Ed’s Threads 070629
Musings by Ed Korczynski on June 29, 2007KLA-Tencor drives productive-information
Inspecting nanometer-scale ICs during fabrication is not easy. Knowing what it is that you’ve found during inspection is even more difficult. KLA-Tencor, long the industry’s top inspection company, has now released a
defect-review scanning electron microscope (DR-SEM) to drive down the time to create defect Paretos in volume production—leading to both faster excursion correction and more learning for greater yield. The company also quietly purchased software company
FabSolve LLC, which might have something to do with all this.
Terabytes of raw data are generated every day in a high-volume modern fab, and careful methodologies are needed to extract signals out of noise. With too many signals to possibly manage, additional processing is vital to filter, process, and extract a sub-set of “productive” information to solve real manufacturing problems. Productive information—sometimes termed “actionable” information, when allowed by legal departments—can be roughly defined as enabling decision-making within a volume production environment. Time to productive-information (TTPI) is thus a critical metric for any fab. For example, a defect-map from an inspection tool is mere data, while defects-of-interest (DOI) separated from background haze is information, but it is only the ultimate DOI
Pareto chart of counts by category that allows for productive decision-making in a fab.
KLA-Tencor has long dominated the inspection tool business, and the company has recently upgraded both
darkfield (Puma91XX) and
brightfield (28XX) systems to increase sensitivity for 45nm node and beyond production. Once an inspection tool has created a wafer-map of detected defects, the wafer needs to be reviewed in a SEM so as to be able to zoom in on individual defect sites. The SEM images can then be analyzed to classify them into different columns in a Pareto, as well as into dreaded SEM non-visual (SNV) defects (meaning the SEM can’t find or resolve them; “visual” is here used for electron imaging).
Applied Materials has been very successful with its defect-review SEM (DR-SEM), but 45nm resolution limitations have opened up a need for a new generation of tools. For example, <50nm defects identified by an inspection tool are often classed as SNV by current DR-SEM tools. “For the biggest semiconductor manufacturer today, 40% or more of total defect counts end up in the SNV bin, and that’s going up 15%-20% each node,” said Christophe Fouquet, director of marketing at KLA-Tencor. Applied has not yet announced a resolution upgrade to its DR-SEM, which provides a window for KLA-Tencor to release its eDR-5200 product.
“So it’s all to get you to the best possible Pareto in the least amount of time,” explained Fouquet. Reportedly, leading fabs today can create only 2-3 Paretos/hour at the 45nm node, sometimes constrained by tool throughputs, sometimes by automated defect classification algorithms. Fouquet claims that KLA-Tencor’s integrated tool-set can often double the number of Paretos/hour at the 45nm node.
Another fab bottleneck can be inspection recipe setup time. Using a DR-SEM instead of an optical tool shortens inspection recipe setup time and provides optimal filtering-settings (defining the noise floor). Lacking sufficient resolution in sensitivity-tuning, you typically end up setting thresholds either too low and get noise, or too high and miss defects. With increased resolution in the DR-SEM, a single cycle of inspect/review can be used to confidently set an optimum inspection recipe.
The increased resolution is due to a different lens design, which is not novel in concept but is rigorous in implementation. Adding x-ray fluorescence detection capability to the lens design was reportedly not easy, nor was the development of topographic review by replacing two side detectors with a new 360° capability that retains the information for later viewing from any side angle to give optimal contrast. This new tool also can take in the optical information from a
brightfield inspection step, providing wavelength information that helps in working with previous-layer defects.
Automated defect classification (ADC) by the DR-SEM is desired, but only partially realized today. For example, if there are ~15 classifications associated with transistor formation, then SEM-ADC may be able to capture four or five but an operator is still needed to manually catch them all. KLA-Tencor’s DR-SEM software allows for learning from operator manual classifications, such that after typically <10 wafers it can automatically classify 80%-90% of DOI at 45nm. The company claims the DOI:SNV ratio increases by a factor of five compared to current tools. When moving to n+1 node wafers, the previous n node defect types are retained while new ones are added to the library.
ADC may be aided by a geographical information systems (GIS) database structure used as a reference for locating and classifying defects. Such a database was acquired by KLA-Tencor on June 28th by purchasing
FabSolve LLC, formerly affiliated with Vietnamese-based image processing algorithm company DolSoft.
KLA-Tencor claims that its DR-SEM beta-tools are already in use by tier-1 customers in Taiwan, Japan, Europe, and the US. The cost of these new tools has not been released, but like most of what passes for
the new goodness (SM) [
buzzphrase servicemark by Ed Korczynski] these days, if you have to ask…you can’t afford it.
—E.K.
Labels: DR-SEM, inspection, KLA-Tencor, productive-information, review, TTPI
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070629: KLA-Tencor drives productive-information
