JP3431290B2 - Interferometer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer for irradiating a laser beam on a surface to be measured and a reference surface and observing interference fringes generated by an interference action of light beams reflected from the surface to be measured and the reference surface.

[0002]

2. Description of the Related Art FIG. 17 shows a conventional interferometer disclosed in Japanese Patent Laid-Open No. 5-107022. In the figure, after the incident light flux is focused by the condenser lens 101, a part of it is reflected by the half mirror 102 to collimate the collimator lens 1.
It is incident on 03. The light flux becomes a parallel light flux by passing through the collimator lens 103, and becomes a focused light flux at the Fizeau reference lens 104, and is incident on the measured surface 106. At this time, a part of the light flux is reflected by the reference surface 105 and goes backward in the optical path upon incidence. Further, a reflected light beam is also generated on the surface to be measured, and the optical path upon incidence is reversed. These two reflected light beams pass through the half mirror 102, reach the optical image detector 110 via the projection lens 107 and the imaging lens 109, and observe the interference fringes due to the interference action of the two reflected light beams at the optical image detector 110. To be done.

Here, the reflected light beam (diffracted zero-order light beam) on the surface to be measured 106 is once converted into a parallel light beam by the projection lens 107, then diverged by the imaging lens 109 and projected on the optical image detector 110. The imaging lens 109 and the optical image detector 110 are integrally moved in the optical axis direction so that the first-order and higher-order diffracted light on the surface to be measured 106 forms an image on the optical image detector 110. As a result, the surface to be measured 10
It is intended to prevent the high-frequency component of the interference image due to the diffracted light of the first or higher order in 6 and the interference fringe from being bent.

[0004]

However, the prior art has the following drawbacks. First, the surface to be measured 10
As the position of 6 changes, the position of the point where the diffracted light on the measured surface 106 is focused by the projection lens 107 changes. Therefore, the imaging lens 10 is used for focusing.
9 and the observation surface are moved integrally, and the space required by the observation optical system is increased. Secondly, since the position of the surface to be measured 106 and the size of the space for focusing are limited, there is a possibility that the diffracted light beam on the surface to be measured cannot be imaged on the observation surface. Third,
Considering the case where the measured surface 106 is a spherical surface such as a lens surface, the measured surface 1 changes as the curvature R of the measured surface changes.
Since the distance between 06 and the reference lens 104 changes, the magnification of the optical system of the apparatus changes, and when measuring an object to be measured with a different R, the magnification range of the rear magnifying optical system must be large. was there. Fourthly, since the incident condition of the light beam incident on the observation optical system is largely changed, it is difficult to remove the aberration over the entire use state, and the focused state of the diffracted light of the first or higher order generated on the surface to be measured is There was a part that got worse.

According to claim 1 of the present invention, the first problem described above is solved, and the working distance is short and the total length is unchanged.
And an interferometer having a compact observation optical system. Claims 2 and 3 according to the present invention solve the above-mentioned second problem and provide an interferometer in which the area where the diffracted light beam on the surface to be measured cannot be formed on the optical image detecting means is small. . A fourth aspect of the present invention solves the third problem described above, and provides an interferometer in which the diameter change of the interference fringes due to the position change of the surface to be measured is small. Claim 5 according to the present invention solves the above-mentioned fourth problem,
It is an object of the present invention to provide an interferometer in which a diffracted light beam on a surface to be measured is well focused by an optical image detecting means.

[0006]

Means and Actions for Solving the Problems FIGS. 1 to 13
Shows the basic concept of the present invention, and in these figures, 1
Is a laser light source. Reference numeral 2 is a collimation optical system for converting a divergent light beam into a parallel light beam. Reference numeral 3 is a conversion optical system for converting the focused state of the parallel light flux emitted from the collimation optical system 2. 4 is a reference surface, 5 is a measured surface,
6 is a beam splitter, 7 is an image forming optical system, 8 is an optical image detecting means, 9 is an optical axis of the apparatus, and 10 is a diaphragm.

In the above structure, the laser light flux emitted from the laser light source 1 enters the collimation optical system 2. The collimation optical system 2 transforms the light beam into a parallel light beam and enters the conversion optical system 3. In the conversion optical system 3, the light flux is converted into a light flux having a wavefront having a shape corresponding to the shape of the reference surface 4. The light flux transmitted through the conversion optical system 3 is incident on the reference surface 4 and the measured surface 5. A reflected light beam is generated on the surfaces of the reference surface 4 and the surface to be measured 5, and the reflected light beam travels in the reverse direction of the optical path at the time of incidence and enters the beam splitter 6. A part of the light flux that has entered the beam splitter 6 passes through the beam splitter 6 and enters the imaging optical system 7.
The imaging optical system 7 focuses or diverges the incident light beam,
It is incident on the optical image detecting means 8. In the optical image detecting means 8, the reflected light flux from the reference surface 4 and the reflected light flux from the measured surface 5 cause an interference action, and interference fringes are observed.

In claim 1 of the present invention, the optical image detecting means 8 is fixed, and the imaging optical system 7 is an optical axis 9 of the apparatus.
It has a mechanism that can move in the direction. The imaging relationship between the optical image detecting means 8 and the surface to be measured 5 will be considered based on such a configuration. The image formed by the image forming optical system 7 of the optical image detecting means 8 is formed at the position PI ₁ in FIG. Further, this image is sequentially propagated by the collimation optical system 2 and the conversion optical system 3, and finally an image is generated at the position PI ₂ .
Here, by aligning the positions of PI ₂ and the surface 5 to be measured, the optical image detecting means 8 and the surface 5 to be measured are in an image forming relationship. Therefore, at the time of measurement, if the surface to be measured 5 is placed at the position PI ₂ , the diffracted light of the first order or more generated on the surface to be measured 5 is focused by the optical image detection means 8 and coincides with the 0th order light position. become. If the position of the measured surface 5 changes,
The position of the imaging optical system 7 is moved in the direction of the optical axis 9, and the surface 5 to be measured and the optical image detecting means 8 are adjusted so as to form an imaging relationship.
In this case, since the working distance of the imaging optical system 7 is limited to the portion of the distance L in FIG. 2, the total length of the optical system in the apparatus does not change.

Next, the operation of claim 2 of the present invention will be described. Consider the image forming position of the optical image detecting means 8 when the focal length fp of the image forming optical system 7 is set. In FIG. 3, the position of the image forming optical system 7 cannot physically come to the right of the optical image detecting means 8. Considering the image forming position of the optical image detecting means 8 by the image forming optical system 7 within the range of the working distance L in FIG. 3, the focus position FBp on the optical image detecting means 8 side of the image forming optical system 7 is the observation plane. When it is on the right side, the image forming position PI ₁ is on the right side of the image forming optical system 7 as shown in FIG. When the position of the light image detecting means 8 and the focus position FBp of the image forming optical system 7 on the side of the light image detecting means 8 coincide, the image forming position becomes infinite as shown in FIG.

As shown in FIG. 5, when the focus position FBp of the image forming optical system 7 on the side of the optical image detecting means 8 comes to the left of the optical image detecting means 8, the image forming position PI ₁ is set. It will be located to the left of the image optical system 7. Here, if the position of the image forming optical system 7 is separated from the optical image detecting means 8, the image forming position PI ₁ and the position of the image forming optical system 7 are close to each other. Then, as shown in FIG. 6, when the optical image detecting means 8 is located to the right of the focus position FBp on the optical image detecting means 8 side of the imaging optical system 7 by fp, the image forming relationship is an equal magnification image forming. . When the image forming optical system 7 is further moved to the left from this state, the image forming becomes a reduction system. When actually making the diffracted light of the first order or higher order on the measured surface 5 coincide with the 0th order light position on the optical image detecting means 8, the position of the image point in the above-mentioned image forming relationship, the conversion optical system 3 and The position of the imaging optical system 7 in the direction of the optical axis 9 is adjusted so that the position of the measured surface 5 by the collimation optical system 2 matches. As a result, the image of the surface to be measured 5 by the conversion optical system 3 and the collimation optical system 2 is propagated to the optical image detecting means 8 by the imaging optical system 7, and the diffracted light fluxes of the first and subsequent orders on the surface to be measured 5 are detected as optical images. It coincides with the focus / zero-order light position on the means 8. Here, the distance between the optical image detecting means 8 and the position of the image of the optical image detecting means 8 by the imaging optical system 7 will be considered. The distance IO between the optical image detecting means 8 and the image of the optical image detecting means 8 formed by the imaging optical system 7 is expressed by the following equation 1.

[0011]

[Equation 1]

In Equation 1, d is the distance from the principal point of the image forming optical system 7 on the collimation optical system 2 side to the image forming position PI ₁ , and d'is the optical image detecting means 8 of the image forming optical system 7. It is the distance from the principal point on the side to the light image detecting means 8. In this equation 1, when 0 ≧ d> −fp, IO ≦ 0, and d =
At −fp, IO = ∞. Further, in the range of d <-fp, IO takes a minimum value when d = -2fp, and at that time, IO = 4fp. This gives 0 <I
It can be seen that O <4fp does not hold. Therefore, the image position of the optical image detecting means 8 by the imaging optical system 7 is determined by the optical image detecting means 8
From the position of 4 to 4 fp to the left of the optical image detecting means, it does not come within the area. That is, it does not fall within the range R in FIG.

Therefore, the image position of the surface to be measured 5 by the conversion optical system 3 and the collimation optical system 2 is the range R in FIG.
If it is within the range, the image position of the optical image detecting means 8 by the image forming optical system 7 and the image position of the measured surface 5 by the conversion optical system 3 and the collimation optical system 2 cannot be made to coincide with each other, and the measured object is measured. It becomes impossible to match / focus the first-order or higher-order diffracted light beams on the surface 5 on the optical image detection means 8 to the zero-order light position. It is desirable to make such an area as small as possible during actual measurement, and set the area to a portion that is rarely used during actual measurement. As a measure against the former, since the size of the non-imaging region is four times the focal length of the imaging optical system 7, as is apparent from FIG. 7, the focal length of the imaging optical system 7 should be made as small as possible. At the same time, it is desirable that the size of the image formed by the collimation optical system 2 and the conversion optical system 3 in the non-imageable region be made as small as possible. That is, the collimation optical system 2 and the conversion optical system 3 in the direction of arrow A in FIG.
It is desirable to make the magnification of 1 as small as possible. As a measure against the latter, as a region where the surface 5 to be measured is not located at the time of actual measurement, the vicinity of the focal point of the light beam emitted from the conversion optical system 3 (that is, the vicinity of the focal position of the conversion optical system 3) can be mentioned. . Since the measured surface 5 has a finite size during actual measurement, the measured surface 5 cannot be located at the focal position of the conversion optical system 3. In addition, it is rare that the radius of curvature is such that it is arranged near the focal position. Therefore, the position of the image formed by the collimation optical system 2 and the conversion optical system 3 in the non-imageable region is set to the conversion optical system 3
It is desirable to place it in the vicinity of the focal position of.

In order to make such an arrangement, it is sufficient to form an image-forming relationship under the condition that a collimated light beam is emitted from the collimation optical system 2 and is incident on the conversion optical system 3. Therefore, the non-imaging range R in FIG. 7 may be arranged in the vicinity of the focal position of the collimation optical system 2 on the side of the optical image detecting means 8. With such an arrangement, the collimation optical system 2 and the conversion optical system 3 in the direction of arrow A in FIG.
Although it is desirable to lower the magnification of, since the non-imaging range is arranged in the vicinity of the focal position of the collimation optical system 2, this magnification depends on the ratio of the focal lengths of the collimation optical system 2 and the conversion optical system 3. It will be decided, and the magnification β is expressed by Equation 2. In Equation 2, fr is the focal length of the conversion optical system 3, and fc is the collimation optical system 2.
Is the focal length of.

[0015]

[Equation 2]

If the magnification β in equation 2 is equal to or larger than 1 ×,
The non-imageable area will be enlarged. Therefore, it is necessary to set a condition such that the image formation relationship between the collimation optical system 2 and the conversion optical system 3 is a reduction system, as shown in Expression 3.

[0017]

[Equation 3]

Next, the operation of claim 3 of the present invention will be described. Considering the working distance of the imaging optical system 7, as shown in FIG. 6, the optical image detecting means 8 is the optical image detecting means 8 of the imaging optical system 7.
It is clear from Equation ₁ above that the distance between the optical image detecting means 8 and the image forming position PI ₁ becomes the minimum when the focus position FBp on the side is located fp to the right. Therefore, if the working distance is ensured so that the state as shown in FIG. 6 is secured, the entire imageable area is covered. As shown in FIG.
In the case where the imaging optical system 7 is a thick optical system, HF in the figure is the principal point position on the collimation optical system 2 side of the imaging optical system 7, and HB is the optical image detecting means 8 side of the imaging optical system 7. , Fb is the focus position of the imaging optical system 7 on the optical image detecting means 8 side. The operating range L of the imaging optical system 7 may be set to be equal to or more than the value expressed by the equation 4.

[0019]

[Equation 4]

By adopting the structure shown by the above relationship, in most cases in actual use, the diffracted light of the first or higher order generated on the surface 5 to be measured is 0 on the optical image detecting means 8. It is possible to match and focus on the position of the next light, and it is possible to reduce the area that cannot be focused to such an extent that practical use is hardly affected.

The operation of claim 4 of the present invention will be described.
Consider the diameter of the observed interference fringes. Reference plane 4
The light flux reflected by the surface to be measured 5 is focused by the imaging optical system 7 as shown in FIG. Assuming that the diameter of the measured surface 5 is equal to the diameter of the light beam emitted from the conversion optical system 3, the diameter φ of the interference fringe image observed by the optical image detecting means 8 at this time is as shown in FIG.
Since it is 0, it is expressed by the equation 5.

[0022]

[Equation 5]

In Equation 5, k is the NA of the collimation optical system 2, β is the magnification of the imaging optical system 7, and m is the imaging optical system 7.
From the principal point on the collimation optical system 2 side to the focal position on the imaging optical system 7 side of the collimation optical system 2, m ′
An imaging optical from the principal point of the optical image detection means 8 side of the imaging optical system 7
The distance to the image point of the system 7 , HH 'is the distance between the principal points of the imaging optical system 7, Ls is the distance from the focus position of the collimation optical system 2 on the imaging optical system 7 side to the light image detecting means 8, fp Is the focal length of the imaging optical system 7. From Equation 5, the minimum value φmin. Is expressed by Equation 6.

[0024]

[Equation 6]

The expression 6 has a minimum value when the expression 7 is obtained.

[0026]

[Equation 7]

In order to minimize the change in the diameter of the interference fringes, the diameter of the interference fringes may be set to a minimum in the middle of the working distance of the imaging optical system 7. The positional relationship at this time is as shown in FIG. Therefore, the equation 8 holds.

[0028]

[Equation 8]

The operation of claim 5 of the present invention will be described.
The focusing state of the diffracted light on the measured surface 5 at the optical image detecting means 8 will be considered. First-order and higher-order diffracted light beams P on the measured surface 5
As shown in FIG. 12, d is a luminous flux (0
The light beam reaches the optical image detecting means 8 along a path different from that of the next light flux Pi. Since the light flux of such a path is often not taken into consideration when designing the conversion optical system 3 and the collimation optical system 2, the focusing state in the optical image detecting means 8 is not good.
Also in the aberration correction by the imaging optical system 7, it is difficult to perform good correction in all states because the change in the propagation path of the light flux due to the position change of the imaging optical system 7 is large. In this case, in order to improve the focused state of the diffracted light in the optical image detecting means 8, it is important to insert a diaphragm at an appropriate position and reduce the excess diffracted light other than the light flux forming the interference fringes as much as possible. Is. In this case, as shown in FIG. 13, if the diaphragm 10 is inserted at the focal position of the collimation optical system 2, the light beams Pi forming the interference fringes are always focused at this position, so that they are blocked by this diaphragm. Instead, only a part of the diffracted light beam Pd of the first order or higher can be transmitted.

[0030]

[Embodiment 1] FIG. 14 shows Embodiment 1 of the present invention, in which 21 is a He—Ne laser tube as a laser light source, and 22 is a condenser lens. Reference numeral 23 is a polarization beam splitter, and the polarization semi-transparent film thereof has a characteristic of transmitting a P-polarized component and reflecting an S-polarized component. 24 is 1 /
A four-wave plate, 25 is a collimator lens as a collimation optical system, and 26 is a reference lens as a conversion optical element. Reference numeral 26a is a reference surface, on which a reflection enhancing coating is applied. Reference numeral 27 denotes a surface to be measured, 28 denotes a lens as an image forming optical system, which has a structure movable in the optical axis 30 direction. 29
Is frosted glass which is an optical image detecting means.

In the above structure, the laser beam emitted from the He-Ne laser tube 21 is condensed by the condenser lens 2.
It is once focused at 2, then diverges and enters the polarization beam splitter 23. Of the incident light flux, only the light flux of the P-polarized component passes through the polarization beam splitter 23, becomes circularly polarized by the quarter-wave plate 24, and enters the collimator lens 25. It is incident on the lens 26. The incident light flux, which was a plane wave, is converted into a spherical wave here and exits from the reference lens 26, but at that time, a part thereof is reflected by the reference surface 26a. The light beam emitted from the reference lens 26 is incident on the surface 27 to be measured and a part thereof becomes a reflected light beam. Reference surface 26a and measured surface 2
The light beam reflected by 7 travels backward in the optical path at the time of incidence, and changes from circularly polarized light to S polarized light by the quarter-wave plate 24 and enters the polarization beam splitter 23. Here, the incident light beam is reflected by the polarization semi-transparent film of the polarization beam splitter 23 and enters the lens 28. The light flux is focused by the imaging lens 28 and enters the frosted glass 29. Here, the reflected light flux from the reference surface 26a and the reflected light flux from the measured surface 27 cause an interference action, and interference fringes are observed. When the position of the surface 27 to be measured changes, the lens 28 is moved in the direction of the optical axis 30 accordingly, and the surface of the frosted glass 29 is observed so that there is no bending around the interference fringes and the interference fringes are sharp. Adjust the position. In this case, the working distance of the lens 28 is L in FIG.
However, the total length of the optical system in the device does not change.

In this embodiment, the collimator lens 25
, The focal length of the reference lens 26 is set to 50 mm, and the focal length of the lens 28 is set to 20 mm. Considering the area of the frosted glass 29 where an image can be formed by the lens 28, the lens 28 is used as the polarization beam splitter 2
80m from the frosted glass 29 to the polarization beam splitter 23 at any position between the 3 and the frosted glass 29.
In the range of m, an image cannot be formed by the lens 28 of the frosted glass 29. Further, considering that this range is projected onto the measured surface 27 side by the collimator lens 25 and the reference lens 26, when the measured surface 27 is located within this range, the diffracted light on the measured surface 27 is Can no longer be focused on the frosted glass 29. However, the range D on the measured surface 27 side can be calculated by the equation 9, and this range is small, and there is almost no obstacle to actual measurement. In Expression 9, fp is the focal length of the lens 28, fr is the focal length of the reference lens 26, and fc is the focal length of the collimator lens 25.

[0033]

[Equation 9]

Incidentally, here, the magnifications by the reference lens 26 and the collimator lens 25 are fr and fc in the equation (9).
The ratio is less than 1, and it is clear that the magnification by the reference lens 26 and the collimator lens 25 is a reduction magnification. Further, in this embodiment, the focal position of the lens 28 on the frosted glass 29 side is 20 mm, and the working distance in the optical axis 30 direction is 4 mm.
5 mm is secured. Here, when the distance between the lens 28 and the frosted glass 29 is set to 40 mm, the image of the frosted glass 29 by the lens 28 becomes an equal-magnification image, and an image is formed at a position closest to the frosted glass 29. That is, in order to cover the entire imageable area,
The relationship is represented by the expression 10.

In Equation 10, L is the optical axis 3 of the lens 28.
Working distance in 0 direction, fb is focal length of lens 28, fp
Is the focal position of the lens 28 on the frosted glass 29 side.

[0036]

[Equation 10]

By moving / adjusting the lens 28 from this position, the diffracted light on the measured surface 27 is focused on the frosted glass 29 if the position of the measured surface 27 is outside the range expressed by the equation (9). To do. Further, in this embodiment, when the NA of the collimator lens 25 is set to 0.167 and the principal point interval of the lens 28 is set to 2 mm, the focal position of the lens 28 on the frosted glass 29 side and the focal length of the lens 28 are equal to each other. Since they coincide with each other, the principal point position of the lens 28 on the frosted glass side coincides with the surface of the lens 28 on the frosted glass 29 side.
Further, the distance from the focus position of the collimator lens 25 on the side of the polarization beam splitter 23 to the frosted glass 20 is 4
The diameter φ of the interference fringe image projected on the frosted glass 30 when it is set to 9 mm is represented by Formula 11. In FIG. 11, k
Is the NA of the collimator lens 25, m is the principal point of the lens 28 on the collimator lens 25 side,
To the focal position on the lens 28 side of the lens, HH 'is the lens 2
8 is the principal point interval, Ls is the lens 2 of the collimator lens 25
Distance from the focus position on the 9 side to the ground glass 30, fp
Is the focal length of the lens 28.

[0038]

[Equation 11]

In this state, the diameter of the interference fringes when the surface to be measured 27 where the aperture of the reference lens is used is measured is the minimum value 6.475 when m = 23.5 mm.
mm. Since the ground glass 29 is used as the light image detecting means, the characteristic effect of this embodiment may be simple. In this embodiment, the collimator lens 25 is replaced with an off-axis parabolic mirror or the frosted glass 2 is used.
The same effect can be achieved by replacing 9 with an acrylic plate or replacing the polarization beam splitter 23 with a half mirror and removing the quarter-wave plate 24.

[0040]

Second Embodiment FIG. 15 shows a second embodiment of the present invention .
Is a laser diode as a laser light source, 42 is a collimator lens as a collimation optical system, 43 is a half prism as a beam splitter, 44 and 45 are condenser lenses as a conversion optical system, 46 is a measured surface, and 47 is a reference surface. Is. Reference numeral 48 is a second collimator lens which is a collimation optical system, and 49 is a diaphragm, which is placed at the focal position of the second collimator lens 48.
Reference numeral 50 is a lens system which is an image forming optical system, and 51 is a CCD camera as an optical image detecting means. 52 is a CCD camera 51
Monitor TV for displaying the video signal output by
53 is an optical axis.

In the above structure, the laser diode 4
The light flux emitted from the beam No. 1 enters the collimator lens 42. In the collimator lens 42, the light flux becomes a parallel light flux, and thereafter enters the half prism 43, and the half prism 43
Is divided into a light beam that passes through the reflection surface of the half prism 43 and a light beam that is reflected by the reflection surface of the half prism 43. Half prism 43
The light flux reflected by the reflecting surface of the light enters the condenser lens 44, and the light flux transmitted through the reflection surface enters the condenser lens 45. The respective luminous fluxes are converged by the condenser lenses 44 and 45, the luminous flux emitted from the condenser lens 44 is incident on the surface to be measured 46, and the luminous flux emitted from the condenser lens 45 is incident on the reference surface 47. A reflected light beam is generated on the surface to be measured 46 and the reference surface 47, travels backward in the optical path at the time of incidence, and is made into parallel light beams by the condenser lenses 44 and 45, and enters the half prism 43. 2 here
The two incident light fluxes are split into a light flux that passes through the reflecting surface of the half prism 43 and a light flux that reflects the parallel light flux that is reflected by the surface to be measured 46 and transmitted through the reflecting surface of the half prism 43, and the reference surface 47. The parallel light flux reflected and reflected by the reflecting surface of the half prism 43 enters the second collimator lens 48. The light flux that has entered the second collimator lens 48 is once focused, passes through the diaphragm 49, then diverges, and enters the lens system 50. The light flux is refocused by the lens system 50 and reaches the light receiving surface of the CCD camera 51. On the light receiving surface of the CCD camera 51, the reflected light flux from the surface to be measured 46 and the reflected light flux from the reference surface 47 cause an interference action to generate interference fringes. The video signal of the CCD camera 51 is displayed on the monitor television 52, and interference fringes are observed on the monitor television 52. At the time of measurement, the position of the lens system 51 is adjusted in the optical axis 53 direction while observing the interference fringes reflected on the monitor TV 52, and the interference fringes around the interference fringes are not bent and the sharpness of the interference fringes is the best. The position of the lens system 50 is adjusted so that the position becomes. At this time, since the CCD camera 51 as the optical image detecting means is fixed similarly to the frosted glass of the first embodiment, the total length of the device does not change at all.

Further, in the present embodiment, the focal lengths of the collimator lens 42 and the second collimator lens 48 are 100 mm, and the focal lengths of the condenser lenses 44 and 45 are 10.
mm, and the focal length of the lens system 50 is set to 10 mm.
Considering the range where the image can be formed by the lens system 50 on the light receiving surface of the CCD camera 51, no matter what position the lens system 50 is between the second collimator lens 48 and the CCD camera 51, the CCD camera 51 can detect the first image. No image can be formed by the lens system 50 on the light receiving surface of the CCD camera 51 in the area of 40 mm on the side of the second collimator lens 48. Further, considering that this range is projected onto the side of the measured surface 46 and the reference surface 47 by the second collimator lens 48 and the condenser lenses 44 and 45, the measured surface 46 and the reference surface 47 are positioned within this range. In this case, the measured surface 46 and the reference surface 47
It becomes impossible to focus the diffracted light on the light receiving surface of the CCD camera 51. However, the range D on the measured surface 46 side and the reference surface 47 side can be calculated by Expression 12, and this range is small, and there is almost no obstacle to actual measurement.

In Expression 12, fp is the focal length of the lens system 50, fr is the focal length of the condenser lenses 44 and 45, and f is
c is the focal length of the collimator lens 42 and the second collimator lens 48.

[0044]

[Equation 12]

Incidentally, here, the magnification by the condenser lenses 44, 45 and the second collimator lens 48 is represented by the ratio of fr and fc in the formula 12, but this ratio is less than 1, and the condenser lenses 44, 45 It is clear that the magnification of 45 and the second collimator lens 48 is a reduction magnification. Further, in this embodiment, the lens system 50
The focal position on the CCD camera 51 side is 8 mm, and the working distance in the optical axis 53 direction is 18 mm. Here, when the distance between the lens system 50 and the light receiving surface of the CCD camera 51 is set to 18 mm, the image of the light receiving surface of the CCD camera 51 by the lens system 50 becomes an equal-magnification image.
An image can be formed at a position closest to the light receiving surface of the D camera 51. That is, in order to cover the entire imageable region, the relationship expressed by the equation 13 is established. In Expression 13, L is a working distance of the lens system 50 in the optical axis 53 direction, fp is a focal length of the lens system 50, and fb is a focal position of the lens system 50 on the CCD camera 51 side.

[0046]

[Equation 13]

By moving / adjusting the lens system 50 from this position, if the positions of the measured surface 46 and the reference surface 47 are outside the range expressed by the equation 12, the diffraction of the measured surface 46 and the reference surface 47 is performed. The light is focused on the light receiving surface of the CCD camera 51. Further, in this embodiment, the NA of the second collimator lens 48 is set to 0.3, and the lens system 50
Is 10 mm, the principal point position of the lens system 50 on the CCD camera 51 side is −2 mm, and the focal point of the second collimator lens 48 on the lens system 50 side is C
When the distance to the light receiving surface of the CD camera 51 is set to 32 mm, the diameter of the interference fringe image projected on the light receiving surface of the CCD camera 51 at this time is expressed by the equation (14). In the number 14,
k is the NA of the collimator lens 42 and the second collimator lens 48, and m is the distance from the principal point of the lens system 50 on the second collimator lens 48 side to the focal position of the second collimator lens 48 on the lens system 50 side. , HH 'is the lens 50
, Ls is the distance from the focal position of the second collimator lens 48 on the lens system 50 side to the light receiving surface of the CCD camera 51, and fp is the focal length of the lens system 50.

[0048]

[Equation 14]

In this state, the diameter of the interference fringes when the surface to be measured 27, which fully uses the aperture of the reference lens, is measured, the minimum value of the interference fringe is 5.94 m when m = 11 mm.
m. Further, at this time, the second collimator lens 4
The distance from the focal position of the lens system 50 side of No. 8 to the light receiving surface of the CCD camera 51 corresponds to the distance Ls represented by Expression 15. In Expression 15, HH 'is the principal point interval of the lens 50, L is the working distance of the lens system 50 in the optical axis 53 direction, HB
Is the principal point position of the lens system 50 on the CCD camera 51 side.

[0050]

[Equation 15]

As a result, the diameters φ of the interference fringes at the two stroke ends of the lens system 50 are the same, and φ = 13.2.
mm. In this case, the change in the diameter of the interference fringe is the smallest. Further, in this embodiment, the diaphragm 49 is installed at the focal position of the second collimator lens 48.
Therefore, most of the diffracted light on the measured surface 46 and the reference surface 47 is blocked by the diaphragm 49. Finally, the light receiving surface of the CCD camera reaches only a limited range of the diffracted light on the measured surface 46 and the reference surface 47, and as a result, the diffracted light is focused on the light receiving surface of the CCD camera 51. The degree is improved and sharper interference fringes can be observed.

The unique effect of this embodiment is that the reference surface can be freely exchanged and its shape is not limited. Therefore, if the reflected light from the surface to be measured and the reference surface is incident on the CCD camera, the aspherical surface can be used. It is also possible to measure shape such as. In this embodiment, even if the CCD camera is replaced with a vidicon camera, its effect does not change. Further, if the aperture diameter of the aperture is small, it is difficult to prevent rusting after processing. Therefore, by manufacturing the aperture with a material that is resistant to rust such as stainless steel, reliability is increased.

[0053]

Third Embodiment FIG. 16 shows a third embodiment of the present invention , in which 61 is a He-Ne laser tube as a laser light source, 62 is a condenser lens, and 63 is a polarization beam splitter. The polarization semi-transparent film of this polarization beam splitter 63 is P
It has the property of transmitting polarized light and reflecting S polarized light. 6
Reference numeral 4 is a quarter wavelength plate, 65 is a collimator lens as a collimation optical system, 66 is a plane parallel plate, and 66a is a reference surface, which is provided with a reflection enhancing coating. A phase type zone plate 67 as a conversion optical system has a function of converting an incident parallel light beam (plane wave) into a converged light beam (spherical wave). 68 is a surface to be measured, 69 is a diaphragm, and the diaphragm 69
Is arranged at the focal position of the collimator lens 65.
70 is a lens which is an imaging optical system, 71 is this lens 70
Is the image plane of. Reference numerals 72a, 72b and 72c are magnifying lenses, 73 is a CCD camera, 74 is a monitor television for displaying video signals from the CCD camera, and 75 is an optical axis. The magnifying lenses 72a, 72b, and 72c are CCDs at different magnifications with the image plane 71 of the lens 70 as an object point.
The image of the image plane 71 is projected on the light receiving surface of the camera 73. Any one of the magnifying lenses 72a to 72c is inserted on the optical axis 75 by a switching mechanism. The phase-type zone plate 67 has a ring zone on its surface such that the m-th radius rm is represented by the equation (16). In Expression 16, λ is the wavelength of the He—Ne laser light, and f is the focal length of the phase type zone plate 67.

[0054]

[Equation 16]

In the above structure, the light beam emitted from the He-Ne laser tube 61 is converged by the condenser lens 62, then diverged, and enters the polarization beam splitter 63. The light beam of the P polarization component is the polarization beam splitter 6
When the light passes through the semitransparent film 3 and the quarter wave plate 64, it becomes circularly polarized light and enters the collimator lens 65. The collimator lens 65 converts the light beam into a parallel light beam, which is then incident on a plane parallel plate 66. On the reference surface 66a of the plane-parallel plate 66, a few percent of the incident light flux becomes a reflected light flux and travels backward in the optical path upon incidence. The luminous flux transmitted through the plane-parallel plate 66 is
It is incident on the phase type zone plate 67. The parallel light flux is converged by the phase type zone plate 67 and is emitted as a focused light flux. The light flux emitted from the phase type zone plate 67 is incident on the measured surface 68. A reflected light beam is generated on the surface to be measured 68, and travels backward in the optical path at the time of incidence to enter the phase type zone plate 67. Here, the reflected light beam, which is a divergent light beam, is converted into a parallel light beam. The light beam emitted from the phase-type zone plate 67 and the light beam reflected by the reference surface 66a are converged by the collimator lens 65 and are changed from circularly polarized light to S-polarized light by the ¼ wavelength plate 64.
Incident on. The incident light flux which is S-polarized light is reflected by the semi-transparent film of the polarization beam splitter 63, exits the polarization beam splitter 63, passes through the diaphragm 69, and enters the lens 70. The incident light beam is converged by the lens 70, is incident on the lens of the magnifying lenses 72a to 72c that is inserted on the optical axis 75, and is emitted to be incident on the light receiving surface of the CCD camera 73. The video signal from the CCD camera 73 is displayed as an image on the monitor television 74. CCD camera 73
In the light receiving surface of, the light flux reflected by the reference surface 66a,
The light flux reflected on the surface 68 to be measured causes an interference effect to form an interference fringe. This interference fringe image is on monitor TV 7.
4 is displayed. In the measurement, the position of the lens 70 is adjusted to the optical axis 75 while observing the interference fringes reflected on the monitor TV 74.
Adjust to the direction, there is no bending of the interference fringes around the interference fringe,
The position of the lens 70 is adjusted so that the sharpness of the interference fringe is maximized. At this time, the light image detecting means C
Since the CD camera 73 is fixed similarly to the frosted glass of the first embodiment and the CCD camera of the second embodiment, the entire length of the device does not change at all.

When the diameter of the surface to be measured is smaller than the diameter of the light beam emitted from the phase type zone plate 67 and the display diameter of the interference fringes on the monitor television 74 is small, the magnifying lenses 72a, 72b, By selecting the one having a large enlargement magnification out of 72c and inserting it on the optical axis 75, the interference fringe image on the monitor television 74 is enlarged and displayed, and the observation becomes easier. Further, in this embodiment, the focal length of the collimator lens 65 is set to 1
00 mm and the focal length of the lens 70 are set to 20 mm. Also, the focal length of the phase type zone plate 67 (equation 16
The inside f) is set to 15 mm. Considering a range of the image plane 71 where an image can be formed by the lens 70, no matter where the lens 70 is between the polarization beam splitter 63 and the image plane 71, the polarization beam splitter 6 moves from the image plane 71 to the polarization beam splitter 6.
In the range of 80 mm on the 3 side, the image on the image plane 71 by the lens 70 cannot be formed. Further, this range is the collimator lens 6
5 and the phase type zone plate 67 to measure surface 68
If it is projected on the side of the
When 8 is positioned, it becomes impossible to match and focus the diffracted light of the first order or more on the measured surface 68 with the position of the 0th order diffracted light on the image plane 71. However, the range on the measured surface 68 side can be calculated by the formula 17, and this range is small,
There is almost no obstacle to the actual measurement. In the number 17,
fp is the focal length of the lens 70, fr is the focal length of the phase zone plate 67, and fc is the focal length of the collimator lens 65.

[0057]

[Equation 17]

Incidentally, here, the phase type zone plate 6
The magnification by 7 and the collimator lens 65 is expressed by the ratio of fr and fc in the equation 17, but this ratio is less than 1, and the magnification by the phase zone plate 67 and the collimator lens 65 is a reduction magnification. it is obvious. Further, in this embodiment, the CC of the lens 70
The focus position on the D camera 73 side is 17 mm, and the optical axis 7
A working distance of 40 mm is secured in five directions. Here, when the distance between the lens 70 and the image plane 71 is set to 40 mm, the image of the image plane 71 by the lens 70 becomes an equal-magnification image, and an image can be formed at a position closest to the image plane 71. That is, in order to cover the entire imageable area,
The relationship is represented by Expression 18. Number 18
Is a working distance of the lens 70 in the optical axis 75 direction,
fp is the focal length of the lens 70, fb is the lens 70 C
This is the focus position on the CD camera 73 side.

[0059]

[Equation 18]

By moving / adjusting the lens 70 from this position, if the position of the measured surface 68 is outside the range represented by Expression 17, the diffracted light of the measured surface 68 will be reflected by the image surface 71.
Focus on. That is, the light is focused on the light receiving surface of the CCD camera 73. Further, in this embodiment, the NA of the collimator lens 65 is set to 0.15, the principal point interval of the lens 70 is 5 mm, the principal point position of the lens 70 on the image plane 71 side is -3 mm, and the collimator lens 6 is also used.
When the distance from the focal position of the lens 70 on the lens 70 side to the image plane 71 is 51 mm, the diameter φ of the interference fringe image projected on the image plane 71 at this time is represented by Formula 19. In Expression 19, k is the NA of the collimator lens 42 and the second collimator lens 48, and m is the principal point of the lens system 50 on the second collimator lens 48 side from the second collimator lens 4
8 to the focal position on the lens system 50 side, HH ′ is the principal point spacing of the lens system 50, and Ls is the second collimator lens 4
8 from the focus position on the lens system 50 side to the CCD camera 51
Is the focal length of the lens system 50.

[0061]

[Formula 19]

In this state, the diameter φ of the interference fringes when measuring the measured surface 68 that uses the full aperture of the phase type zone plate 67 is the maximum when m = 23 mm.
Small value , φ = 5.865 mm. Further, at this time, from the focus position of the collimator lens 65 on the lens 70 side to the image plane
The distance to 71 coincides with the distance Ls represented by Expression 20. In Expression 20, HH ′ is the principal point interval of the lens 70,
L is a working distance of the lens 70 in the optical axis 75 direction, and HB is a principal point position of the lens 70 on the CCD camera 73 side .

[0063]

[Equation 20]

As a result, the diameter φ of the interference fringes at the two stroke ends of the lens 70 is the same, and φ = 13.8 m.
Is. In this case, the change in the diameter of the interference fringe is the smallest. Further, in this embodiment, the diaphragm 69 is installed at the focal position of the collimator lens 65. Therefore, most of the diffracted light on the measured surface 68 is blocked by the diaphragm 69. Finally, the light receiving surface of the CCD camera 73 reaches only the limited range of the diffracted light on the measured surface 68, and as a result, the degree of focusing of the diffracted light on the light receiving surface of the CCD camera 73 is improved. However, sharper interference fringes can be observed. As a unique effect of this embodiment, since the interference fringe image can be magnified by the magnifying lens, it is possible to easily observe the measured surface having a diameter smaller than the radius of curvature.

[0065]

The effects of the first aspect of the present invention can provide an interferometer having a compact observation optical system with a short working distance and no change in the total length . The effects of claims 2 and 3 can provide an interferometer in which the area where the diffracted light beam on the surface to be measured cannot be imaged on the optical image detecting means is small. The effect of claim 4 can provide an interferometer in which the diameter change of the interference fringe due to the position change of the surface to be measured is small. The effect of the fifth aspect is that it is possible to provide the interferometer in which the diffracted light beam on the surface to be measured has a good focusing state on the optical image detecting means.

[Brief description of drawings]

FIG. 1 is a side view of a basic configuration of the present invention.

FIG. 2 is a side view showing the relationship between the surface to be measured and the imaging optical system.

FIG. 3 is a side view showing a relationship between an image forming optical system and an optical system detecting means.

FIG. 4 is a side view showing a relationship between an image forming optical system and an optical system detecting means.

FIG. 5 is a side view showing an image forming position of the image forming optical system.

FIG. 6 is a side view showing 1 × imaging.

FIG. 7 is a side view showing a non-imageable region.

FIG. 8 is a side view showing a relationship between a collimation optical system and a conversion optical system.

FIG. 9 is a side view when the imaging optical system is a thick optical system.

FIG. 10 is a side view showing focusing of a thick optical system.

FIG. 11 is a side view showing a thick imaging optical system.

FIG. 12 is a side view showing focusing of a thick imaging optical system.

FIG. 13 is a side view showing a diaphragm provided in the optical path.

FIG. 14 is a side view of the first embodiment of the present invention.

FIG. 15 is a side view of the second embodiment.

FIG. 16 is a side view of the third embodiment.

FIG. 17 is a side view of a conventional interferometer.

[Explanation of symbols]

1 laser light source 2 Collimation optical system 3 conversion optics 4 reference planes 5 measured surface 6 Beam splitter 7 Imaging optical system 8 Optical image detection means 9 optical axes

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-6-58710 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01B 9/02 G01B 11/24

Claims (5)

(57) [Claims] 1. A laser light source, a beam splitter,
A collimation optical system for collimating the light beam emitted from the laser light source, a conversion optical system for converting the focused state of the light beam emitted from the collimation optical system, a reference surface, and a surface to be measured are optical axes. The optical image detecting means is disposed above and irradiates the reference surface and the surface to be measured with the light flux of the laser light source emitted from the conversion optical system, and the interference fringes generated by the interference action of the light flux reflected from the reference surface and the surface to be measured. In an interferometer for projecting and observing, in the beam splitter, the optical image detecting means is fixed to a side opposite to the side where the collimation optical system is arranged,
An imaging optical system that is movable in the optical axis direction is provided between the beam splitter and the optical image detecting means, and the position in the optical axis direction of the imaging optical system is adjusted so that the distance from the measured surface is increased.
An interferometer characterized in that diffracted light after the next order is focused at the 0th order light position. 2. The focal length f of the collimation optical system
The ratio of c to the focal length fr of the conversion optical system is | fr / f
The interferometer according to claim 1, wherein the relationship is represented by c | <1.0. 3. A focal length fp of the image forming optical system, a focal position fb of the image forming optical system on the optical image detecting means side,
The working distance L of the imaging optical system in the optical axis direction is expressed by the relational expression L.
3. It is represented by ≧ fp + fb.
Interferometer described. 4. The working distance of the imaging optical system in the optical axis direction is L, the principal point spacing of the imaging optical system is HH ', and the principal point position of the imaging optical system on the optical image detecting means side is HB. At some time, the distance Ls from the position of the focal point on the beam splitter side of the collimation optical system to the optical image detecting means is expressed by the relational expression Ls = H.
An interferometer according to claim 2, characterized by being represented by H '+ L-2HB. 5. The interferometer according to claim 2, wherein a stop is placed at a focal position of the collimation optical system.