Angle compensation method

Details Angle compensation method Angle compensation method

2000-12-29

2002-06-18

Tarcza, Thomas H. (Department: 3662)

Optics: measuring and testing

Angle measuring or angular axial alignment

Relative attitude indication along 3 axes with photodetection

C356S138000, C356S139100, C356S150000, C250S559300

Reexamination Certificate

active

06407806

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
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.
2. Description of the Prior Art
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.
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 L
1
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 D
1
, D
2
, D
3
and D
4
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.
When the object surface P is rotated about the Y-axis by angle &ggr;, the position of irradiation of the reflected light L
1
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 &dgr;, the position of irradiation of the reflected light L
1
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.
Here, when the object surface P is rotated up by angle &ggr; around the Y-axis by the actuator
16
and the center position of the irradiation of the reflected light L
1
moves from the irradiation position M
1
on one side toward the irradiation position M
2
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 &ggr; 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 D
2
and light-receiving surface D
3
) from the amount light received on the other side of the a-axis (amount of light received on light-receiving surface D
1
and light-receiving surface D
4
) is proportional to the angle &ggr; when the angle &ggr; is small, and therefore by detecting the light amount difference A, it is possible to seek the angle &ggr;.
Similarly, when the angle &dgr; is small, the angle &dgr; 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 D
3
and light-receiving surface D
4
) from the amount of light received on the other side of the b-axis (amount of light received on light-receiving surface D
1
and light-receiving surface D
2
).
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
.
Degradation of the data accuracy of the light amount differences A and B can occur in the following two modes:
(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.
(II) When the photodiode light-receiving surface D is rotated about the Z
1
-axis, assuming this Z
1
-axis is parallel to the Z-axis of the object surface and is positioned behind the photodiode light-receiving surface D.
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 &agr; with respect to the Y-axis. If the object plane P is inclined by angle &dgr; in this mode, the irradiation of the reflected light L
1
on the photodiode light-receiving surface D generates a locus on the Y-axis (axis inclined by angle &agr; 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 &ggr;, the irradiation of the reflected light L
1
on the photodiode light-receiving surface D generates a locus on the X-axis (axis inclined by angle &agr; from the b-axis) projected on the photodiode light-receiving surface D as shown in FIG.
4
.
Therefore, the light amount difference A on both sides of the a-axis is primarily proportional only to angle &ggr; and is therefore described by A=m·&ggr; (where, m is the compensation factor), but due to the occurrence of angle &agr; (rotational shift around the c-axis of the photodiode light-receiving surface D), it is now described by equation (1).
A=m
·(&ggr;·cos &agr;+&dgr;·sin &agr;)  Equation (1)
Further, the light amount difference B on both sides of the a-axis is primarily proportional only to angle &dgr; and is therefore described by B=n·&dgr; (where, n is the compensation factor), but due to the occurrence of angle &agr; (rotational shift around the c-axis of the photodiode light-receiving surface D), it is now described by equation (2).
B=n
·(&ggr;·cos &agr;+&dgr;·sin &agr;)  Equation (2)
In this way, the factor sin &agr; 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.
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 &bgr; with respect to the Z-axis. If the object plane P is inclined by angle &dgr; in this mode, the irradiation of the reflected light L
1
on the photodiode light-receiving surface D generates a locus on the Y-axis (axis inclined by angle &bgr; 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 &ggr;, the irradiation of the reflected light L
1
on the photodiode light-receiving surface D generates a locus on the X-axis (axis inclined by angle &bgr; from the b-axis) on the photodiode light-receiving surface D as shown in FIG.
6
.
Therefore, the light amount difference A is primarily proportional only to angle &ggr; and is therefore described by A=m·&ggr; (where, m is the compensation factor), but due to the occurrence of angle &bgr; (rotational shift around the Z
1
-axis of the photodiode light-receiving surface D), it is now described by equation (3).
A=m
·(&ggr;·cos &bgr;+&dgr;·sin &bgr;)  Equation (3)
Further, the light amount difference B is primarily p

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