Recent CD AFM probe developments for sub-45 nm technology nodes

ABSTRACT This paper reports on new developments of advanced CD AFM probes after the prior introduction of “trident probes” in SPIE Advanced Lithography 2007 [1]. Trident probes, having sharpened extensions in the tip apex region, make possible bottom CD measurements within a few nanometers of the feature bottom corner; an area where other CD probes have difficulties due to tip shape limitations. Moreover, new metrology applications of trident probes have been developed for novel devices such as FinFET and vertical read/write hard disk heads. For ever smaller technology nodes, new probes evolved from the design of the trident probe. For example, the number of sharpened tip flares was reduced from three (trident) to two (bi-pod) to prevent possible interference of the third leg in the slow scan direction, as shown in Figure 3. Maintaining tip lateral stiffness as the tip size shrinks to less than 30 nm is vital for successful scanning. Consequently, a significant recent improvement is the change of probe shank cross-sectional geometry in or der to maintain tip vertical aspect ratio of 1:5 (and lateral stiffness > 1 N/m). Finally, modifications of probe substrate are proposed and evaluated for current and new CD AFM systems. Hydrophobic, self-assembled monolayer (SAM) coatings were applied on CD probes to reduced tip “pull-away” distance