U.S. patent application number 12/312265 was filed with the patent office on 2010-08-19 for method of smoothing solid surface with gas cluster ion beam and solid surface smoothing apparatus.
This patent application is currently assigned to Japan Aviatiton Electronics Industry Limited. Invention is credited to Emmanuel Bourelle, Jiro Matsuo, Akinobu Sato, Toshio Seki, Akiko Suzuki.
Application Number | 20100207041 12/312265 |
Document ID | / |
Family ID | 39344220 |
Filed Date | 2010-08-19 |
United States Patent
Application |
20100207041 |
Kind Code |
A1 |
Sato; Akinobu ; et
al. |
August 19, 2010 |
Method of Smoothing Solid Surface with Gas Cluster Ion Beam and
Solid Surface Smoothing Apparatus
Abstract
Scratches or similar surface roughness in a solid surface is
reduced by gas cluster ion beam irradiation. A method of smoothing
a solid surface with a gas cluster ion beam includes an irradiation
step in which the solid surface is irradiated with a gas cluster
ion beam, and the irradiation step includes a process of causing
clusters from a plurality of directions to collide with at least an
area (spot) irradiated with the gas cluster ion beam on the solid
surface. Collision of the clusters from a plurality of directions
with the spot is brought about by an irradiation of the gas cluster
ion beam in which flight directions of the clusters diverge with
respect to a center of the beam, for example.
Inventors: |
Sato; Akinobu; (Tokyo,
JP) ; Suzuki; Akiko; (Tokyo, JP) ; Bourelle;
Emmanuel; (Montmirail, FR) ; Matsuo; Jiro;
(Kyoto, JP) ; Seki; Toshio; (Kyoto, JP) |
Correspondence
Address: |
Intellectual Property Law Office of David Lathrop
No. 827, 39120 Argonaut Way
Fremont
CA
94538
US
|
Assignee: |
Japan Aviatiton Electronics
Industry Limited
|
Family ID: |
39344220 |
Appl. No.: |
12/312265 |
Filed: |
October 30, 2007 |
PCT Filed: |
October 30, 2007 |
PCT NO: |
PCT/JP2007/071102 |
371 Date: |
October 21, 2009 |
Current U.S.
Class: |
250/492.3 |
Current CPC
Class: |
H01L 21/3065 20130101;
C23F 4/00 20130101; H01J 37/317 20130101; H01J 27/026 20130101;
H01J 2237/20207 20130101; H01J 2237/20214 20130101; H01J 37/3053
20130101; H01J 37/20 20130101 |
Class at
Publication: |
250/492.3 |
International
Class: |
H01J 37/30 20060101
H01J037/30 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 2006 |
JP |
2006 293686 |
Claims
1. A method of smoothing a solid surface with a gas cluster ion
beam comprising an irradiation step of irradiating the solid
surface with the gas cluster ion beam, wherein the irradiation step
comprises a process of causing clusters from a plurality of
directions to collide with at least an area (spot) irradiated with
the gas cluster ion beam on the solid surface.
2. The method of smoothing a solid surface with a gas cluster ion
beam according to claim 1, wherein the collision of the clusters
from a plurality of directions with the spot is performed by an
irradiation of the gas cluster ion beam in which flight directions
of the clusters diverge with respect to a center of the beam.
3. The method of smoothing a solid surface with a gas cluster ion
beam according to claim 2, wherein the gas cluster ion beam is a
gas cluster ion beam randomly diverging with an angle of at least
2.degree. with respect to the center of the beam.
4. The method of smoothing a solid surface with a gas cluster ion
beam according to any of claims 1 to 3, wherein the collision of
the clusters from a plurality of directions with the spot is
performed by emitting the gas cluster ion beam while moving the
solid.
5. The method of smoothing a solid surface with a gas cluster ion
beam according to any of claims 1 to 3, wherein the collision of
the clusters from a plurality of directions with the spot is
performed by emitting the gas cluster ion beam while rotating the
solid.
6. The method of smoothing a solid surface with a gas cluster ion
beam according to claim 5, wherein the collision of the clusters
from a plurality of directions with the spot is performed by
emitting the gas cluster ion beam while avoiding the irradiation
angle formed by the gas cluster ion beam and the normal to the
solid surface irradiated with the gas cluster ion beam being
0.degree..
7. The method of smoothing a solid surface with a gas cluster ion
beam according to any of claims 1 to 3, wherein the collision of
the clusters from a plurality of directions with the spot is
performed by emitting one or more gas cluster ion beams in addition
to the emission of said gas cluster ion beam.
8. A solid surface smoothing apparatus for smoothing a solid
surface with a gas cluster ion beam; comprising: a beam setup means
adapted to set up the gas cluster ion beam to diverge randomly with
an angle of at least 2.degree. with respect to a center of the
beam; a gas cluster ion beam emission means which emits the gas
cluster ion beam onto the solid surface; and a means adapted to
move the solid and/or a means adapted to rotate the solid.
9. The solid surface smoothing apparatus according to claim 8,
wherein the solid surface smoothing apparatus further comprises one
or more gas cluster ion beam emission means.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of smoothing a
solid surface by gas cluster ion beam irradiation and to an
apparatus therefor.
BACKGROUND ART
[0002] A variety of gas-phase reaction methods have been developed
for the purpose of smoothing surfaces of electronic devices and the
like and have been put to practical use. For example, a substrate
surface smoothing method disclosed in Patent literature 1 smoothes
a substrate surface by sputtering using monatomic or monomolecular
ions of Ar (argon) gas directed onto the substrate surface at a low
angle.
[0003] Recently, solid surface smoothing methods using a gas
cluster ion beam have been attracting attention because they can
reduce surface roughness greatly without damaging the surface
badly. For example, Patent literature 2 discloses a method of
reducing surface roughness by irradiating a solid surface with a
gas cluster ion beam. In this method, gas cluster ions directed
onto the workpiece (solid) dissociate when they collide with the
workpiece. In this process, multibody collisions arise between
atoms or molecules forming the cluster and atoms or molecules
forming the workpiece, causing noticeable motion in a lateral
direction with respect to the workpiece surface (solid surface). As
a result, the workpiece surface is cut laterally. This phenomenon
is called lateral sputtering. The motion of particles in a lateral
direction with respect to the workpiece surface mainly cuts
projecting portions from the surface, performing ultraprecise
polishing to produce a smooth surface at the atomic level.
[0004] In the gas cluster ion beam, an ion has a lower energy than
that in normal ion etching. In other words, a single atom or
molecule forming the cluster has a lower energy. This enables
ultraprecise polishing as needed, without damaging the workpiece
surface. One advantage of solid surface smoothing using a gas
cluster ion beam is that the damage to the workpiece surface is
less than that caused by ion etching, which is disclosed in Patent
literature 1.
[0005] In solid surface smoothing using a gas cluster ion beam, it
is generally recognized that the workpiece surface should be
irradiated with the cluster ion beam at approximately right angles
to the workpiece surface. This angle makes it possible to make
maximum use of the effect of surface smoothing by lateral
sputtering described above.
[0006] Patent literature 2 discloses that a curved surface or the
like may be irradiated in an oblique direction, depending on the
surface condition, but the effect of such oblique irradiation is
not mentioned. Therefore, Patent literature 2 implies that
approximately perpendicular irradiation of the solid surface is the
most efficient for surface smoothing.
[0007] Patent literature 3 discloses another example of solid
surface smoothing by using a gas cluster ion beam. However, Patent
literature 3 does not describe the relationship between surface
smoothing and the angle formed by the gas cluster ion beam and the
solid surface. Since the description indicates that the lateral
sputtering effect is used, it is inferred that, like Patent
literature 2, Patent literature 3 shows data for perpendicular
irradiation.
[0008] Non-patent literature 1 also includes a report of solid
surface smoothing by gas cluster ion beam irradiation. In that
literature, Toyoda and others report that surface roughness is
reduced by irradiating the surface of materials such as Cu, SiC,
and GaN with Ar cluster ions. The surface was irradiated with the
gas cluster ion beam at approximately right angles.
[0009] Non-patent literature 2 describes variations in the
roughness of a solid surface when the solid surface is irradiated
with a gas cluster ion beam at a variety of irradiation angles.
When the solid surface is irradiated at right angles, the
irradiation angle is expressed as 90 degrees (the symbol .degree.
will be used hereafter to express an angle). When the surface is
irradiated laterally, the irradiation angle is expressed as
0.degree.. The literature discloses that the sputtering rate, which
indicates a speed at which the surface is etched, is maximized by
perpendicular irradiation and that the etching rate decreases as
the irradiation angle decreases. The relationship between surface
roughness and irradiation angle was observed through experiments at
different irradiation angles of 90.degree., 75.degree., 60.degree.,
45.degree., and 30.degree.. According to the literature, the
surface roughness increased with a decrease in irradiation angle.
No experiments were made at irradiation angles below 30.degree.. It
may have been thought that such experiments would be useless.
[0010] It was recently found that the roughness of a solid surface
decreased greatly by reducing the angle of gas cluster ion beam
irradiation with respect to the solid surface to below 30.degree.
(refer to Patent literature 4). This technology uses an oblique
irradiation effect, and the smoothing mechanism differs from that
in the conventional lateral sputtering. Patent literature 4
describes the use of a plurality of irradiation angles in
irradiation of the solid surface with the gas cluster ion beam. In
patent literature 4, the irradiation is performed at different
angles in succession. [0011] Patent literature 1: Japanese Patent
Application Laid Open No. H7-58089 [0012] Patent literature 2:
Japanese Patent Application Laid Open No. H8-120470 [0013] Patent
literature 3: Japanese Patent Application Laid Open No. H8-293483
[0014] Patent literature 4: WO2005/031838 [0015] Non-patent
literature 1: Jpn. J. Appl. Phys., Vol. 41 (2002), pp. 4287-4290
[0016] Non-patent literature 2: Materials Science and Engineering R
34 (2001), pp. 231-295
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0017] In the smoothing method disclosed in Patent literature 1,
sputtering is performed by emitting an ion beam of Ar (argon) gas
or the like, and projecting portions are cut off from the solid
surface with priority. Although smoothing is performed to a certain
level, the irradiation energy must be kept below 100 eV or so, in
order to suppress damage to the solid surface. In that case, an
extremely small ion current cannot provide a practical sputtering
rate. Moreover, the smoothing method disclosed in Patent literature
1 has a serious problem in that smoothing is almost impossible if
the solid surface has a scratch or other surface roughness having a
submicrometer (0.1 .mu.m to 1 .mu.m) to micrometer (.mu.m) width
and height.
[0018] The smoothing methods based on lateral sputtering using
approximately perpendicular gas cluster ion beam irradiation, as
disclosed in Patent literatures 2, 3, and 4 and Non-patent
literatures 1 and 2, also have a serious problem in that smoothing
is almost impossible if the solid surface has a scratch or similar
surface roughness having a submicromter to micrometer width and
height.
[0019] In view of the problems described above, an object of the
present invention is to provide a solid surface smoothing method
and apparatus that can reduce surface roughness like a scratch in
solid surface by gas cluster ion beam irradiation.
Means to Solve the Problems
[0020] In order to solve the problems described above, a method of
smoothing a solid surface with a gas cluster ion beam of the
present invention includes an irradiation step of irradiating a
solid surface with a gas cluster ion beam, and the irradiation step
includes a process of causing clusters from a plurality of
directions to collide with at least an area (spot) irradiated with
the gas cluster ion beam on the solid surface. Upon collision of
the clusters coming from a plurality of directions with the spot,
the individual clusters advance sputtering in various
directions.
[0021] The collision of the clusters coming from a plurality of
directions with the spot may be performed by an irradiation of the
gas cluster ion beam in which flight directions of the clusters
diverge with respect to a center of the beam. It is preferred that
the gas cluster ion beam be a gas cluster ion beam randomly
diverging with an angle of at least 2.degree. with respect to the
center of the beam.
[0022] By emitting onto the solid surface the gas cluster ion beam
in which flight directions of the clusters diverge, it becomes
easier for the clusters to collide with the spot from a plurality
of directions.
[0023] The collision of the clusters coming from a plurality of
directions with the spot may also be performed by emitting the gas
cluster ion beam while moving the solid.
[0024] By directing the gas cluster ion beam while the solid is
being moved, clusters can collide with the spot from more
directions.
[0025] The collision of the clusters coming from a plurality of
directions with the spot may be performed by emitting the gas
cluster ion beam while rotating the solid.
[0026] By emitting the gas cluster ion beam while the solid is
being rotated, clusters can collide with the spot from more
directions.
[0027] The collision of the clusters from a plurality of directions
with the spot may be performed by emitting the gas cluster ion beam
while keeping the irradiation angle formed by the gas cluster ion
beam and the normal to the solid surface mismatched.
[0028] By emitting the gas cluster ion beam while keeping the
irradiation angle formed by the gas cluster ion beam and the normal
to the solid surface mismatched, additional smoothing effects by
lateral sputtering or oblique irradiation are produced.
[0029] The collision of the clusters coming from a plurality of
directions with the spot may be performed by emitting a plurality
of the gas cluster ion beams.
[0030] By emitting a plurality of the gas cluster ion beams,
clusters can collide with the spot from more directions.
[0031] In order to solve the problems described above, a solid
surface smoothing apparatus for smoothing a solid surface with a
gas cluster ion beam according to the present invention includes a
beam setup means adapted to set up the gas cluster ion beam to
diverge randomly with an angle of at least 2.degree. with respect
to a center of the beam, a gas cluster ion beam emission means
which emits the gas cluster ion beam onto the solid surface, and a
means adapted to move the solid and/or a means adapted to rotate
the solid. A plurality of the gas cluster ion beam emission means
may be included.
EFFECTS OF THE INVENTION
[0032] According to the present invention, by colliding clusters
with the spot, which is a gas cluster ion beam irradiation area,
from a plurality of directions, sputtering proceeds in various
directions with the individual clusters. In this process, scratches
or similar surface roughness in the solid surface can be
reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1A is a diagram illustrating how a solid surface is
smoothed by lateral sputtering;
[0034] FIG. 1B is a diagram illustrating that a solid surface
having a depression like a scratch is not smoothed out by lateral
sputtering;
[0035] FIG. 2A is a diagram illustrating substance transfer caused
by GCIB irradiation, near the top of a line in a line-and-space
pattern structure;
[0036] FIG. 2B is a diagram illustrating substance transfer at an
edge of the line;
[0037] FIG. 2C is a diagram illustrating that a substance staying
on the side wall around the edge of the line hinders the progress
of smoothing in GCIB irradiation in one direction;
[0038] FIG. 2D is a diagram illustrating that GCIB irradiation from
a plurality of directions does not allow a substance to stay on the
side wall of the line and advances smoothing;
[0039] FIG. 3 is a diagram showing an example structure of a solid
surface smoothing apparatus 100 of an embodiment of the present
invention;
[0040] FIG. 4A is a side view showing a first rotation mechanism of
the solid surface smoothing apparatus 100;
[0041] FIG. 4B is a plan view showing the first rotation mechanism,
a second rotation mechanism, and a scan mechanism of the solid
surface smoothing apparatus 100;
[0042] FIG. 5A is a diagram illustrating that, when irradiation of
a divergent GCIB is combined with X-Y scanning of the target,
clusters coming from a plurality of directions collide with a
target surface substantially simultaneously;
[0043] FIG. 5B is a diagram illustrating that, when irradiation of
a divergent GCIB is combined with the rotation of the target,
clusters coming from a plurality of directions collide with the
target surface substantially simultaneously;
[0044] FIG. 5C is a diagram illustrating that, when oblique
irradiation of a nondivergent (or less divergent) GCIB is combined
with the rotation of the target or the like, clusters coming from a
plurality of directions collide with the target surface
substantially simultaneously;
[0045] FIG. 5D is a diagram showing the target surface; and
[0046] FIG. 6 is a diagram showing an example structure of a solid
surface smoothing apparatus 200 equipped with a plurality of GCIB
emission means.
BEST MODES FOR CARRYING OUT THE INVENTION
[0047] Prior to the description of an embodiment, the principle of
smoothing used in the present invention will be summarized.
[0048] The mechanism of surface smoothing using a gas cluster ion
beam (GCIB) was conventionally thought to be based on the
phenomenon that peaks (projections) are cut and valleys (recesses)
are filled with the cut portions of the projecting portions by
lateral sputtering of transferring the substance of the solid
surface subjected to GCIB irradiation in a lateral direction (a
direction nearly parallel to the solid surface) (refer to Patent
literature 2, for instance). FIG. 1A is a diagram illustrating how
a solid surface is smoothed out by lateral sputtering.
[0049] The inventors observed smoothing of a solid surface having
scratches or the like with widths and heights on the order of a
submicrometer to micrometer. In the observation, GCIB irradiation
was performed by likening a line-and-space pattern structure 900 to
a scratch. Through the observation, it was found that a surface
having scratches was hardly smoothed by the conventional lateral
sputtering. This state is illustrated in FIG. 1B. The reason for
failure of smoothing is that both the top of the line denoted by a
reference numeral 901 (a part around the top of a projecting
portion of the line-and-space pattern structure, corresponding to a
projection) and the bottom of the space denoted by a reference
numeral 902 (a part around the bottom of a grooved portion in the
line-and-space pattern structure, corresponding to a recess) in the
line-and-space pattern structure 900 were etched, making little
difference in height. In other words, because etching proceeds
analogously to the original shape of the surface, little smoothing
arose.
[0050] Substance transfer by GCIB irradiation near the top of the
line (a part of a side wall 903 in the depth direction of the line,
close to the top 901 of the line and far from the bottom 902 of the
space) in the line-and-space pattern structure 900 was closely
observed. FIGS. 2A to 2D are diagrams showing the states. As shown
in FIG. 2A, the phenomenon was observed that the GCIB irradiation
had caused a substance 904 around the top of the line to move along
the side wall 903 of the line to the lower part of the side wall of
the line denoted by a reference numeral 905 (a part of the side
wall 903 in the depth direction of the line, far from the top 901
of the line). The observed transfer is indicated by a broken arrow
in the right diagram in FIG. 2A. A shoulder-like part denoted by a
reference numeral 907 (enclosed with a broken line in FIG. 2B) was
observed on the edge of the line (near the border between the top
901 of the line and the side wall 903 of the line). The right
diagram in FIG. 2B is an enlarged view of a circled part 906 in the
left diagram of FIG. 2B. In the left diagram in FIG. 2B, a broken
arrow represents the lateral movement of a substance near the top
of the line. In the right diagram in FIG. 2B, a reference numeral
908 denotes a substance near the top of the line, and a reference
numeral 909 denotes a substance moved along the side wall 903 of
the line. In this state, the substance near the top of the line
does not move to a wide area across the bottom of the space.
Therefore, both the top of the line and the bottom of the space are
etched, making little difference in height.
[0051] Based on these findings, a variety of experiments were
conducted under different GCIB irradiation conditions, to observe
the transfer of a substance around the top of the line. As a
result, it was found that the conventional GCIB irradiation in one
direction allows the substance to stay on the side wall of the
line, as shown in FIG. 2C, and does not advance smoothing.
[0052] The situation arises because, in perpendicular irradiation,
the side wall 903 of the line is exposed to less GCIB irradiation
than the top 901 of the line or the bottom 902 of the space, making
the substance there less likely to move (see the part denoted by
reference symbol P1 in FIG. 2C). In oblique irradiation, the
cluster readily collides with the side wall of the line facing the
GCIB irradiation, whereas the cluster hardly collides with the
opposite side wall of the line. Even if the substance staying on
the side wall 903 of the line moves, the movement would be limited
to an area near the edge of the space (area around the boundary
between the bottom 902 of the space and the side wall 903 of the
line), hardly advancing the smoothing.
[0053] In contrast, when the GCIB was directed from a plurality of
directions, the substance did not stay on the side wall 903 of the
line, and smoothing proceeded as shown in FIG. 2D.
[0054] Clusters coming from the plurality of directions collide
with the substance (P1) remaining on the side wall 903 of the line,
causing sputtering to proceed in various directions. This makes the
substance (P1) easier to move to the bottom 902 of the space,
allowing substance transfer over a wide range at the bottom 902 of
the space (see the part denoted by reference symbol P2 in FIG. 2D).
This phenomenon was newly discovered through the present
invention.
[0055] The inventors have found the following: To reduce (smooth
out) scratches or similar surface roughness by GCIB irradiation, it
is important to expose a substance in the solid surface transferred
laterally by a collision with clusters to other clusters (or to
repeat collision); this should be achieved by making a spot of a
GCIB irradiation area collided with clusters coming from a
plurality of directions; to promote substance transfer over a wider
range for the purpose of achieving maximum smoothing of the solid
surface, time intervals between cluster collisions should be
minimized so that the clusters collide almost at the same time.
[0056] Clusters coming from a plurality of directions should be
collided with the area (spot) irradiated by the GCIB. Preferably,
roughly simultaneous cluster collisions should be caused to promote
smoothing of the solid surface.
[0057] An embodiment of the present invention and examples will now
be described. The structure and functions of a solid surface
smoothing apparatus 100 that implements the solid surface smoothing
method of the present invention will be described first with
reference to FIG. 3.
[0058] GCIB emission means is structured as follows. Source gas 9
is supplied via a nozzle 10 into a vacuum cluster generation
chamber 11. Gas molecules of the source gas 9 aggregate into
clusters in the cluster generation chamber 11. The cluster size is
determined by the particle size distribution based on the pressure
and temperature of gas at a nozzle outlet 10a and the size and
shape of the nozzle 10. The clusters generated in the cluster
generation chamber 11 are guided into an ionization chamber 13 by a
skimmer 12 as a gas cluster beam. By increasing the skimmer
diameter of the skimmer 12, a relatively random mixture of beams
having different angles can be produced, instead of GCIBs diverging
concentrically and uniformly. In the ionization chamber 13, an
ionizer 14 emits an electron beam of thermal electrons, for
example, to ionize the neutral clusters. The ionized gas cluster
beam (GCIB) is accelerated by an accelerating electrode 15. In a
conventional general GCIB emission apparatus, to produce a
nondivergent GCIB, beams are converged into parallel beams by a
magnetic-field convergence control unit 16 and directed to a
ferromagnetic deflecting cluster size control unit using a
permanent magnet. In the solid surface smoothing apparatus 100,
however, the magnetic-field convergence control unit 16 does not
converge the beams but diverges the beams. In other words, beam
convergence is conducted under more moderate conditions than in
general beam convergence. In FIG. 3, an angle .theta. of 2.degree.
or greater is preferred. The GCIB is symmetric with respect to the
beam center in FIG. 3, but the GCIB may have an asymmetric spread.
The GCIB then enters a sputtering chamber 17. On a target support
18 provided in the sputtering chamber 17, a target 19, which is a
solid (such as a silicon substrate) to be irradiated with the GCIB,
is fixed through a rotary disc 41. The GCIB entering the sputtering
chamber 17 is narrowed to a predetermined beam diameter by an
aperture 21 and directed onto the surface of the target 19. When
the surface of the target 19 of an electrical insulator is
smoothed, the GCIB is neutralized by electron beam irradiation.
[0059] The solid surface smoothing apparatus 100 includes a first
rotation mechanism that rotates the target 19. In the embodiment
described here, the first rotation mechanism rotates the target 19
about an axis nearly parallel to the normal to the target surface.
Because the main point of the present invention is to cause
clusters to collide with the spot from a plurality of directions,
the solid is not always rotated about the axis nearly parallel to
the normal to the target surface. The solid may be rotated about
any desired axis.
[0060] The first rotation mechanism is structured as follows, as
shown in FIGS. 4A and 4B, for example. The target support 18 has a
projecting shaft 41a, and the rotary disc 41 is mounted on the
projecting shaft 41a to rotate on the center of the projecting
shaft 41a. The rotary disc 41 has a flat part 41b, on which the
target 19 is attached. The rotary disc 41 has a great number of
teeth in its rim 41c, and the teeth engage with the teeth of a gear
43. The gear 43 rotates when driven by a motor 42, and the rotation
is transferred to the rotary disc 41, consequently, rotating the
target 19 attached to the rotary disc 41.
[0061] The solid surface smoothing apparatus 100 is also equipped
with a tilting mechanism that can change the GCIB irradiation
angle, as an irradiation angle setting means. In this embodiment,
the tilting mechanism is implemented by a rotation mechanism that
can change the irradiation angle continuously.
[0062] The solid surface smoothing apparatus 100 includes a second
rotation mechanism, as shown in FIG. 4B, for example. A rotation
shaft 21 is fixed to the target support 18, and the target support
18 can rotate on the center of the rotation shaft 21. The rotation
shaft 21 is rotatably supported by stationary plates 22a and 22b.
The rotation shaft 21 is fixed also to the center of a rotation
axis of a gear 24b, and the gear 24b engages with a gear 24a. The
gear 24a rotates when driven by a motor 23, and the rotation is
transferred to the gear 24b and the rotation shaft 21, consequently
rotating the target support 18. The rotation of the target support
18 is reflected in the irradiation angle. The stationary plate 22a
is equipped with an angle detection unit 25a for detecting the
angle of rotation of the target support 18, that is, the GCIB
irradiation angle with reference to the solid surface of the target
19 attached to the target support 18, as a digital value, from the
angle of rotation of the rotation shaft 21. The angle-of-rotation
information detected by the angle detection unit 25a is processed
by an electric circuit unit 25b, and the currently detected angle
(irradiation angle) is displayed in a current angle area 26a of a
display unit 26.
[0063] The solid surface smoothing apparatus 100 is also equipped
with a scanning mechanism for changing the relative position of the
target 19 with respect to the GCIB, such as an XY stage.
[0064] The stationary plates 22a and 22b are fixed to and supported
by a stationary-plate supporting member 22c. The stationary-plate
supporting member 22c and a first actuator 22d are connected via a
first rod 22e. The first actuator 22d can push and pull the first
rod 22e, and this action can change the position of the target
support 18. In the solid surface smoothing apparatus 100 shown in
FIG. 4B, for example, the motion of the first actuator 22d can
change the position of the target support 18 in up and down
directions in the figure.
[0065] The first actuator 22d is fixed to and supported by a second
rod 22g, and the first actuator 22d is connected to second
actuators 22f through the second rod 22g. The second actuators 22f
can push and pull the second rod 22g, and this action changes the
position of the first actuator 22d. Consequently, the position of
the target support 18 connected to the first actuator 22d via the
first rod 22e and the other parts mentioned above can be changed.
The direction in which the first rod 22e can move is nearly
orthogonal to the direction in which the second rod 22g can move.
The scanning mechanism like an XY stage is implemented as described
above. In the solid surface smoothing apparatus 100 shown in FIG.
4B, for example, the motion of the second actuators 22f can change
the position of the target support 18 in the left and right
directions in the figure. Therefore, in combination with the motion
of the first actuator 22d, the target support 18 can be moved up
and down, and left and right in the figure.
[0066] By a combination of divergent GCIB irradiation and X-Y
scanning of the target, clusters coming from a plurality of
directions (viewed from the target) can collide with a solid
surface 51 of the target 19 substantially simultaneously (see FIG.
5A; as shown in FIG. 5D, a projecting portion 50 provided in the
solid surface 51 is analogous to surface roughness in the solid
surface 51). FIG. 5A shows X-Y scanning in a plane nearly parallel
to the solid surface 51. This does not mean that the scanning is
limited to the X-Y scanning in a plane nearly parallel to the solid
surface 51, however. If the target support 18 is positioned to make
perpendicular irradiation with respect to the center of the GCIB,
the scanning mechanism described above implements X-Y scanning in a
plane nearly parallel to the solid surface 51, as shown in FIG. 5A.
If the target support 18 is positioned by the second rotation
mechanism described above to make oblique irradiation with respect
to the center of the GCIB, the scanning mechanism implements X-Y
scanning in a plane which is not nearly parallel to the solid
surface 51.
[0067] By a combination of divergent GCIB irradiation and the
rotation of the target, clusters coming from a plurality of
directions (viewed from the target) can collide with the solid
surface 51 of the target 19 substantially simultaneously (see FIG.
5B). In addition, as shown in FIG. 5C, even if the GCIB is
nondivergent (or less divergent), by irradiating the target 19
obliquely with the GCIB and rotating the target support 18,
clusters coming from a plurality of directions (viewed from the
target) can collide with the solid surface 51 of the target 19
substantially simultaneously.
[0068] In the embodiment described above, clusters coming from a
plurality of directions can collide with the spot by an
appropriately combination of the divergent or nondivergent GCIB,
the movement by the first rotation mechanism, the movement by the
second rotation mechanism, and the movement by the scanning
mechanism.
[0069] Further, by emitting GCIBs from different directions from a
plurality of GCIB emission means, as in a solid surface smoothing
apparatus 200 shown in FIG. 6, clusters coming from a plurality of
directions (viewed from the target) can collide with the surface of
the target 19 substantially simultaneously. FIG. 6 shows an example
with two GCIB emission means, but three or more GCIB emission means
can also be provided as needed.
[0070] In the solid surface smoothing apparatus 100 shown in FIG.
4B, a setup unit 27 is used to set a face of the target support 18
as a reference plane and to input and specify conditions such as
the desired etching amount, the material and etching rate of the
target 19, the gas type, the accelerating energy, the irradiation
angle, and the dose of the GCIB. Then, the target support face is
displayed in a reference plane display area 26b of the display unit
26. An irradiation angle specified with reference to this plane is
displayed in a specified angle area 26c.
[0071] A control unit 28 drives the motors 23 and 42 through a
drive unit 29 to bring the current irradiation angle to a specified
irradiation angle. The control unit 28 also controls the GCIB
emission means to provide a specified dose of GCIB irradiation.
[0072] The control unit 28 has a CPU (central processing unit) or a
microprocessor and performs the control operation and other
operations as described above by executing information processing
of programs required to execute solid surface smoothing, such as
the display operation and motor drive operation described
above.
[0073] The structure and mechanism of the solid surface smoothing
apparatus of the present invention is not limited to those of the
solid surface smoothing apparatus 100 or 200 described above, and
modifications can be made within the scope of the present
invention.
First Example
[0074] A mixture of SF.sub.6 gas and He gas was used as a source
gas, and an SF.sub.6 gas cluster ion beam was generated. The
SF.sub.6 gas cluster ion beam was accelerated by 30 kV and directed
onto the surface of the target 19. The irradiation angle was
specified to bring the beam center of the GCIB (the center of
propagation of the GCIB) nearly perpendicular to the solid
surface.
[0075] The magnetic-field convergence control unit did not converge
the GCIB and made the GCIB a randomly divergent beam with at least
an angle of 2.degree. with respect to the beam center of the GCIB.
The angle .theta. shown in FIG. 3 was 2.degree. or greater. A
silicon substrate having a line-and-space pattern structure formed
thereon beforehand by a semiconductor process was used as the
target 19. More specifically, on the silicon substrate or SOI
(silicon on insulator) substrate used as the target 19, a pattern
structure was formed by the following method: An electron beam
resist was applied on the substrate having a thermally-oxidized
film, and a pattern structure was drawn on the resist by an
electron beam drawing apparatus. After the resist was developed,
the resist pattern was used as a mask, and the thermally-oxidized
film was etched by a reactive ion etching (RIE) apparatus. The
resist was then removed, and silicon was etched by the reactive ion
etching (RIE) apparatus or an inductively coupled plasma reactive
ion etching (ICP-RIE) apparatus, using the thermally-oxidized film
as a hard mask. Then, the thermally-oxidized film was removed by an
ashing apparatus.
[0076] The line-and-space pattern structure had a line-to-space
ratio of 1:1. The lines had a height of about 1 .mu.m and a width
of about 1 .mu.m, and the spaces also had a width of about 1 .mu.m.
The irradiation dose was 6*10.sup.15 ions/cm.sup.2. The symbol *
expresses a multiplication.
[0077] The mean surface roughness of the target surface was
measured by using an atomic force microscope (AFM) before and after
SF.sub.6 gas cluster ion beam irradiation. The mean surface
roughness Ra before SF.sub.6 gas cluster ion beam irradiation was
0.46 .mu.m, whereas the mean surface roughness Ra after SF.sub.6
gas cluster ion beam irradiation was 0.21 .mu.m.
Second Example
[0078] An experiment was conducted in the same manner as in the
first example, except that the target 19 was scanned in the X-Y
direction. The X-direction scanning rate was 1 Hz, and the
Y-direction scanning rate was 0.02 Hz. The roughness of the target
surface was measured by using an AFM after SF.sub.6 gas cluster ion
beam irradiation. The mean surface roughness Ra before SF.sub.6 gas
cluster ion beam irradiation was 0.46 .mu.m, as in the first
example, whereas the mean surface roughness Ra after SF.sub.6 gas
cluster ion beam irradiation was 0.13 .mu.m.
Third Example
[0079] An experiment was conducted in the same manner as in the
first example, except that the target 19 was rotated. Three
rotation rates of 60 rpm, 180 rpm, and 600 rpm were used. The mean
surface roughness of the target surface was measured by using an
AFM after SF.sub.6 gas cluster ion beam irradiation. The mean
surface roughness Ra after SF.sub.6 gas cluster ion beam
irradiation was 0.18 .mu.m, 0.12 .mu.m, and 0.05 .mu.m at a
rotation rate of 60 rpm, 180 rpm, and 600 rpm, respectively.
Fourth Example
[0080] An experiment was conducted in the same manner as in the
third example, except that the target was skewed with respect to
the beam center of the GCIB, to make an angle between the target
and the GCIB, that is, to perform oblique GCIB irradiation. The
irradiation angle was 30.degree., with reference to the angle of
perpendicular irradiation with respect to the target surface being
defined as 0.degree.. The mean surface roughness of the target
surface was measured by using an AFM after SF.sub.6 gas cluster ion
beam irradiation. The mean surface roughness Ra after SF.sub.6 gas
cluster ion beam irradiation was 0.11 .mu.m, 0.06 .mu.m, and 0.02
.mu.m at a rotation rate of 60 rpm, 180 rpm, and 600 rpm,
respectively.
Fifth Example
[0081] An experiment was conducted in the same manner as in the
first example, except that an SiO.sub.2 film (silicon dioxide film)
formed on a silicon substrate without a pattern was used as the
target and that the irradiation dose was 2*10.sup.14 ions/cm.sup.2
(the target was not rotated). The SiO.sub.2 film was formed by
sputtering, and the film thickness was 500 nm. The mean surface
roughness Ra of the target surface was measured by using an AFM
before and after SF.sub.6 gas cluster ion beam irradiation. The
mean surface roughness Ra before SF.sub.6 gas cluster ion beam
irradiation was 0.81 nm, whereas the mean surface roughness Ra
after SF.sub.6 gas cluster ion beam irradiation was 0.23 nm.
[0082] The results of experiments conducted in the examples show
the effects of the present invention clearly. For further
examination of the present invention, experiments for making a
comparison with the prior art were conducted.
First Comparative Example
[0083] An experiment was conducted in the same manner as in the
first example, except that a nearly parallel GCIB was used (the
target was not rotated). The mean surface roughness Ra before
SF.sub.6 gas cluster ion beam irradiation was 0.46 .mu.m, as in the
first example, whereas the mean surface roughness Ra after SF.sub.6
gas cluster ion beam irradiation was 0.42 .mu.m.
Second Comparative Example
[0084] An experiment was conducted in the same manner as in the
fifth example, except that a nearly parallel GCIB was used (the
target was not rotated). The mean surface roughness Ra before
SF.sub.6 gas cluster ion beam irradiation was 0.81 nm, whereas the
mean surface roughness Ra after SF.sub.6 gas cluster ion beam
irradiation was 0.36 nm.
[0085] A comparison between the first example and the first
comparative example shows that the mean surface roughness of the
target was reduced remarkably by using the divergent GCIB beam.
There was just a single difference in the conditions between the
two experiments: whether the GCIB was a divergent beam or a nearly
parallel beam. The remarkable reduction in mean surface roughness
of the target was originated from the divergent GCIB beam. In other
words, collisions with clusters coming from a plurality of
directions advanced smoothing greatly.
[0086] It is understood from the first and second examples that the
mean surface roughness was reduced further by changing the relative
position of the target with respect to the GCIB through scanning of
the target.
[0087] It is understood from the first to third examples that the
rotation of the target was highly effective as a method of changing
the relative position of the target surface with respect to the
GCIB and that smoothing was promoted by increasing the target
rotation rate.
[0088] It is understood from the third and fourth examples that
smoothing proceeds further by oblique irradiation of the target
with the GCIB.
[0089] It is understood from the first and fourth examples that, in
oblique irradiation, appropriate smoothing is performed by setting
the GCIB irradiation angle to 2.degree. or greater with respect to
the normal to the solid surface.
[0090] A comparison between the fifth example and the second
comparative example shows that a target having very small surface
roughness with reference to the surface roughness, as indicated in
the first example, can be smoothed out by using a divergent GCIB
beam.
[0091] In view of the principle and function of the present
invention, conditions, such as the type of the gas cluster to be
used and the accelerating energy, are not limited, and the material
of the target is not limited.
INDUSTRIAL APPLICABILITY
[0092] Since scratches or similar surface roughness on a solid
surface can be reduced, the present invention can be used to
improve the precision of fine structures in semiconductor devices
and optical devices and also to improve the precision of
three-dimensional structures of dies used in fabrication of
semiconductor devices and optical devices and the like.
* * * * *