Electrically conducting probes with full tungsten cantilever and tip for scanning probe applications (original) (raw)
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8th International Conference on High-capacity Optical Networks and Emerging Technologies, 2011
We compare the sharpness of tungsten probe tips produced by the single-step and two-step dynamic electrochemical etching processes. A small radius of curvature (RoC) of 25 nm or less was routinely obtained when the two-step electrochemical etching (TEE) process was adopted, while the smallest achievable RoC was -10 nm, rendering it suitable for atomic force microscopy (AFM) or scanning tunneling microscopy (STM) applications.
Fabrication and Study of Micro Monolithic Tungsten Ball Tips for Micro/Nano-CMM Probes
Micromachines, 2018
Micro ball tips with high precision, small diameter, and high stiffness stems are required to measure microstructures with high aspect ratio. Existing ball tips cannot meet such demands because of their weak qualities. This study used an arc-discharge melting method to fabricate a micro monolithic tungsten ball tip on a tungsten stylus. The principles of arc discharge and surface tension phenomenon were introduced. The experimental setup was designed and established. Appropriate process parameters, such as impulse voltage, electro discharge time, and discharge gap were determined. Experimental results showed that a ball tip of approximately 60 µm in diameter with less than 0.6 µm roundness error and 0.6 µm center offset could be realized on a 100 µm-diameter tungsten wire. The fabricated micro ball tip was installed on a homemade probe, touched by high-precision gauge blocks in different directions. A repeatability of 41 nm ( = 2) was obtained. Several interesting phenomena in the b...
Fabrication of High Performance Probes for Atomic Force Microscope Afm
University of Waterloo, 2021
Atomic force microscope (AFM) is widely used for topographical structure characterization. However, one serious issue with AFM imaging is the intrinsic artifact in the AFM image when mapping a none-flat surface (e.g. a deep and narrow hole/trench) where the tip cannot fully follow the sample surface. The natural solution to overcome this issue is by using thin and high aspect ratio (HAR) tips that can follow the sample surface more precisely. This thesis focuses on the fabrication of HAR AFM probes. The HAR tips are obtained by modifying regular AFM tips having a pyramid shape. The high aspect ratio structure in silicon, sitting on top of a pyramid base, is created by a dry plasma etching process, so the key is to form a hard metal dot right on top of the pyramid tip apex to act as the mask for silicon etching. Three approaches were developed to form the hard mask metal nano-dot on the tip apex. The first method (Chapter 3) employed metal deposition steps with the regular tip mounted on a tilted surface, and its etching back to leave behind metal only at the tip apex (the metal on the sidewall of the pyramid was etched away). Since both metal film deposition and its etching, as well as the subsequent dry plasma etching of silicon using the metal as mask to form the HAR structure, can be carried out on an entire wafer of regular AFM tips, this process is a low-cost and high throughput batch process. The second method (Chapter 6) utilized focused ion beam (FIB). FIB has been extensively used to fabricate HAR tips by milling away the silicon surrounding the tip axis, leaving behind a thin pillar or sharp cone of silicon at the pyramid axis. However, the FIB milling time for each tip is long, leading to high cost. Our method used FIB to mill away only a very thin layer of metal film to leave behind a metal dot at tip apex, thus the expensive FIB machine time is greatly reduced. The third method (Chapter 6) also utilized Ga-ion FIB, but instead of milling a metal dot mask pattern, the Ga ions were implanted to the tip apex area to act as a mask since Ga metal is resistant to fluorine-based plasma etching. For the above three approaches, silicon etching is very critical, so Chapter 5 covers our effort in developing silicon etching recipes using a non-switching pseudo-Bosch process with C4F8-SF6 gas, with a goal of obtaining vertical sidewall profile needed for HAR, high selectivity to mask, and high etching rate. As well, v the etched silicon structures must be further sharpened to reduce its apex radius to below 10nm. So, Chapter 4 covers the process optimization of the oxidation sharpening process that involves thermal oxidation and subsequent oxide etching by HF. It was found that 950°C is a suitable oxidation temperature, and the oxidation sharpening can be carried out more than once to improve tip sharpness. Lastly, inspired by the first approach described above, we also developed the fabrication process for "edge probe" (Chapter 3), for which the tip apex sits right at the end of the cantilever, and thus the tip location can be precisely determined in the view of the integrated optical microscope in an AFM system. Our method involves angle evaporation of a hard mask layer onto the AFM probe, followed by silicon dry etching that etches away the area not covered by the metal layer, i.e., the shadow area of the pyramid-shaped tip. vi Acknowledgments First, I would like to express my appreciation to my supervisor Professor Bo Cui. This work would not be possible without his guidance throughout the entire work. I would also like to thank my examination committee members Professor Karim Karim, Professor Omar Ramahi, Professor Boxin Zhao and Professor Wen-Di Li (external examiner), who agreed to be my committee members and rearranged their schedules to make this exam possible as well as their valuable advices. Also, I would like to thank my group mates for their support. It is worth to mention that the nanopillars wet etch experiment is done in collaboration with Aixi Pan and Xiaoli Zhu, and the ion implantation experiments are performed in collaboration with Huseyn Ekinci and Ripon Dey. Besides, the edge tip and batch HAR tip is accomplished in collaboration with Chenxu Zhu and Shuo Zheng.
Nanofabrication of sensors on cantilever probe tips for scanning multiprobe microscopy
Applied Physics Letters, 1996
A simple method for nanofabricating sensors on cantilever probe tips, used in atomic force microscopy ͑AFM͒, is described. The method uses voltage pulses to evaporate and create a nanometer-scale hole at the very end of a metallized AFM cantilever probe tip. The hole in the metal film can be used as a mask for further device fabrication. We demonstrate this by fabricating a nanothermocouple junction on the probe tip. Thermal images of electrically heated patterned metal lines obtained by this probe suggest the spatial resolution to be about 10 nm. Fabrication of nanosensors on probe tips is likely to assist in the future development of scanning multiprobe microscopy.
Microscopic four-point probe based on SU-8 cantilevers
Review of Scientific Instruments, 2005
A microscopic four-point probe ͑4PP͒ for resistivity measurements on thin films was designed and fabricated using the negative photoresist SU-8 as base material. The device consists of four microscopic cantilevers, each of them supporting a probe tip at the extremity. The high flexibility of SU-8 ensures a stable electrical point contact between samples and probe tip with all four electrodes even on rough surfaces. With the presented surface micromachining process, 4PPs with a probe-to-probe spacing of 10-20 m were fabricated. Resistivity measurements on thin Au, Al, and Pt films were performed successfully. The measured sheet resistances differ by less than 5% from those obtained by a commercial macroscopic resistivity meter. Due to the low contact forces ͑F cont Ͻ 10 −4 N͒, the 4PP is suitable to be applied also to fragile materials such as conducting polymers. Here the authors demonstrate the possibility of performing resistivity measurements on 100-nm-thick pentacene ͑C 22 H 14 ͒ films with a sheet resistance R s Ͼ 10 6 ⍀ / ᮀ.
Physical Review B, 2005
Detailed knowledge of the tip apex structure is necessary for quantitative comparison between theory-based simulations and experimental observations of tip-substrate interactions in scanning probe microscopy ͑SPM͒. Here, we discuss field ion microscopy ͑FIM͒ techniques to characterize and atomically define SPM tungsten tips. The tip radius can be estimated from field emission data, while FIM imaging allows the full atomic characterization of the tip apex. We find that when FIM is applied to tips with a radius of a few nanometers ͑as is desirable for high-resolution atomic force microscopy imaging͒, limitations not apparent with less sharp tips arise; successful resolution of these limitations will extend the utility of FIM. Field evaporation can be used to atomically engineer the apex into a desired atomic configuration. Starting from a W͑111͒ wire, a tip terminating in three atoms can reproducibly be fabricated; due to its geometry and stability, this apex configuration is well suited for application as an atomically defined electrical contact in SPM experiments aimed at understanding contact mechanics at the atomic scale.
A New Method to Fabricate Metal Tips for Scanning Probe Microscopy
IEEJ Transactions on Sensors and Micromachines, 1997
We present a new method to fabricate sharp metal tips on cantilevers for a SPM. The metal tip, which is deposited and patterned as a film on a silicon mold with pyramidal etch pits, is attached by metal-to-metal bonding to a metal pad on a substrate. Then the tip on the substrate is peeled off the mold at room temperature. The tip surface is very smooth without grain boundaries associated with deposited thin films. A platinum tip with a radius curvature of less than 15nm was successfully fabricated. In addition, the mold can be reused because the mold is not dissolved during the tip fabrication. By applying this method in which the tip fabrication process is independent of the cantilever process, we succeeded to form a tip on a piezoresistive cantilevers. Moreover, we used the cantilever with the tip in a piezoresistive AFM and an AFM/STM apparatus and obtained high resolution topography and surface conductance images, respectively.
Microscopic four-point probe (u4PP) based on SU-8 cantilevers
A microscopic four-point probe ͑4PP͒ for resistivity measurements on thin films was designed and fabricated using the negative photoresist SU-8 as base material. The device consists of four microscopic cantilevers, each of them supporting a probe tip at the extremity. The high flexibility of SU-8 ensures a stable electrical point contact between samples and probe tip with all four electrodes even on rough surfaces. With the presented surface micromachining process, 4PPs with a probe-to-probe spacing of 10-20 m were fabricated. Resistivity measurements on thin Au, Al, and Pt films were performed successfully. The measured sheet resistances differ by less than 5% from those obtained by a commercial macroscopic resistivity meter. Due to the low contact forces ͑F cont Ͻ 10 −4 N͒, the 4PP is suitable to be applied also to fragile materials such as conducting polymers. Here the authors demonstrate the possibility of performing resistivity measurements on 100-nm-thick pentacene ͑C 22 H 14 ͒ films with a sheet resistance R s Ͼ 10 6 ⍀ / ᮀ.
Gold nanoparticle coated silicon tips for Kelvin probe force microscopy in air
Nanotechnology, 2013
The tip apex dimensions and geometry of the conductive probe remain the major limitation to the resolution of Kelvin probe force microscopy (KPFM). One of the possible strategies to improve the spatial resolution of surface potential images consists in the development of thinner and more durable conductive tips. In an effort to improve the lateral resolution of topography and surface potential maps, we have evaluated high aspect ratio conductive tips created by depositing gold nanoparticles on standard silicon tips. Besides the already known general topographic resolution enhancement offered by these modified tips, an improvement of surface potential lateral resolution and signal-to-noise ratio is reported here for a variety of samples as compared to other regular conductive probes. We have also observed that the modified conductive tips have a significant auto-regeneration capability, which stems from a certain level of mobility of the nanoparticle coating. This property makes the modified tips highly resistant to degradation during scanning, thus increasing their durability. As demonstrated by the heterogeneous set of structures measured in the present study performed in air, the nanoparticle coated tips are suitable for KPFM analysis. In particular, surface potential difference determination on graphene deposited on silicon, gold sputtered on a salt surface, large and mildly rough areas of ZnO films and small DNA molecules on insulating mica have been achieved with enhanced resolution.