Accuracy considerations for critical dimension semiconductor metrology

Due to greater emphasis on precision than accuracy, many of the measurements made in semiconductor fabrication facilities are not traceable to the SI (Systeme International d'Unites or International System of Units) unit of length. However as the feature sizes of integrated circuits decrease and the use of lithography models becomes more prevalent, the need for accuracy cannot be overemphasized. In response, the National Institute of Standards and Technology (NIST) in conjunction with SEMATECH has developed a reference measurement system (RMS) that can be used to provide accurate measurements for inline metrology tools. The RMS is a critical dimension atomic force microscope (CD-AFM) with traceability to the SI meter. In this paper we present a set of strategies for achieving accuracy for different types of measurands within an RMS and examine several important factors when selecting reference instruments. We also present results of a recent evaluation of linewidth and height using two CD-AFMs and a calibrated AFM with displacement interferometry in all three axes. We further look at the stability of tips such as carbon nanotubes.