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Overlay Metrology Suite for Multiple Patterning

By Ed Korczynski, Sr. Technical Editor

Today, KLA-Tencor Corporation (NASDAQ: KLAC) released two metrology tools and an upgraded data analysis system that can reduce overlay error by 25% when using multi-patterning in leading-edge IC fabs. By taking additional data and using feed-forward control loops, the integrated solution dynamically adjusts the exposures in lithographic steppers to improve both overlay and critical dimension (CD) results in high-volume manufacturing (HVM). The suite of tools has passed beta-site evaluations with fab customers.

“Feed-forward has been used at gate CD to control variations, mostly controlling the Z-dimension of deposition and etch. But this is using feed-forward to control the 2D aspect of overlay.” explained Ady Levy, KLA-Tencor fellow, in an exclusive interview with Solid State Technology and SemiMD. “With the absence of traditional lithography scaling, customers are developing 3D structures that are using other parts of the fab.”

Figure 1 shows an analysis of the origin of patterning errors for Litho-Etch-Litho-Etch (LELE) double-patterning, indicating that traditional lithography processes account for just ~40% of the errors. Most multi-patterning errors originate with the deposition and etching and chemical-mechanical planarization (CMP) of films, inducing wafer-shape variations and thickness non-uniformities.

Fig. 1

The company’s WaferSight™ Patterned Wafer Geometry (PWG) measurement tool is an extension of the WaferSight line to measure bow and warp and other surface non-uniformities on unpatterned wafers, with the added ability to measure both sides to provide data on thickness variations. By incorporating industry-unique vertical wafer hold to minimize gravitational distortion and a sampling density of 3.5 million data points per wafer, the new tool produces highly accurate wafer shape data. “By feeding forward this information we can then correct the exposure on the scanner and correct for the induced overlay error due to stress from a prior process step,” elaborated Levy.

Brunner et al. (Optical Microlithography XXVII, Proc. of SPIE, Vol. 9052, 90520U, 2014) from IBM recently showed the quantified benefits of using PWG feed-forward (PWG-FF) information in stepper exposures to correct for across-wafer stress variation. Stress Monitor Wafers showed overlay errors dominated by wafer distortion effects, with six-times greater distribution of errors compared to distortion-free wafers. Table 1 compares standard linear alignment with High Order Wafer Alignment (HOWA) and with PWG-FF alignment, the latter provides the best results without requiring the slower processing of HOWA.

Proprietary model-based metrology allows the LMS IPRO6 to accurately measure reticle registration for on-device pattern features, as well as standard registration marks for significantly higher sampling. With faster measurement time than its predecessor, the LMS IPRO6 supports measuring the increased number of reticles associated with innovative multi-patterning techniques. The LMS IPRO6 enables generation of pattern-dependent registration error data that improves feedback to the e-beam mask writer, and can be fed forward to the fab’s lithography module for feature-optimized scanner corrections that improve wafer-level patterning.

The K-T Analyzer 9.0 is the latest version of the company’s platform that enables advanced, run-time data analysis for a wide range of metrology system types. Though the company fields a wide portfolio of products, KLA-Tencor doesn’t provide all inspection and metrology tools needed to control a commercial HVM fab line, and so the company provides software loaders to allow data from other tools to be integrated. The data analysis platform upgrade includes in-line methods for calculating scanner corrections per exposure on an on-product, lot-by-lot basis that maintains high accuracy without requiring full wafer measurement data—a production-capable control technique that can reduce pattern overlay error. In addition, the platform includes new scanner fleet management, scanner data analysis, and scanner alignment optimization capabilities.

All of this allows commercial HVM fabs to push the limits of patterning resolution for complex next-generation logic ICs. “Within the lithography module, our Archer™ 500 overlay and SpectraShape™ 9000 CD advanced metrology systems identify and monitor patterning errors,” said Ahmad Khan, group vice president of KLA-Tencor’s Parametric Solutions Group. “Extending beyond the lithography cell, our new WaferSight PWG and LMS IPRO6 systems isolate additional process- or reticle-related sources of patterning errors. These fab-wide, comprehensive measurements, supported by K-T Analyzer 9.0’s flexible data analysis, expand the process window and enable improved production patterning control for our customers’ leading-edge devices.”

—E.K.



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