JP3810027B2 - Object positioning device for optical wave interference device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a subject positioning device for a light wave interference device, and in particular, when measuring the surface shape of a thin plate-like subject surface using light having a short coherence distance, the subject surface can be interfered with. The present invention relates to a subject positioning device of a light wave interference device used for positioning within a range.
[0002]
[Prior art]
For example, in a Michelson type interferometer, coherent parallel light is divided into reference light and test light by a light splitting means, and these reference light and test light are respectively divided into a reference surface and a test surface. After reflecting and recombining with the light splitting means, an interference fringe is formed on the observation surface. By observing the interference fringe, the uneven shape of the test surface can be evaluated. It has become.
[0003]
By the way, when a laser interferometer is used as the interferometer, it is not necessary to accurately set the position of the test surface with respect to the reference surface because the interference distance of the laser light is long. In the case of a transparent thin plate, the reflected light from the back surface of the subject also interferes with the reflected light from the test surface and the reflected light from the reference surface, and interference fringes of noise components are formed on the original interference fringes. It will be superimposed.
[0004]
For this reason, conventionally, when measuring thin glass using a laser interferometer, it has been necessary to take measures such as applying a refractive index matching oil to the back surface that generates ghosts.
[0005]
[Problems to be solved by the invention]
However, taking such measures requires a great deal of labor, and there is a problem of contaminating the subject.
In addition, when the thickness of the specimen is extremely thin, if the matching oil or the like is applied to the back surface, the specimen may be distorted due to the effect of the surface tension, and an accurate measurement of the specimen surface may occur. .
[0006]
Therefore, when measuring the surface shape of thin glass or the like, light having a short coherence distance (light having a coherence distance shorter than twice the thickness t of the subject) is used as measurement light, and only the test surface is interfered. It is conceivable to set it within a possible range.
[0007]
However, in the above prior art, if the coherence distance of light from the light source is SCL, the possible interference range L in which the test surface is to be disposed is L <SCL / 2. For example, when a light source such as a red light emitting diode (LED) having a coherence distance of about 30 μm is used, the possible interference range L is shorter than 15 μm.
[0008]
If the test surface of the subject is not positioned within such a narrow range, interference fringes indicating the relative shape with the reference plate cannot be generated.
Further, at that time, the position of the test surface of the subject changes depending on the thickness of the subject or the subject unit in which the subject is incorporated, and positioning corresponding to this is necessary.
[0009]
In view of the above circumstances, the present invention is a light wave interferometer using light with a short coherence distance, and the object positioning of the light wave interferometer that can easily position the test surface within the interference possible range with a simple configuration. The object is to provide an apparatus.
[0010]
[Means for Solving the Problems]
In order to achieve such an object, the subject positioning device of the light wave interference device of the present invention divides the light from the light source into two systems, one on the subject's subject surface and the other on the reference surface. In the light wave interference device for irradiating, observing interference fringes caused by interference between the test light from the test surface and the reference light from the reference surface, and measuring the surface shape of the test surface based on the observation result,
The interference device main body and the subject support means are provided so as to be capable of relative displacement so that the optical path length between the light split position and the test surface can be adjusted.
The coherence distance of the light is set to a short distance compared to twice the thickness of the subject,
A condensing lens having a focal position within the interference possible range is disposed in an optical path between the light division position and the interference possible range position of the test surface,
The condenser lens is supported by the interference device body ;
The condensing lens is supported by the interference device main body through an optical path length fine adjustment means capable of finely adjusting an optical path length between the light splitting position and the condensing lens. To do.
[0012]
Further, the condenser lens is supported by the interference device main body, and a condenser lens retracting means capable of moving the condenser lens to a retracted position deviating from an optical path between the light splitting position and the test surface. It is also preferable to carry out via.
In that case, it is more preferable that the condensing lens retracting unit includes a condensing lens retracting position retaining unit that retains the condensing lens at the retracted position.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram for explaining a light wave interference device in which the subject positioning device of the present invention is incorporated, and is configured as a Michelson type. This Michelson interferometer includes a light source 1, a collimator lens 2, a beam splitter 3, a reference plate 4, an imaging lens 7, and a CCD element 8, and an object positioning device according to the present invention ( This will be described later), but the position of the subject 5 can be adjusted while being held.
[0014]
The light source 1 emits light having a short coherence distance. The light 1a emitted from the light source 1 is converted into parallel light by a collimator lens 2, and then the reference light and test light are detected by a beam splitter 3. It is supposed to be divided into. Then, the reference light and the test light are respectively reflected by the reference surface 4a of the reference plate 4 and the test surface 5a of the test object 5 supported by the test object positioning device, and then synthesized again by the beam splitter 3 to obtain an imaging lens. 7, an interference fringe is formed on the imaging surface of the CCD 8.
[0015]
By the way, in this interference device, the reflection from the back surface 5b of the subject 5 is formed on the interference fringes formed by the reflected light from the test surface 5a of the subject 5 and the reflected light from the reference surface 4a of the reference plate 4. A light source that emits light 1a having an extremely short interference distance is selected as the light source 1 so that interference fringe noise based on light is not superimposed.
When the light source that emits light having a short coherence distance is used in the interference device in this way, the position of the test surface 5a in the optical axis direction is adjusted so that the optical path lengths of the reference light and the test light are equal to each other. It is necessary to align the test surface distance.
[0016]
The interference possible range L of the test surface 5a shown in FIG. 1 is L <SCL / 2, where SCL is the coherence distance of the light 1a. In addition, the coherence distance SCL is set to be extremely smaller than the thickness t of the subject 5. For example, when the light source 1 is a red LED having a coherence distance SCL≈30 μm, the interference possible range L is a value smaller than 15 μm. Thereby, when the interference fringe based on the test surface 5a of the subject 5 is observed during the interference fringe measurement, the interference fringe based on the back surface 5b of the subject 5 is not observed.
[0017]
Then, the subject 5 is moved in the direction of arrow A by the subject positioning device, and the subject surface 5a is positioned within this possible interference range. Thus, the subject is within the extremely short range 6. It is not easy to position the 5 test surfaces 5a. In particular, when the interference fringe imaged on the CCD 8 is observed on the monitor and the above-mentioned positioning is performed by stopping the movement of the subject at the moment when the interference fringe appears, the interference fringe appears on the monitor. Since the interference fringes move at a high speed in accordance with the movement of the test surface 5a, it is extremely difficult to confirm the appearance of the interference fringes.
[0018]
Therefore, in the subject positioning apparatus according to the present invention, as shown in the drawing, a condensing lens 9 for positioning the subject having a focal position F within the interference possible range 6 is disposed in the optical path. ing.
[0019]
Hereinafter, the function and effect of the subject positioning apparatus using the condenser lens 9 will be described with reference to FIGS. 2 and 3.
First, in FIG. 2A, the test surface 5a of the subject 5 does not reach the interference possible range 6, and the light from the condenser lens 9 is irradiated and reflected on the test surface 5a in a divergent state. Show the case.
[0020]
The condensing lens 9 is arranged in the parallel light beam emitted from the beam splitter 3 shown in FIG. 1. If the test surface 5a exists at a position far from the focal position F of the condensing lens 9, this condensing lens 9 is arranged. The light beam that has passed through the optical lens 9 is irradiated and reflected on the test surface 5a, and this reflected light beam appears as if the light emitting point is at a position F 'symmetrical to F across the test surface 5a. Proceed as you go.
[0021]
When this light beam passes through the condenser lens 9 again, as shown in FIG. 2A, it returns to the beam splitter 3 as converged light instead of parallel light.
FIG. 2B shows a case where the test surface 5 a has just reached the focal position F of the condenser lens 9. In this case, the light beam reflected by the test surface 5a becomes a light beam having a focal point F as a light emission point, and this light beam is again converted into a parallel light beam in the condenser lens 9 and returns to the beam splitter 3.
[0022]
FIG. 2 (c) shows a case where the test surface 5 a has passed the focal position F of the condenser lens 9. In this case, a position F ′ symmetrical to the focal position F across the test surface 5 a becomes an actual point light source, and a divergent light beam from this point light source reenters the condenser lens 9. Since this position F ′ is inside the focal position F of the condensing lens 9, it is emitted from the condensing lens 9, and the backward light beam becomes divergent light and returns to the beam splitter 3.
[0023]
2A, 2B, and 2C, the pattern formed on the CCD 8 in each case is shown in FIGS. 3A, 3B, and 3B in the field of view 20 on the monitor. (C) is displayed.
That is, in the state shown in FIG. 2A, as shown in FIG. 3A, a dark spot 22b is formed in the diameter 21 portion of the diameter of the condenser lens 9, and in the spot 22b, A small bright spot 22a is formed.
[0024]
In the state shown in FIG. 2B, the entire size portion 21 of the diameter of the condenser lens 9 becomes a spot 23 with uniform brightness as shown in FIG. This is equivalent to the periphery of this portion 21.
Further, in the state shown in FIG. 2C, a slightly bright spot 25 is formed in a range larger than the size portion 21 of the diameter of the condenser lens 9 as shown in FIG. 3C. A dark spot 24 is formed so as to coincide with the size portion 321 of the diameter of the condenser lens 9.
[0025]
In this way, the light beam that has passed through the condenser lens 9 forms a spot of a predetermined size or brightness on the CCD 8, and as shown in FIG. It can be detected that the surface 5a to be measured is positioned in the vicinity of the interference possible range 6 when there is almost no distinction between the brightness and the area.
[0026]
In order to make this positioning more accurate, the sensitivity to the change in brightness or the change in spot size may be made sensitive. For this purpose, as is clear from FIG. 2, it is desirable that the condensing angle of the light beam emitted from the beam splitter 3 by the condensing lens 9 is larger. That is, a lens having a small distance to the focal position F with respect to the size of the diameter of the condenser lens 9, in other words, the diameter size of the condenser lens 9 is D, and the distance to the focal position F (focal distance) is Assuming that f / D is as small as possible, sensitivity is better. Here, f / D is the numerical aperture (F number) of the lens, and the smaller the F number, the brighter the lens.
[0027]
Next, a specific configuration of the subject positioning apparatus will be described.
4 and 5 are general views showing a Michelson interferometer 30 in which the subject positioning device 31 is incorporated. FIG. 4 (a) is a front view, FIG. 4 (b) is a right side view, and FIG. a) is a rear view, and FIG. 5B is a top view.
[0028]
As shown in these drawings, the Michelson interferometer 30 includes a base 32, an interference device body 33, a subject support mechanism 34, and a condenser lens holding mechanism 35, and the subject support. The object positioning device 31 is configured by the mechanism 34 and the condenser lens holding mechanism 35.
[0029]
The base 32 includes a pedestal 36 and a pillar 37 fixed to the pedestal 36 and extending upward. The pillar 37 has a substantially upper half formed as a cylindrical portion 37a.
[0030]
The interference device main body 33 is provided with a pair of upper and lower clamping members 38 slidably engaged with the cylindrical portion 37a in the vertical direction at the rear corner, and each of the clamping members 38 includes: The lever 39 is fixed and released from the cylindrical portion 37a. As a result, the interference device main body 33 can move from the position shown in the drawing to a position above the predetermined amount.
[0031]
FIG. 6 is an enlarged view of a main part of FIG.
As shown in the figure, the subject support mechanism 34 includes a base 40 that is bolted to the pedestal 36, a fixed machine frame 41 that is bolted to the base 40, and the fixed machine frame 41. The Z-axis adjustment stage 42 and the two-axis tilt adjustment stage 43, and a subject mounting table 44 on which the subject 5 is placed.
[0032]
The two-axis tilt adjustment stage 43 is placed on the Z-axis adjustment stage 42, and the subject mounting table 44 is placed on the two-axis tilt adjustment stage 43.
[0033]
At the upper end of the fixed machine frame 41, upwardly extending projecting pins 45 are fixed at three locations, and these projecting pins 45 are formed at three locations on the outer peripheral edge of the subject mounting table 44. It is inserted through the through hole 44a. Further, the adjustment micrometer 46 of the Z-axis adjustment stage 42 and the adjustment micrometers 47 and 48 of the two-axis tilt adjustment stage 43 protrude from the side wall portion of the fixed machine frame 41 in directions orthogonal to each other. It is installed.
[0034]
On the other hand, the condenser lens holding mechanism 35 includes a fixed portion 35A and a movable portion 35B, and is fixedly supported on the lower frame 49 of the interference device main body 33 at the fixed portion 35A.
[0035]
FIG. 7 is a detailed sectional view showing the condenser lens holding mechanism 35 as a single product.
As shown in the figure, the fixing portion 35A of the condenser lens holding mechanism 35 includes a housing 51 having a pair of front and rear flanges 51a that are in contact with the lower frame 49 from below and are bolted to the lower frame 49. A linear ball bearing 52 mounted in a vertically extending through hole 51b formed in the housing 51, and a pair of upper and lower retaining plates 53 fixed to the housing 51 to prevent the linear ball bearing 52 from coming off. , 54 and a pair of front and rear L-shaped hooks 55, 56 fixed to the lower end of the housing 51.
[0036]
On the other hand, the movable portion 35B is fixed to the housing 51 via the linear ball bearing 52 so as to be vertically movable, and is screwed and fixed to a lower end portion of the rod 57 so as to extend in an arm shape in the horizontal direction. In addition, the lens holder 58 that holds the condenser lens 9 in the vicinity of the distal end portion, and the abutting plate 59 and the nut 60 that are screwed with the screw portion 57a formed at the upper end portion of the rod 57 are formed.
[0037]
The movable portion 35B rotates the abutting plate 59 while holding the rod 57 by hand, and changes the screwing position of the abutting plate 59 to the rod 57 in the axial direction of the rod 57. Thus, the condenser lens 9 held by the lens holder 58 can be displaced in the vertical direction. At that time, the nut 60 is tightened so as to be brought into pressure contact with the abutting plate 59, thereby positioning and fixing the abutting plate 59 with respect to the rod 57. Even in such a state where the positioning is fixed, the movable portion 35B can rotate around the axis of the rod 57 with respect to the fixed portion 35A.
[0038]
The pair of L-shaped hooks 55, 56 are bolted to the lower surface of the flange 51 a of the housing 51 in a point-symmetric arrangement with the rod 57 as the center. A vertical gap slightly larger than the thickness of the lens holder 58 is formed between the tip portions of the L-shaped hooks 55 and 56 and the lower surface of the flange 51a.
[0039]
In the state shown in FIG. 6, the condenser lens holding mechanism 35 is configured to position the condenser lens 9 in the optical path between the beam splitter 3 and the subject 5. As shown in the figure, the abutting plate 59 is grasped by hand and lifted up to a position where the lens holder 58 contacts the lower surface of the housing 51, and then the abutting plate 59 is rotated 90 ° clockwise, By engaging and mounting the lens holder 58 on the pair of L-shaped hooks 55 and 56, the condenser lens 9 is moved to a retracted position away from the optical path between the beam splitter 3 and the subject 5. It can be moved. FIG. 9 is a perspective view showing in detail how the lens holder 58 is engaged and placed on the pair of L-shaped hooks 55 and 56.
[0040]
As described above, the subject positioning device 31 according to the present embodiment is arranged so that the interference device main body 33 can adjust the optical path length between the beam splitter 3 (light division position) and the test surface. A condensing lens 9 is disposed in the optical path between the beam splitter 3 and the position where interference can be performed on the surface to be measured, and has a focal position within the range where interference is possible. However, since the condensing lens 9 is supported not by the subject support mechanism 34 but by the interference device body 33, the interference device body 33 is moved up and down according to the thickness of the subject 5. Even when the lens is displaced in the direction, the condenser lens 9 is displaced together with the optical system of the interference device main body 33, whereby the focal point of the condenser lens 9 should be positioned on the test surface. Always matched to Rukoto can, the positioning of the test surface of the for subject 5 can be easily performed.
[0041]
As described above, according to the present embodiment, in the Michelson interferometer using light with a short coherence distance, the subject positioning apparatus can easily position the test surface within the interference possible range with a simple configuration. Can be obtained.
In addition, in the present embodiment, the support for the condenser lens 9 by the interference device main body 33 is performed via the condenser lens holding mechanism 35, and the following effects can be obtained.
[0042]
That is, the condenser lens holding mechanism 35 changes the screwing position of the abutting plate 59 with respect to the rod 57 in the axial direction of the rod 57, so that the condenser lens 9 held by the lens holder 58 is changed. The optical path length between the beam splitter 3 and the condensing lens 9 can be finely adjusted, so that the condensing lens can be displaced in the vertical direction. 9 focal positions can be easily set within the interference possible range, and once this setting is made, the focal positions can always be held at a fixed position in the optical system of the interference device body 33. No later adjustment is required.
[0043]
The condenser lens holding mechanism 35 operates the movable portion 35B to move the condenser lens 9 from the position of the optical path between the beam splitter 3 and the subject 5 and the optical path. Since it is configured to be able to move between the retracted position, the interference fringe measurement is performed by moving the condenser lens 9 to the retracted position after positioning the test surface. In this case, it is possible to prevent the spot pattern formed by the condenser lens 9 and the shadow of the lens holder 58 from being formed on the observation screen. In addition, in the present embodiment, the movement to the retracted position can be performed by a simple operation by simply lifting and rotating the butting plate 59 upward.
[0044]
Further, the condensing lens holding mechanism 35 is configured to engage and mount the lens holder 58 on the pair of L-shaped hooks 55 and 56 of the fixed portion 35A at the retracted position. In this case, the condenser lens 9 can be securely held at the retracted position.
[0045]
In the embodiment described above, the condenser lens 9 is manually moved to the retracted position. However, the movement is automatically performed based on a signal capable of recognizing the difference between positioning and interference fringe measurement. You may comprise so that it may be performed.
[0046]
Further, in the above embodiment, as shown in FIG. 1, the shielding plate 10 is moved in the direction of arrow B so that it can be inserted into and retracted from the optical path of the reference light, and the reference light enters the reference plate 4 during the positioning. If S is blocked, the S / N of the spot pattern in the observation visual field 320 is improved, and a more accurate positioning operation can be performed.
Further, as the light receiving element, not only the surface sensor such as the CCD but also a line sensor or a single element sensor can be used.
[0047]
In the embodiment, the retracted position is set at a position deviating from the optical path between the beam splitter 3 and the subject 5. The retraction position may be set at the end position of the observation screen where the spot pattern formed by 9 and the shadow of the lens holder 58 do not disturb the interference fringe measurement.
[0048]
The apparatus of the present invention is not only adapted to the Michelson type interference apparatus, but can also be applied to an interference apparatus that can make the optical path lengths of the test light and the reference light approximately equal distances, for example, a Mach-Zehnder interference apparatus. is there.
[0049]
【The invention's effect】
As described above, in the subject positioning device of the light wave interference device of the present invention, the interference device main body and the subject support means can adjust the optical path length between the light division position and the test surface. A condensing lens that is provided so as to be relatively displaceable and that has a focal position within the interference possible range is disposed in the optical path between the light dividing position and the interference possible range position of the test surface. However, since the condensing lens is supported not on the subject support means but on the interference device body, the interference device body is placed on the subject according to the thickness of the subject or the subject unit in which the subject is incorporated. Even when it is displaced with respect to the subject support means, the condensing lens is displaced together with the optical system of the interference device main body, so that the test surface is located at the focal position of the condensing lens. Always match the power point It is possible, the positioning of the test surface of the for subject can be easily performed.
As described above, according to the present invention, in a light wave interference device using light having a short coherence distance, a subject positioning device that can easily position a test surface within a possible interference range with a simple configuration is obtained. Can do.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining a light wave interference device in which a subject positioning device according to an embodiment of the present invention is incorporated. FIG. 2 is a diagram showing an operation of the light wave interference device. FIG. 4 is an overall view showing a specific configuration of the light wave interference device ((a) is a front view, (b) is a right side view).
FIG. 5 is an overall view showing a specific configuration of the light wave interference device ((a) is a rear view, and (b) is a top view).
FIG. 6 is an enlarged view of a main part of FIG. 4A. FIG. 7 is a detailed sectional view showing a condensing lens holding mechanism of the subject positioning device as a single item. FIG. 8 shows the operation of the subject positioning device. FIG. 9 is a perspective view showing in detail how the lens holder is placed on a pair of L-shaped hooks in the condenser lens holding mechanism.
DESCRIPTION OF SYMBOLS 1 Light source 2 Collimator lens 3 Beam splitter 4 Reference plate 4a Reference surface 5 Subject 5a Test surface 6 Interference possible range 7 Shooting lens 8 CCD
9 Condensing lens 30 Michelson interferometer (light wave interferometer)
31 Object Positioning Device 32 Base 33 Interference Device Main Body 34 Object Support Mechanism (Supporting Means)
35 Condensing lens holding mechanism (light path length fine adjustment means) (condensing lens retracting means)
35A Fixed portion 35B Movable portion 36 Base 37 Pillar 37a Cylindrical portion 38 Holding member 39 Lever 44 Subject mounting base 49 Lower frame 51a Flange 51b Through hole 51 Housing 52 Linear ball bearing 53, 54 Retaining plate 55, 56 L-shaped hook (Condenser lens retracting position holding means)
57 Rod 57a Screw part 58 Lens holder 59 Abutting plate 60 Nut

Claims (3)

The light from the light source is divided into two systems, one is irradiated on the test surface of the subject and the other is irradiated on the reference surface, and interference between the test light from the test surface and the reference light from the reference surface In the light wave interference device for observing the interference fringes generated by the above and measuring the surface shape of the test surface based on the observation result
The interference device main body and the subject support means are provided so as to be capable of relative displacement so that the optical path length between the light split position and the test surface can be adjusted.
The coherence distance of the light is set to a short distance compared to twice the thickness of the subject,
A condensing lens having a focal position within the interference possible range is disposed in an optical path between the light split position and the interference possible range position of the test surface,
The condenser lens is supported by the interference device body ;
The condensing lens is supported by the interference device main body through an optical path length fine adjustment means capable of finely adjusting an optical path length between the light splitting position and the condensing lens. An object positioning device for a light wave interference device. The condensing lens is supported by the interference device body via a condensing lens retracting means that can move the condensing lens to a retracting position that is out of the optical path between the light splitting position and the test surface. subject positioning device according to claim 1 Symbol placement of the optical interference device characterized in that it is carried out. 3. The subject positioning device for a light wave interference apparatus according to claim 2 , wherein the condensing lens retracting means includes condensing lens retracting position retaining means for retaining the condensing lens at the retracted position.

Images