Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
2000-04-14
2003-04-08
Lee, John R. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S306000, C250S307000, C250S216000, C250S458100, C250S311000, C382S130000
Reexamination Certificate
active
06545276
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-106580, filed Apr. 14, 1999; and No. 2000-001026, filed Jan. 6, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a near field optical microscope. More particularly this invention relates to a near field optical microscope using scattering probe and a method for observing samples using the near field optical microscope.
Further, this invention relates to a near field optical microscope. More particularly, this invention relates to a near field optical microscope using scattering probe comprising means for improving the S/N of a near field signal when the signal strength changes in accordance with changes in the wavelength of illumination light.
A scanning probe microscope (SPM) is a general term for devices which provide a probe at a field of less than 1 &mgr;m to the surface of a sample, detect the interactive force between the probe and the sample while the probe scans in the XY direction or the XYZ direction, and perform two-dimensional mapping of this relative effect. SPMs of this type include, for example, a scanning tunneling microscope (STM), an atomic force microscope (AFM), a magnetic force microscope (MFM), and a scanning near field optical microscope (SNOM).
Of the above microscopes, the SNOM in particular has been developed since the late 1980s as an optical microscope which has a resolution exceeding the limits of diffraction, and which detects near field light provided close to a sample, for fluorescent light measurement of living body samples, evaluating measuring elements and materials for photonics (evaluation of various characteristics of dielectric photoconducting wave guides, light-generating spectral measurement of semiconductor quantum dots, evaluation of various characteristics of light-generating elements on the surface of a semiconductor, etc.), and the like.
Basically, the SNOM is a microscope which provides a sharp probe near to the sample under illumination light, and detects the state at the position (position of near field) where the light is near to the sample.
U.S. Pat. No. 5,272,300 (Literature 1) appended by Betzig et al. on Dec. 21, 1993, discloses an SNOM which injects light into a sharp-tipped probe, thereby generating a position of local light near a very small aperture in the tip of the probe, and illuminates a very small section of the sample by touching it with the tip of the probe. A light detector is provided below the sample, and detects the light which has permeated the sample, whereby the SNOM performs two-dimensional mapping of the strength of the permeated light.
This SNOM uses a sharp-tipped rod-like probe such as an optical fiber or glass rod, or a crystal probe.
An improved version of this rod-like probe, wherein the areas of the probe other than the tip are coated with a metallic film, is commercially available.
A microscope using this probe has better horizontal resolution than a microscope using a probe which is not coated with a metallic film.
In “J. Microscopy 177 (1995) p. 115” (Literature 2), Heinzelmann et al. disclosed a method for achieving high resolution by providing a movable light detector, determining the scatter angle dependency of the signal, and using a signal of a specific angle.
The most common type of SPM is the AFM, used as a microscope which obtains information relating to the unevenness of the sample surface.
The AFM has a probe supported on the tip of a cantilever, and uses, for example, an optical displacement sensor to detect the displacement of the cantilever in correspondence with forces acting on the probe when the probe is positioned near the surface of the sample, thereby indirectly obtaining information relating to the unevenness of the sample surface.
For example, one such AFM is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 62-130302 (Literature 3).
This AFM uses a method for measuring the unevenness of the sample by detecting the interactive force between the sample and the probe which is also used in other SPM devices. The method is termed regulation, and comprises maintaining a fixed distance between the sample and the probe.
In “Appl. Phys. Lett. 62(5) p. 461 (1993)” (Literature 4), N. F. van Hulst et al. propose a new SNOM which detects optical information of a sample using a silicon nitride cantilever for AFM to measure the unevenness of the sample by AFM measurement.
In this microscope, the sample is provided on an internally all-reflecting prism, and He-Ne laser light is illuminated from all sides of the prism onto the sample, exciting the sample and forming a spot of evanescent light near the surface of the sample.
The probe supported at the tip of the cantilever is inserted into this spot of evanescent light, converting the local waves of evanescent light into propagated waves of scattered light. A portion of this light enters the probe, which comprises silicon nitride and is almost completely permeable by He—Ne laser light, and escapes to the rear side of the cantilever.
This light is condensed by a lens, provided above the cantilever, and illuminated through a pinhole, provided at a position corresponding to the position of the probe with respect to the lens, into a photo multiplier tube which outputs an SNOM signal.
During the SNOM signal detection, an optical displacement detection sensor measures the displacement of the cantilever as in normal AFM measurement, and for example a piezoelectric scanner is controlled by feedback so that the displacement maintains a predetermined constant value.
Therefore, during one scanning process, SNOM measurement is carried out based on the scanning signal and the SNOM signal. In addition, AFM measurement is carried out based on the scanning signal and the feedback control signal.
In an aperture-type SNOM such as that disclosed by Betzig et al., the probe should preferably be coated with metal in order to achieve a high horizontal resolution.
However, it is not easy to uniformly mass-produce metal-coated probes having apertures in their tips. An SNOM demanding ultra high-resolution requires a resolution exceeding the resolution possible when using a normal optical microscope. To achieve this, the diameter of the aperture in the tip of the probe must be less than 0.1 &mgr;m, and preferably less than 0.05 &mgr;m.
It is extremely difficult to manufacture an aperture of such a small diameter with good reproducibility.
The quantity of light illuminated through the aperture into the probe decreases in proportion to the square of the radius of the aperture. Consequently, there is a problematic trade-off, since, when the diameter of the aperture is reduced with the aim of increasing the horizontal resolution of the SNOM image, the quantity of detected light decreases and the S/N ratio of the detection system worsens.
Accordingly, a new SNOM (dispersion mode SNOM) wherein no aperture is provided in the tip of the probe has been proposed. In this SNOM, a highly refractive dielectric having a structure less than the wavelength, or a metal, strongly scatters the near field light.
Since this SNOM does not require an aperture in the tip of the probe, the problem of difficulty in manufacturing the aperture, and the trade-off problem, do not arise.
Kawada et al. disclosed a scattering-type mode SNOM in Jpn. Pat. Appln. KOKAI Publication No. 6-137847 (Literature 5).
In this SNOM, a needle-like probe scatters evanescent light formed onto the surface of the sample, thereby converting it to propagated light. The propagated light, that is, the scattered light is detected by an objective lens and a light detector, which are provided at the side of the probe, and optical information relating to the sample is obtained based on the detected signal.
In “The 42nd Lecture Meeting of the Japanese Federation of Applied Physics” (Preliminary Papers No. 3, p. 916, March 1995) (Literature 6), Kawada et al. disclosed a device in which
Lee John R.
Olympus Optical Co,. Ltd.
Scully Scott Murphy & Presser
Vanore David A.
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