Study of modification methods of probes for critical-dimension atomic-force microscopy by the deposition of carbon nanotubes

Abstract

The results of an experimental study of the modification of probes for critical-dimension atomicforce microscopy (CD-AFM) by the deposition of carbon nanotubes (CNTs) to improve the accuracy with which the surface roughness of vertical walls is determined in submicrometer structures are presented. Methods of the deposition of an individual CNT onto the tip of an AFM probe via mechanical and electrostatic interaction between the probe and an array of vertically aligned carbon nanotubes (VACNTs) are studied. It is shown that, when the distance between the AFM tip and a VACNT array is 1 nm and the applied voltage is within the range 20-30 V, an individual carbon nanotube is deposited onto the tip. On the basis of the results obtained in the study, a probe with a carbon nanotube on its tip (CNT probe) with a radius of 7 nm and an aspect ratio of 1:15 is formed. Analysis of the CNT probe demonstrates that its use improves the resolution and accuracy of AFM measurements, compared with the commercial probe, and also makes it possible to determine the roughness of the vertical walls of high-aspect structures by CD-AFM. The results obtained can be used to develop technological processes for the fabrication and reconditioning of special AFM probes, including those for CD-AFM, and procedures for the interoperational express monitoring of technological process parameters in the manufacturing of elements for micro-and nanoelectronics and micro-and nanosystem engineering.

Piezoelectric Response of Multi-Walled Carbon Nanotubes

“…When the force decreases from 155 to 0 nN at the initial instant of time ( t = 2.1 s), there is a small surge of current up to −24 nA, followed by its gradual decay back to zero (section 3 in Figure 2 a). The surge of current at t = 2.1 s is probably caused by changing the type of strain of CNTs from bending-strain to stress-strain under the action of adhesion forces holding the CNT on top of the AFM probe during retraction at the initial instant of time [ 27 ]. Thus, when bending the CNT, stretching strain with a positive charge arises on one side of the top of the nanotube, and compressive strain with a negative charge occurs on the other, reducing the total piezoelectric charge [ 4 , 28 ].…”

Scanning Probe Techniques for Characterization of Vertically Aligned Carbon Nanotubes

“…Experimental studies of adhesion were carried out on a VA CNT array (D = 70-120 nm, L = 2.2 μm and n = 8 μm −2 ) when voltage pulses U were applied with an amplitude of 10 V to 30 V and duration of 1 s. The detachment of the VA CNT from the substrate was fixed by the absence of current on the reverse branch of the CVC (with the voltage from the maximum value to zero) obtained in the "substrate/VA CNT/AFM probe" system in the AFM spectroscopy mode (Figure 9). The nanotube is retained on the surface of the AFM probe by the van der Waals forces after removal of the external electric field [19]. This effect was used to create critical-dimension atomic-force microscopy (CD-AFM) probes by depositing a carbon nanotube from a VA CNT array on the tip [19].…”

“…The nanotube is retained on the surface of the AFM probe by the van der Waals forces after removal of the external electric field [19]. This effect was used to create critical-dimension atomic-force microscopy (CD-AFM) probes by depositing a carbon nanotube from a VA CNT array on the tip [19]. As shown by experimental studies, the detachment of a vertically aligned carbon nanotube from the substrate did not occur at U = 10 V; a single nanotube was detached with a reproducibility of about 30% at U = 15 V; a constant detachment of one or two VA CNTs was recorded at U = 20 V; several nanotubes were detached at U > 20 V. The voltage at which the detachment of a single VA CNT from the substrate was observed was likely to vary with the diameter of the nanotube.…”

“…A promising method for developing such nanodiagnostic techniques is a scanning probe microscopy (SPM) method [19][20][21][22][23][24][25]. This method does not require additional fixation of VA CNTs, special sample preparation and formation of contact areas on their tops.…”