JPH08201034A - Non-contact surface shape measuring method and apparatus - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a non-contact surface shape measuring apparatus capable of measuring a target surface at high speed and with high accuracy by simplifying data processing contents relating to measurement. In an interferometer using a white light source 12, a reference mirror 18 is moved at a constant interval in the optical axis direction with respect to a work W whose position is fixed to generate interference fringes, and the position of the reference mirror 18 is moved. The amount is measured by the displacement sensor 22, and the interference fringe is imaged by the camera 26. Then, based on the image data of the interference fringes obtained by the camera 26, the intensity of the interference fringes is detected for each position on the surface to be measured. Further, the above steps are repeated to obtain a plurality of interference fringe intensities, a value corresponding to the differential value of the interference fringe intensities is calculated, and the reference mirror when the value corresponding to the differential value becomes the maximum value or the minimum value. The surface shape of the work W is measured based on the position movement amount of 18. In this way, by setting the data relating to the measurement to the value corresponding to the differential value of the interference fringe intensity, the processing content is simplified, and the measurement can be performed at high speed and with high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact surface shape measuring method and device, and more particularly to a non-contact surface shape measuring method for measuring the surface shape of an object to be measured with an optical interferometer at high speed and high accuracy. Regarding the device.

[0002]

2. Description of the Related Art A method for observing a fine shape of an object by using light interference is widely known. Among them, an interference microscope combining an interferometer and a microscope is Michelson type, Linic type, Mirau type, etc. There are several types. Then, the pattern of the interference fringes on the surface of the object is imaged based on the interference microscope, and the three-dimensional shape of the object is measured based on the obtained image signal while moving the reference surface or the like in the optical axis direction. US Pat. No. 5,133,601
Or Japanese Patent Publication No. 6-1167.

[0003]

By the way, in the method described in the above-mentioned US Pat. No. 5,133,601, at each measurement point of the array type detector, the coherence degree is obtained from interference fringe data of three or more frames having different phases. Since the target surface is calculated and detected, it is necessary to calculate the coherence degree for the entire measurement range in the height direction of the target object. Further, particularly when white light is used as the light source, the coherence degree must be calculated from the data of 5 screens. Therefore, there is a problem that the load of arithmetic processing is heavy and it is difficult to speed up the measurement.

On the other hand, in the method disclosed in Japanese Patent Publication No. 6-1167, since the target surface is detected by detecting the maximum brightness of the interference fringes, the interference fringes are generated at each measurement point of the array type detector. It is necessary to capture the moment when the maximum brightness is reached.
Therefore, do not miss the moment of maximum brightness,
There is a problem in that it is necessary to make the change in the optical path length minute and, as a result, the measurement time becomes long.

The present invention has been made in view of the above circumstances, and a non-contact surface shape measuring apparatus capable of measuring a target surface at high speed and with high accuracy by simplifying data processing contents relating to measurement. The purpose is to provide.

[0006]

In order to achieve the above-mentioned object, the present invention uses a light source having a wide spectrum width, a first optical path length between the light source and the surface to be measured, and a reference surface up to the reference surface. Interference fringes are generated according to the optical path length difference from the second optical path length,
In a non-contact surface shape measuring method for measuring the shape of an object surface to be measured based on the intensity of the interference fringes, the first object surface or the reference surface is moved at a constant interval in the optical axis direction.
And a second step of measuring the position movement amount of the measurement target surface or the reference surface moved by the first step,
Based on the third step of imaging the interference fringes generated by the movement of the first step and the image data of the interference fringes obtained in the third step, for each position of the surface to be measured. A fourth step of detecting an interference fringe intensity and a fifth step of calculating a value corresponding to a differential value of the interference fringe intensity from a plurality of the interference fringe intensities obtained by repeating the first to fourth steps. Step, and the shape of the surface to be measured based on the amount of positional movement of the surface to be measured or the reference surface when the value corresponding to the differential value obtained in the fifth step becomes the maximum value or the minimum value. And a sixth step of measuring

[0007]

According to the present invention, in an interferometer using a light source having a wide spectrum width, in the first step, the light source and the object to be measured which move the surface to be measured or the reference surface at regular intervals in the optical axis direction. A first optical path length to the reference surface and a second optical path length to the reference surface with an optical path length difference at a constant interval to generate interference fringes, and in the second step, the measured object is measured. The position movement amount of the plane or the reference plane is measured, and the interference fringes are imaged in the third step. Then, based on the image data of the interference fringes obtained in the third step, in a fourth step, the interference fringe intensity is detected for each position on the surface to be measured. Furthermore, a plurality of interference fringe intensities are obtained by repeating the first to fourth steps, and a value corresponding to the differential value of the interference fringe strength is calculated in the fifth step, and the value corresponding to the differential value is calculated. In the sixth step, the shape of the measurement target surface is measured based on the position movement amount of the measurement target surface or the reference surface when the maximum value or the minimum value is reached. As described above, since the data processing related to the measurement mainly includes the value corresponding to the differential value of the interference fringe intensity, the processing content is simplified and the surface to be measured can be measured at high speed and with high accuracy.

In the sixth step, the interference fringe intensity data at two points before and after giving the maximum or minimum value corresponding to the differential value and the bias value (DC value) of the interference fringe intensity data. Is obtained, and that value is used as the position movement amount of the measured surface or the reference surface when the maximum value or the minimum value of the values corresponding to the differential value is given. This allows
The position movement amount of the measured surface or the reference surface when giving the maximum value or the minimum value of the values corresponding to the differential value can be calculated with high accuracy, and the accuracy of measurement can be improved.

Further, according to the present invention, in the sixth step, the phase value for the central wavelength of the light source is obtained from the interference fringe intensity data near the maximum or minimum value corresponding to the differential value. By calculating and correcting the position movement amount of the measurement target surface or the reference surface based on the phase value, the shape of the measurement target surface can be measured with higher accuracy.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the non-contact surface shape measuring method and apparatus according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram for explaining the configuration of the non-contact surface shape measuring apparatus of the present invention. As shown in the figure,
This measuring device mainly includes a lamp 12, a collimating lens 14,
Half mirror 16, reference mirror 18, electrostrictive element (PzT) 2
0, a displacement sensor 22, an imaging lens 24, a monochrome solid-state imaging camera 26, a frame memory 28, a central processing unit (CPU) 30, and the like. In the figure, a Twyman-Green type interferometer is described as an example, but a Linic type, a Mirau type interferometer or the like may be used.

The lamp 12 uses, for example, a white light source, and the light emitted from the lamp 12 is collimated by a collimator lens 14 and divided into two directions by a half mirror 16. That is, the light reflected by the half mirror 16 is applied to the measured object (work) W, while the light transmitted through the half mirror 16 is applied to the reference mirror 18. Work W
Is mounted on a fixed stage base (not shown),
The light reflected on the surface of the work W reaches the camera 26 through the half mirror 16 and the imaging lens 24, while the light reflected by the reference mirror 18 is the half mirror 16 and the imaging lens 2.
It reaches the camera 26 through 4.

The PzT 20 is driven by a PzT driver 32 to displace the reference mirror 18 at a constant interval in the optical axis direction, and the displacement sensor 22 is driven via a displacement sensor driver 34 to displace the reference mirror 18. The amount is being measured. The camera 26 images the interference fringes observed corresponding to the difference in optical distance between the two light fluxes (optical path length difference), converts the interference fringe image into a predetermined electric signal, and outputs the electric signal to the frame memory 28. . The frame memory 28 records the interference fringe image with the optical path length difference, that is, the displacement amount of the reference mirror 18 as a variable.

The CPU 30 is connected to the frame memory 28, the PzT driver 32 and the displacement sensor driver 34 via a bus 36, and at the same time, the frame memory 28.
The interference fringe data input via is processed to measure the surface shape of the work W. The data processing will be described later. A keyboard 40 and a monitor TV 42 are connected to the CPU 30, so that the operator can monitor the monitor TV 42.
While watching the display, various inputs can be performed via the keyboard 40, and the work W is displayed on the monitor TV 42.
It is possible to display the surface shape measurement result and the like.

Next, the measuring principle of this measuring apparatus will be described. FIG. 2 is an enlarged view of the interferometer portion of FIG. Assuming that the distance between the half mirror 16 and the reference mirror 18 is LR and the distance between the half mirror 16 and the work W is LW, the optical path difference (OPD) in this case.
Is expressed by the following equation (1).

OPD = 2 × (LR-LW) (1) The OPD is a variable that can be changed by driving the PzT 20 to displace the reference mirror 18 on the optical axis. Define in. Where OPD (=
When Z) is continuously changed near zero, the intensity I (Z) of the interference fringe observed at one point on the camera becomes a function like I (Z) shown in FIG. Also, Z of I (Z) above
The differential with respect to is a function as shown in J (Z) of FIG. In this measuring device, Z is changed within the entire measurement range, and Z value that gives the maximum value (or minimum value) of the above J (Z), that is, Za (or Zb) is obtained for each measurement point on the camera. , The surface shape of the work W is calculated.

Below, Z which gives the maximum value of J (Z)
A method of simply detecting the value, that is, Za will be described. Z can be discretely changed at predetermined constant intervals, an interference fringe image is acquired according to each Z value, and the intensity of the interference fringe is observed from the data of the image. And two consecutive points Z
The differential value J (Zi) is calculated by the following equations (2) and (3) using the interference fringe intensities I (Zi) and I (Zi-1) at i and Zi-1.・ When I (Zi)> I (Zi-1) J (Zi) = I (Zi) -I (Zi-1) (2) ・ When I (Zi) ≤I (Zi-1) J (Zi) = 0 (3) where Zi-Zi-1 = constant C: C is a constant distance for moving the reference mirror 18 0 <Zi-Zi-1 ≦ λ / 6: λ is the central wavelength of the light source And

By changing Z within the entire measuring range, the above J
(Z) is calculated, and a Z value giving the maximum value of J (Z), that is, a set of Zi and Zi-1 is discriminated, and the following equation (4)
Then, Za that gives the maximum value of J (Z) is detected. Za = (Zi + Zi-1) / 2 (4) This makes it possible to easily detect Za.

Further, in place of the equation (4), FIG.
, Zi and Z that give the maximum value of J (Z)
Two points of i-1 A (Zi, I (Zi)) and B (Zi-1, I
The intersection of the straight line l1 connecting (Zi-1)) and the bias value (DC value) of the interference fringe intensity may be detected as Za that gives the maximum value of J (Z). The Za obtained thereby has higher accuracy than the Za obtained from the equation (4).

The DC value can be obtained not only as the brightness value of each pixel outside the coherence range, but also as the average value of a plurality of measurement points or by frequency analysis. Good. By the way, the two consecutive points Z
In addition to calculating the differential value J (Zi) using the interference fringe strengths I (Zi) and I (Zi-1) at i and Zi-1, the differential value is calculated using three consecutive points. Good.

That is, three consecutive points Zi + 1, Zi, Zi-1
Using the interference fringe intensities I (Zi + 1), I (Zi), and I (Zi-1) at, the differential value J (Zi) is calculated by the following equations (5) and (6).・ When I (Zi + 1)> I (Zi)> I (Zi-1) J (Zi) = I (Zi + 1) -I (Zi-1) (5) ・ Other than the above J (Zi) = 0 (6) where Zi + 1-Zi = constant C: C is a constant distance for moving the reference mirror 18 Zi-Zi-1 = constant C0 <Zi-Zi-1≤.lambda. / 6: Let λ be the central wavelength of the light source.

The above J is changed by changing Z within the entire measurement range.
(Z) is calculated, and a Z value that gives the maximum value of J (Z), that is, a set of Zi + 1, Zi, and Zi-1 is determined.
Za which gives the maximum value of J (Z) is detected by the following equation (7). Za = Zi (7) As a result, Za can be easily detected.

Further, instead of the equation (7), FIG.
As shown in, the two points A (Zi + 1, I (Zi + 1)) and B (Zi-) of Zi + 1 and Zi-1 which give the maximum value of J (Z).
A straight line l2 connecting 1 and I (Zi-1) and DC of interference fringe intensity
The intersection with the value may be detected as Za which gives the maximum value of J (Z). The Za obtained in this way is more accurate than the Za obtained from the equation (7).

The measuring procedure of the non-contact surface shape measuring apparatus having the above-mentioned structure will be described with reference to FIG. First, the maximum differential value J ′ for each measurement point (x, y) on the surface of the work W
The memory of φ '(x, y) that gives (x, y) and its maximum value is cleared, the measurement device is initialized, and PzT20
Is driven to move the Z-direction measurement position to the initial position (step 202).

Then, by the above-mentioned method, each measurement point (x,
The differential value J (x, y) in y) is calculated (step 20).
4). Next, J (x, y) obtained in step 204 for each measurement point (x, y) is compared with the maximum differential value J '(x, y) up to the last time stored in the memory. (Step 206), if J (x, y)> J '(x, y), replace J' (x, y) with J (x, y) and obtain the maximum differential value J '(x, y). While updating, Z position φ'at that time
Update (x, y) (step 208). At the initial position, the memory is cleared and J '(x, y) and φ' (x,
y) is not recorded, so J '(x, y),
φ '(x, y) is recorded.

Subsequently, the PzT 20 is driven to drive the reference mirror 18.
Is moved by a certain distance C in the Z direction to move the measurement position (step 210). Step 20 at the measurement position
When steps J4 and 206 are performed and J (x, y)> J '(x, y), J' (x, y) is replaced with J (x, y) and the maximum differential value J '(x , y) and the Z position φ ′ at that time
Update (x, y) (step 208).

On the other hand, in step 206, J (x, y) ≤J '
In the case of (x, y), J '(x, y) is not updated. Similarly, the above steps are repeated until the measurement within the entire measurement range is completed, and when the displacement sensor 22 detects the final measurement position (step 212), the measurement is completed and φ '(x, The surface shape of the work W is obtained based on y) (step 214).

In this embodiment, the case where the replacement of the differential value J '(x, y) is sequentially performed for each measurement position has been described, but the present invention is not limited to this, and a partial range of the measurement range (Z) or The maximum value of the differential value J (x, y) may be calculated after capturing the image data of a plurality of interference fringes in the entire range and storing the image data in the memory. FIG. 6 is a schematic configuration diagram of a non-contact surface shape measuring apparatus showing another embodiment of the present invention. The non-contact surface profile measuring apparatus shown in the figure has a configuration in which a half mirror 52, an interference filter 54, a black-and-white solid-state imaging camera 56, a recording medium 58 and the like are added to the configuration of the non-contact surface profile measuring apparatus shown in FIG. Consists of. The same or similar members in the embodiment of FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

The half mirror 52 splits the light passing through the imaging lens 24 and guides a part thereof to the camera 56, and the interference filter 54 selectively transmits the central wavelength λ of the light source spectrum of the light source lamp 12. Then, only the interference fringes for the single wavelength λ are observed in the imaging section of the camera 56. Based on the interference fringes, the phase shift method is used to further improve the resolution of the surface shape measurement of the work W.

The camera 56 images the interference fringes observed in accordance with the displacement amount of the reference mirror 18, converts the interference fringe image into a predetermined electric signal, and outputs it to the frame memory 28. The frame memory 28 records the interference fringe image using the displacement amount of the reference mirror 18 as a variable. The CPU 30
Cameras 26 and 5 input via the frame memory 28
The interference fringe data from 6 is processed to measure the surface shape of the work W with higher accuracy.

The recording medium 58 is the hard disk drive 6
0 and a floppy disk drive 62, which are connected to the CPU 30 via the serial interface 64 and the bus 36, and can store measured data of the surface shape of the measured work W and the like. FIG. 7 is a flow chart for explaining the measurement procedure of the non-contact surface profile measuring apparatus having the configuration of FIG.

First, each measurement point (x, y) on the surface of the work W
Derivation maximum value J '(x, y) for each and its maximum value φ'
The memory of (x, y) is cleared, the measuring device is initialized, and the PzT20 is driven to move the Z-direction measurement position to the initial position (step 302). Then, the differential value J (x, y) at each measurement point (x, y) is calculated by the method described above (step 304).

Next, step 304 is performed for each measurement point (x, y).
The J (x, y) obtained in step S1 is compared with the maximum differential value J '(x, y) up to the last time stored in the memory (step 30).
6) If J (x, y)> J ′ (x, y), calculate the phase value φ (x, y) for the center wavelength λ at the point (x, y) (step 307), and , J '
(x, y) is replaced with J (x, y) to update the derivative maximum value J ′ (x, y), and the Z position (Za) at that time and φ
The value φ '(x, y) obtained by adding the distance corresponding to (x, y) is updated according to the following equation (8) (step 308).

Φ ′ (x, y) = Za + λ × φ (x, y) / 4π (8) Incidentally, in the initial position, the memory is cleared and J ′ (x, y
Since y) and φ '(x, y) are not recorded, J' (x, y) and φ '(x, y) are automatically recorded. Then PzT
20 is driven to move the reference mirror 18 in the Z direction by a certain distance C, and the measurement position is moved (step 310). Steps 304 to 308 are performed at the measurement position, and if J (x, y)> J ′ (x, y), the phase value φ (x, x about the center wavelength λ at the point (x, y) is obtained. y) is calculated (step 307), and J '
(x, y) is replaced with J (x, y) to update the maximum derivative value J '(x, y), and φ' (x, y) at that time is updated (step 308).

On the other hand, in step 306, J (x, y) ≤J '
In the case of (x, y), J '(x, y) and φ' (x, y) are not updated. Similarly, the above steps are repeated until the measurement within the entire measurement range is completed, and when the displacement sensor 22 detects the final measurement position (step 312), the measurement is completed, and φ ′ (x, x, stored in the memory is stored. The surface shape of the work W is obtained based on y) (step 314).

In this embodiment, the case where the replacement of the differential value J '(x, y) is sequentially performed for each measurement position has been described, but the present invention is not limited to this, and a partial range of the measurement range (Z) or The maximum value of the differential value J (x, y) may be calculated after capturing the image data of a plurality of interference fringes in the entire range and storing the image data in the memory. As described above, the vicinity of the maximum (or minimum) differential value of the interference fringe intensity is calculated based on the interference fringe image data of the camera 26, and the maximum (or minimum) of the differential value is further calculated.
The phase can be calculated by the phase shift method from the interference fringe image data of the camera 56 in the vicinity of which the measurement can be performed with high accuracy.

At this time, the measurement can be performed only by the camera 26, but by using the interference filter having the center wavelength λ and the camera 56 as in the embodiment of FIG. 7, an interference fringe for a single wavelength can be obtained. , More accurate measurement becomes possible. Further, although the light source lamp 12 is described as a white light source in the above-described embodiment, the light source lamp 12 is not limited to this, and the spectrum width may be adjusted by using a filter for the white light source.
Alternatively, a wide area light source having a certain spectral width may be used.

[0037]

As described above, according to the non-contact surface shape measuring method and apparatus according to the present invention, interference fringes are generated by moving the surface to be measured or the reference surface at a constant interval in the optical axis direction. Then, based on the obtained image data of the interference fringes, the interference fringe intensity is detected for each position of the surface to be measured, a plurality of interference fringe intensities are obtained, and a value corresponding to the differential value of the interference fringe intensity. Then, based on the position movement amount of the measured surface or the reference surface when the value corresponding to the differential value becomes the maximum value or the minimum value, it is decided to measure the shape of the measured surface. The data processing content regarding measurement is simplified, and the surface to be measured can be measured at high speed and with high accuracy.

Further, the intersection point between the interference fringe intensity data of two points before and after giving the maximum value or the minimum value of the value corresponding to the differential value and the bias value (DC value) of the interference fringe intensity data is calculated, and By setting the value as the position movement amount of the measured surface or the reference surface when giving the maximum value or the minimum value of the value corresponding to the differential value, the maximum value or the minimum value of the value corresponding to the differential value is obtained. The amount of positional movement of the surface to be measured or the reference surface at the time of application can be calculated with high accuracy, and more accurate measurement can be performed.

Further, a phase value is calculated from interference fringe intensity data in the vicinity that gives a maximum value or a minimum value of the value corresponding to the differential value, and the position of the measured surface or the reference surface is moved based on the phase value. By correcting the amount, the resolution of measurement can be improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a non-contact surface shape measuring apparatus of the present invention.

FIG. 2 is an enlarged view of an interferometer portion of FIG.

FIG. 3 is a graph showing the intensity of interference fringes observed at a certain point on the camera and their differential values.

4A and 4B are differential values J of interference fringe intensity.
A graph for explaining a method of calculating Za, which gives the maximum value of (Z), with high accuracy using a DC value.

5 is a flow chart for explaining a measurement procedure of the non-contact surface shape measuring apparatus of FIG.

FIG. 6 is a schematic configuration diagram of a non-contact surface shape measuring apparatus showing another embodiment of the present invention.

FIG. 7 is a flowchart for explaining a measurement procedure of the non-contact surface shape measuring device of FIG.

[Explanation of symbols]

 12 ... Light source lamp 16, 52 ... Half mirror 18 ... Reference mirror 20 ... Electrostrictive element (PzT) 22 ... Displacement sensor 26, 56 ... Monochrome solid-state imaging camera 28 ... Frame memory 30 ... CPU

Claims (6)

[Claims] 1. A light source having a wide spectrum width is used, and interference fringes are generated in accordance with a difference in optical path length between the light source and a first optical path length to a surface to be measured and a second optical path length to a reference surface. In the non-contact surface shape measuring method for generating and measuring the shape of the surface to be measured based on the intensity of the interference fringes, the first surface to be measured or the reference surface is moved at a constant interval in the optical axis direction. A second step of measuring a position movement amount of the measurement target surface or the reference surface moved by the first step, and an interference fringe image generated with the movement of the first step 3 step, and based on the image data of the interference fringes obtained in the third step,
A fourth step of detecting the interference fringe intensity for each position of the surface to be measured, and a plurality of the interference fringe intensities obtained by repeating the first to fourth steps are converted into a differential value of the interference fringe intensity. A fifth step of calculating a corresponding value, and a position movement amount of the measurement target surface or the reference surface when the value corresponding to the differential value obtained in the fifth step becomes a maximum value or a minimum value. And a sixth step of measuring the shape of the surface to be measured based on the above. 2. The non-contact surface shape measuring method according to claim 1, wherein the sixth step is sequentially performed every time when the first step is performed. 3. The sixth step is performed after repeating the first to fifth steps within the entire movable range of the measured surface or the reference surface or within a part thereof. The non-contact surface shape measuring method according to claim 1. 4. In the sixth step, interference fringe intensity data at two points before and after giving a maximum value or a minimum value of a value corresponding to the differential value, and a bias value (DC value) of the interference fringe intensity data. 2. The non-contact surface shape measuring method according to claim 1, wherein the intersection is defined as a position movement amount of the surface to be measured or the reference surface when a maximum value or a minimum value corresponding to the differential value is given. 5. In the sixth step, a phase value for a central wavelength of the light source is calculated from interference fringe intensity data in the vicinity of which a maximum value or a minimum value corresponding to the differential value is given, and the phase value is calculated. The non-contact surface shape measuring method according to claim 1, wherein the shape of the surface to be measured is measured with higher accuracy based on 6. An interference fringe is generated according to an optical path length difference between a light source having a wide spectrum width, a first optical path length between the light source and a surface to be measured, and a second optical path length up to a reference surface. An interferometer, an imaging unit that images the interference fringes, a scanning unit that moves the measurement target surface or the reference surface at a constant interval in the optical axis direction, and the measurement target surface or reference that is moved by the scanning unit. Position measuring means for measuring the amount of position movement of the surface, based on the interference fringe image data obtained by the imaging means, to detect the interference fringe intensity for each position of the surface to be measured, a plurality of interference fringes of different phases And a calculation unit that calculates a value corresponding to the differential value of the interference fringe intensity from image data, and the measured value when the value corresponding to the differential value obtained by the calculation unit is the maximum value or the minimum value. For moving the position of the target surface or reference surface A non-contact surface shape measuring apparatus characterized by measuring the shape of a surface to be measured based on the above.