Abstract:
In inspecting a substrate having a transparent oxide film or a metal film formed on a surface thereof by using a dark field type inspection apparatus installing a laser light source, an illuminating beam having a high coherence causes variations in reflection strength due to multiple interferences within the transparent oxide film or an interference of scattered beams due to the surface roughness of the metal film occurs and which leads to degradation in the sensitivity of defect detection. The present invention solves the problem by providing a low-coherence but high-brightness illumination using a highly directive broadband light source, and a system in which the conventional laser light source is simultaneously employed to selectively use the light sources, thereby enabling a highly sensitive inspection according to the condition of a wafer.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an inspection technique of detecting defects on an inspection target on the surface of which a pattern is formed on the basis of image information obtained using a light beam, and particularly to an inspection technique of detecting fine defects in which a substrate with a pattern such as a semiconductor wafer is used as an inspection target. 
       BACKGROUND ART 
       [0002]    In a defect inspection for a substrate with a pattern, the sensitivity of defect detection is largely affected depending on how a detected light beam from defects can be detected while being distinguished from a detected light beam (background light noise) from a pattern or a base film. Especially, with advanced fine patterning, detection of finer defects is required in an inspection for a semiconductor wafer, and extracting a weak detected light beam from fine defects while being distinguished from background light noise is a major challenge in an inspection technique. 
         [0003]    Here, a vertical structure of a substrate with a pattern as an inspection target and the types of defects to be detected will be described in  FIG. 2  using a semiconductor wafer as an example. 
         [0004]    In  FIG. 2 , a vertical structure of a semiconductor device will be described using the reference numerals  20  to  35  and  201  to  251 , and defects as inspection targets will be described using the reference numerals  261  to  264 . 
         [0005]    The reference numeral  20  denotes an element separating layer with a structure ( 202 ) in which after digging grooves in a silicon (Si) substrate  201 , oxide silicon (SiO2) as an insulating material is embedded to electrically insulate and separate a transistor element formed on a wafer. The reference numerals  21  and  211  denote a gate and contact layer and a gate electrode portion made of polysilicon (poly-Si), respectively. This area largely affects the performance of the transistor, and is important in an inspection. The reference numeral  212  denotes a contact portion formed in such a manner that metal (tungsten: W and the like) is embedded into a hole formed on an insulating film (oxide silicon: SO2) by etching to connect the transistor portion to an upper wiring layer. The reference numerals  22  to  25  denote wiring layers by which circuits are formed. Each layer is embedded with an insulating film (oxide silicon: SiO2 and the like). The reference numeral  22  denotes a first wiring portion in which a first wiring portion  221  is used to be wired in a planar direction and a first via portion  222  is a portion formed in such a manner that metal is embedded into a hole formed on an insulating film (oxide silicon: SiO2 and the like) by etching to be connected to a further-upper wiring layer. Likewise, the reference numeral  23  denotes a second wiring layer in which the reference numerals  231  and  232  denote a second wiring portion and a second via portion, respectively. The reference numeral  24  denotes a third wiring layer in which the reference numerals  241  and  242  denote a third wiring portion and a third via portion, respectively. The reference numeral  25  denotes a fourth wiring layer in which the reference numeral  251  denotes a fourth wiring layer. In each wiring layer, material of the wiring portions is made of metal such as aluminum (Al) or copper (Cu). Further, the metal embedded into the via portions is made of tungsten (W) or copper (Cu). 
         [0006]    In addition, defects as inspection targets include scratches  261 , short-circuits  262  and disconnections  263  as pattern defects, and foreign particles  264 . 
         [0007]      FIG. 3  are explanatory diagrams of processes, materials, and typical defects in the respective layers of the semiconductor device shown in  FIG. 2 . The respective layers of the semiconductor device are formed by a material deposition process for forming each layer, resist pattern formation by a lithography process, an etching process to remove and process the deposited material in accordance with the formed resist pattern, and a CMP (Chemical Mechanical Polishing) process for flattening. 
         [0008]    For example, as an apparatus for optically inspecting a semiconductor wafer formed through the respective processes, Patent Literature 1 discloses a technique related to a semiconductor wafer defect inspection apparatus having an illumination system of white light sources in addition to an illumination system of laser light sources. 
         [0009]    Further, as a high-coherent broadband light source used for an illumination light source, there is a supercontinuum light source that generates broadband supercontinuum light (SC light) by allowing long and short pulse laser beams to enter a photonic crystal fiber (PCF) in which holes are periodically arranged in the cross-section of the optical fiber as disclosed in Non-patent Literature 1, or an optical frequency comb generator in which electrooptic crystal provided in a resonator is modulated with microwaves by an external transmitter and a single-wavelength laser beam is allowed to enter there to generate light beams with broadband and multi-wavelength spectrums at modulation frequency intervals of microwaves centered on the input single-wavelength laser beam as disclosed in Non-patent Literature 2. Further, as an example of a two-dimensional microshutter array that can be used for a spatial filter of an apparatus for optical inspection, Non-patent Literature 3 and Non-patent Literature 4 disclose a configuration in which thousands to tens of thousands of minute optical shutters having a size to of one to a few hundred of micrometers are arranged and integrated in the X-Y directions using an MEMS (Micro Electro Mechanical Systems) technique, so that each shutter can be individually controlled to be opened or closed. 
       CITATION LIST 
     Patent Literature 
       [0010]    Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2000-105203 
       Non-Patent Literature 
       [0011]    Non-patent Literature 1: J. K. Ranka, R. S. Windeler, A. J. Stentz, “Visible continuum generation in air-silica microstructure optical fibers with anomalous dispersion at 800 nm”, Optical Letter, Vol. 25, No. 1 (2000) 
         [0012]    Non-patent Literature 2: J. L. Hall, S. T. Cundiff, “Carrier-envelope phase control of femtosecond mode-locked lasers and direct optical frequency synthesis”, Science 288 (2000) 
         [0013]    Non-patent Literature 3: S. H. Moseley, “Microshutters Arrays for the JWST Near Infrated Spectrograph”, SPIE 7010 (2008) 
         [0014]    Non-patent Literature 4: Makoto, MITA, “MEMS scanner for two-dimensional scanning LIDAR”: TECHNICAL REPORT OF IEICE, Vol. 107, No. 365 (2007) 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0015]    There are various types of materials used for each layer of a semiconductor device and each process. In addition, there are many types of defects, as detection targets, such as foreign particles in a deposition process, foreign particles and pattern defects in a lithography process and an etching process for pattern formation, and foreign particles and scratches in a CMP process for polishing. 
         [0016]    As described in  FIGS. 2 to 3 , there are a wide variety of shapes and materials of patterns and defects as detection targets in the inspection for a semiconductor wafer. The inspection apparatus is configured to be able to set plural detection condition parameters so as to optimize the sensitivity of defect detection according to the shapes and materials. 
         [0017]    A dark-field optical-type defect inspection apparatus as described in Patent Literature 1 is configured not to collect a specular light beam from the substrate at the objective lens, but to collect a scattered light beam from defects. Further, the light beam collected by the objective lens after being diffracted and scattered from the pattern or base film formed on the substrate is received by the sensor while being suppressed by the polarization filter or the spatial filter. Accordingly, in an inspection image of the dark-field optical-type defect inspection apparatus, defects are exposed as bright spots against a dark background. Thus, if the resolution (the sensor pixel size on the surface of the substrate sample) of the image is rough (up to 1 μm), defects in the order of submicron smaller than the resolution can be detected. Because of this characteristic, the dark-field optical-type defect inspection apparatus is widely used in a production line of semiconductor devices as a high-speed/highly-sensitive inspection apparatus. 
         [0018]    On the other hand, the following problems are involved in the dark-field optical-type defect inspection apparatus. One is changes in sensitivity (reduction in sensitivity) of defect detection caused by changes in reflection intensity due to intramembranous multiple interference in an inspection for a wafer on the surface of which an oxide film (transparent film) is formed, and another is reduction in sensitivity of defect detection caused by an increase in background light noise due to interference of scattered light beams resulting from surface roughness (asperities or grains) of a metal film in an inspection for a wafer on the surface of which a metal film is formed. In a manufacturing process of a semiconductor wafer, an inspection is conducted mostly in a state where an oxide film is formed on the surface, a metal film is formed on the surface, or a metal film pattern is formed on an oxide film, as described in  FIGS. 2 and 3 . In addition, it has been strongly demanded to solve the above-described two problems. 
         [0019]      FIG. 4  is a diagram for explaining changes in sensitivity (reduction in sensitivity) of defect detection caused by changes in reflection intensity due to intramembranous multiple interference in an inspection for a wafer on the surface of which an oxide film (transparent film) is formed. In the drawing, the reference numerals  501 ,  502 , and  503  denote an oxide film deposited on a substrate, a defect on the oxide film, and a lower layer of the oxide film, respectively. The reference numeral  511  denotes illumination light beams (laser light beams) that include components  511   a  that directly illuminate the defect  502  on the oxide film, and components  511   b  that are reflected by the lower layer  503  after penetrating through the oxide film  501  to illuminate the defect  502 . Interference between the two illumination beams corresponds to the amount of light illuminating the defect  502 . Further, light beams scattered by the defect  502  include components  512   a  that directly enter an objective lens  521  to and components  512   b  that are reflected by the lower layer  503  after penetrating through the oxide film  501  to enter the objective lens. The result of interference between the scattered light components corresponds to the amount of light entering the objective lens. 
         [0020]    As described above, the amount of scattered light detected from defects is determined on the basis of the result of interference between illumination light beams and the result of interference between scattered light beams in the defect detection on the oxide film. The amount changes depending on the thickness t of the oxide film  501 . The thickness of the oxide film varies depending on the type of semiconductor device. In addition, the design thicknesses of the oxide films are different in the respective layers of the vertical structure described in  FIG. 2  even in devices of the same type. Further, the film thickness varies by about ±10% even in the same layer. The changes in the film thickness affect the amount of defect detection light, leading to changes in the sensitivity of defect detection. 
         [0021]      FIG. 5  is a diagram for explaining reduction in sensitivity of defect detection caused by an increase in background light noise due to interference of scattered light beams resulting from surface roughness (asperities or grains) of a metal film in an inspection for a wafer on the surface of which a metal film is formed. The reference numeral  601  denotes a metal film;  602 , surface roughness;  611 , an illumination light beam;  621 , an objective lens;  622 , an imaging lens; and  623 , a sensor. “w” indicates a range where a light beam from the substrate is received by one pixel of the sensor. There are plural concaves and convexes in the range of w, and the result of interference between scattered light beams  612   a  and  612   b  determines the amount of light reaching the sensor. If it is assumed that the amplitude of each of the scattered light beams  612   a  and  612   b  is A, the intensity of each light beam is A2, and the simple sum of the intensities is A2+A2=2A2. In the case where the light beams are intensified as a result of interference, the intensity of the light is (A+A)2=4A2, and the sensor receives more intensified light beams, resulting in an increase in background light noise. As a result, the sensitivity of defect detection is reduced. 
         [0022]    The above-described problems are involved in the dark-field optical-type defect inspection apparatus, and a technique for solving the problems has been demanded. As one means, disclosed is a technique of conducting an inspection with low-coherent broadband illumination (multi-wavelength illumination and white illumination). According to this means, the coherence of illumination light beams can be reduced by illuminating light beams with plural wavelengths at the same time, so that changes in the amount of detected light beam caused by optical interference described in  FIGS. 4 and 5  can be reduced. Specifically, changes in reflection intensity caused by intramembranous multiple interference can be reduced for a wafer on the surface of which an oxide film (transparent film) is formed. In addition, background light noise due to surface roughness (asperities or grains) of a metal film can be reduced for a wafer on the surface of which a metal film is formed, and the sensitivity of defect detection for these wafers can be improved. 
         [0023]    Patent Literature 1 discloses a technique related to a semiconductor wafer defect inspection apparatus including an illumination system of white light sources in addition to an illumination system of laser light sources. In the method described in Patent Literature 1, it is assumed to use lamps for the white light sources (broadband light sources). In this case, an illumination spot becomes larger in size as compared to that of laser illumination, and thus it is difficult to illuminate light beams with a high degree of brightness. Accordingly, it is necessary to make longer the exposure time (sampling time) of a sensor to obtain the necessary amount of detected light, and the inspection speed is disadvantageously decreased as compared to laser illumination. Further, an illumination system of broadband light sources needs to be additionally provided together with the laser illumination system. Thus, the system of the apparatus becomes disadvantageously complicated. 
       Solution to Problem 
       [0024]    The representative configurations of the present invention to solve the problems are as follows. 
         [0025]    Specifically, the present invention provides a defect inspection method including the steps of: selecting a high-coherent broadband light beam with a desired wavelength among those emitted from a high-coherent broadband light source; forming the selected high-coherent broadband light beam with the desired wavelength in a shape long in one direction; obliquely irradiating the selected high-coherent broadband light beam with the desired wavelength formed in the shape long in one direction onto an inspection target on the surface of which a pattern is formed; blocking a scattered light beam from the pattern formed on the inspection target among reflected scattered light beams from the inspection target onto which the selected high-coherent broadband light beam with the desired wavelength formed in the shape long in one direction is obliquely irradiated; capturing an image of a scattered light beam that has not been blocked among the reflected scattered light beams from the inspection target; generating an inspection image from a signal obtained by the captured image; and processing the generated inspection image to extract defects. 
         [0026]    Further, the present invention provides a defect inspection apparatus comprising: a broadband light source that emits high-coherent broadband light beams; wavelength selecting unit that selects a high-coherent broadband light beam with a desired wavelength among those emitted from the broadband light source; optical shape forming unit that allows the high-coherent broadband light beam with the desired wavelength selected by the wavelength selecting unit to be formed in a shape long in one direction; irradiation unit that obliquely irradiates the selected high-coherent broadband light beam with the desired wavelength formed in the shape long in one direction by the optical shape forming unit onto an inspection target on the surface of which a pattern is formed; light-collecting unit that collects reflected scattered light beams from the inspection target onto which the selected high-coherent broadband light beam with the desired wavelength formed in the shape long in one direction is obliquely irradiated by the irradiation unit; spatial filter unit that blocks a scattered light beam from a pattern formed on the inspection target among the reflected scattered light beams collected by the light-collecting unit; imaging unit that images an image of a scattered light beam that has not been blocked by the spatial filter unit among the reflected scattered light beams from the inspection target; inspection image generating unit that generates an inspection image from a signal obtained by imaging with the imaging unit; image processing unit that processes the inspection image generated by the inspection image generating unit to extract defects; and control unit that controls the entire apparatus. 
         [0027]    Furthermore, the present invention provides a defect inspection apparatus comprising: irradiation unit that obliquely irradiates a light beam onto an inspection target; detection optical unit that blocks a reflected scattered light beam from a pattern formed on the inspection target among those from the inspection target onto which the light beam is irradiated by the irradiation unit, and images an image of a reflected scattered light beam that has not been blocked; and image processing unit that processes the image of the scattered light beam obtained by imaging with the detection optical unit to extract defects of the inspection target, wherein the irradiation unit includes: a broadband light source that emits high-coherent broadband light beams; a wavelength selecting unit that selects a high-coherent broadband light beam with a desired wavelength among those emitted from the broadband light source; an optical shape forming unit that allows the high-coherent broadband light beam with the desired wavelength selected by the wavelength selecting unit to be formed in a shape long in one direction; and irradiation unit that obliquely irradiates the selected high-coherent broadband light beam with the desired wavelength formed in the shape long in one direction by the optical shape forming unit onto the inspection target on the surface of which a pattern is formed. 
       Advantageous Effects of Invention 
       [0028]    According to the aspects of the present invention, the above-described configurations enable to obtain effects in which the sensitivity of defect detection can be improved by reducing interference due to multiple interference of an oxide film and surface roughness of a metal film, the inspection speed same as that of a conventional system using laser illumination can be realized by high-brightness broadband illumination, and the above-described performance can be realized by a simple optical system. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0029]      FIG. 1A  is a block diagram for showing a basic configuration of a dark-field illumination-type semiconductor wafer defect inspection apparatus in a first embodiment. 
           [0030]      FIG. 1B  is a plan view of a semiconductor wafer for showing an illumination area on the semiconductor wafer by an illumination optical system of the dark-field illumination-type semiconductor wafer defect inspection apparatus in the first embodiment. 
           [0031]      FIG. 2  is a cross-sectional view for showing a vertical structure of a semiconductor device as an inspection target. 
           [0032]      FIG. 3(   a ) is a diagram in which respective layers of the semiconductor device are arranged in the order of manufacturing processes,  FIG. 3(   b ) is a flow diagram for showing a manufacturing process for each layer,  FIG. 3(   c ) shows materials associated with each layer, and  FIG. 3(   d ) is an explanatory diagram of typical defects in the manufacturing process for each layer. 
           [0033]      FIG. 4  is a cross-sectional view of the semiconductor wafer and an objective lens for explaining multiple interference caused by an oxide film (transparent film). 
           [0034]      FIG. 5  is a cross-sectional view of a metal film on the semiconductor wafer and a detection optical system for explaining interference of scattered light beams generated due to surface roughness of the metal film. 
           [0035]      FIG. 6(   a ) is a plan view of a micro-shutter array,  FIG. 6(   b ) is a cross-sectional view of an optical shutter for showing a state in which one optical shutter of the micro-shutter array is closed, and  FIG. 6  ( c ) is a cross-sectional view of the optical shutter for showing a state in which one optical shutter of the micro-shutter array is opened. 
           [0036]      FIG. 7A  is an enlarged perspective view of the semiconductor wafer for showing a state in which an illumination light beam hits irregular patterns formed on the semiconductor wafer and scattered light beams are generated from the irregular patterns. 
           [0037]    FIG.  7 B(a) shows an image of a pupil plane for showing a pattern of scattered light beams formed on the pupil plane of a detection optical system when illuminating a light beam with a single wavelength onto the semiconductor wafer of  FIG. 7A , FIG.  7 B(b) is a plan view of a light-blocking pattern of the micro-shutter array for light-blocking the pattern of the pupil plane of  FIG. 7B  (a), FIG.  7 B(c) shows an image of the pupil plane for showing a pattern of scattered light beams formed on the pupil plane of the detection optical system when illuminating light beams with two wavelengths onto the semiconductor wafer of  FIG. 7A , FIG.  7 B(d) is a plan view of a light-blocking pattern of the micro-shutter array for light-blocking the pattern of the pupil plane of  FIG. 7B  (c), FIG.  7 B(e) shows an image of the pupil plane for showing a pattern of scattered light beams formed on the pupil plane of the detection optical system when illuminating a light beam with a certain-width wavelength onto the semiconductor wafer of  FIG. 7A , and FIG.  7 B(f) is a plan view of a light-blocking pattern of the micro-shutter array for light-blocking the pattern of the pupil plane of FIG.  7 B(e). 
           [0038]      FIG. 8  is a block diagram for showing a basic configuration of a dark-field illumination-type semiconductor wafer defect inspection apparatus in a second embodiment. 
           [0039]      FIG. 9  is a block diagram for showing a basic configuration of a dark-field illumination-type semiconductor wafer defect inspection apparatus in a third embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0040]    Hereinafter, modes for carrying out the present invention will be described using the drawings. 
       First Embodiment 
       [0041]    An example of applying the present invention to a dark-field illumination-type semiconductor wafer defect inspection apparatus is shown in a first embodiment. A basic configuration of the semiconductor wafer inspection apparatus according to the embodiment will be described on the basis of  FIG. 1A . 
         [0042]    The semiconductor wafer inspection apparatus shown in  FIG. 1A  includes an illumination optical system  110 , a detection optical system  120 , an image processing unit  130 , a stage unit  140  on which a semiconductor wafer (substrate)  100  as a sample is mounted, and a control unit  150  that controls the entire apparatus. 
         [0043]    In the illumination optical system  110  of  FIG. 1A , the reference numeral  1112  denotes a high-coherent broadband light source. The illumination light source is switched between a laser light source  111  and the high-coherent broadband light source  1112  by a switching mirror  115  in accordance with a target and object of the inspection. 
         [0044]    The polarization of an illumination light beam  1110  of parallel light fluxes formed in such a manner that a light beam emitted from the light source  111  or  1112  penetrates through a collective lens group  112  is controlled by a polarization control element (wavelength plate or the like)  113 , and the amount of illumination light is controlled by a dimming filter  114  to enter a wavelength selecting element unit  116 . The illumination light beam with a predetermined wavelength having penetrated through the wavelength selecting element unit  116  is reflected by a mirror  117  so that the optical path is bent, and enters a cylindrical lens  118 . Then, while the parallel state of the illumination light beams is kept in one direction by the cylindrical lens  118 , the illumination light beam is collected in the other direction (direction orthogonal to the one direction) to illuminate an area  101  long in one direction of the substrate  100  as shown in  FIG. 1B . 
         [0045]    In this case, as the high-brightness and high-coherent broadband light source  1112 , a supercontinuum light source that generates broadband supercontinuum light (SC light) by allowing long and short pulse laser beams to enter a photonic crystal fiber (PCF) in which holes are periodically arranged in the cross-section of the optical fiber can be used as disclosed in Non-patent Literature 1. Alternatively, as disclosed in Non-patent Literature 2, an optical frequency comb generator in which electrooptic crystal provided in a resonator is modulated with microwaves by an external transmitter and a single-wavelength laser beam is allowed to enter there to generate light beams with broadband and multi-wavelength spectrums at modulation frequency intervals of microwaves centered on the input single-wavelength laser beam can be used. 
         [0046]    As described above, the high-brightness and high-coherent broadband light beam is used as an illumination light source, so that the multiple interference of an oxide film and interference due to the surface roughness of a metal film, as described in  FIG. 4  and  FIG. 5 , are reduced to improve the sensitivity of defect detection. In addition, the inspection speed same as that of a laser illumination system can be realized by the high-brightness broadband illumination, and a simple optical system can be realized. 
         [0047]    The wavelength selecting element unit  116  selects one of wavelength selecting elements  116 - 1  to  116 - 4  to be inserted into the optical path of the illumination light beam. Accordingly, when the broadband light source  1112  is used, only a specific wavelength can be selected for illumination. As settings, the followings are available: (1) use of all wavelengths, (2) use of specific one wavelength, (3) use of specific plural wavelengths, and (4) use of a specific wavelength band. Accordingly, a spatial filter can be used even when the broadband light source  1112  is used (to be described later using  FIG. 8 ). Alternatively, a wavelength with which the sensitivity of defect detection is optimized can be selected based on the fact that optical characteristics (refractive index and absorption coefficient) of material configuring an inspection target are changed depending on wavelengths. 
         [0048]    The collective lens group  112  collects the light beams generated from the light source on the inspection target to illuminate the same with a high degree of brightness. In this case, in order to be able to switch the illumination light source or to be able to correct changes in the light-collected position (focal position) due to the above-described wavelength selection, the collective lens group  112  is configured to include plural lens groups and to be provided with a movable mechanism, so that the inspection target can be illuminated with a high degree of brightness irrespective of the light source or the state of wavelength selection. 
         [0049]    The reference numeral  120  denotes the detection optical system, and an objective lens  121  collects reflected scattered light beams from defects or patterns existing in the area long in one direction of the semiconductor wafer  100  illuminated by the illumination optical system  110 . In a dark-field optical type, no specular light beams from the semiconductor wafer  100  enter the objective lens  121 , and light beams scattered by defects are collected as detection light to detect defects. Therefore, the illumination optical system  110  is required to illuminate with a high degree of brightness as described above. The reference numeral  124  denotes imaging lenses by which a detected image of the illuminated area long in one direction of the semiconductor wafer  100  is imaged on a sensor  125 . The reference numeral  122  denotes a polarization filter (polarization plate or the like) to filter specific polarization components from the detection light. The reference numeral  123  denotes a spatial filter that blocks regular diffracted light beams generated from patterns that are regularly formed on the semiconductor wafer  100 . Thus, background light noise generated at the time of detection can be reduced by the spatial filter to improve the sensitivity of defect detection. The image sensor  125  converts the detected optical image into an electric signal through photoelectric conversion. In general, an array sensor such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor is used. 
         [0050]    In the detection optical system  120 , the reference numeral  126  denotes a wavelength selecting element unit that includes plural wavelength selecting elements  126 - 1  to  126 - 4  as similar to the wavelength selecting element unit  116  in the illumination optical system  110 . The wavelength selection, such as (1) use of all wavelengths, (2) use of specific one wavelength, (3) use of specific plural wavelengths, and (4) use of a specific wavelength band, can be made on the detection optical system side. 
         [0051]    Further, in order to be able to switch the illumination light source or to be able to correct changes in the imaged position (focal position) due to the above-described wavelength selection, for example, the imaging lenses  124  are configured to include plural lens groups and to be provided with a movable mechanism (not shown) in the detection optical system  120 , so that an image of the focused inspection target can be formed on the whole area of the image sensor  125  irrespective of the light source and the state of wavelength selection. Further, the imaging lenses  124  may be provided with a zoom function to control imaging magnifications, so that the sensitivity of defect detection can be optimized. 
         [0052]    Furthermore, the detection optical system  120  includes a pupil plane observation optical system  127 . When observing a pupil plane, a mirror  128  that is detachable with respect to the optical axis of the detection optical system  120  is arranged on the optical axis of the detection optical system  120  to bend a light beam having penetrated through the imaging lenses  124  towards a monitor camera  129 . The monitor camera  129  is arranged at the position conjugate to the pupil plane of the detection optical system  120 , and observes the optical pattern of a reflected scattered light beam that is also formed on the spatial filter similarly arranged at the position conjugate to the pupil plane of the detection optical system  120  and is emitted from the pattern formed on the semiconductor wafer  100  onto which the illumination light beam  1110  is irradiated. The mirror  128  is shifted from the optical axis of the detection optical system  120  at the time of inspection to allow the light beam having penetrated through the imaging lenses  124  to reach the image sensor  125 . 
         [0053]    The image processing unit  130  converts an electric signal output from the image sensor  125  into image data, and detects defects by processing the image data such as comparing the image data with stored reference image data. 
         [0054]    The reference numeral  150  denotes the entire control unit that controls the illumination optical system  110 , the detection optical system  120 , the image processing unit  130 , and the stage  140 , and includes an input/output unit  151  that inputs processing conditions of the image processing unit  130  or outputs processing results. 
         [0055]    The substrate  100  is mounted on the stage  140 , and the entire surface of the substrate can be inspected by moving the stage in the X-Y-Z directions. 
         [0056]    It should be noted that there has been described a configuration in which the illumination optical system  110  is provided with the wavelength selecting element unit  116  and the detection optical system  120  is provided with the wavelength selecting element unit  126  in the above-described embodiment. However, any one of the wavelength selecting element unit  116  and the wavelength selecting element unit  126  may be provided. 
         [0057]    As described above, the dark-field optical-type defect inspection apparatus is configured not to collect a specular light beam from the substrate at the objective lens, but to collect a scattered light beam from defects. Further, the light beam collected by the objective lens after being diffracted and scattered from the pattern or base film formed on the substrate is received by the sensor while being suppressed by the polarization filter or the spatial filter. Accordingly, in an inspection image of the dark-field optical-type defect inspection apparatus, defects are exposed as bright spots against a dark background. Thus, if the resolution (the sensor pixel size on the surface of the substrate sample) of the image is rough (up to 1 μm), defects in the order of submicron smaller than the resolution can be detected. Because of this characteristic, the dark-field optical-type defect inspection apparatus is widely used in a production line of semiconductor devices as a high-speed/highly-sensitive inspection apparatus. 
         [0058]      FIG. 6  are explanatory diagrams of a two-dimensional microshutter array used for the spatial filter  123 . The microshutter array is formed in such a manner that thousands to tens of thousands of minute optical shutters having a size of one to a few hundred of micrometers are arranged and integrated in the X-Y directions using an MEMS (Micro Electro Mechanical Systems) technique as disclosed in Non-patent Literature 3 and Non-patent Literature 4, so that each shutter can be individually controlled to be opened or closed. 
         [0059]    The reference numeral  701  of  FIG. 6(   a ) denotes the entire two-dimensional microshutter array. Each grid serves as an optical shutter. 
         [0060]      FIGS. 6(   b ) and ( c ) are diagrams for explaining opening and closing states of one optical shutter, in which  FIG. 6(   b ) shows a closing state of the shutter and  FIG. 6(   c ) shows an opening state of the shutter. In each drawing, the reference numerals  711 ,  712 , and  713  denote a shutter body, a torsion bar for supporting the shutter, and a structure to keep the strength of the shutter array, respectively. As shown in  FIG. 6(   b ), the shutter is usually closed by the spring force of the torsion bar. Electromagnetic force or electrostatic force is generated at the structure  713  to attract the shutter  711  to the structure  713 , so that the shutter is opened as shown in  FIG. 6(   c ). 
         [0061]      FIG. 7A  shows an example of patterns formed on the surface of the inspection target and is a diagram for explaining diffracted light beams generated from the patterns. On the surface of an inspection target  801 , arranged are patterns  802  at pitches p 1  in the X direction and at pitches p 2  in the Y direction. As the pitch θ of the diffraction angle of a diffracted light beam when an illumination light beam  811  with a wavelength λ is irradiated onto the surface, sin θ 1  is equal to λ/p 1  in the X direction and sin θ 2  (not shown) is equal to λ/p 2  in the y direction. 
         [0062]      FIG. 7B  are diagrams each explaining a light-blocking state by the two-dimensional microshutter array.  FIG. 7B  are diagrams each explaining an image of the diffracted light beam at the spatial filter position (the pupil position of the detection optical system) of the detection optical system and a light-blocking state by the two-dimensional microshutter array. FIG.  7 B(a) shows a case of laser illumination or illumination by selecting specific one wavelength (λ 1 ) from the broadband light source with the wavelength selecting means. The reference numerals  820  and  821  denote the pupil of the detection optical system  120  and a diffraction image, respectively. The diffraction images are generated at equal intervals in the X-Y directions corresponding to the pitches represented by the above-described equations. In response to this, the light-blocking position of the two-dimensional microshutter array is shown by the reference numeral  831  as illustrated in FIG.  7 B(b). The light-blocking position of the two-dimensional microshutter array is determined in such a manner that the pupil plane of the detection optical system  120  is imaged by the camera  129  of the pupil plane observation optical system  127  to detect the optical pattern (FIG.  7 B(a)) of the reflected scattered light beam from the semiconductor wafer  100  in the pupil plane. Specifically, the two-dimensional microshutter array at the position corresponding to the detected optical pattern is driven by the entire control unit  150 , so that the light-blocking pattern of the two-dimensional microshutter array as shown in FIG.  7 B(b) can be formed. 
         [0063]    FIG.  7 B(c) shows a case of illumination by selecting specific two wavelengths (λ 1  and λ 2 ) from the broadband light source with the wavelength selecting means, and diffraction images  821  and  822  at different pitches corresponding to the respective wavelengths are generated. In response to this, the light-blocking position of the two-dimensional microshutter array is shown by the reference numeral  832  as illustrated in FIG.  7 B(d). Further, FIG.  7 B(e) shows a case of illumination by selecting a specific wavelength band (λ 1  to λ 2 ) from the broadband light source with the wavelength selecting means, and a diffraction image  823  corresponding to the wavelength band illuminated is generated. In response to this, the light-blocking position of the two-dimensional microshutter array is shown by the reference numeral  833  as illustrated in FIG.  7 B(f). 
         [0064]    As described above, even when a wavelength is selected using broadband illumination for a light source, the spatial filter can be allowed to effectively function by using the two-dimensional microshutter array for the spatial filter, and the sensitivity of defect detection can be improved. 
         [0065]    As in the embodiment, an inspection is conducted using a light source of low-coherent broadband illumination (multi-wavelength illumination and white illumination), so that the coherence of the illumination light beams can be reduced by illuminating light beams with plural wavelengths at the same time, changes in the amount of detected light beam caused by optical interference can be reduced, and changes in reflection intensity by intramembranous multiple interference can be reduced. Further, even for a wafer on the surface of which a metal film is formed, background light noise caused by the surface roughness (asperities or grains) of the metal film can be reduced by the two-dimensional microshutter array, and the sensitivity of defect detection for the wafer can be improved. 
       Second Embodiment 
       [0066]      FIG. 8  is an explanatory diagram of a second embodiment of the present invention. 
         [0067]    In addition to the configuration of the first embodiment of the present invention described using  FIG. 1 , an optical path branch mechanism  1211  (half mirror or the like) is provided on the objective lens  121  of a detection optical system  1201  in  FIG. 8 . While a first detection system includes optical systems  122  to  126  as similar to the case of the first embodiment, a second detection system branched at the optical path branch mechanism  1211  includes second optical filtering means (a polarization filter  1221 , a spatial filter  1231 , and a wavelength selecting element unit  1261 ), a second imaging lens  1241 , and a second image sensor  1251 . Further, the second optical filtering means of the second detection system can be controlled independently from the first optical filtering means (the polarization filter  122 , the spatial filter  123 , and the wavelength selecting element unit  126 ) of the first detection system. 
         [0068]    It should be noted that the spatial filter  1231  of the second detection system is provided at the pupil plane of the second detection system. 
         [0069]    In this configuration, the patterns of the pupil plane appearing at the positions of the spatial filter  123  and the spatial filter  1231  have the same shape. Thus, the pupil plane observation optical system  127  is provided in the first detection system as similar to the first embodiment, and the spatial filters  123  and  1231  are controlled by an entire control unit  1510  on the basis of the image of the pupil plane of the first detection system observed by the pupil plane observation optical system  127  to form the light-blocking pattern of the two-dimensional shutter array for each filter. 
         [0070]    Accordingly, two inspection images can be obtained at the same time by two image sensors  125  and  1251  under different optical conditions (for example, wavelength selecting elements with different characteristics are set in the wavelength selecting element unit  126  and the wavelength selecting element  1261  to select different wavelengths, or different polarization conditions are set in the polarization filter  122  and the polarization filter  1221 ). The two inspection images are processed by an image processing unit  1310 , so that defects can be determined on the basis of the amount of information greater than image processing with a single image, and the sensitivity of detection can be improved. 
       Third Embodiment 
       [0071]      FIG. 9  is a diagram for showing a configuration of a semiconductor wafer inspection apparatus in a third embodiment of the present invention. In the embodiment, in addition to the configuration of the semiconductor wafer inspection apparatus described using  FIG. 1  in the first embodiment, a second detection optical system  1202 , namely, a second objective lens  1212 , second optical filtering means (a polarization filter  1222 , a spatial filter  1232 , and a wavelength selecting element  1262 ), a second imaging lens  1242 , and a second image sensor  1252  are provided. The configuration and function of the illumination optical system  110  are the same as those described in the first embodiment. 
         [0072]    As similar to the second embodiment, the second optical filtering means can be controlled independently from the first optical filtering means (the polarization filter  122 , the spatial filter  123 , and the wavelength selecting element  126 ) of the first detection optical system  120 . 
         [0073]    In this configuration, the patterns of the pupil plane appearing at the positions of the spatial filter  123  and the spatial filter  1232  are different in the shape from each other. Thus, the first pupil plane observation optical system  127  is provided in the first detection system, and a second pupil plane observation optical system  1272  is provided in the second detection system. The spatial filter  123  is controlled by an entire control unit  1520  on the basis of an image of the pupil plane of the first detection system observed by imaging, using the monitor camera  129 , a reflected scattered light beam from the semiconductor wafer  100  bent by the mirror  128  of the pupil plane observation optical system  127  inserted in the optical path of the first detection system  120 . On the other hand, the spatial filter  1232  is controlled by the entire control unit  1520  on the basis of an image of the pupil plane of the second detection system observed by imaging, using a monitor camera  1292 , a reflected scattered light beam from the semiconductor wafer  100  bent by a mirror  1282  of the pupil plane observation optical system  1272  inserted in the optical path of the second detection system  1202 . Accordingly, the light-blocking pattern of the two-dimensional shutter array is formed for each of the spatial filter  123  and the spatial filter  1232 . 
         [0074]    Accordingly, two inspection images can be obtained at the same time by two image sensors  125  and  1252  under different optical conditions. The two inspection images are processed by an image processing unit  1320 , so that defects can be determined on the basis of the amount of information greater than image processing with a single image, and the sensitivity of detection can be improved. 
         [0075]    It should be noted that the optical axis of the first detection optical system is orthogonal to the surface of the inspection target and the optical axis of the second detection optical system is inclined relative to the orthogonal direction of the surface of the inspection target in  FIG. 9 . However, the present invention is not limited to this arrangement, but the optical axis may be inclined relative to the orthogonal direction of the surface of the inspection target in each of the first and second detection optical systems. 
         [0076]    Further, there has been described a configuration in which the illumination optical system  110  includes the laser light source  111  and the broadband light source  1112  to select one of the light sources using the switching mirror  115  in the above-described first to third embodiments. However, the present invention is not limited to this configuration, but only the broadband light source  1112  may be provided without using the laser light source  111  and the switching mirror  115 . 
         [0077]    In the above description, an inspection for a semiconductor wafer has been described as an example. However, the present invention is not limited to the above embodiments, but may be applied to an inspection method and an inspection apparatus for an inspection target on which patterns are formed. For example, the present invention can be applied to an inspection for substrates of flat panel displays (liquid crystal displays, plasma displays, organic EL displays, and the like) and storage products (DTM: discrete track media and BPM: bit pattern media) on which patterns are formed. 
       INDUSTRIAL APPLICABILITY 
       [0078]    While a substrate with a pattern such as a semiconductor wafer is used as an inspection target, the present invention can be used for an inspection apparatus that detects defects on the inspection target on the surface of which a pattern is formed on the basis of image information obtained using light beams. 
       REFERENCE SIGNS LIST 
       [0079]      100  . . . semiconductor wafer  110  . . . illumination optical system  111  . . . laser light source  1112  . . . high-coherent broadband light source  112  . . . collective optical system  113  . . . polarization control element  114  . . . dimming element  116  . . . wavelength selecting element unit  120  . . . detection optical system  121  . . . objective lens  122  . . . polarization filter  123 . . . spatial filter  124  . . . imaging lens  125  . . . image sensor  126  . . . wavelength selecting element unit  127  . . . pupil plane observation optical system  130  . . . image processing unit  140  . . . stage  150  . . . entire control unit