JP2008209119A - Position determining device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a position determining device capable of accurately determining even the position of an measuring object causing back reflection and making the measurement difficult in a conventional method. <P>SOLUTION: The position determining device includes: an object lens opposed to a surface of an measuring object; a lighting unit for converging illumination light onto the above predetermined position through the object lens; a condenser lens disposed on an axis optically equivalent to an optical axis of the object lens and converging beams reflected by the measuring object and then passing through the object lens in a direction opposite to the illumination light; a light shielding plate for shielding a half of a rear focal plane by setting a straight line passing through an optical axis or the immediate vicinity of the same as the boundary on the rear focal plane of the condenser lens; and a photodetector disposed in the light traveling direction ahead of the light shielding plate and calculating the intensity center position from the distribution of intensity of the light having reached the same, wherein a midpoint light shielding plate is disposed in at least one position on the optical axis between the above object lens and the above light shielding plate to shield a center portion of the beams reaching the photodetector after passing through an area having the optical axis almost a symmetric axis. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a position determination device for determining the positional relationship between a transparent substrate and a device used in a device for processing, film forming, etc. on a transparent substrate such as glass, and this device is mainly automatic. It is used by being incorporated into a focusing device.

The configuration of a conventional position determination device and the principle of measurement will be described with reference to FIG. 1, FIG. 2, and FIG.
In FIG. 1, the objective lens 21 is held so that a predetermined position 15 at a predetermined distance from the apparatus is the object side focal point. The light emitted from the irradiation light source 25 is shaped to an appropriate divergence angle by the diaphragm 26 and the irradiation lens 27, then reflected by the beam splitter 23 as indicated by solid arrows 40a and 40b, and passed through the objective lens 21 to a predetermined position. A focal point, that is, an irradiation beam spot 42 is formed on 15. In this figure, in order to avoid complication, the position of the light beam is expressed with a slight shift, and the light beam transmitted through the beam splitter 23 is not shown.
When the measurement object surface 10a is at the predetermined position 15, the light beam reflected by the measurement object surface 10a passes through the objective lens 21 as indicated by the broken line arrow, passes through the beam splitter 23 as a parallel beam, and is a condensing lens. 22 connects the detector-side surface reflection spot 55 to the rear focal position, and reaches the beam center-of-gravity position detection type photodetector 24. Here, the beam reflected by the beam splitter 23 and the deviation of the light beam due to the refraction effect when passing through the beam splitter 23 are not shown because they are not necessary for the explanation of the principle. On the rear focal plane of the condensing lens 22, a light shielding plate 30 that shields the upper half from the optical axis 20 in the figure, a half plane having a straight line passing through the optical axis 20 as a boundary, is placed. The reflected light from the measurement object surface 10a is punctiform at the rear focal plane of the condenser lens 22 under this condition, that is, when the measurement object surface 10a is at the predetermined position 15, and is blocked by the light shielding plate 30. Therefore, the position of the center of gravity of the beam detected by the photodetector 24 coincides with the optical axis 20.

  Next, the case where the measurement target surface 10a is closer to the objective lens 21 than the predetermined position 15 will be described with reference to FIG. 2 (hereinafter, the near side, the side far from the objective lens 21 is abbreviated as the Far side). On the measurement object surface 10a, since the irradiation beam 40 is before focusing, it reflects in the direction approaching the optical axis 20, connects the irradiation beam spot 52 at a position closer to the objective lens 21 as indicated by a broken line, and the objective lens. 21 is incident. Based on the imaging principle of the lens, a light beam emitted from a position closer to the lens than the object-side focal position passes through the objective lens 21 and becomes divergent light, then passes through the beam splitter 23 and reaches the condenser lens 22. Also in this lens, based on the imaging principle, light from a finite distance is imaged farther from the image-side focal position, so the position of the detector-side surface reflection spot 55 is closer to the photodetector 24 than the light-shielding plate 30. Become. That is, the upper half of the beam is shielded on the light shielding plate 30. Accordingly, the portion of the beam that reaches the photodetector 24 is indicated by the shaded portion in the figure, and the center of gravity of the beam detected by the photodetector 24 becomes the center of gravity of the upper semicircle. When the measurement object surface 10a approaches the predetermined position 15 from the objective lens 21 side. Since the focal point of the condenser lens 22 approaches the light shielding plate 30 from the light detector 24 side, the detected beam center of gravity gradually approaches the optical axis 20 position, and the measurement object surface 10a reaches the predetermined position 15. The beam barycentric position coincides with the optical axis 20 position instantaneously.

The case where the measurement target surface 10a is far from the predetermined position 15 as viewed from the objective lens 21, that is, the case where it is on the Far side will be described with reference to FIG.
Under this condition, the irradiation beam 40 reaches the measurement object surface 10a in a state of being separated from the optical axis 20 after the focal point 42 is formed. Therefore, as shown by the dotted line in the figure, the light is reflected as if it came out from the surface reflection spot 52 far from the measurement object surface 10a when viewed from the objective lens 21. The reflected light 50 becomes a light beam converged by the objective lens 21 and reaches the condenser lens 22 through the beam splitter 23. Based on the imaging principle of the lens, the detector-side surface reflection spot 55 is connected to the inner side of the image-side focal position of the condenser lens 22. Since the light shielding plate 30 shields the upper half, the beam reaching the photodetector 24 is the lower half, and the detected beam center of gravity is the center of gravity of the lower half circle.

A calculation simulation example is shown in FIG. The measurement result depends on the focal length and positional relationship of the lens used.
In this example, the focal length of the objective lens 21 is 9 mm, the focal length of the condenser lens 22 is 14.55 mm, the distance between the objective lens 21 and the condenser lens 22 is 120 mm, and the diameter of the photodetector 24 is 12 mm. The horizontal axis indicates the amount of deviation of the measurement surface from the predetermined position 15 in mm units, and the minus indicates the objective lens 21 side, that is, the Near side from the predetermined position 15. The vertical axis represents the output of the light detector 24 and indicates the position of the center of gravity of the detected beam in mm.
In the graph curve, the position of the center of gravity of the beam is reversed at the predetermined position 15. For example, if the output of the photodetector 24 is positive, the distance between the object to be measured and the objective lens 21 is increased. If the output is stopped at a position where the output of N2 crosses 0 and becomes negative, automatic focusing becomes possible. This position determination method will be referred to as the Near-Far method here.

  As described above, only the reflection from the front surface has been described, but in the case of a transparent body, noise is generated because the transmitted light is reflected from the back surface together with the reflection from the front surface. For example, when the object to be measured is a glass plate, the reflectance of the surface is approximately 3%, so that most of the beam is transmitted through the surface, and the beam is also reflected with a reflectance of approximately 3% on the back surface. Is reflected. This reflected beam goes from the inside of the glass to the surface, where about 3% is reflected again. Accordingly, a beam of about 0.97 × 0.03 × 0.97 of the incident beam is superimposed on the original front surface reflected beam 50 as a back surface reflected beam.

Fig. 5 shows an example of a calculation simulation on a glass substrate having a reflectance of 3%, a thickness of 0.7 mm, and a refractive index of 1.5. The position (curve only) of the spot formed by the condenser lens 22 from the light shielding plate 30 is plotted on the right scale, and the used lens and its positional relationship are the same as in the case of FIG.
The center of gravity of the surface reflected beam represented by a white circle abruptly reverses the position of the center of gravity of the beam at a predetermined position (reference numeral 15 in FIG. 3), whereas the back reflected beam represented by a black circle is 3/4 right of the horizontal axis. The center of gravity of the beam is always located on the plus side near the optical axis 20 in the region. Looking at the barycentric position of the two reflected beams represented by the black squares, there are a wide range of conditions for obtaining the same barycentric position on both sides of the predetermined position 15, so whether or not it is far from the predetermined position 15 is scanned over a wide range. It cannot be judged unless it is from. Further, since the rate of change in the vicinity of the predetermined position 15 is small, it is not possible to expect a highly accurate displacement detection.

  As can be seen from this example, the conventional Near-Far position determination device or the automatic focusing device using it can be operated effectively when the reflection from the back surface cannot be ignored due to the transparency of glass or the like. could not. An object of the present invention is to obtain a position determination device capable of determining a position with high accuracy even for a measurement target in which back surface reflection occurs, which is difficult to measure by the conventional method.

The present invention has been made to overcome the above-mentioned drawbacks of the conventional Near-Far method.
In order to clarify the behavior of the back-surface reflected beam, it is necessary to know the optical behavior of the reflected beam.
In FIG. 5, the spot position of the surface reflected beam 50 changes from positive to negative with δf = 0 as a boundary (δf is the distance between the predetermined position 15 and the measurement object surface 10a).
Here, since both δf and the spot position are positive in the direction farther than the position when δf = 0 when viewed from the lens, when δf is on the negative side, that is, the Near side, a state where the focal point is not originally reached, That is, the spot position formed by the condenser lens 22 is in the positive direction, and is closer to the photodetector 24 than the light shielding plate 30.
Therefore, the detected beam center of gravity is the center of gravity of the upper semicircle in FIG. In FIG. 5, this corresponds to the plus side of the beam center position. When δf passes through 0 and goes to the Far side, it is in a state where the focal point is originally passed, so that the detected beam center of gravity is on the opposite side of the light-shielding plate 30 of the photodetector 24, that is, the lower half circle in FIG. Moving. On the other hand, the back-surface reflected beam has a positive spot position by the condenser lens 22 on the right side of the boundary around δf = −0.13. Since the distance between the light detector 24 and the light shielding plate 30 is generally at least 10 to 20 mm or more, the spot position is between the light shielding plate 30 and the light detector 24 in the region 3/4 to the right of the graph.

An optical path diagram in the vicinity of δf = 0.1 is shown in FIG. Since the measurement object surface 10 a is slightly on the Far side, the surface reflected beam 50 is slightly converged by the objective lens 21, and the light-detector side surface reflected spot 55 is formed slightly before the light shielding plate 30 by the condenser lens 22. tie. Accordingly, the upper half of the surface reflected beam 50 reaching the photodetector 24 is shielded, and the detected beam center is the center of gravity of the lower semicircle.
On the other hand, since the back surface reflection spot 62 due to the measurement object back surface 10b is far from the predetermined position 15, the back surface reflection beam 60 is temporarily connected to the intermediate back surface reflection spot 64 before the condenser lens 22 by the objective lens 21. The condenser lens 22 connects a photodetector-side back surface reflection spot 65 between the light shielding plate 30 and the photodetector 24. That is, the lower half of the back-surface reflected beam that reaches the photodetector 24 is shielded, and the detected beam center is the center of gravity of the upper half circle. Although the center of gravity is close to the optical axis 20, the beam intensity is high because the light is focused.

The barycentric position of the beam detected by the photodetector 24 is obtained as a correlation value between the barycentric position and the beam intensity of each of the front surface reflected beam and the back surface reflected beam. That is,
Beam center of gravity position = (surface reflection beam center of gravity position x surface reflection beam intensity + back surface reflection beam gravity center position x back surface reflection beam intensity) / (surface reflection beam intensity + back surface reflection beam intensity)
Therefore, the center of the beam including the front and back reflection beams is greatly shifted upward. This is why the beam center of gravity of the front and back reflection beams is shifted to the + side from the center to the right side of FIG.

と表される。
一方入射ビーム４１の表面入射位置ｈinは幾何学的に

と表される。
ここで、δfは所定位置１５からのずれで、対物レンズ２１から離れる方向すなわちFar側を正としている。表面反射点５１で計測対象物内部に進んだ光束は、裏面の裏面反射点６１で透過成分と反射成分に分かれるが、ここで問題にしている裏面反射ビームは裏面反射点６１で反射した後表面の表面射出点６３に至ってここで透過して、図７中裏面反射ビーム６０のごとく進む成分である。この光束は、図中に破線で示したように、光軸２０上の裏面反射スポット６２を光源をして発散するかのように進む。計測対象物表面１０ａから測った裏面反射スポット６２の位置δsは、光軸２０から測った表面射出点６３の位置houtを用いて

と表すことができる。表面反射点５１と表面射出点６３の間の距離は

であるから、δsは所定位置１５からのずれδf、屈折率ｎ、計測対象物の厚さtおよび入射角a_iを用いて

と表される。 FIG. 7 is a schematic diagram when the irradiation beam 40 is incident on the measurement object 10.
A point 42 on the optical axis 20 is a position where the irradiation beam 40 is focused, and this is an intersection of the predetermined position 15 where the measurement target surface 10a should be originally positioned and the optical axis 20. Actually, the irradiation beam 40 converges toward the irradiation beam spot 42, but only the irradiation beam 41 incident at an angle αi is shown for simplicity of the drawing.
It is assumed that the thickness of the measurement object is t, and the surface thereof is in the distance δf from the predetermined position 15 when viewed from the objective lens 21. The irradiation beam is once focused at the irradiation beam spot 42, and then becomes a divergent light, and irradiates a circular area centering on the intersection with the optical axis 20 on the measurement object surface 10 a. The position of the incident beam 41 on the measurement object surface 10 a is a surface reflection point 51 at a distance of “hin” from the optical axis 20, and approximately 3% of the beam is reflected and proceeds like a reflected beam 50. About 97% of the incident beam 41 travels into the measurement object. At this time, if the refractive index of the measurement object is n, the refraction angle αr is determined by Snell's law.

It is expressed.
On the other hand, the surface incident position hin of the incident beam 41 is geometrically

It is expressed.
Here, δf is a deviation from the predetermined position 15, and the direction away from the objective lens 21, that is, the Far side is positive. The light beam that has traveled to the inside of the measurement object at the front surface reflection point 51 is divided into a transmission component and a reflection component at the back surface reflection point 61 on the back surface. This is a component that reaches the front surface emission point 63 and passes there and travels like a back surface reflected beam 60 in FIG. As indicated by a broken line in the figure, this light beam travels as if it diverges using the back surface reflection spot 62 on the optical axis 20 as a light source. The position δs of the back surface reflection spot 62 measured from the measurement target surface 10 a is used by using the position hout of the surface emission point 63 measured from the optical axis 20.

It can be expressed as. The distance between the surface reflection point 51 and the surface emission point 63 is

Therefore, δs is obtained by using the deviation δf from the predetermined position 15, the refractive index n, the thickness t of the measurement object, and the incident angle a _i.

It is expressed.

    FIG. 8 is a graph showing the relationship between the position δf of the back surface reflection spot 62 and the deviation δf of the measurement target surface 10a from the predetermined position 15 when the measurement object is 0.5 mm and the focal length of the objective lens 21 is 9 mm. As can be seen, in the region where the absolute value of δf is small, the position of the back surface reflection spot 62, which is the virtual light source of the back surface reflected beam 60, is far from the original measurement target surface when viewed from the objective lens 21, and the irradiation beam The rear surface reflection spot 62 with a component having a large incident angle out of 40 is closer to the surface to be measured. This indicates that the irradiation beam component having a large incident angle is more difficult to distinguish from the surface reflection beam. That is, it can be seen that the irradiation light component having a large incident angle plays a large role as an impediment to the high-accuracy measurement described in FIG.

From these results,
1. The back-surface reflected beam 60 is converged by the objective lens 21 so as to be larger than the surface-reflected beam 50 from the original measurement target surface. Therefore, by providing an intermediate light shielding plate on the rear optical axis 20 of the objective lens 21 that blocks light near the center. The influence of the back surface reflected beam 60 can be reduced (claims 1 to 5).
2. By limiting the component having a large angle of the reflected light from the measurement object 10 incident on the objective lens 21, the influence of the back surface reflected beam 60 can be reduced (Claims 6 and 7).
Two points of knowledge can be obtained.

  The present invention is an apparatus for determining whether the position of a measurement object is within a predetermined position range, an objective lens whose optical axis is held substantially perpendicular to the surface of the measurement object, and the objective lens An illuminating device that irradiates illumination light that is condensed at the predetermined position through, and an object that is installed on an optically equivalent axis to the optical axis of the objective lens and is reflected by the measurement object to reverse the objective lens to the illumination light A condensing lens that condenses the light beam transmitted through the light-shielding plate, a light-shielding plate that shields approximately half of the back focal plane on the back focal plane of the condensing lens, with a straight line passing on or near the optical axis as a boundary; A photodetector that calculates the intensity center position (beam centroid position) from the distribution of light that is placed in the light traveling direction of the light shielding plate and has reached, and the perspective of the position of the measurement object relative to a predetermined position from the output of the photodetector And a position determination device for determining the objective lens Constituting as having an intermediate light shielding plate for shielding a portion of the intermediate light flux reaching the region of the optical axis substantially symmetrical axis as the optical detector in at least one location on the optical axis and the light shielding plate and.

The intermediate light shielding plate is intended to shield a beam that becomes noise when determining a deviation between a position of a measurement object and a predetermined position based on a barycentric position of the beam. Therefore, the shape, size, position, and number can be appropriately determined within a range in which this object can be achieved.
For example, the intermediate light shielding plate is a disk having a diameter smaller than the diameter of the beam, and the center is substantially aligned with the optical axis (Claim 2), or the intermediate shielding plate has a short side shorter than the beam diameter. There is a mode in which the rectangular shape is installed such that its longitudinal direction is substantially parallel to the shielding boundary of the light shielding plate and the center between both long sides is substantially coincident with the optical axis (Claim 3).

The position of the intermediate light shielding plate is preferably a position away from the objective lens by at least 8 times the focal length of the objective lens.
The size of the intermediate light shielding plate is such that the maximum width in the direction perpendicular to the shielding boundary by the light shielding plate is within the range of 1/20 or more and 1/4 or less of the effective diameter of the objective lens or the irradiation beam diameter at the objective lens main surface position. (Claim 5).

In addition to the intermediate light shielding plate, it is also effective to limit the incident angle of the back surface reflected light incident on the objective lens. As a technique, an aperture stop (hereinafter referred to as “objective aperture”) that shields at least a part of the incident light component passing through the outer edge of the objective lens at a position where the effective lens diameter on the measurement object side of the objective lens or inside the objective lens can be determined. It is conceivable to provide a “lens aperture”. As a specific mode of this objective lens stop, a stop having a circular opening substantially centered on the optical axis (Claim 6), the optical axis substantially centered, and the long side of the opening is substantially parallel to the light shielding boundary of the light shielding plate. There is a diaphragm having a rectangular opening such as (Claim 7).
It is preferable to detect the deviation of the measurement object from the predetermined position based on the data measured as described above, and to change the position of the measurement object in conjunction with a known drive mechanism ( Claim 8).

In FIG. 9, one circular intermediate light shielding plate having a radius of 0.5 mm is mounted at a position of 70 mm to 120 mm from the main surface of the objective lens 21 toward the condenser lens 22 so that the center of the circle coincides with the optical axis 20. This is a result of computer simulation of the output of the photodetector 24 when it is turned on. The focal length of the objective lens is 9 mm as in FIGS. Further, the state where the light shielding plate is not inserted is represented by only a solid line.
As shown in this figure, when an intermediate light shielding plate is inserted at a position 90 mm behind the objective lens, the output value range of the photodetector can be separated on both sides of δf = 0. That is, if the position of the detected beam center of gravity (the total value of the front surface reflected beam and the back surface reflected beam) is on the + side from −0.9 mm, it is determined to be the Near side; it can. This is because the intermediate light-shielding plate is placed in the vicinity of the intermediate back surface reflection spot 64 in FIG. 6, and the intensity of the back surface reflection beam is relatively reduced due to the difference in the beam diameter between the front and back surface reflection beams. This is because the ratio of the centroid position of the surface reflected beam 50 to the centroid of the beam detected by 24 has increased.
When the intermediate light shielding plate is located 70 mm behind the objective lens, the back-surface reflected beam in the vicinity of δf = 0 cannot be shielded, so that Far-Near separation cannot be performed. In addition, when the intermediate light shielding plate is at a position of 100 mm or more behind the objective lens, the intermediate light shielding plate functions more on the near side, so that a sufficient shielding effect cannot be obtained on the far side.

The effect of the intermediate shading plate depends on the focal length of the objective lens, the numerical aperture of the objective lens, the thickness of the measurement object, the refractive index, and the size of the intermediate shading plate. It is difficult to determine uniquely. FIG. 10 shows the result of computer simulation when the focal length of the objective lens is 10 mm under the same conditions as in FIG.
In FIG. 9, at the position of 90 mm where the intermediate light shielding plate is effectively acting, there is no effect near δf = 0, and the back surface reflected beam is blocked after the position δf = 0.09 mm on the surface of the measurement object. From this graph, it can be seen that the back-surface reflected beam cannot be removed over the entire area of the surface of the measurement object regardless of the position of the intermediate light shielding plate.
On the other hand, when the intermediate light shielding plate is at a position of 110 mm, a sufficient back surface reflected beam removal effect cannot be obtained after δf = 0.13 mm, but δf = not removed when the intermediate light shielding plate is at a position of 90 mm. The back surface reflected beam can be removed in the range of -0.05 to +0.13. This indicates that two or more intermediate light shielding plates may be loaded at different positions, and each intermediate light shielding plate should be responsible for removing the back surface reflected beam according to the position range of the surface to be measured. ing.
Particularly problematic is that the position of the center of gravity of the beam on the Far side is raised to the + side due to the influence of the back-surface reflected beam, and therefore the back surface that causes the Far-side curve to be pulled up in the region to be lowered. The reflected beam may be shielded by sharing it with two or more intermediate light shielding plates.
In the example of FIG. 10, the right half of the graph is a combination in which the lifting of the curves does not overlap, that is, an intermediate light shielding plate having a radius of 0.5 mm, one at 80 mm or 90 mm and 110 mm, or 100 mm and 120 mm. 1 at a time, the output values of the photodetector are separated on both sides of δf = 0. As a result, it is possible to determine that the beam center of gravity determination position by the photodetector is near side if it is −0.18 mm or more, and the far side if it is −0.24 mm or less.

As a result of examining various conditions by computer simulation, the inventors have found that the position of the intermediate light-shielding plate is appropriate to be at least eight times the focal length of the objective lens behind the objective lens. This range holds for each intermediate light shielding plate even when there are a plurality of intermediate light shielding plates.
As for the size, the effect is higher as it is larger in the direction perpendicular to the light shielding boundary of the light shielding plate, but there is a limit because the influence of shielding the surface reflected beam that is originally the object of measurement becomes larger.

  FIG. 11 is a graph showing the change of the center of gravity of the beam when the radius of the intermediate light shielding plate is changed from 0.2 mm to 1.2 mm. The focal length of the objective lens is 9 mm, the numerical aperture is 0.5, and the objective lens. The distance from the intermediate light-shielding plate was fixed at 90 mm, which gave the desired result in FIG. The irradiation beam radius on the main surface of the objective lens was 6 mm. From this result, when the radius is 0.2 mm, the displacement δf from the predetermined position works effectively only in the range of 0 to 0.8, but when the radius of the intermediate light shielding plate is other than that, it is intermediate over the entire horizontal axis. The effect of the light shielding plate is recognized.

FIG. 12 shows the results of calculating the amounts of the front surface reflected beam and the back surface reflected beam that reach the photodetector when the radius of the intermediate light shielding plate is changed by computer simulation. The distance from the objective lens to the intermediate light shielding plate was 90 mm, the irradiation beam radius was 6 mm, and the radius of the intermediate light shielding plate was changed from 0.25 mm to 1.5 mm. The vertical axis represents the amount of beam reaching the photodetector, and the amount of beam when there is no intermediate light shielding plate is 1. The horizontal axis is the deviation δf from the predetermined position 15. Each curve represents that as the curve goes down, the amount blocked by the intermediate light shielding plate increases.
When the intermediate light shielding plate radius is 0.25 mm, the back-surface reflected beam is greatly reduced in the range of δf = 0 to 0.12 mm, which corresponds to the result of FIG. On the other hand, when the amount of the surface reflected beam when the radius of the intermediate light shielding plate is 1.5 mm is 0, it is 0 in the range of δf = −0.2 to −0.03 mm. That is, it means that the surface reflected beam, which is the original signal, is blocked by the intermediate light shielding plate in this range. Even when the radius of the intermediate light shielding plate is 1.25 mm, 90% of the surface reflected beam is blocked at δf = −0.2 mm.
From these results, it can be seen that, under this optical condition, the radius of the intermediate light shielding plate must be about 0.3 mm or more and about 1.2 mm or less with respect to the irradiation beam radius of 6 mm. This value varies depending on the optical conditions, but as a result of simulation under various conditions, the radius of the intermediate shading plate is 1/20 or more and 1/4 or less of the diameter of the reflected beam and back-surface reflected beam captured by the objective lens. As a result, it was found that the shielding effect of the back surface reflected beam can be obtained and the amount of the surface reflected beam necessary for detection can be secured.

According to this invention, at least a part of the light reflected on the back surface of the measurement object can be shielded by the intermediate shielding plate. Further, by using the intermediate shielding plate together with the objective lens stop for limiting the angle of the reflected light incident on the objective lens described above, it is possible to shield more back surface reflected light. As a result, the noise of the light beam passing through the light shielding plate is reduced, and even if the measurement object is translucent like glass, it is possible to determine whether the measurement object is on the near side or the far side. It can be detected accurately.
In addition, an application example in which an image of the surface of the measurement object is observed simultaneously is also conceivable. In this case, it is necessary to divide the wavelength range (generally visible light) between the light reaching the photodetector and the light reaching the image observation imaging device. In image observation, if the angle incident on the objective lens is limited, the resolution decreases. Therefore, if a material that transmits light for image observation and does not transmit light for position measurement is used, both high-accuracy position determination and high-resolution image observation are compatible.

  Embodiments of the present invention will be described below.

An embodiment of the present invention will be described below with reference to FIG.
In this case, a circular intermediate light shielding plate 31 having the optical axis 20 as the center is inserted between the objective lens 21 and the condenser lens 22 (between the beam splitter 23 and the condenser lens 22). In this figure, since the measurement object surface 10 a is slightly far from the predetermined position 15, the surface reflected beam is slightly converged by the objective lens 21 and enters the condenser lens 22. The detector-side surface reflection spot 55 formed by the condenser lens 22 is located closer to the condenser lens 22 than the position of the light shielding plate 30 that is the rear focal position. Therefore, the upper beam in the figure is blocked by the light shielding plate, and the center of gravity of the beam becomes the center of gravity of the lower semicircular beam.

Since the position of the back surface reflection spot 62 is on the Far side with respect to the front surface reflection spot 52, it converges more quickly by the objective lens 21 and is focused toward the intermediate back surface reflection spot 64. The intermediate light shielding plate 31 is positioned in front of the intermediate back surface reflection spot 64, and all or most of the back surface reflected beam 60 is blocked by the intermediate shielding plate 31 and does not reach the photodetector 24. For this reason, the back-surface reflected beam that causes measurement damage is effectively removed, and highly accurate position determination is possible.
Although only one example of the distance between the measurement object 10 and the objective lens 21 is illustrated, the back surface reflected beam 60 can be shielded in a wide range of Near-Far.

  FIG. 14 shows actual experimental data obtained by this configuration. Compared with the results shown in FIG. 10, the tendency of the presence or absence of the intermediate light shielding plate is very well matched, and it can be seen that the intermediate light shielding plate acts effectively.

FIG. 15 shows a second embodiment of the present invention, in which a first intermediate light shielding plate 31a and a second intermediate light shielding plate 31b are provided behind the objective lens 21 (between the beam splitter 23 and the condenser lens 22). Is. The front surface reflected beam 50a and the back surface reflected beam 60a represent the front surface reflected beam and the back surface reflected beam on the Far side, respectively. The front surface reflected beam 50b and the back surface reflected beam 60b represent the front surface reflected beam and the back surface reflected beam on the Near side, respectively. The parts that do not directly affect the explanation, such as the measurement object surface 10a, the measurement object back surface 10b, the front surface reflection spot 42, and the back surface reflection spot 62, are shown only in the Far side in order to avoid complication.
The surface-reflected beam 50 a on the Far side is slightly converged by the objective lens 21 and enters the condenser lens 22, and a detector-side surface reflection spot 55 a is formed in front of the light shielding plate 30 by the condenser lens 22. On the other hand, since the position of the back surface reflection spot 62 is on the Far side with respect to the front surface reflection spot 52, it converges more quickly by the objective lens 21 and is largely blocked by the intermediate light shielding plate 31a. Therefore, most of the back surface reflected beam 60a does not reach the photodetector 24. However, since the beam diameter of the surface reflected beam 50a at the position of the intermediate light shielding plate 31a is several times larger than the diameter of the intermediate light shielding plate 31a, the intensity of the surface reflected beam 50a is hardly lowered. Therefore, the center of gravity of the beam detected by the photodetector 24 is on the lower side, and it can be determined that the measurement object is on the Far side.

On the other hand, the surface-reflected beam 50 b on the Near side is slightly diverged by the objective lens 21 and enters the condenser lens 22, and a detector-side surface reflection spot 55 b is formed in the back of the light shielding plate 30 by the condenser lens 22. On the other hand, the back surface reflected beam 60b is converged earlier by the objective lens 21 than the front surface reflected beam 50b. However, since the degree of convergence is smaller than that at the Far side, the intermediate light shielding plate 31a still has a large diameter and cannot be sufficiently removed by the intermediate light shielding plate 31a.
Therefore, the back surface reflected beam 60b is removed by providing the second intermediate light shielding plate 31b closer to the condenser lens 22 than the intermediate light shielding plate 31a. Also here, since the beam diameters of the surface reflected beam 50b at the positions of the intermediate light shielding plate 31a and the intermediate light shielding plate 31b are several times larger than the diameters of the intermediate light shielding plate 31a and the intermediate light shielding plate 31b, the decrease in the intensity of the surface reflected beam 50b is small. . Therefore, the position of the center of gravity of the beam detected by the photodetector 24 is on the upper side, and it can be determined that the measurement object is on the Near side (see FIG. 16).

FIG. 17 shows a third embodiment of the present invention.
This is an example of another form of the intermediate shielding plate 31 in FIG. The intermediate light shielding plate 31 inserted between the objective lens 21 and the condenser lens 22 is not circular, the longitudinal direction is substantially parallel to the light shielding boundary of the light shielding plate 30, and the length in the direction perpendicular to the light shielding boundary is the objective lens 21. It is characterized by having a rectangle that is 1/20 or more and 1/4 or less of the diameter determined by the numerical aperture. Since the overall configuration is the same as that in FIG. 13, a view of the intermediate light shielding plate 31 viewed in the light traveling direction is shown.
In the figure, the hatched rectangular portion is the light shielding plate 30, and only the outer edge of the front surface reflected beam 50, the outer edge of the back surface reflected beam 60, and the rectangular intermediate light shielding plate 31 are drawn. As can be seen from this figure, since the ratio of the area where the back surface reflected beam 60 is blocked is much larger than the ratio of the area where the surface reflecting beam 50 is blocked, the back surface reflected beam 60 is effectively removed. And most of the surface reflected beam remains.
Compared with a circular intermediate light shielding plate, there is a disadvantage that the influence of shielding the surface reflection beam 50 is somewhat large, but it is easy to manufacture and is easy to install in the optical system. In the case of a circular intermediate shading plate, the shape of the beam in the photodetector is a semicircle lacking the central portion, whereas in the case of a rectangular shape, the shape of the band-like portion passing through the center of the circle is missing. The upper or lower half. For this reason, the rectangular intermediate light shielding plate lacks a wide portion close to the center. Therefore, the rectangular shape has an advantage that the separation of the center of gravity position above and below the beam becomes clearer than the semicircular shape.
The intermediate shielding plate of this form can be used without being limited to the configuration of FIG.

FIG. 18 shows a fourth embodiment of the present invention. This is because, in addition to the first embodiment in which the intermediate light shielding plate 31 is provided between the objective lens 211 and the condenser lens 22, the objective lens of the beam reflected from the front and back surfaces of the measurement object on the front surface of the objective lens 21. In order to limit the capture angle with respect to 21, a circular aperture stop 32 (objective lens stop) is provided in front of the objective lens 21.
In FIG. 10, the output range of the photodetector 24 cannot be separated on the Near side and the Far side with δf = 0 as a boundary with one intermediate light shielding plate 31. The numerical aperture (NA) of the objective lens 21 at this time was 0.5, but in this embodiment, the numerical aperture is limited to about 0.3 by the objective lens stop 32, and other conditions are the same.
As a result, Near-Far separation can be performed with one intermediate light shielding plate 31 in a wide range of the position of the intermediate light shielding plate 31 from 85 mm to 105 mm. A feature of the effect obtained by limiting the numerical aperture is that the influence of the output of the photodetector 24 being drawn toward the + side close to the optical axis is reduced over the entire range of Δf. As described with reference to FIG. 7, this is because the largest impediment to the measurement is that the component having a large incident angle of the irradiation beam 40 is reflected from the back surface, but this is removed by the circular aperture stop (FIG. 19). reference).
Needless to say, the aperture of the objective lens can be made variable.

  As described above, according to the present invention, in the transparent measurement object with back reflection, one or more intermediate light-shielding plates or back-reflection beams that cause measurement damage are inserted behind the objective lens. By using a circular aperture stop that restricts the angle of the beam that is reflected from the back of the object to be measured and incident on the objective lens, or both of them, it is possible to effectively remove the influence of the back surface reflected beam. Can be determined with high accuracy.

It is a schematic diagram for demonstrating the determination principle of the conventional Near-Far type position determination apparatus. FIG. 10 is a second schematic diagram for explaining a determination principle of a conventional Near-Far type position determination device. FIG. 10 is a third schematic diagram for explaining a determination principle of a conventional Near-Far type position determination device. It is a graph which shows the example without a problem of the measurement result of the conventional Near-Far type position determination apparatus. It is a graph which shows the example which cannot measure with the conventional Near-Far type | mold position determination apparatus. It is a figure which shows the course of the beam containing the back surface reflected beam in the conventional Near-Far type position determination apparatus. It is a figure explaining the front and back surface reflection in the measuring object of transparency in detail. It is a figure which shows that the reflected spot position by back surface reflection is dependent on the incident angle of an irradiation beam, and a component with a large incident angle has a big bad influence. It is a graph of the simulation result which shows that a back surface reflected beam can be removed effectively by inserting an intermediate | middle light-shielding plate, and a position determination is attained. It is a graph of the simulation result which shows that a back surface reflected beam can be effectively removed for every range of distance with a measuring object with a plurality of intermediate shading plates, and a position can be determined. It is a graph of the simulation result which shows the relationship between the radius of an intermediate | middle light-shielding plate, and a beam gravity center. It is a graph of the simulation result which shows the relationship between the radius of an intermediate shielding board, and beam intensity. FIG. 2 is a schematic diagram of a most basic example of a position determination device in which an intermediate light shielding plate 31 is inserted between an objective lens 21 and a condenser lens 22; It is a graph of the measurement data obtained by the basic Example of this invention. FIG. 4 is a schematic diagram of a second embodiment of the present invention in which first and second intermediate light shielding plates 31a and 31b are inserted between the objective lens 21 and the condenser lens 22. It is a graph of the simulation result which shows the beam gravity center position at the time of combining two intermediate | middle light shielding plates. This is a third embodiment of the present invention in which the shape of the intermediate light shielding plate is rectangular. Schematic diagram of the fourth embodiment of the present invention, in which an intermediate light shielding plate 31 is inserted between the objective lens 21 and the condenser lens 22, and a stop having a circular opening is provided at the object side incident portion of the objective lens. It is a graph of the simulation result which shows the change of the beam gravity center in a 4th Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Measurement object 10a Measurement object surface 10b Measurement object back surface 15 Predetermined position 20 Optical axis 21 Objective lens 22 Condensing lens 23 Beam splitter 24 Photo detector 25 Irradiation light source 26 Diaphragm 27 Irradiation lens 30 Light shielding plate 31 Intermediate light shielding plate 31a Intermediate light shielding plate 31b Intermediate light shielding plate 32 Objective lens stop 40 Irradiation beam 40a Irradiation beam 40b Irradiation beam 41 Irradiation beam spot 50 Irradiation beam spot 50a Surface reflection beam 50b Surface reflection beam 50b Surface reflection beam 51 Surface reflection spot 52 Surface reflection spot 55 Detector Side surface reflection spot 55a Detector side surface reflection spot 55b Detector side surface reflection spot 60 Back surface reflection beam 60a Back surface reflection beam 60b Back surface reflection beam 61 Back surface reflection point 62 Back surface reflection spot 63 Surface exit point 64 Intermediate back surface reflection spot 65 Vessel side back reflection spot

Claims (8)

An apparatus for determining whether the position of a measurement object is within a predetermined position range, an objective lens whose optical axis is held substantially perpendicular to the surface of the measurement object, and illumination light through the objective lens An illuminating device that collects light at the predetermined position, and a beam that is installed on an optically equivalent axis to the objective lens optical axis and is reflected by the measurement object and further passes through the objective lens in the direction opposite to the illumination light. A condensing lens, a light shielding plate that shields half of the back focal plane with a straight line passing on or near the optical axis on the rear focal plane of the condensing lens, and a light traveling direction of the light shielding plate. And a photodetector for calculating an intensity center position from the distribution of the intensity of the light that has arrived, wherein the optical axis is substantially at least at one place on the optical axis between the objective lens and the light shielding plate. To the photodetector through the region of symmetry A position determination device having an intermediate light shielding plate that shields a central portion of a beam that reaches. 2. The position determination device according to claim 1, wherein at least one of the intermediate light shielding plates has a circular shape whose optical axis substantially coincides with the symmetry axis and whose diameter is smaller than the diameter of the beam. A rectangle in which at least one of the intermediate light shielding plates is placed so that its longitudinal direction is substantially parallel to the shielding boundary of the light shielding plate, the optical axis substantially coincides with the symmetry axis, and the short side is shorter than the beam diameter. The position determination apparatus according to claim 1, wherein the position determination apparatus is a position determination apparatus. The position determination device according to any one of claims 1 to 3, wherein the position of the intermediate light shielding plate is at least eight times the focal length of the objective lens from the objective lens. The maximum width of the intermediate light shielding plate in the direction perpendicular to the light shielding plate shielding boundary is within the range of 1/20 or more and 1/4 or less of the effective diameter of the objective lens or the irradiation beam diameter at the objective lens main surface position. The position determination apparatus according to any one of claims 1 to 4. A stop having a circular aperture substantially centered on the optical axis is provided on the measurement object side of the objective lens, and the periphery of the aperture of the stop is a material that shields light in the wavelength region that reaches the photodetector. The position determination device according to claim 1. Provided on the object side of the objective lens is a stop having a rectangular opening with the optical axis substantially in the center and the long side of the opening being substantially parallel to the light-shielding boundary of the light-shielding plate. The position determination device according to any one of claims 1 to 6, wherein the position determination device is a material that blocks light in a wavelength range that reaches the photodetector. The position determination apparatus according to claim 1, further comprising a drive mechanism that changes a relative positional relationship with the measurement object in accordance with a determination result of the position determination apparatus.

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