Progress on CD-AFM tip width calibration standards

Abstract

The National Institute of Standards and Technology (NIST) is developing a new generation of standards for calibration of CD-AFM tip width. These standards, known as single crystal critical dimension reference materials (SCCDRM) have features with near-vertical sidewalls. This is accomplished using preferential etching on (110) silicon-on-insulator (SOI) substrates. As such, these structures are particularly useful for CD-AFM tip width calibration. As part of a previous generation of SCCDRMs that was released to the Member Companies of SEMATECH, we were able to deliver structures with linewidths ranging from as low as 50 nm up to 240 nm. These typically had expanded uncertainties (k = 2) of between 1.5 nm and 2 nm. Subsequently, these chips were used as a traceable source of tip width calibration for CD-AFM by SEMATECH and several Member Companies. We are now working on a new generation of SCCDRMs with the goal of reducing linewidth expanded uncertainties, and we are using our new CD-AFM to support this development. The features are patterned using electron beam lithography with equipment available in the new nanofabrication facility within the Center for Nanoscale Science and Technology (CNST) at NIST. Intact features as small as 10 nm have been observed with line width roughness (LWR) sufficiently low to support 1 nm expanded uncertainties. We believe it will be possible to fabricate features as small as 5 nm, and we are now working to refine the fabrication process and to assess the limits of our approach.