Dimension controlled CNT probe of AFM metrology tool for 45-nm node and beyond

Atomic Force Microscope (AFM) is a powerful metrology tool for process monitoring of semiconductor manufacturing because of its non-destructive, high resolution, three-dimensional measurement ability. In order to utilize AFM for process monitoring, long-term measurement accuracy and repeatability are required even under the condition that probe is replaced. For the measurement of the semiconductor's minute structure at the 45-nm node and beyond, AFM must be equipped with a special probe tip with smaller diameter, higher aspect ratio, sufficient stiffness and durability. Carbon nanotube (CNT) has come to be used as AFM probe tip because of its cylindrical shape with small diameter, extremely high stiffness and flexibility. It is said that measured profiles by an AFM is the convolutions of sample geometry and probe tip dimension. However, in the measurement of fine high-aspect-ratio LSI samples using CNT probe tip, horizontal measurement error caused by attractive force from the steep sidewall is quite serious. Fine and long CNT tip can be easily bent by these forces even with its high stiffness. The horizontal measurement error is caused by observable cantilever torsion and unobservable tip bending. It is extremely difficult to estimate the error caused by tip bending because the stiffness of CNT tips greatly varies only by the difference of a few nanometers in diameter. Consequently, in order to obtain actual sample geometry by deconvolution, it is essential to control the dimension of CNT tips. Tip-end shape also has to be controlled for precise profile measurement. We examined the method for the measurement of CNT probe tip-diameter with high accuracy and developed the screening technique to obtain probes with symmetric tip-ends. By using well-controlled CNT probe and our original AFM scanning method called as Advanced StepIn(TM) mode, reproducible AFM profiles and deconvolution results were obtained. Advanced StepIn(TM) mode with the dimension- and shape-controlled CNT probe can be the solution for process monitoring of semiconductor manufacturing at the 45-nm node and beyond.