JP7227604B2 - Three-dimensional shape measuring method and three-dimensional shape measuring device - Google Patents

Description

The present invention provides a correction method and apparatus for matching the focal position of interference fringes and the focal position of an imaging device (hereinafter referred to as a camera as a representative) when using an interference objective lens for an interference microscope. Regarding.

Conventional interference microscopes emphasize the arrangement of an infinite system, and observation of interference fringes was performed by adjusting the position of a reference mirror instead of the focal position on the camera side. Specifically, each objective lens is adjusted so that interference fringes appear at the focal point of the camera without changing the position of the camera sensor.

When the camera is not moved, although there is an advantage that the lateral magnification β does not change, the appearance position of the interference fringes of the objective lens must be adjusted each time, and this manual adjustment work is a burden for the operator.
In the case of a low-magnification lens, since the depth of focus of the objective lens is large, the appearance position of the interference fringes is within the range where the camera is focused, so there may be no mechanism for adjusting the reference mirror.

On the other hand, since the depth of focus of a high-magnification lens is small, adjustment using a reference mirror is essential.
In this way, the interference objective lens itself is generally equipped with an adjustment mechanism. For example, an invention has been made to improve usability of the adjustment mechanism (Patent Document 1).

JP-A-2000-193891

However, when using a microscope, it is rare to use only one objective lens, and it is common to switch and use a plurality of objective lenses with different magnifications.
However, providing a reference mirror adjustment mechanism for each of the multiple interference objective lenses increases weight, and the need for a complicated adjustment mechanism makes it difficult to stabilize quality. be. In particular, an increase in weight leads to an increase in the withstand load of a revolver for attaching a plurality of objective lenses, a motor that is a z-driving mechanism, and a piezo, resulting in a further increase in weight. As a result, blurring of interference fringes, sagging of edges, etc. occur, making it impossible to accurately measure a three-dimensional shape. This poses an obstacle to automating the adjustment of the reference mirror, including countermeasures against temperature drift, from the standpoint of increased weight of the apparatus and measurement accuracy.

Therefore, in optimizing the focus position of the camera and the appearance position of the interference fringes by adjusting the interference objective lens, we solved the above problems and realized a three-dimensional shape image without blurring with a simple configuration. A three-dimensional shape measurement method and apparatus that can be easily obtained is desired.

In order to solve the above problems, the present invention provides an adjustment mechanism only on the camera side so that the focal position of the camera (imaging device) and the appearance position of the interference fringes match, thereby simplifying the configuration. To provide a three-dimensional shape measuring method and an apparatus for obtaining a true three-dimensional shape image without impairing the quality, avoiding deterioration in quality due to an increase in the weight of the apparatus, and without impairing economic efficiency. .

According to the present invention, as a method for accurately measuring a three-dimensional shape, when performing position adjustment based on the difference in distance between the focal position of an imaging device that captures interference fringes based on an interference signal and the appearance position of the interference fringes. , position adjustment is performed by moving the position of the imaging element so that the difference in the distances is equal to or less than a predetermined value.
In addition, the amount of movement of the position of the image pickup device is stored as a correction value for each of the plurality of interference objective lenses to be arranged, and in subsequent measurements, correction is performed based on the correction value corresponding to the interference objective lens to be used. .
Further, lateral magnification correction is performed for changes in lateral magnification that accompany movement of the imaging device.

By doing so, the movement distance for the position adjustment of the imaging element is determined as a correction value for each interference objective lens to be arranged, and when the same interference objective lens is used, only the imaging element is corrected using the same correction value. Therefore, it is possible to provide a three-dimensional shape measuring method that enables accurate three-dimensional shape measurement. Therefore, in order to obtain a three-dimensional shape free from blurring, etc., it is not necessary to adjust the position of each imaging element interference objective lens.

Further, as a three-dimensional shape measuring apparatus according to the present invention, a light source that generates light of a certain wavelength, a beam splitter that splits and reflects/transmits the light, and light reflected by the beam splitter is transmitted in the direction of the optical axis. and an interference objective lens for causing interference between the measurement light reflected from the measurement object and the reference light obtained by branching from the light focused on the measurement object, and the interference objective In a three-dimensional measuring device having an image pickup device that detects and captures an interference signal generated by a lens, the position of the image pickup device that moves the image pickup device in the z-axis direction when adjusting the optical distance between the measurement light and the reference light. It has an adjustment mechanism.

With such a configuration, only the imaging device is required for position adjustment, and an adjustment mechanism for each of the plurality of interference objective lenses is not required. can be avoided. Therefore, when automating, it is only necessary to provide an automating mechanism only for the imaging element, and the apparatus configuration can be simplified.

According to the three-dimensional shape measuring method and apparatus according to the present invention, it is possible to obtain a true three-dimensional shape image with a simple configuration, which is highly economical, and which is easy to operate.

1 is an overall configuration diagram of an interference microscope as one application example of an embodiment of the present invention; FIG. FIG. 4 is a conceptual diagram of alignment between the focal position of the camera and the appearance position of the interference fringes by moving the camera according to the present invention. It is a plot of the longitudinal magnification calculated from the magnification of the objective lens and the measured value. It is a flow chart of the measuring method concerning the present invention. 4 is a flow chart of another measuring method according to the present invention; It is a figure which shows the imaging relationship of a general lens. FIG. 10 is a conceptual diagram of alignment between the focal position of the camera and the appearance position of the interference fringes by moving the reference mirror side in the related art; FIG. 10 is a diagram showing a captured image and a cross-sectional view when the focal position of the camera and the appearing position of the interference fringes match/dismatch.

A mechanism for aligning the interference fringe focal position and the camera focal position for acquisition of a three-dimensional shape image according to the present invention will be described below in detail with reference to FIGS. 1 to 5 using an interference microscope as an example.

FIG. 1 is an overall configuration diagram of an interference microscope that is one application example of an embodiment of the present invention. The interference microscope 100 includes an apparatus main body 10, a stage 20 on which a sample S to be measured (object to be measured) is placed, and a computer (processor) 30 for processing obtained data. The apparatus body 10 includes a light source (white light source) 11, a filter 12, a beam splitter 13, an interference objective lens 14, a camera 15 (sensor (detector)), a piezo actuator 16, and a camera fine adjustment mechanism 17. include.

Irradiation light (white light) emitted from the light source 11 as indicated by an arrow A passes through a filter (for example, a wavelength filter, a polarizing filter, etc.) 12, and is guided to an interference objective lens 14 by a beam splitter 13 (arrow B ). A beam splitter in the interference objective lens 14 splits the irradiation light into two beams: the first irradiation light directed toward the object to be measured (including the sample S itself and the substance inside it) and the second irradiation light directed toward the reference mirror. divided into two. The optical distance L1 of the measurement light from the beam splitter in the interference objective lens 14 arranged facing the measurement object to the measurement object and the optical distance L2 of the reference light from the beam splitter to the reference mirror are equal. Interference occurs when When the appearance position of the interference signal is within the depth of focus, the camera 15 captures this interference signal as interference fringes (interference pattern), and the interference signal is held and stored in the computer 30 . Further, in the embodiment of FIG. 1, since the distance from the beam splitter 13 to the reference mirror is fixed, the distance L1 to the object to be measured can be changed by sweeping using the piezo actuator 16 (movement of arrow C). are changing. Although not shown, the scanning white interference microscope 100 itself may be moved up and down to change L1 without using the piezo. The interference microscope 100 uses a light source with a short coherence length of several micrometers.
With white light, the position where the interference signal is obtained is the z position (height position) where the object to be measured exists. The operator operates the computer 30 of the interference microscope 100, moves the interference objective lens 14 in the height direction along the arrow C, and moves the measurement object (including the sample S and the substance inside it) in the height direction ( z direction) to observe the surface properties (unevenness, etc.) of the object to be measured.

In FIG. 1, a Linnik interferometer type is shown as an interference objective lens so that the optical distance can be easily understood, but the same applies to the Mirau type and the Michelson type.
FIG. 6 shows the imaging relationship in a general lens. The lateral magnification β (corresponding to the so-called lens magnification of the objective lens) is generally given by equation (1).

Especially in an arrangement called an infinite system, β0=f'/f.
On the other hand, the longitudinal magnification α (magnification in the optical axis direction) is given by equation (2).

Here, considering the case of moving Δz, Δz' from the state of the infinite system arrangement, the corrected lateral magnification β' is obtained by the equation (3).

That is, by obtaining the longitudinal magnification α or by obtaining it in advance, since the focal length of the objective lens is constant, correction can be made so that the lateral magnification is always constant from the amount of displacement when Δz is changed. It becomes possible.

When the magnification of the objective lens is 10 times and Δz is 0.1 mm, the difference in lateral magnification is calculated by 0.4%. That is, in a camera (sensor) with 1 million pixels, since one side has 1000 pixels, an error of 4 pixels can occur. Therefore, in order to obtain an accurate three-dimensional shape image when finely adjusting the position of the camera, it is necessary to correct the lateral magnification, which must be suppressed to at least one pixel or less.
Since the above equations 1 to 3 are based on the assumption that paraxial rays hold (sin Θ≈tan Θ≈Θ), they do not hold as the magnification increases.

FIG. 3 shows the calculation of the longitudinal magnification and the magnification of the objective lens and the experimental results. At low magnifications, the calculated values substantially agree with the paraxial approximation, but when the magnification of the objective lens exceeds 20 times, the difference from the calculated values is confirmed. Therefore, it is necessary to obtain the data of FIG. 3 in advance when correcting the lateral magnification of the high-magnification objective lens.

In addition, a motorized mechanism is provided for each objective lens in order to automate the position of the reference mirror of the objective lens.
Also, the focal position of the sensor and the appearance position of the interference fringes are slightly affected by the temperature change. However, manual adjustment each time is not realistic because the operator's work becomes complicated.

In view of such circumstances, the present invention is designed to have an adjustment mechanism for finely adjusting the sensor side in the z direction (movement of arrow F in FIG. 1). This effect eliminates the need for adjustment for each objective lens used, suffices by arranging a new adjustment mechanism at one location on the sensor side, and can minimize the increase in weight of the entire apparatus. In addition, by adding an automatic adjustment function to the new adjustment mechanism, adjustment of the focal position of the sensor and the appearance position of the interference fringes can be performed automatically, eliminating the need for the operator to make adjustments.

Fig. 2 shows the effect of movement of the arrow F in Fig. 1 by the camera fine adjustment mechanism 17. Fine adjustment of the sensor position of the camera is performed so that the focal position of the camera matches the appearance position of the interference fringes of each objective lens of a different individual. .
When the position of the camera is finely adjusted, the lateral magnification slightly changes, but it can be corrected using the above formula (3) and the previously obtained data in FIG.

FIG. 8 shows a photographed image (a) and a photographed image (a') in which the focal position of the camera and the appearing position of the interference fringes match, and a cross-sectional image (b) which similarly matches and a cross-sectional image (b') which do not match. is compared with By matching the focal position of the camera and the appearance position of the interference fringes, blurring of the captured image is eliminated, and sharp edges without sagging can be seen in the cross-sectional image.
Thus, according to the present invention, since the camera side is slightly moved by Δz from the arrangement of the infinity system, strictly speaking, aberration occurs when optical parts are inserted in the middle, but the focus position of the camera and the appearance of interference fringes It has been found that matching the positions is effective in suppressing the influence of aberrations and obtaining a true three-dimensional shape.

FIG. 4 is a flow chart for implementing the observation method according to the present invention. First, before adjusting the position of the camera, optical conditions such as the magnification of the objective lens are recorded (S71). Next, a focus test is performed to find the difference between the focal position of the camera and the appearance position of the interference fringes under these conditions (S72).
The position of the camera is finely adjusted until the value falls below the specified value (S72-S74).
When it reaches the specified value, the finely adjusted camera position is recorded (S75).

Lateral magnification correction (that is, the size per pixel of the camera) due to the change in camera position is performed (S76). Strictly speaking, a paraxial ray does not hold true, and a deviation from the theoretical value occurs at high magnification. Therefore, it is desirable to prepare calibration curves for the magnification and lateral magnification of the objective lens before shipment.
By recording the optical conditions (S71), the corresponding camera position (S75), and the lateral magnification correction (S76), once calibrated, there is no need to readjust until changing to a different objective lens. good too. Therefore, when using the same objective lens, the camera position should be finely adjusted (S74) to the optimum position for measurement (FIG. 5).

It should be noted that the present invention is not limited to the above-described embodiments, and can be modified, improved, etc. as appropriate. In addition, the material, shape, size, numerical value, form, number, location, etc. of each component in the above-described embodiment are arbitrary and not limited as long as the present invention can be achieved.

According to the present invention, the focal position of at least one or more interference objective lenses and the appearance position of interference fringes can be matched simply by moving the camera side, and a true three-dimensional shape can always be obtained. becomes.

10 device body 11 light source (white light source)
12 filters (including wavelength filters)
13 beam splitter 14 interference objective lens (objective lens)
15 Camera (sensor (detector))
16 piezo actuator 20 stage 30 computer 100 interference microscope
S Sample (including object to be measured)

Claims (9)

In a three-dimensional shape measurement method for measuring a three-dimensional shape from an interference signal by irradiating a measurement medium on an object to be measured,
When position adjustment is performed based on the difference in distance between the focal position of an imaging device that captures interference fringes based on the interference signal and the appearance position of the interference fringes, the distance difference is set to a predetermined value or less. A three-dimensional shape measuring method characterized by moving the position of an imaging device to adjust the position. In the three-dimensional shape measurement method according to claim 1,
The amount of movement of the position of the image sensor is stored as a correction value for each of the plurality of interference objective lenses to be arranged, and in subsequent measurements, correction is performed based on the correction value corresponding to the interference objective lens to be used. 3D shape measurement method. In the three-dimensional shape measuring method according to claim 1 or 2,
A three-dimensional shape measuring method for correcting lateral magnification with respect to movement of the imaging device. A light source that generates light of a certain wavelength, a beam splitter that splits and reflects/transmits the light, and the light reflected by the beam splitter is condensed in the direction of the optical axis to irradiate the object to be measured. an interference objective lens for causing interference between the measurement light reflected from the measurement object and the reference light obtained by branching the light focused on the measurement object; and detecting an interference signal generated by the interference objective lens. an imaging element for imaging;
In a three-dimensional measuring device having
A three-dimensional shape measuring apparatus comprising a position adjusting mechanism for moving the imaging element in the z-axis direction when adjusting the optical distance between the measurement light and the reference light. A data processing unit that acquires, stores, and processes an interference signal detected by the imaging element, and the data processing unit corresponds a position adjustment distance obtained by moving the imaging element by the position adjustment mechanism to the interference objective lens. 5. The three-dimensional shape measuring apparatus according to claim 4, further comprising a storage unit for storing/recalling position adjustment distances as corrected correction values. 6. The three-dimensional shape measuring apparatus according to claim 5 , wherein said data processing section comprises a lateral magnification correcting section for compensating a change in lateral magnification with respect to a detection signal when said position adjusting mechanism is operated. In a three-dimensional shape measurement method for measuring a three-dimensional shape from an interference signal by irradiating a measurement medium on an object to be measured,
When position adjustment is performed based on the difference in distance between the focal position of an imaging device that captures interference fringes based on the interference signal and the appearance position of the interference fringes, the distance difference is set to a predetermined value or less. Adjust the position by moving the position of the image sensor,
lateral magnification correction is performed on a measurement result of an interference objective lens with a magnification higher than a predetermined magnification, based on a longitudinal magnification previously acquired corresponding to a displacement amount in movement of the imaging element. Original shape measurement method. In the three-dimensional shape measuring method according to claim 7,
Lateral magnification correction for the measurement result of the interference objective lens with a magnification lower than the predetermined magnification, based on the vertical magnification calculated using a calculation formula defined corresponding to the displacement amount in the movement of the imaging device. A three-dimensional shape measurement method. In the three-dimensional shape measuring method according to claim 7,
The three-dimensional shape measuring method, wherein the predetermined magnification is 20 times.

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