron-beam mask writers and related equipment.