One of the key challenges in critical dimension (CD) metrology is finding suitable calibration standards. Over the last few years there has been some interest in using features measured with transmission electron microscope (TEM) as primary standards for linewidth measurements. This is because some modes of TEM can produce atomic lattice images that are traceable to the SI (Syst me International d Unites or International System of Units) definition of length. As interest in using calibration samples that are closer to the length scales being measured increases, so will the use of these TEM techniques.An area where lattice spacing images produced by TEM has been used as a primary standards is in critical dimension atomic force microscopes (CD-AFM), where they are used for tip width calibration. Two modes of TEM that produce crystal lattice images are high resolution transmission electron microscope (HR-TEM) and annular dark field TEM (ADF-TEM). HR-TEM produces lattice images by interference patterns of the diffracted and transmitted beams rather than the actual atomic columns, while ADF-TEM produces direct images of the crystal lattice. The difference in how both of these techniques work could cause subtle variations in how feature edges are defined.In this paper we present preliminary results from width samples measured using HR-TEM and ADF-TEM. We examine the level of uncertainty that can be obtained when each TEM technique is used for this type of analysis. Next we compare the results with measurements taken from the same location by two different CD-AFMs. Figure 1 shows schematic diagrams of the measurement principle for CD-AFM, HR-TEM and ADF-TEM.Both of the CD-AFM instruments used for this work have been calibrated using a single crystal critical dimension reference material (SCCDRM). These standards were developed by NIST and SEMATECH and used HR-TEM for traceable width calibration. Consequently, the present work and the prior SCCDRM work provide a mutual cross-check on the traceability of the width calibration.
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
ADF-TEM, CD-AFM, HR-TEM, linewidth