JP2003240519A - Optical probe scanning three-dimensional shape measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical probe scanning three-dimensional shape measuring method in which a step (a phase jump) causing a measurement error is corrected by a phase connection processing operation, even when a break is generated in phase information on interference fringes during an optical probe scanning operation so as to generate the step. <P>SOLUTION: The optical probe scanning three-dimensional shape measuring method is provided with a process in which an optical probe is scanned with reference to an object to be measured, so as to calculate a first face shape on the basis of a measured result by measuring a face shape; a process in which a first fragment shape is calculated on the basis of a measured result by measuring a cross-sectional shape of the object to be measured; a process in which a second fragment shape corresponding to a measuring place in the first fragment shape is calculated by an interpolation processing operation on the basis of the first fragment shape; a process in which a first phase jump place generated in the second fragment shape is specified, on the basis of a difference between the first fragment shape and the second fragment shape; a process in which the first face shape is divided into a plurality of fragment shapes, so as to calculate a third fragment shape group; a process in which a fourth fragment shape corresponding to the first phase jump place is selected from the third fragment shape group; a process in which a second phase jump place contained in the fourth fragment shape is specified so as to calculate a correction amount; and a process in which a second phase jump place is calculated by using the second phase jump place and the calculated correction amount. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-dimensional shape measuring technique for highly accurately measuring the surface shape of an object such as an optical component or a mold.

[0002]

2. Description of the Related Art It is widely known to use interference fringe analysis as a method for measuring the surface shape of an object such as an optical component or a mold with high accuracy. Various methods have been proposed for the analysis of interference fringes, and one of them is generated from a measurement light wave containing the shape information of the entire measurement area of the DUT and a reference light wave that serves as a reference, as in the fringe scanning interferometry method. There is a method in which the in-plane phase distribution of the interference fringes thus obtained is taken as the shape distribution of the entire measurement region of the object to be measured and analyzed.

Another method is to analyze the phase change of the interference fringes generated from the measurement light wave containing the shape information of the in-plane part of the object to be measured and the reference light wave serving as a standard, to analyze the in-plane part of the object to be measured. There is a method of analyzing the shape distribution of the entire surface of the measurement area of the measured object by measuring a number of points over the entire surface area of the measured object by using the means for measuring the shape.

As an example of the latter, the phase change of the interference fringes generated from the measurement light wave in which the light beam from the optical probe is surface-reflected on a part of the surface of the object to be measured and the reference light wave as the reference is used to measure An optical probe scanning three-dimensional shape measuring machine that measures the surface shape of the measured object by scanning along the surface shape of the measured object while keeping the distance between the object and the optical probe constant.

As one of the conventional optical probe scanning three-dimensional shape measuring machines, there is an apparatus described in JP-A No. 11-83450.

FIG. 8 is a configuration diagram of the main part thereof, in which 1 is an object to be measured, which is fixed so as not to move during measurement. The Z-axis reference mirror 5 and the X-axis reference mirror 6 are arranged so as to be substantially orthogonal to each other. Two laser length measuring devices (7 is a Z-axis laser length measuring device and 8 is an X-axis laser length measuring device) and an optical probe 2 are arranged on the stage 13 movable in the X and Z directions. .

The stage 13 is arranged so that the focal point of the light beam emitted from the optical probe coincides with the surface of the DUT 1.
It plays a role of controlling movement in the Z direction. Therefore, by scanning the stage 13 in the X direction, it is possible to perform scanning along the surface shape of the object to be measured. In this way
While scanning the surface shape of the object to be measured, the readings of the X-axis laser length-measuring device and the Z-axis laser length-measuring device are stored as coordinate data for each measurement point, and by performing arithmetic processing later, The shape of the measured object can be measured.

In the fringe scanning interferometry, an interference fringe pattern of the measurement light wave and the reference light wave is read by a two-dimensional CCD sensor while changing the phase of the reference light wave in N steps, and the detected light intensity is used to detect each point. The phase information is calculated, and the object shape is calculated from the phase distribution in the measurement area region. The phase information at that time will be calculated using the following Equation 1.

[0009]

[Equation 1] Here, Ij (x, y) is the light intensity at the address (x, y) of the interference fringe during the j-th phase scan, and k is the wave number 2π / λ when λ is the light source wavelength. . In this way, the calculation result of tan ⁻¹ in the calculation of the interference fringe phase information by the fringe scanning interferometry is −π / 2 to + π.
Limited to / 2. Therefore, even if the object has a continuous shape change, the adjacent phase information is −π.
There may be discontinuous phase information that becomes / 2 and + π / 2 (step difference π). For this reason, in general, a phase jump location is detected from the step difference amount of the phase information, and a correction process called phase connection is performed in consideration of the phase jump direction.

Further, in the interference fringes, there is a case where some phase information in the plane is missing due to the influence of dust, noise, pixel defects, and the like. Conventionally, a method has been proposed in which, when there is missing phase information, a continuous phase distribution is calculated using the surrounding phase information excluding the missing part.

As a method of connecting the phases of such interference fringes, there is a technique described in Japanese Patent Laid-Open No. 340843/1993.

According to this method, the phase information including the missing portion shown in FIG. 9B is phase-joined by the procedure of the flowchart shown in FIG. 9A, and the calculated phase information of each point is obtained. Scan the X direction in the X direction to label the region of continuously changing phase information, carry out phase joining in the region of continuously changing phase information, and The continuous phase distribution is calculated from the step of connecting the phases in the Y direction between the regions.

[0013]

The optical probe scanning three-dimensional shape measuring machine is designed to maintain a constant distance in the normal direction between the object to be measured and the optical probe by using the phase information of the detected interference fringes. While controlling the position of the optical probe, scanning is performed over the entire area of the object to be measured, the three-dimensional coordinate value representing the position of the optical probe during that time is detected, and the surface shape of the object to be measured is calculated.

However, when the focal point of the light beam emitted from the optical probe encounters dust adhering to the surface of the object to be measured, there is a problem that the reflected light is interrupted and the phase information of the interference fringes is interrupted. In this case, even if the measurement is continued from the measurement point where the phase information is recovered, there is a possibility that a step is generated before and after the interruption of the phase information. Since the detection of the phase information of the interference fringes is limited to within the range of −π <Δφ <+ π, when dust is encountered and the phase information is interrupted, the continuity of the phase information is interrupted and 2πn (n:
This is because there is a possibility that a step difference of (integer) may occur. In this case, it is considered that 2πn phase connection should be carried out for Δφ, but in that case, the following problems can be considered.

When controlling the position of the optical probe, it is very difficult to always keep the distance between the object to be measured and the optical probe in the normal direction at all times. Therefore, the control constraint condition can be relaxed as follows. it can.

The coordinate value in the Z-axis direction indicating the shape height of the object to be measured is a coordinate value of the Z stage equipped with the optical probe and a deviation amount of the phase information of the optical probe used as a control target value as a correction value. When used, the control of the optical probe position does not necessarily need to keep the phase information of the interference fringe constant (Δφ = 0). The Z-axis coordinate position of the stage equipped with the optical probe is Zp, the change amount of the phase information of the interference fringe is Δφ, the light source wavelength of the optical probe is λ, the inclination angle of the surface shape of the measured object is ψ, the optical probe and the measured object. When the relative distance between the objects in the normal direction is Pl, the Z-axis length measurement value Zm indicating the shape height of the object to be measured can be calculated by Equation 2.

[0017]

[Equation 2] Thus, when the step amount n · λ / 2 generated in the normal direction due to the interruption of the phase information is converted into the step amount in the Z-axis direction,
(N · λ / 2) / cos ψ, which varies depending on the tilt angle ψ of the object to be measured. Therefore, the phase joining method as proposed in the past cannot be used, and it is necessary to measure the surface shape without encountering dust.

Therefore, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to remove dusts adhering to the surface of an object to be measured during optical probe scanning in an optical probe scanning three-dimensional shape measuring machine. Even if a step difference (phase jump) occurs due to the interruption of the phase information of the interference fringes due to the influence, the step difference as a measurement error is corrected by the phase joining process.

Further, even if the interruption of the phase information of the interference fringes occurs, the measurement is continued from the measurement point where the phase information is recovered and the phase connection processing is performed to avoid the re-measurement.

[0020]

[Means for Solving the Problems]
In order to achieve the object, an optical probe scanning three-dimensional shape measuring method according to the present invention is a method for measuring a surface shape of an object to be measured using an optical probe scanning three-dimensional shape measuring machine, wherein the object to be measured is A first step of calculating a first surface shape from a measurement result of measuring the surface shape by scanning an optical probe, and a first fragment shape from a measurement result of measuring the sectional shape of the object to be measured. And a third step of calculating a second fragment shape that matches the measurement point of the first fragment shape from the first surface shape by an interpolation process, and the first step. A fourth step of identifying a first phase jump point occurring in the second fragment shape from the difference between the fragment shape and the second fragment shape, and dividing the first surface shape into a plurality of fragment shapes. Fifth step of calculating the third fragment shape group, and the third fragment shape group A sixth step of selecting et first fourth fragment shape corresponding to a phase jump point, the fourth
Of the second phase skip portion included in the fragment shape and calculating the correction amount, and a second step using the second phase skip portion and the correction amount calculated in the seventh step. And an eighth step of calculating the surface shape.

Further, in the optical probe scanning three-dimensional shape measuring method according to the present invention, in the fourth step, the first value is changed by using a threshold value which changes according to a surface shape inclination angle of the object to be measured. The feature is that the phase jump point of is specified.

In the optical probe scanning three-dimensional shape measuring method according to the present invention, the first surface shape is measured by scanning the optical probe in a spiral shape with respect to the object to be measured, The first fragment shape is measured by scanning the optical probe in the radial direction with respect to the object to be measured, and the third fragment shape group is obtained by dividing the surface shape into a plurality of spiral fragment shapes. It is characterized by seeking.

In the optical probe scanning three-dimensional shape measuring method according to the present invention, the first surface shape is measured by scanning the optical probe concentrically with respect to the object to be measured, The first fragment shape is measured by scanning the optical probe in a radial direction with respect to the object to be measured, and the third fragment shape group is obtained by dividing the surface shape into a plurality of concentric fragment shapes. It is characterized by seeking.

Further, in the optical probe scanning three-dimensional shape measuring method according to the present invention, the first surface shape is measured by scanning the optical probe with respect to the object to be measured in a zigzag shape to obtain the first surface shape. The fragment shape of No. 1 is measured by scanning the optical probe with respect to the DUT in a direction transverse to the meandering scan,
The fragment shape group is characterized in that it is obtained by dividing the surface shape into a plurality of folded fragment shapes.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 2 is a schematic view of a non-contact optical probe scanning three-dimensional shape measuring machine. Here, in order to speed up the probe scanning, two axes orthogonal to the probe scanning method (R axis,
The measurement coordinate axes of the cylindrical coordinate system having the Z axis) and one axis of rotation (θ axis) are adopted.

When the object to be measured has an axially symmetric shape, the designed shape concentric with the axis is defined by the same contour lines, so it is assumed that the shape of the measured object will also be substantially the same contour line. it can. Therefore, by performing probe scanning in the θ-axis rotation direction with the θ-axis and the axis of the DUT substantially aligned, it is possible to suppress changes in the control target value (to suppress the probe tracking change amount to a small amount). Therefore, the constraint condition of the probe scanning speed is relaxed, and the probe scanning speed can be increased. Therefore, the three-dimensional shape measuring machine that aligns the optical axis of the measured object with the θ axis and scans the measured object by concentrically or spirally scanning the probe can reduce the measurement time by high-speed scanning of the probe. Moreover, it is considered that the influence of errors caused by temporal changes and environmental changes can be reduced.

In FIG. 2, reference numeral 1 denotes an object to be measured, which uses an axisymmetric aspherical lens held in the horizontal direction. Reference numeral 2 denotes a probe that scans along the surface shape 1a of the object to be measured, and here, a non-contact type optical probe that does not scratch the lens surface is shown. The optical probe 2 is
It is installed on a Z stage 3 that moves vertically to the object to be measured, and an R stage 4 that moves parallel to the object to be measured, that is, horizontally.

Here, the Z stage 3 controls the movement of the optical probe in the Z direction so that the focal point of the light beam emitted from the optical probe always coincides with the surface of the DUT 1 (hereinafter referred to as servo lock). Have a role. Therefore, when the optical probe is scanned in the R direction using the R stage 4, if the Z stage 3 is servo-locked, the scanning along the surface shape of the measured object becomes possible.

Reference numeral 5 is a Z-axis reference mirror, and 6 is an R-axis reference mirror, which are arranged so as to be substantially orthogonal to each other.
Reference numeral 7 denotes a Z-axis laser length measuring device, which plays a role of detecting a relative distance from the Z-axis reference mirror 5. Therefore, the laser straight-ahead direction and the distance created by the Z-axis laser length measuring device 7 and the Z-axis reference mirror 5 form the Z-axis in this three-dimensional shape measuring machine. Similarly, 8 is R
It is an axial laser length measuring device and has a role of detecting a relative distance from the R-axis reference mirror 6. Therefore, the laser straight-line direction and distance created by the R-axis laser length measuring device 8 and the R-axis reference mirror 6 form the R-axis in the three-dimensional shape measuring machine.

Reference numeral 9 denotes a θ stage which plays a role of rotating an object to be measured, and an axis direction and a rotation angle of a rotation axis of this θ stage (hereinafter referred to as a θ rotation axis) are the θ axis in this three-dimensional shape measuring machine. Is formed. The θ stage here employs an air bearing and is composed of a rotor portion 9a that actually rotates and a stator portion 9b on the fixed side. Further, a scale 10 is attached on the rotor portion 9a, and the scale detector 11 is used to make θ
The rotation angle of the stage is detected.

As described above, in the present embodiment, the object to be measured side is provided with the rotation function of the θ axis, while the optical probe side is provided with the rectilinear function of the R axis and the Z axis. The scanning of the optical probe according to the shape of the measured object can be realized over the entire surface of the measured object.

Next, a surface shape measuring method in the three-dimensional shape measuring machine of this embodiment will be described.

The object to be measured is set so that the apex of the surface is substantially coincident with the θ rotation axis. Then, the position of the optical probe is moved and adjusted using the R stage and the Z stage so that the focal point of the light beam emitted from the optical probe coincides with the surface of the object to be measured, and then the servo lock is started. At this time, the optical probe is controlled to move in the Z direction so that the focal point of the light beam is always incident on the surface of the object to be measured. Therefore, when the θ stage and the R stage are scanned, The Z stage equipped with the optical probe moves up and down according to the surface shape of the measured object according to the scanning position of the R axis. Therefore, the optical probe is scanned over the entire area of the object to be measured, the coordinate values of the R stage and the Z stage indicating the position of the optical probe, the coordinate value of the θ stage indicating the rotational position of the object to be measured, and the phase information of the optical probe. The surface shape of the object to be measured can be calculated by using the deviation.

The i-th measurement value of the surface shape of the object to be measured is expressed as follows using the cylindrical coordinate system.

[0036]

[Equation 3] Here, "Rli" is the reading of the R-axis laser length measuring device 8 for detecting the coordinate value of the R-stage equipped with the optical probe, that is, the relative distance to the optical probe detected with reference to the R-axis reference mirror. Become. "Rc" is a reading value of the R-axis laser length-measuring device 8 when the focal point of the optical probe exists on the θ-rotation axis, that is, between the R-axis reference mirror and the θ-rotation axis expressed by using the optical probe. It is a relative distance. Therefore, "Rli-
“Rc” corresponds to the relative distance from the θ rotation axis to the condensing point of the optical probe, that is, the measurement radius in the R-axis direction of the optical probe. “Θmi” is for the scale detector 11 that detects the angle information of the θ stage. A reading value, that is, the angle information in the θ direction of the object to be measured, and "Zpi" is a reading value of the Z-axis laser length-measuring device 7 for detecting the coordinate value of the Z stage equipped with the optical probe, that is, The relative distance in the Z-axis direction between the Z-axis reference mirror and the optical probe, "Pli" is an interference fringe created from the measurement light wave emitted from the optical probe and reflected by the surface shape of the object to be measured and the reference reference light wave. Is the length measurement value calculated based on the phase information of the, and the relative distance between the actual measurement point on the surface shape of the DUT and the optical probe, "ψi" is the surface shape at the scanning point of the optical probe on the DUT. The inclination angles are shown.

Even if the position of the optical probe is controlled so that the condensing point of the light beam emitted from the optical probe matches the surface shape of the object to be measured, the converging point is always detected only by the null information of the interference fringes. It is difficult to control to the best position, a few μm
There will be some deviation.

FIG. 3 shows the relationship between the Z-axis length measurement value Zmi and the surface shape inclination angle ψi of the object to be measured. FIG. 3A shows a state where the surface shape of the object to be measured has an inclination angle ψi = 0 °,
The measurement point is a point extending from the condensing point of the light flux in the direction normal to the surface shape of the DUT and in contact with the surface shape of the DUT, and the measuring point is the condensing point of the light flux extending in the Z-axis direction. Is a point in contact with the surface shape of the object to be measured, and here the actual measurement point and the measurement point coincide. Further, Pli indicates the distance between the focal point of the light flux and the actual measurement point on the surface shape of the object to be measured. Figure 3 (b)
Indicates a state where the surface shape inclination angle ψi = ψ of the object to be measured, and shows that a deviation occurs between the measurement point and the actual measurement point. FIG. 3C is a diagram showing in detail the measurement error of FIG. 3B. When the surface shape inclination angle ψi of the object to be measured changes, the relative distance between the measurement point and the focal point of the light flux becomes Pli / cosψ
It shows that it becomes i. The influence of the tilt angle ψi described here has already been reflected in the formula (3).

On the other hand, the Z-axis length measurement value Zm expressed by the equation (3)
In the optical probe scanning three-dimensional shape measuring machine for calculating i,
It is considered that the control of the optical probe position does not necessarily require the phase information φi of the interference fringe to be a constant value (Δφi = 0). The coordinate value in the Z-axis direction indicating the shape height of the object to be measured is, along with the coordinate value of the Z stage equipped with the optical probe,
This is because the deviation of the phase information of the optical probe used as the control target value is used as the correction value. That is, even if deviation is allowed in φi (for example, −π / 4 <φ
<+ Π / 4), and the deviation is detected by Pli / cos ψi of the component detected as the phase information of the interference fringes and Zpi indicating the optical probe Z position. At this time, the deviation amount detected by Pli / cos ψi and the deviation amount detected by Zpi are components of the same amount and different signs, so that the deviation amount between the two does not cancel each other out to be a measurement error. As a result, the servo control constraint condition of the optical probe position can be relaxed.

In this manner, the optical probe is scanned over the entire surface along the surface shape of the object to be measured, and the measurement data (Rmi, θmi,
The surface shape of the object to be measured can be measured by detecting Zmi).

However, when the optical probe is scanned spirally or concentrically along the surface shape of the object to be measured, the condensing point of the light beam emitted from the optical probe encounters dust adhering to the surface of the object to be measured. , There is a possibility that the reflected light is interrupted and the phase information of the interference fringes is interrupted. This leads to the release of the servo lock due to the interruption of the control target value of the optical probe position, so the focal point of the light beam emitted from the optical probe cannot always be positioned along the surface shape of the DUT, and the phase information A break in continuity occurs between them.

After the phase information of the interference fringes is recovered by shifting the scanning point so as not to get dust, even if the servo lock and the optical probe scanning are restarted again, the Z-axis measurement value before and after the occurrence of the phase information interruption A step may occur in Zmi. Even if the optical probe position is controlled so that the phase information φi of the interference fringe is always constant (Δφi = 0 °), the phase information of the interference fringe is detected within the range of −π <Δφ <+ π. Therefore, when dust is encountered and the phase information is interrupted, the continuity of the phase information is interrupted, and (n · λ / 2) / co
The step amount of sψ is detected as the Z-axis length measurement value Zm.

Therefore, the phase linking method as conventionally proposed cannot be used. Therefore, even if a step difference (phase jump) occurs due to the discontinuity of the phase information of the interference fringes due to the effect of dust adhering to the surface of the DUT during scanning with the optical probe, the step difference that is a measurement error is corrected by the phase joining process. The method for doing so will be described below.

FIG. 1 is a diagram showing the flow of the phase connecting process in this embodiment. FIG. 1A is a diagram showing a flow of a phase jump processing portion, FIG. 1B is a diagram showing a flow of the entire phase joining processing in the present embodiment, and FIG. 1C is generated during surface shape measurement. FIG. 6 is a diagram showing a flow of handling a break in phase information.

In the optical probe scanning three-dimensional shape measuring instrument, the optical probe is spirally scanned along the surface shape of the object to be measured, and the surface shape is measured during the surface shape measurement. When the phase information of the interference fringes is temporarily interrupted by encountering the dust, the measurement point is shifted to recover the phase information of the interference fringes so as not to get dust as shown in FIG. Restart servo control,
Continue measuring the surface shape. The measurement is continued until the optical probe scanning over the entire surface measurement area of the object to be measured is completed.

Next, as shown in FIG. 1B, the probe is scanned in the radial direction of the object to be measured so as to cross the spiral surface shape measurement data divided by the interruption of the phase information due to dust. Cross-section measurement is performed.

FIG. 4 shows a case where the phase information is interrupted twice due to the encounter with dust while the optical probe is spirally scanned along the surface shape of the object to be measured. Therefore, it means that the scanning of the entire surface measurement area of the DUT has been performed by three times of optical probe scanning, and the measurement point in the first optical probe scanning at that time is "." The measurement point is "o" at the time of the optical probe scan at the third time, "+" at the time of the third optical probe scan after the recovery of the phase information interruption, and it is performed so as to cross the surface shape measurement data of the three divided groups. The measurement points in the measured cross section are indicated by "*". Here, since the surface shape measurement is performed by spiral scanning, by performing the cross-section measurement in the radial direction, all the divided surface shape measurement data can be crossed.

Cross-section measurement data (Rdj, θdj, Z showing three-dimensional coordinate values obtained by cross-section measurement of j points of measurement points)
dj) Removes the design shape Z component,
(Rdj, θdj, std_Zdj). Further, only the design shape Z component is removed from the surface measurement data (Rmi, θmi, Zmi) showing the three-dimensional coordinate values composed of three groups obtained by the surface shape measurement, and the combined surface shape (Rmi, θmi, cmp_Zmi) is obtained. To do. As described above, there is a possibility that a step is generated in cmp_Zmi of the combined surface shape at the position where the phase information is interrupted. Therefore, the cross-section fragment shape (Rdj, θdj, c that matches the cross-section measurement point of the reference cross-section fragment shape)
mp_Zdj) is extracted from the combined surface shape. Since the measurement point of the surface shape measurement does not necessarily exist at the desired cross-section measurement point, the cross-sectional fragment shape to be calculated from the combined surface shape is calculated by interpolation.

It is considered that the probability of encountering dust is significantly low in the cross-section measurement in which the probe scanning distance is significantly shorter than the surface shape measurement. Therefore, the std_Zdj of the reference cross-section fragment shape calculated from the cross-section measurement is considered to have no phase information discontinuity due to dust. And the step amount to be corrected is calculated.

The shape difference change value ΔZdj is calculated from the sectional fragment shape cmp_Zdj and the reference sectional fragment shape std_Zdj.

[0051]     ΔZdj = (std_Zdj-std_Zdj-1)-(cmp_Zdj-cmp_Zdj-1)                                                               ... Equation (4) Incidentally, j indicates the data detection order, and j = 1 to m.

Here, the point where the shape difference change value ΔZdj is larger than the threshold value C1 is set as the phase jump point (step point). FIG. 5 (a) shows how the sectional fragment shape cmp_Zdj and the reference sectional shape std_Zdj are compared, and FIG. 5 (b) shows how the shape difference change value ΔZdj and the threshold value C1 / cosψj are compared.

As described above, since the step amount changes depending on the surface shape inclination angle ψj of the object to be measured, the threshold value also changes according to the surface shape inclination angle ψj of the object to be measured.
It is set as cosψj. As a result, the cross-sectional fragment shape cmp_
If there are two phase jump points in Zdj (j = a1, a2), it can be specified.

Next, the composite surface shape cmp_Zmi is spirally set to 1
Circumferential fragment shape for each circle cmp_Zek, l (k: divided circle circumference order, l: circle data detection order in one circle (maximum value: l_
max)). Combined surface shape at this time cmp_Zmi
And the circumferential fragment shape cmp_Zek, l have the following relationship.

[0055]     cmp_Zek, l = cmp_Zm (k-1) × l_max + l = cmp_Zmi ... Formula (5) The state at this time is shown in FIG.

Next, of the two cross-section fragment shapes that are specified to have a phase jump location, first, a circumferential fragment shape cmp_Zeb including a cross-section fragment shape cmp_Zda1 where j = a1 is included.
Extract 1, l (k = b1) from the circumferential fragment shape group cmp_Zek, l.
The state at this time is shown in FIG. Phase skipped point (stepped point) in the extracted circumferential fragment shape cmp_Zeb1, l
And the correction amount are calculated, and phase connection is performed. At this time, for example, the following method can be used to identify the phase jump location and connect the phases.

In the circumferential fragment shape cmp_Zeb1, l, a shape change value ΔZeb1, l between adjacent data is calculated.

ΔZeb1, l = cmp_Zeb1, l−cmp_Zeb1, l-1 (6) When the shape change value ΔZeb1, l-1 between adjacent data is larger than the threshold value C2 / cosψb1, l, the phase jump occurs. It is specified as the location (step location). FIG. 7A shows a state of the circumferential fragment shape including a step, and FIG. 7B shows a state of comparison between the circumferential fragment shape and the threshold value. The presence / absence of a step is determined at all measurement points of the circumferential fragment shape, and the following correction processing is performed. This threshold value is also the surface shape inclination angle ψb1, l of the object to be measured.
In consideration of the above, C2 / cos ψb1, l is set. Here, the step correction value at the phase jump location is set to hoseik, l, and hoseik, l
= Hosei (k-1) × l_max + l, ΔZeb1, l> C2 / co
If sψb1, l, hoseik, l ＝ hoseik, l-1 + ΔZeb1, l ＝ hosei (k-1) × l_
max + l-1 + ΔZeb1, l ΔZeb1, l ≤ C2 / cos ψb1, l, then hoseik, l = hoseik, l-1 = hosei (k-1) × l_max + l-1 (7) Similarly, The circumferential fragment shape cmp_Zeb2 is extracted from the circumferential fragment shape group cmp_Zek, l including the circumferential fragment shape cmp_Zeb2, l (k = b2) including j = a2.
It is possible to calculate the step correction amount hoseik, l at the phase jump portion existing in 2, l. By this processing, it is possible to calculate the level difference correction amount hoseik, l for the phase jump location due to the two interruptions of the phase information generated during the surface shape measurement of the object to be measured.

By adding this step difference correction amount hoseik, l to the circumferential fragment shape cmp_Zek, l-1, it is possible to correct the phase jump portion caused by the interruption of the phase information and perform the phase connecting process. Therefore, the composite surface shape cmp_
Zmi can also be subjected to phase joining processing according to the following formula.

Cmp_Zmi = cmp_Zek, l-1 + hoseik, l = cmp_Zm (k-1) × l_max + l-1 + hoseik, l (8) As described above, the optical probe scanning three-dimensional shape measuring machine is used. In the above, by performing the phase joining process in the present embodiment, the phase information of the interference fringes is interrupted due to the influence of dust adhering to the surface of the object to be measured during the scanning with the optical probe.
Even if a step (phase jump) not limited to λ / 2 occurs,
By the phase connecting process according to the present embodiment, it is possible to correct a step that causes a measurement error. Further, even if the phase information of the interference fringes is interrupted, it is possible to avoid the re-measurement by continuing the measurement from the measurement point where the phase information is recovered and performing the phase connecting process.

In this embodiment, the correction is performed based on the reference cross-section fragment shape detected from one cross-section measurement. However, when a large number of fragment shape groups exist in the surface shape, or the influence of variations due to noise or the like. When is large, it is considered effective to detect a plurality of reference cross-section fragment shapes by a plurality of cross-section measurements at different measurement locations and correct the surface shape.

In this embodiment, the spiral surface shape measurement and the radial cross-sectional shape measurement have been described as an example, but the concentric surface shape measurement and the radial cross-sectional shape crossing the concentric circular surface shape measurement. The same method can be applied and applied when the measurement or the zigzag surface shape measurement and the cross-sectional shape measurement crossing the surface shape are used.

As described above, in the present embodiment, in the surface shape measurement including the discontinuity of the phase information, the probability of the discontinuity of the phase information due to the influence of dust is remarkably reduced by greatly reducing the probe scanning distance. By using the cross-sectional shape measurement that can be reduced together, the phase jump point (step portion) occurring in the surface shape is specified based on the cross-sectional shape, and the correction amount is calculated, resulting in a surface shape having continuous phase information. Such phase connection is performed.

As a result, in the optical probe scanning three-dimensional shape measuring instrument, the step information (phase jump) occurs due to the interruption of the phase information of the interference fringes due to the influence of dust adhering to the surface of the object to be measured during the optical probe scanning. However, by performing the phase connecting process, it is possible to correct the step that causes a measurement error.

Even if the phase information of the interference fringes is interrupted, the measurement is continued from the measurement point where the phase information is recovered,
By performing the phase connecting process, it is possible to avoid re-measurement. Also, depending on the inclination angle ψ of the measured object,
Even in a situation where the step amount (phase jump amount) does not become (n · λ / 2), it becomes possible to carry out the phase joining.

[0066]

As described above, according to the present invention,
In the optical probe scanning three-dimensional shape measuring instrument, even if a step (phase jump) occurs due to the discontinuity of the phase information of the interference fringes due to the influence of dust adhering to the surface of the measured object during the optical probe scanning, It is possible to correct the step that causes an error by the phase connecting process.

Even if the phase information of the interference fringes is interrupted, it is possible to avoid the re-measurement by continuing the measurement from the measurement point where the phase information is recovered and performing the phase connecting process. .

[Brief description of drawings]

FIG. 1 is a diagram showing a flow of processing according to an embodiment, FIG. 1A is a diagram showing a flow of phase skip processing, and FIG.
FIG. 6 is a diagram showing the overall flow of the phase joining process, and FIG. 7 (c) is a diagram showing the flow when the phase information is interrupted during the surface shape measurement.

FIG. 2 is a schematic view of a main part of a three-dimensional shape measuring machine according to an embodiment.

FIG. 3 is a diagram showing a relationship between a Z-axis length measurement value Zmi and an inclination angle ψi of the surface shape of the object to be measured, where (a) is ψi =
Diagram showing a state of 0 ° (no tilt angle), (b)
Is a diagram showing a state of ψi = ψ (there is a tilt angle),
(C) is a figure which shows the influence of the measurement error in the state of (phi) i = (psi).

FIG. 4 is a diagram showing a state of surface shape measurement in which phase information is interrupted twice due to encounter with dust during measurement, and a state of cross-sectional shape measurement crossing the surface shape measurement.

5A and 5B are views showing a sectional fragmentary shape and a reference sectional shape, FIG. 5A is a view showing a comparison between the sectional fragmentary shape and the reference sectional shape, and FIG. 5B is a sectional fragmentary shape and the reference sectional shape. It is the figure which showed the difference value ΔZdi of the shape and the comparison of the threshold value.

FIG. 6 is a diagram showing division of a measurement surface, (a)
FIG. 6 is a diagram showing a state in which a composite surface shape is divided into circumferential fragment shapes, and FIG. 9B is a diagram showing a manner in which a circumferential fragment shape including a step is selected.

7A and 7B are views showing a fragmentary shape in the circumferential direction, FIG. 7A is a view showing a state of the peripheral fragmentary shape including a step, and FIG. It is the figure which showed the comparison of the value.

FIG. 8 is a schematic view of a main part of a photocatalytic shape measuring instrument of a first conventional example.

FIG. 9 is a diagram showing a second conventional example,
FIG. 7A is a diagram showing a flow of phase joining processing, and FIG. 7B is a diagram showing a state of missing phase information.

[Explanation of symbols]

1 Object to be measured (axisymmetric aspherical lens) 1a Surface shape of DUT 2 optical probe 3 Z stage 4 R stage or X stage 5 Z-axis reference mirror 6 R-axis reference mirror or X-axis reference mirror 7 Z-axis laser length measuring device 8 R-axis laser length measuring device or X-axis laser length measuring device 9 θ stage (air-bearing) 9a Air bearing rotor 9b Air bearing stator 10 scale 11 Scale detector 12 mounts 13 XZ stage

Claims (5)

[Claims] 1. A method of measuring a surface shape of an object to be measured using an optical probe scanning three-dimensional shape measuring instrument, wherein a measurement result obtained by scanning the object to be measured with an optical probe to measure the surface shape. A first step of calculating a first surface shape from the first step, a second step of calculating a first fragment shape from a measurement result of measuring the cross-sectional shape of the measured object, and a measurement of the first fragment shape A third step of calculating a second fragment shape that coincides with the point from the first surface shape by interpolation processing, and a second fragment shape based on the difference between the first fragment shape and the second fragment shape A fourth step of identifying a first phase jump location that occurs in the first step, a fifth step of dividing the first surface shape into a plurality of fragment shapes to calculate a third fragment shape group, the third step A fourth fragment shape corresponding to the first phase jump location is selected from the fragment shape group A sixth step, a seventh step of identifying a second phase jump location included in the fourth fragment shape and calculating a correction amount, and a second phase calculated in the seventh step. An optical probe scanning three-dimensional shape measuring method comprising: an eighth step of calculating a second surface shape by using a flying point and a correction amount. 2. The first phase jump point is specified in the fourth step by using a threshold value that changes according to a surface shape inclination angle of the object to be measured. The optical probe scanning three-dimensional shape measuring method described in 1. 3. The first surface shape is measured by spirally scanning the optical probe with respect to the DUT, and the first fragment shape is obtained by moving the optical probe with respect to the DUT. 3. The third fragment shape group is obtained by dividing the surface shape into a plurality of spiral fragment shapes, and is measured by scanning in a radial direction. Optical probe scanning three-dimensional shape measuring method. 4. The first surface shape is measured by scanning the optical probe concentrically with respect to the measured object, and the first fragment shape is measured with the optical probe against the measured object. 3. The third fragment shape group is obtained by dividing the surface shape into a plurality of concentric fragment shapes, and is measured by scanning in a radial direction. Optical probe scanning three-dimensional shape measuring method. 5. The first surface shape is measured by scanning the optical probe with respect to the object to be measured in a zigzag manner, and the first fragment shape is measured with the optical probe against the object to be measured. 7. The measurement is performed by scanning in a direction transverse to the zigzag scan, and the third fragment shape group is obtained by dividing the surface shape into a plurality of zigzag fragment shapes. 1 or 2
The optical probe scanning three-dimensional shape measuring method described in 1.