U.S. patent application number 09/749947 was filed with the patent office on 2001-07-26 for angle compensation method.
This patent application is currently assigned to AGENCY OF INDUSTRIAL SCIENCE & TECHNOLOGY, MINISTRY OF INTERNATIONAL TRADE & INDUSTRY. Invention is credited to Fujisawa, Satoru, Ogiso, Hisato.
Application Number | 20010009460 09/749947 |
Document ID | / |
Family ID | 18544150 |
Filed Date | 2001-07-26 |
United States Patent
Application |
20010009460 |
Kind Code |
A1 |
Fujisawa, Satoru ; et
al. |
July 26, 2001 |
Angle compensation method
Abstract
An angle compensation method compensates for the angle of the
light-receiving surface of a photodiode disposed in an inclination
detection device. The light-receiving surface is divided into four
parts by an a-axis and a b-axis disposed perpendicular to each
other and receives light reflected from an object surface that is
an X-Y plane. The inclination detection device seeks the
inclination of the object surface from changes in the irradiation
position of the light reflected onto the photodiode light-receiving
surface. The method includes the steps of fixing the
light-receiving surface to a rotary stage that can rotate about a
c-axis that passes through an intersection of the a-axis and b-axis
and is perpendicular to the a- and b-axes and can rotate about a
k-axis that is parallel to a Z axis of the object surface, and
rotating the light-receiving surface about the c-axis and k-axis so
that, when the light-receiving surface is projected onto the object
surface, the a-axis aligns with a Y-axis and the b-axis aligns with
an X-axis.
Inventors: |
Fujisawa, Satoru;
(Tsukuba-shi, JP) ; Ogiso, Hisato; (Tsukuba-shi,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, McCLELLAND,
MAIER & NEUSTADT, P.C.
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
AGENCY OF INDUSTRIAL SCIENCE &
TECHNOLOGY, MINISTRY OF INTERNATIONAL TRADE & INDUSTRY
Tokyo
JP
|
Family ID: |
18544150 |
Appl. No.: |
09/749947 |
Filed: |
December 29, 2000 |
Current U.S.
Class: |
356/139.1 |
Current CPC
Class: |
G01B 11/26 20130101;
G01D 5/285 20130101 |
Class at
Publication: |
356/139.1 |
International
Class: |
G01C 001/00; G01B
011/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 26, 2000 |
JP |
2000-017115 |
Claims
What is claimed is:
1. An angle compensation method for compensating for an angle of a
light-receiving surface of a photodiode disposed in an inclination
detection device, said light-receiving surface being divided into
four parts by an a-axis and a b-axis disposed perpendicular to each
other and receiving light reflected from an object surface that is
an X-Y plane, said inclination detection device seeking an
inclination of the object surface from changes in an irradiation
position of the light reflected on the photodiode light-receiving
surface, said method comprising the steps of fixing the
light-receiving surface to a rotary stage that can rotate both
about a c-axis that passes through an intersection of the a-axis
and b-axis and is perpendicular to the a- and b-axes and about a
k-axis that is parallel to a Z axis of the object surface; and
rotating the light-receiving surface about the c-axis and k-axis so
that, when the light-receiving surface is projected onto the object
surface, the a-axis aligns with a Y-axis and the b-axis aligns with
an X-axis.
2. The angle compensation method according to claim 1, wherein the
light-receiving surface is fixed to a rotary mechanism about the
k-axis supported on a rotary mechanism about the c-axis.
3. The angle compensation method according to claim 1, wherein the
light-receiving surface is fixed to a rotary mechanism about the
c-axis supported on a rotary mechanism about the k-axis.
4. The angle compensation method according to claim 1, wherein the
rotary stage comprises a magnetic sphere and is housed in a sphere
holder having three perpendicular walls, and the sphere is pulled
by magnets disposed in corners formed by the three walls to
facilitate rotation of the sphere.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to an angle compensation method for a
photodiode light-receiving surface in an inclination detection
device wherein reflected light reflected off an object surface is
received on the photodiode light-receiving surface divided into
four parts and the inclination of the object surface is sought from
changes in the position of irradiation of the reflected light on
the photodiode light-receiving surface.
[0003] 2. Description of the Prior Art
[0004] In the prior art, the inclination of the object surface was
detected by an optical lever method in a pin-contact-type surface
roughness tester, scanning probe microscope (atomic force
microscope) or a two-dimensional position sensing detector with
laser beam reflection.
[0005] FIG. 2 is a sketch for explaining the principle of detection
of inclination of an object surface by the known optical lever
method. In FIG. 2, the photodiode light-receiving surface D is
disposed opposite the object surface P, which is the X-Y plane, and
the reflected light L1 when the light beam L is incident on the
object surface P is received by the photodiode light-receiving
surface D. This photodiode light-receiving surface D comprises
light-receiving surfaces D1, D2, D3 and D4 divided into four parts
by an a-axis and a b-axis perpendicular to each other, and when the
photodiode light-receiving surface D is projected on the object
surface P, the position of the photodiode light-receiving surface D
is adjusted such that the projected a-axis (projected a-axis below)
corresponds with the Y-axis and the projected b-axis (projected
b-axis below) corresponds with the X-axis, in which state the
inclination of the object surface P is measured.
[0006] When the object surface P is rotated about the Y-axis by
angle .gamma., the position of irradiation of the reflected light
L1 on the photodiode light-receiving surface D is displaced along
the b-axis depending on the amount of change, and when the object
surface P is rotated about the X-axis by angle .delta., the
position of irradiation of the reflected light L1 on the photodiode
light-receiving surface D is displaced along the a-axis depending
on the amount of change. The light beam L in this case has an
appropriate amount of spread, i.e., an appropriate amount of spread
that can all be contained on the photodiode light-receiving surface
D, and the spread of the beam is adjusted in advanced so that it
will irradiate the center of the photodiode light-receiving surface
D.
[0007] Here, when the object surface P is rotated up by angle
.gamma. around the Y-axis by the actuator 16 and the center
position of the irradiation of the reflected light L1 moves from
the irradiation position M1 on one side toward the irradiation
position M2 on the other side, this movement causes the light to
become thinner on one side of the a-axis and to become thicker on
the other side, and this trend becomes marked as the angle .gamma.
becomes larger. That is, the difference A in the amount of light
obtained by subtracting the amount of light received on one side of
the a-axis (amount of light received on light-receiving surface D2
and light-receiving surface D3) from the amount light received on
the other side of the a-axis (amount of light received on
light-receiving surface D1 and light-receiving surface D4) is
proportional to the angle .gamma. when the angle .gamma. is small,
and therefore by detecting the light amount difference A, it is
possible to seek the angle .gamma..
[0008] Similarly, when the angle .delta. is small, the angle
.delta. can be sought by the difference B obtained by subtracting
the amount of light received on one side of the b-axis (amount of
light received on light-receiving surface D3 and light-receiving
surface D4) from the amount of light received on the other side of
the b-axis (amount of light received on light-receiving surface D1
and light-receiving surface D2).
[0009] However, in the above inclination detection method,
agreement of the Y-axis with the projected a-axis and agreement of
the X-axis with the projected b-axis are prerequisites for
measurement, and if they do not agree, the data accuracy of the
light amount differences A and B will be degraded, which will
degrade the accuracy of measurement of the inclination of the
object surface P. Next, degradation of the data accuracy of the
light amount differences A and B is discussed using FIG. 3 through
FIG. 6.
[0010] Degradation of the data accuracy of the light amount
differences A and B can occur in the following two modes:
[0011] (I) When the photodiode light-receiving surface D is rotated
about the c-axis, which passes through the intersection of the
a-axis and the b-axis and is perpendicular to the a- and
b-axes.
[0012] (II) When the photodiode light-receiving surface D is
rotated about the Z1-axis, assuming this Z1-axis is parallel to the
Z-axis of the object surface and is positioned behind the
photodiode light-receiving surface D.
[0013] In the case of the mode in (I) above, as shown in FIG. 3,
the a-axis projected on the X-Y plane (projected a-axis) is rotated
about the Z-axis by angle .alpha. with respect to the Y-axis. If
the object plane P is inclined by angle .delta. in this mode, the
irradiation of the reflected light L1 on the photodiode
light-receiving surface D generates a locus on the Y-axis (axis
inclined by angle .alpha. from the a-axis) projected on the
photodiode light-receiving surface D as shown in FIG. 4. Also, when
the object surface P is inclined by angle .gamma., the irradiation
of the reflected light L1 on the photodiode light-receiving surface
D generates a locus on the X-axis (axis inclined by angle a from
the b-axis) projected on the photodiode light-receiving surface D
as shown in FIG. 4.
[0014] Therefore, the light amount difference A on both sides of
the a-axis is primarily proportional only to angle .gamma. and is
therefore described by A= m.multidot..gamma. (where, m is the
compensation factor), but due to the occurrence of angle .alpha.
(rotational shift around the c-axis of the photodiode
light-receiving surface D), it is now described by equation
(1).
A=m.multidot.(.gamma..multidot.cos .alpha.+.delta..multidot.sin
.alpha.) Equation (1)
[0015] Further, the light amount difference B on both sides of the
a-axis is primarily proportional only to angle .delta. and is
therefore described by B=n.multidot..delta. (where, n is the
compensation factor), but due to the occurrence of angle .alpha.
(rotational shift around the c-axis of the photodiode
light-receiving surface D), it is now described by equation
(2).
B=n.multidot.(.gamma..multidot.cos .alpha.+.delta..multidot.sin
.alpha.) Equation (2)
[0016] In this way, the factor sin .alpha. interferes with the
light amount differences A and B, and due to this factor, the data
accuracy of the light amount differences A and B is degraded.
[0017] In the case of the mode in (II) above, as shown in FIG. 5,
the line of intersection R between the X-Y plane and the photodiode
light-receiving surface D is rotated about the Z-axis by angle
.beta. with respect to the Z-axis. If the object plane P is
inclined by angle .delta. in this mode, the irradiation of the
reflected light L1 on the photodiode light-receiving surface D
generates a locus on the Y-axis (axis inclined by angle .beta. from
the a-axis) projected on the photodiode light-receiving surface D
as shown in FIG. 6. Also, when the object surface P is inclined by
angle .gamma., the irradiation of the reflected light L1 on the
photodiode light-receiving surface D generates a locus on the
X-axis (axis inclined by angle .beta. from the b-axis) on the
photodiode light-receiving surface D as shown in FIG. 6.
[0018] Therefore, the light amount difference A is primarily
proportional only to angle .gamma. and is therefore described by
A=m.multidot..gamma. (where, m is the compensation factor), but due
to the occurrence of angle .beta. (rotational shift around the
Z1-axis of the photodiode light-receiving surface D), it is now
described by equation (3).
A=m.multidot.(.gamma..multidot.cos .beta.+.delta..multidot.sin
.beta.) Equation (3)
[0019] Further, the light amount difference B is primarily
proportional only to angle .delta. and is therefore described by
B=n.multidot..delta. (where, n is the compensation factor), but due
to the occurrence of angle .beta. (rotational shift around the
Z1-axis of the photodiode light-receiving surface D), it is now
described by equation (4).
B=n.multidot.(.delta..multidot.cos .beta.+.gamma..multidot.sin
.beta.) Equation (4)
[0020] In this way, the factor sin .beta. interferes with the light
amount differences A and B, and due to this factor, the data
accuracy of the light amount differences A and B is degraded.
[0021] As explained above, it is possible to raise the data
accuracy of the light amount differences A and B by deleting the
interfering terms sin .alpha. and sin .beta., which is equivalent
to adjusting the posture of photodiode light-receiving surface D to
make both angle .alpha. and angle .beta. zero.
[0022] However, in adjusting the position of the photodiode
light-receiving surface D as explained above, the adjustment that
makes angle .beta. zero (adjustment about the Z1-axis) has not been
performed at all, and this becomes a factor that can degrade the
measurement accuracy of the inclination of the object surface
P.
[0023] Further, the adjustment that makes the angle .alpha. zero
(adjustment about the c-axis) has been performed, but this
adjustment is based mainly on the experience of the person
performing the measurement, and therefore it cannot be said to be a
highly accurate adjustment and may be factor in further degrading
the measurement accuracy of the inclination of the object surface
P.
[0024] This invention was proposed to address these issues, and its
purpose is to offer an angle compensation method capable of
improving the measurement accuracy of the inclination of an object
surface in an inclination detection device.
SUMMARY OF THE INVENTION
[0025] In order to achieve the above purpose, this invention
provides an angle compensation method for compensating for an angle
of a light-receiving surface of a photodiode disposed in an
inclination detection device, the light-receiving surface being
divided into four parts by an a-axis and a b-axis disposed
perpendicular to each other and receiving light reflected from an
object surface that is an X-Y plane, the inclination detection
device seeking an inclination of the object surface from changes in
an irradiation position of the light reflected on the photodiode
light-receiving surface, the method comprising the steps of fixing
the light-receiving surface to a rotary stage that can rotate both
about a c-axis that passes through an intersection of the a-axis
and b-axis and is perpendicular to the a- and b-axes and about a
k-axis that is parallel to a Z axis of the object surface; and
rotating the light-receiving surface about the c-axis and k-axis so
that, when the light-receiving surface is projected onto the object
surface, the a-axis aligns with a Y-axis and the b-axis aligns with
an X-axis.
[0026] The light-receiving surface can be fixed to a rotary
mechanism about the k-axis supported on a rotary mechanism about
the c-axis or to the rotary mechanism about the c-axis supported on
the rotary mechanism about the k-axis.
[0027] Further, the rotary stage comprises a spherical magnetic
substance and is housed in a sphere holder having three
perpendicular walls, and the sphere is pulled by magnets disposed
in the corners formed by the three walls to facilitate rotation of
the sphere.
[0028] As described above, in this invention the light-receiving
surface is fixed to the rotary stage, and the rotary stage is
rotated about the c-axis and about the k-axis to eliminate any
rotational shift of the light-receiving surface with respect to the
object surface. Therefore, the projected a-axis aligns with the
Y-axis and the projected b-axis aligns with the X-axis. This can
facilitate prevention of degradation of the data accuracy of the
light amount differences A and B, and greatly improve the
measurement accuracy of the inclination of the object surface.
[0029] Further, since the rotary stage is preferably a magnetic
sphere as described above and the sphere is pulled toward the
corners by magnets while being held in the sphere holder, the
sphere can be held stable and angle compensation of the photodiode
light-receiving surface can be performed precisely.
[0030] Other purposes and features of the invention are described
in detail below based on the attached drawings.
BRIEF EXPLANATION OF THE DRAWINGS
[0031] FIG. 1 is an explanatory diagram of the inclination
detection device for implementing the angle compensation method of
this invention.
[0032] FIG. 2 is a diagram for explaining the principle of
inclination detection of the object surface by the known
optical-lever method.
[0033] FIG. 3 is a diagram showing the relationship between the X-
and Y-axes and the projected a-axis and projected b-axis when the
photodiode light-receiving surface is rotated about the c-axis.
[0034] FIG. 4 is a sketch showing the change in the irradiation
position on the photodiode light-receiving surface when the
photodiode light-receiving surface is rotated about the c-axis.
[0035] FIG. 5 is a diagram showing the line of intersection with
the photodiode light-receiving surface in the X-Y plane when the
photodiode light-receiving surface is rotated about the
Z1-axis.
[0036] FIG. 6 is a diagram showing the change in the position of
irradiation on the photodiode light-receiving surface when the
photodiode light-receiving surface is rotated about the
Z1-axis.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0037] The embodiments of the invention are explained below based
on the drawings.
[0038] FIG. 1 is an explanatory diagram of the inclination
detection device for implementing the angle compensation method of
this invention. In the figure, the inclination detection device
comprises a sphere C that is an example of a rotary stage, a
photodiode light-receiving surface D fixed to this sphere C, and an
object surface P, which is the X-Y plane.
[0039] The object surface P and photodiode light-receiving surface
D are disposed such that the reflected L1 resulting when the light
beam L is incident on the object surface P is received by the
photodiode light-receiving surface D. The photodiode
light-receiving surface D comprises the four light-receiving
surfaces D1, D2, D3 and D4 divided up by the a-axis and b-axis
which are perpendicular to each other, these light-receiving
surfaces D1, D2, D3 and D4 are connected to an arithmetic unit (not
shown in figure), and the amount of light detected by each of the
light-receiving surfaces D1, D2, D3 and D4 becomes an electric
signal that is input to the arithmetic unit. The arithmetic unit
uses the light amount signal to seek the light amount differences A
and B described above, and based on these light amount differences
A and B, the inclination (angle .gamma. and angle .delta.) of the
object surface P is sought.
[0040] This object surface P is mounted on an actuator 16 for
inclining the object surface P, and this actuator is configured
such that it can generate angles .gamma. and .delta.
independently.
[0041] The aforementioned sphere C is made from magnetic metal and
is housed in a sphere holder 10 having three walls 11, 12 and 13
intersecting each other. Magnets 15 are disposed in the corners 14
formed by the three walls 11, 12 and 13, and the sphere C housed in
this sphere holder 10 is pulled toward the corners 14 by the
magnets 15 and is held stationary by being in contact with the
three walls 11, 12 and 13.
[0042] The photodiode light-receiving surface D is fixed to the
sphere C as described above, in which case the c-axis, which passes
through the intersection Do of the a-axis and b-axis and is
perpendicular to the a-axis and b-axis, is disposed such that it
passes through the center Co of the sphere C, and the intersection
Do area is in contact with the sphere C and is fixed to the sphere
C by an adhesive, etc.
[0043] The sphere C has a k-axis. This k-axis is formed by linking
the contact point C1 between the sphere C and the wall 11, which
makes up the bottom surface of the sphere holder 10, and the center
Co of the sphere C and is parallel to the Z-axis (axis
perpendicular to the X-Y plane) of the object surface P.
[0044] In order to make the angle .alpha. (rotational shift of the
photodiode light-receiving surface D around the c-axis) zero in
this configuration, first the actuator on which the object surface
P is mounted is moved to incline the object surface P from the
prescribed position by only angle .delta.0 (or .gamma.0) with
respect to the angle .delta. (or .gamma.), and the change in the
light amount difference A (or B) is sought. Next, the sphere C is
rotated about the c-axis by only a small angle, and then the above
procedure is repeated in this condition to seek the light amount
difference A (or B). In this way, the sphere C is sequentially
rotated about the c-axis and the position of the photodiode
light-receiving surface D that yields the minimum light amount
difference A (or B) is sought. Further, when the light amount
difference A (or B) is minimized, the angle .alpha. is zero and any
rotational shift of the photodiode light-receiving surface around
the c-axis is minimized.
[0045] Following this, in order to make angle .beta. (rotational
shift of the photodiode light-receiving surface D about the k-axis)
zero, first the actuator on which the object surface P is mounted
is moved to incline the object surface P from the prescribed
position by a fixed angle .delta.0 (or .gamma.0) with respect to
the angle .delta. (or .delta..gamma.) and the change in the light
amount difference A (or B) is sought as in the case of the
adjustment of the angle .alpha. described above. Next, the sphere C
is rotated about the k-axis by only a small angle, and then the
above procedure is repeated in this condition to seek the light
amount difference A (or B). In this way, the sphere C is
sequentially rotated about the k-axis to seek the position of the
photodiode light-receiving surface D at which the light amount
difference A (or B) is smallest. Further, when the light amount
difference A (or B) has been minimized, the angle .beta. becomes
zero and the rotational shift of the photodiode light-receiving
surface D about the k-axis is eliminated.
[0046] Upon completion of adjustment of the angle .alpha. and angle
.beta., the projected a-axis agrees with the Y-axis and the
projected b-axis agrees with the X-axis.
[0047] The rotation of the aforementioned sphere C about the c-axis
and k-axis can be performed by means of an actuator, or a more
simple manual operation can be used.
[0048] The light-receiving surface can be fixed to a rotary
mechanism about the k-axis supported on a rotary mechanism about
the c-axis or to the rotary mechanism about the c-axis supported on
the rotary mechanism about the k-axis.
[0049] As described above, this invention comprises the above
configuration, and therefore the effects described below can be
expected.
[0050] That is, in this invention, the photodiode light-receiving
surface is fixed to a rotary stage and this rotary stage is rotated
about the c-axis and k-axis to eliminate any rotational shift of
the photodiode light-receiving surface with respect to the object
surface, and therefore the projected a-axis aligns with the Y-axis
and the projected b-axis aligns with the X-axis, thus making it
possible to prevent degradation of the data accuracy of the light
amount differences A and B due to interference. This makes it
possible to greatly improve the accuracy of measurement of the
inclination of the object surface in a contact type surface
roughness meter or scanning probe microscope (atomic force
microscope).
[0051] Further, since angle compensation of the photodiode
light-receiving surface is performed by rotating this sphere, angle
compensation can be performed accurately using a simple
configuration.
[0052] In addition, since the aforementioned sphere is held in a
sphere holder and is pulled toward the corners by magnets, the
sphere can be held in a stable condition, which also makes it
possible to perform accurate angle compensation of the photodiode
light-receiving surface.
* * * * *