Inspection equipment and inspection method

Abstract

The present invention addresses the problem of providing an inspection device that is capable of inspecting samples conveyed at high speed with high resolution, high sensitivity, high S / N, and high precision, and the main purpose of the present invention is to provide an inspection device that is equipped with at least: a conveyance mechanism that conveys samples to be inspected; a radiation source that emits radiation in a radial form into a region through which the conveyed samples pass; a detector that is disposed so as to be able to sense radiation that has passed through the conveyed samples and that converts the detected radiation into an electrical signal; a movement mechanism that moves the detector in the direction of conveyance of the samples by the conveyance mechanism; and an assessment means that determines the presence / absence of defects in the samples on the basis of sample image- information from the detector and obtained during a period in which the samples are passing through the region, and on the basis of movement information regarding the samples from the conveyance mechanism. The invention also proposes using this device to inspect for foreign matter in the samples.

Description

Technical Field

[0001] The present invention relates to an inspection apparatus and an inspection method for inspecting minute defects and the like in an inspection object (hereinafter sometimes referred to as a "sample"). Background Art

[0002] Generally, inspection of foreign matters such as minute metals, defects and the like in a sample is performed by inspection methods suitable for each of them. Among these, in nondestructive inspection, for example, a sample is irradiated with electromagnetic waves such as X-rays, and the transmitted electromagnetic waves are detected. At this time, a difference in electromagnetic transmittance occurs depending on the presence or absence, material and the like of foreign matters and defects in the sample. By detecting this difference and generating a two-dimensional image, the state inside the sample can be inspected.

[0003] In addition, in-line inspection, in which products are manufactured in an assembly line and inspection is also performed simultaneously, is known as a useful means for reducing tact time. For example, when an X-ray inspection apparatus is used to detect foreign matters and the like in a sample and inspection is performed in-line, while the sample is moved in a predetermined direction by a conveying means, an apparatus is known in which an X-ray source and an X-ray detector having pixels arranged linearly are arranged opposite to each other on a straight line substantially orthogonal to a surface on which the sample is placed with the surface interposed therebetween. Accordingly, image data is acquired at a cycle corresponding to the conveyance speed of the sample, and linear X-ray transmission images generated based on the image data are sequentially arranged and combined, whereby a two-dimensional image of the sample can be generated (see Patent Document 1). Prior Art Documents Patent Documents

[0004] Patent Document 1 Japanese Unexamined Patent Publication No. 2015-64336 Patent Document 2 Japanese Unexamined Patent Publication No. 2020-3322 Patent Document 3 Japanese Unexamined Patent Publication No. 2020-143922 Patent Document 4 Japanese Patent Publication No. 2000-221144 [Overview of the project] [Problems that the invention aims to solve]

[0005] In the in-line inspection process described above, there is a need for an inspection device and method that can accurately and quickly inspect minute defects with high resolution. As for in-line inspection using electromagnetic waves such as X-rays, methods have been proposed, as described in Patent Documents 1, 2, and 3, in which a radiation source and a detector are fixed, and the sample is transported between them for inspection. However, if multiple defects overlap along the line connecting the X-ray and the detector, they may be detected as a single defect, resulting in inaccurate defect information such as the number, size, and location of the defects, which can lead to errors in judging whether the product is good or bad.

[0006] Furthermore, while increasing the sample transport speed is desirable for improving productivity, obtaining good images requires a high-speed scan-rate detector capable of high-speed signal processing. Patent Document 2 describes a method for handling high-speed inspection by dividing the data reading process from the detector's detection elements. However, acquiring images at high speed means that information can only be acquired in a short time, resulting in a small amount of electromagnetic wave per output, a dark image, and a low signal-to-noise ratio. Patent Document 3 proposes setting a judgment region in advance and transferring and processing data only for pixels corresponding to that region. However, even with these techniques, there are limits to achieving both high sample transport speed and high sensitivity. The faster the sample transport speed, and the more accurate the inspection image, the stricter the requirements for the detector become. Moreover, in the case of X-ray inspection, the afterglow characteristics of the scintillator, which is a phosphor that converts X-rays into visible light, also become stricter, making it even more difficult to achieve both high speed and high sensitivity, high signal-to-noise ratio, and high resolution.

[0007] Patent Document 4 describes how imaging is performed while moving the detector in the direction of sample movement, thereby reducing the relative speed difference between the detector and the sample and enabling the detector to keep up with high-speed transport. In fact, imaging while transporting the detector reduces image afterimage and improves temporal resolution. However, in the case of low-contrast defects that have high transmittance to electromagnetic waves and are difficult to distinguish from the surrounding normal area, detection becomes difficult. Furthermore, if the sample transport speed increases even more, the entire image becomes darker, and the noise, which is the graininess of the image, worsens relative to the overall brightness, i.e., the signal-to-noise ratio becomes low, making it even more difficult to detect low-contrast defects. In order to brighten the image, one method is to increase the exposure time, but this results in a decrease in temporal resolution, creating a trade-off between temporal resolution and signal-to-noise ratio.

[0008] In view of the above-mentioned problems, the present invention aims to provide an inspection device that can inspect samples transported at high speed with high resolution, high sensitivity, and high S / N ratio and high accuracy. [Means for solving the problem]

[0009] The inspection apparatus of the present invention, which solves the above problems, comprises at least a transport mechanism for transporting a sample to be inspected, a radiation source for irradiating radiation radially into a region through which the transported sample passes, a detector positioned to detect radiation transmitted through the transported sample and converting the detected radiation into an electrical signal, a moving mechanism for moving the detector along the direction in which the sample is transported by the transport mechanism, and determination means for determining the presence or absence of defects in the sample from image information of the sample from the detector and information on the movement of the sample from the transport mechanism obtained during the time the sample passes through the region. Preferably, the transport mechanism and the moving mechanism are configured such that when the transport mechanism moves the sample and the moving speed component of the detector by the moving mechanism in the same direction as the sample movement is Vw, the ratio Vd / Vw to Vw is less than or equal to twice the ratio of the distance between the radiation source and the detector (FDD / FOD) to the distance between the radiation source and the sample (FOD).

[0010] Furthermore, the inspection apparatus is more preferably an inspection apparatus comprising a thickness measuring instrument for measuring the thickness of a sample, and a calculation means for calculating the location of defects in the sample based on the thickness information of the sample measured by the thickness measuring instrument and the image information of the sample from the detector. [Effects of the Invention]

[0011] According to the present invention, it is possible to transport samples at high speeds, overcoming the limitations on transport speed caused by the detector's scan rate, thereby obtaining highly sensitive, high-S / N, and high-resolution images, and enabling highly accurate inspection of minute defects. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram illustrating the general configuration for explaining one embodiment of the present invention. [Figure 2] This is a schematic diagram illustrating the general configuration for explaining one embodiment of the present invention. [Figure 3] This is a schematic diagram illustrating the internal configuration to explain one embodiment of the present invention. [Figure 4] This is a schematic diagram illustrating the internal configuration to explain one embodiment of the present invention. [Figure 5] This is a schematic diagram showing the arrangement of the radiation source, sample, and detector. [Figure 6] This is a schematic diagram illustrating an example in which an endlessly ring-shaped transport belt is used as the movement mechanism for the detection unit. [Figure 7] This diagram illustrates an example of the spatial arrangement of defect groups. [Figure 8] This is an explanatory diagram showing the image taken at time ta. [Figure 9] This is an explanatory diagram showing the image taken at time tb. [Figure 10] This is an explanatory diagram showing the image acquired at time tc. [Figure 11] This is a schematic diagram showing the projection of the drawback 15-(1) at each time point. [Figure 12] This diagram illustrates the steps involved in determining the depth at which defects exist. [Figure 13] These are images viewed from the upper surface of an inspection object used for measurement in the Examples section, wherein (a) is an overall image and (b) is an enlarged image around the foreign substance equivalent. [Figure 14] This is an image near a foreign substance equivalent in an inspection object captured by an X-ray TDI camera, and the black dot indicated by the arrow is the image of the foreign substance equivalent. Mode for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described with reference to the drawings, taking as an example inspection using an X-ray generator as a radiation source. However, the specific examples described below illustrate and explain one embodiment of the present invention, and the present invention should not be construed as being limited to such specific examples. For example, it can be readily understood that the present invention is applicable to any other radiation source as long as it can transmit through a sample. Of course, modifications may be made to the specific examples described below without departing from the spirit of the present invention.

[0014] As a most typical example, an example will be described in which, while a sample is being conveyed, a radiation source and a detector are disposed with the conveyance surface of the sample interposed therebetween, and the conveyance surface of the sample is parallel to the movement line of the detector. Herein, the shortest distance between the X-ray focal point, which is the divergence point of the X-ray beam, and the detector is referred to as FDD (Focus to Detector Distance), and the shortest distance between the X-ray focal point and the sample is referred to as FOD (Focus to Object Distance) (see FIG. 5).

[0015] <Inspection Apparatus> Figures 1 and 2 are schematic diagrams illustrating a general configuration for explaining one aspect of the inspection apparatus of the present invention. Figure 1 shows an in-line inspection apparatus where the sample is transported as a single sheet, while Figure 2 shows an in-line inspection apparatus for continuous film or sheet transport using a roll-to-roll method. The inspection apparatus comprises a housing 1. The housing 1 is equipped with an entrance 3 into which the sample is brought in and an exit 4 out from which the sample is discharged. When ionizing radiation such as X-rays is used as the radiation source, for the safety of the operator, the housing 1, entrance 3, and exit 4 are equipped with shielding walls made of lead, stainless steel, or other materials capable of shielding against ionizing radiation on their inner walls, and the opening of the exit 3 is usually equipped with a rubber shielding cover to prevent leakage of ionizing radiation to the outside. In the case of Figure 1, the sample (sample 2(a) or sample 2(b)) is placed on the sample transport belt 6, and the sample transport belt 6 is moved by the sample transport roll 5 to introduce the sample into the housing. In the case of Figure 2, the sample 2 comes into contact with the sample transport roll 5 and is transported directly into the housing 1.

[0016] Figure 3 schematically shows the interior of Figure 1, and Figure 4 schematically shows the interior of Figure 2. In the case of Figure 3, the housing 1 contains the transported samples (sample 2(a) and sample 2(b)), a thickness measuring sensor 7 for measuring the thickness of the samples, a radiation source 8 for irradiating radiation, and a detector 10 that detects radiation 9 and converts it into an electrical signal. In this example, the thickness measuring sensor 7 is located on the upstream side of the housing 1, immediately after passing through the entrance 3, to measure the thickness of the samples. The thickness H of each transported sample is calculated by measuring the height profile of the sample from the surface of the sample transport belt 6 using the thickness measuring sensor 7. In the case of Figure 4, since the sample is in the form of a film, the thickness measuring sensors 7 are placed above and below the sample, and the distance between each measuring sensor and the sample is measured. If the distance between the upper measuring sensor and sample 2 is Ht, the distance between the lower measuring sensor and sample 2 is Hb, and the distance between the upper and lower measuring sensors is Hd, then the thickness H of sample 2 can be calculated as Hd-Ht-Hb. When radiation is emitted from the point source 8, the radiation spreads radially, and the irradiated space is usually cone-shaped. Because the irradiation is radial, defects located closer to the source 8 in the sample are captured as large images by the detector 10, while defects located further away are captured as small images by the detector 10. When an X-ray source is used as the source 8, auxiliary equipment such as a high-voltage generator to supply high-voltage power to the X-ray tube and an X-ray controller to control the tube voltage and tube current are required, but these are not shown in the figure. The signal (image information) output from the detector 8 is sent to an image processing device that processes the signal, and is processed by a data processing unit (not shown) to determine whether it is good or bad. The signal processing unit and data processing unit can also be housed inside the housing 1.

[0017] <Thickness measurement sensor> The thickness measurement sensor 7 is used to accurately determine the surface position of the sample. Multiple sensors may be arranged in the direction in which the number of measurement points is to be increased, or a single sensor may be capable of measuring at multiple points. The thickness measurement sensor is installed, for example, on the upstream side of the sample transport belt, and measurements are taken sequentially while the sample is being transported. The measuring instrument can be a laser triangulation type displacement meter, a laser interferometer, an ultrasonic distance meter, an eddy current type displacement sensor, a stylus type displacement meter, etc., but a laser triangulation type displacement meter is preferred from the viewpoint of being able to measure without contact, being less affected by the material of the object being inspected, and the ease of achieving response speed and multi-point measurement. Specifically, a method is preferred in which linear light generated by a laser light source called the light section method is irradiated onto the sample, and the trajectory of the reflected and scattered light according to the surface shape is acquired as a height profile. The measuring instrument reads the position of the light trajectory with a light receiving means such as an image sensor and measures the thickness of the sample by quantifying it as the surface shape of the sample surface.

[0018] <Radiation source> In the inspection apparatus of the present invention, the radiation source is not particularly limited as long as it can emit radiation that can penetrate the sample. However, a radiation source that generates electromagnetic waves is preferable because it is easy to handle and high measurement accuracy can be expected, and in particular, an X-ray source is preferred. There are no particular restrictions on the X-ray source that can be used, and known X-ray sources can be used. For example, as the X-ray source, it is preferable to use a microfocus X-ray tube with an X-ray focal point size of 50 μm or less, which is the divergence point of the X-ray beam. There are no particular restrictions on the tube voltage of the X-ray tube. In addition, depending on the type of sample and the inspection method, the radiation source may be a source that emits other radiation such as gamma rays or neutrons, or electromagnetic waves, instead of X-rays, and emits radiation radially from a point source which is the divergence point.

[0019] <detector> A detector has the function of detecting radiation emitted from a radiation source and converting it into an electrical signal. There are no particular restrictions on the element as long as it detects emitted radiation and generates an output according to the detected intensity. Taking the case where the radiation irradiating the sample is X-rays as an example, an indirect conversion type detector element that first converts the X-rays into visible light using a scintillator and then receives the light with a photodiode to generate an output, or a direct conversion type detector element using semiconductors such as a-Se or CdTe that directly converts the X-rays into an electrical signal to generate an output can be applied.

[0020] Furthermore, multiple detectors may be arranged, and examples include line sensors with elements arranged in a straight line, TDI (Time Delay Integration) sensors, and other detectors with photoreceiving elements arranged in a planar manner, such as CCD (Charge-Coupled Device) image sensors and CMOS (Complementary Metal Oxide Semiconductor) image sensors, as well as general-purpose two-dimensional X-ray detectors FPD (Flat Panel Detector). Compared to direct conversion detectors, indirect conversion type FPDs have no restrictions on usable temperature and other factors, and also have superior mechanical strength. Therefore, indirect conversion type X-ray detectors are easy to handle. Moreover, it is preferable that indirect conversion type FPDs be equipped with a cell-type scintillator. In indirect conversion type FPDs, a scintillator panel is used to convert radiation into visible light. A scintillator panel contains a phosphor that emits X-rays, such as cesium iodide (CsI). In response to emitted X-rays, the phosphor emits visible light, which is then converted into an electrical signal by a TFT (Thin Film Transistor), CCD, or CMOS sensor. By transmitting this electrical signal, the X-ray information can be converted into digital image information. However, indirect conversion type FPDs tend to have low image sharpness due to factors such as the scattering of visible light by the phosphor itself when it emits light. On the other hand, FPDs employing cell-type scintillators have phosphors filled within cells separated by partitions, thus suppressing the effects of visible light scattering. As a result, FPDs equipped with cell-type scintillators have high sharpness and can detect minute defects and their locations with high precision. Cell-type scintillators that are large in area and have high sharpness can be easily formed are more preferably those made by processing the partitions using photolithography with a photosensitive paste.

[0021] Furthermore, in the present invention, it is preferable to use a flexible detector that has the flexibility to be bent. Taking a flat panel type detector as an example, a flexible detector can be obtained by arranging a detection unit in which pixels are arranged in a matrix on a substrate made of a flexible resin or the like that can be bent. Each pixel is equipped with, for example, a photodiode that carries a current corresponding to the total amount of energy of the received electromagnetic wave, and a pixel circuit that controls the driving of the photodiode. As a result, each pixel can output an electrical signal corresponding to the total amount of energy received to a control unit.

[0022] <Detector movement mechanism> The inspection apparatus of the present invention includes a moving mechanism that moves the detector along the direction in which the sample is transported by the transport mechanism. As will be described later, the inclusion of such a moving mechanism enables inspection with high resolution, high sensitivity, and high signal-to-noise ratio even at high speeds. Preferably, the moving mechanism includes an endless annular transport belt, and the detector is placed on this transport belt for inspection.

[0023] To illustrate a specific embodiment using Figure 3, in the example shown in Figure 3, the movement mechanism for moving the detector consists of a transport belt 12 driven by a drive means 13 in the direction in which the sample is transported. To image while moving the detector 10, stable movement with high constant velocity and straight-line motion is necessary. Therefore, it is preferable to provide auxiliary means to assist in the smooth movement of the transport belt, and buffer means to absorb the tensile and compressive forces generated by the movement of the transport belt. Examples of these means include bearings and dampers with sufficient stress absorption capacity. Furthermore, when the detector is moved on the transport belt, wiring cables from the detector, such as power supply cables and communication cables for transmitting and receiving signals for image data acquisition, may become entangled, hindering smooth movement. For example, the power supply cable can be connected to an external power cable using a rotating connector, such as a slip ring, which transmits power to a rotating body from the outside. Wireless communication can also be used for the communication cable.

[0024] For example, imaging by the detector is performed by setting the timing of the start of imaging for each row of pixels arranged parallel to the carrier surface and perpendicular to the direction of the detector's movement (X direction). Image acquisition begins when a row of pixels enters the area irradiated by radiation from the source and ends when it leaves the irradiation area. Image data during the image acquisition period is temporarily stored in a memory device installed in the detector, and the image data is transmitted to an external receiver when image acquisition ends. The timing of the start and end of image acquisition can be determined by placing sensors that can detect the passage of the detector on the upstream and downstream sides of the irradiation area and detecting the detector.

[0025] <Means for determining the presence or absence of defects> The means for determining the presence or absence of defects is connected to a detector and acquires image information of the sample from the detector along with information on the movement of the sample from the transport mechanism, and detects defects present in the sample within the irradiation area. It also has means (image information acquisition means, image synthesis means) for generating a mapping image in which the location of defects is identified during the time the sample is in the irradiation area. Preferably, it also has means for acquiring information from the thickness measuring instrument and further obtaining information in the thickness direction of the sample by calculation. The means consists of a defect candidate detection means that calculates defect candidates from the acquired image and a means for determining whether or not the defect candidates correspond to defects.

[0026] <Means for acquiring image information> The signal detected by the detector's pixel 11 and converted into an electrical signal outputs the intensity of the detected radiation as a brightness value. Pixels that strongly detect radiation have a high brightness value (bright), while pixels that weakly detect radiation have a low brightness value (dark). If the size of the detector's pixel 11 is P [mm] and the desired resolution is Re [mm], then a magnification M must be set such that Re = P / M, as shown in Figure 5. In this case, the scan rate f [Hz], which is the number of times the detector takes images per second, is related to the time τ taken for one image by τ = 1 / f [seconds]. If the sample transport speed is Vw [mm / second], the sample is transported at Vw [mm / second] for the length of the desired resolution Re, so the imaging time τ required for one image by the detector is τ = Re / Vw = P / (M·Vw) [seconds]. The higher the resolution, the smaller the detection pixel, the larger the magnification, and the faster the sample transport speed, the shorter the time τ required for one image becomes, and a detector with a high scan rate is required. When the detector is moved by its movement mechanism at a detector movement speed Vd [mm / sec] along the same direction as the sample transport direction, the pixels of the detector appear to move slower by Vd / M [mm / sec] than the transported sample movement speed Vw [mm / sec]. Therefore, the time τ required for one imaging by the detector 10 is τ = Re / |Vw - Vd / M| = P / |M·Vw - Vd| [seconds], which increases the time that can be spent on one imaging. This makes it possible to accommodate a fast sample transport speed with high temporal resolution even with a low scan rate detector. Conversely, it is also possible to increase the sample transport speed by increasing the allowable τ for a certain resolution. For example, when imaging with a sample transport speed Vw = 100 mm / sec, a target resolution Re = 0.05 mm, a detector pixel size P = 0.1 mm, and a magnification of 2x, if the detector transport speed Vd = 0 mm / sec, the imaging time will be τ = 0.05 / 100 = 0.5 msec (scan rate of 2 kHz). If the detector transport speed Vd = 150 mm / sec, imaging can be performed in τ = 0.05 / (100 - 150 / 2) = 2 msec (scan rate of 0.5 kHz). Furthermore, if the detector transport speed Vd = 200 mm / sec, an almost infinitely long imaging time becomes possible. On the other hand, if Vd / M is significantly faster than Vw, the speed difference becomes large, making imaging itself difficult unless the imaging time is shortened.To achieve high imaging accuracy and high transport speed at an even higher level, it is preferable to move the detector so that the speed ratio of Vd to Vw, Vd / Vw, is 2 times or less of the magnification M, and it is even more preferable to move the detector so that Vd / Vw is 1 / 2 or less of the magnification M. Furthermore, by using a detector movement mechanism in which a flexible detector 14, which has the flexibility to bend as shown in Figure 6, is arranged, and moving the transport belt 12 on which the flexible detector 14 is arranged, it becomes possible to image continuous samples such as roll-to-roll samples without interruption.

[0027] <Image synthesis method> It is possible to synthesize an image of the sample at a certain time from the intensity signals from the pixels 11 of the detector placed in the detector 10 and the positional information of the sample from the sample transport mechanism. If defects exist in the sample, these defects will be recognized as differences in contrast.

[0028] For example, description will be given by taking as an example the case where defects 15-(1), 15-(2) and 15-(3) having different sizes and shapes exist in a certain region within a sample as shown in Fig. 7. This figure uses a coordinate system in which the bottom surface of the sample is the XY plane with Z=0, where the center of gravity of the defect 15-(1) is at coordinates (X1, Y1, Z1), the center of gravity of the defect 15-(2) is at coordinates (X2, Y2, Z1), and the center of gravity of the defect 15-(3) is at coordinates (X1, Y1, Z2). Consider an image acquired by a detector when such a sample and the detector are transported. Figs. 8 to 10 show an example where continuous imaging is performed while moving the sample and the detector from left to right in the figure (that is, in the Y-axis direction). Fig. 8 shows the position of the sample at time ta and the image at that position extracted from the continuously captured images, Fig. 9 shows the position of the sample at time tb and the image at that position, and Fig. 10 shows the position of the sample at time tc and the image at that position. Note that ta < tb < tc. Furthermore, in the two-dimensional projected images 16 obtained at each time point ta, tb, and tc, the image corresponding to defect 15-(1) is shown as 17-(1), the image corresponding to defect 15-(2) is shown as 17-(2), and the image corresponding to defect 15-(3) is shown as 17-(3). As can be understood from Figs. 8 to 10, since defects 15-(1) and 15-(2) exist at the same depth (Z1), in the projected image 16, both of the two defects are observed to move while maintaining substantially the same interval. On the other hand, since defects 15-(1) and 15-(3) exist at different depths (Z1 and Z2), their apparent moving speeds in the Y direction are different in the projected image 16, and even if their X and Y coordinates are the same, separated images can be obtained as a certain time elapses. That is, the amount of movement in the projected image (projected movement amount) differs depending on the depth of the defect in the sample. To explain this in more detail, Fig. 11 shows an image extracting the defect 15-(1) and the corresponding image 17-(1) at the time points ta, tb, and tc.Let Dab[mm] = Vw(tb-ta) be the amount of displacement of defect 15-(1) from time ta to time tb, and Dbc[mm] = Vw(tc-tb) be the amount of displacement of defect 15-(1) from time tb to time tc. If Lab is the amount of displacement of the defect image from time ta to time tb in the corresponding image, and Lbc is the amount of displacement of the defect image from time tb to time tc, then using the magnification factor Mz1 = FDD / (FOD-Z1), which takes into account the depth of defect 15-(1) in the sample, we get Lab = Mz1·Dab = Vw(tb-ta)·FDD / (FOD-Z1) and Lbc = Mz1·Dbc = Vw(tb-ta)·FDD / (FOD-Z1). In other words, it can be understood that the amount of displacement of the defect image changes if the depth of the defect in the sample is different.

[0029] Another application method involves using the movement behavior of multiple defect images to superimpose images acquired at other acquisition times, shifting them by the amount of defect movement, around an image acquired at a certain time. This allows images of defects at the depth of interest to overlap, resulting in a strong signal and enabling detection of even low-contrast defects. Specifically, for example, as shown in Figure 12, if the image at time tb (16 in Figure 9) is used as the center, and the defect image movement amounts Lab and Lbc calculated at depth Z1 are used to shift the image at time ta (16 in Figure 8) by -Lab and the image at time tc (16 in Figure 10) by +Lbc, then only the defects at depth Z1 can be positioned at approximately the same coordinates. When the shifted images are then superimposed, defects 15(1) and 15-(2) at depth Z1 overlap, respectively, and a strong signal can be obtained. On the other hand, defects 15-(3) that do not exist at depth Z1 will have different coordinates due to their different apparent movement velocities, and will not result in a large signal intensity due to overlap. Therefore, similar to the method described above, the amount of defect movement relative to Z2 is calculated, and by shifting and adding the values ​​by that amount, the positions of defects 15-(3) present at depth Z2 can be superimposed, resulting in a large signal intensity. Within the sample thickness H, by setting the number of divisions Nz and performing the same operation as above for each ΔZ = H / Nz, defects present at each depth can be extracted. Furthermore, if multiple defects overlap along the line connecting the X-ray and the detector, they will be detected as a single defect, but it is also possible to separate and extract the defects.

[0030] <Defect Assessment> Defect candidates are extracted from the composite image obtained by the aforementioned image synthesis method, and defects are detected using a brightness threshold in the bright direction and a brightness threshold in the dark direction that allows for the separation of defect candidates from non-defective areas. The detection of defect candidates may be narrowed down by the size of the detection area satisfying the threshold, or by the feature quantities of the detected shape. For example, if it is known that a defective foreign object takes on an elongated shape in a specific direction due to a certain process, the orientation (angle) and thickness (aspect ratio) of the detected shape may be used as feature quantities to narrow down the detection. Furthermore, spatial filters may be used prior to detection using brightness thresholds. Defect determination is performed using these methods. [Examples]

[0031] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples, nor should it be interpreted as being limited to these examples. The materials and apparatus used in the examples are shown below.

[0032] (Objects to be inspected) A SUS304 cylinder with a diameter of 50 μm and a height of 50 μm was attached to a commercially available polyethylene terephthalate film as a foreign object equivalent 18, using epoxy resin with its bottom (or top) surface as the adhesive surface, and this was used as the object to be inspected (manufactured by Toray Precision Co., Ltd.). A top view of the object to be inspected is shown in Figure 13. In this case, two SUS304 wires with a diameter of 200 μm (markers 19) were placed so that the location of the foreign object equivalent could be identified in the captured image.

[0033] (Equipment configuration, measurement) X-ray imaging was performed using a commercially available X-ray tube (Hamamatsu Photonics K.K. L9181-02), a commercially available X-ray TDI camera (Hamamatsu Photonics K.K. C12300-121), a commercially available linear stage 1 for transporting the object to be inspected (SMC LEFB32T-1200-S5C5183), and a commercially available linear stage 2 for transporting the X-ray TDI camera (Zaber L40B1150-N2-KM02 X-MCC2-KX14B). The X-ray tube, X-ray TDI camera, linear stage 1, and linear stage 2 were positioned so that the distance FDD from the focal point of the X-ray tube to the X-ray TDI camera was 325 mm, and the distance FOD from the focal point of the X-ray tube to the object to be inspected was 95 mm (see Figure 5). Note that the transport direction by linear stage 1 and linear stage 2 was the same.

[0034] Next, the object to be inspected was placed on linear stage 1, and the X-ray TDI camera was placed on linear stage 2. X-rays were irradiated with an X-ray tube voltage of 40kV and a tube current of 75μA. Linear stage 1 and linear stage 2 were operated under the conditions shown in Table 1, and images were taken with the X-ray TDI camera.

[0035] (Image evaluation) In the images captured by the above device, the minimum brightness So of the area where the foreign object was present, the average brightness Sb of the area where the foreign object was not present, and the standard deviation σb of the brightness of the area where the foreign object was not present were measured. Sb and σb were measured from 400 arbitrarily selected pixels, excluding the area where the foreign object was located and its vicinity (a 20-pixel square area around it (approximately 280 μm × 280 μm in this example)). Brightness was measured using the signal amount of the output X-ray image captured by an X-ray TDI camera. Table 1 shows the CNR (contrast-to-noise ratio), which is the value obtained by dividing the contrast C, which is the absolute value of the difference between So and Sb, by σb. A larger CNR value indicates that the signal intensity contrast of the object being inspected is greater than the noise in the area where the object is not present, making it easier to detect.

[0036] [Table 1] [Industrial applicability]

[0037] According to the present invention, since the detector is moved in the same direction as the sample movement while acquiring a transmission image, a projection image with high temporal resolution can be obtained even with a detector with a low scan rate. Furthermore, by acquiring images taken at various irradiation angles from a point light source at multiple locations, even if multiple defects overlap along a line connecting the radiation source and the detector, the defects can be separated and extracted. Moreover, even low-contrast defects can be detected as large signals from multiple images, enabling high-speed and high-precision inspection of defects. [Explanation of Symbols]

[0038] 1: Cabinet 2, 2(a), 2(b): Sample 3: Loading entrance 4: Exit 5: Sample transport roll 6: Sample transport area 7: Thickness measurement sensor 8: Source 9: Radiation 10: Detector 11: Detector pixels 12: Detector carrier zone 13: Driving means of the moving mechanism 14: Flexible detector 15-(1), 15-(2), 15-(3): Defects present in the sample 16: Projection image 17-(1), 17-(2), 17-(3): Images of defects present in the sample. 18: Foreign object equivalent (cylinder made of SUS304) 19: Marker (wire made of SUS304 stainless steel)

Claims

1. An inspection apparatus comprising at least: a transport mechanism for transporting a sample to be inspected; an X-ray source for radially irradiating an area through which the transported sample passes; a detector positioned to detect X-rays that have passed through the transported sample and converting the detected X-rays into an electrical signal; a movement mechanism for moving the detector along the direction in which the sample is transported by the transport mechanism; and a determination means for determining the presence or absence of defects in the sample from image information of the sample obtained from the detector and movement information of the sample from the transport mechanism during the time the sample passes through the area, An inspection apparatus in which the transport mechanism and the moving mechanism move the sample and the detector such that, when the transport mechanism moves the sample at a speed Vw and the moving velocity component of the detector by the moving mechanism in the same direction as the sample is moved, the ratio Vd / Vw to Vw is less than or equal to twice the ratio (FDD / FOD) of the distance between the X-ray source and the detector to the distance between the X-ray source and the sample (FOD).

2. Furthermore, the inspection apparatus according to claim 1 comprises a thickness measuring instrument for measuring the thickness of a sample, and a calculation means for calculating the location of a defect in the sample based on the thickness information of the sample measured by the thickness measuring instrument and the image information of the sample from the detector.

3. The inspection apparatus according to claim 1 or 2, wherein a plurality of the detectors are arranged along the direction of sample transport.

4. The inspection apparatus according to claim 1 or 2, wherein the moving mechanism is a moving mechanism comprising an endless annular conveying belt, the moving mechanism comprising a driving means for applying a driving force to the conveying belt, an auxiliary means for assisting in the smooth movement of the conveying belt, and a buffer means for absorbing tensile and compressive forces generated on the conveying body as a result of the movement of the conveying belt.

5. The inspection apparatus according to claim 1 or 2, wherein the detector is a flexible detector that can be bent, and the detector is arranged along the direction of movement of the moving mechanism.

6. The inspection apparatus according to claim 1 or 2, wherein the detector is an indirect conversion type detector comprising a scintillator panel having a pixel structure in which a phosphor that emits X-rays is filled in a space partitioned by a grid-like partition formed on a substrate, and a photoelectric conversion element having a cell structure corresponding to the partition and converting the light emitted from the phosphor into photoelectricity.

7. A method for inspecting whether or not there are defects inherent in a sample, The sample to be examined is passed through a transport mechanism into the area irradiated by X-rays from an X-ray source that emits X-rays radially. A step of detecting X-rays and converting them into electrical signals, using a detector provided in the moving mechanism, which is positioned to detect X-rays transmitted through a sample passing through the region, and which converts the detected X-rays into electrical signals, while moving the detector along the direction in which the sample is transported by the transport mechanism, The process includes determining whether or not there are defects in the sample based on image information of the sample from a detector obtained during the time the sample passes through the region and information on the movement of the sample from the transport mechanism. A testing method, An inspection method characterized in that the transport mechanism and the moving mechanism move the sample and the detector such that, when the transport mechanism moves the sample at a speed Vw and the moving velocity component of the moving mechanism of the detector in the same direction as the sample is Vd, the ratio Vd / Vw to Vw is less than or equal to twice the ratio (FDD / FOD) of the distance between the X-ray source and the detector to the distance between the X-ray source and the sample (FOD).

8. Furthermore, the inspection method according to claim 7 is characterized by measuring the thickness of the sample and calculating the location of defects in the sample based on the measured thickness information and the image information of the sample from the detector.

9. The inspection method according to claim 7 or 8, wherein a plurality of detectors are arranged along the transport direction of the sample.

10. The inspection method according to claim 7 or 8, wherein the moving mechanism is a moving mechanism comprising an endless annular conveying belt, and the moving mechanism comprises a driving means for applying a driving force to the conveying belt, an auxiliary means for assisting in the smooth movement of the conveying belt, and a buffer means for absorbing tensile and compressive forces generated in the conveying belt as a result of the movement of the conveying belt.

11. The inspection method according to claim 7 or 8, wherein the detector is an indirect conversion type X-ray detector comprising a scintillator panel having a pixel structure in which a phosphor that emits light when exposed to X-rays is filled in a space partitioned by a grid-like partition formed on a substrate, and a photoelectric conversion element having a cell structure corresponding to the partition and converting the light emitted from the phosphor into photoelectricity.

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