Quantitative Study Of Force And Detection Signal In Electrostatic Force Microscope

Electrostatic power microscopy(EFM)is widely used to characterize the properties of electronic materials and devices by measuring the electrostatic interaction between the probe and the sample to observe the electrostatic energy,charge distribution and charge transport on the sample surface.In this paper,the EFM signals of different materials and the influence of the shape of the probe were systematically and quantitatively studied from the perspectives of the material properties and the probe shape.The following are the main research contents and conclusions of this paper:1.EFM signals of metal samples were studied by using mirror charge method.Firstly,the effect of the position and quantity of the equivalent charge inside the spherical probe on the detection result is analyzed.It is found that the position of the equivalent charge does not affect the final result,and when the number of the equivalent charge reaches three,the corresponding electrostatic force does not change.This result was extended to EFM signal analysis of tapered probe,and it was found that the electrostatic force between the tapered probe and the metal sample decayed exponentially with the increase of probe sample spacing D,and the fitting expression of the electrostatic force was F=-πε0V2RID.2.The EFM signals of dielectric materials and semiconductor materials are quantitatively studied by extending the mirror charge method.Firstly,the relationship between the distance between EFM signal and probe sample and the dielectric constant is studied.It is found that the electrostatic force decreases exponentially with the thickness of the material and increases exponentially with the dielectric constant.Secondly,the variation of potential with the detection position is analyzed.It is found that the potential inside the dielectric material is no longer constant and slowly rises with the detection position,while the potential rapidly rises to V0.Then the Green’s function of multilayer materials is deduced and the signal changes are analyzed.It is found that the uppermost material has the greatest influence on the electrostatic signal,but when the dielectric constant of the uppermost material is small,the lower material may have some interference to the final signal due to its larger dielectric constant.Finally,the signal of the semiconductor material detected by EFM is studied,and the influence of the carrier concentration on the signal is analyzed.It is found that when the dielectric constant and thickness of the sample are the same,the corresponding electrostatic force of the semiconductor material is obviously larger than that of the dielectric material.This research method is expected to be used to extract the information of dielectric constant and carrier concentration from the EFM signals of dielectric and semiconductor materials.3.The influence of probe shape on EFM signal was systematically studied.EFM probe can be used in a variety of models,the probe may wear during use,resulting in changes in electrostatic force.Therefore,the effects of different probe tips,probe half-cone angles and probe tip curvature radius on the detection results are studied.It is found that the static force generated by the blunt conical probe is 6 times of that generated by the spherical probe and the conical probe when the sample spacing is Inm,and the static force generated by the conical probe and the spherical probe varies with the radius of curvature as the square,while the static force generated by the conical probe and the spherical probe varies linearly with the radius of curvature.Based on this result,we can judge whether the tip of the probe is worn by analyzing the signal of the EFM scanning sample.In addition,an extended study on EFM signal analysis in Kelvin mode was conducted,and it was found that SCMPIC probe was more sensitive than SCM-PIT probe,and FM mode was more suitable for working in vacuum while AM mode was more suitable for working in air.When EFM operates in Kelvin mode,this conclusion can be used to select suitable probes to obtain higher sensitivity.