Inspection device and calibration method

Abstract

In order to enable highly accurate inspection and measurement of a semiconductor wafer in a freely selected process without variations between devices, the present invention proposes an inspection device in which a calibration sample having a first region where a film having a first thickness is formed and a second region where a film different in quality from the first region and having a second thickness is formed is held on a stage, the stage is controlled so that the surface of the first region and the surface of the second region are at the same height, and the position of an image forming lens and / or a sensor is adjusted so that the value of the difference between a first output and a second output of the sensor obtained by irradiation with light from an illumination optical system falls within a predetermined range.

Description

Inspection device and calibration method

[0001] The present invention relates to an inspection apparatus and a calibration method.

[0002] In the semiconductor device manufacturing process, optical and SEM (Scanning Electron Microscope) defect inspection systems are used to quickly detect various defects (including foreign particles) that could cause device failure. CD-SEM (Critical Dimension-SEM) is also used to measure the fine pattern widths and hole diameters of devices.

[0003] In optical defect inspection systems, if the focus position of the detection optical system is misaligned with the surface of the sample, the optical image will be defocused, causing a deterioration in image quality and impairing detection accuracy. The same situation applies to SEM defect inspection systems and CD-SEMs, where a misalignment in the focus position of the electron optical system can lead to false detection of defects and errors in measurement values. For this reason, focusing is important, as it involves measuring the surface height of the sample and adjusting the misalignment with the focus position based on the measurement results.

[0004] With the advancement of miniaturization technology for semiconductor integrated circuits, inspection and measurement at high magnifications are required, and the required focus position accuracy is becoming increasingly stringent. Furthermore, given the diversity of sample wafer types and processes, high-precision inspection and measurement must be possible without process differences. Furthermore, since measurement results must be reliable, it is also important that there is no variation in inspection and measurement results between devices.

[0005] A known method for measuring the surface height of a sample is to illuminate the sample surface with light at an oblique incidence, image the reflected light, and then use an optical sensor to detect the position of the optical image to determine the surface height. Furthermore, by using a position sensitive detector (PSD) as the optical sensor, highly accurate surface height measurements can be achieved at low cost.

[0006] For example, Patent Document 1 discloses a technique for measuring the surface height of a sample with high precision by using a broadband lamp such as a halogen lamp or mercury lamp as a light source, shaping the illumination light into one or more slits, and narrowing the slit width. Patent Document 2 discloses a technique for correcting focus position deviation due to changes in the measurement environment over time or variations between devices by performing inspections at various focus positions to obtain a distribution curve of the number of defects detected versus the focus position, and then incorporating the deviation of the peak point as a focus position offset value into the device-specific settings. Patent Document 3 also discloses a technique for correcting focus position deviation due to differences in wafer type and process by incorporating a focus position offset adjustment function into the inspection condition (recipe) creation function.

[0007] Japanese Patent Laid-Open No. 11-183154 Japanese Patent Laid-Open No. 2007-298501 Japanese Patent Laid-Open No. 2007-256271

[0008] In the case of a sample height measurement method similar to those described in Patent Documents 1 and 2, as shown in Figure 1, the reflectivity of light depends on the incident angle, so the detected light intensity distribution exhibits intensity modulation according to the incident angle distribution on the irradiated surface. As a result, as described in Patent Document 1, the true center position of the detected light does not coincide with the center of gravity, resulting in a measurement error in the sample height and resulting in a focus position shift. Furthermore, because the incidence angle dependence of reflectivity varies depending on the material and microstructure of the reflective surface, the amount of focus position shift varies depending on the type of wafer and the process. Furthermore, the difference between the true center position and the center of gravity position increases as the image becomes more defocused. This defocus amount varies between systems due to adjustment errors in the optical system, so the focus position shift also varies between systems. Because the defocus amount cannot be confirmed using a PSD, it is difficult to calibrate the adjustment error, and large defocus may occur. Therefore, as shown in Figure 2, unless the adjustment error is calibrated with high precision, a focus position shift that varies depending on the process and between systems will occur.

[0009] In particular, Patent Document 1 discloses a method for reducing the amount of focus position shift by improving the light source or slit shape, but this method cannot reduce adjustment errors in the optical system itself. Therefore, if the adjustment error is large, there is a possibility that process differences and variations in focus position shift between devices will occur.

[0010] Furthermore, Patent Document 2 discloses a method for correcting inter-instrument variation in focus position using a specific wafer, but this method cannot reduce adjustment errors in the optical system itself, and therefore inter-instrument variation in focus position shift may occur when using a different wafer.

[0011] Furthermore, Patent Document 3 discloses a method for correcting focus position deviation due to differences in wafer type and process, but this method cannot reduce adjustment errors in the optical system itself. Therefore, there is a possibility that process differences in focus position deviation will occur when using different equipment using the same recipe.

[0012] In view of the above circumstances, the present invention proposes a technique that can simultaneously calibrate process differences and inter-device variations in focus position deviation.

[0013] In order to solve the above-mentioned problems, the present invention proposes an inspection device for inspecting a sample, comprising: a stage that holds the sample and is capable of moving the sample in horizontal and vertical directions; a sample height measurement unit that measures the height of the sample; and a control unit that controls the operation of the stage and the sample height measurement unit, wherein the sample height measurement unit includes: an illumination optical system that irradiates light onto the sample; a detection optical system that includes a sensor that detects light emitted from the sample when irradiated with light from the illumination optical system and an imaging lens that images the light emitted from the sample on the sensor; and a position adjustment mechanism that moves the imaging lens or the sensor in the optical axis direction, wherein when the stage holds a calibration sample having a first region on which a film with a first thickness is formed and a second region on which a film with a second thickness and a film quality different from that of the first region is formed, the control unit controls the stage so that the surfaces of the first region and the second region are at the same height, and performs processing to adjust the position of at least one of the imaging lens or the sensor so that a difference value between a first output and a second output of the sensor, respectively obtained by irradiating the light from the illumination optical system, falls within a predetermined range.

[0014] Further features related to the present disclosure will become apparent from the description of this specification and the accompanying drawings. Also, aspects of the present disclosure are achieved and realized by the elements and combinations of various elements and the aspects of the following detailed description and the appended claims. The description of this specification is merely exemplary and does not limit the scope or application of the claims of the present disclosure in any way.

[0015] According to the present invention, the misalignment of the optical system of the sample height measurement means is adjusted with high precision, thereby eliminating process differences and inter-device variations in focus position misalignment, and realizing a high-precision inspection and measurement device with reduced inter-device variations for wafers in any process.

[0016] 1 is a diagram for explaining that focus position shift occurs in the sample height measurement means. FIG. 2 is a diagram for explaining the relationship between process differences in focus position shift and inter-apparatus variation. FIG. 3 is a diagram showing an example of a schematic configuration of the optical inspection apparatus 10 according to the present embodiment. FIG. 4 is a diagram showing an example of a detailed configuration of the sample height measurement means 15, and for explaining the principle for measuring the height of the sample 12. FIG. 5 is a diagram showing an example of a planar configuration of the slit opening 111 as seen from the light source 110 side. FIG. 6 is a diagram showing a slit-shaped illumination area 121, which is an illumination area on the surface of the sample 12 by the illumination optical system 100. FIG. 7 is a flowchart for explaining a position shift adjustment process in the optical axis direction of the imaging lens 113 according to Example 1. FIG. 8 is a diagram showing an example of a configuration of a calibration sample 130 for the imaging lens 113. FIG. 9 is a diagram for explaining a method for acquiring height measurement values ​​of a first region. FIG. 10 is a diagram for explaining a method for acquiring height measurement values ​​of a second region. FIG. 11 is a graph plotting the calculated value difference 143 calculated in step S59 against the optical axis direction position of the imaging lens 113 recorded in step S52. 1 is a diagram showing an example of the configuration of a reference sample 135 composed of a substrate 133 and alignment marks 134, and a calibration sample 136. FIG. 2 is a flowchart for explaining the process of adjusting the positional deviation in the optical axis direction of the imaging lens 113 according to Example 2. FIG. 3 is a diagram showing the displacement of the height displacement of the Z stage 16 between alignment marks 134 and the displacement of the Z coordinate difference value excluding the waviness component.

[0017] This embodiment discloses examples of an optical inspection device, an inspection and measurement device using a charged particle beam, and a calibration method for a sample such as a semiconductor wafer. Each embodiment of the present invention will be described below with reference to the accompanying drawings. In the accompanying drawings, functionally identical elements may be indicated by the same numerals. Note that the accompanying drawings show specific embodiments and implementation examples in accordance with the principles of the present invention, but these are intended to aid in understanding the present invention and should not be used to interpret the present invention in a limiting manner.

[0018] Although the present embodiment and examples are described in sufficient detail to enable those skilled in the art to practice the present disclosure, it should be understood that other implementations and forms are possible, and that configurations and structures can be changed and various elements can be substituted without departing from the scope and spirit of the technical concept of the present invention. Therefore, the following description should not be interpreted as being limited thereto. Note that in the following examples, the present invention will be described using an optical inspection device as an example, but the application of the present invention is not limited to optical inspection devices and can also be applied to inspection and measurement devices that use charged particle beams.

[0019] A first embodiment of the present invention will be described with reference to the accompanying Figures 3 to 10. <Configuration Example of Optical Inspection Apparatus> Figure 3 is a diagram showing a schematic configuration example of an optical inspection apparatus 10 according to this embodiment. The optical inspection apparatus 10 horizontally scans the entire surface or part of the sample 12 while performing automatic focusing so that the surface height of the sample 12 is always constant, and processes an image obtained from an optical image of scattered light of laser light irradiated onto the sample 12, thereby outputting information such as the coordinates and size of defects present on the sample 12. The sample 12 is, for example, a semiconductor wafer having a fine pattern formed on a silicon substrate.

[0020] The optical inspection device 10 comprises an inspection illumination optical system 11 that irradiates laser light onto the sample 12, an inspection detection optical system 13 that detects scattered light of the laser light irradiated onto the sample 12, an inspection processing unit 14 that identifies defect information from the detected scattered light, a sample height measurement means 15 (also referred to as the sample height measurement unit) that measures the surface height of the sample 12, a Z stage 16 that holds the sample 12 and moves it vertically, an XYR stage 17 that moves and rotates the sample 12 horizontally, and an overall control unit 18.

[0021] The inspection illumination optical system 11 has a laser light source 20 that emits laser light of a predetermined wavelength as inspection light, and a beam shaping unit 21 that shapes the laser light into a predetermined shape and intensity. The beam shaping unit 21, for example, widens the illumination range in a direction perpendicular to the scanning direction so that the laser light becomes a thin line on the sample 12, and condenses and narrows the light in the scanning direction, thereby increasing the amount of detected light and enabling highly efficient scanning.

[0022] The inspection detection optical system 13 has a detection lens 23 and a detection sensor 24. In Fig. 3, the optical axis of the inspection detection optical system 13 is perpendicular to the surface of the sample 12. The angle between the optical axis of the inspection detection optical system 13 and the surface of the sample 12 may be any angle that does not interfere with the field of view of the inspection illumination optical system 11. Furthermore, detection sensitivity can be improved by arranging multiple inspection detection optical systems 13 and detecting scattered light in different directions.

[0023] The inspection processing unit 14 has an A / D converter 25 that digitizes the output of the detection sensor 24, and an image processing means 26 that extracts defect information on the sample 12 based on the digitized scattered light intensity information.

[0024] The sample height measuring means 15 comprises an illumination optical system 100 that illuminates the sample 12 with light at an oblique incidence, a detection optical system 101 that detects light from the illumination optical system 100 that is specularly reflected by the sample 12 and outputs information about the detected position, and a focusing processing unit 102 that controls the Z stage 16 based on the output from the detection optical system 101 so that the sample height is constant.

[0025] The overall control unit 18 controls the inspection illumination optical system 11, the inspection detection optical system 13, the sample height measuring means 15, the XYR stage 17, and the entire system, and outputs the results processed by the image processing means 26 together with the coordinate position of the sample 12 to a monitor 27 or a storage means 28.

[0026] <Method of Measuring Sample Height> FIG. 4 shows a detailed example of the configuration of the sample height measuring means 15 and is a diagram for explaining the principle of measuring the height of the sample 12. As shown in FIG.

[0027] The illumination optical system 100 includes a light source 110, a slit aperture 111 that shapes the light from the light source 110 into a slit shape, a polarizing filter 115 that transmits S-polarized light from the light that passes through the slit aperture 111, and a projection lens 112 that focuses the light that passes through the polarizing filter 115 and forms an image on the surface of the sample 12. The light source 110 may be a laser or a light-emitting diode, but a broadband lamp such as a halogen lamp or a mercury lamp is more preferable. This is because, when the surface of the sample 12 is a transparent film such as a resist, monochromatic light can cause multiple interference within the transparent film, resulting in a shift in the projected light and uneven reflection intensity, which can easily result in significant errors. The polarizing filter 115 is used for the same reason: by using only S-polarized light, which is more easily reflected by the surface of a transparent film than P-polarized light, the effects of multiple reflections on the transparent film can be reduced. Furthermore, by increasing the incident angle θ of the incident optical axis 117, the difference in reflectivity between materials can be reduced, for example, to 78°.

[0028] The detection optical system 101 includes a bandpass filter 116 that transmits light in a specific wavelength range from light irradiated from the illumination optical system 100 and specularly reflected from the surface of the sample 12; an imaging lens 113 that magnifies and focuses the light transmitted through the bandpass filter 116 on an optical sensor 114; the optical sensor 114 that detects the position of the optical image and outputs the result to the focusing processor 102; and an adjustment mechanism (not shown) for adjusting the optical axis position of the imaging lens 113 or the optical sensor 114. The use of the bandpass filter 116 reduces chromatic aberration caused by the imaging lens 113 and reduces defocusing on the optical sensor 114 due to chromatic aberration. The optical sensor 114 may be a two-segment photodiode, but a PSD is preferable because it has a simple configuration and enables high-precision position detection. A cylindrical lens (not shown) may be placed in front of the optical sensor 114 to one-dimensionally focus light onto the optical sensor 114 in a direction perpendicular to the incident surface. The plane of incidence refers to a plane that includes the incident optical axis 117 and is perpendicular to the surface of the sample 12. This increases the amount of detected light and averages out uneven reflection intensity in the longitudinal direction of the slit-shaped illumination area 121 (details of which will be described later), thereby reducing errors.

[0029] The focusing processor 102 calculates the surface height of the sample 12 based on the detection position information of the optical image output from the detection optical system 101, and drives the Z stage 16 so that the focus of the detection lens 23 is aligned with the surface of the sample 12. When the height of the reflecting surface of the sample 12 changes by ΔZ during scanning of the XYR stage 17, the detection position of the optical image on the optical sensor 114 is displaced by Δp=2mΔZ sin θ, using the angle of incidence θ and the magnification m of the detection optical system 101. Therefore, automatic focusing control can be performed by calculating ΔZ from the measured Δp and moving the Z stage 16 by −ΔZ.

[0030] <Configuration Example of Slit Aperture 111> Figure 5A is a diagram showing an example of the planar configuration of the slit aperture 111 as viewed from the light source 110 side. Here, the axis perpendicular to the incident plane is defined as the Xa axis, and the axis perpendicular to the incident optical axis 117 within the incident plane is defined as the Ya axis. Two rectangular apertures 120, with the Ya axis direction as the short side, are arranged side by side along the Xa axis direction on the long side. By reducing the width of the apertures 120 in the Ya axis direction, it is possible to suppress focus position shifts caused by the material and microstructure on the sample 12. Note that in the case of a PSD, the effect of using multiple slits is small, so the number of apertures 120 arranged along the Ya axis direction may be one.

[0031] 5B is a diagram showing the slit-shaped illumination area 121, which is the area of ​​the surface of the sample 12 irradiated by the illumination optical system 100. The Xb axis and Yb axis correspond to the projections of the Xa axis and Ya axis onto the surface of the sample 12, respectively.

[0032] The slit-shaped illumination area 121 is formed by magnifying the opening 120 by the magnification of the illumination optical system 100 and projecting it onto the sample 12. An inspection illumination area 122 illuminated by laser light from the inspection illumination optical system 11 and an inspection field 123 of the inspection detection optical system 13 are disposed between the two slit-shaped illumination areas 121. Here, the Xc axis is the scanning direction, the Yc axis is the longitudinal direction of the inspection illumination area 122, and the Xc and Yc axes are perpendicular to each other. The intersection of the incident optical axis 117 and the surface of the sample 12 coincides with the center of the inspection field 123, which is defined as the inspection center 124. By providing the slit-shaped illumination areas 121 on both sides of the inspection field 123 with respect to the Xc axis, high-precision height measurement is possible even near the edge of the sample 12.

[0033] Furthermore, by not overlapping the slit-shaped illumination area 121 and the inspection field of view 123, it is possible to suppress light from the illumination optical system 100 from entering the inspection detection optical system 13 with a simple configuration, thereby improving the accuracy of defect inspection. Note that the slit-shaped illumination area 121 is displaced by ΔZ tan θ in the Yb-axis direction with respect to a change ΔZ in the height of the reflecting surface. Therefore, although it is desirable that the angle α between the Yb axis and the Yc axis is 0 degrees, if it is set to a value other than 0 degrees due to restrictions on the device configuration, etc., the gap between the slit-shaped illumination areas 121 must be sufficiently wider than the width of the inspection field of view 123 in the Xb-axis direction.

[0034] Errors in the adjustment of the optical axis position of the projection lens 112 cause defocusing of the optical image on the sample 12. However, for example, by preparing a sample 12 coated with scattering particles and using an image sensor or other means, the optical image on the sample 12 can be observed. Therefore, errors in the adjustment of the optical axis position of the projection lens 112 can be easily calibrated by directly observing the defocusing of the optical image. On the other hand, errors in the adjustment of the optical axis position of the imaging lens 113 or the optical sensor 114 cause defocusing of the optical image on the optical sensor 114. However, the PSD outputs only two types of signals: the detected light intensity and the detection position, making it impossible to confirm the defocusing of the optical image on the PSD. While it is possible to confirm the defocusing of the optical image by temporarily replacing the PSD with an image sensor or other device, assembly errors can cause the sensor surface to shift, resulting in the optical images on the image sensor and the PSD not strictly matching. Therefore, when the optical sensor 114 is a PSD, it has been difficult to accurately calibrate the defocusing of the optical image on the optical sensor 114.

[0035] <Adjusting Positional Misalignment of Imaging Lens 113 in the Optical Axis Direction> A method for adjusting the position of the imaging lens 113 in the optical axis direction and calibrating the defocus of the optical image on the optical sensor 114 with high precision in the apparatus described above will be described with reference to FIG. 6 . FIG. 6 is a flowchart for explaining the process for adjusting the positional misalignment of the imaging lens 113 in the optical axis direction according to the first embodiment. It is assumed that the position of the projection lens 112 in the optical axis direction is adjusted in advance using the method described above. Furthermore, in this embodiment, a calibration method using adjustment of the position of the imaging lens 113 in the optical axis direction is described, but the position of the optical sensor 114 in the optical axis direction may be adjusted instead. That is, the same effect can be obtained even if the calibration method shown in FIG. 6 is performed by replacing the imaging lens 113 with the optical sensor 114.

[0036] FIG. 7 is a diagram showing an example of the configuration of a calibration sample 130 for the imaging lens 113. As shown in FIG. 7 , the calibration sample 130 may be prepared as follows: a first region 131 on a silicon wafer substrate 133, in which a silicon oxide film of known thickness is formed; and a second region 132 on which the surface of the substrate 133 is exposed (in this case, the film thickness is zero, but a film of a different quality from that of the film in the first region 131 may be formed in the second region 132). The film in the first region 131 and the surface of the substrate 133 have different film qualities (i.e., material and microstructure). In the calibration sample 130, the film thickness of the first region 131 may be selected so as to maximize the reflectance modulation with respect to the incident angle distribution, and may be, for example, 100 nm. The area of ​​each region may be sufficiently larger than the slit-shaped illumination region 121, and the shape may also be arbitrary. Furthermore, by providing alignment marks 134 in at least two locations near the outer periphery of the substrate 133, which allow the optical inspection device 10 to recognize the position and orientation of the calibration sample 130, the XY coordinates of the measurement points on the calibration sample 130 can be determined with high precision, allowing calibration to be performed with good reproducibility. Note that, although the film thickness of the first region 131 and the film thickness of the second region 132 are set to be different here, they may also be the same.

[0037] (i) Step S50 In response to an instruction (command input) from the user (operator) to start processing, the overall control unit 18 starts processing to adjust the positional deviation of the imaging lens 113 in the optical axis direction.

[0038] (ii) Step S51 When the user places (holds) the calibration sample 130 on the Z stage 16 and inputs, for example, an instruction to complete sample placement, the overall control unit 18 corrects the coordinate shift and rotational shift of the calibration sample 130 using the XYR stage 17 based on the alignment mark 134.

[0039] (iii) Step S52 The overall control unit 18 records the position of the imaging lens 113 in the optical axis direction adjusted by the adjustment mechanism (not shown) for the position of the imaging lens 113 in the optical axis direction in, for example, the storage 28.

[0040] (iv) Step S53 The overall control unit 18 moves the XYR stage 17 to a position where the slit-shaped illumination area 121 enters the first area 131, as shown in FIG.

[0041] (v) Step S54 Subsequently, the overall control unit 18 moves the Z stage 16 to a position where the surface height of the first region 131 becomes the designed height value 140. The designed height value 140 is, for example, the designed focal position of the detection lens 23.

[0042] (vi) Step S55: When the surface height of the first region 131 reaches the designed height value 140, the overall control unit 18 uses the focusing processing unit 102 to obtain the calculated surface height value 141 of the first region 131 based on the above-mentioned calculation formula Δp=2mΔZ sinθ.

[0043] (vii) Step S56 The overall control unit 18 moves the XYR stage 17 to a position where the slit-shaped illumination area 121 enters the second area 132, as shown in FIG.

[0044] (viii) Step S57 The overall control unit 18 moves the Z stage 16 by the film thickness difference 144 between the first region 131 and the second region 132, which is 100 nm in this embodiment, so that the surface height of the second region 132 becomes the height design value 140.

[0045] (ix) Step S58 When the surface height of the second region 132 reaches the designed height value 140, the overall control unit 18 obtains a calculated surface height value 142 of the second region 132 using the focusing processing unit 102.

[0046] (x) Step S59 The overall control unit 18 calculates a calculation value difference 143 between the surface height calculation value 141 and the surface height calculation value 142, and determines whether the calculation value difference 143 falls within an allowable range 145. The allowable range 145 is, for example, the depth of field of the detection lens 23. If the calculation value difference 143 is within the allowable range 145 (Yes in step S59), it is determined that the positional deviation of the imaging lens 113 is sufficiently small, and the process proceeds to step S60. On the other hand, if the calculation value difference 143 is outside the allowable range 145 (No in step S59), the process proceeds to step S61.

[0047] (xi) Step S60 The overall control unit 18 ends the process of adjusting the positional deviation of the imaging lens 113 in the optical axis direction.

[0048] (xii) Step S61 The overall control unit 18 changes the position of the imaging lens 113 in the optical axis direction, and then repeats the process of adjusting the positional deviation of the imaging lens 113 in the optical axis direction from step S52.

[0049] <Relationship Between Calculated Value Difference 143 and Tolerance Range 145> Figure 10 shows a graph in which the calculated value difference 143 calculated in step S59 is plotted against the optical axis direction position of the imaging lens 113 recorded in step S52. While this graph does not have a strictly linear relationship, it can be seen that it roughly follows a linear function within a small range expected as an adjustment error. Therefore, by plotting the calculated value difference 143 while changing the position of the imaging lens 113 in accordance with the process for adjusting the positional misalignment of the imaging lens 113 in the optical axis direction shown in Figure 6, it is possible to adjust the imaging lens 113 to a position where the calculated value difference 143 falls within the tolerance range 145 after a maximum of three tries.

[0050] <Technical Effects and Modifications of First Embodiment> According to the first embodiment, the defocus of the optical image in the optical sensor 114 can be calibrated with high precision, so that an inspection apparatus can be provided that can inspect wafers in any process with high precision and without variations between apparatuses.

[0051] 6 so that the calculated value difference 143 becomes zero, step S57 may be omitted if the film thickness of the first region 131 is sufficiently smaller than the focal depth of the imaging lens 113. That is, in step S58, the calculated surface height value 142 of the second region 132 may be acquired while the surface height of the first region 131 remains in a state where it is set to the designed height value 140. In this case, in step S59, the value obtained by subtracting the film thickness difference 144 from the calculated value difference 143 may be compared with the allowable range 145.

[0052] In the first embodiment, it has been described that the adjustment error (positional deviation in the optical axis direction) of the imaging lens 113 can be calibrated using a simple method. However, the method shown in Fig. 6 cannot perform high-precision calibration when the difference in actual surface height between the first region 131 and the second region 132 does not match the film thickness difference 144. A situation in which the difference in actual surface height between the first region 131 and the second region 132 does not match the film thickness difference 144 can occur when the surface height of the substrate 133 varies depending on the location due to, for example, a slight tilt or waviness of the sample support surface of the Z stage 16.

[0053] Therefore, in Example 2, a method that enables highly accurate calibration of the adjustment error of the imaging lens 113 even when there is waviness or the like on the surface of the sample 12 due to an apparatus-related cause will be described with reference to FIGS. 11 to 13 . Note that the example of the apparatus configuration is the same as in Example 1 ( FIGS. 3 to 5 ). In Example 2, as in Example 1, the position of the projection lens 112 in the optical axis direction is adjusted in advance. In Example 2, as in Example 1, the position of the optical sensor 114 in the optical axis direction may be adjusted instead of the position of the imaging lens 113.

[0054] 11 is a diagram showing an example of the configuration of a reference sample 135 including a substrate 133 and an alignment mark 134, and a calibration sample 136. In Example 2, two types of samples, the reference sample 135 and the calibration sample 136, as shown in FIG.

[0055] The calibration sample 136 has a configuration similar to the calibration sample 130 used in Example 1, but differs from the calibration sample 130 in that multiple first regions 131 and second regions 132 are arranged alternately and in contact with each other in the Xc-axis direction. In Example 2, the calibration sample 136 may have four to five first regions 131 and second regions 132 arranged in each of the four or five positions. Furthermore, two (at least two) alignment marks 134 have the same coordinate in the Yc-axis direction and are arranged within the second regions 132 at both ends of the outermost periphery in the Xc-axis direction. For convenience, one alignment mark 134 is referred to as point A, and the other alignment mark 134 is referred to as point B. Furthermore, the reference sample 135 is configured to have alignment marks 134 in the same locations as the calibration sample 136.

[0056] <Process for Adjusting Position Misalignment of Imaging Lens 113 in the Optical Axis Direction> Fig. 12 is a flowchart for explaining the process for adjusting position misalignment of imaging lens 113 in the optical axis direction according to Example 2. Fig. 13 is a diagram showing the displacement of the Z coordinate difference value between alignment marks 134, excluding the height displacement of the Z stage 16 and the waviness component.

[0057] (i) Step S70 In response to an instruction (command input) from the user (operator) to start processing, the overall control unit 18 starts processing to adjust the positional deviation of the imaging lens 113 in the optical axis direction.

[0058] (ii) Step S71 The overall control unit 18 records the position of the imaging lens 113 in the optical axis direction adjusted by the adjustment mechanism (not shown) for the position of the imaging lens 113 in the optical axis direction in, for example, the storage 28.

[0059] (iii) Step S72 When the user places (holds) the reference sample 135 on the Z stage 16 and inputs, for example, an instruction to complete sample placement, the overall control unit 18 corrects the coordinate shift and rotational shift of the reference sample 135 using the XYR stage 17 with reference to the alignment mark 134. Note that the order of steps S71 and S72 may be reversed.

[0060] (iv) Step S73: The overall control unit 18 moves the XYR stage 17 in the Xc-axis direction so that the inspection center 124 scans from point A to point B on the surface of the reference sample 135 while performing automatic focusing using the sample height measurement means 15 so that the surface height of the reference sample 135 becomes the designed height value 140, and acquires Z trace data 151 (see FIG. 13 ) during this movement. Here, the Z trace data 151 is a data group of the coordinates of the Z stage 16 relative to the Xc-axis coordinate. The Z trace data 151 is obtained by adding the focus position deviation to the surface height shape data (including the sample holding surface error component) of the reference sample 135, which has been inverted upside down for automatic focusing. The Z trace data 151 is, for example, data as shown by the dashed line in FIG. 13 .

[0061] (v) Step S74 When the user places (holds) the calibration sample 136 on the Z stage 16 instead of the reference sample 135 and inputs, for example, an instruction to complete sample exchange, the overall control unit 18 corrects the coordinate shift and rotational shift of the calibration sample 136 using the XYR stage 17 based on the alignment mark 134.

[0062] (vi) Step S75: The overall control unit 18 moves the XYR stage 17 in the Xc-axis direction so that the inspection center 124 scans from point A to point B on the surface of the calibration sample 136 while automatically focusing the sample height measurement means 15 so that the surface height of the calibration sample 136 becomes the designed height value 140, and acquires Z trace data 152 during that time. The Z trace data 152 is, for example, data as shown by the solid line in FIG. 13 .

[0063] 13, the overall control unit 18 subtracts the Z trace data 152 from the Z trace data 151 to generate differential trace data 153. The differential trace data 153 has the components of the sample support surface error removed, and becomes trace data corresponding to the relative surface height of the calibration sample 136.

[0064] (viii) Step S77: The overall control unit 18 generates a data point distribution for the Z coordinate difference (vertical axis) of the differential trace data 153, i.e., a differential histogram 154. As shown in FIG. 13 , the differential histogram 154 has two peaks in total, corresponding to the relative surface heights of the first region 131 and the second region 132.

[0065] (ix) Step S78 The overall control unit 18 calculates the difference between the two peak positions of the difference histogram 154 as the peak-to-peak distance 155. The peak-to-peak distance 155 is an index indicating the value obtained by adding the film thickness difference 144 to the focus position shift.

[0066] (x) Step S79 The overall control unit 18 determines whether the value obtained by subtracting the film thickness difference 144 from the peak-to-peak distance 155 (hereinafter, the subtraction value) is within the allowable range 145. If the subtraction value is within the allowable range 145 (Yes in step S79), the process proceeds to step S80. On the other hand, if the subtraction value is outside the allowable range 145 (No in step S79), the process proceeds to step S81.

[0067] (xi) Step S80 The overall control unit 18 determines that the positional deviation of the imaging lens 113 is sufficiently small, and ends the calibration process (processing for adjusting the positional deviation of the imaging lens 113 in the optical axis direction).

[0068] (xii) Step S81 The overall control unit 18 changes the position of the imaging lens 113 in the optical axis direction, and then repeats the calibration process from step S71.

[0069] <Technical Effects of Example 2> According to Example 2, even if there is a slight tilt or waviness on the sample holding surface of the Z stage 16, it is possible to provide an inspection apparatus that can calibrate the defocus of the optical image on the optical sensor 114 with high precision and can inspect wafers in any process with high precision and without variations between apparatuses. Therefore, the technology of Example 2 is very useful for finding problems in semiconductor processes.

[0070] <Modifications of Calibration Sample 130> In Examples 1 and 2, a silicon oxide film with a thickness of 100 nm was used as the first region 131 of calibration sample 130, and the silicon surface of substrate 133 was used as the second region 132. However, the second region 132 may be a region on which a film of a known thickness is formed, as long as it is made of a different material from that of first region 131. Furthermore, by selecting a combination of material and film thickness with more different reflectance characteristics as the materials for first region 131 and second region 132, it is possible to further improve the accuracy of calibration.

[0071] <Modifications of the Inspection Apparatus> In the first and second embodiments, a defect inspection apparatus using a dark-field image formed by scattered light from the surface of the sample (wafer) 12 has been described, but the present invention is not limited to dark-field type inspection apparatuses and can also be applied to bright-field type defect inspection apparatuses using bright-field images formed by reflected light from the surface of the wafer. An example of the configuration of a bright-field type inspection apparatus is described in, for example, Japanese Patent Laid-Open No. 2007-212201, and is well known, so details thereof will be omitted.

[0072] Furthermore, the present invention is not limited to semiconductor wafer defect inspection devices, but can be widely applied to surface inspection devices, appearance inspection devices, mask inspection devices, liquid crystal substrate inspection devices, disk inspection devices, etc. Furthermore, the present invention is not limited to optical inspection devices, but can also be applied to inspection and measurement devices that use charged particle beams, such as SEM defect inspection devices and CD-SEMs, as described in Reference 1.

[0073] 10 Optical inspection device 11 Inspection illumination optical system 12 Sample 13 Inspection detection optical system 14 Inspection processing unit 15 Sample height measurement means 16 Z stage 17 XYR stage 18 Overall control unit 20 Laser light source 21 Beam shaping unit 23 Detection lens 24 Detection sensor 25 A / D converter 26 Image processing means 27 Monitor 28 Storage 100 Illumination optical system 101 Detection optical system 102 Focusing processing unit 110 Light source 111 Slit opening 112 Projection lens 113 Imaging lens 114 Optical sensor 115 Polarizing filter 116 Bandpass filter 117 Incident optical axis 120 Opening (slit) 121 Slit-shaped illumination area 122 Inspection illumination area 123 Inspection field 124 Inspection center 130 Calibration sample 131 First region 132 Second region 133 Substrate 134 Alignment mark 135 Reference sample 136 Calibration sample 140 Design height value 141, 142 Calculated surface height value 143 Calculated value difference 144 Film thickness difference 145 Tolerance range 151, 152 Z trace data 153 Differential trace data 154 Differential histogram 155 Peak-to-peak distance

Claims

1. An inspection device for inspecting a sample, comprising: a stage that holds the sample and can move the sample horizontally and vertically; a sample height measurement unit that measures the height of the sample; and a control unit that controls the operation of the stage and the sample height measurement unit, wherein the sample height measurement unit includes: an illumination optical system that irradiates light onto the sample; a detection optical system that includes a sensor that detects light emitted from the sample when irradiated with light from the illumination optical system and an imaging lens that images the light emitted from the sample on the sensor; and a position adjustment mechanism that moves the imaging lens or the sensor in the optical axis direction, wherein when the stage holds a calibration sample having a first region on which a film of a first thickness is formed and a second region on which a film of a second thickness but different film quality from the first region is formed, the control unit controls the stage so that the surfaces of the first region and the second region are at the same height, and performs processing to adjust the position of at least one of the imaging lens or the sensor so that a difference value between a first output and a second output of the sensor, respectively obtained by irradiating the light from the illumination optical system, falls within a predetermined range.

2. An inspection device according to claim 1, wherein the second film thickness is zero.

3. An inspection device according to claim 1, wherein the control unit corrects at least one of coordinate misalignment or rotational misalignment of the calibration sample by operating the stage based on alignment marks included in the calibration sample, and then performs a process of adjusting the position of at least one of the imaging lens or the sensor.

4. An inspection device according to claim 1, wherein, when the stage holds a reference sample having at least two reference alignment marks at both ends of the outermost periphery of the substrate, the control unit controls the operation of the stage based on the at least two reference alignment marks so as to scan a range corresponding to the first and second regions of the reference sample with the light from the illumination optical system, and during this time acquires reference height data which is a change in height measured by the sample height measurement unit and includes an error component of the sample holding surface of the stage; and when the stage holds the calibration sample, the control unit executes a process of adjusting the position of at least one of the imaging lens or the sensor based on the reference height data, the first output, and the second output.

5. An inspection device according to claim 4, wherein the control unit calculates a first corrected output and a second corrected output corresponding to the first output and the second output from which the sample holding surface error component has been removed by subtracting the reference height data from each of the first output and the second output, and performs processing to adjust the position of at least one of the imaging lens or the sensor so that the difference value between the first corrected output and the second corrected output falls within the specified range.

6. An inspection apparatus according to claim 4, wherein the calibration sample is configured so that a plurality of the first regions and a plurality of the second regions are arranged alternately and includes at least two calibration alignment marks at positions corresponding to the at least two reference alignment marks provided on the reference sample, and wherein the control unit controls the operation of the stage so as to scan the plurality of first regions and the plurality of second regions of the calibration sample with the light from the illumination optical system based on the at least two calibration alignment marks of the calibration sample, acquires sample height trace data corresponding to the first output and the second output, calculates corrected trace data corresponding to the sample height trace data from which the sample holding surface error component has been removed by subtracting the reference height data from the sample height trace data, generates a histogram of the corrected trace data in the height direction, calculates the distance between two peaks included in the histogram that correspond to the first output and the second output, and performs processing to adjust the position of at least one of the imaging lens and the sensor so that the distance between the peaks falls within the predetermined range.

7. A calibration method for adjusting the position of at least one of an imaging lens or a sensor included in an inspection device for inspecting a sample, comprising: an inspection device comprising: a stage for holding the sample and capable of moving the sample in horizontal and vertical directions; a sample height measurement unit for measuring the height of the sample; and a control unit for controlling the operation of the stage and the sample height measurement unit, wherein the sample height measurement unit comprises: an illumination optical system for irradiating light onto the sample; a detection optical system including a sensor for detecting light emitted from the sample by the light irradiation of the illumination optical system and an imaging lens for imaging the light emitted from the sample on the sensor; and a position adjustment mechanism for moving the imaging lens or the sensor in the optical axis direction; and holding a calibration sample on the stage, the calibration sample having a first region on which a film of a first thickness is formed and a second region on which a film of a second thickness and a film quality different from that of the first region is formed. a control unit that controls the stage in response to an input operation start instruction so that the surfaces of the first area and the second area are at the same height, and adjusts the position of at least one of the imaging lens or the sensor so that a difference value between a first output and a second output of the sensor, respectively obtained by irradiating the light from the illumination optical system, falls within a predetermined range.

8. A calibration method according to claim 7, wherein the second film thickness is zero.

9. A calibration method as set forth in claim 7, further comprising the control unit correcting at least one of coordinate shift or rotational shift of the calibration sample by operating the stage based on an alignment mark included in the calibration sample, and the control unit adjusting the position of at least one of the imaging lens or the sensor after correcting at least one of the coordinate shift or rotational shift of the calibration sample.

10. A calibration method as set forth in claim 7, further comprising: causing the stage to hold a reference sample having at least two reference alignment marks on both ends of the outermost periphery of the substrate; and in response to the operation start instruction, the control unit controls the operation of the stage based on the at least two reference alignment marks on the reference sample so that a range corresponding to the first area and the second area of ​​the reference sample is scanned with the light from the illumination optical system, and during this time, acquiring reference height data which is a change in height measured by the sample height measurement unit and indicates an error component of the sample holding surface of the stage; and adjusting the position of at least one of the imaging lens or the sensor is executed when the calibration sample is held on the stage after acquiring the reference height data, and includes adjusting the position of at least one of the imaging lens or the sensor based on the reference height data, the first output, and the second output.

11. A calibration method according to claim 10, wherein adjusting the position of at least one of the imaging lens or the sensor includes: calculating a first corrected output and a second corrected output corresponding to the first output and the second output from which the sample holding surface error component has been removed by subtracting the reference height data from each of the first output and the second output; and adjusting the position of at least one of the imaging lens or the sensor so that the difference between the first corrected output and the second corrected output falls within the predetermined range.

12. As claimed in claim 10, the calibration sample is configured so that a plurality of the first regions and a plurality of the second regions are alternately arranged, and includes at least two calibration alignment marks at positions corresponding to the at least two reference alignment marks provided on the reference sample; adjusting the position of at least one of the imaging lens or the sensor includes: controlling the operation of the stage so that the plurality of first regions and the plurality of second regions of the calibration sample are scanned with the light from the illumination optical system based on the at least two calibration alignment marks of the calibration sample, and acquiring sample height trace data corresponding to the first output and the second output; calculating corrected trace data corresponding to the sample height trace data from which the sample holding surface error component has been removed by subtracting the reference height data from the sample height trace data; generating a histogram of the corrected trace data in the height direction; calculating a distance between two peaks included in the histogram that correspond to the first output and the second output, respectively; and adjusting the position of at least one of the imaging lens or the sensor so that the distance between the peaks falls within the predetermined range.

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