by M. David Levenson, Editor-In-Chief, Microlithography World
As the industry marches from 90nm to 65nm and 45nm, it has become increasingly difficult to achieve fast yield ramp due to random defects, process variations, and other design-for-manufacturing (DFM) issues localized in layout hot spots. Hoping to become the leading company bridging the gap between IC design and manufacturing is Takumi Technology with its automatic layout repair/optimization software.
Takumi Enhance is a layout optimization tool that detects hot spots by measuring the critical dimension (CD) and edge placement errors (EPE) between the contour predicted by a lithography simulator and the corresponding target layout. One representative result (see figure) shows the before and after optimization of a cell layout. The hotspot mechanism was that the poly segment was not violating any design rules under normal conditions, but under a defocus condition it was too close, forcing an extra spacing between the poly and the contact. This simple spacing requirement caused two-dimensional changes to the layout across multiple layers, and along with shifts and rotation of various layers.
All of these took less than a minute to accomplish with the automated system, which would have otherwise taken many days. Doing similar repairs, Takumi claims Enhance reduced the hotspots in a circuit from 47,000 to 40 on an overnight run. The software may, though, be best used to optimize the cell libraries — the automated process on one 500 cell library took 3 hours, rather than the 10 months estimated for a manual process.
Other products include Takumi HSF, a post-layout hot spot fixing tool that uses 2D optimization techniques with cost-aware constraints to provide a GDSII layout that is correct by construction and DRC clean. And Takumi Defect Analyzer does “smart” mask inspection to avoid costly repair of nuisance defects. While layout hotspots are probably unavoidable in the sub-wavelength era, Takumi Technology claims it can now find and correct them automatically. — M.D.L.