Shape measuring device

Abstract

To provide a shape measuring device that can measure the shape of plate-shaped objects, especially notches on wafers with complex shapes, with higher accuracy. [Solution] A shape measuring device for measuring the shape of a plate-shaped object 1 by scanning its surface and acquiring multiple surface images, comprising: an imaging system 10 that irradiates the object with parallel light and acquires a surface image; a stage system 30 that holds the object and adjusts the orientation of the object with respect to the imaging system; and a control device 20, wherein the control device comprises an orientation adjustment unit 21 that controls the imaging system and the stage system to scan the surface while adjusting the orientation and acquire multiple surface images, and an image processing unit that generates a reconstructed model of the three-dimensional shape of the object from the acquired multiple surface images, wherein the orientation adjustment unit 21 adjusts the orientation so that the angle of incidence of parallel light on the surface is within a predetermined range when acquiring surface images.

Description

Technical Field

[0001] The present invention relates to an apparatus for measuring the shape of a plate-shaped object to be measured, particularly the surface of a semiconductor wafer (hereinafter also simply referred to as "wafer"), and the shape of chamfered end faces, etc., and more particularly to a shape measuring apparatus for measuring the three-dimensional shape of a notch portion.

Background Art

[0002] Regarding semiconductor wafers manufactured through processes such as grinding, etching, and polishing, there is a need to measure the edge profiles of work-in-progress and / or products after each process. As a method for measuring this edge profile, the optical projection measurement method is known. The optical projection measurement method projects light onto the chamfered end of the wafer from directions substantially parallel to each of the front and back surfaces of the wafer, and images the projection image (cross-sectional shape cut in the thickness direction) of the end face of the wafer by a camera from a direction opposite to the light projection direction.

[0003] Patent Document 1 describes that when measuring the end face shape of a semiconductor wafer or the like based on its projection image, in order to perform accurate shape measurement without being affected by deposits present on the end face, predetermined image processing is executed for each of the projection images at a plurality of set angles.

[0004] Further, Patent Document 2 describes that when measuring the two-dimensional shape of the outer peripheral edge portion of a semiconductor wafer having a long depth along the optical axis direction, in order to prevent blurring of the contour and occurrence of diffraction fringes in the projection image, a collimator lens is used to irradiate light that is as parallel as possible.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] In the above-mentioned prior art, the methods described in Patent Documents 1 and 2 could only measure the top surface shape (2D) of the notch portion of the wafer, and could not accurately measure the more complex 3D shape of the notch portion. Furthermore, the accuracy of shape measurement was insufficient for the peripheral areas other than the notch portion due to blurring of the contours related to wafer alignment (orientation), crystal orientation, and light diffraction (light wrapping).

[0007] Therefore, the object of the present invention is to provide a shape measuring device that can measure the shape of plate-shaped objects to be measured, particularly notches of wafers with complex shapes, with higher accuracy. [Means for solving the problem]

[0008] As a result of diligent research to solve the above problems, the inventors have found that the above problems can be solved by the following configuration.

[0009] [1] A shape measuring device for measuring the shape of a plate-shaped object by scanning its surface and acquiring multiple surface images, comprising: an imaging system that irradiates the object with parallel light and acquires the surface images; a stage system that holds the object and adjusts the orientation of the object with respect to the imaging system; and a control device, wherein the control device comprises an orientation adjustment unit that controls the imaging system and the stage system to scan the surface while adjusting the orientation and acquire multiple surface images, and an image processing unit that generates a reconstructed model of the three-dimensional shape of the object from the acquired multiple surface images, wherein the orientation adjustment unit adjusts the orientation so that the angle of incidence of the parallel light on the surface is within a predetermined range when acquiring the surface images. [2] The shape measuring device according to [1], wherein the orientation adjustment unit determines the amount of adjustment based on pre-stored design data of the three-dimensional shape of the object. [3] The shape measuring device according to [1] or [2], wherein the stage system includes a chuck table with a five-axis structure, which adds two axes: a yaw axis for rotation and a pitch axis for tilting, in addition to the three axes: the X axis, Y axis, and Z axis. [4] The shape measuring device according to [1] or [2], which has a plurality of imaging systems and an imaging system switching mechanism for switching between the imaging systems, wherein the control device switches the imaging system to be used to a predetermined imaging system based on the correspondence with the object to be measured. [5] The shape measuring apparatus according to [4], wherein the object to be measured is a wafer, and the imaging system includes at least two selected from the group consisting of one for acquiring a white interference microscopy image, one for acquiring a confocal microscopy image, and one for acquiring an image by illuminance difference stereo using a polarizing plate, and the control device switches to the imaging system for acquiring a white interference microscopy image when the wafer is a ground wafer, to the imaging system for acquiring a confocal microscopy image when the wafer is an etched wafer, and to the imaging system for acquiring an image by illuminance difference stereo when the wafer is a polished wafer.[6] The shape measuring apparatus according to [3], wherein the object to be measured is a wafer, and the attitude adjustment unit, when acquiring the surface image of the edge portion of the wafer, rotates the pitch axis with respect to a slope or end face to adjust the incidence angle, and acquires the surface image while scanning the imaging system in the direction of the X axis, and then rotates the yaw axis to acquire the surface image of the outer circumference. [7] The shape measuring apparatus according to [6], when acquiring the surface image of the R portion of the wafer, the attitude adjustment unit divides the pitch axis into rotation increments of a predetermined pitch angle and acquires the surface image. [8] The shape measuring apparatus according to [3], wherein the object to be measured is a wafer, and the attitude adjustment unit, when acquiring the surface image of one R portion of the notch portion of the wafer, fixes the focal length of the imaging system, places the imaging system on the optical axis passing through the center of the R portion, and rotates the yaw axis to acquire the surface image. [9] The shape measuring apparatus according to [3], wherein the object to be measured is a wafer, and the attitude adjustment unit fixes the focal length and yaw axis of the imaging system and adjusts the incident angle when acquiring the surface image of the straight portion of the notch.

[10] The shape measuring apparatus according to [3], wherein the object to be measured is a wafer, and the attitude adjustment unit fixes the focal length of the imaging system when acquiring the surface image of the bottom R portion of the notch of the wafer, places the imaging system on the optical axis passing through the center of the bottom R portion, and acquires the surface image while scanning in the direction of the Z axis and the Y axis. [Effects of the Invention]

[0010] According to the present invention, a shape measuring device can be provided that can measure the shape of plate-shaped objects, particularly notches on wafers with complex shapes, with higher accuracy. [Brief explanation of the drawing]

[0011] [Figure 1] This is a functional block diagram of a shape measuring device according to an embodiment of the present invention. [Figure 2] This is a basic configuration diagram of an imaging system for acquiring white-light interference microscopy images. [Figure 3] This is a basic configuration diagram of an imaging system for acquiring confocal microscopic images. [Figure 4] It is a basic configuration diagram of an imaging system for obtaining an image by the illuminance difference stereo method. [Figure 5] It is a perspective view showing the configuration of the stage system. [Figure 6] It is a configuration diagram seen from the front of the Y-axis showing the relationship between the imaging system and the object to be measured. [Figure 7] It is a configuration diagram seen from the front of the X-axis showing the relationship between the imaging system and the object to be measured. [Figure 8] It is a flowchart showing the measurement procedure of the three-dimensional shape of the object to be measured by the shape measurement device. [Figure 9] It is an explanatory diagram of the measurement procedure of the three-dimensional shape of the notch part of the object to be measured which is a wafer. [Figure 10] It is an explanatory diagram showing a method for obtaining a surface image in the case of data dropout. 2] [Figure 11] It is a front view of the Y-axis showing the relationship between the imaging system and the object to be measured when measuring the outer peripheral edge part. [Figure 12] It is a front view of the X-axis showing the relationship between the imaging system and the object to be measured when obtaining a surface image of the slope of the outer peripheral edge part. [Figure 13] It is a detailed view showing the cross-sectional shape and the imaging direction of the outer peripheral edge part. [Figure 14] It is an explanatory diagram of the posture adjustment when obtaining a surface image of the outer peripheral edge part. [Figure 15] It is a diagram showing the imaging trajectory of the one R part of X3 (end face) in the notch part. [Figure 16] It is a diagram showing the imaging trajectory of the straight part of X3 (end face) in the notch part. [Figure 17] It is a diagram showing the imaging trajectory of the bottom R part of X3 (end face) in the notch part.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on representative embodiments of the present invention, but the present invention is not limited to such embodiments. In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0013] Further, the embodiments shown below are an example of embodying the technical idea of the present invention, and the technical idea of the present invention does not specify the material, shape, structure, arrangement, etc. of the constituent parts to the following embodiments. Also, the drawings are schematic. Therefore, the relationship between the thickness and the planar dimensions, the ratio, etc. may be different from the actual ones, and also the dimensional relationships and ratios between the drawings may be different from each other.

[0014] [Shape Measuring Device] A shape measuring device according to an embodiment of the present invention (hereinafter also referred to as "this shape measuring device") is a shape measuring device that acquires a plurality of surface images while scanning the surface of a plate-shaped object to be measured and measures the shape of the object to be measured. It has an imaging system that irradiates the object to be measured with parallel light and acquires the surface image, a stage system that holds the object to be measured and adjusts the posture of the object to be measured with respect to the imaging system, and a control device. The control device has a posture adjustment unit that controls the imaging system and the stage system to scan the surface while adjusting the posture and acquire a plurality of the surface images, and an image processing unit that generates a restoration model of the three-dimensional shape of the object to be measured from the plurality of acquired surface images. The posture adjustment unit is a shape measuring device that adjusts the posture of the object to be measured so that the incident angle of the parallel light on the surface is within a predetermined range when acquiring the surface image.

[0015] Figure 1 is a functional block diagram of the shape measuring device. The shape measuring device 100 includes a stage system 30 that holds a plate-shaped object to be measured 1 (typically work-in-progress after various processing, and / or a wafer of a finished product is preferred) and controls its orientation, an imaging system 10 that irradiates the object to be measured 1 with parallel light and acquires a surface image, and a control device 20. The control device 20 includes an orientation adjustment unit 21 that controls the imaging system 10 and the stage system 30 to scan the surface of the object to be measured 1 while adjusting its orientation and acquire multiple surface images, and an image processing unit 22 that generates a reconstructed model of the three-dimensional shape of the object to be measured 1.

[0016] The material, shape, and size of the plate-shaped object to be measured 1 are not particularly limited, but semiconductor wafers are typically preferred. The semiconductor wafer may be made by cutting from an ingot; it may have undergone processes such as grinding, etching, and polishing; or it may be a finished product after going through these processes. Furthermore, the material is not particularly limited and may be any of single-crystal silicon, sapphire, silicon carbide, gallium phosphide (GaP), gallium arsenide (GaAS), indium phosphide (InP), and gallium nitride (GaN).

[0017] The imaging system 10 has the function of irradiating the object to be measured 1 with parallel light and acquiring a surface image of the object to be measured 1, and typically preferably has a camera, a parallel light source, a beam splitter, and a focusing optical system. The shape measuring device 100 has one imaging system 10, but the shape measuring device 100 may have multiple imaging systems 10, in which case the shape measuring device 100 may have an imaging system switching mechanism for switching between and using multiple imaging systems 10.

[0018] When the shape measuring device 100 has multiple imaging systems 10, it is preferable that each imaging system 10 is used according to the type of object to be measured 1. Specifically, it is preferable that the control device 20 switches to a predetermined imaging system 10 based on the correspondence with the object to be measured 1.

[0019] For example, if the object to be measured 1 is a wafer after grinding, the surface of the object to be measured 1 will have many grinding marks from the grinding tool, and light irradiated onto the surface of the object to be measured 1 will often be diffusely reflected. In other words, the surface of a wafer after grinding is in a surface state where diffuse reflection is dominant. In such cases, it is preferable to use an imaging system 10 for acquiring white-light interference microscopy images in order to acquire surface images more accurately and efficiently.

[0020] Figure 2 is a basic configuration diagram of the imaging system 10 for acquiring white-white interference microscopy images. Light from a light source 10-1 (laser or LED) having a parallel beam profile passes through a collimating optical system 10-2 (e.g., a beam expander), a beam splitter 10-3, and an objective lens 10-4 to irradiate the object to be measured 1. Note that the light source 10-1 may be a parallel light source, in which case it does not need to have a collimating optical system 10-2.

[0021] Camera 10-7 images the light reflected from the object under test 1, passing through the objective lens 10-4, beam splitter 10-3, and focusing optical system 10-6 (e.g., a focusing lens), as well as the light reflected by the reference mirror 10-5 and returning to the same optical path. When the light reflected from the object under test 1 and the light reflected by the reference mirror 10-5 overlap, a spatial interference pattern (interference fringes) is obtained. These interference fringes contain information about the difference in optical paths between the two, and by analyzing the contrast and phase changes of the interference fringes that appear when the objective lens 10-4 is scanned in the vertical direction, surface topographic data can be obtained.

[0022] Furthermore, for example, if the object to be measured 1 is a wafer after etching (e.g., alkaline etching), the surface reflection characteristics (direct reflection / diffuse reflection of irradiated light) may differ locally (coexist) due to the distribution of crystal orientations on the surface and the presence of etch pits. In such cases, it is preferable to use an imaging system 10 for acquiring confocal microscopic images in order to acquire surface images more accurately and efficiently.

[0023] Figure 3 is a basic configuration diagram of the imaging system 10 for acquiring confocal microscopic images. The imaging system 10 for acquiring confocal microscopic images acquires a three-dimensional image using an optical microscope with a shallow depth of field and a pinhole confocal optical system. Light from the light source 10-1 passes through the collimating optical system 10-2, beam splitter 10-3, and objective lens 10-4, which align the diverging light as shown in Figure 2, and illuminates the object under measurement 1. The pinhole 10-8 is positioned in front of the light source 10-1 and the camera 10-7. Therefore, the camera 10-7 images the light that has been reflected from the object under measurement 1 and passed through the objective lens 10-4, beam splitter 10-3, focusing optical system 10-6, and pinhole 10-8.

[0024] As a result, out-of-focus images are blocked by the pinhole 10-8, preventing the acquisition of strong signals, and consequently, only the focused, pinpoint image is acquired. When performing 3D measurements, a horizontal beam scan is performed to capture the surface, followed by a vertical scan. The pinpoint image is acquired by setting vertical step intervals and capturing surface images at each height. The peak position of the light detection intensity becomes the height of the surface of the target sample, and this can be saved as 3D surface shape data by the image processing unit 22 described later.

[0025] Furthermore, for example, if the object to be measured 1 is a wafer after polishing, the surface is prepared to a mirror-like state, so direct reflection becomes dominant. In such cases, in order to acquire a surface image more accurately and efficiently, it is preferable to use an imaging system 10 for acquiring images using the illuminance difference stereo method with polarizing plates.

[0026] Figure 4 is a basic configuration diagram of the imaging system 10 for acquiring images using the illuminance difference stereo method. The illuminance difference stereo method measures the normal vector, which is the three-dimensional shape information of the object surface, from multiple images taken by changing the position of the light source 10-1. If the surface of the object to be measured 1 is a mirror surface, direct reflection becomes dominant. In this case, it is difficult to acquire accurate images with optical systems for acquiring white interference microscopy images or confocal microscopy images, and it is preferable to use the illuminance difference stereo method and remove highlights, which are areas with high brightness due to gloss.

[0027] Light from light source 10-1 passes through polarizer 10-9, collimating optical system 10-2, beam splitter 10-3, and objective lens 10-4 before being irradiated onto object under measurement 1. Camera 10-7 images the light reflected from object under measurement 1 and passing through objective lens 10-4, beam splitter 10-3, polarizer 10-10, and focusing optical system 10-6. Polarizers 10-9 and 10-10 are arranged with their polarization axes perpendicular to each other at a 90° angle (crossed nicol configuration).

[0028] This optical arrangement eliminates the reflection of light source 10-1 from specularly reflected light (linearly polarized) on the object under measurement 1, and only diffusely reflected light (unpolarized) reaches camera 10-7. As a result, harmful "glare" or "shininess" caused by the reflection of light source 10-1 is eliminated or reduced.

[0029] Returning to Figure 1, the stage system 30 has the function of holding the object to be measured 1 and adjusting the orientation of the object to be measured 1 relative to the imaging system 10, and preferably includes a chuck table with a five-axis structure, typically consisting of the three axes X, Y, and Z, plus two axes: a yaw axis for rotation and a pitch axis for tilt.

[0030] Figure 5 is a perspective view showing the configuration of the stage system 30. The chuck table 16, which holds the wafer, the object to be measured 1, has a posture change mechanism that allows movement in five axes: X, Y, Z, yaw, and two additional pitch axes. Therefore, the entire surface of the object to be measured 1 can be illuminated with measurement light from the imaging system 10 to acquire a surface image.

[0031] Figure 6 is a configuration diagram showing the relationship between the imaging system 10 and the object to be measured 1, viewed from the front along the Y axis. The imaging system 10 shown in Figures 2, 3, and 4 is fixed to the baseboard 15. The chuck table 16 that holds the object to be measured 1 and changes its orientation is preferably a vacuum chuck type and has a 5-axis structure, adding two axes: a yaw axis for rotation and a pitch axis for tilting, in addition to the three axes of X, Y, and Z. This allows the surface of the object to be measured 1 to be gradually scanned with a scan pitch P in the X-axis direction to acquire a surface image.

[0032] Furthermore, the edges 5 on the outer periphery of the object to be measured 1 are imaged by rotating the pitch axis relative to the slope and end face so that the illumination surface by the imaging system 10 is perpendicular (in other words, so that the incident angle is 0°). In addition, the outer periphery can be imaged all the way around by rotating the yaw axis 360 degrees. The imaging system 10 may also be configured so that the baseboard 15 can be moved in the X, Y, and Z axis directions.

[0033] Figure 7 is a configuration diagram showing the relationship between the imaging system 10 and the object to be measured 1, viewed from the front along the X axis. Similar to Figure 7, the surface of the object to be measured 1 is scanned gradually in the Y-axis direction with a scan pitch P, and a surface image is acquired by scanning with parallel measurement light. Furthermore, the outer edge portion 5 is imaged by rotating the pitch axis so that the illumination surface is perpendicular (in other words, so that the incident angle is 0°). In addition, the outer edge can be processed by rotating the yaw axis 360 degrees.

[0034] Returning to Figure 1, the control device 20 is typically a computer having a CPU (Central Processing Unit) and memory, and the functions of the attitude adjustment unit 21 and the image processing unit 22 are realized by the CPU executing a program stored in memory.

[0035] The attitude adjustment unit 21 has the function of controlling the attitude of the object to be measured 1 by controlling the stage system 30, and this is realized by the CPU executing a program stored in the memory of the control device 20. When acquiring a surface image, the attitude adjustment unit 21 adjusts the attitude of the object to be measured 1 so that the angle of incidence of parallel light to the surface of the object to be measured 1 is within a predetermined range.

[0036] It is generally known that the imaging angle (incidence angle of parallel light) at which an accurate image can be acquired differs depending on the optical system (imaging method) of the imaging system 10. For example, in the case of imaging systems for acquiring white interference microscopy images, the Mirau type and the Michelson type are known, but it is known that there are limitations on the range of imaging angles at which an accurate image can be acquired in both cases. This shape measuring device 100 has an attitude adjustment unit 21, and adjusts the incidence angle of parallel light to the surface (imaging angle) according to the imaging system 10 so that it falls within a predetermined range, thereby enabling the acquisition of a more accurate image. There are no particular limitations on the specific incidence angle, but generally, 0 to 30° is preferred, 0 to 15° is more preferred, and in a preferred embodiment, the incidence angle is approximately 0°.

[0037] The method by which the attitude adjustment unit 21 performs the above adjustment is not particularly limited, but it is preferable to determine the amount of adjustment based on the design data of the three-dimensional shape of the object to be measured 1, which is stored in advance in the memory of the control device 20. As the design data of the three-dimensional shape of the object to be measured, for example, if the object to be measured 1 is a wafer, it may be the design drawing (specifications) of the product wafer. Typically, this design data may include data on the outer shape of the wafer (outer periphery and notch area) and the three-dimensional shape of the notch. Specifically, it may take the form of a point cloud represented in a three-dimensional Cartesian coordinate system.

[0038] The image processing unit 22 has the function of generating a reconstructed model of the three-dimensional shape of the object to be measured 1 from multiple surface images acquired while scanning the surface of the object to be measured 1. This is achieved by the CPU executing a program stored in the memory of the control device 20.

[0039] Surface images for 3D reconstruction are obtained, for example, by using laser light as the observation light (measurement light) and extracting and combining the in-focus region from multiple images obtained from an all-focus microscope system, i.e., from an image sensor. High-resolution ultra-depth images can also be obtained by generating all-focus images in which all positions are in focus. Alternatively, the illumination difference stereo method can also be used to simultaneously perform detailed shape measurements of areas with relatively small irregularities (small elevation differences due to slope, for example, elevation differences of 10 nanometers).

[0040] Next, the operation of the shape measuring device 100 will be described. Figure 8 is a flowchart showing the procedure for measuring the three-dimensional shape of an object to be measured using the shape measuring device 100. First, in step S1, design data of the three-dimensional shape of the object to be measured is acquired. There are no particular restrictions on the method of acquiring the data; the CPU may read design data that has been stored in memory in advance, corresponding to the type of object to be measured, or the data may be input from an external source, depending on the object to be measured 1.

[0041] Next, in step S2, the amount of adjustment to the attitude of the object to be measured 1 is determined by the attitude adjustment unit 21, which is controlled by the control device 20, based on the design data. In other words, the trajectory of the movement of the object to be measured 1 relative to the imaging system 10 (imaging trajectory) is calculated. The above will be described in detail later using a specific example.

[0042] Next, in step S3, based on the imaging trajectory calculated in step S2, the attitude adjustment unit 21 controls the imaging system 10 and the stage system 30, scanning the surface while adjusting the attitude of the object to be measured 1, and acquiring a surface image of the object to be measured 1. At this time, the imaging position is adjusted to scan the surface of the object to be measured 1, so that an image of a wide area of ​​the surface of the object to be measured 1 is acquired. Note that in addition to the stage system 30, the imaging system 10 may also be moved at this time. This allows for more efficient adjustment of the attitude.

[0043] Next, in step S4, the image processing unit 22 forms a reconstructed 3D shape model from the multiple surface images obtained in step S3.

[0044] The above measurement procedure will be further explained using the example that the object to be measured 1 is a wafer. Figure 9 is an explanatory diagram of the procedure for measuring the three-dimensional shape of the notch portion 4 of the object to be measured 1, which is a wafer. In recent years, semiconductor wafer production sites have been required to improve the quality of the shape, etc., even in areas extending to the periphery. In particular, the shape of the notch portion 4 is prone to deformation due to processes such as grinding, etching, and polishing, which affects the yield in subsequent processes.

[0045] Figure 9(a) is a plan view of the notch portion 4, and Figure 9(b) is a cross-sectional view of the dashed-dotted line portion of the notch portion 4. The notch portion 4 has a complex three-dimensional shape, and from the left end of Figure 9(a), it consists of (1) a single-sided R portion, (2) a straight portion, (3) a bottom R portion, then a (2') straight portion which has a different slope direction from the (2) straight portion, and a (1') single-sided R portion which is symmetrical to the (1) single-sided R portion.

[0046] Furthermore, the cross-sectional shape has R1 and R2 at both ends of the end face X3, which is perpendicular to the upper surface 2 or lower surface 3 of the wafer (object 1 to be measured), connecting to the inclined surfaces X1 and X2. With respect to the midpoint of X3, X1, X2 and R1, R2 are symmetrical. The upper surface 2 or lower surface 3 of the object 1 to be measured, the end face X3, and the inclined surfaces X1 and X2 are... The crystal orientations are also different. Furthermore, the cross-sectional shape in Figure 9(b) is consistent not only in the notch portion 4 but also in the edge portion 5 of the outer periphery.

[0047] Therefore, the orientation of the imaging system 10 and the object to be measured 1 is changed to match the notch shape, so that the imaging system 10 (angle of incidence of parallel light) is perpendicular to the surface shape of the notch portion 4. In order to make the imaging system 10 perpendicular, the orientation adjustment unit 21 calculates the amount of orientation adjustment (imaging trajectory) of the object to be measured 1 by the stage system 30 based on the information acquired in step S1. (Step S2)

[0048] The attitude adjustment amount is set, in one form, based on the design data (point cloud data in a Cartesian coordinate system, etc.) acquired in step S1, as a condition in which the focal length of the imaging system 10 remains constant, and as a condition in which the incident angle of the irradiated parallel light is within a predetermined range. In other words, the attitude adjustment amount is determined as "optimal optical imaging (image acquisition) conditions for a surface shape" according to the surface condition of the object to be measured 1, based on the three-dimensional coordinates of the notch-shaped surface for which the design value is given.

[0049] Next, the imaging trajectory of the object to be measured 1 is controlled based on the determined attitude adjustment amount, and a surface image of the object to be measured 1 is acquired. (Step S3) The chuck table 16 that holds the object to be measured 1 and changes its attitude is preferably a vacuum chuck type, and in one embodiment, it is preferable to have a 5-axis structure that adds two axes, a yaw axis for rotation and a pitch axis for tilting, in addition to the three axes of X, Y, and Z.

[0050] This shape measuring device 100, through the five-axis movement of the chuck table 16 and the attitude adjustment mechanism, can image the object to be measured 1 even on rough or uneven surfaces while adjusting its attitude. This allows the angle of the imaging system 10 (incident angle of the irradiated light) with respect to the surface shape to be kept within a predetermined range. Therefore, it is possible to accurately image (acquire a surface image of) the surface shape of the object to be measured 1.

[0051] Furthermore, the inclination shape of the surface of the object under measurement 1 can be measured by examining the amount of reflected light from the surface irradiated with parallel light, allowing for the acquisition of accurate white light interference microscopy images, confocal microscopy images, and illuminance difference stereo methods, for example.

[0052] After processing in step S3, depth coordinates, which are three-dimensional coordinates, are obtained from the multiple surface images acquired, and a three-dimensional reconstruction is performed to create a reconstruction model (step S4). After the reconstruction model is created, it may be used for quality judgment of the master wafer (workpiece) and for shape conditions in subsequent processes.

[0053] Surface images for 3D reconstruction can be obtained, for example, by using laser light as the observation light (measurement light) and extracting and combining the in-focus regions from multiple images obtained from an all-focus microscope system, i.e., from an image sensor. Furthermore, high-resolution ultra-depth images can be obtained by generating all-focus images in which all positions are in focus. Alternatively, the illumination difference stereo method can also be used to simultaneously perform detailed shape measurements of areas with relatively small irregularities (small elevation differences due to slope, for example, elevation differences of about 10 nanometers).

[0054] Figure 10 is an explanatory diagram showing how to acquire surface images when data is missing. Data may be missing when the slope of the surface irregularities is large, or when there are defects such as irregular etch pits. For example, existing optical surface texture measuring instruments have an aperture number (NA) of approximately 0.55, which represents the focusing limit when there are no aberrations. With a slope of 7.9° or more, the lens may not be able to capture some of the reflected light from the surface being measured due to the angle tracking capability, which can result in data being missing.

[0055] Therefore, in this case, the pitch angle of the surface to be measured is rotated in increments of 7° or less, and multiple surface images with different imaging angles are obtained from the same location. If the surface to be measured has undulations (irregularities) as shown in Figure 10(a), the surface image from Figure 10(a), the surface image obtained by rotating the surface to be measured counterclockwise as shown in Figure 10(b), and the surface image obtained by rotating the surface to be measured clockwise as shown in Figure 10(c) are combined and the acquired images are integrated. As a result, the surface image of the area of ​​interest is obtained as a consistent shape without any missing data.

[0056] Figure 11 is a Y-axis front view showing the relationship between the imaging system 10 and the object to be measured 1 when measuring the outer edge portion 5. The cross-section of the edge portion 5 has a slope (angle θ) as shown in Figure 11(a) when it is laid flat. Figure 11(b) shows the measurement state of the slope. The attitude adjustment unit 21 rotates the chuck table 16 around the pitch axis so that the illumination surface by the imaging system 10 is perpendicular, in other words, so that the incident angle is approximately 0°, and while scanning the imaging system 10 in the X-axis direction, it causes the imaging system 10 to acquire a surface image.

[0057] Figure 11(c) shows the illumination state of the end face. Similar to Figure 11(b), the pitch axis is rotated so that the incident angle of parallel light is approximately 0° (within a predetermined range) to acquire a surface image. Furthermore, for the outer periphery, the chuck table 16 is rotated 360 degrees around the yaw axis to acquire a surface image of the outer periphery.

[0058] Figure 12 is an X-axis front view showing the relationship between the imaging system 10 and the object to be measured 1 when acquiring a surface image of the slope of the outer edge portion 5. The object to be measured 1 is held on a chuck table 16 similar to that in Figure 9. When acquiring a surface image of the edge portion 5, the attitude adjustment unit 21 controls the attitude of the object to be measured 1 around the pitch axis and tilt axis so that the incident angle of parallel light is within a predetermined range (for example, approximately 0°), thereby acquiring a surface image. The irradiation conditions may be determined according to the crystal orientation and shape.

[0059] Figure 13 is a detailed view showing the cross-sectional shape and imaging direction of the outer edge portion 5. The arrows indicate the direction of incidence of parallel light from the imaging system 10. The cross-sectional shape changes from the upper surface 2 of the object to be measured 1 to a sloped surface X1, then to a rounded section R1, and finally to an end surface X3 that is perpendicular to the upper surface 2.

[0060] Figure 14 is an explanatory diagram of attitude adjustment when acquiring a surface image of the outer edge portion 5. When acquiring a surface image of the edge portion 5 of the object to be measured 1, the incident angle is adjusted by rotating the pitch axis at each part of the edge portion 5 (each part explained in Figure 9(b)), and the scan is performed by tracing the surface. Figure 14(a) shows the attitude control method when acquiring the surface image of X1, Figure 14(c) shows the method for acquiring the surface image of X3, and Figure 14(e) shows the method for acquiring the surface image of X2, and is performed by moving in gradual scan pitch increments. R1 in Figure 14(b) and R2 in Figure 14(d) show the imaging of the R portion, and it is preferable to divide the pitch axis into rotation increments of a predetermined pitch angle, for example, R1 and R2 are 60~70°, so it is preferable to divide it into 3 parts and image.

[0061] Figure 15 shows the imaging trajectory of the (1') single-sided R portion (see Figure 9(b)) of X3 (end face) in the notch portion 4. When acquiring a surface image of the single-sided R portion of the notch portion 4, the attitude adjustment unit 21 fixes the focal length of the imaging system, places the imaging system on the optical axis passing through the center of the (1') single-sided R portion, and rotates the yaw axis of the chuck table 16 to acquire the surface image, as shown in Figure 15(a). By placing the imaging system on the optical axis passing through the center of the (1') single-sided R portion, the arc of the single-sided R portion and the incident direction of the parallel light become approximately perpendicular. That is, by performing attitude adjustment as described above, the entire single-sided R portion can be scanned (scanned in the Z-axis and Y-axis directions) while adjusting the incident angle within a predetermined range to acquire a surface image. Then, once the surface image of the single-sided R portion is acquired in the above manner, it proceeds to the (2') straight portion as shown in Figure 15(b). The same applies to the symmetrical (1) single-sided R portion.

[0062] Figure 16 shows the imaging trajectory of the (2') straight section (see Figure 9(b)) of X3 (end face) in the notch section 4. The surface image of the straight section of the notch section 4 is acquired by scanning in the Y-axis direction as shown in Figure 16, with the focal length and yaw axis fixed and the incident angle adjusted.

[0063] Figure 17 shows the imaging trajectory of the (3) bottom R portion of X3 (end face) in the notch portion 4. As shown in Figure 17(a), the surface image of the bottom R portion of the notch portion is acquired by fixing the focal length of the imaging system, and by controlling the rotation of the yaw axis to position the imaging system on the optical axis passing through the center of the bottom R portion, adjusting the incident angle to be approximately 0°, and scanning in the Z-axis direction and Y-axis direction.

[0064] As described above, the surface image of the object to be measured 1 is optimized by the posture adjustment unit 21 to match the shape of the object to be measured 1, so that even complex three-dimensional shapes like the notch portion 4 can be measured with high accuracy. [Explanation of Symbols]

[0065] 1 Object to be measured, 2 Top surface, 3 Bottom surface, 4 Notch area, 5 Edge area, 10 Imaging system, 10-1 Light source, 10-10 Polarizer, 10-2 Collimating optical system, 10-3 Beam splitter, 10-4 Objective lens, 10-5 Reference mirror, 10-6 Focusing optical system, 10-7 Camera, 10-8 Pinhole, 10-9 Polarizer, 15 Baseboard, 16 Chuck table, 20 Control device, 21 Attitude adjustment unit, 22 Image processing unit, 30 Stage system, 100 Shape measuring device

Claims

1. A shape measuring apparatus for measuring the shape of a wafer based on a surface image of the wafer after grinding, comprising an imaging system that irradiates the wafer with light and acquires the surface image which is a white interference microscopy image, and configured to acquire wafer surface topography data by analyzing the contrast change and / or phase change of interference fringes obtained by the light reflected from the wafer and a reference light.

2. A shape measuring apparatus for measuring the shape of a wafer based on a surface image of the wafer after etching, comprising an imaging system that irradiates the wafer with light and acquires the surface image which is a confocal microscopic image, and configured to acquire a focused image obtained at step intervals in the height direction of the wafer, and to acquire three-dimensional surface shape data of the wafer from the peak position of the light detection intensity.

3. A shape measuring device for measuring the shape of a wafer based on a surface image of the wafer after polishing, comprising an imaging system that irradiates the wafer with light and acquires the surface image by the illuminance difference stereo method, and configured to measure the change in the normal vector of the wafer from an image obtained based on diffuse reflected light obtained by removing specular reflected light from the wafer using a polarizing plate.

Images