LONG-RANGE AFM PROFILER USED FOR ACCURATE PITCH MEASUREMENTS

A long-range atomic force microscope (AFM) profiler system was built b ased on a commercial metrology AFM and a home-made linear sample displ acement stage. The AFM head includes a parallelogram-type scanner with capacitive position sensors for all three axes. A reference cube loca ted close to the tip acts as the counter electrode for the capacitive sensors. Below this metrology AFM head we placed a linear sample displ acement stage, consisting of monolithic flexures forming a double para llelogram. This piezo actuated stage provides a highly linear motion o ver 380 mu m. its displacement is simultaneously measured by a capacit ive position sensor and a differential double-pass plane mirror interf erometer; both measuring systems have subnanometre resolution capabili ty. For the measurement of periodical structures two operating modes a re possible: a direct scanning mode, in which the position of the disp lacement stage is increased point by point while the AFM head measures the height, and a combined scanning mode where the displacement stage produces offsets which are multiples of the pitch to be measured whil e the AFM head is simultaneously scanning to locate an edge or a line centre position. Construction details, system characteristics and resu lts from first pitch measurements are presented. The estimated relativ e combined uncertainties for pitch values on different standards are i n the range 2 x 10(-5) to 8 x 10(-5). Laser diffraction measurements o f comparable uncertainty were performed on the same standards and show a very good agreement.