Masatoshi Yasutake

FABRICATION OF NANOMETER-SCALE STRUCTURES USING ATOMIC FORCE MICROSCOPE WITH CONDUCTING PROBE

Nanometer‐scale structures were fabricated using electric field enhanced oxidation using an atomic force microscope with a conducting probe. The dependencies of thicknesses and widths of oxide stripes on applied voltage and time during which voltage is applied, were investigated. Also, the dependencies of depths of trenches, which are fabricated on the silicon surface by removing oxide stripes, on applied voltage and time during which voltage is applied, were investigated. The oxidation mechanism is discussed based on these investigations.

Modification of Silicon Surface Using Atomic Force Microscope with Conducting Probe

It is demonstrated that nearly atomically flat Si(100) surfaces passivated with native oxides can be modified by applying a negative potential to the conducting probe of an atomic force microscope (AFM) with respect to the silicon substrate. It was verified from the detection of OKLL Auger electrons and SiLVV Auger electrons excited by the electron beam that silicon surfaces are modified by the oxidation of silicon. This oxidation is enhanced by an electric field.

Surface potential measurements using the Kelvin probe force microscope

Abstract The Kelvin probe force microscope (KFM) can measure both the surface potential and the topographic image simultaneously without contacting the sample surface. Furthermore, both conducting and non-conducting thin layers can be measured directly with a millivolt range potential resolution and a sub-micrometer lateral resolution. In this paper, we report two improvements on the KFM which entail a new method of controlling the tip-sample distance to obtain accurate surface potentials, and a new method for increasing the topographic lateral resolution. With these improvements, we can obtain a potential resolution that is less than 1 mV and a lateral resolution of about 10 nm. Also, we report some potential measurements on Langmuir-Blodgett thin films.

Quantitative Analysis of the Magnetic Properties of Metal-Capped Carbon Nanotube Probe

Magnetic properties of an individual Fe-alloy-capped nanotube synthesized by catalytic chemical vapor deposition have been investigated for use as probes for magnetic force microscopy (MFM). The remanent magnetization for one unit volume of the Fe-alloy-capped nanotube is 297 emu/cm3 which is comparable to that of a conventional MFM tip. The MFM measurements have been performed using a combination of the Fe-alloy-capped nanotube tip and a frequency modulation detection system in order to improve the sensitivity of MFM.

Improvement of Kelvin probe force microscope (KFM) system

The Kelvin probe force microscope (KFM) is a useful tool that measures the surface potentials of both conducting and nonconducting materials. Recently, we have succeeded in improving the accuracy of potential measurements and increased the lateral resolution of the topographic image. Furthermore, Z axis servo control was improved to prevent the tip from coming into contact with the sample surface during scanning. Finally, the force gradient between the tip and the sample became steeper during the acquisition of the topographic image due to the inactivation of the modulation AC voltage. As a result, the potential resolution was less than 1 mV and the lateral resolution of the topographic image was improved to as high as 10 nm.

Performance of the carbon nano-tube assembled tip for surface shape characterization

The carbon nano-tube (CNT) has ideal properties for atomic force microscope (AFM) tips. We assembled a CNT using 2 three-axial manipulators in a scanning electron microscope (SEM) chamber. In this process, the length and angle of the CNT were adjusted by observing the SEM image, after which the CNT was glued by amorphouscarbon. The results of performance are as follows. The lifetime of the CNT tip proved to be 5 times better than that of the silicon tip when continuously measuring the micro-roughness of a Czochralski (Cz) P-type (100) silicon wafer. The CNT tip is able to trace a narrow space (width less than 1 microm) better than the conventional silicon tip because of its high aspect ratio. The relationship between the observed image and CNT geometry is discussed herein.

Critical Dimension Measurement Using New Scanning Mode and Aligned Carbon Nanotube Scanning Probe Microscope Tip

We have developed a new scanning mode and an aligned carbon nanotube tip for atomic force microscopy (AFM) for measuring the critical dimension of deep structures. The aligned carbon nanotube (A-CNT) was assembled in the scanning electron microscope (SEM) chamber. The diameter of the tip is uniformly around 20 nm and the tip attachment angle is within ±1.5° to the sample normal. The aspect ratio (length/diameter) of the tip is greater than 30. The new scanning mode is composed of two functions, namely transporting the tip along the steep trench structure and detecting the sample surface. This mode can faithfully trace the steep side wall using a flexible CNT tip without damaging the tip. The critical dimension (CD) measurements of the shallow trench isolation (STI) were performed using the newly developed scanning mode and the A-CNT tip.

Electron Tunneling through Chemical Oxide of Silicon

Carrier transport between gold and n+-Si through chemical oxides of Si was measured for the first time using an atomic force microscope with a conducting probe. It was found from the theoretical calculation of carrier transport in 0.7-nm-thick chemical oxide formed in a mixed solution of H2SO4 and H2O2 that the carrier transport can be explained as a direct tunneling of electrons through chemical oxide.

First Observations of 0.1 μm Size Particles on Si Wafers Using Atomic Force Microscopy and Optical Scattering

We have developed a new technique on the basis of an optical scattering phenomenon to link the coordinates of a commercially available wafer inspection system (WIS) to an analyzer with a high precision of ±0.1 μm. This new technique has been installed in a large sample atomic force microscope (AFM) capable of observing wafers of 8 in. size. One of the most remarkable features of this newly developed AFM is the ability to observe the same position on a wafer before and after certain processes. In this paper, we report on the results of the first observations of 0.10 μm size particles such as crystal-originated particles (COPs) and dusts on a polished (100) CZ-type Si wafer before and after SC1 cleaning by using the newly developed AFM. It was first found that the 0.10 μm size COPs are inherently juts before SC1 cleaning. After SC1 cleaning, these COPs turned into a deep crystalline pit. These pits run parallel to the axis of the wafer and have four facets with an angle of 54° with respect to the surface of the wafer. Second, the actual size of the dust particles were found to be much bigger than expected by using the WIS. The difference is considered to be attributed to the correction method used in the WIS by comparing with 0.10 μm in size polystyrene latex standard particles. These results show that the AFM combined with an optical scattering system is useful in the evaluation of 0.1 μm sized particles as well as in the wafer cleaning process.

Electron tunneling through chemical oxide of silicon

Abstract Carrier transport between gold and n + -Si through chemical oxide of Si was measured using an atomic force microscope with a conducting probe. A direct evidence for the effect of SiH bonds on the electron tunneling current was obtained.