Patent Document

BACKGROUND 
       [0001]    The present invention relates to a method and apparatus for optically detecting a defect in a sample surface and, more particularly, to an optical inspection method and apparatus suitable for detecting a recess or a flaw in the surface of a conventional magnetic disk and foreign matters adhered to both faces of a magnetic disk. 
         [0002]    For example, Japanese Patent Application Laid-Open Publication No. 2002-257742 (hereinbelow, referred to as patent document 1) and Japanese Patent Application Laid-Open Publication No. 2008-268189 (hereinbelow, referred to as patent document 2) describe an apparatus for detecting a defect in a surface of a magnetic disk as a conventional continuous recording magnetic medium. The patent document 1 discloses a configuration of obliquely irradiating a rotating magnetic disk with a laser beam, forming an image by regular-reflection light from the surface of the disk on a detector having plural light receiving elements, and processing a detection signal of the light to detect a defect. 
         [0003]    The patent document 2 discloses an inspection apparatus which obliquely irradiates a rotating magnetic disk with a laser beam, detects regular-reflection light and scatting light from the surface of the disk, and processes detection signals of the regular-reflection light and scattering light to detect and classify a defect in the surface of the disk. 
         [0004]    The patent document 2 also describes that a mask is provided so that regular-reflection light does not enter a lens provided on the side of regular reflection from a substrate (disk) to thereby interrupt regular-reflection light other than scatting light. It also describes that a half mirror is provided in place of a mask, and regular-reflection light is reflected by the half mirror and detected by a detector. 
         [0005]    As the recording capacity of a magnetic disk increases, the recording density of the magnetic disk becomes higher, the size of a defect to be detected is decreasing, and the number of kinds of defects to be detected is increasing. 
         [0006]    To address such demands, the patent document 1 describes that an image of regular-reflection light from the surface of the disk which is obliquely irradiated with a laser beam is detected by “n” pieces of light receiving elements arranged linearly, and the size of a recessed or projected defect in the surface of a substrate is detected with high precision on the basis of detection signal levels of the light receiving elements. However, it is not considered that a smaller defect in the surface of the substrate, for example, a shallow flaw defect (shallow defect) or a defect on the inside of the substrate is detected so as to be discriminated from the other defects. 
         [0007]    The patent document 2 describes that a substrate is illuminated from multiple directions, regular-reflection light and scattering light from the substrate is detected, the state of a wave in the substrate itself or a local wave is determined from the waveform of the detection signals, and a defect is detected from the state. However, it is not described that a smaller defect in the surface of the substrate, for example, a shallow flaw defect (shallow defect) or a defect on the inside of the substrate is detected so as to be discriminated from the other defects. 
         [0008]    The patent document 2 also describes that a mask is provided so that regular-reflection light does not enter a lens provided on the side of regular reflection from a substrate (disk) to thereby interrupt regular-reflection light other than scatting light, and that a half mirror is provided in place of a mask, and regular-reflection light is reflected by the half mirror and detected by a detector. However, it is not considered that a smaller defect in the surface of the substrate, for example, a shallow flaw defect (shallow defect) or a defect on the inside of the substrate is detected so as to be discriminated from the other defects by using detection signals of scattering light around the regular-reflection light excluding the regular-reflection light and a detection signal of the regular-reflection light. 
       SUMMARY 
       [0009]    An object of the present invention is to address the problems and to provide an optical inspection apparatus for inspecting a magnetic disk, capable of detecting a smaller defect in the surface of a substrate, for example, a shallow flaw defect (shallow defect) or a defect on the inside of the substrate so as to be discriminated from the other defects. 
         [0010]    To achieve the object, in the present invention, an optical inspection apparatus for detecting a defect in a surface of a sample is constructed by including: a stage which rotates a sample and continuously moves the sample in one direction; a light irradiator which irradiates a surface of the sample which is rotated and continuously moved in one direction by the stage, with illumination light which is incident in a direction obliquely to the surface of the sample; a first detector which detects an image of forward scattering light around an optical axis of regular-reflection light by using reflection light including the forward scattering light around the optical axis of the regular-reflection light while excluding the regular-reflection light from the surface of the sample irradiated with the illumination light from the light irradiator; a second detector which condenses and detects lateral scattering light which scatters laterally with respect to an incidence direction of the illumination light in the scattering light from the surface of the sample irradiated with the illumination light from the light irradiator; and a defect extractor which processes signals detected by the first and second detector to extract a defect including a scratch defect in an arbitrary direction in the surface of the sample. 
         [0011]    To achieve the object, in the present invention, an optical inspection apparatus for detecting a defect in a surface of a sample is constructed by including: a stage which rotates a sample and continuously moves the sample in one direction; a light irradiator which irradiates a surface of the sample which is rotated and continuously moved in one direction by the stage, with illumination light which is incident in a direction obliquely to the surface of the sample; a first detector which detects regular-reflection light from the surface of the sample irradiated with the illumination light from the light irradiator; a second detector which condenses and detects lateral scattering light which scatters laterally with respect to an incidence direction of the illumination light in the scattering light from the surface of the sample irradiated with the illumination light from the light irradiator; and a defect extractor which processes signals detected by the first and second detector to extract a defect including a scratch defect in an arbitrary direction in the surface of the sample. 
         [0012]    Further, to achieve the object, in the present invention, an optical inspection method of defecting a defect in a surface of a sample includes the steps of: irradiating a surface of a sample which is rotated and continuously moved in one direction with illumination light which is incident in a direction obliquely to the surface of the sample; detecting an image of forward scattering light around an optical axis of regular-reflection light by using reflection light including the forward scattering light around the optical axis of the regular-reflection light while excluding the regular-reflection light, from the surface of the sample irradiated with the illumination light; condensing and detecting lateral scattering light which scatters laterally with respect to an incidence direction of the illumination light, in the scattering light from the surface of the sample irradiated with the illumination light; and processing a signal obtained by detecting the forward scattering light around the optical axis of the regular-reflection light and a signal obtained by condensing and detecting the lateral scattering light to extract a defect including a scratch defect in an arbitrary direction in the surface of the sample. 
         [0013]    Further, to achieve the object, an optical inspection method for detecting a defect in a surface of a sample includes the steps of: irradiating a surface of a sample which is rotated and continuously moved in one direction with illumination light which is incident in a direction obliquely to the surface of the sample; detecting regular-reflection light from the surface of the sample irradiated with the illumination light; condensing and detecting lateral scattering light which scatters laterally with respect to an incidence direction of the illumination light, in the scattering light from the surface of the sample irradiated with the illumination light; and processing a signal obtained by detecting the regular-reflection light and a signal obtained by condensing and detecting the lateral scattering light to extract a defect including a scratch defect in an arbitrary direction in the surface of the sample. 
         [0014]    According to the present invention, at the time of detecting scattering light from a sample and classifying defects extracted, defect information included in forward scattering light around the optical axis of the regular-reflection light can be also used. Therefore, defects including a scratch defect (shallow defect) which is shallow in an arbitrary direction in a surface of a sample can be extracted. 
         [0015]    These 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 
         [0016]      FIG. 1A  is a block diagram showing a general schematic configuration of an optical inspection apparatus in a first embodiment; 
           [0017]      FIG. 1B  is a side view of detection optics in the optical inspection apparatus in the first embodiment; 
           [0018]      FIG. 1C  is a plan view of the detection optics in the optical inspection apparatus in the first embodiment; 
           [0019]      FIG. 2  is a plan view showing a state of defects in a magnetic disk to be inspected; 
           [0020]      FIG. 3A  is a section of a magnetic disk to be inspected, having a scratch defect; 
           [0021]      FIG. 3B  is a section of a magnetic disk to be inspected, having a projected defect; 
           [0022]      FIG. 4A  is a detection signal having a noise, which is obtained when the surface of a magnetic disk having a defect is inspected; 
           [0023]      FIG. 4B  is a detection signal which is obtained when the surface of a magnetic disk having a defect is inspected and from which noise is eliminated; 
           [0024]      FIG. 5  is a flowchart of processes for detecting and classifying a defect in the first embodiment; 
           [0025]      FIG. 6A  is a block diagram showing a general schematic configuration of an optical inspection apparatus in a second embodiment; 
           [0026]      FIG. 6B  is a side view of detection optics in the optical inspection apparatus in the second embodiment; 
           [0027]      FIG. 7  is a table showing the presence or absence of a detection signal in each of detection systems for each of defect kinds; 
           [0028]      FIG. 8  is a flowchart of processes for detecting and classifying a defect in the second embodiment; 
           [0029]      FIG. 9  is a side view of detection optics in an optical inspection apparatus in a third embodiment; 
           [0030]      FIG. 10  is a sectional view of a magnetic disk showing an example of small defects existing on a thin film and in a middle part and in a lower part of the thin film formed on the surface of a magnetic disk; 
           [0031]      FIG. 11A  is a block diagram showing a general schematic configuration of an optical inspection apparatus in a fourth embodiment; 
           [0032]      FIG. 11B  is a side view of detection optics in the optical inspection apparatus in the fourth embodiment; 
           [0033]      FIG. 11C  is a front view of a one-dimensional sensor array of the optical inspection apparatus in the fourth embodiment; 
           [0034]      FIG. 12A  is a cross section of a substrate of a part having a recessed defect; 
           [0035]      FIG. 12B  is a graph showing an example of output waveform from photo diode elements (pixels) of the one-dimensional sensor array when reflection light from the part having the recessed defect is detected by the one-dimensional sensor array; 
           [0036]      FIG. 13A  is a cross section of a substrate of a part having a projected defect; 
           [0037]      FIG. 13B  is a graph showing an example of output waveform from photo diode elements (pixels) of the one-dimensional sensor array when reflection light from the part having the projected defect is detected by the one-dimensional sensor array; 
           [0038]      FIG. 14A  is a block diagram showing a general schematic configuration of an optical inspection apparatus in a modification of the fourth embodiment; 
           [0039]      FIG. 14B  is a side view of detection optics in the optical inspection apparatus in the modification of the fourth embodiment; and 
           [0040]      FIG. 14C  is a plan view of the detection optics of the optical inspection apparatus in the modification of the fourth embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0041]    To improve performance of classifying defects, the present invention provides a technique of separately detecting regular-reflection light from a substrate irradiated with illumination light and scattering light around the optical axis of the regular-reflection light, detecting a defect on a surface of the substrate by using a detection signal of an image of the scattering light around the optical axis which is separately detected, or a detection signal of an image of the scattering light around the optical axis and a detection signal of the regular-reflection light, and a detection signal of lateral scattering light, and classifying the kind of the detected defect. 
         [0042]    Embodiments of the present invention will be described below with reference to the drawings. 
       First Embodiment 
       [0043]    The configuration of an optical magnetic disk inspection apparatus according to a first embodiment will be described with reference to  FIGS. 1A to 10 . 
         [0044]    An optical magnetic disk inspection apparatus  100  according to the first embodiment has, as shown in  FIGS. 1A and 1B , illumination optics  110 , detection optics  140  configured to include regular-reflection light detection optics  120  and scattering light detection optics  130 , a stage system  150 , and a general control system  170 . 
         [0045]    The illumination optics  110  include a laser source  111 , a beam expansion lens  112  expanding a laser beam emitted from the laser source  111 , a collimate lens  113  converting the laser beam expanded by the beam expansion lens  112  to parallel rays, and a convergence lens  114  converging the parallel laser beams whose diameter is enlarged onto the surface of a sample  10 . 
         [0046]    The regular-reflection light detection optics  120  in the detection optics  140  are disposed along the optical axis of regular-reflection light from the sample  10  irradiated with the laser beam converged by the illumination optics  110 , and include a condenser lens  121  for condensing reflection light including the regular-reflection light and the scattering light from the sample  10 , a mask  122  for blocking the regular-reflection light from the sample  10  in the light which passed through the condenser lens  121 , an image forming lens  123  for forming an image from reflection light (scattering light) from the sample  10  which is not blocked by the mask  122  at a predetermined magnification, and a detector  124  for detecting the image of the reflection light (scattering light) from the sample  10 , which is formed by the image forming lens  123 . By using an aspheric lens as the condenser lens  121 , an optical system having a larger NA (numerical aperture) can be constructed, and defect detection sensitivity can be increased. The image forming lens  123  can be also constructed by an aspheric lens. The detector  124  is an array sensor formed by arranging plural detection elements in an array. 
         [0047]    On the other hand, the scattering light detection optics  130  in the detection optics  140  include a condenser lens  131  for condensing lateral scattering light from the sample  10  which is irradiated with a laser beam and a detector  132  for detecting the scattering light condensed by the condenser lens  131 . 
         [0048]    The stage system  150  includes a rotatable spindle shaft  151  on which the sample  10  is placed, a stage  152  for moving the spindle shaft  151  in one direction in a plane, and a stage driving unit  153  for driving the spindle shaft  151  and the stage  152 . 
         [0049]    The general control system  170  has a signal process/control system  160 , a memory  171  that stores inspection data and data of inspection parameters, and an input/output unit  172  having a display screen  173 . 
         [0050]    The signal process/control system  160  includes: an illumination light source control unit  161  for controlling the laser source  111  of the illumination optics  110 ; a detection signal processing unit  162  for receiving output signals of the detector  124  of the regular-reflection light detection optics  120  and the detector  132  of the scattering light detection optics  130 , amplifying them, A/D converting the signals to digital signals, and performing signal process on the digital signals to detect a defect candidate; a defect continuity determining unit  163  for extracting a continuous defect in the sample  10  by using the information of the defect candidate detected by the detection signal processing unit  162 , the information of rotation of the spindle shaft  151 , and the information of the position of the stage  152 ; a defect feature amount extracting unit  164  for extracting a feature amount of the defect detected by the detection signal processing unit  162  including the continuous defect extracted by the defect continuity determining unit  163 ; a defect classifying unit  165  for classifying a defect by using the information of the feature amount of the defect extracted by the defect feature amount extracting unit  164 ; a stage control unit  166  for controlling the operation of the spindle shaft  151  and the stage  152  by controlling the stage driving unit  153 ; and an MUP  167  for controlling the illumination light source control unit  161 , the detection signal processing unit  162 , the defect continuity determining unit  163 , the defect feature amount extracting unit  164 , the defect classifying unit  165 , and the stage control unit  166 . 
         [0051]    The illumination optics  110 , the regular-reflection light detection optics  120 , and the scattering light detection optics  130  are disposed in the relations with respect to the sample  10  as shown in the plan view of  FIG. 1C . The arrows in  FIG. 1C  indicate the direction of rotation and the direction of linear movement of the substrate  10 . 
         [0052]    Defects in the sample  10  are detected by the optical magnetic disk inspection apparatus  100  having the above-described configuration.  FIG. 2  illustrates an example of defects on the sample  10  to be inspected. 
         [0053]      FIG. 2  is a plan view of a magnetic disk as the sample  10  to be inspected. In the magnetic disk as the sample  10 , thin films in multiple layers including a magnetic film layer are formed on the surface by various manufacturing processes. By the various manufacturing processes, various defects are caused. In many cases, foreign matters  201 - 1  to  201 - 3  adhered to the surface of the sample  10  do not cause a problem because they are washed out by cleaning before the sample  10  is assembled in a hard disk drive. On the other hand, each of a bump defect  202  as an expansion of the surface of the sample  10 , a pit defect  203  as a recess in the surface, and the like is often a gentle defect which spreads thinly (a few nm to tens nm) in a large area (1 mm 2 ) in the surface of the sample  10 . Those defects do not cause a problem when the sample  10  is assembled in a hard disk drive to make a magnetic head float by high-speed rotation. However, they may become a cause of a change in the thickness of a recording layer which is formed in a deposition process. 
         [0054]    Scratches  204 - 1  and  204 - 2  are defects which occur when an abrading agent comes off from an abrasive pad and have a shape such as a long streaky shape or a short flaw, in which a recess and a projection are mixed. The defect having such a sharp projection may interfere with a magnetic head when the sample  10  is assembled in a hard disk drive to make the magnetic head float by high-speed rotation. The defect may cause a critical failure in the hard disk drive. It is therefore important to inspect the sample (magnetic disk)  10  before assembly to the hard disk drive to detect those defects and to prevent the sample  10  having a defect as a defective from being passed to the next process. 
         [0055]      FIG. 3A  is a cross section of the sample  10  in a region having the scratch defect  204  in the surface. FIG.  3 B is a cross section of the sample  10  in a region having the bump defect  203  as a projection in the sample surface. 
         [0056]    In the case where light falls on the scratch defect  204  shown in  FIG. 3A  from the direction of the arrow, relatively strong scattering light is generated from edge portions  2041  and  2042 . The scattering light has a characteristic such that it is generated relatively weak in the longitudinal direction of the scratch defect  204  (the direction perpendicular to the drawing sheet of  FIG. 3A ) and relatively strong in the direction orthogonal to the longitudinal direction. When light is emitted along the longitudinal direction of the scratch defect  204 , relatively strong scattering light is generated in the longitudinal direction but the strength of the scattering light in the direction orthogonal to the longitudinal direction of the scratch defect  204  is relatively weak. That is, in the example of the sample  10  shown in  FIG. 2 , in the case of illuminating the sample  10  by the illumination optics  110  shown in  FIG. 1  (in  FIG. 2 , illuminated along the radial direction of the sample  10 ), relatively strong reflection light is generated in the radial direction of the sample  10  from the scratch  204 - 1  which is long in the radial direction and the scratch  204 - 2  which is long in the circumferential direction. On the other hand, the strength of scattering light which is generated in the circumferential direction is relatively low. That is, in the case of detecting the scratch defect  204  by the scattering light detection optics  130 , the directivity is higher than that in the case of detecting a defect of another shape. 
         [0057]    On the other hand, in the direction of the regular-reflection light generated from the sample  10  illuminated by the illumination optics  110 , almost constant reflection light (including the regular-reflection light and scattering light) is generated regardless of the directions of the scratches  204 - 1  and  204 - 2 . Although the regular-reflection light from the sample  10  is also generated from a part having no defect, scattering light is generated from a part having a defect. Consequently, by detecting scattering light separately from the regular-reflection light, the scratch defect  204  can be always detected regardless of the orientation of the scratch defect  204 . 
         [0058]    Therefore, by disposing the detector in the direction of the regular-reflection light and blocking the regular-reflection light to incident in the detector and detect an image of the scattering light generated from the scratch  204 - 1  or  204 - 2 , the defect can be detected regardless of the orientation of the scratch  204 - 1  or  204 - 2 . It is particularly effective to detect a shallow scratch defect (shallow defect). 
         [0059]    The regular-reflection light detection optics  120  of  FIG. 1A  are constructed in consideration of the above mentioned idea. By blocking the regular-reflection light from the sample  10  by the mask  122  and forming an image of scattering light generated around the optical axis of the regular-reflection light by the image forming lens  123  on the detector  124 , the scratch  204  in the sample  10  can be detected without overlooking. 
         [0060]      FIG. 4A  shows an example of a detection signal from the detector  124  or  132 . The detection signal from the detector  124  or  132  includes a defect signal in a state where it is buried in a noise signal. By cutting off the signals equal to or less than a predetermined level in the detection signal as noises, a signal as shown in  FIG. 4B  is obtained. A threshold value (TL) is set for the signal, a signal exceeding the threshold value is extracted as a defect signal, and information of an inspection position on the sample  10  corresponding to the extracted defect signal is obtained, from the stage driving unit  153  via the stage control unit  166 . And the obtained information is supplied as the position information of the defect to the detection signal processing unit  162 . 
         [0061]    Next, the flow of processes executed by the signal process/control system  160  to detect a defect in the sample  10  on the basis of the above-described idea by using the inspection apparatus shown in  FIGS. 1A and 1B  will be described with reference to  FIG. 5 . 
         [0062]    First, the spindle shaft  151  and the stage  152  are driven by the stage driving unit  153  which is controlled by the stage control unit  166  in a state where the sample  10  is placed on the spindle shaft  151  to continuously move the sample  10  in one direction while rotating the sample  10 . In this state, the laser source  111  of the illumination optics  110  is driven by the illumination light source control unit  161  to emit a laser beam to the sample  10 . Reflection light from the sample  10  irradiated with the laser beam is detected by the regular-reflection light detection optics  120  and the scattering light detection optics  130 , and detection signals from the detectors  124  and  132  are supplied to the detection signal processing unit  162  (S 501 ). 
         [0063]    The detection signal processing unit  162 , to which the detection signals from the detectors  124  and  132  are supplied, amplifies each of the input signals, A/D converts the amplified signals to digital signals, processes the digital signals, and checks them with each other to extract a defect candidate (S 502 ). 
         [0064]    The information of the extracted defect candidate is sent to the defect continuity determining unit  163 , continuity of the defect is determined by using the information of the rotation of the spindle shaft  151  and the information of the position of the stage  152  obtained from the stage control unit  166  (S 503 ), and a scratch defect is extracted. 
         [0065]    The digital signals based on the signals from the detectors  124  and  132  are also sent to the defect feature amount extracting unit  164  where feature amounts (shape, size, and the like) of the defect are extracted (S 504 ). 
         [0066]    The information of the extracted feature amounts of the defect is sent to the defect classifying unit  165  and subjected to defect classifying process. In the defect classifying process, the size of defect which is extracted by the defect feature amount extracting unit  164  is judged whether the size is 100 μm or larger from the signal obtained from the detector  124  of the regular-reflection light detection optics  120  (S 505 ). In the case the defect has a size of 100 μm or more, the defect is determined whether or not the defect is a linear defect by using the result of the process of S 503  (S 506 ). If YES, the defect is determined as a linear defect (S 507 ). On the other hand, in the case where the defect is not determined as a linear defect in S 506 , the defect is determined as a planar defect caused by contamination (S 508 ). 
         [0067]    For the defect determined that its size is not equal to or larger than 100 μm in S 505 , it is judged from an output signal of the detector  132  whether or not a detection signal corresponding to the defect is also detected by the scattering light detection optics  130  (S 509 ). In the case where it is determined that the signal is not detected by the scattering light detection optics  130 , the size of the signal obtained from the detector  124  of the regular-reflection light detection optics  120  is compared with a preset level (S 510 ). When the case where the size is larger than the preset level, the defect is determined as a large bright point (S 511 ). When the size is equal to or less than the preset level, the defect is determined as a small bright point (micro defect) (S 512 ). 
         [0068]    In the case where it is determined in S 509  that the signal is detected by the scattering light detection optics  130 , it is judged whether or not the defect is also detected by the regular-reflection light detection optics  120  (S 513 ). When the defect is not detected by the regular-reflection light detection optics  120 , the size of the defect is compared with a preset value (S 514 ). In the case where the size of the defect is larger than the preset value, the defect is determined as a defect (defect existing inside the film) existing in the sample  10  (in a thin film formed on the surface of the sample  10 ) (S 515 ). In the case where the size is equal to or less than the preset value, the defect is determined as a defect (defect existing under the film) under the thin film formed on the surface of the sample  10  (S 516 ). 
         [0069]    In the case where the defect is also detected by the regular-reflection light detection optics  120 , the size of the defect is compared with a preset value (S 517 ). When the size of the defect is larger than the preset value, the defect is determined as a foreign-matter defect (S 518 ). When the size is equal to or less than the preset value, the position on the sample  10  determined from the signal detected by the regular-reflection light detection optics  120  and the position on the sample  10  determined from the signal detected by the scattering light detection optics  130  are compared with each other (S 519 ). When the positions are the same, the defect is determined as a defect on the surface of the sample  10  (S 520 ). When the positions are not the same, the defect is determined as a defect in/below the thin film formed on the surface of the sample  10  (S 521 ). 
         [0070]    The information of each of the defects classified as described above is recorded and stored in the memory  171 . 
         [0071]    As described above, by detecting and classifying a defect by using the information of scattering light of a part around the optical axis of the regular-reflection light obtained from the detection signal of the regular-reflection light detection optics  120  and the information of lateral scattering light obtained from the detection signal of the scattering light detection optics  130 , the detected defect can be classified more finely. 
       Second Embodiment 
       [0072]    A second embodiment of the present invention will now be described with reference to  FIGS. 6A and 6B . 
         [0073]    In the embodiment, the mask  122  in the regular-reflection light detection optics  120  of the inspection apparatus shown in  FIG. 1  is replaced by a reflecting mirror  622  as shown in  FIG. 6A  to detect the regular-reflection light. That is, for detection and classification of a defect, information of the regular-reflection light from the sample  10  is also used. 
         [0074]    A magnetic disk inspection apparatus  600  in the second embodiment shown in  FIGS. 6A and 6B  has, is similar to the configuration of the inspection apparatus  100  in the first embodiment described with reference to  FIGS. 1A to 1C . The magnetic disk inspection apparatus  600  includes illumination optics  610 , detection optics  640  including regular-reflection light detection optics  620  and scattering light detection optics  630 , a stage system  650 , and a general control system  670 . The configuration is basically similar to that of  FIG. 1A  except that the mask  122  of the regular-reflection light detection optics  120  is replaced with the reflecting mirror  622  as shown in  FIG. 6A  and a regular-reflection-light detection system  625  having a condenser lens  626  and a detector  627  is newly provided. Consequently, detailed description of the configuration will be omitted. 
         [0075]    The magnetic disk inspection apparatus  600  can also use the information of the regular-reflection light for classification of a defect, so that the precision of the classification can be further improved.  FIG. 7  is a table showing the relations between the lateral scattering light detection signal, the regular-reflection light detection signal, and a defect kind. By using the regular-reflection light detection signal, a shallow defect (a shallow defect among scratch defects) can be detected. 
         [0076]    Next, the flow of processes of detecting/classifying a defect in the magnetic disk inspection apparatus  600  will be described with reference to  FIG. 8 . 
         [0077]    First, reflection light from the sample  10  irradiated with a laser beam in a state where the sample  10  is moved in one direction while being rotated is detected by the regular-reflection light detection optics  620  and the scattering light detection optics  620  as illustrated in  FIG. 6B , and detection signals from detectors  624  and  632  are supplied to a detection signal processing unit  662  (S 801 ). 
         [0078]    The detection signal processing unit  662 , to which the detection signals from the detectors  624  and  632  are supplied by amplifying and converting from analog signals to digital signals, processes the digital signals, and checks them with each other to extract a defect candidate (S 802 ). 
         [0079]    The information of the extracted defect candidate is sent to a defect continuity determining unit  663  where continuity of the defect is determined by using the information of the rotation of a spindle shaft  651  and the information of the position of a stage  652  obtained from a stage control unit  666  (S 803 ), and a scratch defect is extracted. 
         [0080]    The digital signals based on the signals from the detectors  624  and  632  are also sent to a defect feature amount extracting unit  664  where feature amounts (shape, size, and the like) of the defect are extracted (S 804 ). 
         [0081]    The information of the extracted feature amounts of the defect is sent to a defect classifying unit  665  and subjected to defect classifying process. In the defect classifying process, the size of defect which is extracted by the defect feature amount extracting unit  664  is judged whether the size is 100 μm or larger from the signal obtained from the detector  624  of the regular-reflection light detection optics  620  (S 805 ). In the case the defect has a size of 100 μm or more, the defect is determined whether or not the defect is a linear defect by using the result of the process of S 803  (S 806 ). If YES, the defect is determined as a linear defect (S 807 ). On the other hand, in the case where the defect is not determined as a linear defect in S 806 , the defect is determined as a planar defect caused by contamination (S 808 ). 
         [0082]    For the defect determined that its size is not equal to or larger than 100 μm in S 805 , it is judged from an output signal of the detector  632  whether or not a detection signal corresponding to the defect is also detected by the scattering light detection optics  625  and also it is checked if the defect is not detected by the scattering light detection optics  630  (S 809 ). If YES, that is, in the case where the signal is detected by the regular-reflection light detection optics  625  and is not detected by the scattering light detection optics  630 , the defect is determined as a shallow defect (S 810 ). 
         [0083]    On the other hand, in the case where NO is determined in S 809 , it is checked whether or not the detection signal corresponding to the defect is also detected by the scattering light detection optics  630  from the output signal of the detector  632  (S 811 ). When it is found that the signal is not detected by the scattering light detection optics  630 , the size of the signal obtained from the detector  624  of the regular-reflection light detection optics  620  is compared with a preset level (S 812 ). In case the size is larger than the preset level, the defect is determined as a large bright point (S 813 ). In case the size is equal to or less than the preset level, the defect is determined as a small bright point (micro defect) (S 814 ). 
         [0084]    In the case where it is determined in S 811  that the signal is detected by the scattering light detection optics  130 , it is determined whether or not the defect is also detected by the regular-reflection light detection optics  620  (S 815 ). When the defect is not detected by the regular-reflection light detection optics  620 , the size of the defect is compared with a preset value (S 816 ). In the case where the size of the defect is larger than the preset value, the defect is determined as a defect (defect existing inside the film) existing in the sample  10  (in a thin film formed on the surface of the sample  10 ) (S 817 ). In the case where the size is equal to or less than the present value, the defect is determined as a defect (defect existing under the film) existing under the thin film formed on the surface of the sample  10  (S 818 ). 
         [0085]    When it is determined in S 815  that the defect is also detected by the regular-reflection-light detection optics  620 , the size of the defect is compared with a preset value (S 819 ). When the size of the defect is larger than the preset value, the defect is determined as a foreign-matter defect (S 820 ). When the size is equal to or less than the preset value, the position on the sample  10  determined from the signal detected by the regular-reflection light detection optics  620  and the position on the sample  10  determined from the signal detected by the scattering light detection optics  630  are compared with each other (S 821 ). When the positions are the same, the defect is determined as a defect on the surface of the sample  10  (S 822 ). When the positions are not the same, the defect is determined as a defect in/below the thin film formed on the surface of the sample  10  (S 823 ). 
         [0086]    The information of each of the defects classified as described above is recorded and stored in a memory  671 . 
         [0087]    As described above, by detecting and classifying a defect by using the information of scattering light of a part around the optical axis of the regular-reflection light obtained from the detection signals of the regular-reflection light detection system  625  and the regular-reflection light detection optics  620  and the information of lateral scattering light obtained from the detection signal of the scattering light detection optics  630 , the detected defect can be classified more finely. 
       Third Embodiment 
       [0088]    In a third embodiment, an example of constructing the scattering light detection optics  130  of the magnetic disk inspection apparatus  100  described in the first embodiment by image formation optics as shown in  FIG. 9  will be described. 
         [0089]    The configuration of a magnetic disk inspection apparatus in the third embodiment is similar to that of the magnetic disk inspection apparatus  100  described in the first embodiment except for the point that the scattering light detection optics  130  are constructed by image formation optics as shown in  FIG. 9 . 
         [0090]      FIG. 9  is a side view of a detection optics  940  including a scattering light detection optics  930  of the third embodiment and the regular-reflection light detection optics  120  in the first embodiment. 
         [0091]    The scattering light detection optics  930  include a condenser lens  931  for condensing scattering light from the sample  10  irradiated with a laser beam, an image forming lens  932  for forming an image of the scattering light from the sample  10  condensed by the condenser lens  931 , and a detector  933  for detecting the image of the scattering light formed by the image forming lens  932 . 
         [0092]    Since the configuration other than the detection optics  940  in the third embodiment is substantially the same as that described in the first embodiment, description will be given by applying the configuration of  FIG. 1 . 
         [0093]    In the third embodiment, an optical image is detected by both the detectors  124  and  933 . Consequently, the detection signal processing unit  162  adjusts positions of the pixels in each of the images obtained by the detectors and, after that, detects a defect from the images whose positions are adjusted. The defect feature amount extracting unit  164  extracts feature amounts of a defect from each of the images whose positions are adjusted. Further, the defect classifying unit  165  classifies the defect by using the information of the feature amounts of the defects in the images extracted by the defect feature amount extracting unit  164 . 
         [0094]    By constructing the scattering light detection optics with the image forming optics as described above, defects on the sample are detected discriminately from a detected image. For example, as shown in  FIG. 10 , a defect  15  existing on the surface of a thin film layer  12  (in  FIG. 10 , simply shown as a single layer) formed on a substrate  11  of the sample  10 , a defect  16  existing in the thin film layer  12 , and a defect  17  existing in a lower part of the thin film layer  12  can be detected discriminately from one another. 
         [0095]    In the third embodiment, a defect is detected and classified by using an image obtained by the regular-reflection light detection optics and an image obtained by the scattering light detection optics, so that higher-precision defect detection and higher-reliability defect classification can be performed. 
       Fourth Embodiment 
       [0096]    In the foregoing first to third embodiments, at least the regular-reflection light detection optics is constructed by the image forming optics. In a fourth embodiment, regular-reflection light from a sample is detected without using the image forming optics. 
         [0097]      FIGS. 11A to 11C  show the configuration of an optical magnetic disk inspection apparatus  1100  in the fourth embodiment. 
         [0098]    As shown in  FIG. 11A , the magnetic disk inspection apparatus  1100  has illumination optics  1110 , detection optics  1140  configured to include regular-reflection light detection optics  1120  and scattering light detection optics  1130 , a stage system  1150 , and a general control system  1170 . 
         [0099]    In a manner similar to the case of the first embodiment, the illumination optics  1110  include a laser source  1111 , a beam expansion lens  1112  expanding a laser beam emitted from the laser source  1111 , a collimate lens  1113  converting the laser beam expanded by the beam expansion lens  1112  to parallel rays, and a convergence lens  1114  converging the parallel laser beams whose diameter is enlarged onto the surface of the sample  10 . 
         [0100]    As shown in  FIG. 11C , the regular-reflection light detection optics  1120  in the detection optics  1140  is constructed by a one-dimensional array sensor  1122  formed by disposing plural photo diode elements  1121  in an array. 
         [0101]    On the other hand, as shown in  FIG. 11B , the scattering light detection optics  1130  in the detection optics  1140  include a condenser lens  1131  for condensing lateral scattering light from the sample  10  which is irradiated with a laser beam and a detector  1132  for detecting the scattering light condensed by the condenser lens  1131 . 
         [0102]    The stage system  1150  includes a rotatable spindle shaft  1151  on which the sample  10  is placed, a stage  1152  for moving the spindle shaft  1151  in one direction in a plane, and a stage driving unit  1153  for driving the spindle shaft  1151  and the stage  1152 . 
         [0103]    The general control system  1170  has a signal process/control system  1160 , a memory  1171  that stores inspection data and data of inspection parameters, and an input/output unit  1172  having a display screen  1173 . 
         [0104]    The signal process/control system  1160  includes: an illumination light source control unit  1161  for controlling the laser source  1111  of the illumination optics  1110 ; a detection signal processing unit  1162  for receiving output signals of the array sensor  1122  of the regular-reflection light detection optics  1120  and the detector  1132  of the scattering light detection optics  1130 , amplifying them, A/D converting the signals to digital signals, and performing signal process on the digital signals to detect a defect candidate; a defect continuity determining unit  1163  for extracting a continuous defect in the sample  10  by using the information of the defect candidate detected by the detection signal processing unit  1162 , the information of rotation of the spindle shaft  1151 , and the information of the position of the stage  1152 ; a defect feature amount extracting unit  1164  for extracting a feature amount of the defect detected by the detection signal processing unit  1162  including the continuous defect extracted by the defect continuity determining unit  1163 ; a defect classifying unit  1165  for classifying a defect by using the information of the feature amount of the defect extracted by the defect feature amount extracting unit  1164 ; a stage control unit  1166  for controlling the operation of the spindle shaft  1151  and the stage  1152  by controlling the stage driving unit  1153 ; and an MUP  1167  for controlling the illumination light source control unit  1161 , the detection signal processing unit  1162 , the defect continuity determining unit  1163 , the defect feature amount extracting unit  1164 , the defect classifying unit  1165 , and the stage control unit  1166 . 
         [0105]    As shown in  FIG. 11A , the regular-reflection light detection system  1120  of the detection optics  1140  has a configuration to directly detect regular-reflection light from the sample  10  by the one-dimensional array sensor  1122  without using a lens system. 
         [0106]      FIGS. 12A and 12B  and  FIGS. 13A and 13B  show an example of outputs from the photodiode elements (pixels)  1121  constructing the one-dimensional array sensor  1122  when regular-reflection light from the sample  10  is detected by the regular-reflection light detection optics  1120 . 
         [0107]      FIG. 12B  shows an example of outputs from the photodiode elements (pixels)  1121  when illumination light is emitted from the direction of the arrow to the recessed defect shown in  FIG. 12A  and regular-reflection light which is reflected from the sample  10  in the direction of the arrow by the illumination of the illumination light is detected by the one-dimensional array sensor  1122 . There is a characteristic such that, in the case where regular-reflection light from a surface having no defect (normal face) of the sample  10  is received, outputs from the elements  1121  of the one-dimensional array sensor  1122  forms a waveform corresponding to a uniform distribution of the wavefront strength of the regular-reflection light. On the other hand, in the case where reflection light from a region including a recessed defect is detected by the photodiode elements (pixels)  1121  of the one-dimensional array sensor  1122 , the peak level of signals output from photodiode elements (pixels) which detects regular-reflection light from the recessed defect is higher than a level of signals output from photodiode elements (pixels) which detects regular-reflection light from in the periphery of the recessed defect (the case of  FIG. 12B  shows an output of the fifth photodiode element (pixel)  1121 ) which detects regular-reflection light from the recess defect shown in  FIG. 12A ). 
         [0108]    On the other hand,  FIG. 13B  shows an example of outputs from the photodiode elements (pixels)  1121  when illumination light emitted from the direction of the arrow to a projected defect shown in  FIG. 13A  and regular-reflected in the direction of the arrow is detected by the one-dimensional array sensor  1122 . There is a characteristic such that, in the case where regular-reflection light from the projected defect part is detected by the one-dimensional array sensor  1122 , the detection level of the photodiode element (pixel)  1121  which detects regular-reflection light from a region including the projected defect becomes lower than the regular-reflection light detection level of the photodiode element (pixel) which detects regular-reflection light from a region in the periphery of the projected defect (the case of  FIG. 13B  shows an output of the ninth photodiode element (pixel)  1121 ) which detects regular-reflection light from the projected defect shown in  FIG. 13A ). 
         [0109]    In such a manner, the position and the kind of a defect can be specified from the characteristics of the changes in the output signal level from the photodiode elements (pixels)  1121  of the one-dimensional array sensor  1122 . Since the detection signal of the regular-reflection light and the detection signal of the scattering light can be distinguished from the level of the signal detected by each of the photodiode elements (pixels)  1121  of the one-dimensional array sensor  1122 , a continuous defect such as a scratch defect can be classified by a method similar to that described in the second embodiment. 
       Modification of Fourth Embodiment 
       [0110]      FIGS. 14A to 14C  show an example of an optical disk inspection apparatus  1400  in which the regular-reflection-light detection optics and the lateral scattering light detection optics are constructed separately from each other. 
         [0111]    As shown in  FIG. 14C , the optical systems in the modification are separated as regular-reflection light detection optics  1480  and scattering light detection optics  1490 . A right-side part in the rotating sample  10  is inspected by the regular-reflection light detection optics  1480  and a left-side part is inspected by the scattering light detection optics  1490 . By presetting the positional relations on the sample  10  inspected by the regular-reflection light detection optics  1480  and the scattering light detection optics  1490 , the positions on the sample  10  of a defect detected by the regular-reflection light detection optics  1480  and a defect detected by the scattering light detection optics  1490  can be made correspond to each other. 
         [0112]    The configuration of the optical magnetic disk inspection apparatus  1400  shown in  FIG. 14A  of the modification is substantially the same as that of the magnetic disk inspection apparatus  1100  described with reference to  FIGS. 11A to 11C  except for the point that the scattering light detection optics  1490  is provided. Specifically, the optical magnetic disk inspection apparatus  1400  has regular-reflection light detection optics  1480  including high-angle illumination optics  1410  and regular-reflection light detection optics  1420 , scattering light detection optics  1490  including low-angle illumination optics  1430  and lateral scattering light detection optics  1440 , a stage system  1450 , and a general control system  1470 . 
         [0113]    In a manner similar to the case of the fourth embodiment, the high-angle illumination optics  1410  in the regular-reflection light detection optics  1480  have a laser source  1411 , a beam expansion lens  1412  expanding a laser beam emitted from the laser source  1411 , a collimate lens  1413  converting the laser beam expanded by the beam expansion lens  1412  to parallel rays, and a convergence lens  1414  converging the parallel laser beams whose diameter is enlarged onto the surface of the sample  10 . The regular-reflection light detection optics  1420  are constructed by a one-dimensional array sensor  1422  formed by disposing a plurality of photodiode elements in an array in a manner similar to that shown in  FIG. 11C . 
         [0114]    On the other hand, like the high-angle illumination optics  1410 , the low-angle illumination optics  1430  in the scattering light detection optics  1490  have a laser source  1431 , a beam expansion lens  1432  expanding a laser beam emitted from the laser source  1431 , a collimate lens  1433  converting the laser beam expanded by the beam expansion lens  1432  to parallel rays, and a convergence lens  1434  converging the parallel laser beams whose diameter is enlarged onto the surface of the sample  10 . The lateral scattering light detection optics  1440  include, as shown in  FIG. 14B , a condenser lens  1441  for condensing lateral scattering light from the sample  10  irradiated with a laser beam and a detector  1442  for detecting the scattering light condensed by the condenser lens  1441 . 
         [0115]    The stage system  1450  includes a rotatable spindle shaft  1451  on which the sample  10  is placed, a stage  1452  for moving the spindle shaft  1451  in one direction in a plane, and a stage driving unit  1453  for driving the spindle shaft  1451  and the stage  1452 . 
         [0116]    The general control system  1470  has a signal process/control system  1460 , a memory  1471  that stores inspection data and data of inspection parameters, and an input/output unit  1472  having a display screen  1473 . 
         [0117]    As shown in  FIG. 14A , the signal process/control system  1460  includes: an illumination light source control unit  1461  for controlling the laser source  1411  of the high-angle illumination optics  1410  and the laser source  1431  of the low-angle illumination optics  1430 ; a detection signal processing unit  1462  for receiving output signals of the array sensor  1422  of the regular-reflection light detection optics  1420  and the detector  1442  of the scattering light detection optics  1440 , amplifying them, A/D converting the signals to digital signals, and performing signal process on the digital signals to detect a defect candidate; a defect continuity determining unit  1463  for extracting a continuous defect in the sample  10  by using the information of the defect candidate detected by the detection signal processing unit  1462 , the information of rotation of the spindle shaft  1451 , and the information of the position of the stage  1452 ; a defect feature amount extracting unit  1464  for extracting a feature amount of the defect detected by the detection signal processing unit  1462  including the continuous defect extracted by the defect continuity determining unit  1463 ; a defect classifying unit  1465  for classifying a defect by using the information of the feature amount of the defect extracted by the defect feature amount extracting unit  1464 ; a stage control unit  1466  for controlling the operation of the spindle shaft  1451  and the stage  1452  by controlling the stage driving unit  1453 ; and an MUP  1467  for controlling the illumination light source control unit  1461 , the detection signal processing unit  1462 , the defect continuity determining unit  1463 , the defect feature amount extracting unit  1464 , the defect classifying unit  1465 , and the stage control unit  1466 . 
         [0118]    In a manner similar to the fourth embodiment, the regular-reflection light detection optics  1420  of the regular-reflection light detection optics  1480  directly detect scattering light including regular-reflection light from the sample  10  by the one-dimensional array sensor  1422  without condensing the scattering light by using lenses. 
         [0119]    By using the optical magnetic disk inspection apparatus  1400  having such a configuration, defects in the sample  10  can be detected and classified by a method similar to the method described in the fourth embodiment. 
         [0120]    Although the present invention achieved by the inventors herein has been concretely described above on the basis of the embodiments, obviously, the present invention is not limited to the foregoing embodiments but can be variously modified without departing from the gist. 
         [0121]    The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Technology Category: 3