We have developed a new atomic force microscope method that we call Step-in mode. The Step-in mode can realize a high aspect ratio structure observation without tip damage because of its unique probing method. Three types of high aspect ratio probe, a silicon probe sharpened by focused ion beam, a high density carbon probe and a carbon nanotube probe, are analyzed to make clear which probe is appropriate for high aspect ratio structure metrology. It is demonstrated that fine measurement can be carried out with all types of probe and we conclude that the high density carbon probe is the best at the present time. Experimental results show that the pitch repeatability for a standard grating sample is 1.2 nm at 3σ, height repeatability is 1.2 nm at 3σ and width repeatability of a poly-silicon gate with side-wall is less than 3 nm at 3σ. It is also demonstrated that there is no tip damage after taking 1000 profiles of 512 data points in the Step-in mode. The experimental results show that the Step-in mode has a potential for application to critical dimension metrology for a LSI process monitor.
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