Critical dimension atomic force microscopes (CD-AFMs) are rapidly gaining acceptance in semiconductor manufacturing metrology. These instruments offer non-destructive three dimensional imaging of structures and can provide a valuable complement to CD-SEM and optical metrology. Accurate CD-AFM metrology, however, is critically dependent upon calibration of the tip width. In response to this need, NIST developed prototype single crystal critical dimension reference materials (SCCDRMs).In 2004, a new generation of SCCDRMs was released to the Member Companies of SEMATECH a result of the fruitful partnership between several organizations. These specimens, which are fabricated using a lattice-plane-selective etch on (110) silicon, exhibit near vertical sidewalls and high uniformity can be used to calibrate CD-AFM tip width to a standard uncertainty of about 1 nm.Following the 2004 release, NIST began work on the next generation of SCCDRM standards. A major goal of this thrust was to improve upon the SCCDRM characteristics that impact user-friendliness: the linewidth uniformity and cleanliness. Toward this end, an experiment was designed to further optimize the process conditions. The first round of this experiment was recently completed, and the results show great promise for further improvement of the SCCDRM process.Among other observations, we found that the minimum linewidth and linewidth uniformity were primarily sensitive to different factors - and can thus be independently tuned to meet our future goals which include linewidths as small as 20 nm and a standard uncertainty due to non-uniformity at the 0.5 nm level. Our future work will include a new refining experiment to further optimize the important factors that we have identified, and extension of the methodology to a monolithic 200 mm implementation.
Proceedings Title: Proceedings of SPIE
Conference Dates: February 26, 2007
Conference Location: San Jose, CA
Conference Title: Metrology, Inspection, and Process Control for Microlithography XXI
Pub Type: Conferences
calibration, CD, CD-AFM, linewidth, metrology, SCCDRM, standards, traceability, uncertainty