Comparison and Uncertainties of Standards for CD-AFM Microscope Tip Width Calibration
Ronald G. Dixson, Ndubuisi G. Orji
Since the advent of critical-dimension atomic force microscopes (CD-AFMs) inthe 90s, these tools have enjoyed growing acceptance in semiconductormanufacturing both for process development and to support in-line criticaldimension (CD) metrology. The most common application of CD-AFMs has beento support critical-dimension scanning electron microscope (CD-SEM) andscatterometer metrology as a reference for tool matching or as anon-destructive alternative to transmission electron microscopy (TEM) andscanning electron microscopy (SEM) cross sections.For many years, CD-AFM users typically developed in-house referencestandards for tip width calibration - often based on SEM or TEM crosssections. But the uncertainty of such standards was often large or unknown.Tip characterizer samples - which used a sharp ridge to calibrate the tipwidth - are commercially available. However, scanning such samples canresult in tip damage, and the uncertainty of tip calibrations based on thismethod is at least 5 nm.In 2004, NIST, SEMATECH, and VLSI Standards collaborated on the developmentand release of single crystal critical dimension reference materials(SCCDRMs) to SEMATECH member companies. These specimens, which arefabricated using a lattice-plane-selective etch on (110) silicon, exhibitnear vertical sidewalls and high uniformity and can be used to calibrate CDAFM tip width to approximately 1 nm standard uncertainty (k = 1). Also in2004, commercial critical dimension standards (CCDS) were introduced.Using CD-AFM instruments at both NIST and SEMATECH, we have performed acomparison of nominal 45 nm and 70 nm CCDS specimens with the SCCDRMcalibration. Our observations show that these two independently performedcalibrations are in agreement.
Proceedings of SPIE
February 26, 2007
San Jose, CA
Metrology, Inspection, and Process Control for Microlithography XXI