Patent Publication Number: US-8970836-B2

Title: Defect inspecting apparatus and defect inspecting method

Description:
BACKGROUND 
     The present invention relates to a defect inspecting apparatus and a defect inspecting method for inspecting a semiconductor wafer and a liquid crystal substrate. 
     When manufacturing an LSI and a liquid crystal substrate, there are repeated patterns formed on an object to be processed (for example, a semiconductor wafer). In manufacture of such an LSI or liquid crystal substrate, if a foreign substance adheres to a surface of the object to be processed or a defect occurs, it will become a cause of a defect, such as bad insulation of wiring and a short circuit, for example. Here, as the circuit pattern becomes minute, it has become difficult to discriminate between a pattern formed on the object to be processed (a non-defect part) and a minute foreign substance and a defect. Here, the defect is a particle adhering on a sample that is the object to be processed, a crystal defect COP (Crystal Originated Particle), and scratch resulting from polishing. 
     There is U.S. Pat. No. 6,617,603 (patent document 1) as a background art of this technology. This patent gazette describes a method for detecting a defect (abstract) by imaging a picture at a scan position on a disk plate that has a characteristic such that a center in an arrangement direction of n amplification type light receiving elements (avalanche photodiodes) in a light receiving area formed thereby takes a peak value and an amount of received light gradually decreases to its both sides actually in contrast and by using a fact that a profile of an amount of received light varies depending on existence/absence of the defect. 
     SUMMARY 
     Due to miniaturization of an inspection object (for example, a semiconductor pattern), a size of a defect to be inspected has become microminimized and an intensity of scattered light from the defect decreases considerably. In detecting very small scattered light from this defect, an existing CCD (Charge Coupled Device) array sensor and a TDI (Time Delay Integration) array sensor are insufficient in sensitivity. Although in U.S. Pat. No. 6,617,603, an element such that amplification type sensors are arranged in an array form is used for improvement in sensitivity, it comes with the following problem. When a light quantity of the scattered light varies greatly depending on a portion of the inspection object, if the sensitivity is set to a bright section so that the sensor may not be saturated, the sensitivity of a dark section will fall increasingly. 
     Moreover, there is reflection of a lens etc., weak defect scattered light is buried in these reflected lights, and the sensitivity falls. 
     Explaining briefly an outline of a representative mode among modes of the invention disclosed by the present application, it goes as follows: (1) A defect inspecting apparatus that has: an illuminating optical system having a laser light source for irradiating light onto a sample on whose surface a pattern is formed; a detecting optical system having a sensor for detecting light generated from the sample illuminated by the illuminating optical system; and a signal processing unit that extracts a defect from an image based on the light detected by the detecting optical system, in which an amplification rate of the sensor is dynamically changed during a time when the light is detected by the detecting optical system. 
     According to the present invention, it is possible to provide the defect inspecting apparatus and the defect inspecting method that realize a high sensitivity defect detection accuracy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing an outline configuration of a first embodiment of an optical inspecting apparatus according to a first embodiment of the present invention; 
         FIG. 2  is a plan view of an illuminating optical system of the optical inspecting apparatus according to the first embodiment of the present invention; 
         FIG. 3  is a side view of the illuminating optical system of the optical inspecting apparatus according to the first embodiment of the present invention; 
         FIG. 4  is a diagram showing a thin line width adjustment mechanism of illumination according to the first embodiment of the present invention; 
         FIG. 5  is a diagram showing a side lobe inhibition mechanism of the illumination according to the first embodiment of the present invention; 
         FIG. 6  is a diagram showing a difference in an image by an amplification rate of a sensor array according to the first embodiment of the present invention; 
         FIG. 7  is a diagram showing an amplification rate adjustment result of the sensor array according to the first embodiment of the present invention; 
         FIG. 8  is a flowchart of deciding of the amplification rate according to the first embodiment of the present invention; 
         FIG. 9  is a diagram showing gate mode sampling by an oblique illumination system according to the first embodiment of the present invention; 
         FIG. 10  is a diagram showing gate mode sampling by an epi-illumination system according to the first embodiment of the present invention; 
         FIG. 11  is a diagram showing a film thickness analysis part according to the first embodiment of the present invention; 
         FIG. 12  is a block diagram showing an image processing configuration according to the first embodiment of the present invention; 
         FIG. 13  is a block diagram showing an image processing configuration according to the first embodiment of the present invention; 
         FIG. 14  is a block diagram showing an image processing configuration according to the first embodiment of the present invention; 
         FIG. 15  is a block diagram showing an image processing configuration according to the first embodiment of the present invention; 
         FIG. 16  is a block diagram showing a detector configuration of an optical inspecting apparatus according to a second embodiment of the present invention; and 
         FIG. 17  is a block diagram showing an image processing configuration according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments will be described using drawings. 
     First Embodiment 
     A first embodiment of an optical inspecting apparatus according to the present invention will be described using  FIG. 1  to  FIG. 15 . Below, the dark field inspecting apparatus will be explained taking the inspection of a semiconductor wafer with the dark field inspecting apparatus as an example. 
       FIG. 1  is a diagram showing the first embodiment of the optical inspecting apparatus according to the present invention. An illuminating optical system  110  illuminates a sample (semiconductor wafer)  100  that is an inspection object mounted on a stage part  170  with illumination light from a direction slanting relative to a normal direction of a surface of the semiconductor wafer  100  (oblique illumination), or illuminates it with a linear beam from the normal direction (epi-illumination), and detects scattered light that is scattered from the irradiated semiconductor wafer  100  with a detecting optical system  120 . An array of APDs (Avalanche Photodiodes) whose amplification rate n is high and can be controlled at a high speed etc. is used to detect only the scattered light from the wafer in high sensitivity. In that occasion, the semiconductor wafer  100  that is mounted on the stage part  170  is scanned with the illumination light from an illuminating optical system  110   a  or  110   b  by driving the stage part  170  in a plane. A signal processing and control system  250  detects a defect existing on the semiconductor wafer  100  by processing the scattered light from the semiconductor wafer  100  detected by the detecting optical system  120 . 
     [Oblique Illuminating Optical System  110   a ] 
     The illuminating optical system  110   a  is comprised by having a laser light source  111 , a light quantity adjustment unit (an attenuator, an ND (Neutral Density) filter)  112 , a beam expander  113 , a polarization generation part  114  comprised of a polarizer and a wave plate, a linear beam generation part (a linear illumination system)  115  for irradiating the inspection object (the semiconductor wafer)  100  with a linear beam. The laser light source  111  emits a laser beam. At this time, as the light source  111 , a gas laser, a semiconductor laser, a solid state laser, a surface emitting laser, etc. are usable. Although regarding the wavelength of the light, lights in the infrared range, the visible range, and ultraviolet range can be used, since optical resolution improves as the wavelength becomes shorter, it is recommended to use light in the ultraviolet ranges such as UV (Ultra Violet), DUV (Deep Ultra Violet), VUV (Vacuum Ultra Violet), and EUV (Extreme Ultra Violet) lights in observing a minute defect. The beam shaping unit  113  shapes the laser beam emitted from the laser light source  111 .  FIG. 2  is a plan view of the illuminating optical system  110 , and  FIG. 3  is a side view thereof. In this embodiment, a beam shaping unit  113  is formed with a beam expander  1131  for enlarging a diameter of the laser beam emitted from the laser light source  111  and a collimating lens  1132  for forming an enlarged laser beam into collimated light. The polarization generation part  114  is comprised by having a polarizer  1141  and a wave plate  1142 , and adjusts a polarization characteristic of the light whose beam diameter is enlarged by the beam expander  1131  of the beam shaping unit  113 . The linear beam generation part  115  is comprised of a cylindrical lens etc. 
     In the above-mentioned configuration, the laser beam emitted from the laser light source  111  is adjusted in light quantity by the light quantity adjustment unit (attenuator, ND filter)  112 , is expanded in beam diameter by the beam expander  1131  in the beam shaping unit  113 , is formed into the collimated light by the collimating lens  1132 , is controlled in polarization state by the polarization control part  114 , and is focused into a one direction by the linear beam generation part  115  to become a linear beam  101  parallel to the y-axis, which is irradiated onto a linear area on the surface of the semiconductor wafer  100 . At this time, illumination in an azimuth β with respect to the y-axis of the illuminating optical system shown in  FIG. 2  can be realized by taking an arbitrary direction including the y-axis direction. Moreover, a polar angle γ that is an angle from the z-axis of the illuminating optical system shown in  FIG. 3  is selected in a range of 0° to 90°. Incidentally, the illumination azimuth β and the polar angle γ are set not to interfere with the detecting optical system  120 . At this time, the polarization generation part  114  may also be disposed after the linear beam generation part  115 . The linear beam  101  thus formed is irradiated onto the surface of the semiconductor wafer  100  so that a stage y direction may coincide with a longitudinal direction of the linear beam  101 . 
     [Epi-Illuminating Optical System  110   b ] 
     The epi-illuminating optical system  110   b  is comprised by having a branching mirror  116  for branching an optical path from the oblique illuminating optical system  110   a , a mirror  117  for bending the optical path, a linear illuminating system (a linear beam generation part)  118 , an illumination mirror  119  onto a wafer, and an objective lens  121  of the detecting optical system  120 , and forms the linear beam  101  on the wafer. When using an oblique illuminating optical system  110   a , the branching mirror  116  and the illumination mirror  119  are evacuated from the optical system. Although a disposition place of the branching mirror  116  may be in front of the beam shaping unit  113  and the polarization generation part  114 , in that case, a polarization generation part and a beam formation unit become necessary for an epi-illuminating optical system. 
     Incidentally, in the optical system using linear illumination, a difference between the line width of the linear beam and side lobes becomes a difference of sample scattered light, which causes a difference of the detection sensitivity to occur. Since the line width and the side lobes have a relationship of the Fourier transform with pupil surfaces of the linear illuminating optical systems  115 ,  118 , they can be controlled by a pupil surface shape.  FIG. 4  is a diagram showing a thin line width adjustment mechanism of the illumination according to the first embodiment of the present invention, and  FIG. 5  is a diagram showing a side lobe inhibition mechanism of the illumination according to the first embodiment of the present invention. As shown in  FIG. 4 , since the line width depends on an illumination NA, the line width can be controlled in a direction that makes the line width thick by controlling the pupil with an aperture  1152  whose diameter is smaller than a pupil diameter  1151 . As shown in  FIG. 5 , side lobes  1153  can be reduced by varying the transmissivity from a boundary of the pupil inward toward its center continuously. Moreover, in order to obtain the same effect, there is also a technique of providing a minute structure that is decided by the pupil diameter and the wavelength in the pupil. 
     [Detecting Optical System  120 ] 
     The detecting optical system  120  will be explained in detail using  FIG. 1 . The detecting optical system  120  is comprised by having the objective lens  121 , a spatial filter  123 , an ellipsometer  124 , an imaging lens  125 , an amplifying sensor array  126 , a beam sampler  127 , and a pupil observation optical system  128 . The pupil observation optical system  128  observes the pupil on an outgoing side of the objective lens  121 . For leading the light to the pupil observation optical system  128 , the light is led thereto from the detecting optical system  120  using the beam sampler  127  that can be taken into and out of an optical path of the detecting optical system  120 . Incidentally, as a replacement for the pupil observation optical system  128 , if it is possible that a relationship of a position and a shape of the spatial filter  123  with an intensity of an image acquired by the line sensor is obtained in advance and an intensity distribution at a pupil position is grasped from the relationship, the pupil observation optical system  128  for directly observing the pupil surface can be omitted. The objective lens  121  converges the reflected, scattered, and diffracted lights going in different directions from the surface of the semiconductor wafer  100 . The spatial filter  123  shields a part of reflected, scattered, and diffracted lights from the surface of the semiconductor wafer  100  that are converged by the objective lens  121 . Here, the spatial filter  123  is disposed at a position of the outgoing side pupil position of the objective lens  121  or at a position equivalent (conjugate) to the pupil position. As the spatial filter  123 , a light shielding filter comprised of multiple rods having multiple thicknesses that can be arranged in vertical and horizontal directions, a filter that can allow light to pass or shield it at desired places two-dimensionally at the pupil surface, or the like is used. Especially, as the two-dimensional filter, one that uses an electrooptical effect such as a liquid crystal, one that uses a magnetooptical effect, a MEMS (Micro Electro Mechanical Systems) shutter, etc. are used. Incidentally, in this embodiment, in order that the illumination light is made into a linear shape with the y direction coinciding with the longitudinal direction, the light is focused in the y direction by the linear beam generation part  115 . Therefore, a diffraction pattern on the pupil surface becomes a diffraction pattern that has a spreading in the y direction that depends on a focusing NA. In this case, the diffracted light is appropriately removable with a rod like filter disposed in a one direction. 
     The ellipsometer  124  is comprised by having the polarizer and the wave plate, and adjusts the polarization characteristic of the scattered light that was not shielded by the spatial filter  123 . The polarization generation part  124  is comprised, for example, by having a ¼ wave plate, a ½ wave plate, and the polarizer, and each of these elements is controllable in rotation individually, which enables an arbitrary polarized light to be transmitted therethrough. 
     The imaging lens  125  makes the scattered light that was not shielded by the spatial filter  124  be transmitted, and images an optical image. Here, positions of the polarization analysis part spatial filter  124  and the imaging lens  125  may be interchanged. 
     The amplifying sensor array  126  is disposed at a position such that an image of the scattered light that is focused and imaged by the imaging lens  125  is imaged on a detection plane of the amplifying sensor array  126 , and detects an optical image of the scattered light. As the amplifying sensor array  126 , an APD (Avalanche Photodiode) array whose amplification rate can be varied at a high speed for every pixel by a voltage and whose sensor ON/OFF can be controlled at a high speed with an electrical signal, or the like is used. Since the amplification rate of the APD array varies depending on temperature, a voltage added with a temperature correction of a temperature monitor part  193  is applied to an amplifier  191  by a voltage controller  192 . 
     By using an amplification rate control function by a voltage of the sensor array  126 , a dynamic range of the sensor can be expanded.  FIG. 6  is a diagram showing a difference in image by an amplification rate of the sensor array according to the first embodiment of the present invention, and  FIG. 7  is a diagram showing an amplification rate adjustment result of the sensor array according to the first embodiment of the present invention.  FIG. 6  shows a relationship between an image profile acquired by the inspection and a sensor amplification rate. In an obtained image, there is an area (a bright section)  30  where a scattered light intensity that reaches to the sensor array  126  is strong and a weak area (a dark section)  31  where it is weak, partly due to an effect of insertion of a spatial filter. When an area  30  where the scattered light intensity is strong is acquired by lowering the amplification rate, the intensity is weak in the area  30  where the scattered light intensity is weak and there is a possibility of overlooking a defect. On the other hand, when the sensitivity of an area  31  where the scattered light intensity is low is raised by increasing the amplification rate, the signal goes to be saturated in the area  30  where the scattered light intensity is strong, which will make defect inspection impossible. Therefore, by setting the amplification rate low in the area  30  where the scattered light intensity is strong and by setting the amplification rate high in the area  31  where the scattered light intensity is weak, it is made possible to perform inspection with a widened dynamic range. That is, the image is acquired by dynamically changing a relationship between the scattered light intensity and the sensor amplification rate while the sensor amplification rate is being scanned so that the intensity may not reach the sensor saturation intensity as shown in  FIG. 7 . 
     A setting method of the sensor amplification rate will be explained in detail. If the amplification rate is made variable according to a detection intensity of only each pixel, there will be a possibility that a defect signal with high intensity may be detected with a low amplification rate and the sensitivity may fall. Therefore, the amplification rate is set for the bright section  30  and for the dark section  31 , respectively, namely for each area where the scattered light intensity is the same, and the inspection is performed.  FIG. 8  is a flowchart of deciding of the amplification rate according to the first embodiment of the present invention. Before the inspection, in order to decide conditions of the polarization generation part  114 , the spatial filter  123 , and the polarization analysis part  124 , the inspection object is subjected to a scan test (S 101 ). A boundary of the bright section and the dark section in a scanned image under inspection conditions obtained at that time is found and a setting area of the amplification rate is decided. Here, the boundary of the bright section and the dark section is found by carrying out statistical processing on brightness information in the image (S 102 ). For example, this can be done by using a fact that variance is small in a place where brightness difference of the image is small, and the brightness difference is large and the variance becomes large near the boundary, that is, the area is set up by calculating a variance value of a fixed area over the entire image and determining a boundary value of the bright section and the dark section based on a magnitude of the variance. Next, an inspection scan is performed, and in each area set in S 102 , the amplification rate at the time of detecting the area is decided based on the intensity of the specified number of pixels acquired first in that area (S 103 ). The amplification rate is decided as follows: a relationship between the detection intensity and the amplification rate has been decided first; an average intensity of first n pixels that are scanned in a certain area; and when the intensity is saturated, the amplification rate is reduced, and when the intensity is less than or equal to a fixed intensity, the amplification rate is increased so that the detection intensity may become suitable. This is performed repeatedly while being scanned (S 104 ). By keeping setting the amplification rate in real time, a suitable amplification rate can be set in almost the entire area of the inspection object except near the boundary. When the same patterns exist in multiple places like a semiconductor pattern, the amplification rate decided in a first pattern may be applied to the same patterns. Moreover, at the time of setting the area, the setting may be done in advance using design data. 
     When detecting the weak scattered light from the defect, the reflected light etc. occurring at each optical element becomes stray light, and the scattered light from the defect will be buried therein. It is possible to reduce this stray light by using the pulsed light source for the laser light source and making the sensor array  126  perform a high-speed response of switching ON/OFF of the detection within a time shorter than a pulse interval of the pulsed light source  111 . This can be done just by using a gate mode of detecting light only at a timing when the scattered light from the defect by the pulsed illumination light reaches the sensor array  126  and its adjacent times.  FIG. 9  and  FIG. 10  are diagrams showing gate mode sampling by the oblique illumination system according to the first embodiment of the present invention. Stray light removal by combining the oblique illuminating optical system  110   a  and the gate mode of the sensor array  126  will be explained using  FIG. 9 . A time (an optical path difference) required for the pulse generated by the laser light source  111  to reach the sensor array  126  through the inspection object from the generation can be easily calculated with thicknesses of the optical elements, refractive indices, and a propagating distance in air. In the oblique illuminating optical system  110   a , weak reflected light occurring in each optical element also irradiates the inspection object. Moreover, also when the scattered light from the inspection object propagates inside the detecting optical system  120 , reflected light occurs at each optical element, and scattered light other than the direct scattered light from the inspection object reaches the sensor array and becomes stray light  51  there. Then, since a time for the scattered light from the inspection object that should be detected to reach the sensor array  126  is known, the stray light  51  can be removed by performing sampling just before and after a timing when it reaches (ideally, only direct scattered light  50  from the inspection object). Pieces of the stray light resulting from these optical elements cause sensitivity lowering more in the case of the epi-illuminating optical system  110   b . Although the epi-illuminating optical system  110   b  uses a TTL (Through The Lens) system that makes the epi-illumination system and an upper detecting optical system coexist by using a detection lens of the detecting optical system also at the time of illumination, the use of the TTL system becomes a factor of large sensitivity lowering because reflected light  53  arising when the input light whose light quantity is large as compared with the scattered light of the inspection object passes through the detection lens reaches the sensor array  126  as shown in  FIG. 10 . Regarding the signal based on the scattered light detected in this way, an analog signal outputted from the sensor array  126  is amplified by the A/D conversion part  129 , and subsequently is converted into a digital signal, which is sent to the signal processing and control part  250 , where the signal is processed. 
     [Stage Part  170 ] 
     The stage part  170  is comprised by having an x-stage  170   a , a y-stage  170   b , a z-stage  170   c , and a θ-stage  170   d . The x-stage  170   a  is a stage that is movable in an x direction and mounts thereon a semiconductor wafer  100  that is a sample to be inspected and on whose surface a minute pattern is formed. The y-stage  170   b , the z-stage  170   c , and the θ-stage  170   d  are also stages similarly movable in the y direction, a z direction, and a θ direction, respectively, that mounts thereon the semiconductor wafer  100  that is the sample to be inspected and on whose surface a minute pattern is formed. 
     [Reflected Light Analysis Part  300 ] 
     In the image obtained by the detecting optical system  120 , its intensity is governed by interference of a thin film on a surface of the inspection object. Therefore, existence of film thickness unevenness makes unevenness in the brightness of the obtained image occur. Although it will be described later, defect detection is performed based on a difference of brightness between a normal section and a defect section by die comparison of the inspection object, there is a case where performance of the defect detection may lower if there exists unevenness in brightness over the whole of the image. Therefore, a reflected light analysis part  300  analyzes direct reflected light from the inspection object under the illumination light by the oblique illuminating optical system  110   a  to estimate a film thickness of the thin film, and compensates brightness unevenness resulting from the film thickness unevenness of the image that is detected by the detecting optical system  120 . 
       FIG. 11  is a diagram showing a film thickness analysis part according to the first embodiment of the present invention.  FIG. 11  explains details of compensation of the brightness unevenness. The direct reflected light from the oblique illuminating optical system  110   a  is imaged on a sensor  320  with a lens  310 . Either of a micro linear polarizer or a micro circular polarizer is disposed in front of each pixel of the sensor  320 . The film thickness is estimated by a film thickness estimation part  330  using a technique of the ellipsometry that is a general method of film thickness analysis, i.e., by specifying four combinations of micro linear polarizers  321  to  323  and a micro circular polarizer  324  that are different in an azimuth of transmission axis as one group and detecting polarized lights of multiple states using a range defined by these four pixels as a spatial resolution. A difference in a scattered light quantity by a film thickness variation can be assumed by an optical simulation provided that a structure of the inspection object is known, and this corresponds to the brightness unevenness of an image. The brightness unevenness of the image obtained here is compensated before performing image processing. Alternatively, the brightness unevenness may be fed back to the amplification rate of the sensor array  126  to directly acquire an image whose brightness unevenness is compensated. 
     When using the epi-illuminating optical system  110   b , the branching mirror  116  is specified to be a beam splitter through which regular reflected light can pass by an amount that enables the detection, and the brightness unevenness is reduced similarly with the oblique illuminating optical system  110   a . In this occasion, although the scattered light of the oblique illuminating optical system  110   a  also reaches the sensor array  126 , its detection is avoided by the gate mode sampling of the sensor array  126 . 
     [Signal Processing and Control Part  250 ] 
     The signal processing and control part  250  is comprised by having an image processing part  200 , an operation part  210 , a control part  220 , a display part  230 , and a height detecting part  160 . Concrete examples of a signal processing part are shown in  FIG. 12  to  FIG. 15 . 
       FIGS. 12 to 15  are block diagrams each showing an image processing configuration according to the first embodiment of the present invention. Processing of a signal processing part  200   a  shown in  FIG. 12  is generally known as die comparison processing. That is, an image of a certain die has been memorized in delay memory  32 , when an image of an adjacent die is acquired, the registration is performed by a registration circuit  33  in order to correct positional shift resulting from vibration etc., and an acquired image is subtraction processed by a subtraction circuit  34 . In parallel with this, the image that was subjected to the registration is memorized in memory  35 , and a threshold is calculated by a threshold processing circuit  36 . The signal that was subjected to the above-mentioned subtraction processing and the threshold are subjected to the comparison processing in a comparator circuit  37 , and a foreign substance signal and the defect signal are extracted by a defect determination part  38 . The extracted foreign substance and defect signals are outputted, as it is, as a defect map, or are sorted for each of foreign substance kinds and defect kinds by a sorting and sizing processing part  39 , whereby sizes of the foreign substances and the defects are found. 
     Processing of a signal processing part  200   b  shown in  FIG. 13  is generally known as cell comparison processing. That is, when the obtained image includes a signal from a pattern that is originally in an identical shape, the image is shifted by an image shift circuit  40 , in order to take a corresponding point between the image before the shift and the image after the shift, the registration is performed by the registration circuit  33 , and the obtained image is subtraction processed by the subtraction circuit  34 . In parallel with this, the image that was subjected to the registration is memorized in the memory  35 , and a threshold is calculated by the threshold processing circuit  36 . The signal that was subjected to the above-mentioned subtraction processing and the threshold are subjected to the comparison processing and the foreign substance signal and the defect signal are extracted by the defect determination part  38 . The extracted foreign substance and defect signals are outputted, as it is, as a defect map, or are sorted for each of the foreign substance kinds and the defect kinds by the sorting and sizing processing part  39 , whereby the sizes of the foreign substances and the defects are found. 
     Processing of a signal processing part  200   c  shown in  FIG. 14  is generally known as design data comparison processing. That is, the design data from design data  41  is sent to a reference image generation part  42 , where the reference image is generated. The reference image is subjected to registration in order to take corresponding points with an actual image and the obtained image is subtraction processed in the subtraction circuit  34 . In parallel to this, the image that was registered is memorized in the memory  35 , and a threshold is calculated by the threshold processing circuit  36 . The signal that was subjected to the above-mentioned subtraction processing and the threshold are subjected to the comparison processing in the comparator circuit  37 , and the foreign substance signal and the defect signal are extracted by the defect determination part  38 . The extracted foreign substance and defect signals are outputted, as it is, as a defect map, or are sorted for each of the foreign substance kinds and the defect kinds by the sorting and sizing processing part  39 , whereby the sizes of the foreign substances and the defects are found. 
     A system of a signal processing part  200   d  shown in  FIG. 15  is generally known as a self referencing system. That is, the signal processing part  200   d  carries out defect determination by searching a similar pattern in the obtained image and performing the comparison processing on the similar patterns, and determines a defect based on feature quantities of the pattern and the defect. In addition to this, although it is not illustrated, a processing system that forms an image from an average value of multiple similar patterns and performs the comparison processing using the image as the reference image is also known. 
     Second Embodiment 
     A second embodiment of the optical inspecting apparatus according to the present invention will be described using  FIG. 16  and  FIG. 17 .  FIG. 16  is a block diagram showing a detector configuration of an optical inspecting apparatus according to the second embodiment of the present invention, and  FIG. 17  is a block diagram showing an image processing configuration according to the second embodiment of the present invention. Below, the dark field inspecting apparatus will be explained taking inspection of the dark field inspecting apparatus as an example. 
     Although the detecting optical system was single in the first embodiment, the optical system of the second embodiment has multiple detecting optical systems.  FIG. 16  shows only the detecting optical system. The dark field inspecting apparatus has oblique detecting systems  120   x ,  120   y  in addition to the same upper detecting optical system  120  as that of the first embodiment. The configurations of the oblique detecting systems  120   x ,  120   y  are the same as that of the upper detecting optical system  120 . However, since a common portion of the focal plane of the oblique detection lens and the inspection object becomes a linear shape, unless a width of a thin line of the illumination light is made thin to the same level as the focal depth of the detecting optical system, out-of-focus light will also be detected by the sensor array and an image with a high contrast cannot be obtained. 
     The scattered light of the defect differs in the scattered direction depending on its shape and a medium. Because of this, improvement in a capture ratio is expected by detecting the scattered light going in multiple azimuths with multiple detectors. Moreover, accuracies such as of defect sorting and sizing are improved by using a ratio of the defect signals acquired by the detectors. Below, the image processing part  200  at the time of acquiring two images will be explained in detail. The image processing part  200  generates an image  1261  based on the scattered light acquired by the detecting optical system  120  and a reference image  1261   r  acquired at a portion having the same shape as that of the acquisition place of the image  1261  in an adjacent die or cell; an image registration processing part  2011   a  performs registration on this generated image  1261  and the reference image  1261   r  with an accuracy less than or equal to a pixel unit of the sensor; a brightness compensation part  2012   a  compensates brightness of the inspection image  1261  and the reference image  1261   r  that arises from the sample such as a sample surface and a thickness of a thin film on the surface layer or arises from the optical system such as a difference of height between the lens and the wafer at the time of inspection; and a difference processing part  2013   a  performs difference processing whereby corresponding pixels of the inspection image  1261  and the reference image  1261   r  are subtracted from each other to obtain a difference image  1261   d . In this case, the reference image  1261   r  generated based on the scattered light that was acquired by the detecting optical system  120  at a portion having the same shape as that of an acquisition place of the image  1261  in a die, a cell, or the like that is adjacent is temporarily memorized in an unillustrated image memory. The image registration processing part  2011   a  calls the reference image  1261   r  from the image memory, and performs registration processing with the image  1261  with an accuracy less than or equal to the pixel unit. Moreover, an image  1263  that contains a defect and a reference image  1263   r  are generated from a signal acquired from the detecting optical system  120   x , and the processing is performed on this image  1263  and the reference image  1263   r  by the same configuration, which gives a difference image  1263   d.    
     Next, in a defect determination part  2014 , a rectangular coordinate system in which a luminance value of the difference image  1261   d  is represented on a horizontal axis x 1  and a luminance value of the difference image  1263   d  is represented on a vertical axis x 2  is configured and luminances of corresponding pixels of the two difference images  1261   d  and  1263   d  are plotted in this rectangular coordinate system x 1 , x 2 . Since noises are residuals of subtraction between a defect image and a reference image in an x 1 -x 2  space of the rectangular coordinate system, both components x 12 , x 2  are small and the noises are distributed near the origin. On the other hand, intensity of the brightness of the defect image is large as compared with noises, and the defect image is plotted so as to be located at a position away from the origin in the x 1 -x 2  space. Then, by providing a boundary  350  near the origin of the rectangular coordinate system, a noise  322  and a defect  321  are separated and the defect determination is carried out ( 2014 ). A circle, a combination of lines, etc. are usable for the boundary  350 . For example, when a circle is used, what is necessary is that a boundary line is drawn in an area that satisfies the following formula (Formula 1) with a radius of the circle set to A. 
     The following formula shall hold. 
     
       
         
           
             
               
                 
                   
                     
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                     ⁢ 
                     
                       x 
                       i 
                       2 
                     
                   
                   = 
                   
                     
                       A 
                       2 
                     
                     ⁡ 
                     
                       ( 
                       
                         
                           i 
                           = 
                           1 
                         
                         , 
                         2 
                       
                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     Although the example about the two images was shown here, the same processing can be also used even when using three or more images. From the features such as a scattered light distribution, the intensity, etc. of these extracted defect candidates, the defect determination and the sorting and sizing are carried out in a sorting and sizing processing part  2015 .