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BACKGROUND OF THE INVENTION
The present invention relates to a near-field optical head, a manufacturing
method of the near-field optical head, and an optical recording/readout
system using the near-field optical head.
Recently, an optical recording using near-field light has received
attention as a method for making an optical disc device extremely dense.
For example, the following experimental results were reported in Applied
Physics Letters, Vol. 61, No. 2, pp. 142-144, 1992: a probe was made by
shaving the top of an optical fiber into a cone and by coating it with
metal except for several tens nm of the top and was mounted on a precision
actuator using a piezo device, and a recording mark of 60 nm in diameter
was recorded or read out on or from a platinum/cobalt multi-layer by
controlling the position of the probe. In this case, a shear-force method
applying an atomic force to the control of a gap between the probe is used
and a recording medium and an areal density reached 45 gigabit/in.sup.2,
which is about 20 times the present areal density. Further, in Japanese
Unexamined Patent Publication No. 3-171434, a method is disclosed wherein
near-field light is excited by focusing light on a small pinhole by a lens
and a gap between the small pinhole and a recording medium is controlled
with the use of an atomic force generated between a cantilever having the
small pinhole at the top thereof and the recording medium, and another
method is disclosed wherein a slider which receives a light source, a lens
and a small pinhole is arranged on a medium and is flown by air to control
a gap between the small pinhole and the recording medium.
SUMMARY OF THE INVENTION
In an optical information-recording/readout system, in order to increase an
information transfer rate, it is necessary to increase a relative speed of
a recording medium to an optical head for recording/reading-out
information.
However, in the above-mentioned first conventional example using the
shear-force method applying the atomic force to the control of the gap
between the probe and the recording medium, the gap between the recording
medium and the optical head, that is, the fiber probe is required to be
controlled with a scanning force microscopy with extremely high accuracy
and hence there exists a problem in that if an information-recording disc
is rotated at high speeds, the gap between a substrate having a high
frequency produced by a radial positioning error of the disc and that the
probe can not be controlled with high accuracy and therefore an
information data transfer rate can not be increased.
Further, in the conventional example using the cantilever, a change in
capacitance or a laser interferometric measurement is used as a method for
detecting a displacement of the cantilever and hence there exists a
problem in that a large-scale optical system or a capacitance measurement
system other than an illumination optical system for exciting near-field
light is required and that the system is made larger and more complex.
Furthermore, the following optical lever method was reported in Applied
Physics Letters, Vol. 68, No. 25, pp. 3531-3533, 1996: the displacement of
a cantilever was converted into the movement of a light point on a linear
photodiode by irradiating the cantilever with laser light at the back
thereof to detect the displacement of the cantilever. However, also in
this case, there exits a problem in that a large-scale optical system
other than an illumination optical system for exciting near-field light is
required and that the system is made larger and more complex.
Furthermore, in the conventional example having the slider which receives
the light source, the lens and the small pinhole on the medium, many
optical parts such as light source, lens and the like are mounted on the
slider and hence the mass of the slider is increased to deteriorate the
following of an up-down oscillation caused by the rotation of the
recording medium by the slider, which makes it impossible to constitute
the system. Still further, in Japanese Unexamined Patent Publication No.
3-171434, a method for mounting and forming the pinhole, the laser light,
and the lens is not disclosed in the concrete.
An object of the present invention is to provide a near-field optical head
capable of increasing a relative speed of a recording medium to the
optical head for recording/reading-out information so as to increase an
information data transfer rate of an ultra-high density optical
recording/readout system using a probe for exciting near-field light.
Further, another object of the present invention is provide a near-field
optical head which does not need an additional unit for detecting a gap
between the recording medium and the optical head and hence is reduced in
size and weight and constituted simply. Furthermore, still another object
of the present invention is to provide an optical recording/readout system
using this kind of near-field optical head.
To solve the above-mentioned problems, the present invention adopts the
following means.
A cylindrical or prismatical pad for controlling the state of contact or
flying of an optically transparent slider with or to an
information-recording medium and a probe for exciting near-field light
having a small spot size are mounted on the surface of the slider opposite
to the information-recording medium such that the pad is near to the
probe, wherein the slider moves relatively to the information-recording
medium while keeping contact with or a nearly constant gap to the
information-recording medium, and further the height of the probe is
nearly equal to and smaller than the height of the pad from the surface of
the slider opposite to the information-recording medium. Accordingly, the
near-field optical head is integrally formed with the slider to constitute
a near-field optical head which is reduced in size and weight and is
simply constituted and has the same performance as a head used in a
conventional hard disc drive. Further, since the slider is reduced in size
and weight, it is possible to increase a relative speed of the recording
medium to the optical head for recording/reading-out information.
Further, in the near-field optical head described above, the near-field
optical head having a small spot size can be excited by forming an
optically opaque film, for example a metallic film, on the pad and the
probe, and further by making at the top the probe a small aperture in
which the constituent of the probe is exposed and the surface of the
exposed constituent of the probe and in which the surface of the metallic
thin film are substantially on the same plane.
Still further, in the near-field optical head described above, the probe
can be shaped into an arbitrary pyramidal structure or the small aperture
can be made in the top of the probe by arranging the pad in such a way to
surround the probe and by dividing the pad into at least a plurality of
parts and by arranging the divided parts in such a way that the probe can
be seen through a gap between the divided parts when viewed from the side
of the pad and by etching the probe by irradiating the probe with a
particle beam from the side of the probe. Furthermore, an optical
recording readout system of ultra-high density can be constituted with the
use of the near-field optical head, a light source for supplying
illumination light to the near-field optical head, an optical recording
medium, a detection system for detecting a modulated signal of the
near-field light excited by the near-field optical head by the recording
medium.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a perspective view showing a first preferred embodiment of a
near-field optical head according to the present invention. FIG. 1B is a
cross-sectional view taken on a line A-A' in FIG. 1A.
FIG. 2A and FIG. 2B are perspective views showing examples of probes used
in a near-field optical head. FIG. 2C is a cross-sectional view thereof.
FIG. 3 is a perspective view showing another example of a probe used in a
near-field optical head.
FIG. 4A and FIG. 4B are perspective views showing the other examples of
probes used in a near-field optical head. FIG. 4C is a cross-sectional
view taken on a plane EE'E"E'" in FIG. 4B.
FIG. 5 is a perspective view showing another example of a probe used in a
near-field optical head.
FIG. 6 is a cross-sectional view showing a semiconductor laser probe used
in the present invention.
FIG. 7A is a perspective view showing a second preferred embodiment of the
present invention using a contact type slider. FIG. 7B is a
cross-sectional view taken on a line F-F' in FIG. 7A.
FIG. 8A is a perspective view showing a third preferred embodiment of the
present invention. FIG. 8B is a cross-sectional view taken on a line G-G'
in FIG. 8A.
FIG. 9A to FIG. 9F show a manufacturing process of various types of
near-field optical heads shown in FIG. 1 to FIG. 8.
FIG. 10 shows the magnitude of an aperture at the top of the near-field
optical head shown in FIG. 4, FIG. 5, and FIG. 6.
FIG. 11 is a perspective view showing a recording medium of an optical
recording/readout system to which a near-field optical head according to
the present invention is applied with parts partially broken away.
FIG. 12 shows in detail an optical head used in FIG. 11.
FIG. 13 shows a servo operation in an optical recording/readout system
according to the present invention.
FIG. 14A shows a fourth preferred embodiment of a near-field optical head
according to the present invention. FIG. 14B shows a fifth preferred
embodiment of a near-field optical head according to the present
invention.
FIG. 15 shows a sixth preferred embodiment of a near-field optical head
according to the present invention.
FIG. 16A shows a seventh preferred embodiment of a slider according to the
present invention. FIG. 16B shows the eighth preferred embodiment of a
slider according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be described
hereinafter with reference to the attached drawings.
FIG. 1 is a preferred embodiment of the present invention. FIG. 1A is a
perspective view of a near-field optical head according to the present
invention. FIG. 1B is a cross-sectional view taken on a line A-A' in FIG.
1A. In this respect, to make it easier to understand a relationship
between the near-field optical head and an information-recording medium
11, the information-recording medium 11 and a support substrate 10 thereof
are shown together in FIG. 1B. Further, the information-recording medium
11 and the support substrate 10 thereof are shown together also in FIG.
7B, FIG. 8B. FIG. 14A, FIG. 14B, and FIG. 15.
In FIG. 1A, a numeral 1 designates a slider made of optically transparent
substance. Since the case in which a semiconductor laser having a
wavelength of 780 nm is a light source is described in the present
preferred embodiment, quartz is selected as the material of the slider,
but it is not intended to limit the material of the slider to the quartz.
Numerals 2, 3 designate pads for controlling the state of flying to the
information-recording medium 11 of the slider 1. In the present preferred
embodiment, four-divided pads 2 are provided at the center of one end
portion of a surface of the slider 1 opposite to the information-recording
medium 11 and pads 3 are provided on both sides of the other end portion
thereof. A pyramid-shaped probe 4 shaped for exciting near-field light is
provided at the center of the four-divided pads 2. The probe 4, as shown
in FIG. 1B, is coated with a metallic thin film 5 having a thickness of
several tens nm. Further, an anti-wearing thin film, for example a carbon
film 6, of about 10 nm thick is formed on the surface of the slider 1
opposite to the information-recording medium 11 except for the probe 4.
In FIG. 1B, a numeral 7 designates an objective lens for focusing
semiconductor laser light 8 on the probe 4 for exciting near-field light.
The focused semiconductor laser light 8 is converted into near-field light
9 having a small spot size near the top of the probe 4 for exciting
near-field light. The slider 1 travels at a flying height of several tens
nm to the recording medium 11 and, with the use of the above-mentioned
near-field light 9, information 12 is recorded on or read out from the
recording medium 11 formed on the support substrate 10.
Here, the height h' of the probe 4 is required to be surely smaller than
the height h of the pad 2. In this respect, there are two heights for the
height of the probe 4: one height is the height of a pyramid made by
shaving a part of the slider 1 and including the metallic thin film 5
formed thereon, as shown in FIG. 2A to FIG. 2C, or FIG. 3 and the other
height is the height of only a frustum made by cutting off the top of the
pyramid including the metallic thin film 5 formed thereon, as shown in
FIG. 4A to FIG. 4C, or FIG. 5. In the description of the probe 4 in the
preferred embodiments described below, mention will not be made of the
difference in the heights, unless it is necessary.
As shown in FIG. 1B, the slider 1 travels at a flying height of only
several tens nm to the surface of the recording medium 11. The top surface
of the pad 2 is a sliding surface of the slider 1 to the surface of the
recording medium 11. Therefore, when the slider 1 is put into contact with
the recording medium substrate 10 during a recording/readout operation by
the present head, the top surface of the pad 2 is put into contact with
the recording medium substrate 10. If the height h' of the probe 4 is
larger than the height h of the pad 2, the top of the probe 4 is put into
contact with the recording medium substrate 10 to wear the probe 4. To
prevent this problem, the h' is required to be surely smaller than the h.
It is necessary not only to make the height h' surely smaller than the
height h, but also to make the difference between the height h' and the
height h extremely small. It is known that the intensity of the near-field
light 9 does not substantially change when a distance from the top of the
probe 4 is nearly the size of the top of the probe 4 but it decreases
rapidly when the distance from the top of the probe 4 is greater than the
size of the top of the probe 4. The size of the top of the probe 4 ranges
from several tens nm to 100 nm, and if the gap between the probe 4 and the
recording medium 11 is greater than that, the intensity of the near-field
light 9 becomes extremely small on the recording medium 11. Since the
slider 1 travels at a flying height of several tens nm to the surface of
the recording medium 11, to keep the gap between the probe 4 and the
recording medium 11 at the size of the top of the probe 4, that is, from
several tens nm to not more than 100 nm, it is necessary to make the
height h' nearly equal to the height h and to keep the gap between the top
of the probe 4 and the surface of the recording medium 11 at about several
tens nm when the slider 1 travels. To this end, it is necessary to control
the difference between the height h' and the height h in a nm order. This
is an important point in manufacturing the present near-field optical head
and a manufacturing method therefor will be described later in detail.
If the near-field optical head is employed in which the probe for exciting
near-field light is integrated with the slider as described above, it is
possible to constitute a near-field optical head which is reduced in size
and weight and is constituted simply and has the same performance as a
conventional hard disc drive. Further, since the slider is made compact
and lightweight, the relative speed of the recording medium to the optical
head for recording/reading-out information can be increased, which can
increase an information data transfer rate.
Next, the probe for exciting near-field light employed in the present
preferred embodiments will be described in detail with the use of FIG. 2
to FIG. 6.
FIG. 2A is an enlarged view of the probe shaped like a pyramid used in FIG.
1. FIG. 2B is an enlarged view of the probe shaped like a triangular
prism. Further, FIG. 2C is a cross-sectional view taken on a plane which
passes the summit of the pyramid and the center points B, B' of the two
sides of a bottom face in FIG. 2A (in parallel to the polarization
direction of the semiconductor laser light 8), and a plane which passes
the center points C, C', C" of the three sides of the triangular prism in
FIG. 2B (in parallel to the polarization direction of the semiconductor
laser light 8).
In FIG. 2A, if the probe 4 is made of quartz, for example, the metallic
thin film 5 formed on the probe 4 can be selected from various kinds of
metals. However, if there is a specific relation between the kind of metal
and the half cone angle .theta. of the summit of the pyramid shown in FIG.
2C, high efficiency can be obtained. The semiconductor laser light 8 is
focused near the top of the probe 4 and the wavefront thereof can be
regarded as a plane. In this case, if a combination of the above-mentioned
half cone angle .theta. and the kind of metal is suitable, a surface
plasma wave 16 is excited in the metallic thin film 5. The surface plasma
wave 16 can propagate even in a thin metallic film of several tens nm
thick and hence the semiconductor laser light converted into the surface
plasma wave 16 propagates effectively to the top of the probe 4 to excite
the near-field light 9 with high efficiency. For example, when quartz is
used as the probe, the half cone angle .theta. is about 42 degrees if
aluminum is used as metal, about 42 degrees if gold is used, and about 44
degrees if silver is used. In FIG. 2B, since the probe 13 is shaped like a
triangular prism, light focused near the top of the probe is focused only
in a plane parallel to the cross section C, C', C". Therefore, linear
near-field light 15 is excited in the case of FIG. 2B, which is different
from the case in FIG. 2A. Even in the shape shown in FIG. 2B, if the
relation between the half cone angle .theta. of the summit and the kind of
metal 14 is set at the same level as the above-mentioned relation, high
efficiency can be obtained.
Although the sizes of the probes 4 and 13 are not limited to a specific
size, taking into account that it needs to be easily manufactured and
that, for example, if laser light having a wavelength of 780 nm is focused
by an objective lens with a numerical aperture of 0.6, the focusing spot
thereof is about 1.3 .mu.m, and that all the laser light is focused on the
probe effectively, it is preferable that one side of the square bottom
face of the pyramid is 3 to 4 .mu.m long in the case of FIG. 2A. Further,
it is preferable that two sides parallel to the cross section C, C', C"
are about 3 to 4 .mu.m long in the case of FIG. 2B, but two sides
perpendicular to the cross section C, C', C" can assume various values
according to the spot size of the near-field light 15.
FIG. 3 shows a probe 17 shaped like a cone. Also in this case, if the
relation between the half cone angle .theta. of the summit of the cone and
the kind of metallic thin film 18 formed on the probe 17 satisfies the
specific conditions described above, the near-field light 10 can be
excited with high efficiency.
FIG. 4 is another probe for exciting near-field light. FIG. 4A shows the
probe in which the top of the square-pyramid-shaped probe 4 shown in FIG.
2A is cut away. FIG. 4B shows the probe in which the top of the
triangular-prism-shaped probe 13 shown in FIG. 2B is cut away. FIG. 4C
shows a cross-sectional view taken on a plane which passes four points of
center points D and D'" of the two sides of the square top face of a
square frustum and the center points D', D" of the two sides of the square
bottom face thereof in FIG. 4A (in parallel to the polarization direction
of the semiconductor laser light 8), and a plane which passes four points
of center points E and E'" of the two sides of the square top face of a
probe and the midpoints E', E" of the two sides of the square bottom face
thereof in FIG. 4B (in parallel to the polarization direction of the
semiconductor laser light 8).
In the probe 19 shown in FIG. 4A, the top of the pyramid is cut away and an
aperture 21 is made. In the probe having the aperture, an optically opaque
thin film 20, for example, a metallic thin film formed on the surface of
the probe is used as a light-shield film for the semiconductor laser light
8 focused by the objective lens 7. In this case, the size of near-field
light 22 used for recording/readout is the sum of the magnitude d of the
aperture 21 and the skin depth of the light to the metallic thin film. If
a manufacturing method described below in detail is used, the magnitude of
the aperture can be made about 20 nm at the minimum. Various kinds of
metals such as gold, silver, platinum, aluminum, chromium can be used as
the light-shield metal. The skin depth of light having a wavelength of 780
nm to these metals ranges typically from 10 to 20 nm, and hence the
near-field light spot of about 40 nm can be made at the minimum. In FIG.
4B, since the probe 23 is shaped like a triangular prism and the aperture
25 is shaped like a narrow rectangle, linear near-field light 26 is
excited. In this case, the size of near-field light in the cross section
EE'E"E'" is the same as that in FIG. 4A, but the size in the direction
perpendicular to the cross section EE'E"E'" can be freely selected by
selecting the length of the longer side of the rectangle.
If the value of the half cone angle .phi. of the probe shown in FIG. 4C is
made about 30 to 60 degrees, the probe having a high throughput can be
obtained. If the half cone angle .phi. is too small, the length of the
tapered portion of the probe is made larger. In general, light propagating
in the space can not propagate in the region smaller than the wavelength
of the light and hence, in the preferred embodiment shown in FIG. 4C, most
of the optical power is absorbed by the metallic thin films 20 to 24 to
reduce the throughput thereof. On the other hand, if the half cone angle
.phi. is too large, most of the light is reflected by the probe.
Accordingly, it is preferable that the half cone angle .phi. is set at a
suitable value in the range described above so as to prevent the leakage
of light to the metallic thin film and the reflection of light.
Although the sizes of the probes 19 and 23 are not limited to a specific
size, taking into account that it needs to be easily manufactured and that
if laser light having a wavelength of 780 nm is focused by an objective
lens with a numerical aperture of 0.6, the focusing spot thereof is about
1.3 .mu.m and that all laser light is effectively focused on the probe,
for example in the case of FIG. 4A, it is preferable that one side of the
square bottom face of the pyramid is 3 to 4 .mu.m long. Further, although
it is preferable that the sides parallel to the cross section EE'E"E'" are
about 3 to 4 .mu.m long in the case of FIG. 4B, two sides perpendicular to
the cross section EE'E"E'" can assume various values according to the spot
size of the near-field light 26.
In FIG. 5, a probe 27 is shaped like a cone and a portion near the summit
thereof is cut away and a circular aperture 29 is made. Also in this case,
the size of the near-field light 30 is the sum of the magnitude of the
aperture 29 and the skin depth of the light to a light-shield film 28 and
can be made about 40 nm at the minimum. Further, if the value of the half
cone angle .phi. of the cone is made about 30 to 60 degrees, as is the
case with the above-mentioned case in FIG. 4C, the probe having a high
throughput can be obtained.
In the cases of the probes 19, 23, and 27 having the aperture, researches
in improving the throughput have been conducted with respect to the probe
made by etching an optical fiber chemically. For example, the following
results are described in Applied Physics Letters, Vol. 68, No. 19, pp.
2612-2614, 1996: the leakage of light to the metallic thin film 32 was
prevented and the reflection of the light by the probe 31 was prevented,
as shown in FIG. 6B, by changing the cone angle of the probe 31 in two
steps, that is, by making the cone angle at the root of the probe smaller
and the cone angle of the top thereof larger, so that the probe having a
higher throughput could be obtained. Also in the present invention,
according to a manufacturing method described below, the probe having the
high throughput as shown in FIG. 6B can be obtained easily. Further, the
following results are described in Applied Physics Letters, Vol. 71, No.
13, pp. 1756-1758, 1997: a probe having a high throughput could be
obtained, as shown in FIG. 6C, by making the shape of the probe 35
unsymmetrical with respect to the center line of the probe to excite a
surface plasma wave. Also in the present invention, according to a
manufacturing method described below, the probe having the high throughput
as shown in FIG. 6C can be easily obtained.
FIG. 7 is the second preferred embodiment according to the present
invention to which a contact type slider is applied. FIG. 7A is a
perspective view of a near-field optical head of the present preferred
embodiment. FIG. 7B is a cross-sectional view taken on a line F-F' in FIG.
7A. In FIG. 7A, on a slider 1 made of optically transparent substance,
pads 2 are provided for controlling the state of contact of the slider 1
and an information-recording medium. Although three pads are provided on
the bottom face of the slider 1 in the preferred embodiment shown in FIG.
1, four-divided pads 2 are provided in the present preferred embodiment. A
pyramid-shaped probe 4 for exciting near-field light is provided at the
center of the pads 2. The probe 4 is coated with a metallic thin film 5
having a thickness of several tens nm as shown in FIG. 7B. Further, an
anti-wearing thin film 6, for example a carbon film, having a thickness of
about ten nm is formed on the pads 2 and on the surface of the slider 1
opposite to the recording medium 11. Although an example is shown in FIG.
7B in which the material of the metallic thin film 5 is different from
that of the anti-wearing thin film 6, the bottom face of the slider 1 and
the surface of the probe 4 can be coated with the material, for example a
chromium film, which can satisfy both the wear resistance and the exciting
ability of the surface plasma wave in the case of the probe with no
aperture described with reference to FIG. 2 and FIG. 3, or both the wear
resistance and the light-shield ability in the case of the probe with an
aperture described with reference to FIG. 4 to FIG. 6. This makes a
manufacturing process easier. An anti-wearing carbon thin film 39 having a
thickness of several nm is formed on the surface of the
information-recording medium 11 and further polymeric lubricant is applied
thereto in a thickness of several nm. The carbon thin film 39 and the
lubricant improve the wear resistance of the information-recording medium
11. The slider 1 travels in contact with the recording medium substrate 10
and information 12 is recorded and read out, by the above mentioned
near-field light 9, on and from the information-recording medium 11 formed
on the recording medium substrate 10.
FIG. 8 is a third preferred embodiment according to the present invention
using a flying type slider. FIG. 8A is a perspective view of the
near-field optical head of the present preferred embodiment. FIG. 8B is a
cross-sectional view taken on a line G-G' in FIG. 8A. In FIG. 8A, on a
slider 1 made of optically transparent material, pads 2 and 3 are provided
for controlling the state of flying of the slider 1 and an
information-recording medium 11. In the present preferred embodiment,
three pads are provided on the bottom face of the slider 1. The pad 2, one
of them, is divided into four parts and a pyramid-shaped probe 4 for
exciting near-field light is provided at the center thereof. In the
present preferred embodiment, the height of the four-divided small pads of
the pad 2 is designed to be smaller than the height of the whole pad 2 and
the height of the pad 3 from the bottom face of the slider 1, so that the
height from the bottom face to the top face of the pad can be freely
designed irrespective of the size of the probe 4 and hence a flying height
of the slider 1 can be freely set. Further, the height of the four-divided
small pads of the pad 2 is set slightly higher than the height of the
probe 4, as is the case with a first preferred embodiment. Since the
height of the small pad can be set according to the shape and the size of
the probe 4 without taking into account the flying height of the slider 1,
the degree of flexibility in manufacturing the probe 4 is increased.
Although a probe having a shape shown in FIG. 2A was described as an
example in the above-mentioned preferred embodiments 2 and 3, the shapes
of the sliders shown in the preferred embodiment 2 and 3 can be applied
similarly to all other shapes of the probes shown in FIG. 2 to FIG. 6.
FIG. 9 and FIG. 10 show a process for manufacturing the near-field optical
head shown in FIG. 1 to FIG. 8.
First, as shown in FIG. 9A, photo resist 40 is applied to a substrate 1 and
is exposed to light and is developed and then only portions where pads 2
and 3 and a probe 4 are made are left as a mask. Next, as shown in FIG.
9B, a mask pattern formed in FIG. 9A is transferred to the substrate 1,
for example, by dry etching using argon gas. Next, as shown in FIG. 9C,
the photo resist 40 is removed and then a protection film 6 for protecting
the bottom face of the slider and the surface of the pad is formed by a
sputtering method. Next, as shown in FIG. 9D, the probe is shaped into a
predetermined shape by etching using a focused ion beam (hereinafter
referred to as FIB) 41. In the case of using a gallium ion for the FIB, an
acceleration voltage is made about several tens kV and a beam current is
made about several tens pA. The beam size at the focusing position of the
FIB 41 is about several tens nm. This is a sufficient resolution for
manufacturing the probe according to the present invention. In the shaping
process using the FIB, while a sample to be shaped is being irradiated
with the ion beams, a secondary electron image is taken and while the
secondary electron image is being looked, the ion-irradiated position can
be controlled freely, so that the probe can be flexibly shaped with ease
in a short time. In the shaping process of the probe, the probe is etched
by irradiating the center projection thereof to be shaped with the ion
beams from one side of the substrate 1 through a gap between the pads 2,
so that the center projection is shaped from a rectangular solid into a
triangular prism. When the probe 13 or 23 is made, this is the end of the
shaping process. When the probe is shaped into a pyramid like the probe 4,
after the above-mentioned process is ended, the substrate 1 is turned 90
degrees around an axis parallel to the center axis of the probe and then
the probe is etched again by irradiating the probe with the ion beams from
the direction at 90 degrees to the direction of the ion beams when the
probe is etched first, through a gap between the pads 2, whereby the probe
is finally shaped into a pyramid. The total shaping time is about ten
minutes, depending on the material of the substrate 1. As described above,
the height of the probe is made nearly equal to and slightly smaller than
the height of the pad by manufacturing the probe by applying the FIB from
the side of the substrate 1. After the probe is shaped by the FIB, as
shown in FIG. 9E, the pad and the other bottom face of the slider are
covered by the photo resist 40 and only the probe is exposed and then the
metallic thin film 5 is formed on the probe. Finally, the metal formed on
the pad and the other bottom face of the slider is removed by a lift-off
method to make the near-field optical head shown in FIG. 9F.
Further, in the case of manufacturing the probe with an aperture shown in
FIG. 4 to FIG. 6, as shown in FIG. 10, the probe of a finished state shown
in FIG. 9F is irradiated with the FIB 41 again from the side of the
substrate to cut away the top thereof. The size of the aperture can be
freely changed by controlling a slicing depth shown in FIG. 10.
Furthermore, according to the present method, as shown in FIG. 10, the top
of the cut probe is flat and the height thereof does not exceed the height
of the pad. Accordingly, the top of the probe does not collide with and
break the recording medium 11, which can improve reliability. Still
further, in the case of manufacturing the probe of specific shapes shown
in FIG. 6B and FIG. 6C, when the probe is shaped by the FIB as shown in
FIG. 9D, the probe is etched by controlling the position of the ion beams
according to the shape to be intended. It is the main effect of the
manufacturing method using the FIB that the probe can be shaped into a
desired shape in a short time as described above.
FIG. 11 is a perspective view of an optical recording/readout system to
which the near-field optical head according to the present invention is
applied. A disc 43 comprising the recording medium substrate 10 and the
recording medium film 11 is fixed to a spindle 44 joined to a spindle
motor fixed to a base 42 and is rotated relatively to the slider 1 on
which any of the near-field optical heads shown in FIG. 2 to FIG. 8. An
actuator 49 for positioning the slider 1 is also fixed to the base 42 and
the movable part 48 thereof is provided with an arm 50 and a suspension
52. The movable part 58 is rotated around a center axis thereof to move
the slider 1 fixed to the top of the suspension 52 in the radial direction
of the disc 43. Further, in the case of using a disc with a small tracking
pitch, an actuator 51 capable of positioning the slider 1 further finely
than the actuator 49 is fixed to the top of the arm 50. A connector 46 is
joined to an interface 45 fixed to the base 42 and an electric power
supply for driving the present system, and a recording/readout
instruction, an input of recording information and an output of readout
information to the system are performed through the cable joined to the
connector 46. A supply of laser light to the near-field optical head, a
detection of recording information, a detection of a position error of the
slider from the track, and a detection of a position error of the
objective lens and the slider are performed by using an optical head 53
fixed to the base 42, which is described in detail with reference to FIG.
12. A movable part 54 mounted with a Garvano mirror, an objective lens,
and an actuator for moving the objective lens is disposed just under the
slider 1. The movable part 54 is moved in the radial direction of the disc
43 by the actuator for moving the whole movable part in response to the
slider 1.
Next, the operation of the optical head 53 and the movable part 54 will be
described in detail with reference to FIG. 12. The laser light excited by
a semiconductor laser 55 is converted into the collimated beam by a
collimate lens 56 and then is passed through a beam splitter 57 and has
the direction thereof changed by the Garvano mirror. The laser light
having the direction changed by the Garvano mirror is focused on the probe
4 by the objective lens 7 to excite the near-field light, whereby the
operation of recording/readout of information on/from the recording medium
formed on the disc 43 is performed. Although the probe 4 (and the slider 1
mounted with it) shown in FIG. 2A will be described as an example of the
probe, the following content is absolutely the same for any probe shown in
FIG. 2 to FIG. 8. The laser light having intensity changed by the
information of the recording medium is passed through the objective lens 7
and has the direction thereof changed again by the Garvano mirror 58 and
is reflected by the be | | |
