Abstract:
To process a signal from a plurality of detectors without being affected by a variation in the height of a substrate, and to detect more minute defects on the substrate, a defect inspection device is provided with a photoelectric converter having a plurality of rows of optical sensor arrays in each of first and second light-collecting/detecting unit and a processing unit for processing a detection signal from the first and the second light-collecting/detecting unit to determine the extent to which the positions of the focal points of the first and the second light-collecting/detecting unit are misaligned with respect to the surface of a test specimen, and processing the detection signal to correct a misalignment between the first and the second light-collecting/detecting unit, and the corrected detection signal outputted from the first and the second light-collecting/detecting unit are combined together to detect the defects on the test specimen.

Description:
BACKGROUND 
       [0001]    The present invention concerns a method of detecting a minute defect occurred on a test specimen and a device therefor, and more particularly relates to a defect inspection method suitable for detecting a minute defect occurred on a semiconductor wafer with a fine pattern formed on its surface and a device therefor. 
         [0002]    A semiconductor wafer is made more and more multi-layered in structure as the shape of a pattern to be formed on the wafer is more and more refined with high-integration of a circuit, and the number of producing steps thereof is being steadily increased. In order to stably produce a highly reliable high-integrated circuit by surely forming the fine pattern on the wafer, it becomes important to confirm that the fine pattern is surely formed and a defect such as a foreign matter or the like does not occur by inspecting the wafer on which the pattern is formed. 
         [0003]    As a means for inspecting the wafer with the pattern formed thereon, there exist, for example, a pattern inspection device of light-field-based optical system (a light-field pattern inspection device), a defect inspection device of dark-field-based optical system (a dark-field defect inspection device) and others. 
         [0004]    Although the applications of the light-field pattern inspection device and the dark-field inspection device are different from each other in general, the dark-field defect inspection device has such a feature that throughput of inspection is higher than that of the light-field pattern inspection device. 
         [0005]    In such a dark-field defect inspection device as mentioned above, how a more minute defect is to be detected at a higher speed without being affected by light scattered from the pattern formed on the wafer is one of problems. 
         [0006]    As a means for solving this problem, in Japanese Patent Application Laid-Open No. 2000-105203 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2001-512237 (Patent Document 2), there is a description that a wafer is obliquely irradiated with linear illumination light which is finely squeezed in one direction and light which has been scattered from a surface of the wafer with the linear illumination light is detected by a detection system above the wafer and detection systems disposed on its both sides while continuously moving the wafer in a direction orthogonal to a longitudinal direction of the illumination light, thereby detecting a defect on the wafer by using respective detection signals. 
         [0007]    In addition, in Japanese Patent Application Laid-Open No. 2010-256340 (Patent Document 3), there is a description that a TDI (Time Delay Integration) sensor is used in a detection system and it is configured to asynchronously control a line rate of the TDI sensor and a stage scan speed to illuminate an object to be inspected with finely squeezed linear light so as to make only an arbitrary pixel line of the TDL sensor receive scattered light from the inspected object such that an aspect ratio of the size of a detection pixel can be controlled with a speed ratio of the line rate of the TDI sensor to the stage scan speed, thereby making inspection possible at a scan speed higher than the line rate of the TDI sensor. 
         [0008]    Further, in Japanese Patent Application Laid-Open No. 2010-190722 (Patent Document 4), there is a description that a wafer is obliquely irradiated with linear illumination light which is finely squeezed in one direction, light which has been scattered upward from a surface of the wafer with the linear illumination light is collected while continuously moving the wafer in a direction orthogonal to a longitudinal direction of the linear illumination light and is branched in accordance with a state of polarization, light transmitted through a spatial filter is detected by filtering diffracted light and scattered light from a normal pattern by the arrayed spatial filter, thereby detecting a defect independently of polarization characteristics of scattered light from the defect. 
       SUMMARY 
       [0009]    In order to efficiently detect the more minute defect and to classify the kind of the detected defect, a method of detecting it by separating a scattering orientation by utilizing scattering characteristics which are different depending on the kind of the defect can be conceived of. That is, by arranging detectors in a plurality of places and processing and combining together signals detected at the respective places, it becomes possible to actualize a signal that scattered light from a more minute defect which would be buried in noise in detection from one direction has been detected and it becomes possible to more finely classify the kind of the detected defect. 
         [0010]    That the scattered light from the defect is detected by arranging the detectors in a plurality of directions as mentioned above is described in Patent Documents 1 and 2. In the configurations of the inspection devices described in FIG. 25 of Patent Document 1 and in FIG. 2 of Patent Document 2, the plurality of detectors are arranged obliquely relative to a normal direction of a substrate. 
         [0011]    In the configurations described in Patent Documents 1 and 2, linear illumination light is irradiated to the substrate and scattered light from the substrate is detected while moving a stage with the substrate placed thereon in a direction perpendicular to a longitudinal direction of the linear illumination at a fixed speed. It is known that positional variations such as pitching (a vertical variation) and yoking (a lateral variation) occur on a table when the stage is moved at the fixed speed. Misalignment occurs in position on the substrate surface to be detected by the detectors arranged in different azimuth directions due to a variation in the height of the substrate caused by the pitching in these, and mutual positional misalignment occurs between signals that the same pattern formed on the substrate surface has been detected by the respective detectors. This becomes remarkable when detecting a more minute defect of about several tens nm or less. 
         [0012]    However, in the inventions described in Patent Documents 1 and 2, nothing is considered with respect to positional misalignment of detection signals among the plurality of detectors which occurs with the variation in the height of the substrate. 
         [0013]    In addition, in Patent Documents 3 and 4, that the defect on the substrate is detected by arranging the plurality of detectors in the different azimuth directions is not described. 
         [0014]    An object of the present invention is to provide defect inspection method and device therefor making it possible to detect a more minute defect on a substrate by processing signals from a plurality of detectors which are arranged in plurality directions without being affected by the variation in the height of the substrate. 
         [0015]    In order to solve the above-mentioned problem, in the present invention, in a defect inspection device including a stage unit which is movable at least in one direction with a test specimen placed thereon, a light irradiation unit which irradiates the test specimen placed on the stage unit with linearly shaped light from a direction inclined relative to a normal direction of a surface of the stage on which the test specimen is placed, a first light collecting/detecting unit which collects and detects light reflected/scattered in a first direction from the test specimen irradiated with the linearly shaped light by the light irradiation unit, a second light collecting/detecting unit which collects and detects light reflected/scattered in a second direction from the test specimen irradiated with the linearly shaped light by the light irradiation unit, a processing unit which processes a detection signal output from the first light collecting/detecting unit and a detection signal output from the second light collecting/detecting unit to detect a defect on the test specimen and a control unit for controlling the stage unit, the light irradiation unit, the first light collecting/detecting unit, the second light collecting/detecting unit and the processing unit, each of the first light collecting/detecting unit and the second light collecting/detecting unit has a photoelectric converter provided with a plurality of optical sensor arrays, the processing unit obtains misalignment of a focal position of the first light collecting/detecting unit relative to a surface of the test specimen by using detection signals from the plurality of optical sensor arrays of the first light collecting/detecting unit, obtains misalignment of a focal position of the second light collecting/detecting unit relative to the surface of the test specimen by using detection signals from the plurality of optical sensor arrays of the second light collecting/detecting unit, corrects the detection signal output from the first light collecting/detecting unit and the detection signal output from the second light collecting/detecting unit in accordance with the obtained misalignment of the focal position of the first light collecting/detecting unit and the obtained misalignment of the focal position of the second light collecting/detecting unit, combines together the detection signal output from the first light collecting/detecting unit and the detection signal output from the second light collecting/detecting unit which have been corrected to detect the defect on the test specimen. 
         [0016]    In order to solve the above-mentioned problem, in the present invention, in a defect inspection device including a stage unit which is movable at least in one direction with a test specimen placed thereon, alight irradiation unit which irradiates the test specimen placed on the stage unit with linearly shaped light from a direction inclined relative to a normal direction of a surface of the stage on which the test specimen is placed, a first light collecting/detecting unit which collects and detects light reflected/scattered in a first direction from the test specimen irradiated with the linearly shaped light by the light irradiation unit, a second light collecting/detecting unit which collects and detects light reflected/scattered in a second direction from the test specimen irradiated with the linearly shaped light by the light irradiation unit, a processing unit which processes a detection signal output from the first light collecting/detecting unit and a detection signal output from the second light collecting/detecting unit to detect a defect on the test specimen and a control unit which controls the stage unit, the light irradiation unit, the first light collecting/detecting unit, the second light collecting/detecting unit and the processing unit, each of the first light collecting/detecting unit and the second light collecting/detecting unit has a photoelectric converter provided with a plurality of optical sensor arrays, the control unit controls the stage unit to continuously move the stage unit in the first direction and controls the photoelectric converter of the first light collecting/detecting unit and the photoelectric converter of the second light collecting/detecting unit to detect reflected and scattered light from the test specimen irradiated with the linearly shaped light by the light irradiation unit in synchronization with movement of the stage unit, and the control unit further controls the processing means to process detection signals output from the photoelectric converter of the first light collecting/detecting unit and the photoelectric converter of the second light collecting/detecting means at a timing different from the synchronization with movement of the stage unit and to combine together the detection signals which have been output from the photoelectric converter of the first light collecting/detecting unit and the photoelectric converter of the second light collecting/detecting unit and have been processed at the timing different from the synchronization, thereby detecting a defect like the test specimen. 
         [0017]    Further, in order to solve the above-mentioned problem, in the present invention, a defect inspection method is configured by while moving a stage with a test specimen placed thereon in one direction, irradiating a surface of the test specimen with linearly shaped light which is long in a direction rectangular to the one direction that the stage moves from a direction inclined relative to a normal direction of the surface of the test specimen, collecting and detecting light reflected/scattered in a first direction from the surface of the test specimen irradiated with the linearly shaped light by a first light collecting/detecting unit provided with a plurality of optical sensor arrays, collecting and detecting light reflected/scattered in a second direction from the surface of the test specimen irradiated with the linearly shaped light by a second light collecting/detecting unit provided with a plurality of optical sensor arrays, obtaining misalignment of a focal position of the first light collecting/detecting unit relative to the surface of the test specimen by using detection signals from the plurality of optical sensor arrays and output from the first light collecting/detecting unit and obtaining misalignment of a focal position of the second light collecting/detecting unit relative to the surface of the test specimen by using detection signals from the plurality of optical sensor arrays and output from the second light collecting/detecting unit, correcting the detection signal output from the first light collecting/detecting unit and the detection signal output from the second light collecting/detecting unit in accordance with the misalignment of the focal position of the first light collecting/detecting unit and the misalignment of the focal position of the second light collecting/detecting unit which have been so obtained, and combining together the detection signal output from the first light collecting/detecting unit and the detection signal output from the second light collecting/detecting unit which have been so corrected to detect a defect on the test specimen. 
         [0018]    Still further, in order to solve the above-mentioned problem, in the present invention, a defect inspection method is configured by while moving a stage with a test specimen placed thereon in one direction, irradiating a surface of the test specimen with linearly shaped light which is long in a direction rectangular to the one direction that the stage moves from a direction inclined relative to a normal direction of the surface of the test specimen, collecting and detecting light reflected/scattered in a first direction from the surface of the test specimen irradiated with the linearly shaped light by a first light collecting/detecting unit having a plurality of optical sensor arrays in synchronization with movement of the stage in the one direction, collecting and detecting light reflected/scattered in a second direction from the surface of the test specimen irradiated with the linearly shaped light by a second light collecting/detecting unit having a plurality of optical sensor arrays in synchronization with movement of the stage in the one direction and processing detection signals output from a photoelectric converter of the first light collecting/detecting unit and a photoelectric converter of the second light collecting/detecting unit at a timing different from the synchronization with the movement of the stage and combining together the detection signals output from the photoelectric converter of the first light collecting/detecting unit and the photoelectric converter of the second light collecting/detecting unit which have been processed at the timing different from the synchronization to detect a defect on the test specimen. 
         [0019]    According to the present invention, it becomes possible to process the detection signals of the plurality of detectors by combining them together without being affected by the variation in the height direction of the substrate under inspection and therefore it becomes possible to detect more minute defect. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a block diagram explaining the principle of an embodiment 1 of the present invention. 
           [0021]      FIG. 2  is a plan view showing a schematic configuration of an optical system of the embodiment 1 of the present invention. 
           [0022]      FIG. 3A  is a front view showing the schematic configuration of the optical system of the embodiment 1 of the present invention. 
           [0023]      FIG. 3B  is a front view showing a schematic configuration of an illumination optical system of the embodiment 1 of the present invention. 
           [0024]      FIG. 3C  is a front view showing a schematic configuration of a detection optical system of the embodiment 1 of the present invention. 
           [0025]      FIG. 4  is a block diagram of the detection optical system, explaining misalignment in detection position on a sensor caused by AF misalignment. 
           [0026]      FIG. 5  is a block diagram showing a configuration of an image processing means concerning the embodiment 1 of the present invention. 
           [0027]      FIG. 6  is a plan view of a wafer and an enlarged diagram of a chip formed on the wafer. 
           [0028]      FIG. 7  is a graph showing an example that signal feature amounts of defect candidates detected by three detection optical systems of the embodiment 1 of the present invention are plotted in a three-dimensional space. 
           [0029]      FIG. 8  is a graph showing a profile of illumination and a PSF (Point Spread Factor) of the detection system when assuming that a pixel size is infinitesimal. 
           [0030]      FIG. 9A  is a block diagram of the detection optical system, explaining misalignment in detection position occurring by AF misalignment on an obliquely arranged sensor. 
           [0031]      FIG. 9B  is a graph showing the PSF of the detection system when taking a beam profile of linear illumination light and the pixel size into account. 
           [0032]      FIG. 10  is a sectional diagram of a semiconductor wafer with a pattern formed thereon. 
           [0033]      FIG. 11A  is a block diagram of the detection optical system showing a relationship between the obliquely arranged sensor and reflected/scattered light from a test specimen in the embodiment 1 of the present invention. 
           [0034]      FIG. 11B  is a graph showing a relationship between the beam profile of the linear illumination light and the PSF of the illumination system in the embodiment 1 of the present invention. 
           [0035]      FIG. 11C  is a graph showing a relationship between the beam profile of the linear illumination light and the PSF as a system that an amount of misalignment from the center of the illumination system is corrected in the embodiment 1 of the present invention. 
           [0036]      FIG. 12  is a graph showing a relationship between the resolution of a linear illumination system alone and the resolution of the illumination system in the embodiment 1 of the present invention. 
           [0037]      FIG. 13A  is a graph showing sensor outputs when reflected/scattered light from a repeated pattern on a test specimen has been detected in the presence of AF misalignment in the embodiment 1 of the present invention. 
           [0038]      FIG. 13B  is a graph showing a sensor output when reflected/scattered light from a repeated pattern on a test specimen has been detected in the presence of AF misalignment in detection by a conventional TDI sensor. 
           [0039]      FIG. 14A  is a graph showing output waveforms of each sensors in a case where the AF misalignment has occurred when using a two-stage sensor in the embodiment 1 of the present invention. 
           [0040]      FIG. 14B  is a graph showing sensor outputs when reflected/scattered light from a repeated pattern on a test specimen has been detected in the presence of the AF misalignment in the embodiment 1 of the present invention. 
           [0041]      FIG. 15  is a block diagram showing a configuration of a height misalignment information calculation unit in the embodiment 1 of the present invention. 
           [0042]      FIG. 16  is a block diagram explaining the principle of an embodiment 2 of the present invention. 
           [0043]      FIG. 17A  is a graph showing a beam profile of linear illumination light and pixel-array-based PSFs of a TDI sensor in the embodiment 2 of the present invention. 
           [0044]      FIG. 17B  is a graph showing the beam profile of the linear illumination light and a PSF as a system that outputs from each pixels of the TDI sensor are misaligned by a predetermined amount and are added together in the embodiment 2 of the present invention. 
           [0045]      FIG. 18  is a graph showing outputs from the TDI sensor when reflected/scattered light from a repeated pattern on a test specimen has been detected in the presence of the AF misalignment in the embodiment 2 of the present invention. 
           [0046]      FIG. 19  is a block diagram showing a configuration of an image processing means according to the embodiment 2 of the present invention. 
           [0047]      FIG. 20  is a diagram plotting arrangement of defect candidates from outputs of the TDI sensor, explaining a method of correcting an AF misalignment amount of outputs of the TDI sensor in the image processing means according to the embodiment 2 of the present invention. 
           [0048]      FIG. 21  is a block diagram explaining the principle of an embodiment 3 of the present invention. 
           [0049]      FIG. 22  is a block diagram showing a configuration of a height misalignment information calculation unit in the embodiment 3 of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0050]    In the following, embodiments of the present invention will be described using the drawings. 
       Embodiment 1 
       [0051]    A first embodiment of the present invention will be described using  FIGS. 1 to 22 . 
         [0052]      FIG. 1  is a diagram explaining the principle of the present embodiment. In the present embodiment, illumination light  116  is squeezed in one direction by a lens unit  101  so as to be shaped into light which is parallel in a direction perpendicular to it and is obliquely irradiated to a surface of a test specimen  150  with a fine pattern formed. In inspection, the test specimen  150  is moved by a later described stage means at a fixed speed in an arrow direction. 
         [0053]      102  is a detection optical system which collects light reflected/scattered in a direction of the detection optical system  102  in reflected/scattered light from the test specimen  150  irradiated with the linearly shaped illumination light  116  and forms an image of a linearly irradiated region of the test specimen  150  on detection element arrays  104 ,  105  of a detector  115 . 
         [0054]    In the detector  115 , there are a two-stage sensor (two-dimensional CCD or Dual Line Sensor)  103  having the detection element arrays  104 ,  105  and respectively providing read out registers  106  and  107  for reading out signals for them, switches  108  and  109  for switching outputs from the read out registers  106  and  107  of the two-stage sensor in accordance with a moving direction of the test specimen  150 , A/D conversion units  109  and  110  for converting analog signals simultaneously output from the read out registers  106  and  107  into digital signals, an FIFO (First In First Out) memory  111  for temporarily storing the digital signal output from the A/D converter  110  and outputting it in timing with the digital signal output from the A/D converter  109 , and an adder  113  for adding together and outputting an output signal from the FIFO memory  111  and the output signal from the A/D converter  109 ,  112  is a height misalignment information calculation unit for obtaining information on height misalignment of the test specimen  150  by using the output signal from the A/D converter  109  and the output signal from the A/D converter  110 .  114  is an image processing unit for receiving an output signal from the detector  115  to detect a defect on the test specimen  150 . 
         [0055]      FIG. 2  is a plan view showing a configuration of an optical system of a defect inspection device according to the present embodiment. In the optical system of the defect inspection device according to the present invention, a light source  206  and the lens unit  101  for linearly shaping the illumination light  116  emitted from the light source  206  into a beam are provided on the side of an illumination optical system. The light source  206  emits ultraviolet laser such as UV light, DUV light or the like. On the other hand, the detection optical system  102  is configured by being provided with a first oblique detection optical system  102 A and a first detector  115 A, an upward detection optical system  102 B and an upward detector  115 B, and a second oblique detection optical system  102 C and a second detector  115 C. Output signals from the first detector  115 A, the upward detector  115 B and the second detector  115 C are input into the image processing unit  114  and are processed. 
         [0056]    In addition, the defect inspection device according to the present embodiment is provided with a height detection unit for detecting the height of the surface of the test specimen  150 . The height detection unit is configured by a light source unit  201  for emitting a plurality of linear light patterns  207 , a light collecting lens  202  for collecting and radiating the linear light patterns  207  emitted from the light source unit  201  to the surface of the test specimen  150  from a direction inclined relative to a normal direction of the test specimen  150 , a light collecting lens  203  for collecting reflected light (regularly reflected light) from the test specimen  150  irradiated with the plurality of linear light patterns  207  and a photo-detector  204  for detecting the reflected light so collected, and a height detection unit  205  for receiving and processing a signal that the reflected light from the test specimen  150  has been detected by the photo-detector  150  to extract height information of the test specimen  150 . 
         [0057]      FIG. 3A  is a front view showing a configuration of an inspection optical system  100  of the defect inspection device according to the present embodiment.  303  is a Z-stage which is movable in a height direction,  304  is an X-stage which is movable in an X direction,  305  is a Y-stage which is movable in a Y direction perpendicular to a paper surface, and movements thereof are respectively controlled by a stage control means  302 . The test specimen  150  is placed on the Z-stage  303 . In the configuration shown in  FIG. 3 , each of the first oblique detection optical system  102 A, the upward detection optical system  102 B and the second oblique optical system  102 C is provided with an objective lens  1021 , a spatial filter  1022 , a focusing lens  1023 , a polarizing filter  1024 , and an imaging lens  1025 , and shields a diffracted light pattern by diffracted light which is generated by radiating light to a fine repeated pattern on the test specimen  105  by the spatial filter  1022  and images reflected/scattered light transmitted through the spatial filter  1022  by the imaging lens  1025  on a detection surface of the detector  115  as shown in  FIG. 3C . Since the configuration shown in  FIG. 3C  is common to the first oblique detection optical system  102 A, the upward detection optical system  102 B and the second oblique detection optical system  102 C, notation of the last A, B, C of the respective constitutional components are omitted. 
         [0058]    In addition, a configuration of the illumination optical system side is shown in  FIG. 3B . The illumination optical system is provided with the light source  206  for emitting a laser beam and the lens unit  101 . The lens unit  101  is provided with a beam expander  1011  for expanding a diameter of the laser beam emitted from the light source  206 , a collimator lens  1012  for collimating the diameter-expanded laser, a polarizing plate  1013  for adjusting a polarized state of the laser, a light amount adjusting unit  1014  for adjusting a light amount, a condenser lens  1015 , and a cylindrical lens  1016  for condensing the diameter-expanded laser beam in one direction and shaping it into linear light which is maintained in a parallel state in a direction perpendicular to it. 
         [0059]      301  is a general control unit for controlling the light source  206  on the illumination side, the light source unit  201  of the height detection unit, and the stage control means  302  and receives outputs from the image processing unit  114  and the height detection unit  205  to output a result of inspection of the test specimen  150 . 
         [0060]    In the configurations shown in  FIG. 2  and  FIG. 3 , in inspection, the x-stage  304  is controlled by the stage control means  302  to move it in one direction at a constant speed, and detection signals are output from the first detector  115 A, the upward detector  115 B and the second detector  115 C in synchronization with movement of the X-stage  304 . When inspection up to an end on the test specimen  150  is completed by moving the X-stage  304 , the Y-stage  305  is controlled by the stage control means  302  to shift the inspection region of the test specimen  150  to the next inspection region. Next, the X-stage  304  is controlled by the stage control means  302  to move it at a constant speed in a reverse direction (a −x direction) to the one direction. The entire surface of the test specimen  150  can be inspected by repeating the above moving. 
         [0061]    When driving the X-stage  304  to move the test specimen  150  in the X direction or the X direction at the constant speed as mentioned above, a variation in the height in the vertical direction which is called pitching occurs on the X-stage  304 . In addition, the variation in the height in the vertical direction also occurs by two-dimensional deflection of the test specimen. When such a variation in the height occurs on the X-stage  304  during inspection, incident angles of the light reflected/scattered from the surface of the test specimen  150  and incident upon the first oblique detection optical system  102 A and the second oblique detection optical system  102 C are changed as shown in  FIG. 4  and misalignment in the position for receiving the reflected/scattered light from the surface of the test specimen  150  occurs on respective light receiving surfaces of the first detector  115 A and the second detector  115 C. On the other hand, no misalignment occurs on a light receiving position for light reflected/scattered from the test specimen  105  and incident upon the upward detector  115 B. 
         [0062]    In practice, the stage control means  302  is controlled by the general control unit  301  on the basis of height information of the surface of the test specimen  150  detected by the height detection unit configured by the light source unit  201  to the height detection unit  205  shown in  FIG. 2  or  3 , and thereby the position (the height) is adjusted in the Z-axis direction of the Z-stage  303 . However, misalignment (AF (Auto Focus) misalignment) in a height direction occurs due to offset of adjustment, a time-lag and the like. If signals from the respective detectors are combined together and processed in a state the AF misalignment occurring, an image will become blurred by the amount of the AF misalignment and as a result accuracy in defect detection will be degraded. 
         [0063]    As a method of reducing the AF misalignment, there exists a method of narrowing the line width of the linear illumination light to illuminate the test specimen  150 . However, as described later, the influence of the AF misalignment cannot be sufficiently reduced simply by narrowing the line width of the illumination light and the influence of the AF misalignment on the accuracy in detection cannot be sufficiently eliminated and will be left behind. 
         [0064]      FIG. 5  is a block diagram showing a configuration of the image processing means  114 . 
         [0065]    From the signal output from the first detector  115 A in synchronization with movement of the X-stage  304  in the X direction, a signal  509 A which is output from the adder  113  and is addition of outputs from the two detection element arrays  104  and  105  is branched into two and one of them is input into a buffer memory designated by  501 A.  501 A is the FIFO type buffer memory which outputs an image which delays integral multiples of a die. Incidentally, among them, noise reduction can be promoted by superposing images which are away from each other by a plurality of dies.  511 A is a first position alignment processing unit which detects positional misalignment between images which are away from each other by integral multiples of the die and outputs the branched two images such that positional misalignment does not occur and inputs them into a differentiator  502 A. A signal that patterns of the same shape on the test specimen  150  have been detected or a signal that patterns in the same regions of adjacent dies on the test specimen  150  have been detected and which has been input into the buffer memory  501 A in advance is used as a reference signal, a difference with the reference signal is calculated (cell comparison or die comparison), and a calculated differential image signal  503 A is input into a second position alignment circuit unit  504 A. In addition, in outputs from the first detector  115 A, an output signal  510 A from the height misalignment information calculation unit  112  is also input into the position alignment circuit unit  504 A, correction of the amount of height misalignment is performed on the separately input differential image signal  503 A, and an image of the defect candidate is output. 
         [0066]    Similarly, respective signals which have been output from the upward detector  115 B and the second detector  115 C in synchronization with movement of the X-stage  304  in the x direction are processed, difference images  505 B,  505 C (images of the defect candidates) which have been corrected by the amount of height misalignment by position alignment circuit units  504 B and  504 C are extracted and are input into an integration determining unit  506 . In the integration determining unit  506 , the difference images  505 A to  505 C (the images of the defect candidates) which have been corrected by the amount of the height misalignment are integrated to generate one image. The image generated by the integration determining unit  506  is compared with a threshold value by a threshold value determination unit  507 , and a defect signal  508  which has been extracted as a result of comparison is output to the general control unit  301 . 
         [0067]      FIG. 6  visibly shows die comparison to be executed by the differentiators  502 A to  502 C. A plurality of dies (chips)  600  are formed on a semiconductor wafer which is the test specimen  150  and patterns  601  to  605  of the same shape are formed on corresponding places on the respective dies. In the differentiators  502 A to  502 C, for example, an image of a die pattern  603  is compared with an image of a die pattern  604  formed on the chip adjacent to the chip on which the die pattern  603  is formed and is used as reference image to calculate a difference image between the both images is calculated. 
         [0068]      FIG. 7  shows an example that image characteristic amounts extracted from the respective defect candidate images which have been output from the respective position alignment circuit units  504 A to  504 C, to which the respective difference images are input from the respective position alignment circuit units  504 A to  505 C, to be executed by the combination determination unit  506  are plotted in a three-dimensional space. When the image characteristic amounts of the defect candidates are plotted in the three-dimensional space as mentioned above, although the characteristic amounts of images of parts which are not true candidates are distributed densely on the center, the characteristic amount of an image including a defect is present at a part separated from the distribution of the difference images calculated from an image of a normal part. Therefore, the true defect can be detected by integrating the images of the defect candidates obtained from the respective detectors, plotting them in the three-dimensional space as shown in  FIG. 7  and extracting outliers. 
         [0069]    However, in order to accurately detect the defect by integrating the images of the defect candidates obtained from the respective detectors and plotting features extracted from the integrated images in a multi-dimensional space as shown in  FIG. 7 , it is essential that positional misalignment of the defect candidate obtained from each detector be corrected, that is, the alignments of the defect candidates obtained from the respective detectors match one another. However, it is extremely difficult to align the images of, for example,  115 A to  115 C with one another by using a generally performed image matching technique. Because detection conditions of the respective images are different from one another and therefore patterns appeared on the respective images are different from one another. 
         [0070]      FIG. 8  is a graph that a profile  801  of illumination and a profile  802  of the detection system relative to a stage scanning direction are plotted. Here, in calculation of the profile  801  of the illumination, it is assumed that a beam width is 1.8 μm, the illumination is oblique illumination and the intensity of the illumination exhibits the Gaussian distribution. In addition, in calculation of the profile  802  of the detection system, assuming that scattered light by the Fraunhofer diffraction is generated from the pattern on the test specimen  150  by taking a case where detection is performed through an optical system which is arranged in a direction inclined by 45 degrees relative to the normal direction of the test specimen and is 0.5 in NA (Numerical Aperture) with the pixel size of the detector made infinitesimal as an example, a Point Spread Function (PSF) d(x) of the optical system is obtained by (Numerical Formula 1). 
         [0000]    
       
         
           
             
               
                 
                   
                     
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         [0071]    where 
         [0072]    λ: wavelength 
         [0073]    χ: distance from center 
         [0074]    θ: detection system angle from test specimen normal direction 
         [0075]    From the graph in  FIG. 8 , it is shown that the illumination of the oblique illumination system relatively spreads out when compared with the PSF of the detection system and a sufficient resolution of the image cannot be obtained simply by the illumination system relative to the stage scanning direction. In order to promote improvement of resolution of the device, it is effective to improve the resolution of the detection system. 
         [0076]    Although a case where calculation is performed by making the pixel size of the detector infinitesimal is shown on the graph in  FIG. 8 , in actual, the pixel of the detector has a finite size. Therefore, in a case where calculation is performed by setting the pixel size of the detector  115 C to 2.5 μm for later described reasons and other conditions are set as in the case in  FIG. 8  as shown in  FIG. 9A , the result is as shown by a graph in  FIG. 9B . 
         [0077]    Here, assuming that misalignment of ±0.5 μm has occurred with the AF misalignment as shown in  FIG. 9A  because the test specimen  150  is continuously moved in the X direction and the height of the surface of the test specimen  150  is varied, the pixel size of the detector  115 C which is required to allow the AF misalignment of ±0.5 μm when light of 1.8 μm in beam width has been irradiated should be 1.8+1.0/sqrt(2)=2.5 μm on the wafer. 
         [0078]    The PSF of the detection system at that time is obtained by convolution of the PSF of the detection system as expressed by the (Numerical Formula 1) and pixel size as expressed by (Numerical Formula 2), and exhibits characteristics as shown in  FIG. 9B . 
         [0000]    
       
         
           
             
               
                 
                   
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         [0079]    where 
         [0080]    P is the pixel size 
         [0081]    In the graph shown in  FIG. 9B , the resolution of the detection system is worsened in comparison with that of the illumination system shown in  FIG. 8 . That is, it is found from the graph in  FIG. 9B  that in a case where the detector having the finite pixel size is used in such a simple configuration as shown in  FIG. 9A , the resolution of the illumination light in the beam line width direction (the stage moving direction) is determined by the resolution of the illumination system. 
         [0082]      FIG. 10  shows an example that a fine pattern  1004  is formed on a lower layer, an optically transparent thin film  1002  such as a silicon dioxide (SiO2) film or a silicon nitride (SiN) film is formed thereon, and a pattern  1007  is formed on a surface as the test specimen  150 . In a case where illumination light having such a beam profile as denoted by  1001  has been irradiated to the test specimen  150  having such a sectional structure, the illumination light is transmitted through the optically transparent film  1002 , is reflected/scattered by the lower-layer fine pattern  1004  and is transmitted through the optically transparent film  1002  turning to light having such a beam profile as denoted by  1003 , and it interferes with incident light, resulting in such a distribution characteristic as denoted by  1008 . 
         [0083]    In a case where the test specimen  150  has such a structure that the influence of the reflected light from the base pattern is no negligible, it occurs that the resolution of the illumination system is lowered in appearance. 
         [0084]    In order to avoid occurrence of such a phenomenon as mentioned above, it is necessary to improve the resolution of the detection system. In order to improve the resolution of the detection system, it is found that it is effective to reduce the pixel size of the detection system as apparent from comparison between  FIG. 8  and  FIG. 9B . 
         [0085]      FIG. 11A  shows a state that similarly to the configuration shown in  FIG. 9A , two pixels  104  and  105  are arranged and the size thereof is set to 1.25 μm which is one half of that in the case in  FIG. 9A . It shows a state that the positions of a region to be irradiated with illumination light on the test specimen  150  and the pixels of the detection system are adjusted such that the center of the beam irradiated to the test specimen  150  is projected onto the middle between the two pixels  104  and  105 . 
         [0086]    A beam profile of the illumination light and distributions of reflected/scattered light detected by the respective pixels  104  and  105  in the configuration shown in  FIG. 11A  are shown in FIG.  11 B. 
         [0087]    At that time, a profile  1101  of the illumination is expressed by (Numerical Formula 3) 
         [0000]    
       
         
           
             
               
                 
                   
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         [0088]    where 
         [0089]    w: line width of illumination 
         [0090]    On the other hand, the PSF when the pixel size of the detection system is made infinitesimal is expressed by (Numerical Formula 4). 
         [0000]    
       
         
           
             
               
                 
                   
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         [0091]    However, in actual, the pixel of the detection system has a finite size and when taking this into account, the PSF of the detection system is expressed by ((Numerical Formula 5). 
         [0000]      PSF( x )=1( x )(rect(( x ±α)/ p )1( x ))  (Numerical Formula 5)
 
         [0092]    p: pixel size in the stage moving direction 
         [0093]    α:p/2 
         [0094]    Here, assuming that 2S is a moving amount of the stage synchronizing with acquisition of images of one line of the detection system having a multi-stage line sensor, in a case where i(x) obtained by the numerical formula 3 is almost constant, a shift amount can be set to ½ of the pixel size as in the case where it is detected by a general multi-stage line sensor (for example, a TDI sensor (Time Delay Integration sensor)). However, when the beam profile  1101  is made steeper by more finely squeezing the width of the illumination light, the shift amount is not determined by the pixel size, but it is determined by the beam profile of the illumination light and the resolution of the detection system to be expressed as shown by (Numerical Formula 6). 
         [0000]    
       
         
           
             
               
                 
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         [0095]    While in a generally used TDI sensor, the shift amount which is denoted by s is ½ of the pixel size, when the configuration of the present invention is adopted, s becomes smaller than ½ of the pixel size. This is almost equivalent to that the pixel size as the system is reduced and even in a case where a large pixel size is used, a high resolution can be obtained. In this situation, in a case where the moving amount is moved by the amount equal to the pixel size on the test specimen as in the case where the general TDI sensor is utilized, the resolution of the pixel is degraded. 
         [0096]      FIG. 11C  shows a graph that the PSF as the system is plotted by superposing with the beam profile of the illumination light. In this case, the FSF as the system is obtained by adding the distributions of the reflected/scattered light detected by the respective pixels  104  and  105  by shifting them by the shift amount from the center obtained on the basis of (Numerical Formula 6) (the above shifting means controlling by the general control unit  301  to make it synchronize with movement of the X-stage  304  in the X-direction so as to let the multistage line sensor  103  have a time delay relative to a synchronous signal for detecting the reflected/scattered from the test specimen  150 ). It is seen from this result that the resolution of the detection system is greatly improved comparing to the case shown in  FIG. 9B . 
         [0097]      FIG. 12  shows a graph that superposes the characteristics of the resolution attained by thinning the illumination light and the characteristics of the resolution of the present embodiment in which the resolution of the detection system has been improved by using the two-stage line sensor for the thinned illumination light. 
         [0098]    It can be seen that the resolution is improved by adopting the detection system using the two-stage line sensor according to the present embodiment. 
         [0099]      FIG. 13A  shows a result of the simulation of sensor outputs in a case where the AF misalignment is occurring and in a case where the AF misalignment is not occurring when test patterns are illuminated with thinned light by the optical system as shown in  FIG. 11A  using the two-stage line sensor. Results of the simulation of a sensor output  1302  free from the AF misalignment, a sensor output  1301  when the AF misalignment of −0.5 μm is occurring, and a sensor output when the AF misalignment of +0.5 μm is occurring are shown. It can be seen that the detection signal greatly varies by the AF misalignment. While this variation range 6 of the signal is ±0.5/sqrt(2)=±0.35 (μm) when adding them by reducing the shift amount of the image to one half of the pixel size by the conventional manner using the two-stage sensor as shown in  FIG. 11A , the variation range δ can be reduced down to 0.18 μm when setting the shift amount of the image of the two-stage sensor to the value calculated by using (Numerical Formula 5) (the line width of illumination: 1.5 μm, the pixel size: 1.25 μm) as in the present embodiment. 
         [0100]    On the other hand,  FIG. 13B  shows a result of the simulation of a sensor output in a case where the AF misalignment which is the same as that in the case shown in  FIG. 13A  has occurred when using the conventional detection system that the pixel size is 2.5 μm as shown in  FIG. 9A . In this case, since the pixel size is large enough to cover the variation amount of beam position caused by the AF misalignment, no change occurs in the position of the pattern to be detected regardless of occurrence of the AF misalignment. However, since the pixel size is large in the case in  FIG. 13B , the sensitivity of defect detection is reduced in comparison with the case in  FIG. 13A . 
         [0101]      FIG. 14A  shows output waveforms from the pixel arrays  104  and  105  of the two-stage sensor  103  in occurrence of the AF misalignment. As described in  FIG. 11A , the positions of the region to be irradiated with the illumination light on the test specimen  150  and the pixels of the detection system are adjusted such that the center of the beam which has been irradiated to the test specimen  150  in the absence of the AF misalignment is projected onto the middle between the two pixels  104  and  105 . When the AF misalignment occurs for the so adjusted detection system and the central position of the beam on the sensor surface is displaced, an output level of a signal  1401  output from the pixel array  104  and a level of a signal  1402  output from the pixel array  105  of the two-stage sensor  103  are changed. This change in signal level corresponds to the AF misalignment amount. 
         [0102]      FIG. 14B  shows an output waveform  1403  from the pixel array  104  and an output waveform  1404  from the pixel array  105  when the reflected/scattered light from the repeated pattern formed on the test specimen  150  is detected by the two-stage sensor  103  when the X-stage  304  moves to scan the beam on the test specimen  150  in a state that the AF misalignment is occurring. Since a constant difference is generated in the signal level between the output waveform  1403  and the output waveform  1404  as shown, it is possible to estimate the AF misalignment amount by adding the output signals from the pixel array  104  and output signals from the pixel array  105  over a certain scan range of the X-stage  304 . The addition of the output signals from the pixel array  104  and the output signals from the pixel array  105  over the certain scan range of the X-stage  304  is executed by the height misalignment information calculation unit  112  shown in  FIG. 1 . 
         [0103]      FIG. 15  shows a configuration of the height misalignment information calculation unit  112 .  1503  and  1504  are signal adders. A signal  1501  output from the A/D converter  109  is added by the signal adder  1503  and a signal  1502  output from the A/D converter  110  is added by the signal adder  1504  when the X-stage  304  is moving in one direction at a constant speed. Added signals output from the signal adder  1503  and the signal adder  1504  are respectively input into a processing unit  1505  and are normalized by, for example, dividing a signal value output from the signal adder  1503  with a signal value output from the signal adder  1504 . A result of normalization is compared with data in a look-up table (LUT) for recording a relationship between an AF misalignment amount which has been set in advance and a normalized value in a comparison unit  1506 , and thereby the AF misalignment amount is obtained. 
         [0104]    As shown in  FIG. 5 , information  510 A to  510 C on the AF misalignment mounts obtained by the height misalignment information calculation unit  112  is sent to the image processing unit  114  and correction of the amount of height misalignment is performed on the difference images  503 A to  503 C output from the differentiators  502 A to  502 C using the respective pieces of AF misalignment amount information in the position alignment circuit units  504 A to  504 C. Incidentally, in a case where  102 A and  102 C are symmetrically arranged, height misalignments detected with  510 A and  510 C mutually match in principle. Thus, getting more stable results in the calculation of the AF misalignment amount is possible by calculating an average of the height misalignment amounts detected with  510 A and  510 C, inputting it into  504 A and  504 C and using it. In addition, getting further more stable results in the calculation of the AF misalignment amount is possible by performing time-based average processing on the signals of  510 A and  510 C by taking a feature that the AF misalignment amount is not greatly varied in a short period of time into account. In addition, in a case where  102 B is arranged with no inclination, misalignment of images does not occur even when the AF misalignment has occurred. Therefore,  510 B and  504 B may be eliminated from  FIG. 5 . 
         [0105]    The difference images  505 A to  505 C subjected to correction of the amount of height misalignment are sent to the integration determining unit  506  and are integrated to generate a three-dimensional vector image. The image generated by the integration and determination unit  506  is sent to the threshold value determination unit  507  in which, then, an image characteristic amount is extracted from each of the defect candidates, an isolated defect candidate is extracted. The isolated defect candidate is separated, by exceeding a previously set threshold value, from a characteristic amount region where the defect candidates are densely present in the characteristic amounts of the defect candidates which are plotted in the three-dimensional space as described in  FIG. 7 . The extracted defect signal  508  is output to the general control unit  301 . 
         [0106]    As described above, according to the present embodiment, it becomes possible to perform synthetic processing on the images obtained by imaging from different directions after performing correction of the amount of the AF height alignment, and thereby the defect can be detected with higher sensitivity and the accuracy in classification of the detected defect can be improved. 
       Embodiment 2 
       [0107]    While in the embodiment 1, the example that the two-stage sensor  103  is adopted for the detector  115  is shown, in the present embodiment, an example that a three-stage TDI sensor  1604  is used in place of the two-stage sensor  103  will be described. A configuration of the defect inspection device in the present embodiment is basically the same as that shown in  FIGS. 2 and 3 , and configurations of the detectors  115 A to  115 C and configurations or operations of parts of the image processing unit  114  and the general control unit  301  are different from those described in the embodiment 1. 
         [0108]      FIG. 16  is a diagram explaining the principle of the embodiment 2. The illumination light emitted from a light source (not shown) is squeezed by the lens  101  in one direction (in the X-direction in the case in  FIG. 16 ), is shaped into light which is parallel in a direction perpendicular to it and is obliquely irradiated onto the test specimen  150 . At that time, the test specimen  150  is being moved by the X-stage  304  at a constant speed in the X-direction. Light directed toward the detection optical system  102  among the reflected/scattered light from the test specimen  150  which has been irradiated with the illumination light  116  is collected by the detection optical system  102  and is imaged on pixel arrays  1601 ,  1602 ,  1603  which are arranged on a light receiving surface of a TDI sensor  1610  of a detector  1615 . Signals detected by the pixel arrays  1601 ,  1602 ,  1603  are output from a downstream side read out register  1604  or  1605  and are input into an A/D converter  1612  by a change-over switch  1611 . 
         [0109]    The output signal from the TDI sensor  1610  which has been converted from an analog signal into a digital signal by the A/D converter  1612  is input into and processed by an image processing unit  1614 , and thereby a defect on the test specimen  150  is detected. 
         [0110]    Since, from the TDI sensor  1610 , the signals detected by the respective pixel arrays  1601 ,  1602 ,  1603  are sequentially integrated and output from the read out register  1604  or  1605 , the output signals are equally affected by the AF misalignment and therefore a circuit corresponding to the height misalignment information calculation unit  112  of the detector  115  in the embodiment 1 is not needed. 
         [0111]    In  FIG. 17A , together with the profile  1101  of the section in the line width direction of the linearly shaped illumination light  116 , a result of calculation of the PSF for each of the pixel arrays  1601 ,  1602 ,  1603  when the reflected/scattered light from the test specimen  150  irradiated with the illumination light  116  has been detected by the TDI sensor  1610  in the absence of the AF misalignment is plotted as waveforms  1701 ,  1702 ,  1703  by superposing with the profile  1101  of the section of the illumination light. Incidentally, calculation was made by setting the pixel size of each of the pixel arrays  1601 ,  1602 ,  1603  of the TDI sensor  1610  in the X-stage scanning direction to 0.833 μm. 
         [0112]    Outputs from the TDI sensor  1610  can be continuously processed by setting the shift amount of the image detected by the pixel array  1601  and the pixel array  1602  and the shift amount of the image detected by the pixel array  1602  and the pixel array  1603  to the same amount by setting the number of stages of the TDI sensor  1610  to three. In addition, s when using the three-stage TDI sensor, that is, ½ of the moving amount of the stage synchronized with acquisition of the image of one line of the detection system can be calculated by setting α in (Numerical Formula 6) to the pixel size p in the stage moving direction. Also, in this case, s becomes a value smaller than ½ of the pixel size. As in the case in the embodiment 1, if the moving amount of the stage synchronized with acquisition of the image of one line is made equal to the pixel size in the stage moving direction on the test specimen similarly to the case of utilizing the general TDI sensor in this situation, the resolution of the image will be degraded. 
         [0113]    In the present embodiment, the case where the number of stages of the pixel arrays of the TDI sensor  1610  is set to three has been described. However, since an image shift amount between adjacent pixel arrays is made different between the central part and the peripheral part with four or more stages of pixel arrays, it becomes impossible to continuously process the outputs from the TDI sensor  1610 . Therefore, as for the number of stages of the TDI sensor  1610 , two or three stages are suitable. 
         [0114]      FIG. 17B  shows a graph that a PSF  1704  as a system resulting from addition of the PSF waveforms of the respective pixel arrays  1601 ,  1602 ,  1603  of the TDI sensor  1610  by shifting them by the shift amount obtained on the basis of (Numerical Formula 5) is plotted by superposing with the beam profile  1101  of the illumination light. From this result, it can be seen that the PSF of the detection system is improved in comparison with the profile of the illumination light. 
         [0115]      FIG. 18  shows a result of the simulation of outputs of the TDI sensor  1610  in the case where the AF misalignment is occurring and in the case where the AF misalignment is not occurring when test patterns is illuminated with thinned light by the optical system similar to that shown in  FIG. 11A  by using the three-stage TDI sensor  1610 . It shows the result of the simulation of a sensor output  1802  in the absence of AF misalignment, a sensor output  1801  when the AF misalignment of −0.5 μm is occurring, and a sensor output  1803  when the AF misalignment of +0.5 μm is occurring. It can be seen that the detection signal is greatly varied with occurrence of the AF misalignment. As for the variation range δ of the signal, in a case where the shift amount of the image of the TDI sensor is set to the value calculated by using (Numerical Formula 5) as in the present embodiment (the line width of illumination; 1.5 μm, the pixel size: 1.25 μm), the variation range 6 can be reduced down to ±0.21 μm. Although this is slightly large when compared with the case in the embodiment 1, it is greatly improved when compared with a conventional system that the line width of illumination is wide. 
         [0116]      FIG. 19  shows a configuration of the image processing unit  1614  of the defect inspection device in the embodiment 2. Although it is similar to the configuration in the embodiment 1 described in  FIG. 5 , there is no inputting of signals corresponding to the output signals  510 A- 510 C from the height misalignment information calculation unit  112  described in  FIG. 5 . 
         [0117]    In the configuration shown in  FIG. 19 , one of the signals branched from an output  1613 A from a first detector  1615 A is input into the buffer memory  501 A, and position alignment is performed by the first position alignment processing unit  511 A as described in  FIG. 5 . The other branched signal is input into the differentiator  502 A. A signal input in the buffer memory  501 A in advance which is a signal that is obtained by detecting patterns of the same shape on the test specimen  150  or a signal that is obtained by detecting patterns in the same regions of the adjacent dies on the test specimen  150  is set as a reference signal. Then a difference between the other branched signal and the reference signal is calculated (cell comparison or die comparison). A calculated difference image  1901 A is compared with a first threshold value signal level which has been set in advance in a temporary defect determination unit  1902 A, and a pseudo defect is removed from the difference image  1901 A. A signal  1903 A from which the pseudo defect signal has been removed is input into an AF misalignment calculation unit  1904 . 
         [0118]    An output  1613 B from a second detector  1615 B and an output  1613 C from a third detector  1615 C are similarly processed, are compared with the first threshold value signal level which has been set in advance in a temporary defect determination units  1902 B and  1902 C, and signals  1903 B and  1903 C from which the pseudo defect signal has been removed are input into the AF misalignment calculation unit  1904 . 
         [0119]    A method of obtaining the AF misalignment amount in the AF misalignment calculation unit  1904  will be described using  FIG. 20 . In  FIGS. 20 ,  2001  and  2006  designate positions of defect candidates detected by the first detector  1615 A,  2002  and  2004  designate positions of defect candidates detected by the second detector  1615 B, and  2003  and  2007  designate positions of defect candidates detected by the third detector  1615 C. Assuming that the defect candidates which are present in a comparatively short range have the same AF misalignment amount, the AF misalignment amount is estimated from coordinate information of the defect candidates among which a corresponding relationship is best (in the case in  FIGS. 20 ,  2001 ,  2002  and  2003 ). Then, height misalignment among the signals  1903 A to  1903 C from which the pseudo defect signal has been removed is corrected using information on the estimated AF misalignment amount. The signals  1905 A to  1905 C corrected in height misalignment by the AF misalignment calculation unit  1904  are input into a integration determining unit  1906 , are combined into a three-dimensional vector differential image which is, then, compared with a threshold value which has been set in advance by a threshold value determination unit  1908  to extract a defect therefrom. Information  1909  on the extracted defect is output to the general control unit  301 . 
         [0120]    According to the present embodiment, it becomes possible to perform synthetic processing after performing correction of the amount of the AF height misalignment on the images obtained by imaging from different directions, and therefore the defect can be detected with higher sensitivity and the accuracy in classification of the detected defect can be improved. 
       Embodiment 3 
       [0121]    In the present embodiment, a system for determining the AF misalignment on the basis of a pattern to be detected is shown  FIG. 21 . The configuration of the defect inspection device according to the present embodiment is basically the same as the configuration shown in  FIGS. 2 and 3  in the embodiment 1, and only parts of the configurations of the detectors  115 A to  115 C are different from the configurations and operations described in the embodiment 1. In the embodiment 1, the two-stage sensor  103  is adopted in the detector  115  and the misalignment between detection positions caused by the AF misalignment has been calculated by the height misalignment information calculation unit  112 . The height misalignment information calculation unit  112  has calculated the height by evaluating the contrast ratio calculated from the signal output from the A/D converter  109  and the signal output from the A/D converter  110  as shown in  FIG. 15 . 
         [0122]    On the other hand, in the present embodiment, as shown in  FIG. 21 , the AF misalignment is calculated by using a height misalignment information calculation unit  2101  in place of the height misalignment information calculation unit  112 . In the configuration shown in  FIG. 21 , the two-stage sensor  103  is the same as that described in the embodiment 1 using  FIG. 1 . In addition, switches  2108  and  2109  switch the outputs from the read out registers  106  and  107  of the two-stage sensor  103  in accordance with the moving direction of the test specimen  150 . A signal  2102  output from an A/D converter  2109 , a signal  2103  output from an A/D converter  2110  and a signal  2104  added and synthesized by an adder  2113  are input into the height misalignment information calculation unit  2101 . 
         [0123]    Processing of the height misalignment information calculation unit  2101  will be described using  FIG. 22. 2201  is a low pass filter for restricting a high spatial frequency in the stage scanning direction shown by an arrow in  FIG. 21  relative to the signal of the signal  2104  added and synthesized by the adder  2113  to output a signal  2204 .  2203  is an adder for adding together the signal  2102  output from the A/D converter  2109  and the signal  2103  output from the A/D converter  2110  to output a signal  2205 . Since this signal  2205  is an image, the resolution of which is degraded in the stage scanning direction relative to the signal  2104  added and synthesized by the adder  2113 , the signal  2204  and the signal  2205  are extremely similar images. Therefore, the misalignment amount is calculated by pattern-matching the signal  2204  and the signal  2205  by a pattern matching unit  2202 . As for the signal  2205 , the position of the pattern is hardly changed with the AF misalignment. On the other hand, as for the signal  2204 , the position of the pattern is changed with the AF misalignment. Thus, it becomes possible to calculate the AF misalignment by obtaining the misalignment amount of the signal  2204  using the signal  2205  as a reference. 
         [0124]    The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 
       DESCRIPTION OF REFERENCE NUMERALS 
       [0000]    
       
         
           
               100  . . . inspection optical system,  101  . . . lens,  102 ,  102 A,  102 B,  102 C . . . detection optical system,  103  . . . two-stage sensor,  112  . . . height misalignment information calculation unit,  113  . . . adder,  114  . . . image processing unit,  115 ,  115 A,  115 B,  115 C . . . detector,  201  . . . light source unit,  202  . . . collecting lens,  203  . . . collecting lens,  204  . . . photo-detector,  205  . . . height detection unit,  301  . . . general control unit,  302  . . . stage control means,  303  . . . Z-stage,  304  . . . X-stage,  305  . . . Y-stage,  501 A,  501 B,  501 C . . . buffer memory,  502 A,  502 B,  502 C . . . differentiator,  504 A,  504 B,  504 C . . . position alignment circuit unit,  506  . . . integration determining unit,  507  . . . threshold value determination unit,  1610  . . . TDI sensor,  1614  . . . image processing unit,  1615  . . . detector,  1902 A,  1902 B,  1902 C . . . temporary defect determination unit,  1904  . . . AF misalignment calculation unit,  1906  . . . integration determining unit,  1908  . . . threshold value determination unit.