This paper reports on new developments of advanced CD AFM probes after the prior introduction of "trident probes" in
SPIE Advanced Lithography 2007 . 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 order 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"
distance1 during CD AFM scanning. Test results show that the pull away distance can be reduced more than 5 times on
average (in some cases, by a factor of 15). Consequently, use of hydrophobic SAM coatings on CD probes mitigates
pull-away distance thus allowing narrow trench CD measurements.
We discuss limitations of prior CD AFM probes and design considerations of new CD probes. The characterization of
first prototypes and evaluation of scan performance are presented in this work.