JP2014178233A - Shape measurement device and shape measurement method - Google Patents

Abstract

A shape measuring device and a shape measuring method capable of measuring a wide height range with high accuracy while having a simple device configuration.
A shape measuring apparatus (1) includes a light source (2) that generates light to be irradiated onto a surface (S) of a measurement object (4) and a light source (2) between the light source (2) and the measurement object (4) so that a lattice pattern is projected onto the surface (S). The lattice moving means (grid driving device 30) for moving the lattice 3 in a predetermined direction so that the lattice 3 to be arranged and the projected lattice pattern are changed, and the angle of the lattice 3 with respect to the predetermined direction is changed. And a grid rotating means (lattice driving device 30) for rotating the grid 3. Phase distribution φ1 (x, y), which is the phase distribution of the grating pattern projected when the angle of the grating 3 is the first angle 0, and the grating projected when the angle of the grating 3 is the second angle ω The height distribution H (x, y) of the surface S is calculated based on the phase distribution φ2 (x, y) that is the phase distribution of the pattern.
[Selection] Figure 1

Description

  The present invention relates to a shape measuring apparatus and a shape measuring method for measuring the surface shape of an object based on a lattice pattern projected on the surface of the object.

  As one of methods for measuring the surface shape of an object, that is, the height distribution on the surface, in a non-contact manner, a lattice pattern projection method is known. In the grid pattern projection method, a grid pattern is projected onto the surface of an object to be measured, and a surface shape is calculated based on deformation of the projected grid pattern. The projection of the lattice pattern is performed by placing a lattice between the light source and the object and irradiating the surface of the object with light through the lattice.

  When calculating the surface shape based on the deformation of the lattice pattern, a so-called phase shift method is used. The phase shift method acquires a plurality of lattice patterns projected and deformed on the surface of an object in a state where the positions (phases) of the lattices are different from each other, and based on the obtained plurality of lattice patterns, The phase distribution is calculated. By converting the phase distribution into a height distribution, the surface shape of the object is calculated.

  By the way, while the height of the object surface can be various values, the phase of the grating pattern is a value that periodically changes within a limited range of −π to + π. That is, the height of the object surface and the phase of the lattice pattern do not correspond one to one. For this reason, when the phase distribution of the lattice pattern is converted into a height distribution, the height changes discontinuously at the upper limit (+ π) and lower limit (−π) of the phase. Will occur.

  Therefore, in order to convert the height distribution obtained with the phase jump into the original (smoothly connected) height distribution, so-called “phase connection” needs to be performed. For example, Patent Document 1 below describes a method of calculating two phase distributions by using two gratings having different pitches, and performing phase connection based on these. According to this method, it is possible to widen the range of height that can be calculated correctly without causing phase jumps compared to the case of using a single grating.

JP 2006-064590 A

  However, since the method described in Patent Document 1 uses two gratings having different pitches, the configuration of the shape measuring device used is complicated. In addition, there is a possibility that an error in the pitch of each of the two grids may be superimposed, and further errors may occur in the drive (positioning) for switching the grid to be used. May become difficult.

  The present invention has been made in view of such a problem, and an object thereof is a shape measuring apparatus and a shape measuring method capable of measuring a wide height range with high accuracy while having a simple device configuration. Is to provide.

  In order to solve the above-described problems, a shape measuring apparatus according to the present invention is a shape measuring apparatus that measures a surface shape of an object based on a lattice pattern projected on the surface of the object, and light that irradiates the surface of the object. The grating is arranged between the light source and the object so that the grating pattern is projected onto the surface of the object, and the grating is set so that the projected grating pattern changes. Grid moving means for moving in a direction and grid rotating means for rotating the grid so that the angle of the grid with respect to the predetermined direction changes, and the angle of the grid with respect to the predetermined direction is set as a first angle A first phase distribution, which is a phase distribution of the grating pattern projected in a state, and the case projected in a state where the angle of the grating with respect to the predetermined direction is a second angle. A second phase distribution pattern is a phase distribution, based on, is characterized by calculating the distribution of the height in the surface of the object.

  The shape measuring apparatus according to the present invention includes a grating moving means and a grating rotating means. The lattice moving means moves the lattice in a predetermined direction so that the lattice pattern projected on the surface of the object changes. By changing the phase of the grating pattern projected and deformed on the surface of the object by the grating moving means, it is possible to calculate the phase distribution using the phase shift method.

  The grating rotating means rotates the grating so that the angle of the grating with respect to the predetermined direction (the moving direction of the grating by the grating moving means) changes. When the grating is rotated in this way, the pitch of the grating pattern when viewed along the moving direction of the grating can be changed.

  In the present invention, the first phase distribution which is the phase distribution of the grating pattern projected in the state where the angle of the grating with respect to the predetermined direction is the first angle, and the state where the angle of the grating with respect to the predetermined direction is the second angle The height distribution on the surface of the object is calculated based on the second phase distribution which is the phase distribution of the projected grating pattern. These two phase distributions can be equated with the two phase distributions obtained respectively by using two gratings having different pitches.

  For this reason, based on the first phase distribution and the second phase distribution, for example, phase connection by a calculation method similar to the conventional one can be performed. On the other hand, since only one grating is actually mounted on the shape measuring apparatus, the apparatus configuration can be simplified as compared with the conventional one. In addition, it is possible to measure a wide height range with high accuracy without causing error superposition due to the use of a plurality of gratings.

  In the shape measuring apparatus according to the present invention, a phase difference calculating unit that calculates a phase difference distribution that is a difference between the first phase distribution and the second phase distribution, and the phase difference distribution are continuous in a predetermined range. It is also preferable to further include a first processing unit that performs a continuation process on the phase difference distribution.

  In this preferable aspect, a phase difference calculation unit that calculates a phase difference distribution that is a difference between the first phase distribution and the second phase distribution is provided. In addition, a first processing unit is further provided for performing a continuation process on the phase difference distribution so that the phase difference distribution is continuous in a predetermined range.

  The phase difference distribution calculated by the phase difference calculation unit is a distribution that is substantially proportional to the height of the object surface, but the distribution is discontinuous in some places due to phase jumps. That is, there is a height at which the magnitude of the phase difference deviates discontinuously from the proportional relationship. However, if the phase difference proportional to the height of the object surface is limited to a range where the phase difference is −π to + π, the discontinuous distribution in the range can be easily corrected (continuation process). Specifically, at a height where the magnitude of the phase difference deviates discontinuously from the proportional relationship and falls outside the range from −π to + π, either 2π is added to or subtracted from the phase difference. Therefore, the discontinuous distribution can be easily corrected.

  The first processing unit performs continuation processing by such a method, and converts the phase difference distribution so as to be continuous in a predetermined range. The phase difference distribution after the continuous processing is performed is a distribution proportional to the height of the object surface in a predetermined range.

  Therefore, in the predetermined range, the phase difference and the height of the object surface can be made to correspond one-to-one. The range of the object surface height where the phase difference distribution is from −π to + π is greater than the range of the object surface height where the first phase distribution or the second phase distribution is from −π to + π. wide. That is, the range in which the correct height is calculated without causing phase jump can be made wider than when a single grating is used.

  The shape measuring apparatus according to the present invention further includes a second processing unit that performs phase connection processing on the first phase distribution based on the phase difference distribution after the continuation processing is performed. Is also preferable.

  In order to calculate the height distribution of the object surface based on the phase difference distribution after the continuation processing is performed, it is also possible to calculate by directly matching the phase difference and the height of the object surface. However, the phase difference calculated from the first phase distribution and the second phase distribution includes errors due to variations in the grating pitch from the design value, errors in the rotation angle by the grating rotating means, and the like. There is a possibility that both of the errors included in the two-phase distribution are included. Therefore, in order to reduce the error included in the calculated height distribution, it is desirable to perform the phase connection process only on the first phase distribution and convert this to the height distribution.

  In this preferable aspect, the 2nd processing part which performs a phase connection process with respect to a 1st phase distribution based on the phase difference distribution after a continuation process was performed by the 1st processing part is further provided. Since the calculated height distribution includes only the error of the first phase distribution, the error can be reduced.

  In order to solve the above problems, a shape measuring method according to the present invention includes a light source that generates light to be irradiated on the surface of an object, and a light source and the object so that a lattice pattern is projected onto the surface of the object. A shape that measures the surface shape of the object by a shape measuring device that includes a lattice disposed between and a lattice moving means that moves the lattice in a predetermined direction so that the projected lattice pattern changes. A first acquisition step of obtaining a first phase distribution which is a phase distribution of the grating pattern projected in a state where the angle of the grating with respect to the predetermined direction is a first angle; and the predetermined direction An angle converting step of changing the angle of the grating with respect to the first angle to the second angle, and the grating projected in a state where the angle of the grating with respect to the predetermined direction is a second angle A shape calculation for calculating a height distribution on the surface of the object based on a second acquisition step of acquiring a second phase distribution that is a phase distribution of turns, and the first phase distribution and the second phase distribution. And a process.

  Further, in the shape measuring method according to the present invention, a phase difference calculating step for calculating a phase difference distribution which is a difference between the first phase distribution and the second phase distribution, and the phase difference distribution are continuous in a predetermined range. It is also preferable to further include a first processing step of performing a continuation process on the phase difference distribution.

  The shape measuring method according to the present invention further includes a second processing step of performing a phase connection process on the first phase distribution based on the phase difference distribution after the continuation process. Is also preferable.

  According to the present invention, it is possible to provide a shape measuring device and a shape measuring method capable of measuring a wide height range with high accuracy while having a simple device configuration.

It is a figure which shows typically the structure of the shape measuring device which concerns on embodiment of this invention. It is a figure which shows typically the structure of the grating | lattice contained in the shape measuring apparatus shown in FIG. It is a figure which shows typically the structure of the grating | lattice drive device contained in the shape measuring apparatus shown in FIG. It is a block diagram which shows the structure of the arithmetic processing apparatus contained in the shape measuring apparatus shown in FIG. It is a flowchart which shows an example of the shape measuring method which concerns on embodiment of this invention. It is a flowchart which shows an example of the shape measuring method which concerns on embodiment of this invention. It is a graph which shows the relationship between the height of an object surface, and the phase measured by the shape measuring apparatus. It is a graph which shows the relationship between the height of an object surface, and the calculated phase difference. It is a graph which shows the relationship between the height of an object surface, and the phase difference in which the 1st correction | amendment was performed. It is a graph which overlaps and shows the relationship between the height of an object surface, and the phase difference in which the 2nd correction | amendment was performed, and the relationship between the height of an object surface, and the phase measured by the shape measuring apparatus. It is a graph which overlaps and shows the relationship between the height of an object surface, and the phase difference in which the 2nd correction | amendment was performed, and the relationship between the height of an object surface, and the phase measured by the shape measuring apparatus. It is a graph which shows the relationship between the height of an object surface, and the phase connected in phase. It is a graph which shows frequency distribution of the value which deducted the phase measured by the shape measuring apparatus from the phase difference in which the 2nd correction was performed.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same constituent elements in the drawings will be denoted by the same reference numerals as much as possible, and redundant description will be omitted.

  FIG. 1 is a diagram schematically showing a configuration of a shape measuring apparatus 1 according to the present embodiment. The shape measuring device 1 is a device for measuring the surface shape (height distribution of the surface S) of the measurement object 4 placed on the stage 14. Specifically, it is an apparatus that projects a lattice pattern on the surface S of the object to be measured 4 and calculates the height distribution of the surface S based on the deformation of the projected lattice pattern. As shown in FIG. 1, the shape measuring device 1 includes a light source 2, a grating 3, a grating driving device 30, and an image sensor 6.

  The light source 2 generates light that irradiates the surface S of the measurement object 4. As the light source 2, a fluorescent discharge tube, a low-pressure mercury lamp, a xenon lamp, a semiconductor laser, a light emitting diode (LED), or the like can be used.

  The grating 3 is arranged between the light source 2 and the surface S. The grating 3 is arranged to project a grating pattern on the surface S by transmitting a part of the light from the light source 2 and blocking a part of the light. FIG. 2 is a diagram schematically showing the configuration of the grating 3. As shown in FIG. 2, the grating 3 is arranged such that a plurality of light-transmitting portions 3A formed in a linear shape and light-shielding portions 3B formed in a linear shape are alternately arranged in a plane. . Hereinafter, the plane is also referred to as a “lattice plane”. In addition, the direction in which the light transmitting portions 3A and the light shielding portions 3B are alternately arranged on the lattice surface (the direction indicated by the arrow AR1 in FIG. 2) is also referred to as “periodic direction” below. The grating 3 is arranged so that the grating plane is substantially perpendicular to the path of light reaching the surface S from the light source 2.

  The width of the light transmitting part 3A and the width of the light shielding part 3B are all the same. That is, on the lattice surface of the lattice 3, the light transmitting portions 3A and the light shielding portions 3B are periodically arranged at the lattice pitch P1. The grating pitch P1 is equal to the sum of the width of one light transmitting portion 3A and the width of one light shielding portion 3B. In FIG. 2 and the like, the grating pitch P1 is drawn large for the sake of explanation, but the actual grating pitch P1 is a minute pitch of about 100 μm.

  Returning to FIG. 1, the description will be continued. The lattice driving device 30 is a device that moves and rotates the lattice 3. The grating driving device 30 can move the grating 3 in the periodic direction along the grating surface. Further, the lattice driving device 30 can rotate the lattice 3 along the lattice plane. The specific configuration of the lattice driving device 30 and the specific movement of the lattice 3 by the lattice driving device 30 will be described in detail later.

  The image sensor 6 is a CCD element arranged to receive light emitted from the light source 2 and reflected by the surface S. The image sensor 6 can acquire a lattice pattern projected on the surface S and deformed (hereinafter also referred to as “deformed lattice pattern”).

  As shown in FIG. 4, an arithmetic processing device 300 is connected to the image sensor 6. The arithmetic processing device 300 is a computer device including a storage device such as a RAM, a CPU, and the like. The deformed lattice pattern acquired by the image sensor 6 is recorded on the recording unit 301 (for example, a hard disk) of the arithmetic processing device 300 as a light intensity distribution. Note that a plurality of modified lattice patterns (light intensity distributions) can be recorded in the recording unit 301.

  The arithmetic processing device 300 performs various arithmetic processes based on the modified lattice pattern recorded in the recording unit 301. The arithmetic processing device 300 includes a phase calculation unit 302, a phase connection unit 303, and a height calculation unit 304 as parts for performing the respective calculation processes. The arithmetic processing device 300 also includes a control unit 305 for controlling the operation of the lattice driving device 30 and the like. Note that such division in the arithmetic processing unit 300 is conceptual, and the phase calculation unit 302 and the like may be a plurality of programs executed by the same CPU. A specific calculation method in the phase calculation unit 302 and the like will be described later.

  The shape measuring device 1 is disposed to project the deformed grating pattern on the image sensor 6 and the light projecting optical system 20 which is a group of optical elements disposed to image the deformed grating pattern on the surface S. And a light receiving optical system 25 which is a group of optical elements.

  The light projecting optical system 20 includes an illumination lens 21, a condenser lens 22, an aperture stop 23, and a projection lens 24. These constitute a projection optical system using Koehler illumination, and light reaches the mounting surface of the stage 14 without unevenness. The illumination lens 21 converts light emitted from an arbitrary point of the light source 2 into parallel light. The grating 3 is illuminated with light that has passed through the illumination lens 21 and has become a plane wave.

  The condensing lens 22 condenses the light transmitted through the grating 3. The light condensed by the condenser lens 22 passes through the aperture stop 23 and reaches the projection lens 24. The aperture stop 23 is disposed on the rear focal plane of the condenser lens 22.

  The projection lens 24 is a lens arranged to form an image of the grating 3 on the surface S, and makes the light transmitted through the aperture stop 23 parallel light and enter the surface S. The optical axis of the illumination lens 21, the optical axis of the condenser lens 22, and the optical axis of the projection lens 24 are coincident with each other and are inclined with respect to the mounting surface of the stage 14. The light transmitted through the projection lens 24 is incident on the surface S of the measurement object 4 placed on the stage 14 at an incident angle θ. The condensing lens 22, the aperture stop 23, and the projection lens 24 constitute a bilateral telecentric lens. When the lateral magnification of the both-side telecentric lens is M, when the surface S is flat, the pitch P2 of the projected image of the grating 3 (pitch of the deformed grating pattern) is M / COSθ times the grating pitch P1.

  The light receiving optical system 25 includes a condenser lens 26, an aperture stop 27, and an imaging lens 28. The condensing lens 26 condenses the light reflected by the surface S. The light condensed by the condenser lens 26 passes through the aperture stop 27 and reaches the imaging lens 28. The aperture stop 27 is disposed on the rear focal plane of the condenser lens 26.

  The imaging lens 28 is a lens arranged to form an image of the deformed lattice pattern on the image sensor 6, and makes the light transmitted through the aperture stop 27 enter the image sensor 6 as parallel light. The condenser lens 26, the aperture stop 27, and the imaging lens 28 constitute a bilateral telecentric lens. The image sensor 6 is disposed at the image forming point of the both-side telecentric lens.

  The optical axis of the condensing lens 26 and the optical axis of the imaging lens 28 coincide with each other and are inclined with respect to the mounting surface of the stage 14. These optical axes are arranged along the path of light reflected at the reflection angle θ on the surface S. That is, the optical axis of the projection lens 24 and the optical axis of the condenser lens 26 are on the same plane and intersect on the stage 14.

  A specific configuration of the lattice driving device 30 will be described with reference to FIG. FIG. 3 is a diagram schematically illustrating the configuration of the lattice driving device 30. As shown in FIG. 3, the lattice driving device 30 includes a stage 31, a male screw shaft 34, and a motor 35.

  The stage 31 is a substantially rectangular stage movable along a linear direction (direction indicated by an arrow AR2 in FIG. 3) by driving a motor 35 described later. The movement of the stage 31 is guided by the guide shaft 36.

  The grating 3 is fixed on the upper surface of the stage 31, and the grating 3 moves together with the stage 31. The grating 3 is fixed so that its grating surface is along the moving direction of the stage 31, and in a state where the stage 31 is relatively close to the motor 35 as shown in FIG. The direction coincides with the moving direction of the stage 31. The stage 31 is formed with a through-hole whose inner surface is machined with a female screw. The through-hole has a central axis along the moving direction of the stage 31.

  The male screw shaft 34 is a shaft inserted into the through hole of the stage 31. The outer surface of the male screw shaft 34 is subjected to male screw processing, and is screwed with a female screw formed in the through hole of the stage 31. For this reason, when the male screw shaft 34 rotates around its central axis, the stage 31 moves in a direction along the central axis.

  The motor 35 is a rotary motor connected to one end (right end in FIG. 3) of the male screw shaft 34, and rotates the male screw shaft 34 about its central axis. The rotation speed, rotation amount, and the like of the rotation are controlled by the control unit 305 of the arithmetic processing device 300.

  A fixed support 32 is fixed on the upper surface of the stage 31, and the lattice 3 is fixed in a rotatable state in the vicinity of the upper end of the fixed support 32. That is, the vicinity of the upper end (reference numeral 33) of the fixed support 32 and the corner of the lattice 3 (the corner near the upper end) are fixed, and the lattice 3 rotates along the lattice surface with the fixed portion as the center. It is possible.

  An upper stopper 38 is disposed above the lattice 3 to restrict the rotation range of the lattice 3. The upper stopper 38 is supported by a column 37 disposed at a position opposite to the motor 35 with the male screw shaft 34 interposed therebetween. In the state shown in FIG. 3A, that is, in a state where the periodic direction of the lattice 3 is parallel to the central axis of the male screw shaft 34, the lattice 3 is further rotated clockwise by a stopper (not shown). Is no longer possible. On the other hand, in the state shown in FIG. 3B, that is, in the state where the lattice 3 is rotated counterclockwise from the state of FIG. 3A and the upper end portion thereof is in contact with the upper stopper 38 from below, The lattice 3 can no longer be rotated counterclockwise.

  A string-wound spring 39 is disposed between the support column 37 and the lattice 3. One end of the string spring 39 is fixed to the column 37, and the other end is fixed near the lower end of the lattice 3. The string spring 39 changes its length depending on the position of the stage 31 and applies a force to the lattice 3 according to the length. The direction of the force is a direction along the central axis of the male screw shaft 34. Further, the position where the force is applied in the grid 3 (the position where the other end of the string spring 39 is connected) is below the rotation center (reference numeral 33) of the grid 3.

  In the state where the stage 31 is relatively close to the motor 35 as shown in FIG. 3A, the string-wound spring 39 is longer than its natural length. Therefore, the lattice 3 receives a force that rotates clockwise by the string spring 39 and is pressed against a stopper (not shown) so that the rotation is restricted. Even if the stage 31 moves in the vicinity of the position, the grating 3 does not rotate and moves while the periodic direction of the grating 3 coincides with the moving direction of the stage 31. At this time, the angle formed by the periodic direction of the grating 3 with respect to the moving direction of the stage 31 is 0 (first angle).

  On the other hand, in the state where the stage 31 is relatively far from the motor 35 as shown in FIG. 3B, the string spring 39 is shorter than its natural length. Accordingly, the lattice 3 receives a force that rotates counterclockwise by the string spring 39 and is pressed against the upper stopper 38 from below so that the rotation is restricted. Even if the stage 31 moves in the vicinity of the position, the grating 3 does not rotate and moves while the periodic direction of the grating 3 is inclined with respect to the moving direction of the stage 31. At this time, the angle formed by the periodic direction of the grating 3 with respect to the moving direction of the stage 31 is ω (second angle).

  As described above, the lattice driving device 30 can move the lattice 3 along a predetermined direction (a direction along the central axis of the male screw shaft 34). At this time, the grating 3 moves in a state where the angle between the periodic direction and the moving direction is 0 (first angle), or the angle formed between the periodic direction and the moving direction is ω (second angle). Move with.

  FIG. 3 shows an example of the configuration of the lattice driving device 30, and it goes without saying that other configurations may be used. The lattice driving device 30 moves the lattice 3 in a predetermined direction along the lattice surface, and moves the lattice 3 in the predetermined direction while rotating the lattice 3 by a predetermined angle along the lattice surface. If you can. For example, it is good also as a structure provided with the motor for moving the grating | lattice 3, and the motor for rotating the grating | lattice 3, respectively.

  A method for measuring the surface shape (height distribution of the surface S) of the DUT 4 using the shape measuring apparatus 1 having the above configuration will be described. 5 and 6 are flowcharts showing an example of a shape measuring method using the shape measuring apparatus 1.

  In the first step S100, the measurement object 4 is placed on the placement surface of the stage 14, as shown in FIG. The stage 14 may include a drive mechanism that finely adjusts the position of the DUT 4.

  The grating 3 is moved to a predetermined initial position by the grating driving device 30. At the initial position, the angle formed by the periodic direction of the grating 3 with respect to the moving direction of the stage 31 is 0 (first angle). When step S100 is completed, the lattice 3 is in a state in which it can move along the lattice surface and in the direction along the central axis of the male screw shaft 34. The periodic direction of the grating 3 coincides with the moving direction. In step S101 to step S106 described below, the lattice 3 moves without rotating.

  In step S101 following step S100, the arithmetic processing unit 300 assigns 1 to a variable m that takes a natural number. The variable m is a variable for recording the number of deformed grating patterns acquired for performing the phase shift method.

  In subsequent step S102, a grid pattern is projected onto the surface S of the DUT 4 while the light source 2 is caused to emit light. On the surface S, a deformed lattice pattern corresponding to the shape appears. The deformed grating pattern is incident on the image sensor 6 as reflected light.

In step S103, the image of the modified lattice pattern imaged by the image sensor 6 is recorded in the recording unit 301 as the light intensity distribution I ₁₁ (x, y) incident on the CCD element. x and y are coordinates indicating the position on the light receiving surface of the image sensor 6 and correspond to the coordinates indicating the position on the surface S on a one-to-one basis. In the present embodiment, the x coordinate axis is arranged on the light receiving surface along the direction corresponding to the moving direction of the grating 3. Further, the y coordinate axis is arranged on the light receiving surface so as to be orthogonal to the x coordinate axis.

Imaging by the image sensor 6 is performed while moving the grating 3 by the grating driving device 30. That is, while the grating 3 is moved in the periodic direction at a constant speed by 1/2 of the grating pitch P1, the deformed grating pattern that moves with the grating 3 is continuously imaged. As a result of time integration of the intensity of light incident on the CCD element of the image sensor 6, the light intensity distribution I ₁₁ (x, y) recorded in the recording unit 301 is as shown by the following equation (1). Cosine wave distribution.

Here, A ₁ and B ₁ are constants, A ₁ indicates an amplitude, and B ₁ indicates a bias term. P2 is the pitch of the deformed lattice pattern when the surface S is a flat surface (a surface having the same height in all coordinates). The value of A ₁ is determined by the lens characteristics of the condenser lens 22, the projection lens 24, the condenser lens 26, etc., the light intensity of the light emitted from the light source 2, the reflectance of the surface S, and the sensitivity of the image sensor 6. The value of B ₁ is determined by factors such as stray light in addition to the lens characteristics, the reflectance of the surface S, the light intensity of the light emitted from the light source 2, and the sensitivity of the image sensor 6. φ ₁ (x, y) is a phase distribution, which corresponds to a distribution of a phase change amount accompanying the deformation of the lattice pattern projected on the surface S.

  In step S104 following step S103, it is determined in the arithmetic processing unit 300 whether the value of the variable m is 4 or more. If the value of the variable m is less than 4, it means that the number of deformed grating patterns acquired for performing the phase shift method is less than 4, and the process proceeds to step S105.

At this time, the grating 3 has moved by ½ of the grating pitch P1 from the position at the start of acquisition of the light intensity distribution I ₁₁ (x, y). In step S105, the grating 3 is further moved by 3/4 of the grating pitch P1 while the recording of the light intensity distribution by the image sensor 6 is stopped. Instead of such movement, the grating 3 may be moved in the reverse direction by 1/4 of the grating pitch P1. In any case, the phase of the deformed grating pattern projected on the surface S is in a state advanced by π / 2 in the x direction from the phase at the start of acquisition of the light intensity distribution I ₁₁ (x, y). .

In subsequent step S106, 1 is added to the value of variable m in arithmetic processing unit 300, and steps S102 and S103 are executed. In step S103, the image of the deformed lattice pattern captured by the image sensor 6 is recorded again, but the phase of the deformed lattice pattern at the start of recording advances by π / 2 in the x direction as described above. The light intensity distribution I ₁₂ (x, y) recorded in the recording unit 301 is a cosine wave distribution as shown by the following equation (2).

Thereafter, Step S102, Step S103, Step S105, and Step S106 are repeated until the value of the variable m becomes 4. As a result, the light intensity distribution I ₁₃ (x, y) represented by the following formula (3) and the light intensity distribution I ₁₄ (x, y) represented by the formula (4) are recorded in the recording unit 301.

If the value of the variable m is 4 in step S104, the four light intensity distributions I ₁₁ (x, y), I ₁₂ (x, y), I ₁₃ (x, y) necessary for performing the phase shift method are used. , I ₁₄ (x, y) has been acquired, and the process proceeds to step S200.

  In step S <b> 200, the lattice 3 is rotated by the lattice driving device 30. The lattice driving device 30 moves the stage 31 in a direction away from the motor 35 so that the lattice 3 is pressed against the upper stopper 38 from below. As described with reference to FIG. 3, at this time, the angle formed by the periodic direction of the grating 3 with respect to the moving direction of the stage 31 is the second angle ω. When step S200 is completed, the lattice 3 is in a state in which it can move along the lattice surface and in the direction along the central axis of the male screw shaft 34. The periodic direction of the grating 3 is inclined at a second angle ω with respect to the moving direction.

  In step S201 to step S206 described below, the lattice 3 moves without rotating. That is, since the grating 3 moves further away from the motor 35 from the state shown in FIG. 3B, the periodic direction of the grating 3 is always kept inclined at the second angle ω with respect to the moving direction. Is done.

  In step S201 following step S200, 1 is assigned to the variable k taking a natural number in the arithmetic processing unit 300. The variable k is a variable for recording the number of deformed grating patterns acquired for performing the phase shift method.

  In the subsequent step S202, a grid pattern is projected onto the surface S of the object 4 to be measured while the light source 2 is caused to emit light. On the surface S, a deformed lattice pattern corresponding to the shape appears. The deformed grating pattern is incident on the image sensor 6 as reflected light.

  Here, if the surface S is flat, the actual pitch of the lattice pattern projected onto the surface S is P2. However, in view of the fact that the lattice pattern projected onto the surface S is also rotated by the second angle ω as the lattice 3 is rotated in step S200, it follows the moving direction of the lattice pattern. Thus, the pitch (also referred to as an effective pitch related to height measurement) can be regarded as P2 / cos ω.

In step S203, similarly to the case of step S201, the image of the modified lattice pattern imaged by the image sensor 6 is recorded in the recording unit 301 as the light intensity distribution I ₂₁ (x, y) incident on the CCD element.

Imaging by the image sensor 6 is performed while moving the grating 3 by the grating driving device 30. That is, while the lattice 3 is moved at a constant speed by 1/2 of P1 / cos ω, the deformed lattice pattern that moves with the lattice 3 is continuously imaged. As a result of time integration of the intensity of light incident on the CCD element of the image sensor 6, the light intensity distribution I ₂₁ (x, y) recorded in the recording unit 301 is as shown by the following equation (5). Cosine wave distribution.

Similar to φ ₁ (x, y), φ ₂ (x, y) is a phase distribution, which corresponds to the distribution of the amount of phase change caused by the deformation of the lattice pattern projected on the surface S. It is.

  In step S204 following step S203, it is determined in the arithmetic processing unit 300 whether the value of the variable k is 4 or more. If the value of the variable k is less than 4, it means that the number of deformed grating patterns acquired for performing the phase shift method is less than 4, and the process proceeds to step S205.

At this time, the grating 3 has moved by 1/2 of P1 / cos ω from the position at the start of acquisition of the light intensity distribution I ₂₁ (x, y). In step S205, with the recording of the light intensity distribution by the image sensor 6 stopped, the grating 3 is further moved by 3/4 of P1 / cos ω. Instead of such movement, the grating 3 may be moved in the reverse direction by 1/4 of P1 / cosω. In any case, the phase of the deformed grating pattern projected onto the surface S is advanced by π / 2 in the x direction from the phase at the start of acquisition of the light intensity distribution I ₂₁ (x, y). .

In subsequent step S206, 1 is added to the value of variable k in arithmetic processing unit 300, and steps S202 and S203 are executed. In step S203, the image of the deformed grid pattern captured by the image sensor 6 is recorded again, but the phase of the deformed grid pattern at the start of recording advances by π / 2 in the x direction as described above. The light intensity distribution I ₂₂ (x, y) recorded in the recording unit 301 is a cosine wave distribution as shown by the following equation (6).

Thereafter, Step S202, Step S203, Step S205, and Step S206 are repeated until the value of the variable k becomes 4. As a result, the light intensity distribution I ₂₃ (x, y) represented by the following formula (7) and the light intensity distribution I ₂₄ (x, y) represented by the formula (8) are recorded in the recording unit 301.

When the value of the variable k is 4 in step S204, the four light intensity distributions I ₂₁ (x, y), I ₂₂ (x, y), and I ₂₃ (x, y) necessary for performing the phase shift method are used. , I ₂₄ (x, y) has been acquired, and the process proceeds to step S301 in FIG.

In step S301, among the plurality of light intensity distributions recorded in the recording unit 301, light intensity distributions I ₁₁ (x, y), I ₁₂ (x, y), I ₁₃ (x, y), I ₁₄ (x , Y) is read out. In the phase calculation unit 302, the phase distribution (first phase distribution) φ ₁₁ (x, y) is calculated by the following equation (9).

Phase distribution φ ₁₁ (x, y) phase phi ₁₁ of each point represented by are each a range from - [pi] + [pi. That is, the height at an arbitrary point on the surface S can be various values, whereas the phase φ ₁₁ corresponding to the height is a value that periodically changes within a limited range of −π to + π. .

FIG. 7 is a graph showing the relationship between the height of the surface S and the phase φ ₁₁ at the point corresponding to the coordinates (0, 0). As shown in FIG. 7, the height of the surface S is increased, after the phase phi ₁₁ is that increased to [pi, so that the folded back discontinuously - [pi]. The height range Δh ₁ of the surface S corresponding to one period (from −π to + π) of the phase φ ₁₁ is expressed by the following formula (10).

If the height of the surface S is within the height range Δh ₁ as described above, the height and the phase φ ₁₁ correspond one-to-one. Therefore, in this case, the height of the surface S can be accurately obtained based on the phase φ ₁₁ . In order to calculate the height distribution H (x, y) of the surface S, first, the phase distribution φ ₁ (x, y) is calculated by the following equation (11). The calculated phase distribution φ ₁ (x, y) is recorded in the recording unit 301. Note that N in Expression (11) is an integer that is appropriately set so that the absolute value of the value of the phase distribution φ ₁ (x, y) does not exceed 2π for each coordinate (x, y).

In step S302 following step S301, among the plurality of light intensity distributions recorded in the recording unit 301, light intensity distributions I ₂₁ (x, y), I ₂₂ (x, y), I ₂₃ (x, y), I ₂₄ (x, y) is read out. In the phase calculation unit 302, the phase distribution (second phase distribution) φ ₂ (x, y) is calculated by the following equation (12).

As in the case of the phase φ ₁₁ , the phase φ _{21 at} each point represented by the phase distribution φ ₂₁ (x, y) is in the range of −π to + π. That is, the height at an arbitrary point on the surface S can have various values, whereas the phase φ ₂₁ corresponding to the height has a value that periodically changes within a limited range of −π to + π. . As shown in FIG. 7, when the height at an arbitrary point on the surface S at the point corresponding to the coordinates (0, 0) increases, the phase φ ₂₁ is discontinuously folded back to −π immediately after increasing to π. It will be. A height range Δh ₂ of the surface S corresponding to one period (from −π to + π) of the phase φ ₂₁ is expressed by the following formula (13). As apparent from the equation (13), the height range Δh ₂ is slightly larger than the height range Δh ₁ .

Similarly to the case of φ _1, the phase distribution φ ₂ (x, y) is calculated by the following equation (14). The calculated phase distribution φ ₂ (x, y) is recorded in the recording unit 301. Note that N in the equation (14) is an integer appropriately set so that the absolute value of the phase distribution φ ₂ (x, y) does not exceed 2π for each coordinate (x, y).

In step S303 following step S302, the phase distribution φ ₁ (x, y) and the phase distribution φ ₂ (x, y) recorded in the recording unit 301 are read. In the phase connection unit 303, the phase difference distribution φ _D (x, y) is calculated as the difference between the phase distribution φ ₁ (x, y) and the phase distribution φ ₂ (x, y) by the following equation (15). The The phase difference distribution φ _D (x, y) indicates a difference (phase difference) between the phase φ ₁ and the phase φ _{2 at} an arbitrary point (x, y).

FIG. 8 is a graph showing the relationship between the height of the surface S and the phase difference φ _D. As shown in FIG. 8, the phase difference φ _D is also discontinuous with respect to the height of the surface S. Therefore, in step S304, first correction (continuous process) performed with respect to the phase difference phi _D, converts the phase difference phi _D so as continuous in a predetermined range.

Specifically, the phase unwrapping section 303, the value of the phase difference phi _D is when -π smaller adds 2π to the value. The value of the phase difference phi _D is the larger than π subtracting 2π from the value. By performing such addition and subtraction, the phase difference distribution φ _D (x, y) is converted into the phase difference distribution φ _CD1 (x, y).

FIG. 9 is a graph showing the relationship between the height of the surface S and the phase difference φ _CD1 . As shown in FIG. 9, the phase difference φ _CD1 is continuous with respect to the height of the surface S in a predetermined range (the phase difference φ _CD1 is in a range from −π to + π). Further, the height range Δh ₁₂ of the surface S corresponding to one period (from −π to + π) of the phase φ _CD1 is expressed by the following formula (18) using the height range Δh ₁ and the range Δh ₂ .

Furthermore the phase unwrapping section 303, the second correction performed with respect to the phase difference phi _CD1, so that the inclination with respect to the height of the surface S is equal to the slope of the phase phi ₁ (FIG. 7), converts the phase difference phi _CD1 (Step S305). Specifically, the phase difference distribution φ _CD1 (x, y) is converted into the phase difference distribution φ _CD2 (x, y) by multiplying the value of the phase difference φ _CD1 by (Δh ₁₂ / Δh ₁ ).

FIG. 10 is a graph showing the relationship between the height of the surface S and the phase difference φ _CD1 when the value of Δh ₁₂ / Δh ₁ is 4. In the figure, the relationship between the height of the surface S and the phase φ ₁ is shown superimposed. As shown in FIG. 10, the range of values that the phase difference φ _CD2 can take is in the range of −4π to 4π, and is continuous in this range. Further, in the range from −π to π, the phase difference distribution φ _CD2 (x, y) and the phase distribution φ ₁ (x, y) substantially coincide.

Further, the phase connection unit 303 calculates the difference between the phase difference φ _CD2 and the phase φ ₁ for each coordinate on the light receiving surface of the image sensor 6 (for each coordinate on the surface S), and the value obtained by dividing this by 2π is the largest. Calculate the nearest integer n.

  The right side of equation (20) should theoretically always be an integer, but may not be an integer due to measurement error. For this reason, the integer n closest to the value on the right side is calculated by rounding off the right side. The integer n calculated in this way is a value indicating the order of phase jump (step S306).

FIG. 11 is a graph showing the relationship between the height of the surface S and the difference between the phase difference φ _CD2 and the phase φ ₁ superimposed on the graph of FIG. As shown in FIG. 11, the difference between the phase difference φ _CD2 and the phase φ ₁ is a stepped graph, and the number of steps corresponds to the integer n.

In subsequent step S307, the phase connection unit 303 phase-connects the phase φ ₁ using the integer n with respect to all the coordinates on the light receiving surface of the image sensor 6. Specifically, the phase φ _1C after the phase connection is calculated by adding 2nπ to the phase φ _{1 at} each coordinate.

FIG. 12 is a graph showing the relationship between the height of the surface S and the phase difference φ _1C . As shown in FIG. 12, the phase difference φ _1C is continuous in a wide range with respect to the height of the surface S (the phase difference φ _1C is in a range from −4π to + 4π). Further, the height range Δh ₁₂ of the surface S corresponding to one period (from −4π to + 4π) of the phase difference φ _1C is the height of the surface S corresponding to one period (from −π to + π) of the phase φ _1. It is wider than the range Δh ₁ .

In step S308 following step S307, the height calculation unit 304 calculates the height distribution H (x, y) of the surface S based on the distribution of the phase φ _1C after phase connection, that is, the phase distribution φ _1C (x, y). ) Is calculated. Considering that the phase φ ₁ becomes 2π when the height is Δh ₁ , the height distribution H (x, y) is calculated by the following equation (22).

As described above, in the shape measuring apparatus 1 according to the present embodiment, the phase distribution φ ₁ (x, x, x) of the grating pattern projected in a state where the angle of the grating 3 with respect to the moving direction of the stage 31 is 0 (first angle). y) (first phase distribution) and the phase distribution φ ₂ (x, y) (second phase distribution) of the grating pattern projected in the state where the angle of the grating 3 with respect to the same direction is ω (second angle) , The height distribution on the surface S of the DUT 4 is calculated. These two phase distributions can be equated with the two phase distributions obtained respectively by using two gratings having different pitches.

Therefore, phase connection is performed based on the phase distribution φ ₁ (x, y) and the phase distribution φ ₂ (x, y), and the height distribution H (x, y) of the surface S is calculated. On the other hand, since only one grating 3 is actually mounted on the shape measuring apparatus, the apparatus configuration is simpler than in the prior art.

In the shape measuring apparatus 1, the phase connection unit 303 calculates a phase difference distribution φ _D (x, y) that is a difference between the phase distribution φ ₁ (x, y) and the phase distribution φ ₂ (x, y). To do. Further, in the phase unwrapping section 303, so that the phase difference distribution phi _D (x, y) is continuous in a predetermined range, the phase difference distribution phi _D (x, y) first correction (continuous process on ). The phase difference distribution φ _CD1 (x, y) after the continuous process is performed is a distribution proportional to the height of the object surface in a predetermined range.

Therefore, in the predetermined range, the phase difference φ _CD1 and the height of the surface S can be made to correspond one-to-one. The range (Δh ₁₂ ) of the height of the surface S such that the phase difference distribution φ _CD1 (x, y) is from −π to + π is the phase distribution φ ₁ (x, y) or the phase distribution φ ₂ (x, y). y) is wider than the range of height of the surface S (Δh ₁ , Δh ₂ ) such that −π to + π. That is, the range in which the correct height is calculated without causing phase jump is made wider than when a single grating is used.

Further, in the shape measuring apparatus 1, the phase distribution φ ₁ (x, y) is used in the phase connection unit 303 based on the phase difference distribution φ _CD1 (x, y) subjected to the first correction (continuation processing). Phase connection processing is performed on Specifically, the phase difference distribution φ _CD1 (x, y) with respect to the second correction alms obtained phase difference distribution φ _CD2 (x, y) based on the integer n indicating the order of the phase jump The phase connection is performed using the integer n.

Here, in order to calculate the height distribution of the surface S based on the phase difference distribution φ _CD2 (x, y), the phase difference φ _CD2 and the height of the surface S can also be directly calculated. is there. However, in the phase difference φ _CD2 calculated from the phase distribution φ ₁ (x, y) and the phase distribution φ ₂ (x, y), an error due to the variation of the grating pitch P1 from the design value, the grating driver 30 There is a possibility that both of the errors included in the phase distribution φ ₁ (x, y) and the phase distribution φ ₂ (x, y), such as an error in the rotation angle due to the above, are included.

Therefore, in the present embodiment, the height of the surface S is not directly calculated based on the phase difference distribution φ _CD2 (x, y), but a phase connection process is performed on the phase distribution φ ₁ (x, y). Based on this, the height of the surface S is calculated. Since the calculated height distribution H (x, y) includes only the error of the phase distribution φ ₁ (x, y), the error can be reduced.

In the present embodiment, as illustrated in FIG. 10, the phase φ ₁ and the phase φ ₂ when the height of the surface S is 0 are both assumed to be 0. However, in actual measurement, the phase φ ₁ or the phase φ ₂ when the height of the surface S is 0 may deviate from 0 due to reasons such as poor positioning accuracy of the grating 3 by the grating driving device 30. Can occur. That is, the initial phase between the phase φ ₁ and the phase φ ₂ may be shifted.

In order to correct such an initial phase shift, a distribution of values obtained by subtracting the phase φ ₁ from the phase difference φ _CD2 is calculated, and it is examined how much the value that appears most frequently deviates from 2nπ.

FIG. 13 is a graph showing a frequency distribution of values obtained by subtracting the phase φ ₁ from the phase difference φ _CD2 . When there is no deviation in the initial phase between the phase φ ₁ and the phase φ ₂ , the distribution is centered on 2nπ as shown in FIG. On the other hand, when the initial phases of the phase φ ₁ and the phase φ ₂ are shifted, the center of the distribution is shifted from 2nπ as shown in FIG.

Therefore, the initial phase shift can be corrected by subtracting the shift amount from the phase φ ₂ for all coordinates on the light receiving surface of the image sensor 6. In the example shown in FIG. 13B, π / 2 may be subtracted from all phases φ ₂ .

  The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. In other words, those specific examples that have been appropriately modified by those skilled in the art are also included in the scope of the present invention as long as they have the characteristics of the present invention. For example, the elements included in each of the specific examples described above and their arrangement, materials, conditions, shapes, sizes, and the like are not limited to those illustrated, but can be changed as appropriate. Moreover, each element with which each embodiment mentioned above is provided can be combined as long as technically possible, and the combination of these is also included in the scope of the present invention as long as it includes the features of the present invention.

1: Shape measuring device 2: Light source 3: Grating 3A: Translucent part 3B: Light shielding part 4: Object to be measured 6: Image sensor 14: Stage 20: Projection optical system 21: Illumination lens 22: Condensing lens 24: Projection Lens 25: Light receiving optical system 26: Condensing lens 28: Imaging lens 30: Lattice drive device 31: Stage 32: Fixed column 34: Male screw shaft 35: Motor 36: Guide shaft 37: Column 38: Upper stopper 300: Arithmetic processing Device 301: Recording unit 302: Phase calculation unit 303: Phase connection unit 304: Height calculation unit 305: Control unit S: Surface

Claims (6)

In the shape measuring device that measures the surface shape of the object based on the lattice pattern projected on the surface of the object,
A light source that generates light to irradiate the surface of the object;
A grating disposed between the light source and the object such that a grating pattern is projected onto the surface of the object;
Grating moving means for moving the grating in a predetermined direction so that the projected grating pattern changes;
Grid rotation means for rotating the grid so that the angle of the grid with respect to the predetermined direction changes,
A first phase distribution that is a phase distribution of the grating pattern projected in a state where the angle of the grating with respect to the predetermined direction is a first angle;
A second phase distribution that is a phase distribution of the grating pattern projected in a state where the angle of the grating with respect to the predetermined direction is a second angle;
A shape measuring device that calculates a height distribution on the surface of the object based on the above. A phase difference calculation unit that calculates a phase difference distribution that is a difference between the first phase distribution and the second phase distribution;
A first processing unit that performs a continuation process on the phase difference distribution so that the phase difference distribution is continuous in a predetermined range;
The shape measuring device according to claim 1, further comprising:   The system according to claim 2, further comprising a second processing unit that performs phase connection processing on the first phase distribution based on the phase difference distribution after the continuous processing is performed. Shape measuring device. A light source that generates light to irradiate the surface of the object;
A grating disposed between the light source and the object such that a grating pattern is projected onto the surface of the object;
Grating moving means for moving the grating in a predetermined direction so that the projected grating pattern changes;
A shape measuring method for measuring the surface shape of the object by a shape measuring device comprising:
A first acquisition step of acquiring a first phase distribution which is a phase distribution of the grating pattern projected in a state where the angle of the grating with respect to the predetermined direction is a first angle;
An angle conversion step of changing the angle of the grating with respect to the predetermined direction from the first angle to a second angle;
A second acquisition step of acquiring a second phase distribution that is a phase distribution of the grating pattern projected in a state where the angle of the grating with respect to the predetermined direction is a second angle;
Based on the first phase distribution and the second phase distribution, a shape calculating step for calculating a height distribution on the surface of the object;
A shape measuring method characterized by comprising: A phase difference calculating step of calculating a phase difference distribution which is a difference between the first phase distribution and the second phase distribution;
A first processing step of performing a continuation process on the phase difference distribution so that the phase difference distribution is continuous in a predetermined range;
The shape measuring method according to claim 4, further comprising:   6. The method according to claim 5, further comprising a second processing step of performing phase connection processing on the first phase distribution based on the phase difference distribution after the continuous processing is performed. Shape measurement method.