JP3784035B2 - 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 the surface shape of a subject surface of a subject is measured using light having a short coherence distance, the subject surface is within a range where interference is possible. The present invention relates to a subject positioning apparatus that positions the test surface in the optical axis direction so as to be positioned.
[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 can be done.
[0003]
By the way, when a laser interferometer is used as the interferometer, since the interference distance of the laser light is long, it is not necessary to set the position of the test surface accurately with respect to the reference surface. In the case of a transparent parallel 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. However, taking such measures requires a great deal of labor, and there is a problem of contaminating the subject. In particular, when the thickness of the specimen is very thin, applying matching oil or the like to the back side may cause a problem that the specimen is distorted due to the surface tension and accurate measurement of the specimen surface cannot be performed. To do.
[0005]
Therefore, when measuring the surface shape of a thin glass plate or the like, it is conceivable to use light having a short coherence distance as a measurement light using a red light emitting diode or the like as the light source and position only the test surface within the interference possible range . At that time, it is preferable that the test surface can be positioned at an optimum position within a possible interference range (a position where an interference fringe with the best contrast is obtained).
[0006]
[Problems to be solved by the invention]
However, in this case, since interference fringes appear only within a very narrow interference possible range, when moving the subject in the optical axis direction for positioning, this is very slow in the optical axis direction. If it is not moved, the surface to be measured will pass through the above-described interference possible range. For this reason, it is not easy to position the test surface within the interference possible range, and it is difficult to perform time efficient positioning.
[0007]
In view of the above circumstances, the present invention is a lightwave interference device that uses light with a short coherence distance, and that can significantly reduce the operation time required to position the test surface to the optimum position within the interference range. An object of the present invention is to provide an object positioning device for an apparatus.
[0008]
[Means for Solving the Problems]
The subject positioning device of the light wave interference device of the present invention divides light from a light source having a short coherence distance into two systems, one is irradiated on the subject's test surface, and the other is irradiated on the reference surface. In the light wave interference apparatus for 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 test surface An object positioning device for positioning in the optical axis direction of
A filter having an interference filter part and a light attenuation filter part is inserted and disposed in the optical path between the light source and the light split position or between the split position and the interference fringe formation position ,
The interference fringe contrast is configured to be obtained by a characteristic in which the characteristic of the interference filter unit and the characteristic of the light attenuation filter unit are superimposed .
[0009]
It is preferable that the light attenuation filter unit is composed of an ND filter having substantially the same transmittance as the interference filter unit.
Further, the filter is configured to be able to change an insertion amount ratio between the interference filter unit and the light attenuation filter unit in the optical path, or the interference filter unit and the light attenuation filter. It is preferable that the portion is provided so as to be movable so that the portions can be alternately arranged in the optical path.
As the movement of the filter in the latter case, it is possible to employ, for example, a rotational movement, a reciprocating movement, or the like.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view showing an object positioning apparatus according to an embodiment of the present invention, which is applied to a Michelson interferometer.
This Michelson interferometer includes a light source 1, a collimator lens 2, a beam splitter 3, a reference plate 4, an imaging lens 5, an imaging device 6, an object holding drive mechanism (not shown), and a filter 7. It is prepared.
[0011]
The light 1 a emitted from the light source 1 is collimated by a collimator lens 2 and then split into reference light and test light by a beam splitter 3. 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 8a of the subject 8 supported by the subject holding and driving mechanism, and then synthesized again by the beam splitter 3. The imaging lens 7 is configured to form interference fringes on the imaging surface (CCD) 6a of the imaging device 6.
[0012]
By the way, in this interference device, a light source that emits light having a short coherence distance is used as the light source 1. Specifically, a red light emitting diode (LED) is used. Thus, the reflected light from the back surface 8b of the subject 8 is reflected on the interference fringes formed by the reflected light from the test surface 8a of the subject 8 and the reflected light from the reference surface 4a of the reference plate 4. The interference fringe noise based on it is not superimposed.
[0013]
When a light source that emits light having a short coherent distance is used in this way, a test for adjusting the position of the test surface 8a in the optical axis direction so that the optical path lengths of the reference light and the test light are equal to each other. It is necessary to perform surface distance adjustment (that is, positioning). In the present embodiment, the filter 7 is provided to facilitate the positioning. This will be described later. Here, first, the positioning when the filter 7 is not provided will be described. To do.
[0014]
The interference possible range L of the test surface 8a shown in FIG. 1 is L <SCL / 2 when the coherence distance of the light 1a emitted from the light source 1 is SCL. Since a red LED is used as the light source 1, the coherence distance SCL is SCL≈30 μm. Therefore, the interference possible range L is a value smaller than 15 μm. Thereby, when the interference fringe based on the subject 8 is observed during the interference fringe measurement, the interference fringe based on the back surface 8b of the subject 8 is not observed.
[0015]
The subject 8 is moved in the direction of arrow A by a subject holding drive mechanism (not shown), and the subject surface 8a is positioned within the interference possible range L. In this way, within the extremely short range L. It is not easy to position the test surface 8a of the subject 8.
[0016]
Therefore, in the present embodiment, as shown in the drawing, during the positioning, in the optical path between the beam splitter 3 and the imaging surface 6a of the imaging device 6 (specifically, the beam waist portion of the imaging lens 5). The filter 7 is inserted and arranged. The filter 7 is formed in a disc shape, and a rotation shaft 7a at the center thereof is driven by a driving means (not shown) so as to rotate at a high speed in the direction indicated by an arrow B. The filter 7 can be moved in the direction indicated by the arrow C to the retracted position outside the optical path after the positioning is completed.
[0017]
As shown in FIG. 2, the filter 7 includes an interference filter portion 7A and an optical attenuation filter portion 7B that are separated by a predetermined center angle about the rotation shaft 7a. The interference filter unit 7A and the light attenuation filter unit 7B are alternately arranged in the optical path (in the drawing, the position of the imaging surface 6a is indicated by a two- dot chain line) by the high speed rotation.
[0018]
FIG. 4 is a diagram showing the characteristics of the filter 7. FIG. 4A is a diagram showing a spectral distribution after the light from the light source 1 has passed through the light attenuation filter unit 7B, and FIG. 4B shows the light from the light source 1 being the interference filter. It is a figure which shows the spectrum distribution after permeate | transmitting the part 7A.
[0019]
As shown in FIG. 4A, the light attenuating filter unit 7B is configured by an ND filter so that light from the light source 1 having a peak at 660 nm is attenuated in intensity and transmitted. It has become. On the other hand, as shown in FIG. 4 (b), the interference filter section 7A has a very narrow characteristic (half width 10 nm) in a wavelength band having a peak at 660 nm of light from the light source 1, that is, a wavelength of 660 nm. It is designed to transmit monochromatic light. The light attenuation filter unit 7B has the ND filter concentration set so that the transmittance is substantially equal to that of the interference filter unit 7A.
[0020]
The light transmitted through the light attenuating filter unit 7B basically has the same characteristics as the light from the light source 1, and a plurality of wavelengths of light are mixed. 1 is limited to the range of L shown in FIG. 1, whereas the light transmitted through the interference filter unit 7A is monochromatic light having a wavelength of 660 nm, and therefore has a wavelength range other than that. There is no light-attenuating action, and the range of possible interference greatly extends to the range of L ′ (L ′> L) as shown in FIG.
[0021]
FIG. 5 is a diagram showing the contrast size of the interference fringes formed on the imaging surface 6a during the positioning.
As shown in FIG. 4B, if the filter 7 is composed only of the light attenuation filter portion 7B, interference fringes are formed within the interference possible range L, and the contrast is the best at the center position P. It becomes. In this case, after positioning the test surface 8a within the interference possible range L, it is easy to position the test surface 8a at the optimum position. However, since the interference range L is extremely narrow, Positioning within the interference possible range L is not easy.
[0022]
On the other hand, as shown in FIG. 5A, if the filter 7 is composed only of the interference filter portion 7A, interference fringes are formed in the interference possible range L ′, and the contrast is the best at the center position P. It will be something. In this case, although it is easy to position the test surface 8a within the interference possible range L ′ , it is not easy to position the test surface 8a at the optimum position due to the gentle characteristics.
[0023]
In this regard, in the present embodiment, the filter 7 includes the interference filter unit 7A and the light attenuation filter unit 7B, and rotates at high speed around the rotation shaft 7a. As shown in FIG. 5C, the contrast of the interference fringes formed on 6a can be obtained with the characteristics in which the characteristics of the interference filter section 7A and the characteristics of the light attenuation filter section 7B are superimposed. . For this reason, it is easy to position the test surface 8a within the interference possible range L, and then it is also easy to position the test surface 8a to the optimum position.
[0024]
As described above, according to the present embodiment, in the light wave interference device using light having a short coherence distance, the operation time required for positioning the test surface 8a to the optimum position within the interference possible range is greatly shortened. be able to. Moreover, such an effect can be achieved with a simple configuration in which the filter 7 is simply inserted and arranged in the optical path. In the above embodiment, after the positioning is completed, the filter 7 is moved in the direction of the arrow C to the retracted position outside the optical path. Observation can be performed with a bright image not passing through the filter 7.
[0025]
Note that, among the characteristics shown in FIG. 5C, when it is desired to enhance the characteristics shown in FIG. 5A (that is, when it is easier to position the test surface 8a within the interference possible range L). In this case, the center angle of the interference filter portion 7A in the filter 7 may be increased, and conversely, when it is desired to enhance the characteristics shown in FIG. If it is desired to make the positioning of the filter 7 easier, the central angle of the interference filter portion 7A in the filter 7 may be reduced.
[0026]
In the above-described embodiment, the case where a red LED is used as the light source 1 has been described. However, even when a light source that emits light with a short coherence distance is used, the light source 1 depends on the characteristics of the light source. By using the filter, it is possible to obtain the same effect as the above embodiment.
[0027]
In the above embodiment, since the filter 7 is inserted and arranged in the optical path at the beam waist portion of the imaging lens 5 , the filter 7 can be formed in a small size. 7 may be provided at any position within the optical path between the beam splitter 3 and the imaging surface 6a of the imaging device 6 or within the optical path between the light source 1 and the beam splitter 3. . At this time, if the filter 7 is inserted and disposed in the optical path at a portion where the light beams are parallel, the function of the interference filter portion 7A can be more fully exhibited.
[0028]
In the above embodiment, the filter 7 is configured to rotate at high speed by the driving means, but the rotation speed is not particularly limited. At that time, when the rotation speed of the filter 7 is relatively slow and becomes a value close to the scanning speed of the television signal of the imaging device 6, it is preferable to rotate the filter 7 in synchronization with the television signal. Thus, it is possible to prevent the occurrence of problems such as flicker.
[0029]
In the above-described embodiment, the filter 7 has been described as being movable in the direction of the arrow C to the retracted position outside the optical path. However, it is not always necessary to configure in this way. That is, when the positioning is completed, if the light attenuation filter unit 7B is set so as to be disposed in the optical path, the brightness is sacrificed to some extent, but the filter 7 is not retreated outside the optical path. It is possible to observe interference fringes in the state.
[0030]
Moreover, in the said embodiment, although the said filter 7 is formed in disk shape and comprised so that it may rotate at high speed, it replaces with such a structure, as shown in FIG. A filter 7 'that is formed and reciprocates at high speed in the direction of the arrow D shown in the figure may be used. In this case, the interference filter unit 7A ′ and the light attenuation filter unit 7B ′ are alternately arranged in the optical path (the position of the imaging surface 6a is indicated by a two- dot chain line in the drawing) in accordance with the high-speed reciprocation. You can do it.
[0031]
Further, instead of rotating the filter 7 at a high speed (or reciprocating at a high speed) as in the above embodiment, as shown in FIG. 6, the filter 17 including the interference filter portion 17A and the light attenuation filter portion 17B is replaced with the filter 17 described above. In positioning, it may be configured to be simply inserted and arranged in the optical path. Even in this case, the characteristics shown in FIG. 5C can be obtained.
[0032]
Alternatively, as shown in FIG. 7, a filter 17 ', which is composed of an interference filter portion 17A' and an optical attenuation filter portion 17B 'and can be rotated around a rotation shaft 17a', is simply placed in the optical path at the time of positioning. It is good also as a structure only to do. In this case, the amount of insertion into the optical path between the interference filter unit 17A ′ and the light attenuation filter unit 17B ′ is changed by manually fine-tuning the filter 17 ′ in the direction of the arrow E shown in the figure. Is possible. As a result, the characteristics shown in FIG. 5C can be appropriately modified.
In the above embodiment, the object positioning apparatus applied to the Michelson interferometer has been described. However, the present invention can also be applied to other two-beam bundle interferometers such as a Mach-Zehnder interferometer. In this case, the same effect as in the above embodiment can be obtained.
[0033]
【The invention's effect】
As described above, in the present invention device, in the light wave interference device using light having a short coherence distance, the positioning of the test surface in the optical axis direction is performed between the light source and the light division position or Since the filter having the interference filter unit and the light attenuation filter unit is inserted and disposed in the optical path between the division position and the interference fringe formation position, the following effects can be obtained. .
[0034]
That is, the interference range of the transmitted light of the light attenuation filter is very narrow, but after positioning the test surface within the interference range, this is the optimum position (the position where the interference fringes with the best contrast are formed). ) Is easy to position. On the other hand, although the interference possible range of the transmitted light of the interference filter section is wide, it is not easy to position the test surface in the optimum position after positioning the test surface within the interference possible range. In this respect, since the filter has an interference filter part and an optical attenuation filter part, first, positioning within the interference possible range is performed by the interference fringe by the transmitted light of the interference filter part, and then the optical attenuation is performed. Positioning can be completed in a short time by performing positioning within the interference possible range and positioning to the optimum position by the interference fringes by the filter transmitted light.
[0035]
As described above, according to the present invention, in the light wave interference device using light having a short coherence distance, it is possible to greatly reduce the operation time required for positioning the test surface to the optimum position within the interference possible range. it can. In addition, such an effect can be achieved with a simple configuration in which the filter is inserted and arranged in the optical path.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of an object positioning device of a light wave interference apparatus according to the present invention. FIG. 2 is a diagram showing a filter of the embodiment as a single product. FIG. 3 is a diagram showing a modification of the filter. FIG. 4 is a diagram showing wavelength-intensity characteristics of the filter of the embodiment. FIG. 5 is a diagram showing a possible interference range of the embodiment. FIG. 6 is a diagram showing another modification of the filter. Figure showing still another modification of the filter 【Explanation of symbols】
DESCRIPTION OF SYMBOLS 1 Light source 2 Collimator lens 3 Beam splitter 4 Reference board 4a Reference surface 5 Imaging lens 6 Imaging device 6a Imaging surface (CCD)
7, 7 ', 17, 17' filters 7a, 17a 'Rotating shafts 7A, 7A', 17A, 17A 'Interference filter units 7B, 7B', 17B, 17B 'Optical attenuation filter units (ND filters)
8 Subject 8a Test surface L, L 'Interference possible range P Optimal position

Claims (6)

The light from the light source with a short coherence distance is divided into two systems, one is irradiated on the test surface of the subject and the other is irradiated on the reference surface. The test light from the test surface and the reference surface In the light wave interference device for observing interference fringes caused by interference of the reference light and measuring the surface shape of the test surface based on the observation result, an object positioning device for positioning the test surface in the optical axis direction There,
A filter having an interference filter part and a light attenuation filter part is inserted and disposed in the optical path between the light source and the light split position or between the split position and the interference fringe formation position ,
A subject positioning device for a light wave interference device, characterized in that the contrast of the interference fringes is obtained by a property obtained by superimposing the properties of the interference filter unit and the light attenuation filter unit .   2. The subject positioning apparatus for a light wave interference apparatus according to claim 1, wherein the light attenuation filter section is constituted by an ND filter having substantially the same transmittance as the interference filter section.   3. The light wave interference device according to claim 1, wherein the filter is configured to be able to change a ratio of an insertion amount in the optical path between the interference filter unit and the optical attenuation filter unit. 4. Subject positioning device.   3. The light wave interference device according to claim 1, wherein the filter is movably provided so that the interference filter unit and the light attenuation filter unit can be alternately arranged in the optical path. Subject positioning device.   5. The object positioning device for an optical interference device according to claim 4, wherein the movement of the filter is caused by a rotational motion.   5. The object positioning device for an optical interference device according to claim 4, wherein the movement of the filter is caused by a reciprocating motion.

Images