U.S. patent application number 10/050814 was filed with the patent office on 2002-08-01 for electron exposure apparatus.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Hashizume, Tomihiro, Heike, Seiji, Ishibashi, Masayoshi, Kajiyama, Hiroshi, Wada, Yasuo.
Application Number | 20020101573 10/050814 |
Document ID | / |
Family ID | 27551813 |
Filed Date | 2002-08-01 |
United States Patent
Application |
20020101573 |
Kind Code |
A1 |
Ishibashi, Masayoshi ; et
al. |
August 1, 2002 |
Electron exposure apparatus
Abstract
To provide an electron exposure apparatus capable of providing
high resolution and performing electron exposure at high speed,
integrated tips are used, only the tips provided at ends control
distances between the tips and the surface of a wafer and the tips
used for electron exposure follow the wafer according to
deformations of cantilevers, which occur due to the Coulomb force
resultant from a voltage applied to each tip.
Inventors: |
Ishibashi, Masayoshi;
(Hiki-gun, JP) ; Heike, Seiji; (Hiki-gun, JP)
; Hashizume, Tomihiro; (Hiki-gun, JP) ; Wada,
Yasuo; (Bunkyou-ku, JP) ; Kajiyama, Hiroshi;
(Kawasaki-shi, JP) |
Correspondence
Address: |
MATTINGLY, STANGER & MALUR, P.C.
Suite 370
1800 Diagonal Road
Alexandria
VA
22314
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
27551813 |
Appl. No.: |
10/050814 |
Filed: |
January 18, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10050814 |
Jan 18, 2002 |
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09090942 |
Jun 5, 1998 |
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10050814 |
Jan 18, 2002 |
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08696089 |
Aug 13, 1996 |
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Current U.S.
Class: |
355/69 ;
250/492.2; 250/492.22; 355/68; 355/71; 850/11; 850/33; G9B/9.001;
G9B/9.003 |
Current CPC
Class: |
H02N 1/006 20130101;
H02N 1/008 20130101; G11B 9/1409 20130101; G11B 9/1418 20130101;
Y10S 977/864 20130101; G01Q 80/00 20130101; Y10S 977/855 20130101;
G11B 9/14 20130101 |
Class at
Publication: |
355/69 ; 355/71;
355/68; 250/492.2; 250/492.22 |
International
Class: |
G03B 027/72 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 1997 |
JP |
9-151857 |
Jun 24, 1997 |
JP |
9-166851 |
Aug 18, 1995 |
JP |
7-210406 |
Dec 18, 1995 |
JP |
7-328707 |
Apr 12, 1996 |
JP |
8-90778 |
Claims
1. An electron exposure apparatus comprising: a plurality of tips;
a plurality of springs for respectively holding said plurality of
tips; a holder for collectively holding said springs for said
plurality of tips; a coarse mechanism for moving said holder to
allow said plurality of tips to relatively approach a wafer whose
surface is covered with a resist layer to be subjected to electron
exposure; a transfer mechanism for correcting inclinations of the
tips at ends, of said plurality of tips toward the wafer; a drive
mechanism for relatively X-Y driving the wafer and said plurality
of tips on the surface of the wafer; a control device for
controlling said respective mechanisms; a device for supplying
currents to said plurality of tips; means for detecting the
currents supplied to said plurality of tips; a control device for
allowing target values of the currents supplied to said plurality
of tips to coincide with detected values; and a pattern input
device for supplying a target value corresponding to an
electron-exposure pattern to said each control device.
2. An electron exposure apparatus according to claim 1, wherein
said plurality of tips are arranged in a row at predetermined
intervals, and the tips located at both ends of these tips are used
to correct inclinations toward the wafer and control distances
between the tips being under electron exposure and the wafer and
other tips thereof are used for electron exposure.
3. An electron exposure apparatus according to claim 1, wherein
said plurality of tips are arranged on an X-Y plane at
predetermined intervals, and the tips located at three ends of
these tips are used to correct inclinations toward the wafer and
control distances between the tips being under electron exposure
and the wafer and other tips thereof are used for electron
exposure.
4. An electron exposure apparatus according to claim 2, wherein
displacements of the tips used to correct inclinations toward the
wafer and control distances between the tips being under electron
exposure and the wafer are detected by currents.
5. An electron exposure apparatus according to claim 2, wherein
displacements of the tips used to correct inclinations toward the
wafer and control distances between the tips being under electron
exposure and the wafer are detected by an optical lever deflection
sensor type atomic force microscope.
6. An electron exposure apparatus according to claim 2, wherein
displacements of the tips used to correct inclinations toward the
wafer and control distances between the tips being under electron
exposure and the wafer are detected by changes in capacitances
between electrodes placed on the backs of cantilevers and the
cantilevers.
7. An electron exposure apparatus according to claim 3, wherein
displacements of the tips used to correct inclinations toward the
wafer and control distances between the tips being under electron
exposure and the wafer are detected by currents.
8. An electron exposure apparatus according to claim 3, wherein
displacements of the tips used to correct inclinations toward the
wafer and control distances between the tips being under electron
exposure and the wafer are detected by an optical lever deflection
sensor type atomic force microscope.
9. An electron exposure apparatus according to claim 3, wherein
displacements of the tips used to correct inclinations toward the
wafer and control distances between the tips being under electron
exposure and the wafer are detected by changes in capacitances
between electrodes placed on the backs of cantilevers and the
cantilevers.
10. An electron exposure apparatus according to claim 2, wherein
currents supplied to the tips used for electron exposure are set to
values different from one another at a latent-image creation
portion and a latent-image non-creation portion.
11. An electron exposure apparatus according to claim 3, wherein
currents supplied to the tips used for electron exposure are set to
values different from one another at a latent-image creation
portion and a latent-image non-creation portion.
12. An electron exposure apparatus comprising: a plurality of
one-dimensionally arranged tips; a plurality of springs for
respectively holding said plurality of tips; a holder for
collectively holding said springs for said plurality of tips; a
coarse mechanism for moving said holder to allow said plurality of
tips to relatively approach a wafer whose surface is covered with a
resist layer to be subjected to electron exposure; a transfer
mechanism for correcting inclinations of the tips at ends, of said
plurality of tips toward the wafer; a drive mechanism for driving
the wafer rotatably about said tips; a control device for
controlling said respective mechanisms; a device for supplying
currents to said plurality of tips; means for detecting the
currents supplied to said plurality of tips; a control device for
allowing target values of the currents supplied to said plurality
of tips to coincide with detected values; and a pattern input
device for supplying a target value corresponding to an
electron-exposure pattern to said each control device.
13. An electron exposure apparatus according to claim 12, wherein
the tips located at both ends, of said plurality of tips are used
to correct inclinations toward the wafer and control distances
between the tips being under electron exposure and the wafer and
other tips thereof are used for electron exposure.
14. An electron exposure apparatus comprising: a plurality of tips;
a plurality of springs for respectively holding said plurality of
tips; a holder for collectively holding said springs for said
plurality of tips; a coarse mechanism for moving said holder to
thereby allow said tips to relatively approach a wafer whose
surface is covered with a resist layer to be subjected to electron
exposure; a transfer mechanism for correcting inclinations of the
tips at ends, of said plurality of tips toward the wafer; a drive
mechanism for relatively X-Y driving the wafer and said plurality
of tips on the surface of the wafer; a control device for
controlling said respective mechanisms; a device for supplying
currents to said plurality of tips; means for detecting the
currents supplied to said plurality of tips; a control device for
allowing target values of the currents supplied to said plurality
of tips to coincide with detected values; and a pattern input
device for supplying a target value corresponding to an
electron-exposure pattern to said each control device; wherein said
tips are formed at leading ends of movable portions of an
electromechanical transducer having a plurality of electrostatic
actuators formed on one substrate, one of said two actuators being
a cascade structure in which a fixed electrode is formed in
association with a movable electrode of the other actuator and
being capable of driving a movable electrode in intersecting
two-axis directions.
15. An electron exposure apparatus according to claim 14, wherein
said plurality of tips are arranged in a row at predetermined
intervals, and the tips located at both ends of these tips are used
to correct inclinations toward the wafer and control distances
between the tips being under electron exposure and the wafer and
other tips thereof are used for electron exposure.
16. An electron exposure apparatus according to claim 14, wherein
said plurality of tips are arranged on an X-Y plane at
predetermined intervals, and the tips located at three ends of
these tips are used to correct inclinations toward the wafer and
control distances between the tips being under electron exposure
and the wafer and other tips thereof are used for electron
exposure.
17. An electron exposure apparatus according to claim 15, wherein
displacements of the tips used to correct inclinations toward the
wafer and control distances between the tips being under electron
exposure and the wafer are detected by currents.
18. An electron exposure apparatus according to claim 16, wherein
displacements of the tips used to correct inclinations toward the
wafer and control distances between the tips being under electron
exposure and the wafer are detected by currents.
19. An electron exposure apparatus according to claim 14, wherein
currents supplied to the tips used for electron exposure are set to
values different from one another at a latent-image creation
portion and a latent-image non-creation portion.
20. An electron exposure apparatus according to claim 15, wherein
currents supplied to the tips used for electron exposure are set to
values different from one another at a latent-image creation
portion and a latent-image non-creation portion.
21. An electron exposure apparatus comprising: a plurality of tips;
a plurality of springs for respectively holding said plurality of
tips; a holder for collectively holding said springs for said
plurality of tips; a coarse mechanism for moving said holder to
thereby allow said plurality of tips to relatively approach a wafer
whose surface is covered with a resist layer to be subjected to
electron exposure; a slider for holding relative positions of said
holder and the wafer in a state of being interposed between said
holder and the wafer whose surface is covered with the resist
layer; a drive mechanism for relatively X-Y driving the wafer and
said plurality of tips on the surface of the wafer; a control
device for controlling said respective mechanisms; a device for
supplying currents to said plurality of tips; means for detecting
the currents supplied to said plurality of tips; a control device
for allowing target values of the currents supplied to said
plurality of tips to coincide with detected values; and a pattern
input device for supplying a target value corresponding to an
electron-exposure pattern to said each control device.
22. An electron exposure apparatus according to claim 21, wherein
said plurality of tips are arranged in a row at predetermined
intervals, and capacitances between electrodes of these tips, which
are provided at both ends of said holder, and a conductor portion
of said wafer are used to correct inclinations of said tips toward
the wafer and control distances between the tips being under
electron exposure and the wafer.
23. An electron exposure apparatus according to claim 21, wherein
said plurality of tips are arranged on an X-Y plane at
predetermined intervals, and capacitances between electrodes of
these tips, which are provided at three ends of said holder, and a
conductor portion of said wafer are used to correct inclinations of
said tips toward the wafer and control distances between the tips
being under electron exposure and the wafer.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 08/696,089 filed on Aug. 13, 1996, Notice of
Allowance to which was issued on Mar. 16, 1998 and the disclosure
of which is incorporated herein by reference.
BACK GROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an electron exposure
apparatus employed in a micro-fabrication technique using a
scanning probe microscope.
[0004] 2. Description of the Related Art
[0005] Nanometer-scale-fabrication technique is indispensable for
fabricating higher integrated electronic device and higher
densificated recording media. However, the minimum feature size of
the electronic device is limited to about 100 nm by the wavelength
of light source and a lens material used in optical lithography.
Further, the resolution margin in a master plate of a recording
media is expected to be smaller in the near future. A
nanometer-scale-fabrication technique using a scanning probe
microscope, such as described in, S. C. Minne et al., "Fabrication
of 0.1 .mu.m metal oxide semiconductor field-effect transistor"
Appl. Phys. Lett. 66(6) 6 February 1995 pp. 703-705, or Hyongsok T.
Soh et al., "Fabrication of 100 nm pMOSFETs with Hybrid AFM/STM
Lithography" (1997 SYMPOSIUM ON VLSI TECHNOLOGY), is promising for
fabricating nanometer-scale device and recording media. In general,
this method is performed by applying a voltage between tip and
wafer, and the resolution is atomic level in principle.
[0006] Further, a lithography system having a plurality of
cantilevers has been also proposed as disclosed in U.S. Pat. No.
5,666,190.
SUMMARY OF THE INVENTION
[0007] In the case of using the scanning probe microscope as an
electron exposure apparatus, high speed scanning under the
simultaneous use of a plurality of tips is effective as in a
micro-fabricated device with integrated electrostatic actuators,
which has been proposed in U.S. Pat. No. 5,666,190 or the parent
application of the present application. On the one hand, however,
this method needs to control two, i.e., exposure doses and
wafer-to-tip distances with respect to respective tips. This method
also requires not only their drivers but also a control system for
generally controlling all of them, thereby leading to a complex
apparatus.
[0008] The present invention has taken note of the fact that the
Coulomb forces, which are generated by the exposure current, is
enough large to bend the cantilever and to allow the respective
tips to contact the wafer surface. Namely, the distance between the
tip group and wafer surface is roughly controlled for exposing a
current at the start of the electron exposure. In this case, each
side of the tip group may be set to have a suitable wafer-to-tip
distance. If done in this way, then all the tips can have suitable
wafer-to-tip distances within a range of given dispersion incident
to the fabrication of the tip group. After once the electron
exposure has been started, the wafer-to-tip distances at the each
side of the tip group are monitored and controlled to keep the
distance determined at the start of the electron exposure.
[0009] In other words, in the present invention, electron exposure
is carried out while each side of a tip group are kept a suitable
wafer-to-tip distance determined at the start of the electron
exposure. In doing so, individual tips automatically bend along the
surface of the wafer, even if the surface has micro-roughness, by
the Coulomb force supplied from exposure current. Thus,
wafer-to-tip distance control is not required on each individual
tip during electron exposure. Of course, the exposure-current
control is required for each individual tip.
[0010] Typical ones of various inventions of the present inventions
have been shown in brief. However, the various inventions of the
present application and specific configurations of these inventions
will be understood from the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] While the specification concludes with claims particularly
pointing out and distinctly claiming the subject matter which is
regarded as the invention, it is believed that the invention, the
objects and features of the invention and further objects, features
and advantages thereof will be better understood from the following
description taken in connection with the accompanying drawings in
which:
[0012] FIG. 1 is a block diagram showing the concept of a
configuration of an embodiment according to an electron exposure
apparatus of the present invention;
[0013] FIG. 2A is a perspective view illustrating cantilevers of
the electron exposure apparatus shown in FIG. 1 and its holder;
[0014] FIG. 2B is a plan view thereof as seen from the back sides
of the cantilevers shown in FIG. 2A;
[0015] FIG. 3A is a plan view showing other embodiments of the
cantilevers of the electron exposure apparatus of the present
invention and its holder as seen from the ventral sides of the
cantilevers;
[0016] FIG. 3B is a side view illustrating the embodiments shown in
FIG. 3A;
[0017] FIG. 4A is a perspective view depicting embodiments of an
integrated tip driver group and a holder thereof capable of being
employed in the present invention;
[0018] FIG. 4B is a cross-sectional view showing the structure of
each unitary tip driver of the integrated tip driver group shown in
FIG. 4A;
[0019] FIG. 5 is a block diagram illustrating the concept of a
configuration of another embodiment of an electron exposure
apparatus according to the present invention;
[0020] FIG. 6 is a diagram showing one example of the relationship
between an exposure dose of a current applied from each tip
employed in an electron exposure apparatus of the present invention
and a line width of a wafer;
[0021] FIG. 7 is a perspective view depicting embodiments different
from the cantilevers and the holder thereof shown in FIG. 2A;
[0022] FIG. 8A is a plan view showing modifications of the
cantilevers and its holder shown in FIG. 3A as seen from the
ventral sides of the cantilevers;
[0023] FIG. 8B is a side view depicting the modifications;
[0024] FIG. 8C is a rear elevation illustrating the
modifications;
[0025] FIG. 9A is a plan view showing other modifications of the
cantilevers and its holder shown in FIG. 3A as seen from the
ventral sides of the cantilevers;
[0026] FIG. 9B is a side view illustrating the modifications shown
in FIG. 9A;
[0027] FIG. 10A is a plan view depicting further modifications of
the cantilevers and its holder shown in FIG. 3A as seen from the
back sides of the cantilevers;
[0028] Fig. 10B is a side view showing the modifications shown in
FIG. 10A;
[0029] FIG. 11A is a plan view showing an example illustrative of
parameters of a cantilever, for describing a displacement thereof
due to the Coulomb force;
[0030] Fig. 11B is a side view showing the example illustrative of
the parameters shown in FIG. 11A;
[0031] FIG. 12A is a plan view depicting an example illustrative of
other parameters of a cantilever, for describing a displacement
thereof due to the Coulomb force; and
[0032] FIG. 12B is a side view illustrating the example
illustrative of the parameters shown in FIG. 12A.
DESCRIPTION OF THE PREFERRED EMBODIMENT
EMBODIMENT I
[0033] In the present embodiment, an embodiment of an electron
exposure apparatus wherein a plate wafer is moved or displaced in a
plane direction thereof to draw an image or perform electron
exposure, will be described with reference to FIGS. 1 and 2.
[0034] FIG. 1 is a block diagram showing the concept of a
configuration of a first embodiment of an electron exposure
apparatus of the present invention. A micro-fabrication
image-drawing or electron-exposure head 1 comprises a
micro-fabrication electron exposure unit 4 and a slop or
inclination corrector 5. The micro-fabrication electron exposure
unit 4 comprises conductive springs 22a, 22b, 22c and 22d
respectively used as cantilevers and conductive probes or tips 21a,
21b, 21c and 21d respectively connected to the springs and a holder
24 for collectively holding these. The holder 24 is coupled to the
slope corrector 5 through piezo elements 25 and 26. The slope
corrector 5 has the opposite side of a surface coupled to the piezo
elements 25 and 26, which is held by an unillustrated electron
exposure apparatus body. Further, the slope corrector 5 supplies a
voltage to each of the piezo elements 25 and 26 in response to an
inclination correction signal supplied from a drive and exposure
controller 13 to be described later to thereby correct the
inclination of the holder 24 so that a line connecting the tips 21a
and 21d at both ends to each other becomes parallel to the surface
of a resist layer 11 of a wafer 8 to be subjected to electron
exposure. A voltage application part 7 controls voltages to be
applied to the tips 21a through 21d in response to a control signal
supplied from the drive and exposure controller 13. In this case,
the voltage application part 7 controls the voltages to be applied
to the tips 21a through 21d so that they become suitable voltages
respectively where the inclination of the holder 24 is corrected
using the tips 21a and 21d provided at both ends and electron
exposure is performed by using the tips 21b and 21c. A current
detector 6 detects each of currents applied to the resist layer 11
through the tips and feeds back its detected output to the drive
and exposure controller 13. Upon execution of the inclination
correction, the drive and exposure controller 13 supplies a
suitable voltage to each of the tips 21a and 21d and controls
voltages to be applied to the piezo elements 25 and 26 so that
their currents become equal to one another. Upon execution of the
electron exposure, the drive and exposure controller 13 controls
the voltage to be applied to each of the tips 21b and 21c, i.e.,
the voltage application part 7 so that it becomes a current
corresponding to a control signal associated with an
electron-exposure pattern supplied from a pattern input part 60.
Now consider a current to flow through the resist layer 11. When
the resist layer 11 is high in insulation, the current results in a
field emission current, whereas when the resist layer 11 is
conductive, it results in a so-called current. In the present
invention, this will be defined as "current" without drawing a
distinction between the two.
[0035] The drive and exposure controller 13 supplies a transfer or
movement signal to a moving or transfer part 12 in response to the
control signal supplied from the pattern input part 60. The
transfer part 12 has one surface held by the unillustrated electron
exposure apparatus body and a surface different from one surface
thereof, which is provided with drive mechanisms 16, 17 and 18 for
displacing a transfer stage 15 in X, Y and Z directions according
to the transfer signal. Although the drive mechanisms have been
shown by the blocks 16, 17 and 18 in a sense that they are
triaxially driven in the X, Y and Z directions, those having
configurations used in the form of arbitrary mechanisms such as a
Pattern Alighter, etc. may be adopted. A displacement of the
transfer stage 15 is measured by a high-resolution measuring device
such as a laser interferometer or the like. The result of
measurement thereof is fed back to the drive and exposure
controller 13 where it is controlled precisely. The wafer 8 is
mounted on the transfer stage 15.
[0036] Prior to the electron exposure, the transfer part 12 moves
the transfer stage 15 in response to an approach signal supplied
from the drive and exposure controller 13 until the tips 21a
through 21d are placed in their corresponding predetermined
positions by the Z-axis drive mechanism 18 with respect to the
surface of the resist layer 11 of the wafer 8 to be subjected to
the electron exposure, thereby allowing the resist layer 11 of the
wafer 8 to approach the tips 21a through 21d. At this time,
suitable voltages are applied to the tips 21a through 21d
respectively. When a current detected from any of the tips has
reached a predetermined value, its approach is stopped.
[0037] After the inclination correction has been performed, the
transfer part 12 moves the transfer stage 15 on an X-Y surface
through the X-axis drive mechanism 16 and the Y-axis drive
mechanism 17 so that a pattern is drawn on the resist layer 11 of
the wafer 8. In order that while the pattern is being drawn
thereon, the magnitude of a current is monitored using the tips 21a
and 21d located at both ends to thereby maintain the distance
between the resist layer 11 and each tip as a suitable value, the
transfer part 12 is controlled by the drive and exposure controller
13 so as to continue position control in a Z-axis direction.
[0038] The wafer 8 consists of a glass-made substrate 9, a
conductive layer 10 formed by evaporating chromium onto the
substrate 9 over a range of 20 nm to 100 nm in thickness, and a
resist layer 11 (corresponding to a layer coated with a
Negative-type resist (RD2100N; product of Hitachi Chemical Co.,
Ltd.) corresponding to, for example, an Azide/phenolic resin
resist) having a thickness of about 100 nm. A resist employed in
the resist layer 11 may be a resist composed of a mixture of a
novolak resin and a photo-active compound, a chemically amplified
resist or polymethyl methacrylate. The substrate 9 may use an
arbitrary material to be processed, such as silicon, doped silicon
or the like. When the doped silicon is used for the substrate 9,
the conductive layer 10 may be omitted due to the conductivity of
the substrate 9 itself. The conductive layer 10 is electrically
grounded so that the current flows through the resist layer 11
according to the voltage applied to each tip. When the conductive
substrate 9 is used, it may be directly grounded.
[0039] FIG. 2A is a perspective view showing the cantilevers and
the holder therefor of the electron exposure apparatus shown in
FIG. 1. FIG. 2B is a plan view showing the cantilevers as seen from
the back sides thereof. The tips 21a through 21d are provided at
the leading ends of the springs 22a through 22d which serve as the
cantilevers, respectively. Further, conductive films 23a through
23d are formed on one surfaces of the springs 22a through 22d
respectively. These conductive films are electrically connected to
the voltage application part 7 and the current detector 6 through
unillustrated connectors. The tips 21a through 21d and the springs
22a through 22d are held by the holder 24 but integrally formed by
a silicon single crystal using a micro-fabrication technique, for
example. These may be silicon oxide or silicon nitride. The piezo
elements 25 and 26 for correcting the slope of the holder 24 and
performing the above transfer for approach are provided on a
cantilever-free surface of the holder 24.
[0040] A radius of curvature of the leading end of each tip 21, a
spring constant of each spring 22 and a resonant frequency may
suitably be in the ranges of 10 nm to 100 nm, 0.05 N/m to 5 N/m and
10 kHZ to 50 kHZ respectively. Further detailed data about these
parameters will be described later.
[0041] It can be said that although the leading positions of the
respective tips 21a through 21d with respect to the wafer 8 depend
on working accuracy, they can be kept in a dispersion range of less
than or equal to 50 nm and substantially placed on the same line.
Each conductive film 23 is a titanium thin film ranging from 10 nm
to 50 nm in thickness, which is formed by evaporation. In addition
to titanium, tungsten, molybdenum, titanium carbide, tungsten
carbide or molybdenum carbide may be used as the conductive
film.
[0042] An electron exposure procedure using the electron exposure
apparatus shown in FIGS. 1 and 2 will be collectively explained.
The electron exposure takes a procedure for approaching each tip by
the wafer 8 as a first stage, correcting the slope of each tip as a
second stage and performing electron exposure as a final stage.
[0043] As mentioned previously, the wafer 8 is first mounted on the
transfer stage 12 and thereafter a suitable voltage is applied to
each of the tips 21a through 21d by the voltage application part 7.
These currents resultant from the voltage are detected by the
current detector 6. Further, the transfer stage 12 is moved in the
Z-axis direction under the control of the drive and exposure
controller 13 until the current flowing through any of the tips
reaches a predetermined value to thereby allow the wafer 8 to
approach each tip. At this time, the voltage application part 7
varies a voltage V applied between each of the tips 21a and 21d and
the wafer 8. A current I that flows at this time, is detected by
the current detector 6. Thereafter, the capacitance between the
wafer 8 and each tip may be calculated from I/(dV/dt) to estimate
the distance between each tip and the wafer 8.
[0044] Next, the drive and exposure controller 13 supplies a signal
to the slop corrector 5 so that the difference in current between
both tips 21a and 21d provided at both ends is brought to nothing,
thereby controlling the piezo elements 25 and 26, whereby an
inclination formed between a line for connecting these tips to each
other and the plane of the wafer 8 is controlled so as to be
eliminated. Alternatively, it may be practiced to calculate the
capacitance, estimate the slope from the distance, and supply a
signal from the drive and exposure controller 13 to the slope
corrector 5 so as to control the piece elements 25 and 26, thereby
correct the slope.
[0045] The distance between each of the tips 21a through 21d and
the wafer 8 becomes less than or equal to a predetermined value.
After the completion of the slope correction, the electron exposure
apparatus proceeds to an electron exposure process. A set value of
the distance between each of the tips 21a through 21d and the wafer
8 may suitably range from 10 nm to 1 .mu.m.
[0046] A description will next be made of the electron exposure.
The electron exposure is performed by applying a voltage
corresponding to an electron-exposure pattern supplied from the
pattern input part 60 between each of the tips 21c and 21d and the
conductive layer 10 by the voltage application part 7 under the
control of the drive and exposure controller 13 while moving the
wafer 8 on the transfer stage 12 along the X-Y surface. Thus,
currents flow in the resist layer 11 directly below the tips 21c
and 21d and thereby resist molecules react with each other to form
a latent image within the resist layer 11.
[0047] The voltage therebetween applied from the voltage
application part 7 is varied by the drive and exposure controller
13 so that the currents detected by the current detector 6 or
currents obtained by correcting currents charged and discharged
through capacities between the tips and the substrate become
constant as exposure doses (exposure currents). This can be
controlled in various forms. Specific examples will be enumerated
as follows:
[0048] (1) when a current I is controlled, a voltage value given by
an expression 1 is outputted:
V(t)=G.sub.1.intg..sub.0.sup.t(I.sub.S-I(t))dt (1)
[0049] where G.sub.1 indicates feedback gain and I.sub.s indicates
a set current.
[0050] (2) when power P=IV is controlled, a voltage value
represented by an expression 2 is outputted:
V(t)=G.sub.p.intg..sub.0.sup.t(P.sub.S-I(t)V(t))dt (2)
[0051] where G.sub.p indicates feedback gain and P.sub.s indicates
set power.
[0052] (3) When capacitances C, which exist between the tips 21a
through 21d and springs 22a through 22d and the substrate 9 are
taken into consideration, a charge and discharge current given by
an expression 3 flows as a voltage V varies: 1 I C ( t ) = C V t (
3 )
[0053] the output voltage at current control, which is given by the
expression 1, is rewritten as the following expression in
consideration of the expression 3: 2 V ( t ) = G i 0 t { I s - ( I
( t ) - C V t ) } t ( 4 )
[0054] Further, the output voltage at power control, which is given
by the expression 2, is rewritten as follows: 3 V ( t ) = G P 0 t {
P s - ( I ( t ) - C V t ) V ( t ) } t ( 5 )
[0055] (4) Further, a feedback control system constructed by the
current detector 6 and the drive and exposure controller 13 has a
time constant T and thereby removes a high-frequency component.
This feedback control system serves as a filter even with respect
to the charge and discharge current Ic. In order to accurately
eliminate the influence of Ic, the above expression (4) is
rewritten in the following manner in consideration of the time
constant .tau.: 4 V ( t ) = G i 0 t { I s - ( I ( t ) - C C 0 t V t
e t ' - t t ' ) } t ( 6 )
[0056] Thus, the above expression (5) is given as follows: 5 V ( t
) = G P 0 t { P s - ( I ( t ) - C C 0 t V t e t ' - t t ' ) V ( t )
} t ( 7 )
[0057] In the present embodiment, the wafer 8 coated with the
resist RD2100N having the thickness of 100 nm is moved at 0.1 mm/s
so that the voltage applied between each of the tips 21c and 21d
and the conductive layer 10 is set to the neighborhood of -85V and
the current is set to be 100 pA, i.e., the exposure dose is set to
be 10 nC/cm.
[0058] During a period in which the latent image is being formed
within the resist layer 11, the tips 21b and 21c undergo the
Coulomb force, which acts between each of the tips 21b and 21c and
the conductive layer 10 by the voltage applied to create the latent
image. Due to the Coulomb force, the respective springs 22b and 22c
are bent or deformed and the respective tips are held in contact
with the resist layer 11. There are also portions in which no
latent images are formed according to patterns to be created. Since
the portions do not need the currents, it is unnecessary to apply
the voltage to the corresponding tips at these positions. However,
since the Coulomb force, which has acted on the tips, is brought to
nothing when the voltage is set to 0V, no respective springs 22b
and 22c are deformed and thereby spaced away from the surface of
the resist layer 11. In the case, the Coulomb force abruptly acts
on the tips when the voltage is applied thereto at the position to
form the latent image again, so that the respective springs 22b and
22c are suddenly deformed. Therefore, there is a high possibility
that the tips will hit against the resist layer 11 heavily to
thereby break. Thus, when the latent-image creation-free portions
are subjected to electron exposure, it is better to control the
voltage so that such a small current as not to form the latent
image flows. In the present embodiment, the current becomes less
than or equal to 1 pA when the voltage to be applied is set to -70V
or less, and hence no latent image was not formed. On the other
hand, the current used for position monitoring by the tips located
at both ends is naturally performed to this extent or less.
However, the impressed voltage may preferably be set to such a
voltage as to merely supply a smaller current in such a manner that
the respective springs 22a and 22d are not deformed by the Coulomb
force wherever possible.
[0059] A brief description on development of the latent image drawn
by the present invention is as follows:
[0060] The latent image is developed by being immersed in a
tetramethylammonium hydroxide solution of 0.83% for one minute. As
a result, when a negative-type resist is used for the resist layer
11, only a resist with a latent image formed thereon is left behind
without its dissolution, so that a convex type line resist pattern
having a line width of 100 nm can be created. When a positive-type
resist is used for the resist layer 11, only a resist with a latent
image formed thereon is dissolved to thereby create a concave type
line resist pattern having a line width of 100 nm. FIG. 6 shows the
relationship between a pattern width and an exposure dose employed
in the embodiment of the present invention. The same drawing shows
the case in which since the pattern width depends on the exposure
dose, an arbitrary pattern width of 100 nm or more can be formed by
adjusting the exposure dose.
[0061] In the present invention, the electron exposure takes a
procedure for approaching each tip by the wafer 8 as a first stage,
correcting the slope of each tip as a second stage and performing
electron exposure as a final stage. Tips at ends, of many tips are
used for positioning and monitoring of positions being under
electron exposure, and other tips are used for electron exposure,
whereby tips used for electron exposure may simply perform current
control alone. Further, the present invention could provide a
useful approach or method in that an attention has been focused on
the fact that the electron exposure could be achieved by the
current control alone without strict position control due to the
deformation of each tip by the Coulomb force upon formation of the
latent image. In the description of the above embodiment, the
number of tips is less because of only four. However, the more the
number of the tips increases, the more the merit of the present
invention becomes great. Incidentally, the aforementioned
embodiment shows the case in which the approach of each tip to the
wafer 8 is made by moving the wafer 8 in the Z-axis direction.
However, the piezo elements 25 and 26 on the holder 24 holding the
tips thereon may be used for this approach.
EMBODIMENT II
[0062] FIG. 3A is a plan view showing other embodiments of the
cantilevers of the electron exposure apparatus of the present
invention and its holder as seen from the back sides of the
cantilevers. FIG. 3B is a side view thereof. As is understood in
contrast with FIGS. 2A and 2B, a tip unit 30 having a number of
springs 31a, 31b. . . , 31k, . . . , 31n, and 32a, . . . 32m, . . .
3jm is shown as an illustrative example. These springs are
respectively held within holders 34a, 34b, 34c and 34d and their
holders are held by a common holder 35. While conductive lines for
respective tips are typically designated at numerals 33, they are
caused to lead through unillustrated connectors to provide
necessary connections. As shown in FIG. 3B, piezo elements 36
through 36c corresponding to the piezo elements 25 and 26 shown in
FIG. 2A are provided on the back of the common holder 35. The piezo
element 36a is not seen from the drawing. The piezo elements 36a
and 36b are used to control a slope or inclination in an X
direction shown in the drawing using the tips 31a and 31n. The
piezo elements 36b and 36c are used to control an inclination in a
Y direction shown in the drawing using the tips 31n and 3jm.
EMBODIMENT III
[0063] FIG. 4A is a perspective view showing embodiments of an
integrated tip driver group and a holder thereof both capable of
being employed in the present invention. FIG. 4B is a
cross-sectional view showing the structure of each unitary tip
driver shown in FIG. 4A.
[0064] FIG. 4A is a conceptual diagram showing the structure of an
embodiment in which a number of tip drivers 420 shown in FIG. 4B
are two-dimensionally in X and Y direction and held by a coarse
mechanism 410 to thereby allow control on the positions of the
tips. The number of tip drivers 420 corresponding to the respective
tips and springs shown in FIGS. 3A and 3B are two-dimensionally
placed in the X and Y directions. The structure in which a group of
the tip drivers 420 is held by the coarse mechanism 410
corresponding to the common holder 35 and piezo elements 36a
through 36c shown in FIGS. 3A and 3B to thereby allow control on
the positions of the tips, is shown in the drawing.
[0065] If done in this way, then the coarse mechanism 410 can
perform XY two-dimensional driving for electron exposure as well as
to execute an approach and a slope correction. It is of course
needless to say that their functions may be divided into parts so
as to bear their burdens as in the aforementioned embodiment.
[0066] The structure of the coarse mechanism 410 employed in the
present embodiment will not be described in detail. However, if the
structure thereof is devised by micro-fabrication in a manner
similar to the fabrication of the tip drivers 420 shown in FIG. 4B
and the combination of it with the piezo elements is devised, it
can be then easily fabricated. Conversely, the simple holder and
piezo elements shown in FIG. 2A may be utilized in combination.
[0067] An example of the tip driver 420 will be explained ran below
with reference to FIG. 4B. FIG. 4B is a block diagram showing one
example of the structure of the tip driver 420. The present
embodiment is equivalent to one in which a first integrated
electrostatic actuator 2100 and a second integrated electrostatic
actuator 2500 are cascade-connected. Namely, a fixed electrode 270
of the second actuator 2500 is electrically connected to a movable
electrode 210 of the first actuator 2100. A tip 220 is mounted to a
drawn or extended leading end of the movable electrode 250 of the
second actuator 2500. Further, the first integrated electrostatic
actuator employed in the present embodiment is one actuator and can
be driven in X and Y directions. Thus, movements in the X and Y
directions and a movement in a Z direction are controlled by the
first actuator 2100 and the second actuator 2500 respectively.
[0068] Fixed electrodes 211 of the actuator 2100 are provided at
the leading end of a base 230. A spring 240 comprised of plate
springs 241 and connecting portions 242 for respectively coupling
the plate springs 241 to each other is provided at the leading end
of the base 230 in the same manner as described above. The movable
electrode 210 of the actuator 2100 is coupled to its corresponding
connecting portion 242 of the spring 240. The other ends of the
fixed electrodes 211 of the actuator 2100 are coupled to base end
portions 232. A spring 240' made up of plate springs 241' and
connecting portions 242'for coupling the plate springs 241' to each
other is provided at the base end portions 232. The movable
electrode 210 of the actuator 2100 is coupled to a connecting
portion of the spring 240' and a Z-drive shaft 270 is coupled to
the connecting portion of the spring 240'. Since driving forces,
which act between the fixed electrodes 211 and the movable
electrode 210 of the actuator 2100, bend the springs 240 and 240'
respectively, the Z-drive shaft 270 takes positions in an X
direction (parallel to the sheet and in the left and right
directions) and a Y direction (normal to the sheet) corresponding
to the driving forces of the actuator 2100.
[0069] The integrated electrostatic actuator 2500 is provided at
the leading end of the Z-drive shaft 270 in the form of the Z-drive
shaft 270 as the aforementioned base 230. Namely, fixed electrodes
251 supported by a frame portion 270' formed integrally with the
Z-drive shaft 270 are formed. Similarly, a spring 260 comprised of
plate springs 261 with the frame portion 270' as a fixed portion
and connecting portions 262 for coupling the plate springs 261 to
each other, and a spring 260' comprised of plate springs 261' and
connecting portions 262' for coupling the plate springs 261' to
each other, are formed. A tip supporter 280 whose leading end is
provided with the tip 220, is coupled to a connecting portion 263
of the spring 260 and a connecting portion 263' of the spring 260'.
Further, the movable electrode 250 of the actuator 2500 is coupled
to the tip supporter 280. Since driving forces, which act between
the fixed electrodes 251 and the movable electrode 250 of the
actuator 2500, flexes the springs 260 and 260' respectively, the
tip supporter 280 assumes a position in an Z direction (parallel to
the sheet and in upward and downward direction). In the present
embodiment, the Z-drive shaft 270 performs control in the X and Y
directions through the actuator 2100 and the tip performs control
in the Z direction in this condition.
[0070] Although descriptions about wiring or interconnections to
the respective electrodes, interconnections for a voltage to be
applied to each tip and the need or not for insulation have been
omitted in the illustrated embodiment to simplify illustrations in
the drawing, they can be implemented by arbitrary configurations as
needed. Therefore, a further description will be omitted.
[0071] A plurality of the structures each illustrated in the
embodiment shown in FIG. 4B are one-dimensionally placed in
parallel so as to be brought into integration by a semiconductor
micro-fabrication technique with one substrate as a base. Further,
the base 230 and the base end portions 232 may be directly mounted
on one substrate used as the base and other portions are processed
by the semiconductor micro-fabrication technique, whereby
integrated tip drivers having integrated electrostatic actuators
can be configured in form away from the substrate. Thus, the
integrated tip drivers one-dimensionally placed on one chip in
parallel can be extremely easily constructed.
[0072] Two-dimensionally disposed integrated tip drivers can be
also easily formed by stacking the structures of the integrated tip
drivers one-dimensionally placed in parallel on one chip, according
to the present embodiment on one another in plural form.
[0073] In the present invention, since the number of tip drivers
420 are enough if the entire approach, the slope correction and the
position control being under electron exposure are carried out, it
is essentially unnecessary to control the positions of the
individual tips 220 of many tip drivers. However, this ability is
useful if a correction to partial electron exposure or the like is
taken into consideration.
EMBODIMENT IV
[0074] An embodiment used as an electron exposure apparatus for
rotating a wafer to make electron exposure will next be described
with reference to FIG. 5. The present embodiment essentially
remains unchanged as compared with the electron exposure apparatus
according to the embodiment shown in FIG. 1. However, the present
embodiment is equivalent to one in which a wafer 8 is rotated and a
micro-fabrication electron exposure head 1 is placed so as to be
put to one side of the wafer 8. Elements of structure used in
common in both embodiments are identified by the same reference
numerals. The transfer part 12, the transfer stage 15 and the drive
mechanisms 16, 17 and 18 to be moved in the X, Y and Z directions,
which are employed in the embodiment shown in FIG. 1, are replaced
by a rotatable driving part 61, a rotatable stage 65 and a
rotatable shaft 66 respectively. A drive and exposure controller 13
supplies a rotation signal to the rotatable driving part 61 in
response to a control signal supplied from a pattern input part 60.
This rotation signal allows the rotatable stage 65 to be rotated
through the rotatable shaft 66 and information about this rotation
is fed back to the drive and exposure controller 13, where position
control is performed precisely.
[0075] Although an approach operation is done prior to the electron
exposure even in the present embodiment, this operation allows the
rotatable shaft 66 to be shift (Z-axis driven) upwardly according
to a signal supplied to the rotatable driving part 61 from the
drive and exposure controller 13. When the rotatable stage 65 is
moved until tips 21a through 21d take predetermined positions with
respect to the surface of a resist layer 11 of the wafer 8 to be
subjected to electron exposure, their approaches are brought to
completion. Thereafter, a slope correction is carried out and
consecutively the rotatable stage 65 is rotated to draw a pattern
on the resist layer 11 of the wafer 8. The rotatable driving part
61 is controlled by the drive and exposure controller 13 to
continue position control in an Z-axis direction in such a way as
to monitor the magnitudes of currents using the tips 21a and 21d
located at both ends and thereby maintain the distance between the
resist layer 11 and each tip as a suitable value while the pattern
is being drawn. Further, the present embodiment is considered to
frequently need the operation of correcting a slope resultant from
rotation by a corrector 5 even during the electron exposure as
compared with the embodiment shown in FIG. 1. However, the
operation can be executed without any hindrance owing to the
monitoring of positions by the tips located at both ends.
[0076] Since the micro-fabrication electron exposure head 1 is
relatively small as compared with the wafer 8 in the present
embodiment, a complete round-shaped resist pattern usable in a
recording track of an optical disk, for example can be formed if
the wafer 8 is developed after having been rotated 360 by the wafer
rotatable stage 65. Further, if the wafer 8 is developed after
having been rotated 360 by the wafer rotatable stage 65 while the
micro-fabrication electron exposure head 1 is being moved in the
direction of the center of rotation thereof from side to side with
a certain point thereof as the center while a constant exposure
dose is being radiated continuously, then a waveformed resist
pattern can be formed in circular form. Alternatively, if the wafer
8 is developed after the micro-fabrication electron exposure head 1
has been fixed and the wafer 8 has been rotated 360 by the wafer
rotatable stage 65 while switching is made between a latent-image
formable exposure dose and a latent-image unformable exposure dose,
then a dot pattern usable for data information and address
information in the optical disk can be formed in circular form. If
this operation is continuously performed so as to draw patterns
over the entire area of the wafer 8, then the patterns can be drawn
over the entire area thereof in twenty hours under the condition
that the tips are arranged at 0.1 mm pitches, track pitches are
defined as 100 nm and the rotational speed is at 50 rpm.
[0077] An original plate for the optical disk can be created by
combining the methods shown in the above. Further, if a concave
type dot resist pattern is formed over the entire surface of the
disk and a magnetic material such as an iron, cobalt, nickel,
iron-cobalt alloy, a cobalt-nickel alloy, an iron-nickel alloy or
the like is buried in the dot pattern by electric plating with a
conductive layer 10 as an electrode, then an ultrahigh-density
magnetic recording medium with magnetic dots as isolated recording
bits can be created.
EMBODIMENT V
[0078] Next, FIG. 7 is a perspective view showing different
embodiments of the cantilevers and their holder shown in FIG.
2A.
[0079] The present embodiment illustrates one, as an example, in
which displacements in cantilevers 22a and 22d located at both ends
are detected by an optical level deflection sensor type atomic
force microscope. Reference numerals 83 and 81 indicate light
sources and reference numerals 84 and 82 indicate photo-detectors.
Since the atomic force microscope does not need to allow currents
to flow between tips 21a and 21d and a wafer 8, it is unnecessary
to apply a voltage to each tip 21. Thus, springs are not deformed
by experiencing the Coulomb force resultant from the voltage
applied to each of the tips 21a and 21d. Therefore, when the atomic
force microscope is used to monitor positions by the tips located
at both ends, stable position control and slope control can be
achieved.
EMBODIMENT VI
[0080] FIG. 8A is a plan view showing modifications of the
cantilevers and their holder shown in FIG. 3A as seen from the back
sides of the cantilevers. FIG. 8A is a side view thereof. FIG. 8C
is a rear elevation thereof.
[0081] As is clearly understood in the present embodiment from the
contrasts between FIG. 3A and FIG. 8A and between FIG. 3B and FIG.
8B, holders 34a through 34d are divided into two: 34a', 34a ' to
34d', 34d' every rows of cantilevers. Further, the cantilevers are
inclined toward their corresponding holders and set identical to
one another in direction. Moreover, the present embodiment shows
one in which displacements in cantilevers 31a, 31n and 3jm at ends
are detected by an optical lever deflection sensor type atomic
force microscope in a manner similar to the embodiment shown in
FIG. 7. Reference numerals 91, 93 and 95 indicate light sources and
reference numerals 92, 94 and 96 indicate photo-detectors,
respectively. The present embodiment brings about an advantageous
effect in that since the cantilevers are set to have the same
slopes and directions, springs of cantilevers effectively act on
irregularities or projections and depressions of the surface of a
resist 11 upon movement of a wafer 8, whereby the possibility that
tips will be damaged, can be reduced. Further, since the
displacements in the cantilevers are detected by the atomic force
microscope, an advantageous effect can be also brought about in
that stable position and slope control can be achieved in a manner
similar to the previous embodiment. In the present embodiment, as
is apparent by reference to FIG. 8C, some of a holder 35 must be
cut so as to cause light to pass therethrough in order to transmit
light of the atomic force microscope for detecting a displacement
in the cantilever 3jm
EMBODIMENT VII
[0082] FIG. 9A is a plan view showing other modified embodiments of
the cantilevers and their holder shown in FIG. 3A as seen from the
ventral sides of the cantilevers. FIG. 9B is a side view
thereof.
[0083] As is clearly understood from the contrasts between FIG. 8A
and FIG. 9A and between FIG. 8A and FIG. 9A, the present embodiment
shows one, as an example, in which as an alternative to the
detection of the displacements in the cantilevers 31a, 31n and 3jm
at the ends by the atomic force microscope, the approach of the tip
unit 30 to the wafer 8 and the monitoring of their positions are
carried out by providing electrodes 41, 42 and 43 at three points
of the surface of a holder 35 on the cantilever side and detecting
capacitances between the electrodes and a conductor portion of the
wafer.
[0084] In the present embodiment, when the wafer is set to a
transfer stage 15, no capacitances cannot be substantially
detected. However, when the approach to the wafer 8 proceeds and
the tip unit 30 approaches the wafer 8 to some extent, the
capacitances can be detected. The approach of the tip unit 30 to
the wafer 8 can be completed using this. Further, even the
monitoring of their positions during electron exposure can be
performed using it.
EMBODIMENT VIII
[0085] FIG. 10A is a plan view showing further embodiments
illustrative of modifications of the cantilevers and their holder
shown in FIG. 3A as seen from the ventral sides of the cantilevers.
Fig. 10B is a side view thereof.
[0086] As is clearly understood from the contrasts between FIG. 9A
and FIG. 10A and between FIG. 9B and Fig. 10B, the present
embodiment is one in which the relationship in position between a
tip unit 30 and a wafer 8 is directly held by sliders 51, 52, 53
and 54 interposed therebetween. Weak spring devices 55, 56, 57 and
58 (57 and 58 not shown in the drawing) are provided at the four
corners of the back of a holder 35 so that these sliders are kept
in contact with the wafer 8 by a weak force.
[0087] In the present embodiment, the wafer 8 is set to a transfer
stage 15 and thereafter the holder 35 is pressed against the wafer
8 by a weak force at an approach stage. Afterwards, if this state
is kept as it is, it is then unnecessary to perform position
control being under electron exposure in particular.
Examples of Parameters for Cantilevers
[0088] FIG. 11A is a plan view showing one example illustrative of
parameters for each cantilever, for describing a displacement in
cantilever by the Coulomb force. Fig. 11B is a side view thereof.
The cantilever illustrated in this example has a width of W , a
length of L and a thickness of t. Further, the length of a tip
ranges from about 10 to 15 .mu.m. In this example, the Coulomb
force was roughly calculated by a parallel plate capacitor formed
between the conductive layer 10 and each cantilever 22 shown in
FIG. 1.
[0089] A force F, which acts between electrode plates of the
parallel plate capacitor, is first given by the following equation.
In the equation, .di-elect cons..sub.0 indicates a dielectric
constant of a dielectric that exists between the electrode plates,
S indicates the area of each electrode plate, V indicates a voltage
applied between the electrode plates, and d indicates the distance
between the electrode plates. 6 F = 0 SV 2 2 d 2
[0090] The three samples of A through C different in constant from
each other are now prepared as the cantilevers. Their parameters
are respectively as follows:
1 Spring Width Length Thickness constant Sample W .mu.m L .mu.m t
.mu.m CN/m A 50 450 2.0 0.1 B 60 450 4.0 2.0 C 30 225 5.0 20.0
[0091] Assuming now that the area of electrode plate S is same as
the area of the cantilever holding the tip, the result of
calculation made to the Coulomb force between the cantilever and
wafer face is given in Table shown below.
2 Distance Voltage between between Area of electrode electrode
Coulomb cantilever plates plates force S d V F 50 .mu.m .times. 450
.mu.m 16 .mu.m 40 V 630 nN
[0092] The result of calculation made to the amounts of deformation
or bending of the above samples by now noting an example in which
the Coulomb force is 630 nN, is given in Table shown below.
3 Amount of Sample bending (nm) A 6300 B 315 C 32
[0093] As is understood even from the example, such a large force
and deformation or bending occur even when the voltage is 40V.
Thus, when 80V is applied upon the aforementioned electron
exposure, each cantilever greatly deforms or bends and hence
control on the position of each cantilever for electron exposure
does not make sense. Conversely, the cantilevers stably follow the
non-uniformity of the thickness of the resist layer 11 due to this
deformation. This is an important point of view of the present
invention to be noted.
[0094] Next, FIG. 12A is a plan view showing another example
illustrative of further parameters of a cantilever, for describing
a displacement in cantilever by the Coulomb force. FIG. 12B is a
side view thereof. The cantilever shown in this example is a
two-point supported beam. Two examples having 4 .mu.m defined as
widths W of their leading ends, 0.4 .mu.m defined as their
thicknesses t, 200 .mu.m and 100 .mu.m defined as their lengths L,
0.02 and 0.09 defined as spring constants and about 6 .mu.m defined
as tip lengths were calculated. The two examples are identical to
each other in leading-end's structure and configuration and
different from one another in length L alone. When the area of a
tip with respect to the surface of each of the cantilevers in the
examples is defined as 3700 .mu.m.sup.2, the distance d between
electrode plates is defined as 6 .mu.and the applied voltage is
defined as 40v, the Coulomb force was 730 nN. If the force
corresponding to this extent is given, then the cantilever will
cause deformations of about 37000 nm and 8100 nm in a manner
similar to the cantilever shown in FIG. 11. Thus, even this type of
cantilever can take full advantage of deformation.
[0095] Although the tip drivers shown in FIGS. 4A and 4B have no
cantilevers and do not construct a parallel plate capacitor as in
these examples, the Coulomb force that acts on each tip, can be
fully utilized because springs 261 and 261' are extremely soft.
[0096] According to the present invention, as has been described
above, since one control on each tip with respect to the wafer may
be performed only at each side of the tip group and only control on
the currents may be carried out at other tips, an electron exposure
apparatus capable of performing electron exposure at high speed can
be easily fabricated.
[0097] Since it is unnecessary to strictly perform the approach and
the slope control, such structures as shown in FIGS. 9 and 10 may
be used as the simplest structure or may be one, although not shown
in the drawing, of a type wherein electrodes are placed on the
backs of cantilevers and displacements in cantilevers are detected
from changes in capacitance between the two.
[0098] While the present invention has been described with
reference to the illustrative embodiments, this description is not
intended to be construed in a limiting sense. Various modifications
of the illustrative embodiments, as well as other embodiments of
the invention, will be apparent to those skilled in the art on
reference to this description. It is therefore contemplated that
the appended claims will cover any such modifications or
embodiments as fall within the true scope of the invention.
* * * * *