JPH1089940A - Equipment for measuring fine surface shape of object - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect the surface of an object perfectly through noncontact measurement wherein the extent of irregularities on the surface of the object is measured based on the difference of outputs from first and second photoelectric conversion means. SOLUTION: A photoelectric conversion element 6 generates an electric signal Sγ corresponding to the combined quantity of reference light Pir . An optical head 8 irradiates a measuring point 7a on the surface of an object 7 with a first measuring light Pia and an optical head 9 irradiates the measuring point 7a with a second measuring light Pib . A photoelectric conversion element 10 generates an electric signal Sa corresponding to the combined quantity of reflected light of the first measuring light Pia from the measuring point 7a . A photoelectric conversion element 11 generates an electric signal Sb corresponding to the combined quantity of reflected light of the second measuring light Pib from the measuring point 7a . An operating unit 13 operates the difference between the electric signal Sr and the electric signal Sa or the electric signal Sb A controller 14 measures the extent of irregularities of the object 7 at the measuring point 7a based on the difference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine shape measuring device for an object surface, and more particularly to a fine shape measuring device for an object surface applicable to a surface roughness meter and a three-dimensional laser digitizing system.

[0002]

2. Description of the Related Art There is a so-called "contact probe method" as one of known techniques of a surface roughness meter used for surface inspection of an ultra-precision machined object. In this method, the vertical movement of the needle tip is recorded while moving the tip of the needle against the surface of the object to be inspected. Depending on the size of the needle, extremely high measurement accuracy on the order of nanometers can be obtained. . The stylus method measures the three-dimensional shape of an object and, for example, uses a CAE (computer a)
A system that generates input information to computer application devices such as ided engineering (3D laser digitizing,
System).

[0003]

However, the stylus method involves bringing a "needle" into contact with the surface of an object.
When the contact force is too strong or the material of the contact surface is soft, there is a problem that the object surface is damaged. Therefore, an object of the present invention is to provide a non-contact fine shape measuring device that does not damage the object surface at all.

[0004]

The invention according to claim 1 is
A light source that generates coherent light, a light splitting unit that splits the light into a first light and a second light, a deflecting unit that deflects the first light, and a second light that deflects the second light. First photoelectric conversion means for generating an electric signal having a magnitude corresponding to a combined light amount with the first light, and irradiation for irradiating the surface of the measurement target object with the second light and the deflected first light Means, a second photoelectric conversion means for generating an electric signal having a magnitude corresponding to the amount of light reflected from the surface of the object to be measured, and an output of the first photoelectric conversion means and an output of the second photoelectric conversion means. Measuring means for measuring the size of the irregularities on the surface of the object to be measured based on the difference from the output.

According to a second aspect of the present invention, in the first aspect of the present invention, the first light and the second light have different wavelengths. The invention according to claim 3 is the invention according to claim 1.
In the invention according to the above, the optical axis of the irradiation light of the irradiation means or another irradiation light having the same characteristics as the irradiation light is larger than 0 degree and 90 degrees with respect to a vertical line of the surface of the measurement object. The angle is smaller than the degree.

[0006]

[Function] Coherent light is converted into two lights (first light, second light).
When the two lights are irradiated on the surface of the object to be measured by deflecting one of them, the irradiation points of the two lights on the surface are separated according to the amount of deflection.
Now, for convenience, if the irradiation points are represented as A and B, respectively, A,
When the heights of B are the same, the frequencies and phases of the two reflected lights from A and B match, but when the heights of A and B do not match, the two reflected lights A difference occurs in the frequency or phase of the light, and the difference corresponds to the height. Therefore, the first photoelectric conversion means having the above-described configuration provides an electric signal (for convenience) corresponding to the phase difference between the two lights (the second light and the first light after the deflection) before irradiating the surface of the measurement object. (Referred to as “reference signal”), and the second
The photoelectric conversion means of (2) includes two reflected lights (a reflected light of the second light and a reflected light of the first light after the deflection) from the surface of the object to be measured.
An electric signal (referred to as a “measurement signal” for convenience) is taken out, and the difference between the reference signal and the measurement signal indicates the height of the surface of the object to be measured.
It is possible to measure the shape of the surface in a non-contact manner, and to provide a fine shape measuring device which does not damage the surface of the object at all.

Alternatively, if the wavelengths of the first light and the second light are made different, the frequency of the reference signal and the frequency of the measurement signal become low according to the wavelength difference, so that wide-band photoelectric conversion means is not used. It is preferable because the cost can be reduced. Or
When the second light and the first light after deflection are irradiated at an angle larger than 0 degree and smaller than 90 degrees with respect to the vertical line of the measurement target object, the vertical plane of the measurement target object is detected, This is preferable because phase jump can be avoided.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings, but before that, the principle of the present invention will be explained. (Principle) Wave of frequency f ₁ and frequency f ₂ (for convenience, f ₁ >
When the waves of f ₂ ) are mixed, a wave of frequency f ₁ −f ₂ is formed. When two waves having the same frequency are mixed, the phase difference can be obtained. In the radio wave area, the local oscillation signal is mixed with the high-frequency reception signal (heterodyne detection) to convert it to a low-frequency signal (intermediate frequency signal) corresponding to the frequency difference, facilitating the handling of the signal inside the receiver. Is being planned. On the other hand, coherent light such as laser light is also a “wave”, so if “light” at frequency f ₁ and “light” at frequency f ₂ are similarly mixed,
Frequency f ₁ of the -f ₂ can "light", also when mixing two light P _1, P ₂ of the same frequency, it is possible to retrieve the phase difference.

Here, it is assumed that P ₁ and P ₂ are irradiated on the surface of the object to be measured, and the intensity of the reflected light (mixed wave) is measured. The height of the irradiation point of the P ₁ and P ₂ is not generated phase difference as long as they match, the slightest there is a height difference from the phase difference corresponding to the difference is generated, P ₁ based on the phase difference and it is possible to know the altitude difference of the irradiation point of P _2,
By measuring and plotting the altitude difference over the entire measurement range, the fine surface shape of the object to be measured can be quantitatively measured. A preferred embodiment based on such a principle is as follows. (Embodiment) FIGS. 1 to 9 are views showing an embodiment of an apparatus for measuring a fine shape of an object surface according to the present invention.

First, the configuration will be described. In FIG. 1, 1
Is the light P ₀ (coherent light) whose phase is aligned at a single wavelength
Which is not particularly limited, but here,
He that generates coherent light with a wavelength of 633 nanometers
-Ne laser is used. Reference numeral 2 denotes a spectroscopic unit and a deflecting unit.
b, an acousto-optic element 2c, a plano-concave lens 2d, and a cylindrical lens 2e are sequentially arranged.

The acousto-optic element 2c is a device for controlling the deflection of the light P ₀ by utilizing the diffraction of light caused by the periodic density created in the medium by the ultrasonic waves. A first light P ₁ having a fixed deflection amount and a second light P ₂ having a variable deflection amount are extracted. Note that the first light P ₁
When the amount of deflection of the second light P ₂ is adapted to be controlled by the signal from the operation unit 2f. In addition to the acousto-optic element 2c, a mechanical optical deflector that changes the direction of reflected light by rotating or oscillating a reflecting mirror around an appropriate axis, or electro-optical light deflection using the Pockels effect and birefringence. Can be used.

Reference numerals 3 and 4 denote beam splitters for distributing the first light P ₁ and the second light P ₂ together in two directions. Hereinafter, two lights (P _i ; i is 1 and 2) that have passed straight through the lower beam splitter 3 are converted into a first measurement light (P _i a).
) And said, refers to two light bent at a right angle at the upper side of the beam splitter 4 and the second measurement light and (P _i b), further, the reference light two light passing through the upper beam splitter 4 straight to (P _i r) and say it.

[0013] 6 photoelectric conversion element for generating an electrical signal Sr corresponding to the synthesized light intensity of the reference light P _i r, 7 is a measured object. 8 an optical head for irradiating a first measuring beam P _i a measuring point 7a on the surface of the measured object 7, the optical head for irradiating a second measuring beam P _i b in the measuring point 7a 9, 10 the first measuring beam P _i a of the reflected light P _i a 'from the measurement point 7a photoelectric conversion element for generating an electric signal Sa corresponding to the synthesized light intensity (hereinafter, the first means and the reflected light), 11 This is a photoelectric conversion element that generates an electric signal Sb corresponding to a combined light amount of reflected light P _i b ′ of second measurement light P _i b (hereinafter, referred to as second reflected light) from the measurement point 7a.

The two optical heads 8, 9 and the two photoelectric conversion elements 10, 11 are preferably mounted on a common head mechanism 12, and the free movement of the head mechanism 12 allows the measurement of the object 7 to be measured. The point 7a can be irradiated with light from various directions and receive the reflected light. Numeral 13 denotes an arithmetic unit for calculating the difference ΔS between the electric signal Sr and the electric signal Sa or between the electric signal Sr and the electric signal Sb, and 14 measures the size of the unevenness of the measuring point 7a of the measuring object 7 based on the difference. And the head mechanism 12, the stage 7b of the object 7 to be measured, and the optical deflector 2c.
Is a controller that performs sequence control of each unit such as the operation unit 2f.

Next, the operation will be described. As already mentioned,
When the two lights are mixed, information on the phase difference between the two lights can be extracted. Now, assuming that the frequencies of the two lights P _i are f ₁ and f ₂ , P _i can be represented by the following equations (1) and (2). _{P 1 (t) = A 1} exp {i2πf 1 t + φ 1} ......... (1) P 2 (t) = A 2 exp {i2πf 2 t + φ 2} ......... (2) However, A _1, A ₂ is The amplitudes of P ₁ and P ₂ , φ ₁ and φ ₂ are the initial phases of P ₁ and P ₂ , t is time, and i is an imaginary unit.

The intensity I of the case of causing interference P _1, P _{2 is, I = <P 1 + P} 2> 2 ......... (3) _{next, Δf = f 1 -f 2 .........} (4) Δφ = placing phi ₁ -.phi ₂ ......... (5), the above equation (3) ^{_{is, I = a 1 2 + a}} 2 2 + 2A 1 a 2 cos (2π + Δft + Δφ) can be written as ......... (6), Since the AC component of the third term on the right side of the equation (6) includes information on the frequency difference (Δf) and phase difference (Δφ) of the two lights P _i , the magnitude corresponding to the first and second terms on the right side By removing the first and second terms by applying a bias, the above frequency difference (Δf) and phase difference (Δφ) are obtained as I = 2A ₁ A ₂ cos (2π + Δft + Δφ) (6) ′. Can be extracted by the change of I.

Here, assuming that Δf is 0, the following operation is obtained. That is, when the surface shape of the measurement points 7a of the measured object 7 conveniently assumes that as in FIG. 2 (a), irradiation with P _i a at any position of the measurement point 7a, P ₁ a, P ₂
When there is an altitude difference h at each irradiation position of a,
There is a difference between the optical path lengths of P ₁ a and P ₂ a, and a phase difference φ occurs according to the difference in the optical path length as shown in FIG.

[0018] Thus, P _i a of the reflected light intensity I in the case of causing interference (second reflected light P _i a ') is the equation (6)
Since the information of the phase difference φ in FIG. 2B is included,
Between the phase difference [Delta] [phi and height difference Delta] h, the relationship expressed by the following equation (7), Δh = λ · Δφ / 4π ......... (7) the combined light of the second reflected light P _i a ' Is received by the photoelectric conversion element 10 and converted into an electric signal Sa, the surface shape of the measurement target object 7 can be measured with an accuracy of the wavelength λ or less of the light. For example, the wavelength λ of the He-Ne laser is About 63
Since the resolution of the phase measurement is 1 degree because of 3 nm, Δh can be measured with a high accuracy of about 0.88 nm.

The frequencies f ₁ and f ₂ are, in principle, equal (f
₁ = f ₂ ), but the photoelectric conversion elements 6, 10, 1
1 requires the use of a high band (metal-metal point contact diode, Josephson diode, etc.), so that from the viewpoint of cost, Δf is 10 ⁵ to 10 ⁶ Hz.
It is desirable to set f ₁ and f ₂ to such values as to be about the same. A general photodetector can be used.

In this embodiment, the first measurement light (P _i
Other a) using the second measurement light (P _i b), but the reason is as follows. The measurement method of the present embodiment is excellent in that an extremely high resolution of less than the wavelength of light can be obtained. For example, the height difference h in FIG. If a phase difference φ exceeding the integral multiple (φ = 360 degrees + α degrees) occurs, “360 degrees + α degrees” cannot be distinguished from “α degrees”, and erroneous measurement cannot be avoided. FIG. 3 is a diagram showing an example in which such erroneous measurement is likely to occur. P ₁ a and P ₂ across the step
Since a is located, the difference between the optical path lengths of P ₁ a and P ₂ a becomes considerably large, and depending on the degree of the step, a phase difference φ exceeding an integral multiple of one wavelength occurs.

The second measuring beam of the present embodiment (P _i b) and related elements (photoelectric conversion element 11) that is an addition element for avoiding such erroneous measurements, matters and its essential,
The irradiation angle of the second measurement light (P _i b) to the measurement target object 7 is larger than 0 degree and smaller than 90 degrees with respect to the irradiation angle of the first measurement light (P _i a). The point is that the photoelectric conversion element 11 is arranged at a position where the reflected light (the second reflected light P _i b ′) of the second measurement light (P _i b) can be received. Note that the critical meaning of the angles (0 degree, 90 degrees) becomes the same as the first measurement light at 0 degrees, and at 90 degrees or more, the optical head interferes with the object to be measured. It is because.

According to this, as shown in FIG. 4, since the second measuring beam (P _i b) is irradiated on the vertical surface of the stepped, P
₁ b 'and P ₂ b' becomes small phase difference, can detect the presence of the step, because it discards the measurement result at that time, it can be avoided detection of the phase difference φ exceeds the integral multiple of wave. The first measuring light optical axis (P _i a), suitably, be configured to allow a smaller than larger and 90 degrees than 0 degrees, the first measurement light (P _i a) It can also be used as the second measurement light.

In this embodiment, one of the two lights (P
Although the amount of deflection of ₂ a) are variable and the variable width may exceed a mixed limit distance of the two light, to become unavailable principle (heterodyne detection) mentioned at the outset, devised as follows There is a need. That is, as shown in FIG. 5, while irradiating the point X with the reference side light (P ₁ a),
One light (P ₂ a) is deflected to sequentially shift its irradiation position, but if it is shifted further, a limit point at which a combined light of the reflected light (P _i a ′) of the two lights cannot be obtained. (Preferably the point just before) When the object reaches y, the measurement object 7
, The irradiation point of the reference side light (P ₁ a) is moved to y, one of the lights (P ₂ a) is again deflected, and the operation of sequentially shifting the irradiation position is repeated. By doing so, it is possible to set the deflection amount to an appropriate variable width.

Furthermore, in this embodiment, as shown in FIG. 6, the optical heads 8, 9 and the photoelectric conversion elements 6, 10, 11 are rotatably arranged around the X, Y, and Z axes. against a possible light irradiation or light from any direction, for example, as shown in FIG. 7, the measuring light (P _i
Even if the reflection angle of a ′) deviates from the direction of the photoelectric conversion element 10, the deviation can be corrected and normal light reception can be performed by appropriately rotating the optical head and the photoelectric conversion element.

FIG. 8 is a measurement flowchart of the present embodiment described above. In this flowchart, when the measurement range of the measurement target object 7 is input (step 20), the measurement pitch (see FIG. 5A) is specified (step 21), and measurement start is instructed (step 22). 1 of the measuring light (P _i a) and the second measuring beam (P _i b) perform the measurement from two directions with (step 23), if possible light (No judgment in step 24) the head mechanism 12 is moved (step 25) and step 23 is executed again. If light can be received (Yes in step 24), it is determined whether or not the plane is a vertical plane (step 26). If it is a vertical plane (Yes in step 26), the head mechanism 1
2 is moved (step 27) and step 23 is re-executed. If it is not a vertical plane (No in step 26), the measurement result is output (step 28), and the above operation ends the measurement range (step 26). The processing is repeatedly executed until the determination is Yes at 29).

FIG. 9 is a flowchart for generating the surface shape data of the measurement object 7 based on the phase difference information measured in the flow of FIG.
This is an application example to a three-dimensional laser digitizing system that generates input information to be used for numerical simulation of a finite element method (FEM) using an AE computer.

In the flow of FIG. 9, first, the phase difference Δφ is converted into an altitude difference Δh by using the above equation (7), and all the values of the altitude difference Δh are developed into three-dimensional coordinates (step 40). . Next, the interval between adjacent altitude differences Δh in the three-dimensional plane is determined (step 41). If the interval is larger than the diameter of the beam spot (Yes in step 42), the interval is subjected to curve interpolation. (Step 43) When the diameter is smaller than the beam spot diameter (N in Step 42)
In o determination), a wire frame is created (step 45) by linearly interpolating the interval (step 44). Next, in order to create a model for FEM analysis, after designating the desired number of elements as a whole, a part to be finely divided and a part to be roughly divided (step 46), the number of input elements and the volume and surface area of the model are appropriately determined. The element length is determined, and a node is created from each measurement point to perform element division to execute a meshing operation (steps 47, 48, and 49).
Finally, the necessary analysis conditions are input to create an input file for the analysis tool (step 50), and the process ends.

[0028]

According to the present invention, since extremely accurate surface shape measurement can be performed without damaging the object,
A particularly advantageous effect that can be provided for a shape inspection apparatus suitable for use in a shape inspection of a hyperfine processed object or a three-dimensional laser digitizing system, which is not available in the related art, is obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual configuration diagram of an embodiment.

FIG. 2 is a schematic diagram illustrating a relationship between an optical path difference and a phase difference between two lights.

FIG. 3 is an explanatory schematic diagram of a phase jump.

FIG. 4 is an explanatory schematic diagram for avoiding phase jump.

FIG. 5 is an operation schematic diagram of a deflection amount.

FIG. 6 is a schematic view of the movement of a head mechanism.

FIG. 7 is an explanatory diagram of light receiving failure.

FIG. 8 is a measurement flowchart of one embodiment.

FIG. 9 is a flowchart of generating meshing data according to one embodiment;

[Explanation of symbols]

 1: light source 2: spectral means and deflecting means 6: photoelectric conversion element (first photoelectric conversion means) 7: object to be measured 8: optical head (irradiation means) 10: photoelectric conversion element (second photoelectric conversion means) 13 : Computing unit (measuring means) 14: Controller (measuring means)

Claims (3)

[Claims] A light source for generating coherent light; a light splitting means for splitting the light into a first light and a second light; a deflecting means for deflecting the first light; and the second light. A first photoelectric conversion means for generating an electric signal having a magnitude corresponding to a combined light amount of the first light after the deflection and the first light after the deflection; Irradiating means for irradiating the surface; second photoelectric conversion means for generating an electric signal having a magnitude corresponding to the amount of reflected light from the surface of the measurement object; output of the first photoelectric conversion means and the second Measuring means for measuring the size of the irregularities on the surface of the object to be measured based on the difference from the output of the photoelectric conversion means. 2. The apparatus according to claim 1, wherein the first light and the second light have different wavelengths. 3. An illuminating light of said irradiating means or an optical axis of another irradiating light having the same characteristic as said irradiating light is larger than 0 degree with respect to a vertical line of the surface of said object to be measured by 9 degrees.
2. An angle smaller than 0 degree.
An apparatus for measuring a fine shape of an object surface according to the above.