Shigeru Wakiyama

Effect of Atomic Force on the Surface Corrugation of 2H-NbSe2 Observed by Scanning Tunneling Microscopy

Anomalously large surface corrugation of 2H-NbSe2 crystal was observed by scanning tunneling microscopy (STM). Besides mounds representing the Se atoms, hollow sites and Nb-atom sites clearly appeared as dips and saddle points, respectively. The lateral resolution was proved to be better than 0.2 nm. The large corrugation amplitude was attributed to the effect of atomic force between the tip and the sample.

Imaging of hydrogen‐induced Si(111) surface with the scanning tunnelling microscope

We have directly observed the hydrogen‐induced changes of the Si(111)7times7 surface using a scanning tunnelling microscope (STM). The 7times7 reconstructed atomic structure was formed on a clean surface of Si(111). But when the clean surface was dosed with typically 1–2 L [1 L (Langmuir) = 1·33 times 10−4 Pa. sec] hydrogen, the 7 times 7 image was gradually smeared out and then a 1 times 1 unreconstructed pattern appeared. After dosing with 5–10 L hydrogen, the STM image exhibited a new long‐periodic structure together with the 1times1 structure underneath. These experimental results may be ascribed to the chemisorption of hydrogen atoms on clean Si surfaces.

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.

Scanning tunneling microscopy of [112̄] oriented steps on a cleaved Si(111) surface

Scanning tunneling microscopy on cleaved Si(111) surfaces reveals stress‐induced microstructures with two types of terraces: triangular‐shaped terraces and long and narrow terraces with parallel [112] oriented steps, which is contrary to the previous observation [112] steps. Dimer rows in Si(111) 2×1 structures are found on the triangular terraces. On the parallel‐stepped terraces, rows run in the [112] direction and their separation was appreciably smaller than that of the dimer rows in the 2×1 structure. A new model for this structure is proposed.

Observation of atomic image of 2H-NbSe2 surface by scanning tunneling microscope

The atomic image of 2H-NbSe2 surface was successfully recorded with a scanning tunneling microscope (STM) at room temperature. The trigonal pattern of the image is in good agreement with the results of the X-ray diffraction experiments. The STM apparatus developed here showed resolutions of 0.3 nm in the lateral scale and 0.05 nm in the vertical scale.

Instrumentation of a wafer inspection large sample atomic force microscope

Particle detection at the 0.1 μm level has become increasingly important in producing reliable devices that demand smaller line widths. However, because the position alignment accuracy between the commercial optical particle inspection system and the particle evaluation instrument is insufficient, it is extremely difficult to detect 0.1 μm size particles. To solve these problems, we have succeeded in increasing the coordinate positioning accuracy at the 0.1 μm level by combining a large sample atomic force microscope (G. Bing, C. F. Quate and Ch. Gerber, Phys. Rev. Lett., 56 (1986) 930) with an optical scattering system. Using this system, we can now observe defects and particles on bare wafers and the possibility of particle detection is virtually 100%. Furthermore, the observation time necessary to position on a particle is substantially reduced.

Tungsten Deposited Scanning Probe Microscope Tips for Critical Dimension Measurement

We fabricated a robust and high aspect ratio tungsten deposited tip (TD tip) using a Focused Ion Beam (FIB). This tip was well controlled during fabrication. Tip diameter is uniform at around 90nm and its growing length is proportional to the irradiation time of the ion beam. Tip shape is a cylindrical pillar and aspect ratio (length/diameter) is greater than 10. Growing angle of the tip is identical to the incident angle of the ion beam. Critical dimension (CD) measurement of shallow trench isolation (STI) was performed using this tip.

Measurement of Local Density of States by Scanning Tunneling Spectroscopy at Low Temperature

A scanning tunneling microscope (STM) with a capability of spectroscopic measurement for operation for 300 K to 1.2 K was constructed. Measurements of the current-voltage characteristics (I-Vs) were performed on 2H-NbSe2 and a high-Tc superconductor Y-Ba-Cu-O. Spatial variations in the local density of states (LDOS) relevant to the low temperature phases, CDW and superconductivity, were extracted from data statistics.