Results and discussion
In this work, three different lateral force calibration methods for AFM were quantitatively compared with the aim to demonstrate the legitimacy and to establish confidence in the quantitative integrity of the proposed approaches. The results of the calibration from the Flat-Wedge and Multi-Load pivot methods are in good agreement with each other within the experimental uncertainty. The uncertainties for the measurements of the two methods were comparable to each other at less than about 15%. The Flat-Wedge method is fast, and it entacapone outputs a reliable calibration factor. However, to improve the accuracy, it is preferred to conduct the scan under high normal forces, which may increase tip wear. In contrast, the Multi-Load Pivot method may be more time consuming, but it can be implemented as a non-contact method. In addition, the Multi-Load Pivot method is less susceptible to assumptions or corrections. It was also found that the lateral force sensitivities that were determined by the Lateral AFM Thermal-Sader method were found to be generally smaller than those of the other two methods. The torsional mode correction may be partly responsible for such an underestimation of the lateral force sensitivity by the Lateral AFM Thermal-Sader method. By assuming that the torsional mode correction factor is 8/, which is the case for the ideal cantilever without an added mass, the lateral force sensitivity of the Lateral AFM Thermal-Sader method is in good agreement with that from the Flat-Wedge and Multi-Load pivot methods. A clear path to determine the torsional correction factor with accuracy, especially for the AFM cantilever with an integrated tip, may be needed to establish confidence in the Lateral AFM Thermal-Sader method.
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (NRF-2014R1A1A2058201).
The future of the semiconductor industry depends critically on the ability to map dopants rapidly at high spatial resolution, and with high sensitivity. New spectroscopic techniques are in considerable demand to cope with the advent of next generation semiconductor devices having ultra-shallow junctions. Hence, dopant profiling at a resolution of sub-10nm and detection sensitivity over a range of ~1016 to 1020 dopants cm−3 are important requisites.
Using a scanning electron microscope (SEM), it is possible to provide a rapid and contactless technique for the two-dimensional mapping of electrically active dopant profiles based on secondary electron (SE) doping contrast [1-5]. Under standard imaging conditions, the p-type regions appear bright and the n-type regions appear dark, therefore doping contrast can be used to determine the position of electrical p–n junctions. The doping contrast mechanism is due to the built-in electric field across a p–n junction, modified by the effects of surface band-bending and external patch fields as the SEs are scattered by the surface electric potentials . Oatley et al.  first studied SE doping contrast from p–n junctions where it was shown that reverse biasing enhances contrast by changing the electric potentials of the semiconductor. Since then, recent developments in instrumentation have hitherto evolved the application of doping contrast to quantitative dopant profiling in the SEM at the required high spatial resolution, sensitivity and quantification accuracy. A resolution up to 1nm is achievable , and sensitivity to dopant concentrations ranging from 1014 up to 1020dopantscm−3[1,8,9,10,3] can be obtained at a quantification accuracy of at least ±3% . As SE doping contrast is able to characterise dopants with high sensitivity over the required range and resolution, it is highly viable compared to a number of alternative techniques having limited range and resolution, are time-consuming, costly or destructive, or provide only 1-D measurements (e.g. spreading resistance profiling, secondary ion mass spectroscopy, atom probe tomography or scanning capacitance microscopy).