JPH11257930A - Three-dimensional shape measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable high-precision three-dimensional shape measurement of an object of measurement having a reflective surface by an unexpensive construction, and to perform its speedy measurement at a stretch even if it has a large area. SOLUTION: In a three-dimensional shape measuring apparatus which is provided with a shaded stripe pattern formed on an index board 3 by changing the brightness of a parallel stripe pattern sinusoidally in one direction, and measures time surface shape of an object of measurement having a reflective surface, an image of the stripe pattern reflected by the surface of the object of measurement containing information corresponding to the surface shape is picked up by a CCD camera 4, and the surface shape of the object of measurement is found on the basis of the picture image information obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-dimensional shape measuring apparatus for measuring a three-dimensional shape of a surface of a measuring object having a reflecting surface.

[0002]

2. Description of the Related Art Conventionally, an interferometer is known as an apparatus for measuring the flatness (three-dimensional shape) of a reflecting object having a reflecting surface such as an IC wafer or a liquid crystal substrate. Among them, a grazing incidence interferometer is suitable for measuring large undulations. Such an interferometer uses laser light to generate interference fringes by light reflected from a reference surface by a mirror or a prism and light reflected from a surface to be measured, and performs measurement based on the light intensity of the interference fringes. Is going.

[0003] In addition, an attempt has been made to perform an inspection by projecting a reference linear pattern on a reflective surface and using the fact that the linear pattern appears deformed due to surface irregularities.

[0004]

However, the conventional interferometer has a drawback that components such as lenses and mirrors are required to have a manufacturing accuracy on the order of wavelength and are very expensive. In recent years, IC wafers and liquid crystal substrates have become larger and larger, and a large area cannot be captured at once due to restrictions on the size of optical components and the like, which requires time for measurement. was there. It is difficult to increase the size of the optical system in terms of accuracy and cost.

On the other hand, those using a reference pattern are mainly sensory tests by visual inspection, and high-precision quantitative analysis has not been performed.

SUMMARY OF THE INVENTION In view of the above problems, the present invention can measure the three-dimensional shape of a mirror-like object with high accuracy using an inexpensive configuration.
It is an object of the present invention to provide a three-dimensional shape measuring device capable of measuring a large area without requiring a long time.

[0007]

Means for Solving the Problems In order to solve the above problems, the present invention is characterized by having the following configuration.

(1) In a three-dimensional shape measuring apparatus for measuring the surface shape of a measuring object having a reflecting surface, a striped pattern plate in which a striped pattern having a sinusoidal gray-scale brightness in one direction is formed in parallel, Imaging means for imaging the fringe pattern reflected including information corresponding to the surface shape of the measurement object, and shape analysis means for determining the surface shape of the measurement object based on image information from the imaging means, It is characterized by having.

(2) The three-dimensional shape measuring device of (1)
Switching means for switching the direction of the stripe pattern so as to be two types forming a predetermined angle with each other; and changing the phase of the stripe pattern in at least three steps before and after the switching with respect to the measurement object. Moving means for relatively moving the stripe pattern, and storage means for storing image information of the stripe pattern imaged by the imaging means each time switching by the switching means and movement by the moving means; The means determines the surface shape based on the plurality of pieces of image information stored in the storage means.

(3) The moving means of (2) is characterized in that the fringe pattern is moved in units of 1/4 of the fringe pitch.

(4) The switching means of (2) is characterized in that the stripe patterns are arranged so that their directions are orthogonal to each other.

(5) The three-dimensional shape measuring apparatus according to (2), further comprising position input means for inputting a coordinate position of an arbitrary point on the surface of the object to be measured, wherein the shape analyzing means comprises:
Based on a plurality of pieces of image information stored in the storage unit, a phase in two types of directions of the stripe pattern switched by the switching unit is obtained, and a pixel on an image sensor included in the imaging unit is obtained from the obtained phase data. An analysis unit is provided for correlating points on the stripe pattern and geometrically obtaining the surface shape of the measurement object starting from the position input by the position input unit.

[0013] (6) In the three-dimensional shape measuring apparatus (5), said analyzing means, pixels on the image sensor points P _rk on fringe pattern is reflected by P _sk point input by the position input means tangent plane and determining a P _sk, P _{sk + 1} is the tangent plane points on the measurement surface corresponding to a pixel P _{ck + 1} adjacent to the pixel P _ck in P _sk point when imaged on P _{ck Determining} the coordinate position of the point _{Psk + 1} as being approximately on _Psk , and determining the surface shape by sequentially executing the program for all pixels on the image sensor. It is characterized by the following.

(7) The three-dimensional shape measuring device of (1)
The present invention is applied to an apparatus for measuring the flatness of a semiconductor wafer or an ophthalmologic apparatus for measuring a corneal shape of an eye to be examined.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a three-dimensional shape measuring apparatus for measuring flatness of a semiconductor wafer according to an embodiment, and FIG. 2 is an explanatory diagram of a measurement coordinate system of the apparatus.

Reference numeral 1 denotes an inspection stage.
A wafer 2 to be measured is placed on the top. The inspection stage 1 can be moved by the driving device 13 in each of the XYZ axis directions. Reference numeral 3 denotes an index plate, on the surface of which a gray-scale stripe pattern in which the gray-scale brightness changes sinusoidally is formed in parallel at predetermined intervals. The interval between the light and light stripe patterns is a pitch p. The light and shade pattern on the index plate 3 is
And is imaged by a CCD camera 4 having an imaging element 4a and an imaging lens 4b.

As for the measurement coordinate system, as shown in FIG. 2, an XYZ coordinate system is considered with the origin of the apparatus being O (0, 0, 0).
The principal point of the imaging lens 4b of the CCD camera 4 is defined as D (0,
d _y , d _z ), and the optical axis Lp is disposed so as to pass through the origin O. Further, when a plane parallel to the upper surface of the inspection stage 1 and passing through the origin O is considered, the optical axis L is perpendicular to this plane.
A reference point E (0,
e _y , e _z ). Then, the imaging center point o of the imaging device _{4a (0, o y, o} z) to the origin was X'Y 'coordinate system, the reference point E is set to the X "Y" coordinate system as the origin, the coordinate systems X 'axis and X "axis are parallel to the X axis, and the Y' axis and Y" axis are in the YZ plane.

With this configuration, when the inspection stage 1 is moved so that the center of the surface of the wafer 2 is near the origin O of the XYZ coordinate system, and the light and shade pattern reflected on the surface of the wafer 2 is imaged by the CCD camera 4, A light and dark stripe pattern image deformed according to the surface shape of the wafer 2 is obtained.

In FIG. 1, reference numeral 11 denotes an index plate 3 of X "Y".
Reference numeral 12 denotes a rotation driving device which moves the index plate 3 about a reference point E in the X "Y" plane. Reference numeral 14 denotes a detection device that detects a coordinate position of an arbitrary point on the wafer surface, and can be configured by, for example, an XY movement mechanism and a distance sensor. A control unit 10 controls the entire apparatus, and processes an image obtained by the CCD camera 4 to analyze a three-dimensional shape. Reference numeral 15 denotes a memory that stores an image obtained by the CCD camera 4, and 16 denotes a monitor that displays a captured image and a measurement result.

Next, the operation of the apparatus will be described. The wafer 2 to be measured is placed on the inspection stage 1 by a wafer transfer device (not shown). When the wafer 2 is placed on the inspection stage 1, the control unit 10 moves the index plate 3 by the moving device 11 in the sine wave direction of the gray stripe pattern in units of 縞 of the stripe pitch p. In synchronization with this movement, the wafer 2
Is captured by the CCD camera 4, and the four grayscale pattern images having different phases for each of the captured p / 4 are stored in the memory 15.

When four gray-scale fringe pattern images having different phases in one direction have been captured, the index plate 3 is rotated by 90 degrees about the point E by the rotary driving device 12. By this rotation, the light and dark stripe pattern reflected on the wafer 2 is also rotated by 90 degrees. Thereafter, the index plate 3 is relatively moved in the sine wave direction of the gray stripe pattern in units of p / 4 in the same manner as described above.
Four light and shade pattern images having different phases for each p / 4 imaged by the CD camera 4 are stored in the memory 15.

The eight phases having different phases obtained as described above are obtained.
The three-dimensional shape of the wafer surface is measured based on the two light and stripe pattern images. Hereinafter, the measurement method will be described.

First, the control unit 10 calculates a pattern from each of the eight gray-striped pattern images having different phases stored in the memory 15.
The phase (φ _k , φ _k ′) of the gray stripe pattern reflected on the wafer 2 is determined based on a known phase shift method.
Since the phase here is a discontinuous distribution, the connection of the phase and the extraction of the region for the three-dimensional analysis are performed with the reference point E of the index plate 3 as the 0th order. In connecting the phases,
An index light source or the like is placed in advance at the reference point E, and a position where a reflection index image formed on the wafer 2 is formed on the image sensor 4a is detected.
The position may be used as a reference.

Next, the coordinates of each pixel of the CCD camera 4 on the index plate 3 (on the light and dark stripe pattern) are associated with each other based on the obtained two types of phase data. Now, as shown in FIG. 3 (FIG. 3 shows a schematic diagram of the gray stripe pattern), the gray stripe before the rotation of the index plate 3 forms an angle θ (rad) with respect to the X ″ axis, and It is assumed that the gray stripes after rotation of the plate 3 form an angle θ ′ (rad) with respect to the X ″ axis. Then, _{assuming that} the phase of each gray-striped pattern in an arbitrary pixel P _ck is φ _k , φ _k ′, X ″ corresponding to P _ck
A point P _rk (x _rk ″, Y on the stripe pattern in the Y ″ coordinate system
y _rk ″) can be obtained as the intersection of the following two straight lines.

(Equation 1)

Therefore, by solving the simultaneous equations of the equations (1) and (2), P _rk (x _rk ″, y _rk ″) is changed to the following equation (3) (where θ ≠ θ ′ ≠ π / 2) Can be obtained as

(Equation 2)

When θ or θ ′ is π / 2, equations (1) and (2) are expressed by the following equations (1 ′) and (2 ′), respectively.
Therefore, P _rk (x _rk ″, y _rk ″) can be obtained from the simultaneous equations of (1 ′) and (2) or (1) and (2 ′).

(Equation 3)

Here, the point P _rk (x _rk , y _rk , z _rk ) is represented by X
When converted to the coordinate position of the YZ coordinate system,

(Equation 4) Becomes

Next, the coordinates of the point _Pck on the pixel are displayed as coordinate positions in the XYZ coordinate system. Assuming that the coordinates of the point P _{ck in} the X′Y ′ coordinate system are (x _ck ′, y _ck ′), XY
The coordinates (x _ck , y _ck , z _ck ) in the Z coordinate system are the coordinates (0, o) of the imaging center point o of the CCD camera 4 in the XYZ coordinate system.
_y , o _z ),

(Equation 5) Becomes

The correspondence between the pixel coordinates and the coordinates of the gray-striped pattern obtained in this way reflects the surface shape of the object to be measured. It can be calculated geometrically starting from a point. Hereinafter, this calculation method will be described with reference to FIG.

A point P _rk on the gray stripe pattern is reflected at a point P _sk on the surface of the wafer 2, and the image pickup device 4 of the CCD camera 4
_Assume that an image is formed on the pixel _Pck on a, and the point _Psk is set as a starting point. The XYZ coordinates of the starting point _Psk are detected by the detection device 14 and input to the control unit 10. The position of the pixel P _ck corresponding to P _sk at this time is obtained from an image captured by the CCD camera 4. For example, a point _Psk detected by the detection device 14 is set as a target position on the measurement target (in the case of a wafer, the position of the intersection of the circumference of the circle and an orientation flat (Orientational Flat)), and this is imaged. The pixel _Pck can be obtained from the pixel position. Alternatively, the detection device 14 is placed on the Z-axis, and the stage 1 is moved from the detection information from the detection device 14 so that the surface of the measurement object comes to the position of the origin O.
To move. As a result, the point _Psk is given as the origin O, and the pixel _Pck becomes the imaging center point o of the CCD camera 4.

The point P _sk coordinates given knowing the coordinate of P _ck, P _rk since also obtained from the phase data corresponding thereto, P _rk, P _sk, Law in the P _sk using the P _ck The line vector N _k (x _nk , y _nk , z _nk ) is obtained. That is,
Normal vector N _k is obtained as a bisector vector of the unit vectors alpha _k 'unit vectors alpha _k and the reflection light of the incident light. Unit vector α _k (xα _k , y
α _k , zα _k )

(Equation 6) And the unit vector α _k ′ (xα _k ′, y
α _k ', zα _k') is,

(Equation 7) _Therefore , a normal vector N _k (x _nk , y _nk , z _nk ) which is a bisector vector of the unit vector α _k of the incident ray and the unit vector α _k ′ of the reflected ray is

(Equation 8) Becomes This gives a plane with the normal vector N _k ,
That is, the equation of the tangent plane P _pk at P _sk (x _k , y _k , z _k ) is

(Equation 9) Becomes

[0032] In addition, the pixel next to the _{P ck P ck + 1 (x} ck + 1, y
_{ck + 1} , z _{ck + 1} ) and the equation of a straight line passing through the lens principal point D (0, _dy , _dz ) is

(Equation 10) And _{Psk + 1} corresponding to the pixel _{Pck + 1} is approximately the plane P
Assuming that they exist on _pk , the intersection of the equations (9) and (10) is obtained as P _{sk + 1} (x _{k + 1} , y _{k + 1} , z _{k + 1} ) as follows.

[Equation 11]

Similarly, P _{sk + 2} is calculated using P _{rk + 1} , P _{sk + 1} , and P _{ck + 1} . By repeating this for all the pixels, the XYZ coordinates of each point on the wafer 2 are obtained, and the three-dimensional shape of the surface can be obtained.

The measurement result is displayed on the monitor 16 as a wire frame display or a cross section thereof, for example. The inspector can know the flatness of the surface of the wafer 2 based on the information.

In this way, the three-dimensional shape of the measuring object having the reflecting surface can be accurately measured with a simple configuration without providing an expensive mirror or lens. Even when the measurement target has a large area, it can be easily coped with by changing the arrangement position and size of the index plate of the light and light stripe pattern accordingly.

While the apparatus for measuring the surface shape of a semiconductor wafer has been described above as an example, the present invention can be similarly applied to a measuring object having a reflective surface. For example, it can be used not only for industrial materials such as glass and iron plate and general household goods such as mirrors, but also as an ophthalmologist measuring instrument for measuring the corneal shape of the human eye in detail.

Further, by using a liquid crystal panel as the index plate 3, the moving device 11 and the rotation driving device 12 can be dispensed with. That is, a gray-scale fringe pattern is displayed on the liquid crystal panel so that the gray-scale brightness changes sinusoidally, and the display is controlled to move or rotate the gray-scale fringe pattern.

<Second Embodiment> A modification of the mechanism for detecting the coordinate position of an arbitrary point on the measurement object will be described with reference to FIG. In the figure, the same reference numerals as in the first embodiment denote the same elements.

Reference numeral 20 denotes a pair of infrared light sources provided symmetrically with respect to the projection optical axis, and the light flux of the light source 20 which is alternately turned on is a condenser lens 21 and an index plate 22 having a spot aperture.
To illuminate. The light beam emitted from the index plate 22 passes through the beam splitter 23, and then forms an index image on the measurement target 2 'by the objective lens 24. The luminous flux of the target image reflected by the measurement target 2 ′ is reflected by the beam splitter 23 through the objective lens 24, and forms an image on the two-divided light receiving element 25 arranged at a position conjugate with the target plate 22. The position where the two target images formed by the light source 20 are focused is set as the origin O of the XYZ coordinate system, and the photographing optical axis Lp of the CCD camera 4 is set.
Are arranged to pass through the origin O.

After the object 2 'is placed on the inspection stage 1, the light sources 20 are turned on alternately. 2-split light receiving element 25
By moving the inspection stage 1 in the vertical direction so that the respective light amount differences detected by the above are the same, the surface of the measurement target 2 ′ comes to coincide with the origin O. The coordinates of one point on the surface of the measurement object 2 '(that is, the coordinates of the origin O) are obtained, and a starting point _Psk for three-dimensional shape measurement can be given. At this time, the pixel P _ck corresponding to the starting point P _sk becomes the imaging center point o of the CCD camera 4. In this way, the coordinate position of a point on the measurement target can be easily obtained.

[0041]

As described above, according to the present invention, it is possible to measure a three-dimensional shape with high accuracy with an inexpensive configuration even for a measuring object having a reflecting surface. In addition, a large area can be captured at once and speedy measurement is possible.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a three-dimensional shape measuring apparatus according to an embodiment.

FIG. 2 is an explanatory diagram of a measurement coordinate system according to the embodiment.

FIG. 3 is a schematic diagram of a light and shade pattern projection of the embodiment.

FIG. 4 is an explanatory diagram of a method of calculating three-dimensional coordinates.

FIG. 5 is a schematic configuration diagram of a three-dimensional shape measuring apparatus as a modification.

[Description of Signs] 3 reference plate 4 CCD camera 10 control unit 11 moving device 12 rotation drive device 14 detection device 15 memory

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[Procedure amendment]

[Submission date] March 17, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 6

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

[0013] (6) In the three-dimensional shape measuring apparatus (5), said analyzing means, pixels on the image sensor points P _rk on fringe pattern is reflected by P _sk point input by the position input means tangent plane and determining a P _pk, P _{sk + 1} is the tangent plane points on the measurement surface corresponding to a pixel P _{ck + 1} adjacent to the pixel P _ck in P _sk point when imaged on P _{ck Determining} the coordinate position of the point _{Psk + 1} as being approximately on _Ppk , and determining the surface shape by sequentially executing the program for all pixels on the image sensor. It is characterized by the following.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

[0018] With such a configuration, the surface center of the wafer 2 is moved to the inspection stage 1 to come near the origin O of the XYZ coordinate system is imaged by the CCD camera 4 and streaks pattern reflected on the surface of the wafer 2 Thus, a light and light stripe pattern image deformed according to the surface shape of the wafer 2 is obtained.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction contents]

Next, the coordinates of the point _Pck on the pixel are displayed as coordinate positions in the XYZ coordinate system. Assuming that the coordinates of the point P _{ck in} the X′Y ′ coordinate system are (x _ck ′, y _ck ′), XY
The coordinates (x _ck , y _ck , z _ck ) in the Z coordinate system are the coordinates (0, o) of the imaging center point o of the CCD camera 4 in the XYZ coordinate system.
_y , o _z ),

(Equation 5) Becomes

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0032

[Correction method] Change

[Correction contents]

[0032] In addition, the pixel next to the _{P ck P ck + 1 (x} ck + 1, y
_{ck + 1} , z _{ck + 1} ) and the equation of a straight line passing through the lens principal point D (0, _dy , _dz ) is

(Equation 10) And _{Psk + 1} corresponding to the pixel _{Pck + 1} is approximately the plane P
Assuming that they exist on _pk , the intersection of the equations (9) and (10) is obtained as P _{sk + 1} (x _{k + 1} , y _{k + 1} , z _{k + 1} ) as follows.

[Equation 11]

Claims (7)

[Claims] 1. A three-dimensional shape measuring apparatus for measuring a surface shape of a measurement object having a reflecting surface, wherein a stripe pattern plate having a sinusoidal stripe pattern having a gray-scale brightness formed in parallel in one direction is formed, An imaging unit for imaging the stripe pattern reflected including information corresponding to the surface shape of the object, and a shape analysis unit for obtaining a surface shape of the measurement object based on image information from the imaging unit are provided. A three-dimensional shape measuring device, characterized in that: 2. The three-dimensional shape measuring apparatus according to claim 1, wherein the switching means switches the direction of the fringe pattern to two types forming a predetermined angle with each other, and the phase of the fringe pattern before and after the switching. Moving means for moving the stripe pattern relative to the object to be measured in at least three steps, and a stripe pattern imaged by the imaging means every time switching by the switching means and movement by the moving means are performed. Storage means for storing image information of the three-dimensional shape, wherein the shape analysis means obtains a surface shape based on a plurality of pieces of image information stored in the storage means. 3. The three-dimensional shape measuring apparatus according to claim 2, wherein the moving means moves the stripe pattern in units of １ ／ of the stripe pitch. 4. The three-dimensional shape measuring apparatus according to claim 2, wherein the switching means is arranged so that the directions of the stripe patterns are orthogonal to each other. 5. The three-dimensional shape measuring apparatus according to claim 2, further comprising: position input means for inputting a coordinate position of an arbitrary point on the surface of the measuring object, wherein the shape analyzing means stores the coordinate in the storage means. Based on the stored plurality of pieces of image information, the phases of the stripe pattern switched by the switching unit in two directions are obtained, and the pixels on the image sensor of the imaging unit and the stripe patterns on the stripe pattern are obtained from the obtained phase data. 3. A three-dimensional shape measuring apparatus, comprising: an analyzing means for making a correspondence between the above points and geometrically obtaining a surface shape of the object to be measured starting from the position input by the position input means. 6. The three-dimensional shape measuring apparatus according to claim 5, wherein said analyzing means reflects a point P _rk on the stripe pattern at a point P _sk input by the position input means, and the pixel P _rk on the image sensor. tangent plane P _sk and determining a, the pixel point P on the measurement surface corresponding to a pixel P _{ck + 1} adjacent to _ck P _{sk + 1} is the tangent plane P in P _sk point when imaged _ck calculating a coordinate position of the point P _{sk + 1} as being approximately on _sk , and determining the surface shape by sequentially executing the program for all pixels on the image sensor. A three-dimensional shape measuring device characterized by the following. 7. The three-dimensional shape measuring apparatus according to claim 1, wherein the three-dimensional shape measuring apparatus is applied to an apparatus for measuring flatness of a semiconductor wafer or an ophthalmologic apparatus for measuring a corneal shape of an eye to be inspected.