Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making named article
Reexamination Certificate
2002-07-15
2004-02-10
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making named article
C250S493100
Reexamination Certificate
active
06689545
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of fabricating a near-field light-generating element for shining or detecting near-field light used in a near-field optical microscope or near-field optical memory device and, more particularly, to a method of fabricating a near-field light-generating element having a minute scattering body inside an aperture.
2. Description of the Related Art
Scanning probe microscopes (SPMs) typified by scanning tunneling microscopes (STMs) and atomic force microscopes (AFMs) are used to observe microscopic regions on the nanometer order on sample surfaces. In SPM, a probe having a sharpened tip is scanned across a sample surface. An interaction such as a tunneling current or atomic force produced between the probe and the sample surface is taken as a subject to be observed. An image of a resolution dependent on the topography of the probe tip can be obtained. However, relatively strict limitations are imposed on observed samples.
Accordingly, a scanning near-field optical microscope (SNOM) attracts attention today. The microscope takes an interaction produced between near-field light produced at the tip of a probe and a sample surface as a subject to be observed to thereby permit observation of microscopic regions on the sample surface.
In SNOM, near-field light is shone onto a sample surface from an aperture formed at a sharpened tip of optical fiber. The aperture has a size of less than the diffraction limit of the wavelength of light introduced into the optical fiber. For example, it has a diameter of about 100 nm. The distance between the aperture formed at the tip of the probe and the sample is controlled by SPM techniques. The value is less than the size of the aperture. At this time, the spot diameter of the near-field light on the sample is almost equal to the size of the aperture. Therefore, optical properties of a sample in a microscopic region can be observed by scanning the near-field light impinging on the sample surface.
Such a near-field light-generating element can be applied as a high-density optical memory device which creates near-field light of high energy density in the aperture portion of a probe by introducing light of relatively large intensity toward the sample through the probe and locally modifying the structure or physical property on a recording medium surface by the near-field light. The optical memory device can also be used as a microscope. Attempts have been made to increase the angle at the tip of the probe in order to obtain near-field light of large intensity. Furthermore, in applications of such a memory device, some devices where a probe having an aperture in a flat substrate unlike a sharpened probe is used as a record/read head have been devised.
In these elements making use of near-field light, formation of an aperture is important. As one method of forming the aperture, a method disclosed in patent publication No. 21201/1993 is known. In the method of forming an aperture of patent publication No. 21201/1993, a sharpened optical waveguide on which a light-shielding film is deposited is used as a sample for forming an aperture. The method of forming the aperture consists of pressing the sharpened optical waveguide having the light-shielding film thereon against a hard flat board with a quite small amount of push that is controlled well by a piezoelectric actuator to thereby plastically deform the light-shielding film at the tip.
Another method of forming an aperture is disclosed in patent laid-open No. 265520/1999. In the method of forming an aperture in patent laid-open No. 265520/1999, the subject in which an aperture is formed is the tip of a protrusion formed on a flat board or plate by a focused ion beam (FIB). The method of forming the aperture is carried out by directing an FIB onto a light-shielding film at the tip of the protrusion from a side and removing the light-shielding film at the tip of the protrusion.
In addition, in order to improve the resolution and to increase the intensity of scattering light produced as a result of an interaction created between the probe and the sample, a method making use of a phenomenon where fine metal particles are made to produce plasmons by incident light has been proposed.
Okamoto et al. have proposed a probe having fine particles of a metal such as Au (gold) or Pt (platinum) fixed at the tip of a probe body that is made of a transparent material such as SiN (silicon nitride) and is a sharp, tapering member (Takayuki Okamoto and Ichirou Yamaguchi, “Near-field scanning optical microscope using a gold particle”,
Jpn. J. Appl. Phys.
36, L166 (1997)).
In such a probe where the metal fine particles are fixed at the tip of a sharpened probe body made of a transparent material, the metal fine particles are made to produce plasmons by incident light. The scattering efficiency is higher compared with the prior art probe having no metal fine particles. A larger amount of detected light can be obtained. Since the resolution is determined by the position at which metal fine particles are fixed at the tip, the radius of curvature, the kind of the metal fine particles, and so on. Therefore, a higher resolution can be derived by fixing appropriate fine metal particles to the tip of a probe.
Furthermore, according to the optical fiber probe and method of fabricating same as disclosed in U.S. Pat. No. 3,117,667, a protruding portion of a core protruding from a clad is formed at one end of optical fiber. A metal film is formed on the surface of the protruding portion except for the front-end portion. The outer portion of the protruding portion is made to recede from the front-end surface. A metal sphere is formed at the tip of the inner portion. Therefore, an optical fiber probe can be obtained which can detect near field at high sensitivity and high resolution without being affected by scattering light scattered by the base portion of the probe or by scattering light due to the surface roughness of the sample.
In addition, according to the method of creating metal fine particles at the tip of a member, fixing the particles, apparatus therefor, and probe disclosed in patent laid-open No. 2001-83069, a method of forming a metal sphere at the tip of a probe by immersing a sharp member in a metal solution and deoxidizing ions by near-field light, a probe, and apparatus are provided.
Generally, narrowing the aperture lowers the intensity of near-field light produced near the aperture. Where this is scattered or modulated by a sample (or recording medium), the intensity of modulated and propagating light reaching the detector drops. In order to compensate for this, even if the gain of the detection system is increased, the signal-to-noise ratio (S/N) rather deteriorates considerably because of dark current intrinsic to the detector and thermal noise in the amplifier circuit. Of course, increase in the power of laser light introduced into the aperture portion and decrease in the optical spot of laser focused in the aperture portion are advantageous.
However, as the aperture is reduced in size, the thickness of the light-shielding film is urged to be reduced because of restrictions on the micromachining using an FIB or the like and by the effects of attenuation of the introduced light dependent heavily on the ratio between the in-plane dimensions of the aperture and the thickness. Therefore, thinning of the light-shielding film deteriorates the light shielding and increases the dc light component reaching the optical detector. If comparable optical intensity modulation is obtained due to the sample (or recording medium), equivalent signal quality deterioration results. Also, where light is collected using a lens near the aperture portion, the geometrical optics is fundamentally based on the prior art geometrical optics. Consequently, it is impossible to shine light onto the vicinities of the aperture portion at a sufficiently high energy density due to the diffraction limit.
Accordingly, with the conventional method, it is quite d
Kasama Nobuyuki
Kato Kenji
Maeda Hidetaka
Mitsuoka Yasuyuki
Niwa Takashi
Adams & Wilks
McPherson John A.
Seiko Instruments Inc.
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