Patent Publication Number: US-2005122508-A1

Title: Method and apparatus for reviewing defects

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a method and apparatus for inspecting the defects occurring in semiconductor-manufacturing processes, and more particularly, to a method and apparatus suitable for closely reviewing defects using a scanning electron microscope.  
      In semiconductor-manufacturing processes, the presence of foreign particle on semiconductor substrate (wafer) causes insulation defect and short circuit defect of wiring. In addition, as semiconductor elements are followed on being formed super minute pattern, superfine foreign particles also cause insulation defects in capacitors and the destruction of gate oxide films or the like. These foreign particles enter in the semiconductor wafer in various states by various reasons (various causes) such as origination from the movable section of a transfer apparatus, origination from the human body, production by reaction inside a processing apparatus due to process gas usage, or entrainment in chemicals or materials. As the various states, scratches on semiconductor wafers, residues of a material and particles etc. can be mentioned, for example. On the result, these entered foreign particles A foreign substance will affect manufacturing throughput of the semiconductor elements.  
      It is therefore necessary to detect the defects that have occurred on semiconductor substrates in manufacturing processes, classify detected defects, immediately locate the sources of the defects, and prevent the occurrence of defects in great quantities.  
      The conventional methods of seeking for the causes of defects in this way comprises a step of identifying position of defects on the surface of the substrate by using an optical type of foreign particle inspection apparatus or an optical-type visual inspection apparatus and a step of presuming the cause of generating of the defect by using a review apparatus such as a scanning electron microscope (SEM). In the optical type of foreign particle inspection apparatus, the positions of defects on a semiconductor substrate are identified by illuminating dark-field illumination to the surface of the substrate and then detecting light scattered from foreign particles present on the substrate. In the optical-type visual inspection apparatus, the positions of defects on a semiconductor substrate are identified by detecting a bright-field optical image being generated from the substrate and then comparing this image with a reference image. Then, in the review apparatus, the step of presuming the cause of generating of the defect includes the steps of classifying the defects identified the position by reviewing in close the defect by the SEM and comparing this classified defect with the database.  
      These review methods are disclosed in Japanese Patent Laid-Open Nos. 2001-133417, 2003-7243, Hei 05-41194, and others.  
      During the detection of foreign particles on the surface of a semiconductor substrate using an optical type of foreign particle inspection apparatus, the surface of the semiconductor substrate is scanned and illuminated by increasing the spot size of the laser beam for illuminating the substrate surface in a dark field in order to increase inspection throughput. For this reason, large-error components are contained in the accuracy of the position coordinates calculated from the position of the laser beam spot scanning the surface of the semiconductor substrate.  
      If closely reviews based on the defect position information containing these large-error components are to be conducted using an SEM, the defect to be observed may not be covered in the image captured by the SEM used for reviewing at magnifications much higher than those of the optical-type foreign particle inspection apparatus. In such a case, although the intended defect is to be searched for by moving the visual field of the SEM in order for the defect to come into this field, the search requires a long time, resulting in SEM review throughput decreasing.  
      Also, in the method that uses an optical-type visual inspection apparatus, the semiconductor substrate to be inspected is illuminated in a bright field and then the image obtained by imaging is compared with a reference image to detect defects. However, if the surface of the semiconductor substrate is covered with an optically transparent film, the defects detected will be defects present in or under the optically transparent film, as well as those present on the film.  
      If it is going to review (observe) the defects in close by SEM based on position information of the defects detected by using the optical-type visual inspection apparatus, in SEM, since only the information on the surface of the sample is generally acquired, the defect that exists in or under the film detected with the optical-type visual inspection apparatus is undetectable. In such a case, there has been the problem that the SEM-aided review apparatus recognizes that the optical-type visual inspection apparatus has made errors in detection.  
     SUMMARY OF THE INVENTION  
      The present invention is a method and apparatus for conducting SEM-aided close reviews on the defects detected by using an optical type of foreign particle inspection apparatus or an optical-type visual inspection apparatus so that the detected defects can be reliably placed within the reviewing field of view of the SEM.  
      More specifically, an object of the present invention is to provide a defect-reviewing apparatus including: a detection optical system which detects a second position information of defects on a surface of a sample which a repetition pattern previously is formed and an optically transparent film is covered, on the basis of first position information of the defects on the sample that have been previously detected by using an external inspection apparatus; a position correcting unit which corrects the first position information of the defects on the sample, on the basis of the second position information of the defects detected by the detection optical system; a scanning electron microscope which reviews (observes) the defects on the sample that were detected by using the external inspection apparatus, on the basis of the position information of the defects corrected by the position correcting unit; a table (stage) which moves the sample whose defects are detected by the optical detection means, to the scanning electron microscope; and a vacuum chamber which provides the detection optical system and the scanning electron microscope in addition to the table included in an interior, the interior being exhausted into a vacuum state. In this configuration, the detection optical system includes: a bright-field image acquisition unit which acquires a bright-field image of the sample by conducting bright-field illumination; a dark-field image acquisition unit which acquires dark-field images of the sample by conducting sequential dark-field illuminations from plural directions different from one another in terms of incident angle; and an image-processing unit which detects the defects on the sample by processing the bright-field image acquired in the bright-field image acquisition unit or the dark-field images acquired in the dark-field image acquisition unit; wherein the image-processing unit is configured so that the defects on the sample can be detected, and a defect existing on the optically transparent film and a defect existing in or under the optically transparent film can be discriminated (identified), by processing the dark-field images obtained by the sequential dark-field illuminations to the sample.  
      Another object of the present invention is to provide a defect-reviewing method including the steps of: detecting by using a detection optical system, defects on a sample which a repetition pattern previously is formed and an optically transparent film is covered, on the basis of first position information of the defects on the sample that have been previously detected by using an external inspection apparatus; correcting the first position information of the defects on the sample, on the basis of the detected position information of the defects; and reviewing (observing) via a scanning electron microscope, the defects on the sample that were detected by using the external inspection apparatus, on the basis of the corrected position information of the defects. In this defect-reviewing method, during the step of detecting the second position information of defects on the basis of the first position information, the sample is illuminated in a dark field from plural directions different from one another in terms of incident angle, then the scattered light generated from the sample by the dark-field illumination of each of the plural directions is detected, and the signals obtained by detecting the scattered light in each of the plural directions are processed in order for the defects so as to discriminate (identify) a defect existing on a surface of the optically transparent film and a defect existing in or under the optically transparent film of the sample. Also, during the step of reviewing the defects via the scanning electron microscope, includes the step of reviewing (observing) the defect discriminated (identified) as the defect existing on the surface of the optically transparent film of the sample.  
      According to the present invention, when the defects detected with an optical type of extraneous substance inspection apparatus or an optical-type visual inspection apparatus are to be closely reviewed by using an SEM, it is possible to reliably move detected defects into the reviewing field of view of the SEM and thus to improve throughput in SEM-aided close reviewing of the defects.  
      These and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a front view showing a schematic configuration of an object surface defect inspection apparatus according to the present invention;  
      FIGS.  2 ( a ) and  2 ( b ) are schematic configuration diagrams explaining a configuration of the optical system for illumination, shown in  FIG. 1 ;  
       FIG. 3  is a layout diagram explaining the configuration of the optical system for illumination;  
       FIG. 4  is a schematic configuration diagram explaining a configuration of the optical system for detection, shown in  FIG. 1 ;  
      FIGS.  5 ( a ) to  5 ( c ) are diagrams explaining the spatial filters of the optical system for detection, shown in  FIG. 4 ;  
      FIGS.  6 ( a ) and  6 ( b ) are diagrams that explain processing intended to calculate defect coordinates from a detected image;  
       FIG. 7  is a diagram explaining a sectional profile of the defect image shown in FIGS.  6 ( a ),  6 ( b );  
       FIG. 8  is a block diagram explaining the signal-processing block shown in  FIG. 1 ;  
      FIGS.  9 ( a ) to  9 ( c ) are diagrams showing other embodiments of the optical system for illumination;  
      FIGS.  10 ( a ) and  10 ( b ) are diagrams that explain methods of illumination for detecting defects on a transparent film;  
      FIGS.  11 ( a ) and  11 ( b ) are configuration diagrams showing yet other embodiments of the optical system for illumination;  
      FIGS.  12 ( a ) to  12 ( c ) are configuration diagrams showing other embodiments of the defect detection devices shown in  FIG. 1 ;  
       FIG. 13  is a flow diagram of SEM reviewing the defects detected by the defect detection device shown in  FIG. 1 ; and  
      FIGS.  14 ( a ) and  14 ( b ) are block diagrams showing the whole configuration of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Embodiments of the present invention are described below using the accompanying drawings.  
      As shown in  FIG. 1 , the object surface defect inspection apparatus constructed according to the present invention includes: a transfer system  125  equipped with an XY stage  120  for resting and moving a substrate  100  to be inspected (such as any one of the wafers obtained from a variety of product types and manufacturing processes), and with a controller  80 , a dark-field illumination system  300  that sets the laser light L 1  emitted from a laser light source  30 , to a size via a beam diameter-changing element  33  and then provides irradiation from a diagonally upward direction of the substrate  100  via a retardation plate (½ λ plate) (what rotates the polarization direction 90 degrees)  35  and a mirror  38 , a defect detection device  140  that has a detection optical system  350  including objective lenses  13 , a beam splitter  20 , a first lens group  11 , a spatial filter  10 , a second lens group  12 , an optical filter  19 , and a light detector  15  such as a charge-coupled device (CCD), these system components being arranged above a table of the XY stage  120  for resting the substrate  100 , a signal processor  400  for detecting defects from the image signal that is output from the light detector  15  located inside the detection optical system  350 , and a whole control unit (a main control unit)  130  for conducting whole sequence control, the whole control unit  130  having an input/output unit  73  (including a keyboard and a network), a display unit  72 , and a storage unit  71 .  
      A scanning electron microscope (SEM)  110  with an electron beam axis  112  is provided at a position coaxial with the defect detection device  140  in a Y-direction thereof, and spaced from the defect detection device  140  by a distance of “d” in an X-direction thereof. The SEM  110  is an apparatus that irradiates an electron beam onto the substrate  100  to scan it and then to review (observe) images at high magnifications by detecting the secondary electron generated from the substrate. After another inspection apparatus has detected any defects on the substrate  100  and output defect map data to the SEM  110 , the SEM receives the defect map data as position information on the detected defects, via the input/output unit  73  (keyboard and network included). On the basis of the defect map data, the SEM  110  moves the XY stage  120  to a position almost matching the electron beam axis  112  of the SEM  110  in XY directions thereof. After this, a focus detection system  90  (in  FIG. 1 , only the light-projecting side is shown and the light-receiving side is omitted) detects a position on the substrate  100  in a Z-direction thereof, and the SEM  110  reviews (observes) each defect on the substrate  100  while the whole control unit  130  is controlling a focus of the electron beam in order to obtain a clear SEM image. A secondary-electron detector (not shown) includes, for example, an electron dispersive X-ray (EDX) analyzer, and a photo-electric converter provided so as to face a crossing point of the electron beam axis  112  and the substrate  100 .  
      Next, the dark-field illumination system  300  is described below using FIGS.  1  to  3 . The laser light L 1 , after being emitted from the laser light source  30 , passes through a shutter  31  opened or closed by the appropriate driving signal sent from the whole control unit  130 . Next, the laser light L 1  enters the inside of a vacuum chamber  150  through the beam diameter-changing element  33 , the retardation plate  35 , and a window  36 , and reflects at the mirror  38  or a mirror  39  (the two mirrors differ from each other in reflection angle), and is irradiated onto the surface of the substrate  100 . At this time, the light scattered from the defects on the surface of the substrate  100  reaches the detection optical system  350  having an optical axis  312 , and regularly reflected light reaches a light attenuator  37 . The light attenuator  37  is an optical element acting to cancel incident light by means of absorption, interference, and/or the like, and has a needle-like protrusion formed on the surface in order to acquire the incident light.  
      The beam diameter-changing element  33  is, as shown in FIGS.  2 ( a ),  2 ( b ), constituted by, for example, two groups of lenses,  33   a  and  33   b . The lens group  33   b  is driven in an optical-axis direction (X-direction) via a lens holder  41  by a motor  40  (e.g., a pulse motor) and a ball screw  42 . The lens group  33   b  is adapted to change an irradiation range by converging the pencil of laser light irradiated onto the surface of the substrate  100  to be inspected. That is to say, after a movable portion  45  of a positioning sensor provided at a front end of the lens holder  41  has detected a position of a home position sensor  46 , rotation pulses of the motor  40  are controlled via a controller not shown, by use of the driving signal sent from the whole control unit  130 .  
      Sensors  47  and  48  are limit sensors installed across the home position sensor  46 . An optical sensor, a magnetic sensor, or the like is usable as the positioning sensor. Successive operation of these sensors is controlled in accordance with a command from the whole control unit  130 . The illumination range is set synchronously with detection magnification selection of the detection optical system  350 . The illumination range is determined by beam diameter and the relationship in position of the lens group  33   b . Illumination range data is prestored within the whole control unit  130 , and can also be measured by providing a calibration plate (not shown) or the like on part of a resting table  122 .  
      The detection optical system  350  has an optical axis at a position spaced from the electron beam axis  112  of the SEM  110  by a distance of “d”, and the entire optical system is movable in a Z-direction by a Z-stage  61 . The Z-stage  61  moves in a Z-direction by rotation control of a motor  60  controlled by a control driving circuit  410 . The motor  60  is controlled via the control driving circuit  410  by the appropriate control signal sent from the whole control unit  130 . The detection optical system  350  and the vacuum chamber  150  are connected by a deformable coupling  50  and constructed so that even while the Z-stage is moving, the degree of vacuum inside the vacuum chamber is maintained.  
      That is, the detection optical system  350  includes, as shown in  FIG. 4 , a mirror  17 , objective lenses  13 , a beam splitter  20 , a first lens group  11 , a spatial filter  10 , a second lens group  12 , an optical filter  19 , and a light detector  15 . The detection optical system  350  detects the light L 3  scattered from a defect  55  present on the surface of the substrate  100  to be inspected. It is possible to use, as the laser light source  30 , a laser (or the like) that emits light of a single or white color falling within a visible or ultraviolet light region. The light detector  15  uses light-receiving elements having light-receiving sensitivity with respect to a wavelength of the light emitted from the laser light source  30 .  
      An exit window  14  is a transparent window provided between the objective lenses  13  and the mirror  17 , and the degree of vacuum inside the vacuum chamber  150  is maintained by a vacuum sealing material  16 . The defect-scattered light L 3 , after passing through the objective lenses  13 , passes through the beam splitter  20  and then reaches the light detector  15  via the first lens group  11 , the spatial filter  10 , and the second lens group  12 . The light detector  15  is, for example, a TDI sensor or CCD that has a one-dimensional or two-dimensional array of light-receiving elements (pixels), and has a function that changes a received-light accumulation time. The signal processor  400  then processes the electrical signal output from the light detector  15 , and processing results are sent to the whole control unit  130 .  
      The spatial filter  10  is disposed at a Fourier transformation position (equivalent to an exit pupil) of the objective lenses  13 , and shields the light reflected from the substrate  100  (e.g., a Fourier image due to reflected/diffracted light from a regular repetition pattern or the like). Such light becomes noise when defects or foreign particles are detected. For example, when a pupil-reviewing optical system  200  formed up of a mirror  201  retractable in a Y-direction during inspection, a projection lens  202 , and a TV camera  203 , is provided in an optical path of the detection optical system  350  and then a reflected/diffracted light image  501  (shown in  FIG. 5 ( a )) from a repetition pattern at the Fourier transformation position is acquired using the TV camera  203 , the spatial filter  10  shields luminescent spots  502  of the diffracted image by means of a light-shielding plate  510  having a rectangular light-shielding pattern  503 .  
      The light-shielding pattern  503  can have its pitch “p” variable via a mechanism not shown, and is adjusted so that the image acquired by the TV camera  203  will be an image  504  free of a luminescent spot. The signal processor  400  processes the appropriate signals sent from the TV camera  203  and conducts adjustments based on commands from the whole control unit  130 . The spatial filter  10  can be installed in and retracted from an optical path via a movement element  21 .  
      When defects present on the substrate  100  to be inspected are reviewed with the SEM, the substrate  100  is unloaded from a substrate cassette (not shown) by a robot arm, transferred onto the resting table  122  of the XY stage  120  by the transfer system  125 , and fixed in place.  
      Next, the defects to be reviewed are positioned on the optical axis of the detection optical system  350  in accordance with the defect map data outputted from the external inspection apparatus after being previously input from the input/output unit  73  to the whole control unit  130 . Images of the defects are then acquired by the light detector  15  and input to the signal processor  400 . The signal processor  400  detects the defects from the input images and outputs detection results to the whole control unit  130 .  
      The whole control unit  130  issues a driving signal to the XY stage  120  via the driving circuit, and the XY stage  120  moves in the X-direction through the spacing distance “d” between the electron beam axis  112  of the SEM and the optical axis  312  of the detection optical system  350 . The defects that were detected by the defect detection device  140  are then moved onto the electron beam axis  112  of the SEM, and the defects are confirmed and analyzed. On the display unit  72 , an image to be reviewed through the SEM and the image that was acquired by the light detector  15  can be displayed for reviewing, by selecting either image or by arranging both images on one screen. If no defects are detected in the signal processor  400 , the detection optical system is to have its detection field on the substrate  100  enlarged or reduced to search for defects. At this time, the illumination range of the laser light L 1  is also to be varied by moving the lens group  33   b.    
      Next, detection of defects from the image that was acquired by the light detector  15  is described below. FIGS.  6 ( a ),  6 ( b ) are schematic diagrams showing a light-receiving surface of the light detector  15 , and these diagrams apply to an arrangement of “m×n” pixels.  
      Surface defects of the substrate  100  generate scattered light when illuminated with the laser light L 1  from the laser light source  30  or illuminated from a bright-field illumination light source  23 . As a result, defect images  56  are formed on light-receiving surface  402  of the light detector  15  and acquired therefrom into the signal processor  400 . During the acquisition of these images, focus is changed by moving the Z-stage  61  step-by-step in predetermined increments in the Z-direction. A position in the Z-direction where luminance I in an X(Y) direction of one defect image  56  takes a maximum value of Imax in  FIG. 7  is taken as a just-in-focus position. Differences XL, YL between a central position  403  of the light-receiving surface  402  and a position of the defect image  56  thereon, with respect to the image obtained at the above position in the Z-direction, are calculated and these values are used as offset values when the defect is moved to a position on the electron beam axis of the SEM optical system. For example, if the defect image  56  spans over multiple pixels as shown in  FIG. 6 ( b ), center-of-gravity pixels  58  are stored as typical coordinates of the defect.  
       FIG. 8  shows a configuration of the signal processor  400 . An image signal  25  that has been output from the light detector  15  is converted from analog form into digital form by an A/D converter  405  and then input to a division processing circuit  420 . The division processing circuit  420  matches a position of a reference image  415  free from defect information, and a position of the image output from the light detector  15 , and then after performing divisions for each pixel, outputs division results to a comparison circuit  440 .  
      The comparison circuit  440  conducts pixel-by-pixel comparisons between a threshold “Th” that has been output from a thresholding circuit  430 , and the output of the division processing circuit  420 . This means that the comparison circuit  440  sets the threshold “Th” with respect to a brightness signal of each pixel of a two-dimensional image “f(i, j)” and judges whether the pixel is in excess of the threshold. The comparison circuit  440  assigns “1” to each pixel exceeding the threshold, and “0” to all other pixels, and outputs judgment results to a detected-coordinates analyzing and processing circuit  450 .  
      The detected-coordinates analyzing and processing circuit  450  takes only “1” pixels of all input image signals, as defect candidates, stores coordinates of a pixel of a center of gravity as coordinates of a defect into the whole control unit  130 , and compares the coordinates of the defect with the defect map coordinates being previously inputted from the external inspection apparatus. If both sets of coordinates are outside the field of the detection optical system  350  on the wafer  100  of the light detector  15 , the coordinate positions are updated. In all other cases, reference is made to the defect map coordinates.  
      Either the shading image of illumination light that was acquired prior to the inspection, or image data that was obtained by imaging the chips or memory cells repeatedly formed on the substrate  100  is used as the reference image  415 . In this configuration, the reference pattern image that originally is to take the same shape as that of the to-be-inspected pattern existing at the chips or memory cells arranged adjacently to or in the neighborhood of the defect coordinates can be selected by opening/closing a switch provided in related circuits when the XY stage  120  is moving with the spatial filter  10  remaining disposed in the optical path of the detection optical system  350 .  
      Higher-density integration of semiconductors is bringing about a tendency towards further super minute reduction in the line widths of the patterns formed on the substrates  100  to be inspected. Since pattern edges each have a shape with super minute depressions and protrusions, laser light irradiation results in speckle noise arising from the edges. The speckle noise changes a scattering state of light at the edges according to particular laser light irradiation conditions. Accordingly, even for patterns of the same shape, the pattern images detected by the light detector  15  differ from one another in terms of shape, and during chip comparison, the corresponding portions are judged to be mismatching and normal portions are recognized as defects. For these reasons, the need has arisen to ensure stable detection of patterns by reducing the speckle noise at the pattern edges.  
      Therefore, a configuration in which directivity of the speckle noise at pattern edges can be suppressed by, as shown in FIGS.  9 ( a ) to  9 ( c ), irradiating light from plural different directions with respect to the surface of the substrate  100  to be inspected has been adopted for the dark-field illumination system. This configuration has made it possible to reduce the speckle noise at pattern edges within a detection field of the light detector  15  and hence to stably detect patterns.  
       FIG. 9 ( a ) shows an example of a dark-field illumination system  301  in which the surface of a substrate  100  to be inspected is illuminated so as to reduce the speckle noise by combining light sources  161  to  163  of the same wavelength or of different wavelengths and condensing lenses  171  to  173 . The light sources  161  to  163  illuminate the surface of the substrate  100  continuously or discontinuously by means of switch elements (not shown) arranged inside the light sources themselves or in optical paths thereof. An exposure time synchronous with surface illumination of the substrate  100  by the light sources  161  to  163  is set for a light detector  15 .  
      FIGS.  9 ( b ) and  9 ( c ) show embodiments of illuminating the substrate  100  so as to reduce the speckle noise from plural directions using a single light source.  
      The dark-field illumination system  302  shown in  FIG. 9 ( b ) irradiates lights (the S polarization laser light L(S) and the P polarization laser light L(P)) from a laser light source  30  onto the surface of a substrate  100  via a condensing lens  181 , a scanning element  182 , a collimator lens  184 , a condensing lens  186 , and the each of mirrors  38  and  39  (not shown). More specifically, laser light that has been condensed within the scanning element  182  by the condensing lens  181  is irradiated for scanning in, for example, the Z-direction by use of an acousto-optic (AO) deflector, a microdevice mirror, a galvanomirror, and/or the like, under the state where one scan cycle of time of the laser light and an exposure time of light detector  15  are synchronized. Thus, the surface of the substrate  100  is illuminated with laser light L 3  so as to reduce the speckle noise from a direction different in terms of time.  
      The dark-field illumination system  303  shown in  FIG. 9 ( c ) is an example not requiring the above-mentioned scanning element  182 . In this example, after laser light has been spread in any direction by a beam expander  190 , transparent rods  193  different from one another in terms of length L are arranged on an optical path and laser light L 4  is irradiated from a different direction onto one section (a same portion) of the surface of a substrate  100  via a condensing lens  194  provided facing an exit end of each transparent rod  193  and the each of mirrors  38  and  39 . An incident plane of each transparent rod  193  is set to fit a particular illumination region of the substrate  100 , and length L of each transparent rod  193  is set so that the difference in length L between any two rods matches an optical path length difference equal to or greater than a coherence length of a light source  30  so as to reduce the speckle noise. In addition, each of the dark-field illumination system  301 - 303  is provided the retardation plate  35  which converts to each of S polarization laser light L(S) and the P polarization laser light L(P).  
      As shown in FIGS.  10 ( a ),  10 ( b ), the surface of the substrate  100  to be inspected has a transparent film (e.g., oxide film)  804  formed during a multilayering process, and a process of forming patterns on that film is repeated to form a multilayer wafer. The need for detecting only the foreign particle  803  and pattern defect existing on the surface of the oxide film of the wafer is increasing. During the use of a pattern/foreign particle inspection apparatus, however, illumination light also reaches the inside of the transparent film and is irradiated to any defects existing therein. Therefore, not only the defect and the foreign particle  803  on the transparent film surface, but also the defect and foreign particle  802  inside the transparent film are detected, so both the surface defect/foreign particle and the in-film defect/foreign particle are considered to be mixedly present in an inspection map of the pattern inspection apparatus.  
      It is understood, however, that the defect  802  inside the transparent film is difficult to review using the SEM. For this reason, even if the defect coordinates are positioned directly under the electron beam axis  112  of the SEM, the defect cannot be confirmed and thus the pattern inspection apparatus may be recognized as having made a mistake in detection. In the present invention, therefore, when light is illuminated, an angle of the illumination is changed according to particular angles of the mirrors  38 ,  39  arranged in the dark-field illumination system  300 . Thus, transmission of the illumination light through the transparent film and reflection of the illumination light are adjusted for greater quantities of light illuminated to either the surface defects or the in-film defects. This allows the detection optical system  350  to determine whether the defects that have been detected by the optical-type visual inspection apparatus are defects present on the film or inside the film, and hence allows feedback to the SEM. The mirror  38  is constructed so that illumination light of a small incident angle (close to a vertical angle) illuminates any defects present inside the transparent film, and the mirror  39  is constructed so that illumination light of a large incident angle (close to a horizontal angle) illuminates the surface of the transparent film in great quantities.  
      That is to say, by rotating a retardation plate  35  disposed on an optical path around its optical axis by using a rotating drive means (not shown), there are a case of S polarization which makes direction of linear polarization of laser light vertical to the paper surface of  FIG. 3 , and a case of P polarization which makes it parallel to the paper surface. A reflection film having such characteristics that the S polarization laser light L(S) is all reflected by the mirror  39  and the P polarization laser light L(P) is all reflected by the mirror  38 , is formed on the each surface of mirrors  38  and  39 . The optimum illumination angle value of each mirror is set from the results obtained from both.  
      In the construction as described above, in the case of S polarization which makes direction of linear polarization of laser light vertical to the paper surface of  FIG. 3  by adjusting a rotation angle of the retardation plate  35 , the S polarization laser light L(S) enters to the mirror  39  by evacuating the mirror  38  to a position outside the optical path of the S polarization light L(S) by a driving means (not shown), all are reflected by the mirror  39 , and as shown in  FIG. 10 ( a ), reaches the surface of the sample (substrate) at an incident angle of “αL”. Most of the S polarization laser light L(S) that has entered the transparent film  804  at the incident angle of “αL” is reflected on the surface of the transparent film  804 , and scattered light S 1  generates from the defect  803  on the surface. The scattered light S 1  passes through the detection optical system  350  shown in  FIG. 1 , and reaches the light detector  15 , by which S 1  is then detected.  
      Conversely, a case of P polarization which makes direction of linear polarization of laser light vertical parallel to the paper surface by adjusting the rotation angle of the retardation plate  35 , the P polarization laser light L(P) enters to the mirror  38  by driving and inserting the mirror  38  into the optical path of the P polarization laser light L(P) by the driving means (not shown), all are reflected by the mirror  38 , and as shown in  FIG. 10 ( b ), reaches the surface of the sample at an incident angle of “αs”. The P polarization laser light L(P), after entering the transparent film  804  at the incident angle of “αs”, is irradiated to the defect  802  in or under the film, and scattered light generates from the defect  802 . Scattered light S 2  also generated from the defect  802  in or under the film passes through the detection optical system  350  shown in  FIG. 1 , and reaches the light detector  15 , by which S 2  is then detected.  
      During illumination with the light reflected by the mirror  38 , scattered light is generated from the defect  803  on the surface of the transparent film  804  and from the defect  802  within the film. But, during illumination with the light reflected by the mirror  39 , scattered light is not generated from the defect  802  within the transparent film  804 . Therefore, depending on the presence/absence of the defect signal detected by the light detector  15  and selection of the reflection mirror  38  or  39 , it is possible to identify (discriminate) whether the defect is the defect  803  present on the surface of the transparent film  804  or the defect  802  present in or under the film. In other words, information on the light scattered from the defect  803  on the surface of the transparent film  804  can be discriminated from information on the light scattered from the defect  802  in or under the film.  
      If no defects have been detected in the signal processor  40 , although the detection field of the detection optical system on the substrate  100  is to be enlarged for defect searching, illuminance per unit area decreases since the illumination range of the laser light L 1  is also enlarged. As shown in FIGS.  11 ( a ),  11 ( b ), therefore, the surface of the substrate  100  is scanned with the laser light L 1  in XY directions to minimize decreases in the illuminance of the illumination light.  
      More specifically, the laser light L 1  that has passed through a beam diameter-changing element  33  is reflected as a parallel pencil of rays by a mirror  141 , and after being condensed by a lens  155 , becomes a parallel pencil of rays once again before reaching a lens  156 . After that, L 1  is reflected by a mirror  38  or  39  via a lens  157  and then condensed in spot form onto the surface of the substrate  100 . The mirror  141  and a mirror  144  are installed on the motors  161  and  164 , respectively, that rotate or oscillate by means of electrical signals, and thus the surface of the substrate  100  can be two-dimensionally scanned with the laser light L 1  (L(S) or L(P)). Conducting two-dimensional scans with the laser light L 1  (L(S) or L(P)) in this manner makes part of the light scattered from the substrate  100  enter the detection optical system  350 , in which the L 1  light is detected by the light detector  15 .  
      The electrical signals input to the motors  161 ,  164  are, for example, triangular wave or saw-tooth signals, and these electrical signals input have their frequency and amplitude determined appropriately according to particular spot size and illumination width of the laser light irradiated, and a light accumulation time of the light detector  15 . Also, a two-dimensional vibration mirror formed using semiconductor technology, or a polygonal mirror is usable as a spot-scanning element. Although the mirrors vibrated by motors are shown as an example in the present invention, since the SEM is an apparatus very susceptible to vibration, the SEM needs to be mounted in combination with a vibration-insulating device not shown. A similar effect can also be obtained by using an optical oscillator such as an acousto-optic deflector (AOD).  
      Next, a sequence for inspecting defects using the defect inspection apparatus of the present invention that has the above configuration is described below using  FIGS. 13 and 14 ( a ),  14 ( b ).  
      First, the substrate  100  that has undergone a required processing process in device-manufacturing equipment is inspected using an inspection apparatus not shown (i.e., an optical-type visual inspection apparatus for detecting pattern defects or an extraneous substance inspection apparatus), and defects present on the substrate  100  are detected. Position coordinate information on the detected defects is transferred to the whole control unit  130  via a communications element not shown, and stored into the whole control unit.  
      Next, the substrate  100  that has been subjected to the defect inspection is stored into a cassette not shown, then carried to a gate valve  242 , and in step S 110 , supplied to a load-lock chamber  160  by opening/closing of the gate valve  242 . After this, the load-lock chamber  160  is vacuum-exhausted in step S 1110 , and after this, a gate valve  243  is opened/closed, whereby a transfer robot  244  positions the substrate  100  onto the XY stage  120  of the vacuum chamber within the SEM and rests the substrate on the XY stage.  
      In step S 1120 , in accordance with the position coordinate information that was stored into the whole control unit  130  after the defect detection by the above inspection apparatus not shown, the XY stage  120  is driven to move the coordinate positions of the defects on the substrate  100  to the field of the defect detection device  140 . In step S 1130 , the surface of the substrate  100  is illuminated with laser light from the laser light source  30  for dark-field illumination, and any luminescent spots that indicate defects are automatically searched for within the field of the defect detection device  140 . Thus, a defect  803  present on the surface of a transparent film  804  is detected in step S 1140 . After the movement of the defect coordinate positions, if a desired defect cannot be detected within the field of the defect detection device  140 , the XY stage is driven to spread the searching region with the defect coordinates as its reference to conduct searching operations once again.  
      When the defect  803  on the surface of the transparent film  804  is detected, coordinates of the defect on the substrate  100  remaining rested on the XY stage  120  are derived in accordance with the luminescent spots of a defect detection image within the light detector  15 . If the thus-derived coordinate information differs from the defect coordinate data that the inspection apparatus not shown has calculated from the previously detected defects and the difference is in excess of a certain level, the particular defect coordinate data is updated and then stored in step S 1150 . In this step, the difference exceeding a certain level, for example, an error whose magnitude is such that the image oversteps the detection field of the defect detection device  140 , may be usable as a reference value. Alternatively, a definition may be conductible using the amount of pixel shift within the detection field of the defect detected by the defect detection device  140  during position matching based on the defect coordinate data that the inspection apparatus not shown has calculated from the previously detected defects.  
      If the difference between the above defect coordinate information and defect coordinate data is in excess of a certain level, the coordinate data is modified first, then the substrate  100  is moved by the XY stage  120 , and the defect detected by the defect detection device  140  is positioned within a reviewing field of the SEM. Next, after focusing by electron beam adjustment of the SEM, detailed images of the defects are acquired by defect imaging with the SEM, and then reviewed. Use of ADC (Automatic Defect Classification) technology further makes it possible to analyze the SEM-acquired detailed defect images in step S 1180  and thus to classify the defects from particular characteristics of the defect images and identify the kinds of defects.  
      Basically, defect searching uses dark-field illumination with laser light. However, defects can also be detected according to the detection scheme adopted for the above inspection apparatus not shown. For example, if the defect position coordinate information previously stored into the whole control unit  130  following completion of inspection is information that was detected by a bright-field illumination type of defect inspection apparatus not shown, the substrate  100  is illuminated with a bright-field illumination light source  23 , then the surface of the substrate  100  is imaged using the detection optical system  350 , and defects are detected using the foregoing search method. The XY stage is finely adjusted so that the thus-detected defects are positioned in the center of the field and the defect position information prestored within the whole control unit  130  is modified in accordance with position information on the finely adjusted XY stage.  
      Alternatively, if the defect position coordinate information previously stored into the whole control unit  130  following completion of inspection is information that was detected by a dark-field illumination type of defect inspection apparatus not shown, a rotation angle of the retardation plate  35  is adjusted using the dark-field illumination system  300 , then the laser light emitted from the laser light source  30  is reflected by the mirror  38  or  39 , and thus the substrate  100  is illuminated to detect any defects thereof. At this time, scattered dark-field illumination light from the pattern formed on the substrate  100  is shielded by the spatial filter  10  of the detection optical system  350  and only scattered light from detected defects reaches the light detector  15 .  
      As described above, the SEM is basically unable to review accurately the defects existing in the transparent film of the substrate  100 . For this reason, signals of scattered light by the defects that were detected using the dark-field illumination system  300  are processed by the signal processor  400 , and each defect is identified (discriminated) whether it is the defect  803  existing on the surface of the transparent film  804  or the defect  802  existing in or under the film. Identification results are stored together with position information of the defect into the whole control unit  130 , and during SEM reviewing, the results and the defect position information are fed back. The detection can thus be prevented from being determined to be a detection error in the inspection apparatus for detecting defects beforehand (this inspection apparatus is not shown).  
      In addition, as shown in  FIG. 14 ( b ), during defect searching, for example, the dark-field image  260  obtained in the defect detection device  140  by imaging a luminescent spot  56  of a defect by use of the light detector  15  is stored into the whole control unit  130 , and then during SEM reviewing, the luminescent spot  56  is displayed, together with the dark-field image  260 , in a SEM-reviewing screen  250 . Furthermore, an index  253  indicating a reviewing position, and an index  262  are displayed in the SEM-reviewing screen  250  and the dark-field image  260 , respectively. Thus, matching in characteristics between the dark-field image and the image reviewed through the SEM can be established in real time by moving both indices in synchronization with a movement stroke of the XY stage.  
      The construction shown in  FIG. 12 ( a ) may be adopted for the defect detection device  140  as another embodiment of identifying whether a particular defect is one present on the surface of the transparent film  804  formed on a substrate  100  or one present in the film. More specifically, it is possible to install above the substrate  100  a detection optical system  350   a  with the same function as that of the foregoing detection optical system  350 , and to provide a light source  300  capable of irradiating light from a direction of illumination angle “γ” with respect to the surface of the substrate  100 . Furthermore, a detection system  350   b  can also be provided at a horizontal angle of “φ” in a direction of detection angle “θ”. It is possible, by providing these measures, to suppress the occurrence of stray light from the substrate  100  and detect only very small defects.  
      As set forth above, according to the present invention, when SEM-aided defect reviewing based on the defect coordinates obtained from inspection with an external inspection apparatus is to be executed, it is possible to discriminatively detect defects present on the surface of the transparent film and defects present in or under the film, and feed back the results during SEM reviewing. It thus becomes unnecessary to conduct an operation in which such defects in or under the transparent film formed on the surface of the substrate under inspection that are difficult to review through the SEM are to be searched for in accordance with the defect coordinates obtained from inspection using an external optical inspection apparatus. Consequently, since the defects on the film surface to be reviewed through the SEM can be reliably and easily moved to stay within the field of the SEM, close reviewing of the defects on the film surface can be conducted easily.  
      Furthermore, use of the ADC technology allows the kinds of defects to be identified from particular characteristics of SEM-acquired, detailed defect images. Besides, displaying a SEM image and a dark-field image in parallel and adopting index-based navigation yields the effect that the time required for visual defect searching during SEM reviewing can be reduced.  
      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 that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.