JP2000074622A - Method and instrument for displacement measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and instrument for displacement measurement which can measure the position and displacement of a measured body with high precision irrelevantly to whether or not the surface state of the measured body is good. SOLUTION: The light emitted by a light source 12 is condensed by an objective 15 to irradiate the surface of the measured body 16 and the light reflected by the surface of the measured body 16 is received by an optical detector 20. At plural positions of the measured body 16, light intensity curves are found while the objective 15 is moved along the optical axis. The light intensity curves which are thus obtained are put together to find the light intensity composite curve and the focus position of the objective 15 when the light intensity composite curve becomes maximum is decided as the surface position of the measured body 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a displacement measuring method and a displacement measuring device. In particular, the present invention relates to a displacement measuring method and a displacement measuring device for measuring a surface position and a surface displacement of an object to be measured in a non-contact manner.

[0002]

2. Description of the Related Art The configuration of a conventional displacement measuring device is shown in FIG. This displacement measuring device 1 uses a confocal optical system, and light emitted from a light source 2 such as a laser diode passes through a collimating lens 3 and becomes parallel light.
It passes through the beam splitter 4. The light that has passed through the beam splitter 4 is condensed by the objective lens 5 and illuminates the surface of the DUT 6. The light reflected on the surface of the device under test 6 passes through the objective lens 5 again and passes through the beam splitter 4.
Is incident on the beam splitter 4, and the light whose direction is bent by 90 degrees is condensed by the condenser lens 7, and only the light that has passed through the pinhole 8 disposed at the focal position of the condenser lens 7 is a photodetector. 9 and the light intensity is measured.

In this displacement measuring apparatus 1, the objective lens 5 can be moved and adjusted in the direction of the optical axis (up and down direction in FIG. 1). The light intensity measured by the detector 9 changes as shown in FIG. 2 according to the position of the objective lens 5, and the distance between the surface of the measured object 6 (light irradiation position) and the objective lens 5 is When it becomes equal to the effective focal length, the light intensity P of the photodetector 9 becomes the maximum value Pmax. Accordingly, if the position z ₀ of the objective lens 5 when the light intensity reaches the maximum value Pmax is obtained from the change (light intensity curve) of the light intensity P, a position distant from the position z _{0 by} the focal position of the objective lens 5 is obtained. Can be measured as the position of the surface of the DUT 6.

[0004]

In the displacement measuring apparatus 1 as described above, when the surface of the measured object 6 is close to a mirror surface, the light intensity P when the position of the objective lens 5 is changed is changed.
Is a stable chevron-shaped light intensity curve having a shape as shown in FIG. 2, and highly accurate position measurement is possible.

However, if the surface of the object 6 has irregularities, light intensity curves as shown in FIGS. 3 and 4 can be obtained due to fine and random irregularities at the portions irradiated with light. Such irregular that the light intensity curve corresponding to the light intensity maximum value (light intensity maximum when the objective lens position) to determine the z ₀ is difficult, can position measurement or displacement measurement precision Did not.

In the method of detecting the surface position of the object to be measured from the maximum value of the light intensity curve, when a large light intensity is suddenly detected due to noise or the like (see FIG. 16), the measurement result is excessive. Was output, and the measurement operation was likely to be unstable.

The mirror surface is defined as having a surface roughness Ra of 0.01.
μm or less, and the uneven surface means a surface roughness Ra of 0.
It refers to a surface of about 01 to 1 μm.

The present invention has been made in order to solve the above-mentioned technical problems, and an object of the present invention is to determine the position and displacement of an object to be measured irrespective of the quality of the surface condition of the object. An object of the present invention is to provide a displacement measuring method and a displacement measuring device capable of measuring with high accuracy.

[0009]

DISCLOSURE OF THE INVENTION A displacement measuring method according to the present invention projects light on an object to be measured through an objective lens, receives reflected light from the object to be measured, and moves the focal position of the objective lens along the optical axis direction. By measuring the change in light intensity due to the focal point movement of the objective lens, the changes in the light intensity measured at a plurality of measurement points on the measured object are combined, and the displacement of the measured object is calculated based on the combined result. Is measured.

In this method, for example, a light emitting section for emitting light, an objective lens for projecting the light emitted from the light emitting section to an object to be measured, and a lens for moving the objective lens along the optical axis direction Driving means, lens position detecting means for detecting the position of the objective lens, a light receiving section for receiving reflected light from the object to be measured, and means for moving the light projection position of the objective lens along the surface of the object to be measured Means for combining a change in the light intensity measured by the light receiving unit while moving the objective lens at a plurality of measurement positions on the measurement object, and measuring a displacement of the measurement object based on the synthesis result. Can be implemented by a displacement measuring device.

According to such a displacement measuring method, since the displacement of the object to be measured is determined based on the result of combining the light intensities obtained at a plurality of measurement points, the light intensity is large and the error is small. , The weight of the light intensity having a small light intensity and a large error can be reduced, and the influence of the scattering of the uneven surface of the object to be measured can be reduced. Therefore, according to the present invention, it is possible to measure the position and displacement of the surface of the object to be measured with high accuracy and stably.

The displacement of the object to be measured can be obtained from the position where the change in the combined light intensity is maximum, based on the combined light intensity at a plurality of locations.
According to this method, the calculation for determining the displacement of the measured object can be simplified.

Further, a threshold value is obtained from a curve representing a change in the combined light intensity, a center of gravity of an area surrounded by the curve and the threshold value is obtained, and a displacement of the surface of the object is measured from the position of the center of gravity. By doing so, the displacement of the object to be measured can be obtained with an accuracy smaller than the sampling interval in the focus moving direction of the objective lens. Further, since a threshold value is set and data equal to or higher than the threshold value is used, unnecessary noise components can be removed, and the measurement accuracy can be further improved.

Further, if a predetermined curve approximating a curve representing the change of the combined light intensity is obtained and the displacement of the surface of the object to be measured is measured based on the approximate curve, a curve close to the ideal can be obtained. The focal position of the objective lens can be determined, and thereby the displacement of the measured object can be obtained.

Further, if the surface position of the object to be measured is obtained from the position of the center of gravity of the light intensity curve or the approximate curve, even if suddenly large light intensity is measured due to noise or the like, the measurement results are stable without being affected by the large light intensity. Can be obtained.

[0016]

(First Embodiment) FIG. 5 is a diagram showing a configuration of a displacement measuring device 11 according to a first embodiment of the present invention. The light source 12 includes a laser diode, a laser driving circuit, and the like, and light (laser light) emitted from the light source 12 is automatically adjusted by an auto power controller (APC) 23 to have a constant light intensity. . The light source 12 is arranged such that its light emitting point is the focal position of the collimator lens 13, and the divergent light emitted from the light source 12 is converted by the collimator lens 13 into parallel light. The light that has passed through the collimator lens 13 and turned into parallel light enters the beam splitter 14, and a part of the light passes through the beam splitter 14 and enters the objective lens 15.

The objective lens 15 is provided with a lens driving device 21.
Is driven at a constant amplitude and a constant cycle. For example, the lens driving device 21 vibrates the objective lens 15 in the optical axis direction at an amplitude of 100 μm and a frequency of 1 kHz by applying a magnetic force to a magnetic body provided on the objective lens 15 by an alternating magnetic field generated in a voice coil. Can be used. In addition, a position sensor 22 that can detect the position of the objective lens 15 with high accuracy is provided near the objective lens 15.

The light transmitted through the objective lens 15 is condensed by the objective lens 15 and is applied to an object 16 to be measured, which is set to face the objective lens 15 and stand still. The light reflected by the DUT 16 passes through the objective lens 15 again, and a part of the light is reflected by the beam splitter 14. The light reflected by the beam splitter 14 is turned by 90 degrees and enters the condenser lens 17. A light-shielding plate 18 having a pinhole 19 is provided at a focal position of the condenser lens 17, and light passing through the condenser lens 17 is collected in the pinhole 19. The light passing through the pinhole 19 is received by a photodetector 20 including a photodiode, a phototransistor, a CCD, and the like.

The position information of the objective lens 15 detected by the position sensor 22 and the light intensity value P measured by the photodetector 20 are sent to a data processing unit 24. Therefore,
The data processing unit 24 captures the position information from the position sensor 22 and the value P of the light intensity from the photodetector 20 while oscillating the objective lens 15 with the lens driving device 21 and performs necessary processing, for example, The light intensity curve as shown in FIG. 2 can be repeatedly measured.

The measuring head 26 of the displacement measuring device 11
(Containing the optical system of the displacement measuring device 11) can be moved in a direction parallel to the surface of the object 16 by the head driving device 25.

As a result, the displacement measuring device 11 is
As shown in (1), a light intensity curve when the objective lens 15 is moved is obtained at different locations on the surface of the object having fine irregularities, and is stored. The movement pitch δ of the measuring head 26 at this time is determined by the surface condition of the object 16, and may be, for example, about one to several times the size of the unevenness on the surface of the object 16. Further, if the spot diameter of the light applied to the DUT 16 is too large, all the light intensity curves become the same, so that the minimum spot diameter of the light needs to be an appropriate size. The spot diameter may be determined by trial and error according to the measured object 16, but is desirably several times the size of the flat portion of the measured object 16, particularly preferably about twice as large.

Thus, for example, A1, A2, A in FIG.
Assuming that the light intensity curves measured at points 3 and A4 are the curves B1, B2, B3 and B4 shown in FIG.
The data processing unit 24 calculates these light intensity curves B1, B2, B
3 and B4 are added to obtain a light intensity synthesis curve B as shown in FIG. Next, as shown in FIG. 9, the data processing unit 24 obtains a position z _{max at} which the light intensity reaches the maximum value Pmax from the light intensity synthesis curve B, and determines the focal position of the objective lens 15 at that time. Judge as the surface position.

As shown in FIG. 10, the head driving device 25 intermittently feeds the measuring head 26 at a constant pitch δ, and moves the measuring head 26 to each point A1, A2, A3, A4.
Each light intensity curve may be measured in the state where the light intensity is stopped. Alternatively, as shown in FIG. 11, the measuring head 26 is moved at a constant speed by the head driving device 25, and the points A1, A2, A3, and A4 for each pitch of δ are moved while moving the measuring head 26 at a constant speed. The light intensity curve may be measured. In the latter case, the moving speed of the measuring head 26 by the head driving device 25 is
It is necessary to make the moving speed slower than the moving speed of the objective lens 15. In the method of pitch-moving the measuring head 26 as shown in FIG. 10, since the same position is measured during the measurement of the light intensity curve, this is a driving method suitable for the purpose of the head driving device 25. Must be repeated, so that it is difficult to feed the pitch at high speed, and the operation may be unstable. On the other hand, the measuring head 26
In the method of moving the measuring head at a constant speed, the measuring head 26 moves even during the measurement of the light intensity curve, which may include some errors. However, since the measuring head 26 moves at a constant speed, the speed is increased. , And stable operation becomes possible.

In this way, the displacement measuring device 11 can measure the displacement amount of the surface of the object to be measured, the displacement from the reference position, or the distance from the displacement measuring device 11. Alternatively, two macro points as described above (that is, two points separated by a distance larger than the moving pitch δ)
, The displacement, height difference, etc. can be measured. For example, it is possible to measure the displacement and the thickness in the height direction of the ceramic substrate and the electrodes printed thereon.

According to the displacement measuring apparatus 11 of the present invention using the confocal optical system as described above or its measuring principle, the light intensity distribution at a plurality of fine positions is added to reduce the scattering of the uneven surface. The influence can be reduced, and the displacement, distance, and the like of the DUT 16 can be stably measured. That is,
When the surface of the DUT 16 is close to a mirror surface, the light intensity of the reflected light is relatively large and the measurement error is small, but when the influence of the uneven surface on the surface of the DUT 16 is large, Since the light intensity of the reflected light becomes relatively small, even if the average value of the uneven surface is obtained, the error increases.
The measurement principle of the present invention utilizes this point. If the surface position of the DUT 16 is simply obtained by averaging the focal positions of the objective lens 15, the case where the error is large and the case where the error is small are averaged with the same weight. On the other hand, if the light intensity curves are added and combined, the weight when the light intensity is large and the error is small increases, and the weight when the light intensity is small and the error is large decreases. As a result, the position and displacement of the surface of the object 16 can be measured with high accuracy and stably even when the surface of the object 16 has large irregularities.

Moreover, the maximum value Pmax of the light intensity synthesis curve B
From the position z ₀ of the objective lens 15 corresponding to
If the displacement and position of are calculated, the number of calculations can be reduced as compared with other embodiments.

(Second Embodiment) Next, a second embodiment of the present invention will be described. In the first embodiment, the surface position of the DUT 16 is obtained from the maximum value Pmax of the light intensity composite curve B. In this embodiment, however, the surface position of the DUT 16 is obtained from the center of gravity of the light intensity composite curve B. Ask for. Hereinafter, this embodiment will be described. The configuration of the displacement measuring device 11 (FIG. 5)
The process up to the point where the light intensity curves at a plurality of positions are combined in the data processing unit 24 is the same as that of the first embodiment, and a description thereof will be omitted.

The light intensity synthesis curve B as shown in FIG.
If it is expressed as f (z) as a function of the position z of the objective lens 15, the data processing unit 24 calculates the light intensity synthesis curve f
From (z), the position of the center of gravity z _G in the moving direction of the objective lens 15 is obtained by the following equation (1). Note that, in equation (1), z ₁ ,
z ₂ is the position when the objective lens 15 is at the end of the movement (vibration) range. And the data processing unit 24
As shown in (2), the center of gravity position z _G is obtained, and the focal position when the objective lens 15 is at the center of gravity position z _G is determined as the surface position of the DUT 16.

[0029]

(Equation 1)

[0030] Note that when the light intensity synthesizing curve f (z) is the data f of the discrete positions zi of the objective lens 15 (zi) is the center of gravity position z _G in the moving direction of the objective lens 15, the following
It is obtained by equation (2).

[0031]

(Equation 2)

In the first embodiment, the measurement cannot be performed with a precision smaller than the sampling interval in the moving direction of the objective lens 15, but as in this embodiment, the position of the object 16 to be measured is determined from the position of the center of gravity of the light intensity curve B. By calculating the position and the displacement, the position and the displacement of the DUT 16 can be obtained with an accuracy smaller than the sampling interval in the moving direction of the objective lens 15.

(Third Embodiment) Next, a third embodiment of the present invention will be described. In the second embodiment, the position of the center of gravity of the entire light intensity synthesis curve is obtained. However, in this embodiment, a threshold is set, the position of the center of gravity in a region of light intensity larger than the threshold is obtained, and the center of gravity is obtained. Measured object 16 from position
Find the surface position of.

First, the data processing unit 24 calculates the light intensity composite curve B by adding the light intensity curves, and then calculates the threshold value P _th from the light intensity composite curve B. One of the methods for determining the threshold value P _{th is} to set the maximum value P _max of the light intensity synthesis curve B to α
% (However, 0 <α <100). That is, the threshold value is determined by _Pth = α × _Pmax / 100. Another method for determining the threshold value P _{th is} to perform position measurement of the objective lens 15 in advance by sample measurement as shown in FIG.
₃ , z ₄ (the position of the objective lens 15 corresponding to the approximate area where the object 16 is present) is determined, and the section [z ₃ , z ₄ ]
In the area under the intensity synthetic curve, determine the gravity center P _G of the light intensity axis direction, which is the threshold P _th = P _G.

When the threshold value P _th is determined by any of the methods, the data processing unit 24 calculates the center of gravity z _{G in} the moving direction of the objective lens 15 from the light intensity synthesis curve f (z) according to the following equation (3). Ask for. Incidentally, (3) In the equation, z _5, z ₆ is the position of the objective lens 15 when the light intensity P is equal to the threshold P _th. Then, the data processing unit 24 obtains the position of the center of gravity z _G as shown in FIG. 14, and determines the focal position when the objective lens 15 is at the position of the center of gravity z _G as the surface position of the DUT 16.

[0036]

(Equation 3)

When the light intensity synthesis curve f (z) is discrete data f (zi), the position of the center of gravity z _G of the moving direction of the objective lens 15 can be obtained by the following equation (4).

[0038]

(Equation 4)

Also in this embodiment, by calculating the position and displacement of the object 16 from the position of the center of gravity of the light intensity synthesis curve B, the position of the object 16 can be calculated with a precision smaller than the sampling interval in the moving direction of the objective lens 15. The position and displacement can be determined. Furthermore, since the position of the center of gravity is determined from the light intensity P _{equal to} or higher than the light intensity threshold _{Pth in} order to remove unnecessary noise components, the measurement accuracy can be further improved.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described.
An embodiment will be described. In this embodiment, as shown in FIG. 15, the light intensity synthesis curve B is approximated by a curve, and the surface position of the DUT 16 is obtained from the reference position of the approximate curve C.

For example, the approximate curve C is expressed by the following equation (5). Here, a, b, and c are constants. k (z) = a · exp {−b (z−c) ² } (5) The data processing unit 24 determines the values of the constants a, b, and c from the calculation by the least square method or the like. Then, the center z = c of the approximate curve C is set as a reference position, and the focal position of the objective lens 15 when the objective lens 15 is at the reference position is determined as the surface position of the DUT 16. Alternatively, the approximate curve C
May be determined as the reference position, and the focal position when the objective lens 15 is at the reference position may be determined as the surface position of the DUT 16.

It is needless to say that a function other than the above function may be used as the approximate curve. And
Depending on the form of the approximation function, the position where the light intensity is maximum or the position of the center of gravity may be used as the reference position.

In the method using the approximate curve as described above, it is possible to determine the focal position of the curve close to the ideal.

Further, as in the second or third embodiment,
If the surface position of the DUT 16 is obtained from the position of the center of gravity of the light intensity curve, or the surface position of the DUT 16 is obtained from the approximate curve as in the fourth embodiment, measurement is performed in an unstable state. Therefore, if a large value is suddenly measured due to noise or the like while measuring the light intensity while moving the objective lens 15 (that is, even if a spike occurs in the light intensity curve as shown in FIG. 16), A relatively stable measurement result can be obtained without being affected. On the other hand, in the method of obtaining the surface position of the DUT 16 from the maximum value of the light intensity curve as in the conventional example, if the light intensity protruding in a spike shape due to noise or the like is measured, the measurement result that was immediately passed. Was output, and the measurement result was likely to be unstable.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a conventional displacement measuring device.

FIG. 2 is a diagram showing an ideal light intensity curve measured by the displacement measuring device.

FIG. 3 is a diagram showing a light intensity curve obtained from an object to be measured having an uneven surface.

FIG. 4 is a diagram showing another light intensity curve obtained from an object to be measured having an uneven surface.

FIG. 5 is a schematic diagram showing a configuration of a displacement measuring device according to an embodiment of the present invention.

FIG. 6 is an enlarged view of the surface of the device under test.

FIG. 7 is a diagram showing light intensity curves measured at different positions on an object to be measured.

FIG. 8 is a view showing a light intensity synthesis curve obtained by synthesizing the light intensity curves of FIG. 7;

FIG. 9 is a diagram for explaining a method for detecting a surface position of an object to be measured in the embodiment.

FIG. 10 is a diagram illustrating a method of feeding a measuring head.

FIG. 11 is a diagram illustrating another method of feeding the measuring head.

FIG. 12 is a diagram illustrating a method for detecting a surface position of an object to be measured in another embodiment of the present invention.

FIG. 13 is a diagram illustrating a method for determining a threshold value of light intensity in still another embodiment of the present invention.

FIG. 14 is a diagram for explaining a method for detecting a surface position of an object to be measured in the embodiment.

FIG. 15 is a diagram illustrating a method for detecting a surface position of an object to be measured in still another embodiment of the present invention.

FIG. 16 is a diagram illustrating a state in which spike-shaped noise is on a light intensity curve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 Light source 14 Beam splitter 15 Objective lens 16 Object to be measured 17 Condensing lens 19 Pinhole 20 Photodetector 21 Lens driving device 22 Position sensor 24 Data processing unit

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Shintaro Koike 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Co., Ltd. Inside Murata Manufacturing Co., Ltd. (72) Ryo Nishiki 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Co., Ltd. F-term in Murata Manufacturing (reference) 2F065 AA02 AA06 AA09 AA24 AA25 AA30 DD04 FF41 GG06 GG12 HH02 HH04 HH13 JJ01 JJ03 JJ18 JJ26 LL04 LL30 MM14 MM24 MM28 NN02 QQ17 QQ25 QQU U

Claims (5)

[Claims] 1. A focal point shift of an objective lens by projecting light onto an object to be measured through an objective lens, receiving reflected light from the object to be measured, and moving a focal position of the objective lens along an optical axis direction. Measuring a change in light intensity associated with the measurement, synthesizing a change in each light intensity measured at a plurality of measurement points on the measured object, and measuring a displacement of the measured object based on the synthesized result. Displacement measurement method. 2. The displacement measuring method according to claim 1, wherein the displacement of the object to be measured is measured from a position where a change in the combined light intensity is maximum. 3. A threshold is determined from a curve representing the change in the combined light intensity, a center of gravity of an area surrounded by the curve and the threshold is determined, and a displacement of the object is measured from the position of the center of gravity. The displacement measuring method according to claim 1, wherein: 4. The method according to claim 1, wherein a predetermined curve approximating a curve representing the change in the combined light intensity is obtained, and the displacement of the device under test is measured based on the approximate curve. Displacement measurement method. 5. A light emitting unit for emitting light, an objective lens for projecting the light emitted from the light emitting unit to an object to be measured, and a lens driving unit for moving the objective lens along an optical axis direction; Lens position detecting means for detecting the position of the objective lens; a light receiving section for receiving reflected light from the object to be measured; means for moving the light projection position of the objective lens along the surface of the object to be measured; Means for synthesizing a change in light intensity measured by the light receiving unit while moving the objective lens at a plurality of measurement positions of the object, and measuring a displacement of the object to be measured based on a result of the synthesis. .