JPH0769158B2 - Lens surface shape measurement method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an X-Y of a lens surface to be measured in a shape measuring apparatus.
The present invention relates to a lens surface shape measuring method for obtaining a measurement origin in the Z coordinate.

2. Description of the Related Art When measuring the shape of a lens surface to be measured, the measurement origin must first be set at the center point of the lens surface to be measured.

On the other hand, conventionally, if the lens surface to be measured is a convex surface, the measurement point is moved in the XY direction while looking at the Z coordinate at the tip portion of the lens surface and if it is a concave surface at the bottom portion.

However, in the above-mentioned conventional example, since the measurement origin is obtained while searching, there is a problem not only in terms of speed but also in its accuracy.

In view of the above problems, it is an object of the present invention to provide a lens surface shape measuring method capable of efficiently and accurately obtaining a measurement origin.

Means for Solving the Problems In order to achieve the above object, the present invention uses an arbitrary point on a lens surface to be measured as an initial origin, and measures two X-Z coordinates at the same Y coordinate position near the initial origin. , The target origin of the X coordinate is obtained by obtaining the amount of deviation in the X coordinate direction from the center of the lens surface to be measured at the above-mentioned coordinate position of the initial origin (the uppermost point for a convex surface, the lowermost point for a concave surface). The Y-Z coordinates of two positions in the coordinate position are measured, the amount of deviation in the Y coordinate direction from the center of the lens surface to be measured at the coordinate position of the initial origin is obtained, and the target origin of the Y coordinate is obtained. And the target origin of Y coordinate is XYZ of the measured lens surface.
It is characterized in that it is the measurement origin in coordinates.

Operation In the above configuration, when the first target origin is obtained at the same Y coordinate position, (X ₁ , Zd ₁ ) near the initial origin (Xa, Za)
And the two positions of (X ₂ , Zd ₂ ) are measured. Since the radius of curvature of the lens surface shape in this range can be regarded as equal to the radius of curvature of the lens surface to be measured, the inclination of the two positions (Zd ₁
-Zd ₂₎ / (from X ₁ -X _2), it can be determined amount of deviation from the center of the measured lens surface year Y coordinate position of the initial origin. The first target origin thus obtained is located on a line passing through the center of the lens surface to be measured in the Y direction.

Next, at the same X coordinate position as the first target origin, two positions in the vicinity of the first target origin are measured, and the first position is similarly measured.
The amount of deviation from the center of the measured lens surface at the X coordinate of the target origin can be obtained. The second target origin thus obtained coincides with the center of the lens surface to be measured.

As described above, according to the present invention, the center of the lens surface to be measured can be obtained stepwise from the initially selected arbitrary initial origin, so that the measurement origin can be efficiently and accurately obtained.

In addition, by setting the center of the lens surface as the measurement origin, XY
In addition to being able to efficiently measure a range symmetrical to the direction, it is also possible to determine the measurement position for polar coordinate measurement.

Example 1 An optical measuring device according to an example of the present invention is shown in FIGS.
It will be described with reference to FIG.

This device measures the XYZ coordinate position based on the optical heterodyne method, and uses semiconductor laser light (λ = 780n
m) G is focused on the measured surface 2 of the DUT 1, focus servo is applied based on the reflected light, and measurement He-
The Ne-Zeeman laser light (λ = 633 nm) F is converged perpendicularly to the measured surface 2, and the shape of the measured surface 2 is measured while tilt correction servo is applied based on the reflected light.

In the overall structure of the apparatus shown in FIG. 2, 3 is a lower stone surface plate as a main body base, 4 is an X table 5 and a Y table 6 between the lower stone surface plate 3 and the lower stone surface plate 3 in the XY direction. A movable upper stone surface plate, 7 is a Z moving portion provided on the front surface of the upper stone surface plate 4 and movably supported in the Z direction, 8 is an L-shaped holding table for holding the DUT 1, 9 Y this holding table 8
An air spindle 10 that rotates about a direction axis P (see FIG. 11) is a swivel base that supports the air spindle 9 so that it can move up and down and that can swivel about an axis Q in the Z direction.

As shown in FIG. 3, the Z moving portion 7 is suspended from the upper stone surface plate 4 by a spring 11 via a linear motor 10. Z
Inside the moving part 7, as shown in FIG. 4, a semiconductor laser 12 that emits the semiconductor laser light G is installed. The semiconductor laser light G emitted from the semiconductor laser 12 passes through the lens 13, the polarizing prism 14, and the λ / 4 wavelength plate 15, and is totally reflected downward by the dichroic mirror 16 to obtain the objective lens 17.
The light is incident on the full aperture of and the light is condensed on the measured surface 2 of the measured object 1. The condensing position of the semiconductor laser light G substantially coincides with the irradiation position of the measuring light Fz ₁ used for the Z coordinate measurement of the Zeeman laser light F. If the surface to be measured 2 is tilted, a part of the reflected light of the semiconductor laser light G is reflected toward the outside of the opening of the objective lens 17, but the rest is reflected toward the inside of the opening of the objective lens 17. . The reflected light returning to the objective lens 17 is totally reflected by the dichroic mirror 16 and the polarization prism 14,
It is condensed by the lens 18 and divided into two by the half mirror 19.
Each of the divided reflected lights passes through the respective pinholes 20 provided before and after the focus and is applied to the respective photodetectors 21. If the condensing position of the objective lens 17 is on the measured surface 2, as shown in FIG. 5, the amount of light detected by each photodetector 21 becomes maximum. When the distance (Z direction) between the surface to be measured 2 and the objective lens 17 changes, the irradiation position on each photodetector 21 shifts and the amount of light decreases, as shown in FIG. A focus error signal is generated by the focus error signal generator 22 shown in FIG. 3 from the difference between the outputs of these photodetectors 21. Third
When the switch SW ₂ is in the position shown by the phantom line in the figure, the drive circuit 23 controls the linear motor 10 so that this focus error signal becomes zero, and moves the Z moving unit 7 in the Z direction. In this way, the focus servo is applied so that the focus position of the measurement light Fz ₁ of the semiconductor laser light G and the measurement light Fz ₁ of the Zeeman laser light F described below is always on the measured surface 2.

Part of the laser light F emitted from the He-Ne Zeeman frequency-stabilized laser 24 that oscillates at _two frequencies f ₁ and f ₂ is
After passing through the half mirror 25 of the second half mirror 26
And is used for measuring the XY coordinates of the measurement position.
On the other hand, the laser light Fz reflected by the first half mirror 25
Is used to measure the Z coordinate of the measurement position. This laser light
Fz is separated by the polarization prism 27 into the measurement light Fz ₁ and the reference light Fz ₂ . The difference between the frequency f ₂ of the frequency f ₁ and the reference light Fz ₂ of the measuring beam Fz ₁ is several hundred KHz, and has a mutually perpendicular linearly polarized light. Laser light Fx, Fy used for XY coordinate measurement
Also, in the middle of each optical path, the respective corner cubes 44 separate the measurement lights Fx ₁ and Fy _{1 into the} reference lights Fx ₂ and Fy ₂ .

As shown in FIG. 7, the measurement light Fz ₁ used for the Z coordinate measurement has a special polarization prism 28 that totally transmits P polarization and partially transmits S polarization, a Faraday element 29, and a λ / 2 plate 30. And is converted into S-polarized light and totally reflected by the polarizing prism 31. Then, the measurement light Fz ₁ which has passed through the λ / 4 plate 32 and the condenser lens 33 and is condensed and reflected on the mirror 34 is P by the λ / 4 plate 32.
The polarized light is completely transmitted through the polarizing prism 31, enters the objective lens 17, and is vertically condensed on the measured surface 2. The reflected light from the surface to be measured 2 returns along the same optical path as the incident light, but S
After being polarized and partially reflected by the special polarization prism 28,
The light is totally reflected by the polarizing prism 27 and reaches the Z-axis photodetector 35. When measuring the shape of the surface 2 to be measured, the frequency of the reflected light is Doppler-shifted according to the changing speed of the Z coordinate of the measurement point on the surface 2 to be measured, and becomes f ₁ + Δ. When the optical path of the reflected light tends to deviate depending on the inclination of the surface 2 to be measured, the four-division photodetector 36 detects the reflected light partially reflected by the special polarization prism 28 and moves the condenser lens. X by means of means 37
By moving in the −Y direction to change the incident position of the incident light on the objective lens 17, the tilt correction servo is applied so that the reflected light always returns to the same optical path.

On the other hand, the reference light Fz ₂ is totally reflected by the polarizing prism 27, and then is condensed on the Z-axis mirror 39 by the lens 38, reflected and reaches the Z-axis photodetector 35. The frequency of the reflected light becomes f ₂ + δ due to an error such as the movement straightness of the X and Y tables 5 and 6. Therefore, in the Z-axis photodetector 35, (f ₁ +
Δ) − (f ₂ + δ) is detected as a beat signal, and the Z coordinate of the measurement position of the surface 2 to be measured can be accurately obtained at the Z coordinate detection position 37.

The X and Y coordinates of the measurement position on the surface to be measured 2 are calculated by the Z moving unit 7.
Fx ₁ and Fy ₁ focused on the X and Y axis mirrors 38 and 39 installed at
Reflected light and X and Y axis mirrors installed on the lower stone surface plate 1 side
The X- and Y-axis photodetectors 42 and 43 detect the difference in frequency between the reflected lights of the reference lights Fx ₂ and Fy ₂ condensed on the lights 40 and 41.

As shown in FIG. 8, the holding table 8 for holding the DUT 1 moves in the Z-X direction via a slide guide device basically composed of a Z-axis slide plate 45, an X-axis slide plate 46, and a substrate 47. Possibly attached to the air spindle 9. The Z-axis slide plate 45, the X-axis slide plate 46, and the substrate 47 are made of a magnetic material. The Z-axis slide plate 45 has a Z-direction concave groove portion 48 formed on the back side thereof fitted in a Z-direction convex portion 49 formed on the front side of the X-axis slide plate 46 in a surface contact state. The concave groove portion 50 in the X direction formed on the back side of the X-axis slide plate 46 is the convex portion 51 in the X direction formed on the front surface side of the substrate 47.
It is fitted in the surface contact state. The surfaces of the concave groove portions 48, 50 and the convex portions 49, 51 are polished smoothly.

The holding member 52 fixed to the upper surface of the X-axis slide plate 46 is
The shaft feed screw 53 is rotatably held. Z-axis feed screw
The screw portion of 53 is screwed into a female screw portion 54 screwed on the upper portion of the Z-axis slide plate 45. One of the frame members 55 attached to both side surfaces of the X-axis slide plate 46 rotatably holds the X-axis feed screw 56. The screw part of the X-axis feed screw 56 is the board
It is screwed into a female screw portion 57 formed on one side of 47. A female screw portion 59 that is screwed into a screw portion of a fixing screw 58 that fixes the slides of the Z-axis slide plate 45 and the X-axis slide plate 46 is provided at a substantially central portion of the substrate 47. X-axis slide plate 46
An elongated hole 60 in the X direction for inserting the shaft portion of the fixing screw 58 is formed in the substantially central portion of the. A large-diameter square hole 61 is formed in the Z-axis slide plate 45 at a substantially central portion thereof so as to pass through the shaft portion. Four circular holes 62 are formed in the X-axis slide plate 46, and a cylindrical magnet 64 having a cylindrical collar 63 made of a non-magnetic material on the periphery is fitted into each circular hole 62. Both end surfaces of the magnet 64 are
It is slightly submerged from the surface of the X-axis slide plate 46. In this embodiment, the adhesion of the X-axis slide plate 46 to the Z-axis slide plate 45 and the substrate 47 is further improved by the attraction force of the magnet 64 to the magnetic body. The material of the magnet 64 is preferably samarium cobalt, but other materials may be used.

In such a slide guide device, when the DUT 1 on the holding table 8 is moved in the Z direction, the Z-axis feed screw 53 is rotated to operate the Z-axis slide plate as shown in FIG.
Finely slide 45. When moving in the X direction,
As shown in FIG. 10, the X feed screw 56 is rotated to finely slide the X axis slide plate 46. When fixing, tighten with the fixing screw 58. According to the slide guide apparatus of the present embodiment, there is virtually no rattling that occurs when measuring the surface 2 to be measured in polar coordinates, and this contributes to the realization of ultra-high accuracy measurement of the surface 2 to be measured.

As shown in FIG. 2, the swivel base 10 includes a support plate 65 on which the air spindle 9 is installed and fixed, four support pillars 66 for guiding and supporting the support plate 65, and these support pillars 66.
And a revolving base 67 on which is erected. The swivel base 67 is pivotably supported by a pivot pin 68. On the swivel base 67, a feed screw 69 that is screwed into a female screw portion formed in the support plate 65, and a motor 70 that rotates the feed screw 69 are arranged. The feed screw 69 is rotated via a gear 71 fixed to the lower portion thereof and a worm 72 meshing with the gear 71.

According to the swivel base 10 configured in this way, when the object 1 to be measured is held by the holding base 8 and the shape of the surface 2 to be measured is measured, the measurement position shown in FIG. 11 and FIG. Holding table 8
Set up. When measuring the shape of a larger DUT 1, as shown in FIG. 11, the motor 70 is driven to lower the air spindle 9 to a position where the upper end of the air spindle 9 is lower than the lower end of the upper stone surface plate 2. Let Next, in this state, turn the swivel base 10,
The pivot pin 68 is pivoted in the direction shown by the arrow in FIG. As a result, the holding table 8 can be moved from the measurement position below the Z moving unit 7 to the retracted position, and the Z moving unit 7 can be moved.
The space below can be expanded. When performing polar coordinate measurement, the air spindle 9 is moved up and down by the motor 70 so that the approximate center of curvature of the measured surface 2 coincides with the rotation axis P of the air spindle 9.

Next, the focus servo system will be described in detail with reference to FIGS. 3 and 13.

In FIG. 3, 73 is a position detector that detects the amount of displacement of the Z moving portion 7 from the equilibrium position in the Z direction, 74 is a position signal generation circuit that generates a position signal by the output from the position detector 73, and 75 is Position display means for displaying the position of the Z moving unit 7 in the Z direction based on the position signal, 76 is a 0.3 Hz frequency oscillator, 77 is a volume for moving the Z moving unit 7 in the Z direction, and 78 is a volume 77. A differential amplifier that amplifies the position signal so as to eliminate the influence of the restoring force of the spring 11 based on the operation setting voltage and sends the signal to the drive circuit 23, 79 is a gain control circuit, and 80 is a reflectivity of the measured surface 2. Is an operation unit for performing a servo gain switching operation. As shown in FIG. 13, the operation section includes a reflectance changeover switch for changing the respective reflectances of the semiconductor laser light G and the Zeeman laser light F on the measured surface 2 into three ranges, and both laser light rays. G,
An interlock switch for selecting the interlocking of the reflectance switching of F and the independent operation, and a reflected light amount monitor meter for displaying the amount of reflected light of each laser light G, F are provided.

As a result, the respective servo gains can be switched according to the reflectance of the surface 2 to be measured, so that the servo gain can be made substantially constant over a wide range of reflectances, and highly accurate measurable objects can be measured. The range of surface 2 can be expanded. Further, since it is possible to cope with the difference in reflectance due to the wavelengths of the laser beams G and F on the same surface to be measured 2,
The focus servo and the tilt servo can be operated normally according to their respective reflectances. Furthermore, the gain can be switched while confirming the reflectance of the surface 2 to be measured during measurement with the respective laser beams G and F. Although the range of the reflectance that can be dealt with in this embodiment is 3 to 100%, it may be 0 to 100%.

In the optical measuring device configured as described above, when the non-curved lens is used as the DUT 1 and the shape of the DUT surface 2 is measured, the DUT 1 is first held on the holding table 8. At this time, the air spindle 9 is lifted or the slide guide device is finely slid in the XZ direction so that the rotation axis P of the air spindle 9 passes through the center of curvature of the surface 2 to be measured. Next, the volume 77 is operated to move the Z moving unit 7 in the Z direction, and as shown in FIG. 14, the objective lens 17 is initially set to a position 1 to 2 mm above the focus position with respect to the tip of the surface to be measured 2. Set the position. At this time, it is preferable to install a scale 81 as shown in the figure on the front side of the upper stone surface plate 4.

When the switch Sw ₁ is turned on, the Z moving unit 7 moves down until a focus error signal is output, that is, the objective lens 17 reaches the focus pull-in range. When the focus error signal is detected, switch Sw ₂ is switched to activate the focus servo. This allows the objective lens 17 to be pulled to the focus position.

Next, the measurement origin S in the XYZ coordinates of the surface to be measured 2
A method for obtaining (not shown) will be described with reference to FIG.

Let the current focus position of the laser beam G on the measured surface 2 be the initial origin (Xa, Za) S _0, and the deviation amount from the center of the measured surface 2 at the same Y coordinate position of this initial origin S _0. Seeking the first target point
In order to obtain S ₁ , the XZ coordinates of two positions are measured in the fixed range near the initial origin S _{0 at} the same Y coordinate position. Each X
The −Z coordinates are (X ₁ , Zd ₁ ) and (X ₂ , Zd ₂ ).

Letting Zd be the amount of deviation from the calculated spherical surface (phantom line in FIG. 1) of the measurement surface (solid line in FIG. 1) obtained by the measurement, X ² + Y ² + (Z + R−Zd) ² = R ² can be set. However, R is the radius of curvature near the initial origin S ₀ . On the other hand, the calculation sphere is The measurement surface is So Zd Becomes

If X << R, then Zd≈R−X ² ÷ 2R−R + (X + Xa) ² ÷ 2R−Za = [(X + Xa) ² −X ² ] / 2R−Za ≈Xa · X ÷ R + Xa ² ÷ 2R− Za Here, since Xa ² ÷ 2R = Za, Zd = Xa · X ÷ R.

Therefore, Xa = R ÷ X · Zd = R · (Zd 1 -Zd 2) in the ÷ (X ₁ -X ₂₎ above, it is possible to obtain the first target origin S _1. Hereinafter, similarly, the YZ coordinates of two positions at the same X coordinate position near the _first target origin S ₁ are measured, and the amount of deviation of the first target origin S ₁ from the center of the measured surface 2 is measured. To obtain a second target origin S ₂ (not shown).

Since the second target origin S ₂ corresponds to the center of the surface to be measured 2, the shape measurement of the surface to be measured 2 as a measurement origin S of the target origin S ₂ in X-Y-Z coordinates of the measured lens surface By doing so, it is possible to measure a range that is symmetrical in the X-Y direction. It is also possible to determine the measurement position for polar coordinate measurement based on this.

The present invention can be constructed in various modes in addition to the above-mentioned embodiments.

For example, the measurement can be performed from the XZ coordinates of two positions at the same X coordinate position near the initial origin. Although the lens shape of the aspherical convex lens is measured in the above embodiment, the present invention can be applied to aspherical concave lens, concave mirror, and various spherical lenses and mirrors. still,
The configuration of the optical measuring device used in the present invention is not limited to that shown in the above embodiment, and the present invention can be applied to, for example, an optical measuring device equipped with a contact type measurement probe.

EFFECTS OF THE INVENTION Since the present invention has the above-mentioned configuration and operation, the measurement origin can be efficiently and accurately obtained.

In addition, it is possible to efficiently measure a range symmetrical with respect to the X-Y direction, and it is possible to determine the measurement position for polar coordinate measurement.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view for obtaining a target origin from an initial origin in the Y direction on a surface to be measured in an optical measuring device according to an embodiment of the present invention, and FIG. 2 is a schematic perspective view showing the overall configuration of the device, FIG. 3 is a block diagram of a focus servo system in the same apparatus, FIG. 4 is its optical path diagram, FIG. 5 is an optical path diagram when the objective lens is in the focus position, and FIG. 6 is when the objective lens is out of the focus position. Optical path diagram, No. 7
FIG. 8 is an optical path diagram of a tilt servo system in the device, and FIG. 8 is an exploded perspective view of a slide guide device for guiding and supporting a holding frame of an object to be measured in the device so as to be movable in an XZ direction with respect to an air spindle, FIG. 9 is a longitudinal side view of the same, FIG. 10 is a cross-sectional plan view thereof, FIG. 11 is a front view of a swivel base in the same apparatus, FIG. 12 is its plan view, and FIG. 13 is a reflectance switching operation in the same apparatus. FIG. 14 is a front view of the part, and FIG. 14 is an explanatory view of the position setting of the objective lens in the device. 2 ... Surface to be measured, S ₀ ... initial origin, S ₁ ... first target origin, S ₂ ... second target origin, S ... measurement origin.

Claims (1)

[Claims] 1. An arbitrary origin of a lens surface to be measured is set as an initial origin, and X-Z coordinates of two positions at the same Y coordinate position near the initial origin are measured, and the measured lens surface at the coordinate position of the initial origin is measured. Find the amount of deviation in the X coordinate direction from the center of the
The target origin of the coordinates is obtained, the YZ coordinates of two positions at the same X coordinate position are measured, and the amount of deviation in the Y coordinate direction from the center of the lens surface to be measured at the coordinate position of the initial origin is obtained to obtain the Y coordinate of the Y coordinate. A method for measuring the shape of a lens surface, wherein a target origin is obtained, and the obtained target origin of the X and Y coordinates is used as the measurement origin in the XYZ coordinates of the lens surface to be measured.