JP4566534B2 - Shape measuring method and shape measuring apparatus - Google Patents

Description

  The present invention relates to a shape measuring method and a shape measuring apparatus for measuring a three-dimensional shape of an optical element such as a lens and a mirror.

  In order to measure the shape of an optical element such as a lens and a mirror with high accuracy, a probe-type three-dimensional shape measuring apparatus is used. This shape measuring apparatus includes a probe that comes into contact with a measurement surface, coordinate measuring means that measures the position of the probe, probe moving means that moves the probe in three dimensions, and the like.

  For example, the shape measuring apparatus disclosed in Japanese Patent Application Laid-Open No. 10-19504 includes a three-axis stage using a ball screw as probe moving means for moving the probe. Further, the coordinate measuring means has a reference mirror arranged in a direction orthogonal to the respective axes of the three-axis stage.

  The 3-axis stage has an axis for moving the probe up and down (Z-axis) and two axes (X-axis and Y-axis) for moving the probe back and forth and left and right. The distance between the probe and the reference mirror The three-dimensional shape data of the measurement surface is obtained by measuring.

  When measuring such a circular measurement surface as shown in FIG. 11 using such a shape measuring apparatus, first, the probe is placed on the end (start point A) of the measurement surface by driving the Z axis (touch down). ), The scanning operation is performed and only the X axis is operated to measure only one linear line and scan to the end B of the measurement surface. Thereafter, the XY axes are moved to move the probe to the start point C of the next straight line. Then, only the X axis is operated again to measure the next line, and after scanning to the end D as described above, the XY axis is operated to move the probe to the start point F of the next straight line and measure. Measurement is performed while repeating such linear scanning, and scanning is performed up to the end point G of the final line to obtain shape data of the entire measurement surface. That is, the measurement is performed while scanning one line at a time in parallel, and as a result, the entire measurement surface is measured.

On the other hand, in recent years, as shown in FIG. 12, an optical element (diffractive optical element) in which a diffraction grating is engraved on a measurement surface has been used. As shown in FIG. 13A, when the cross section of the optical surface of the diffractive optical element W ₀ is seen, a sawtooth diffraction grating R ₀ is engraved. When the optical surface is viewed from the front, an elliptical diffraction grating R ₀ is concentrically engraved as shown in FIG.

When the diffractive optical element W ₀ is measured by scanning similar to the conventional example, the probe is scanned as shown in FIG. That is, a measurement path in which the probe is landed on the starting point A in FIG. 13C, sequentially scanned in the X direction along the line L1, line L2, line L3, line L4,. Follow. However, when the measurement is performed by such a method, the following problems occur.

  (1) In the vicinity of the top of the diffraction grating, the scanning control cannot be stably performed, and measurement stops due to an error or the like.

(2) Even if the entire measurement surface can be traced without stopping measurement due to an error etc., the vicinity of the apex of the diffraction grating is often not processed or molded as designed, and such instability Even if the shape of the optical element is evaluated using the shape data of the part, accurate evaluation cannot be performed.
Japanese Patent Laid-Open No. 10-19504

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and can measure a complicated three-dimensional shape of a diffraction grating efficiently and with high accuracy, thereby stabilizing the shape evaluation of a diffractive optical element. It is an object of the present invention to provide a shape measuring method and a shape measuring apparatus that can be accurately performed.

In order to solve the above problems, the shape measuring method of the present invention is a shape measuring method for measuring a three-dimensional shape of an optical element by contacting a probe that scans two-dimensionally with an optical element having an annular diffraction grating. A plurality of scanning paths orthogonal to the annular zone of the diffraction grating are determined by calculation using design shape information of the optical element, and the height of the probe is scanned while scanning the probe along each scanning path. The position is measured.

Wherein calculating the gradient direction of the grating from the phase function of the diffraction grating, it may be determined each scan path by stitching the calculation points shifted by a minute amount in a direction orthogonal to the gradient direction.

Shape measuring apparatus of the present invention, an XY stage on the base is movable two-dimensionally holding an optical element having a diffraction grating annular shape, and the Z stage is movable on the XY stage vertically A probe held on the Z stage, a Z position measuring means for measuring the position of the Z stage while the probe is in contact with the object to be measured, and obtaining Z position data of the probe, and the XY XY position measuring means for measuring the position of the stage and obtaining scanning position data of the probe, and controlling the XY stage based on the design shape information of the diffraction grating, and a plurality of parallel to the annular zone of the diffraction grating And stage control means for sequentially scanning the probe along a scanning path.

  Using the design shape information of the optical element, the scanning path of the probe is set so as to be parallel to the annular zone (unevenness) of the diffraction grating. By scanning the probe so as not to cross the vertex of the annular zone of the diffraction grating as much as possible, an error in scanning control is prevented, and the shape data of the vertex having a large error is avoided.

  Measurement errors and errors are reduced by avoiding measurement at the apex of the annular zone of the diffraction grating, where the shape is unstable and scanning control errors are likely to occur. This makes it possible to stably measure a highly accurate three-dimensional shape and accurately evaluate the quality of the diffractive optical element.

Figure 1 of the diffraction grating shape of the diffractive optical element W ₁ to be measured shown in (a), is movable in three dimensions by the three-axis stage of a shape measuring device M shown in the figure (b) Probe 11, the scanning paths T _{1 to} T ₈ of the probe 11 are determined based on the design shape information of the diffractive optical element W ₁ as will be described later. From the scan starting point S ₁ on the inner periphery of the measuring surface, is scanned with the probe 11 along the scanning path T _1, Once we arrived to the end point E ₁ of the scanning path T _1, the start point of the next scan path T ₂ S ₂ moving the probe 11 until, scanning the scanning path T _2. The same operation as described above is scanned until the remaining scanning path _{T 3 → T 4 → T 5} → T 6 → T 7 → T 8 and repeatedly scanning end point E _8, the height position of the probe 11 in the scan Z By capturing the position data together with the scanning position data (XY data), the shape data of the entire measurement surface is obtained.

Here, in determining each of the scanning paths T _{1 to} T ₈ , a curve that is parallel to the annular zone of the diffraction grating on the measurement surface is obtained by calculation using the design shape information of the diffraction grating to be each scanning path. .

That is, when calculating the above scanning paths T _{1 to} T ₈ , the calculation points shifted by a minute amount in a direction orthogonal to the grating gradient direction calculated from the phase function of the diffraction grating are connected to each other to connect the calculation points. Form.

Since each of the scanning paths T _{1 to} T ₈ does not pass through the annular zone of each diffraction grating, that is, the apex of the unevenness, the measurement operation is interrupted due to an error, or an error is generated by capturing data near the apex where the shape is unstable. It is possible to effectively avoid such troubles and perform stable and highly accurate measurement.

Shape measuring device M includes a base 1, a jig 2 for holding the diffractive optical element W ₁ on the base 1, tertiary for moving along each scan path in contact with the probe 11 to the diffractive optical element W ₁ Has a former stage.

  The three-dimensional stage includes an X slider 13 that moves in the X direction on an X guide 12 that is integral with the base 1, an X motor 14 that drives the X slider 13, and a Y guide 15 that is integral with the X slider 13. A Y slider 16 that moves in the Y direction, a Y motor 17 (not shown) having a ball screw 17a that drives the Y slider 16, a Z guide 18 that is integral with the Y slider 16, and a Z that moves on the Z guide 18 in the Z direction A slider 19 and a Z motor 20 that drives the Z slider 19 are provided, and the probe 11 is held by the Z slider 19. That is, the probe 11 can be moved three-dimensionally by a Z slider 19 which is a Z stage on an XY stage including an X slider 13 and a Y slider 16 on the base 1.

  The Z slider 19 has XY position measuring means including X interferometers 21 and 22 for measuring the position of the probe 11 in the X direction and a Y interferometer (not shown) for measuring the position of the probe 11 in the Y direction. And a Z interferometer 23 which is a Z position measuring means for measuring the position of the probe 11 in the Z direction. Each interferometer is a reference mirror such as mirrors 24 and 25 integrated with the Z slider 19. Opposite to.

The output of each interferometer is a stage control means having a function of obtaining and storing the scanning paths T _{1 to} T ₈ shown in FIG. 1A by calculation using design shape information of the diffractive optical element W _1. Input to the apparatus 30, X, Y, Z motors 14, 17, 20 are controlled, and scanning position data and Z position data of the probe 11 in each of the scanning paths T _{1 to} T ₈ are captured.

Figure 2 is intended to explain the shape of the diffractive optical element W _1, 2 one optical surface a diffractive optical element W ₁ elliptical, the optical surface a of the upper surface side of the b is a diffraction grating R shown in FIG. 3 ₁ , R ₂ , R ₃ , R ₄ ... _Re .

Design shape of a surface having a diffraction grating R _e, as shown in FIG. 3, is defined by two of the phase function that defines the base plane and a diffraction grating R _e is a plane. The base surface F _b (x, y) is defined as follows with respect to the XYZ coordinates shown in FIG.

However, r in the formula (1) is 250 mm in this embodiment. The phase function F _p (x, y) that defines the diffraction grating is
F _p = R ... (2)
It is defined as However, in this embodiment, R is
F _p = 0.1x ² + y ² (3)
It is. In order to convert from the phase function F _p to the diffraction grating shape F _p1 , conversion is performed by the method shown in FIG. That is, if the step height of the diffraction grating is λ,
F _p1 = F _p −INT (F _p / λ) × λ (4)
Thus, the phase function F _p is converted into the diffraction grating shape F _p1 . However, INT (...) in the equation (4) means that the integer part of the number in parentheses is taken out.

In this embodiment, the shape obtained by removing the diffraction grating pattern that is determined from the base surface defined by equation (1) in equation (4) has become a design value F _d of a surface. Expressed as an expression

The effective measurement range of the measurement surface in this example is relative to the coordinate system shown in FIG.
(X ² + y ² ) <5 ²
An area that satisfies The unit in the above formula is mm.

The scanning paths T _{1 to} T ₈ when scanning the measurement surface (a surface) defined as described above are obtained by the following procedure.

  (1) The number n of lines to be measured is determined. In this embodiment, n = 8.

  The calculation results are shown in Table 1 below.

(3) From now on, the gradient ▽ F _p in P _s1 is

となる。

It becomes.

As a calculation example, calculation data of the scanning path T ₃ is shown in Table 2.

  Table 4 shows the calculation results.

As shown in FIG. 8, this embodiment measures the three-dimensional shape of a circular diffractive optical element, and the phase function F _p (x, y) of the circular diffraction grating is defined as follows.
F _p = x ² + y ²

Also, the effective measurement range of the measurement surface is relative to the coordinate system similar to FIG.
(X ² + y ² ) <10 ²
An area that satisfies The unit in the above formula is mm.

  In obtaining the scanning path when scanning the measurement surface defined above, the basic method of calculating the scanning path is the same as that of the first embodiment. The calculation conditions in this example are shown below.

As an example, Table 6 shows calculation data of the scanning path T ₃ .

Example 1 will be described, in which (a) is a diagram showing a scanning path of a probe, and (b) is a schematic diagram showing a shape measuring apparatus. FIG. 2 is a diagram illustrating an overall shape of a diffractive optical element used in Example 1. It is a figure explaining the coordinate which shows a diffraction grating shape. It is a figure explaining the phase function showing a diffraction grating shape. It is a figure explaining the calculation start point of the scanning path | route of FIG. It is a figure explaining the linear path | route which connects the scanning path | route of FIG. It is a figure explaining the linear path | route which connects the measurement point from which the value of a phase function differs. It is a figure which shows the scanning path | route set in Example 2, and its calculation start point. It is a figure which shows the measurement path | route of the probe which moves along the scanning path | route calculated | required in Example 2. FIG. It is a figure explaining the calculation method of the linear path | route which connects the scanning path | route of FIG. It is a figure explaining the scanning path | route by a prior art example. It is a bird's-eye view of a general diffractive optical element. 1 shows an elliptical diffractive optical element, where (a) is a sectional view, (b) is a plan view, and (c) is a diagram showing a scanning path.

Explanation of symbols

T _{1 to} T ₈ scanning path 1 base 2 jig 11 probe 13 X slider 16 Y slider 19 Z slider 21, 22 X interferometer 23 Z interferometer 24, 25 mirror 30 control device

Claims (3)

The optical element having an annular shape of the diffraction grating, a shape measuring method for measuring a three-dimensional shape of the optical element in contact with the probe to scan two-dimensionally, using the design shape information of the optical element A shape measuring method comprising: determining a plurality of scanning paths parallel to the annular zone of the diffraction grating by calculation, and measuring the height position of the probe while scanning the probe along each scanning path.   2. The scanning path is determined by calculating a gradient direction of the grating from a phase function of the diffraction grating and connecting calculation points shifted by a minute amount in a direction orthogonal to the gradient direction. Shape measurement method. Z stage and the XY stage on the base is movable two-dimensionally holding the optical element is movable on the XY stage vertically with zonal shape of the diffraction grating, which is held on the Z stage A probe, Z position measuring means for obtaining the Z position data of the probe by measuring the position of the Z stage in a state where the probe is in contact with the object to be measured, and measuring the position of the XY stage. XY position measuring means for obtaining scanning position data of the probe, and the XY stage is controlled on the basis of the design shape information of the diffraction grating, and the probes are sequentially arranged along a plurality of scanning paths parallel to the annular zone of the diffraction grating. And a stage control means for scanning the shape measuring apparatus.

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