Kimitake Fukushima

Millions of cantilevers for atomic force microscopy

Millions of single-crystal silicon cantilevers were fabricated by anisotropic etching of silicon by KOH. They could be tailored to measure from 500 nm to 100 μm in length and from 30 to 100 nm in thickness. Since the tips and the cantilevers were formed by a combination of crystal-line facets, they had very high uniformity, well-defined shape, and size. The density of the cantilevers was over 1 mil cantilevers per square centimeter. Typical mechanical characteristics of cantilevers measuring a few microns in length were spring constant a few N/m, natural frequency around 10 MHz, Q factor 5 in air, and 104 in vacuum. The natural frequency of cantilevers within the same row differed by 0.01%. Displacement measurement of the cantilever from the back surface of the silicon substrate by an infrared Fizeau interferometer had a visibility of 0.1.

Development of a Versatile Atomic Force Microscope within a Scanning Electron Microscope

We have developed a new versatile scanning electron microscope (SEM)-atomic force microscope (AFM) system capable of simultaneous SEM and AFM operation. The system consists of a SEM and a detachable AFM module that can be taken outside of the SEM chamber. By keeping the height of AFM module to less than 36 mm, and the AFM tip 5 mm below the highest point of the AFM module, clear SEM image and variable viewing angle are achieved. The AFM utilizes the conventional optical lever method. The sample stage of the AFM module is equipped with remote controlled piezoelectric actuators enabling three degree-of-freedom positioning with sub-nanometer resolution and millimeter range. The optical lever path can also be modified by remote control after the module is placed within the SEM. The SEM-AFM system can also be used as a tool for micro scale processing and manipulation by replacing the cantilever with a designated probe.

Fabrication of a silicon based nanometric oscillator with a tip form mass for scanning force microcopy operating in the GHz range

The detectable force resolution of a mechanical oscillator used in scanning force microscopy can be improved by increasing its natural frequency fo and quality factor Q, and by decreasing the spring constant k and the temperature of operation T. For an oscillator having a structure that can be modeled as a concentrated mass-spring model, decreasing the mass of the oscillator is desirable since high fo can then be obtained without increasing the spring constant k. We have developed a novel fabrication technique for fabricating a nanometric oscillator by selective etching of silicon on insulator (SOI) wafers. The oscillator has the form of a tip supported by an elastic neck, and the tip serves as the mass. The tip and the neck length measure approximately 100 nm when fabricated using a separation by implanted oxygen wafer, and are around 1000 nm when fabricated using a bonded SOI wafer. The tips were made of silicon and the necks were made of silicon dioxide. The oscillator could be tailored to have its nat...

Fabrication of Silicon-Based Filiform-Necked Nanometric Oscillators

For the purpose of improving the resolution of force and mass detection of a noncontact-mode atomic force microscope (AFM), we are developing a mechanical oscillator of nanometric size which consists of a head mass supported by an elastic neck. A silicon-on-insulator (SOI) wafer with the laminated structure top Si layer/buried SiO2 layer/base Si is used in the fabrication of the nanometric oscillators. By selective etching of Si and SiO2, nanometric oscillators are successfully obtained. The top Si layer is etched to form a tetrahedral Si dot, which is the mass of the oscillator, and the buried SiO2 layer is etched to form the elastic neck resting on the base Si. The size of the tetrahedral Si dot is determined by the thickness of the top Si layer without depending on the precision of the lithography technique. We found that the cross-sectional shape of the SiO2 neck is a right-angled triangle and that the neck is situated at the center of the tetrahedral Si dot. According to calculations, the oscillators we obtained have spring constants around 1 N/m and a resonance frequency from 3 MHz to 300 MHz according to their dimensions.

Measurement of mechanical properties of three-dimensional nanometric objects by an atomic force microscope incorporated in a scanning electron microscope

An atomic force microscope that mounts on a sample stage of a scanning force microscope (SEMAFM) was developed. It was implemented for measurement of static mechanical properties of three-dimensional nanometric objects. The sample stage of the AFM was equipped with piezoelectric actuators enabling raster scanning as well as three degrees of freedom positioning with sub nm resolution and mm movable range. This enabled centering the AFM tip to the field of view of the SEM. Measurement of the spring constant and rupture force of three-dimensional nanometric structures was made possible. The SEMAFM also functioned as a conventional AFM.

Strength measurement and calculations on silicon-based nanometric oscillators for scanning force microcopy operating in the gigahertz range

Abstract For an oscillator having a structure that can be modeled as a concentrated mass–spring model with constant Q factor, its minimum detectable force gradient is proportional to ( KM ) 1/2 , where M is the mass and K is the spring constant. Miniaturization of the oscillator acts favorably in increasing the force resolution, since drastic decrease of the mass can then be achieved. With the aim of increasing the force and mass resolution of the oscillator used for force detection in scanning force microscopy (SFM), we have developed a novel fabrication technique of nanometric oscillators by selective etching of laminated silicon substrates such as SOI (silicon on insulator) or SIMOX (separation by implanted oxygen). The oscillator has a tetrahedral or a conical tip supported by an elastic neck, and the tip serves as the mass. Typical size of the oscillator lies in the range of 100–1000 nm. The oscillator could be tailored to have its natural frequency in the range of 0.01–1 GHz, and a spring constant between 10 −1 and 10 2 N/m. The strength of the nanometric neck was 10 8 N/m 2 for both shear and normal forces, indicating that a neck 10 nm in diameter can withstand forces up to around 50 nN. Calculations on the different vibrational modes of the oscillator gave a better guideline to the design of the oscillators.

Fabrication of array of single-crystal Si multi probe cantilevers with several microns size for parallel operation of atomic force microscope

For the purpose of improvement in resolution of force gradient and mass detection in atomic force microscope (AFM), we are developing cantilevers measuring from 100 nm to several microns. We succeeded in fabrication of single crystal Si cantilever with several microns size and measurement of its mechanical characteristics. Silicon-on-insulator (SOI) wafer is used for the fabrication. Fabrication is based on three anisotropic etching by KOH and two local oxidation processes of Si. Without depending on precision of lithography technique, triangular shaped cantilevers measuring several microns with tetrahedral tips on their ends are fabricated with high uniformity. The thickness of the cantilever is chosen from 20 nm to 120 nm. Typical spring constant, resonance frequency and Q factors of the single-crystal Si cantilevers are several N/m, 1 to 10 MHz and around 10/sup 4/ in vacuum, respectively. The density of the cantilever is up to 10,000 cantilevers/mm/sup 2/. We aim to scan an area of up to a few mm/sup 2/ simultaneously with this multi-probe cantilever array.

Measurement of characteristics of nanometric mechanical oscillators

For the purpose of making a small probe for scanning force microscopy (SFM), we have succeeded in fabricating nanometric oscillators with a tip mass of silicon and a neck of silicon dioxide by micromachining Si-SiO/sub 2/-Si laminated substrates. The size of the head ranged from 100 nm to 3 /spl mu/m and the diameter of the neck range from 10 nm to 200 nm. The resonant frequency is calculated to be in MHz order. Results of the test done by an atomic force microscope built within a scanning electron microscope showed that the oscillators are elastic and strong enough for use as SFM cantilevers.