Silicon nitride cantilevers with oxidation-sharpened silicon tips for atomic force microscopy

Edward L. Ginzton Lab., Stanford Univ., CA
Journal of Microelectromechanical Systems (Impact Factor: 1.75). 09/2002; 11(4):317 - 321. DOI: 10.1109/JMEMS.2002.800924
Source: IEEE Xplore


High-resolution atomic force microscopy (AFM) of soft or fragile samples requires a cantilever with a low spring constant and a sharp tip. We have developed a novel process for making such cantilevers from silicon nitride with oxidation-sharpened silicon tips. First, we made and sharpened silicon tips on a silicon wafer. Next, we deposited a thin film of silicon nitride over the tips and etched it to define nitride cantilevers and to remove it from the tips so that they protruded through the cantilevers. Finally, we etched from the back side to release the cantilevers by removing the silicon substrate. We characterized the resulting cantilevers by imaging them with a scanning electron microscope, by measuring their thermal noise spectra, and by using them to image a test sample in contact mode. A representative cantilever had a spring constant of ∼0.06 N/m, and the tip had a radius of 9.2 nm and a cone angle of 36° over 3 μm of tip length. These cantilevers are capable of higher resolution imaging than commercially available nitride cantilevers with oxidation-sharpened nitride tips, and they are especially useful for imaging large vertical features.

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Available from: Randal J. Grow, Feb 26, 2015
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    • "Silicon has eight {1 1 1} planes, which have the slowest etch rate in various aqueous alkaline etchants. This fact has been widely utilized in (1 0 0) silicon for fabricating pyramid shapes, by exposing four of the eight {1 1 1} planes that are tilted at 54.7 • from the wafer top [1] [2] [3] [4]. In this case, the total pyramid cone angle is 109.4 "
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    • "Some alternatives include (boron (B)-doped) diamond like carbon (DLC) [7] [8] [9], nickel (Ni) [10] [11], GaAs [12] and SU-8 [13]. Examples where the tip and the cantilever material differ are Si x N y cantilever with Si tip [14] [15], Si cantilever with focused ion beam (FIB) modified tungsten (W) tip [16], Ni cantilever with B-doped DLC tip [17] and quartz resonators with attached metal tips [18] [19]. Examples of applications requiring electrically conducting AFM probes, such as electrical analysis in contact mode or non contact mode, like Kelvin probe microscopy (KPM), demand better suited probes than currently available commercial varieties. "
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    • "In contrast, SiN almost has no absorption to visible light. Despite the advantages, few reports on the fabrication of thin Si cantilevers with Si tips and only one report on the fabrication of Si tips on SiN cantilevers appeared [13]. This situation reflects the difficulties of fabrication of thin Si cantilever tips. "
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