Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-07-14
2002-01-08
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S306000, C250S307000
Reexamination Certificate
active
06337477
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a probe having a micro-projection and also to a method of manufacturing such a probe. More particularly, the present invention relates to a probe having a micro-projection and adapted to detect an evanescent wave used in a near field scanning optical microscope as well as a method of manufacturing such a probe. More specifically, the present invention relates to a probe having a micro-projection with a tip having a small radius of curvature, which perform well in the above application with a multiple arrangement, and which can be manufactured on a mass production basis, as well as a method of manufacturing such a probe.
2. Related Background Art
The recent invention of the scanning tunneling microscope (hereinafter referred to as “STM”) made it possible to visually observe the electronic arrangement of the surface atoms of an electrocoductive specimen [G. Binnig et al. Phys. Rev. Lett., 49, 57 (1983)] so that now a real space image of a specimen is visually observable with an enhanced level of resolution, regardless if it is crystalline or amorphous. Since then, massive research efforts have been paid on the scanning probe microscope (hereinafter referred to as “SPM”) particularly in the technological field of evaluation of fine structures of various materials.
The SPM includes the scanning tunneling microscope (STM) adapted to scrutinize the surface structure of a specimen by utilizing the tunnel current, the atomic force, the magnetic force or the light caused there when the probe having a micro-projection is brought close to the specimen, the atomic force microscope (AFM), the magnetic force microscope (MFM) and the near field scanning optical microscope (NSOM).
Of the SPM, the SNOM is used to observe, in a non-destructive way, the surface of a specimen showing a fine pattern by means of evanescent light emitted from a very small pin-hole with an enhanced level of positional resolution of less than &lgr;/2 that has been unachievable by any known optical microscope.
With the SNOM, it is possible to observe a specimen of part of the body of a living thing or a cell that used to be hardly observable. Therefore, it has broadened the scope of observable specimens as well as its applications.
Three techniques are known for detecting an evanescent wave.
With a first known technique, illuminant light is applied to the surface of a specimen from the rear side in a way of allowing total reflection of light of the surface and the evanescent wave generated on the surface of the specimen by the illuminant light is detected by way of a micro-projection having a micro-aperture (E. Betzig, et al., “Collection mode near-field scanning optical microscopy”, Appl. Phys. Lett. 51 (25), 1987, pp2088-2090). With this technique, an image of an evanescent wave can be obtained with an enhanced level of resolution and it currently provides the most extensive theme of study.
This first technique, however, uses a sharpened glass pipette or glass fiber as a micro-projection, which is manufactured by machine-grinding. This leads to poor productivity and high production cost, and it is difficult to manufacture the aperture with good reproducibility and high precision.
With a second known technique, scattered light of an evanescent wave is detected by means of a thin film cantilever having a micro-projection with no aperture and made of silicon nitride film that is used for the AFM (N. F. van Hulst, et al., “Near-field optical microscope using a silicon-nitride probe”, Appl. Phys. Lett. 62 (5), 1993, pp461-463).
A micro-projection to be used for the above technique may be a micro-projection of monocrystal silicon that can be prepared by using anisotropic etching that is popular in the field of semiconductor manufacturing process technology (U.S. Pat. No. 5,221,415)
FIGS. 1A through 1G
show a typical known method for preparing such a micro-projection. Firstly, a pit
518
is formed by anisotropic etching in a silicon wafer
514
coated with silicon dioxide mask layers
510
,
512
as shown in FIG.
1
A. Then, as shown in
FIG. 1B
, the silicon dioxide layers
510
,
512
are removed and then the wafer is coated with silicon nitride layers
520
,
521
over the entire surface thereof to produce a cantilever and a pyramid-shaped pit
522
that operates as a female mold for molding a micro-projection. Subsequently, as shown in
FIG. 1C
, the silicon nitride layer
520
is patterned to the form of a cantilever. Thereafter, as shown in
FIG. 1D
, the silicon nitride layer
521
on the rear side is removed and a glass plate
530
having a saw-cut
534
and a Cr layer
532
is bonded to the silicon nitride layer
520
. Then, the glass plate
530
is machined to form a mountain block
540
as shown in FIG.
1
E. Subsequently, the silicon wafer
514
is etched out to produce a probe supported by the mountain block
540
and provided with a micro-projection of silicon nitride and a cantilever as shown in FIG.
1
F. When it is used for a optical lever type AFM, a metal film layer
542
is formed on the top as a reflection layer as shown in FIG.
1
G. This technique can produce a micro-projection showing a very acute profile at the tip and provides a high productivity and a high reproducibility.
However, an NMOS image obtained by using a micro-projection prepared by means of this second technique shows a level of resolution lower than an NMOS obtained by using a micro-projection with an aperture prepared by means of the above first technique.
While the above two known techniques provide a micro-projection to be used as an optical pickup so that an evanescent wave is detected by a photo detector comprising a photomultiplier arranged at an upper part of the micro-projection, a known third technique provides a method of directly detecting scattered light of an evanescent wave by a photodiode on a thin film cantilever (S. Akamine, et al., “Development of a microphotocantiliver for near-field scanning optical microscopy”, Procedings IEEE Microelectro Mechanical Systems Workshop 1995, p145-150).
FIG. 2
shows a cross sectional view of such a micro-projection.
Referring to
FIG. 2
, the illustrated micro-projection comprises a silicon thin film cantilever of a p-layer
601
supported by a silicon substrate
600
at the end thereof, a p-n junction
603
photodiode prepared by forming an n-layer
602
and Al metal wires
605
arranged on a silicon oxide film
604
to take out the signal of scattered light detected by the photodiode. An etching stop layer
606
used when preparing the cantilever is found on the lower surface of the thin film cantilever. As a result of arranging a photo detecting section of a photodiode at the free end of the cantilever, the photo detecting section and the specimen can be brought close to each other to improve the S/N ratio and the resolution of the output. Additionally, the system configuration can be simplified by this technique.
However, this third technique uses the tip of the thin film cantilever as the tip of the probe
607
and the thin film cantilever is prepared by means of a photolithography process and etching so that the micro-projection is less reproducible and it is difficult to produce a lot of products showing the same and identical tip profile if compared with the micro-projection of the second known technique.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to solve the above identified problems of the known techniques and provide a probe with a micro-projection that shows an improved S/N ratio and an excellent level of resolution for the detection of light or temperature and also a method of manufacturing such a probe.
Another object of the invention is to provide a probe showing a highly reproducible uniform profile and having a sharp tip that can be manufactured at reduced cost with an improved productivity and also a method of manufacturing such a probe.
According to a first aspect of the invention, the above objects are achieved by providing a probe with
Kuroda Ryo
Shimada Yasuhiro
Yagi Takayuki
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Lee John R.
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