JP2017125707A - Measurement method and measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measurement device that is advantageous in terms of measurement accuracy.SOLUTION: Provided is a measurement device for measuring the shape of an object to be measured, said device including: a projection unit 4 for projecting a plurality of pattern lights differing in cycle from each other to the object to be measured; an imaging unit 7 for capturing the image of the object to be measured to which the plurality of pattern lights are projected, and acquiring an image that corresponds to each of the plurality of pattern lights; and a processing unit 10 for finding information about the shape of the object to be measured on the basis of the images. The processing unit 10 finds information about the shape of the object to be measured on the basis of luminance information pertaining to an image that corresponds to one of the plurality of pattern lights, and phase information pertaining to a synthesized pattern light of the plurality of pattern lights that is obtained from phase information pertaining to the plurality of pattern lights.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a measurement method and a measurement apparatus.

  As an apparatus for measuring the shape of an object to be measured, an optical measurement apparatus using a pattern projection method is known. In the pattern projection method, a predetermined pattern is projected onto an object to be imaged, the pattern in the captured image is detected, and distance information at each pixel position is calculated from the principle of triangulation, thereby measuring the shape of the object to be measured. Seeking.

  As a typical pattern projection method, there is a phase shift method. In this method, a fringe pattern whose luminance changes in a sine wave shape is projected and imaged on the object to be measured while shifting by a predetermined phase, and the shape of the object to be measured is obtained based on a plurality of captured images. The distance information at each pixel position is obtained in correspondence with the phase. Since the phase obtained from the captured image is discontinuous, the fringe order n of the pixel (a value representing the fringe of the nth cycle counted from one end to the other end in the image) is specified and continuous. The value needs to be determined (phase connection).

  Phase connection can be difficult, for example, when the change in the height direction of the object to be measured is abrupt or discontinuous, or when measuring the height of the object to be measured with high precision by reducing the pattern pitch. . As a technique corresponding to the case where the change in the height direction is large, there are a method of sequentially projecting and imaging two fringe patterns having different periods (Patent Document 1) and a method of simultaneously projecting (Patent Document 2). In addition, there is a method in which the relationship between the defocus information of the projection pattern and the distance information in the height direction is acquired in advance by calibration, and the fringe order is obtained using the acquired relationship (Patent Document 3).

JP 2010-91570 A JP 2004-361142 A JP 2010-271199 A

  However, it is difficult for the method of Patent Document 1 to cope with a fine pattern pitch. The method of Patent Document 2 requires a configuration for separating two fringe patterns and individually imaging each fringe pattern, which may be disadvantageous in terms of cost. The method of Patent Document 3 requires a highly accurate stage device for calibration and sufficient measurement time, which may be disadvantageous in terms of cost and measurement time.

  An object of the present invention is to provide a measurement device that is advantageous in terms of measurement accuracy, for example.

  In order to solve the above problems, the present invention is a measurement apparatus that measures the shape of an object to be measured, and includes a projection unit that projects a plurality of pattern lights having different periods on the object to be measured, and a plurality of pattern lights. An imaging unit that images the projected object to be measured and acquires an image corresponding to each pattern light, and a processing unit that obtains information on the shape of the object to be measured based on the image. Measured based on the luminance information of the image corresponding to any one of the plurality of patterns and the phase information of the combined pattern light obtained by combining the plurality of pattern lights obtained from the phase information of the plurality of pattern lights It is characterized by obtaining information on the shape of an object.

  According to the present invention, for example, it is possible to provide a measurement device that is advantageous in terms of measurement accuracy.

It is the schematic which shows the structure of the measuring device which concerns on 1st Embodiment. It is a flowchart which shows the arithmetic processing process which concerns on 1st Embodiment. It is a graph which shows the relationship between contrast and the position of a height direction. It is a figure which shows the change of the relationship between the contrast and stripe order by the fineness of a pitch. It is a flowchart which shows the arithmetic processing process which concerns on 2nd Embodiment. It is a graph which shows the relationship between a stage position and contrast.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic diagram illustrating a configuration of a measurement apparatus according to the present embodiment. The measurement apparatus according to this embodiment includes a light source 1, a collimator lens 2, a pattern generation unit 3, a projection optical system (projection unit) 4, a stage 6, an imaging optical system (imaging unit) 7, and a light receiving unit. 9 and a processing unit (calculation unit) 10. The light emitted from the light source 1 passes through the collimating lens 2 and becomes parallel light, and is incident on the pattern generation unit 3 that generates a fringe pattern in which a bright part and a dark part change periodically (in a sine wave form). The pattern generation unit 3 can use a mask, a liquid crystal element, a DMD, or the like having a pattern in which light transmitting portions and light shielding portions are alternately arranged. The pattern control unit 11 controls the pattern generation unit 3 to spatially modulate the pattern to be generated at high speed. In the present embodiment, two types of patterns are separately projected onto the measurement object 5. The height direction of the measurement object 5 is defined as the Z direction, and the directions perpendicular thereto are defined as the X direction and the Y direction.

  The light beam that has passed through the pattern generation unit 3 enters a projection optical system 4 that includes a plurality of lenses. The projection optical system 4 enlarges the incident light beam and projects it onto the measurement object 5 mounted on the stage 6. The stage 6 is driven in the optical axis direction. When a pattern with a small pitch is projected for high-accuracy measurement, the depth of focus becomes narrow. In order to ensure a wide measurement range, it is necessary to perform measurement while scanning the focus position with respect to the measurement object 5 at intervals of about the depth of focus. The light beam reflected by the surface of the measurement object 5 enters the imaging optical system 7 including a plurality of lenses. The incident light is emitted to the light receiving unit 9 after the spatial frequency is reduced by the aperture stop 8 in the imaging optical system 7. The light receiving unit 9 includes a CCD, a CMOS, or the like, and detects (images) the intensity of incident light. In the present embodiment, since two types of patterns are separately projected onto the measurement object 5, two images are acquired. The processing unit 10 obtains the shape of the measurement object 5 based on the image captured by the light receiving unit 9.

FIG. 2 is a flowchart showing an arithmetic processing step performed by the processing unit 10. In S <b> 101, the processing unit 10 calculates a phase for each pattern from the image acquired by the light receiving unit 9. Consider a case where imaging is performed while shifting the phase N times by Δφ. The phase (phase information) θ (x) at the position (x, y) is obtained by performing a discrete Fourier transform (DFT) on the change in intensity (luminance information) I _k (x, y) at the position (x, y) of each pixel. , Y) is obtained from the following [Equation 1].

  In S102, the processing unit 10 calculates contrast (luminance information) for at least one image. The contrast γ (x, y) at the position (x, y) is obtained from the following [Equation 2].

In S103, the processing unit 10 combines the two patterns to be projected, and calculates the phase of the combined pattern (synthesized pattern light) in each pixel. The substantial periods λ ₁ and λ ₂ of each pattern to be projected on the measurement object 5 are λ ₁ = p ₁ / cos α, where p ₁ and p ₂ are pitches, and α is an incident angle (convergence angle). λ ₂ = p ₂ / cos α. The period Λ ₁₂ of the pattern after synthesis is obtained by λ ₁ × λ ₂ / | λ ₁ −λ ₂ |. If the phase of each pattern is θ ₁ and θ ₂ , the phase Θ ₁₂ of the combined pattern is obtained as θ ₂ −θ ₁ . For example, when λ ₁ = 100 μm and λ ₂ = 101 μm, Λ ₁₂ = 10.1 mm, and the period is enlarged by about 100 times.

  In S104, the processing unit 10 reads data (FIG. 3) indicating the relationship between the contrast and the length measurement value (position information) in at least one image. This data is acquired in advance and stored in a storage unit (not shown). For example, it can be obtained by placing a flat plate with a known surface roughness on the stage, driving the stage in the optical axis direction, and performing pattern projection, phase shift and contrast calculation at a plurality of positions. The obtained data is shown as a curve in FIG. The horizontal axis is contrast, the right vertical axis is the stage position (measured value), and the left vertical axis is the stripe order. The fringe order is calculated by dividing the length measurement value by the pitch (cycle) and rounding off the fraction. In FIG. 3, the pitches are indicated by dotted lines at equal intervals in the vertical axis direction, and the staircase graph indicated by the solid line indicates the stripe order. The data read here is data corresponding to the pattern whose contrast is calculated in S102.

In S105, the processing unit 10 determines the fringe order _{M 1} of the pattern after synthesis from the following equation (3). First, based on the contrast calculated in S102, the processing unit 10 refers to the relationship between the contrast read in S104 and the length measurement value (stripe order), and calculates the length measurement value (stage position) L _stage and the stripe order M. Ask. The fringe order M is the fringe order of the pattern projected at the time of acquiring the image whose contrast was obtained in S102. By substituting the obtained L _stage and the stripe order M into the following [Equation 3], the stripe order M ₁ is obtained.

ここで、関数ｒｏｕｎｄは小数点以下の四捨五入を表す関数である。

Here, the function round is a function that represents rounding after the decimal point.

In S <b> 106, the processing unit 10 calculates a length measurement value based on one of the patterns projected from the following [Equation 4]. In the present embodiment, it calculates the measurement value H ₁ by the most pitch fine pattern. The parameters to be used are the period, fringe order, and phase of the pattern with the finest pitch among the plurality of patterns to be projected. In the present embodiment, the period is lambda _1. The phase is θ ₁ (x, y) calculated in S101. In the phase shift method, the finer the pitch of the pattern to be projected, the better the measurement accuracy. However, it is generally difficult to specify the fringe order as the pitch becomes finer. FIG. 4 is a diagram showing a change in the relationship between the contrast and the stripe order due to the fineness of the pitch. The horizontal axis is the contrast, and the vertical axis is the stripe order. A solid line or a broken line curve indicates a length measurement value, and a stepped solid line and a broken line represent the stripe order. According to this figure, it can be seen that as the pitch becomes finer, the sensitivity of the fringe order to the contrast increases. The fringe order value M ₂ (x, y) to be substituted into [Formula 4] is obtained using the following [Formula 5] and [Formula 6]. In [Formula 5], a length measurement value H ₂ (x, y) obtained based on the combined image is used. H ₂ (x, y) is calculated by [Equation 6]. M ₁ to be substituted into [Equation 6] is obtained in S105, and Θ ₁₂ is obtained in S103.

  As the fringe order used in [Equation 4], the fringe order of the combined pattern is used. In this embodiment, the cycle of the combined pattern is enlarged by about 100 times, and as shown in FIG. 4, the sensitivity of the fringe order to the contrast is low. Therefore, according to the measurement apparatus (measurement method) of the present embodiment, phase connection does not become difficult even when pattern light with a fine pitch is used.

  In S107, the processing unit 10 calculates the three-dimensional shape of the measurement object 5 from the length measurement value obtained in S106. As described above, the shape of the measurement object 5 can be measured by repeating the scanning of the stage 6, pattern projection, imaging, and steps S <b> 101 to S <b> 107 within the measurement range. Here, the measurement range refers to the distance between the light receiving unit 9 and the object to be measured 5 (stage 6) that can ensure a contrast capable of determining the brightness of the pattern.

  As described above, according to the present embodiment, it is possible to provide a measurement device that is advantageous in terms of measurement accuracy.

(Second Embodiment)
In the present embodiment, by moving the stage 6 beyond the measurement range, FIG. In S201, the processing unit 10 acquires an image obtained by the light receiving unit 9. S202 to S204 are the same as S101 to S103 of the first embodiment. In S205, the driving unit (not shown) moves the stage 6 in the z direction, and the processing unit 10 determines whether or not the moving amount exceeds the measurement range. S201 to S205 are repeated until the measurement range is exceeded (Yes).

  In S206, the processing unit 10 determines the stage position where the contrast obtained in S203 is maximized. Based on the determined stage position, the three-dimensional shape of the measurement object 5 is calculated. FIG. 6 is a graph showing the relationship between the stage position (coordinates) and the contrast at an arbitrary pixel position (x, y). The white circle is the contrast calculated at each stage position. In this figure, calculation is performed at four positions. The approximate curve created from these plots is a dotted curve. The maximum value of this curve is the maximum contrast value.

In S207, the processing unit 10, a fringe order _{M 1} pattern after combining the stage coordinate _L'Stage calculated in S206 is determined by the following equation [Expression 7]. Hereinafter, S208 and S209 are the same as S106 and S107 of the first embodiment. The measuring apparatus of this embodiment also has the same effect as that of the first embodiment.

  In the embodiment described above, two pattern lights are used. However, more than two pattern lights having different periods may be used.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

DESCRIPTION OF SYMBOLS 3 Pattern production | generation part 4 Projection optical system 5 Object to be measured 6 Stage 7 Imaging optical system 9 Light-receiving part 10 Processing part

Claims (8)

A measuring device for measuring the shape of an object to be measured,
A projection unit that projects a plurality of pattern lights having different periods on the object to be measured;
An imaging unit that images the measurement object onto which the plurality of pattern lights are projected, and obtains an image corresponding to each pattern light;
A processing unit for obtaining information on the shape of the object to be measured based on the image,
The processor is
Based on luminance information of an image corresponding to any one of the plurality of patterns of light and phase information of combined pattern light obtained by combining the plurality of pattern lights obtained from the phase information of the plurality of pattern lights. A measuring apparatus for obtaining information on the shape of the object to be measured.   The processing unit uses any one of the plurality of patterns by using the luminance information of the image corresponding to any one of the plurality of patterns and the relationship between the luminance information and the stripe order obtained in advance. The measuring apparatus according to claim 1, wherein a fringe order of the pattern light is obtained, and information on a shape of the object to be measured is obtained based on the fringe order of any one of the plurality of patterns. . The processing unit has M _{1 as} the fringe order of the combined pattern light, Λ ₁₂ as the period of the combined pattern light, M as the fringe order of any one of the plurality of patterns, and the measurement obtained from the relationship. When the long value is L _stage ,

Here, round is a function representing rounding after the decimal point.
Measurement device according to claim 2, wherein the obtaining the information of the shape of the object to be measured based on the fringe order M ₁ of the synthetic pattern light calculated by the equation (1). The processing unit has a period of any one of the plurality of patterns as λ ₁ , phase information as θ ₁ , and phase information of the combined pattern light as Θ ₁₂

The value H ₂ is calculated by equation (2),

Here, round is a function representing rounding after the decimal point.
The value M ₂ is calculated by equation (3),

Measurement device according to claim 3, wherein the obtaining the information of the shape of the object to be measured based on the value H ₁ obtained by Equation (4).   The processing unit obtains information on the shape of the object to be measured, using the fringe order when the luminance information is maximized in the relationship as the fringe order of any one of the plurality of patterns. The measuring apparatus according to claim 2. A plurality of pattern lights having different periods are projected onto the object to be measured, the object to be measured on which the plurality of pattern lights are projected is imaged, and the object to be measured is based on an image corresponding to each pattern light. A measurement method for obtaining shape information,
From the phase information of the plurality of patterns, obtain phase information of the combined pattern light obtained by combining the plurality of pattern lights,
A measurement method characterized in that information on the shape of the object to be measured is obtained based on the obtained phase information and luminance information of an image corresponding to any one of the plurality of patterns.   Using the luminance information of the image corresponding to any pattern light of the plurality of patterns and the relationship between the luminance information and the stripe order obtained in advance, the pattern light of any of the plurality of patterns The measuring method according to claim 6, wherein a fringe order is obtained, and information on the shape of the object to be measured is obtained based on a fringe order of any one of the plurality of patterns.   8. The information on the shape of the object to be measured is obtained by using the fringe order when the luminance information is maximized in the relationship as the fringe order of any one of the plurality of patterns. The measurement method described.

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