JP2000074621A - Displacement measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a displacement measuring method which can measure the position and displacement of a measured body with high precision irrelevantly to the surface state of the measured body. 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 a photodetector 20. On the surface of the measured body 16, the light intensity curve is found while the objective 15 is moved along the optical axis. A threshold Pth is found from plural light intensity curves which are thus obtained, the gravity center position of the area encircled with the light intensity curves and the threshold, and the focus position of the objective 15 when objective 15 is at the gravity center position is decided as the surface position of the measured body 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a displacement measuring method. In particular, the present invention relates to a displacement measurement method for measuring a surface position and a surface displacement of an object to be measured without contact.

[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 an 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. 10), an excessive measurement result is obtained. 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]

According to a first aspect of the present invention, there is provided a displacement measuring method, wherein light is projected onto an object to be measured through an objective lens, reflected light from the object is received, and a focal position of the objective lens is shifted in an optical axis direction. Measure the change in light intensity due to the focal point movement of the objective lens by moving along, find the threshold from the curve representing the change in light intensity, find the center of gravity of the area surrounded by the curve and the threshold, The displacement of the object to be measured is measured from the position of the center of gravity.

According to the present invention, a threshold value is obtained from a curve representing a change in 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 to be measured is obtained from the position of the center of gravity. Since the measurement is performed, the displacement of the object to be measured can be obtained with an accuracy smaller than the sampling interval in the focal point moving direction of the objective lens, and the measurement accuracy can be improved as compared with the related art.
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, according to this displacement measuring device, since the surface position of the object to be measured is obtained from the position of the center of gravity of the light intensity curve, even if suddenly large light intensity is measured by noise or the like, it is affected by it. And stable measurement results can be obtained.

According to a second aspect of the present invention, there is provided a displacement measuring method, wherein light is projected onto an object to be measured through an objective lens, reflected light from the object is received, and a focal position of the objective lens is shifted in an optical axis direction. Along with moving the objective lens, the change in light intensity due to the focus movement of the objective lens is measured, a predetermined curve approximating a curve representing the change in light intensity is obtained, and the displacement of the object to be measured is measured based on the approximate curve. It is characterized by doing. For example, the displacement of the measured object can be obtained based on the center line, the center of gravity, and the maximum value of the approximate curve.

Further, if a predetermined curve approximating a curve representing the change of the synthesized light intensity is determined 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.

[0014]

(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, A light intensity curve as shown in FIG. 2 can be measured.

As shown in FIG. 6, the displacement measuring device 11
While irradiating light on the surface of the DUT with fine irregularities,
Move the object lens 15 in the optical axis direction and measure the change in light intensity.
Then, a light intensity curve B is obtained and stored. The light thus obtained
If the intensity curve B is as shown in FIG.
The data processing unit 24 determines a threshold value P based on the light intensity curve B.
Set th. Threshold P_thOne way to decide
Maximum value P of intensity curve B _maxΑ% (where 0 ≦ α <1
00). That is, P_th= Α × P_max/
The threshold is determined by 100. Threshold P_thDecide
Another method, as shown in FIG.
Of the objective lens 15_Three, Z_Four(Rough DUT 1
(The position of the objective lens 15 corresponding to the existing area of No. 6)
In advance, the interval [z_Three, Z_Four], The area under the light intensity curve
Of the center of gravity P in the light intensity axis direction_GAnd calculate this as the threshold P
_th= P_GAnd

It is assumed that a light intensity curve B as shown in FIG. 7 is represented by f (z) as a function of the position z of the objective lens 15, and the threshold value P _th is obtained by any of the methods. , The data processing unit 24 obtains the barycentric position z _G in the moving direction of the objective lens 15 from the light intensity curve f (z) by the following equation (1). In the expression (1), z ₁ and z ₂ are positions of the objective lens 15 when the light intensity P is equal to the threshold value P _th .
Then, the data processing unit 24 obtains the center of gravity position z _G as shown in FIG. 9, and determines the focal position when the objective lens 15 is at the center of gravity position z _G as the surface position of the DUT 16.

[0020]

(Equation 1)

[0021] 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).

[0022]

(Equation 2)

In this way, according to the displacement measuring device 11, it is possible to measure the displacement 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 a confocal optical system, since the surface position of the object 16 is obtained from the position of the center of gravity of the light intensity curve, the measurement can be performed in an unstable state. Therefore, even when 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. 10), A relatively stable measurement result can be obtained without being affected by this. 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.

In this embodiment, the position and displacement of the object 16 are calculated from the position of the center of gravity of the light intensity curve B, so that the position of the object 16 is smaller than the sampling interval in the moving direction of the objective lens 15. The position and displacement of the measurement object 16 can be obtained. 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.

(Second Embodiment) Next, a second embodiment of the present invention will be described.
An embodiment will be described. In this embodiment, as shown in FIG. 11, 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 (3). 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.

After obtaining the approximate curve, as shown in FIG. 12, the DUT 1 is moved to the focal position when the objective lens 15 is located at the position zmax where the approximate curve has the maximum value Pmax.
6 may be determined to be located. Or,
After the approximate curve is obtained, the position of the center of gravity of the approximate curve is obtained in the same manner as in the first embodiment, and the surface of the DUT 16 is positioned at the focal position when the objective lens 15 is located at the position of the center of gravity. May be determined to be located.

As described above, the method using the approximate curve has a feature that the focal position of the curve close to the ideal can be determined.

[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 a light intensity curve measured on the surface of a measurement object.

FIG. 8 is a diagram illustrating a method for determining a threshold value of light intensity.

FIG. 9 is a diagram illustrating a method for detecting a surface position of an object to be measured.

FIG. 10 is a diagram illustrating a state in which a spike-like noise is on a light intensity curve.

FIG. 11 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. 12 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.

[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, Japan Inside Murata Manufacturing Co., Ltd. (72) Ryo Nishiki 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto, Japan F-term in Murata Manufacturing (reference) 2F065 AA02 AA09 AA17 AA30 DD04 FF44 FF67 GG06 JJ01 JJ02 JJ18 JJ25 LL30 NN02 QQ01 QQ08 QQ18 QQ23 QQ29

Claims (2)

[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. The change in light intensity is measured, and the threshold is determined from the curve representing the change in light intensity, the center of gravity of the area surrounded by the curve and the threshold is determined, and the displacement of the device under test is measured from the position of the center of gravity. A displacement measurement method. 2. Focus shift of the objective lens by projecting light onto the object through the objective lens, receiving reflected light from the object, and moving the focal position of the objective lens along the optical axis direction. Measuring a change in light intensity associated with the measurement, obtaining a predetermined curve approximating a curve representing the change in light intensity, and measuring a displacement of the object to be measured based on the approximate curve.