Abstract:
To increase the illumination efficiency by facilitating the change of the incident angle of illumination light with a narrow illumination width according to an inspection object and enabling an illumination region to be effectively irradiated with light, provided is a defect inspection method for obliquely irradiating a sample mounted on a table that is moving continuously in one direction with illumination light, collecting scattered light from the sample obliquely irradiated with the illumination light, detecting an image of the surface of the sample formed by the scattered light, processing a signal obtained by detecting the image formed by the scattered light, and extracting a defect candidate, wherein the oblique irradiation of the light is implemented by linearly collecting light emitted from a light source, and obliquely projecting the collected light onto the surface of the sample, thereby illuminating a linear region on the surface of the sample.

Description:
BACKGROUND 
       [0001]    The present invention relates to a defect inspection method which optically inspects defects of a minute pattern or foreign matters formed on a sample through a thin film process typically included in a semiconductor manufacturing process or a flat panel display manufacturing process, and more particularly to a defect inspection method and its device including an illumination optical system which is suitable for detecting the minute defects or foreign matters. 
         [0002]    WO 1999/006823 A (Patent Literature 1) discloses a conventional semiconductor wafer inspection device. This patent literature discloses a system for illuminating a laser beam linearly onto a wafer. As the illumination system, in the disclosed technique, the cylindrical lens or the main surface of the mirror is arranged, parallelly to the wafer, and the wafer is illuminated in a linear pattern. 
         [0003]    JP 5-209841 A (Patent Literature 2) discloses a system for linearly illuminating the wafer. The literature discloses a technique for condensing a laser beam onto a diffraction grating and obliquely forming an image of the condensed light. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: JP 1999/006823 A 
         Patent Literature 2: JP 5-209841 A 
       
     
       SUMMARY 
       [0006]    In the example of a target semiconductor wafer to be inspected, there are different numbers of layers of a multi-layer structure, different wiring materials in layers, different widths or forms of the pattern, and different processing steps for forming the pattern, in accordance with a variety of products (memory product or logical product) or the generation of the wiring node. Thus, there are a wide variety of defects to be detected. Typical examples of defects includes short-circuit or open-circuit in the same layer or different layers (interlayer wiring). 
         [0007]    To detect the defects with high sensitivity, it is necessary to detect an image with a visualized defect image and to perform a defect determination image process. To detect an image in which there is a high contrast of the defect image, it is necessary to adjust illumination conditions and detecting conditions, in accordance with target defects to be detected. 
         [0008]    Adjustment parameters as illumination conditions in a device having a laser as a light source include an incidence angle, direction, polarization, and line width of the illumination. The line width is preferably very minute, and the conditions for actualizing the defect image are different in accordance with the above-described defect type (variety), in relation to another incidence angle, direction, and polarization. Thus, it is preferred to set the illumination conditions corresponding to targets defect to be detected in each manufacturing process for wafer. 
         [0009]    Patent Literature 1 discloses that a cylindrical lens or a cylindrical mirror is arranged, and light is condensed and illuminated above the wafer. When the width of light condensing illumination is minute, that is, in a range from 1 to 2 μm or smaller than that, it is necessary to sufficiently restrain the wavefront aberration in the light condensing illumination. Thus, the curvature or thickness of the cylindrical lens or mirror needs to correspond to a particular incidence angle or direction. To realize the configuration in which the incidence angle is changed to, for example, 60 degrees or 70 degrees, in accordance with the target object to be inspected, it is necessary to realize a configuration which includes a replaceable cylindrical lens or mirror, in accordance with the incidence angle. To realize the width of the condensing light in a range 1 to 2 μm or smaller than that, it is necessary to remarkably enhance the profile irregularity of the lens or mirror or the positioning accuracy at the replacement. At this time, a problem is that it takes quite a long time to replace the cylindrical lens or mirror. 
         [0010]    Patent Literature 2 does not disclose a technique for changing the incidence angle or direction of the illumination. 
         [0011]    In Patent Literature 1, in the configuration using the cylindrical lens or mirror, a light beam in a direction orthogonal to the plane of incidence with respect to the lens or mirror is not condensed onto one point of the wafer and is spread into the direction of the plane of incidence, when a circular laser beam with a Gaussian distribution obliquely enters a cylindrical lens or mirror to illuminate above the wafer. The spread is equal to or greater than 5 to 10 nm, when the illumination conditions are: the light condensing width is 1 to 2 μm, the wavelength is 355 nm, and the incidence angle is 70 degrees. Thus, the actual illumination is in a range from 5 to 10 nm, even if the required illumination range is set to 1 to 2 mm, thus lowering the illumination intensity in the required illumination range. To avoid lowering of the inspection speed due to the lowering of the illumination, a problematic subject is that an expensive high output laser needs to be used. 
         [0012]    The present invention aims to solve the problem of the conventional technique and to provide an illumination method and a defect inspection device using the method, for facilitating changing of an incidence angle of illumination light with a narrow illumination width in accordance with a target to be inspected and for enhancing the illumination efficiency by efficiently irradiating illumination light into an illumination range. 
         [0013]    To solve the above-described object, according to the present invention, there is provided a defect inspection device comprising: a table unit on which a target sample to be inspected is mounted; an illumination optical system unit configured to obliquely illuminate the sample mounted on the table unit; a detecting optical system unit which condenses scattered light generated from the sample on which illumination light is obliquely irradiated by the illumination light optical system unit, and detects an image on a surface of the sample using the scattered light; an image processing unit configured to process a signal obtained by detecting the image on the surface of the sample using the scattered light by the detecting optical system unit, to extract defect candidates on the surface of the sample; and a control unit which controls the table unit, the illumination optical system unit, the detecting optical system unit, and the image processing unit, and wherein the illumination optical system unit includes a laser light source which emits a laser beam; a beam expander which expands a diameter of the laser beam; an anamorphic optical unit which controls a size of the laser beam in a particular direction; a cylindrical optical unit which condenses the laser beam passed through the anamorphic optical unit in one direction and forms a linearly condensed light image as an intermediate image; and a relay lens unit which forms the linearly condensed light image on a surface of the specimen mounted on the table unit to illuminate a linear region on the specimen, wherein a polarization condition of the laser beam passing through the anamorphic optical unit and the cylindrical optical unit is a specific linearly polarized condition, wherein optical coatings are applied to surfaces of a cylindrical lens of the cylindrical optical unit, said optical coating corresponding to the polarization state of the laser beam to reduce power loss of the laser beam, and wherein the relay lens unit includes a polarization control element which controls polarization condition of the laser beam illuminating the specimen. 
         [0014]    The solve the above-described object, according to the present invention, there is provided a defect inspection method comprising the steps of: irradiating illumination light obliquely onto a sample mounted on a table which is continuously moved in one direction; detecting an image on a surface of the sample using scattered light, by condensing the scattered light generated on the sample onto which the illumination light is obliquely irradiated; and processing a signal obtained by detecting the image on the surface of the sample using the scattered light to extract defect candidates on the surface of the sample, and wherein the irradiating the illumination light obliquely onto the sample includes illuminating a linear region of the surface of the sample, by forming an image of condensed light by linearly condensing light emitted from a light source, projecting the image of the condensed light obliquely onto the surface of the sample mounted on a table which is moved continuously in one direction, and forming the image on the surface of the sample. 
         [0015]    According to the present invention, the line width of the illumination can be minutely formed, in a range from 1 to 2 μm or lower, and it is possible to adjust the incidence angle, direction, and polarization of illumination light in relation to each target defect to be inspected. As a result, it can be expected to improve the inspection sensitivity by actualizing a defect image with a very minute defect. Further, it is possible to set a plurality of illumination incidence angles without changing to an expensive condensing mirror or lens, thus restraining the cost for the device. The light output from the laser can be formed with low loss and without spreading the illumination range more than necessary. Therefore, relatively a low output laser is applicable, and it is possible to realize low cost of laser and suppress damage on illumination components. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]      FIG. 1  is a block diagram illustrating a schematic configuration of a defect inspection device in a first embodiment. 
           [0017]      FIG. 2A  is a block diagram illustrating a configuration of a beam irradiation unit, in which a diffraction grating with relatively a narrow grating pitch is used, in the first embodiment. 
           [0018]      FIG. 2B  is a block diagram illustrating a configuration of a beam irradiation unit, in which a diffraction grating with relatively a wide grating pitch is used, in the first embodiment. 
           [0019]      FIG. 3  is a perspective view of the beam irradiation unit, illustrating the scheme of the irradiation incidence angle and the change of the direction by in-plane rotation of the diffraction grating, when an image of light condensed by a cylindrical lens is formed on the grating plane of the diffraction grating, in the first embodiment. 
           [0020]      FIG. 4  is a perspective view of the beam irradiation unit, illustrating the scheme of the irradiation incidence angle and the change of the direction by in-plane rotation of the diffraction grating, when an image of light condensed by a cylindrical lens is formed in front of the diffraction grating, in the first embodiment. 
           [0021]      FIG. 5  is a perspective view illustrating a configuration of the beam irradiation unit, when a reflection type diffraction grating is used as a diffraction grating, in the first embodiment. 
           [0022]      FIG. 6  is a block diagram illustrating a schematic configuration of a defect inspection device in a second embodiment. 
           [0023]      FIG. 7A  is a block diagram illustrating a configuration of a beam irradiation unit, when an incident angle of illumination light to a wafer is set to θ3, in the second embodiment. 
           [0024]      FIG. 7B  is a block diagram illustrating a configuration of the beam irradiation unit, when an incident angle of illumination light to a wafer is set to θ4, in the second embodiment. 
           [0025]      FIG. 8  is a block diagram illustrating a configuration of the beam irradiation unit, having a slit for transmitting a image of light condensed by a cylindrical lens in a position for forming the image of the condensed light, as a first modification of the beam irradiation unit in the second embodiment. 
           [0026]      FIG. 9A  is a front view of a slit plate. 
           [0027]      FIG. 9B  is a side view of the slit plate. 
           [0028]      FIG. 10A  is a front view of a beam irradiation unit which is formed of a concave mirror and a convex mirror, as a second modification of the beam irradiation unit in the second embodiment. 
           [0029]      FIG. 10B  is a side view of a beam irradiation unit which is formed of a concave mirror and a convex mirror, as a second modification of the beam irradiation unit in the second embodiment. 
           [0030]      FIG. 11A  is a block diagram illustrating a schematic configuration of a defect inspection device according to a third embodiment. 
           [0031]      FIG. 11B  is a cross sectional view illustrating a schematic configuration of a low angle scattered light detecting optical system of a detecting optical system of a defect inspection device in an third embodiment. 
           [0032]      FIG. 12  is a block diagram illustrating a schematic configuration of a defect inspection device in a fourth embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    Preferred embodiments of the present invention will now be described using the drawings. 
       First Embodiment 
       [0034]    Descriptions will now be made to an example in which the present invention is applied to a defect inspection device  1000  which inspects defects, such as a short-circuit defect, an open defect, or a foreign matter defect of the pattern of a semiconductor wafer, using any  FIG. 1  to  FIG. 5 .  FIG. 1  illustrates a configuration of the defect inspection device  1000 . 
         [0035]    The defect inspection device  1000  includes a stage unit  1300 , an illumination optical system  1100 , a detecting optical system  1200 , an image processing unit  1400 , a mechanism control unit  1500 , a system control unit  1600 , a storage unit  1610 , and a display unit  1620 . The stage unit  1300  is provided for placing thereon a semiconductor wafer (hereinafter referred to as a wafer)  1  having a circuit pattern on a target surface to be inspected, and is movable in an X-Y plane and in a height direction (Z direction). The illumination optical system  1100  irradiates illumination light to the wafer  1  placed on the stage unit  1300 . The detecting optical system  1200  detects scattered light from the wafer  1  to which the illumination light is irradiated. The image processing unit  1400  processes a scattered light detecting signal from the wafer  1 , output from the detecting optical system  1200 . The mechanism control unit  1500  controls operations of the mechanism units of the illumination optical system  1100 , the detecting optical system  1200 , and the stage unit  1300 . The system control unit  1600  controls the image processing unit  1400  and the mechanism control unit  1500 . The storage unit  1600  stores inspection results and inspection conditions. The display unit  1620  includes a screen for inputting the inspection conditions and displaying the inspection results. 
         [0036]    The illumination optical system  1100  includes a laser light source  10 , a beam expander  12 , an anamorphic prism  14 , a mirror  15 , and a beam irradiation unit  1110 . The beam expander  12  expands the beam diameter of a laser emitted from the laser light source  10 . The anamorphic prism  14  expands the laser beam expanded by the beam expander  12  into a particular direction. The mirror  15  reflects the laser beam emitted from the anamorphic prism  14  to change the optical path. The beam irradiation unit  1110  irradiates the laser beam whose optical path has been changed by the mirror  15  to the wafer  1  placed on the stage unit  1300 , from an oblique direction toward an elongated region (linear region)  35  thereof. A configuration of the beam irradiation unit  1110  will specifically be described later. 
         [0037]    The stage unit  1300  includes a chuck  2 , a Z stage  3 , an X stage  5 , a Y stage  7 , and a base plate  8 . The chuck  2  absorbs to chuck and holds the wafer  1 . The Z stage  3  is provided for placing thereon the chuck  2  and movable in a height direction (Z direction). The X stage  5  is provided for placing the Z stage  3  thereon and movable in an X direction in a plane. The Y stage  7  is provided for placing the X stage  5  thereon and movable in a Y direction in a plane. The base plate  8  is provided for placing the Y stage  7  thereon. The stage unit  1300  further includes a position sensor which detects the positions of the Z stage  3 , the X stage  5 , and the Y stage  7 , and no illustration thereof is given. 
         [0038]    The detecting optical system  1200  includes an objective lens  40 , a spatial filter  42 , a polarizing filter  44 , an imaging lens  45 , and an image sensor  50 . The objective lens  40  captures and condenses light scattered above the wafer  1 , of scattered light generated from the region  35  illuminated by the illumination optical system  1100 , in the wafer  1  held by the chuck  2  of the stage unit  1300 . The spatial filter  42  shields the strong diffraction light generated by the light scattered from fine repetitive patterns formed on the wafer  1 , of the scattered light from the wafer  1  as captured by the objective lens  40 . The polarizing filter  44  transmits only a specific polarization, of the scattered light from the wafer  1  that has passed through the spatial filter  42  without being shielded by the spatial filter  42 . The imaging lens  45  is provided for imaging the specific polarization transmitted through the polarizing filter  44 . The image sensor  50  detects the image of the scattered light, as imaged by the imaging lens  45 . 
         [0039]    The image processing unit  1400  includes an A/D conversion unit  1401 , a signal processing unit  1402 , and a defect detecting unit  1403 . The A/D conversion unit  1401  amplifies a detection signal (an analog signal) output from the image sensor  50 , and converts it into a digital signal (A/D conversion). The signal processing unit  1402  processes the A/D converted signal to acquire an image signal. The defect detecting unit  1403  processes the image signal acquired by the signal processing unit  1402 , extracts defect candidates, and obtains an image feature amount of the extracted defect candidate. 
         [0040]    The defect inspection device  1000  including the above configuration is used for inspecting defects on the surface of the semiconductor wafer  1  having the circuit pattern formed thereon. 
         [0041]    The semiconductor wafer  1  as a target to be inspected is absorbs to chuck by the chuck  2 . This chuck  2  is placed on the Z stage  3  which mounts on the X stage  5  and the Y stage  7 . The entire surface of the wafer  1  is inspected by the horizontal movement of the X stage  5  and the Y stage  7 . 
         [0042]    The laser light source  10  of the illumination optical system  1100  may be of a type that outputs a continuous wave laser or a type that outputs a pulsed laser. Candidates of the laser light source  10  include those having wavelengths of 532 nm, 355 nm, 266 nm, and gas lasers with 248 nm (KrF), 193 nm (ArF), 157 nm (F2). 
         [0043]    A laser beam  11  oscillated by the laser light source  10  is expanded by the beam expander  12  into a predetermined beam diameter, and expanded by the anamorphic prism  14  only in a particular direction, to be formed in an elliptic light flux. In this case, the particular direction implies a condensed direction on the wafer  1 . 
         [0044]    The laser beam  11  formed as the elliptic light flux is reflected on planar mirrors  15  and  16 , and enters the beam irradiation unit  1110 . As illustrated in  FIG. 2A , the laser beam of the elliptic light flux which has entered the beam irradiation unit  1110  enters the cylindrical lens  20 , and is condensed in the form of a narrow light flux on a transmission diffraction grating  25 . To reduce the aberration in the condensing unit and to have a narrower width of the condensed light, the convex surface of the cylindrical lens  20  preferably has an aspherical surface form. The laser beam  11  emitted from the cylindrical lens  20  enters the transmission diffraction grating  25 , and its incidence angle may be any of 0° angle of incidence as perpendicular illumination or an oblique angle. 
         [0045]    Of the laser beam.  11  entering the transmission diffraction grating  25 , particular high-order diffracted light  28  diffracted by the transmission diffraction grating  25  enters a relay lens  30  including lenses  31  and  33 , and a linear condensing line formed by the narrow light flux condensed on the surface of the transmission diffraction grating  25  obliquely enters the wafer  1 , to form an image on the longitudinal in the X direction of the wafer  1  and in the narrow region (linear region)  35  in the Y direction thereof. The relay lens  30  is a both-side telecentric relay lens. The illumination light irradiated onto the linear region  35  of the wafer  1  is longitudinal in the X direction. The relay lens  30  is set in a manner that the surface of the wafer  1  and the transmission diffraction grating  25  are in a conjugate relationship. The light condensed in the form of a narrow light flux on the surface of the transmission diffraction grating  25  is projected in the linear region of the  35  on the wafer. Therefore, it is possible to illuminate the wafer  1  with the linearly condensed light. 
         [0046]    It is preferred to set the angle of the laser beam  11  entering the transmission diffraction grating  25  after transmitting through the cylindrical lens  20  is set to an angle at which the diffraction efficiency of the particular high-order diffracted light  28  for use in the illumination will be high. When the magnification of the relay lens  30  is equal magnification, the number of grating members (or grating pitch) per unit length of the transmission diffraction grating  25  may be set in a manner that the angle of the high-order diffracted light from the normal line of the diffraction grating coincides with the angle of incidence on the wafer  1 . To change the angle of incidence on the wafer  1 , a non-illustrative driving unit is used for changing the transmission diffraction grating  25  to the transmission diffraction grating  26  which has different number of gratings (or grading pitch) of the diffraction gratings per unit length. 
         [0047]    Further, generally, in the diffraction grating, the grating efficiency is changed in accordance with the polarization. As this diffraction efficiency is high, the efficiency for light utilization as an illumination system is increased. It is therefore possible to apply the light source which oscillates an inexpensive low-output laser, as the laser light source  10 . To acquire the maximum diffraction efficiency, the incident polarization of light to the transmission diffraction grating  25  may be any of S polarization and P polarization. The P or S polarization light which has been adjusted to obtain the maximum diffraction efficiency is assumed as the incidence polarization light for the diffraction grating. However, to visualize the defects generated on the wafer  1 , it is necessary to be able to change the polarization state of the light between S/P/circular polarization in accordance with the defect type. 
         [0048]    Therefore, a wavelength plate  32  is embedded between the lenses  31  and  33  which form the relay lens  30  arranged between the transmission diffraction grating  25  and the wafer  1 . The plate  32  is formed of a ½ wavelength plate, a ¼ wavelength plate, or a combination thereof, which is independently rotatable. The grating pitch of the diffraction grating  25  is set equal to or smaller than the resolution of the relay lens  30 . As a result, it is possible to reduce the light and darkness occurring in the illumination light irradiated in the linear region  35  on the wafer  1 . The light and darkness is due to the periodic structure of the transmission diffraction grating  25 . 
         [0049]    With the objective lens  40 , the detecting optical system  1200  captures light scattered above the wafer  1 , of light scattered by the pattern or defects formed in the linear region  35  of the wafer  1 , using illumination light irradiated in the linear region  35  on the wafer  1 . The system  1200  shields the diffracted light from the normal pattern by the light shielding pattern formed in the spatial filter  42  arranged in the Fourier transform region of the objective lens  40 . Of light transmitted through the spatial filter  42 , light having a particular polarized component transmits through the polarizing filter  44 . Then, a dark field image of the wafer  1  is formed on the image sensor  50 , by the imaging lens  45 . 
         [0050]    Candidates of the image sensor  50  are of a CCD (Charge Coupled Device) type or a CMOS (Complementary Metal Oxide Semiconductor) type. The configuration illustrated in  FIG. 1  is that of the one-dimensional image sensor which continuously detects images while scanning the Y stage  7  with uniform speed. This one-dimensional image sensor  50  may be a plural-line sensor, such as a TDI (Time Delay Integration) sensor, a dual line sensor, and the like. 
         [0051]    The image processing unit  1400  amplifies an analog signal output from the image sensor  50  which has detected the dark field image of the wafer  1 , using the A/D conversion unit  1401 , and converts it into a digital signal (A/D conversion). Then, the A/D converted digital signal is input to the signal processing unit  1402  and image-processed, thereby obtaining a digital image. This digital image is sent to the defect detecting unit  1403 , and is image-processed (including die comparison or cell comparison), thereby extracting defect candidates and calculating an image feature amount of the extracted candidates. The position information of the defect candidates and information regarding the image feature amount are sent to the system control unit  1600 . 
         [0052]    The system control unit  1600  displays a GUI (Graphical User Interface) with the user who instructs the defect inspection device  1000  for an operation, on the display screen of the display unit  1620 . Thus, it is possible to browse information regarding defects that the user would like to detect, through the GUI, and also a past inspection history or inspection recipe stored in the storage unit  1610 . The information sent from the image processing unit  1400  is stored in the storage unit  1610 . Each mechanism operates in response to an instruction made by the user through the GUI displayed on the display unit  1620 , through the mechanism control unit  1500 . The mechanisms to be controlled include the ON/OFF of the laser light source  10  of the illumination optical system  1100 , the expansion ratio of the beam expander  12 , the exchange of the transmission diffraction grating  25 , the rotation angle of the wavelength plate unit  32 , the shielding pattern of the spatial filter  42  of the detecting optical system  1200 , the rotation angle of the polarization filter  44 , and the instruction for the operation of each stage of the stage unit  1300  or timing to capture images into the image processing unit  1400 . 
         [0053]      FIG. 2A  and  FIG. 2B  illustrate the scheme to change the illumination incidence angle onto the wafer  1  by switching the transmission diffraction gratings  25  and  26  using a non-illustrative switching mechanism, in the beam irradiation unit  1110 . In  FIG. 2A , a laser beam  19  enters the cylindrical lens  20 , transmits through the cylindrical lens  20 , and then is linearly condensed on the transmission diffraction grating  25 . In the laser beam  19 , the cross sectional shape of the optical axis is formed as an ellipse. Of the light transmitted through the transmission diffraction grating  25 , the angle of θ 1  is set between the high-order diffracted light diffracted on the side of the relay lens  30  and for use in the illumination and the normal line of the transmission diffraction grating  25 . An equal magnification relay system  30  causes a condensed light image of the laser beam  19  to obliquely enter the wafer  1  at the incidence angle θ 1 , to form an image (oblique projection) in the linear region  35  on the wafer  1 . Note that this image of the laser is one that has linearly been condensed on the transmission diffraction grating  25 . 
         [0054]      FIG. 2B  illustrates a configuration in which the incidence angle to the wafer  1  is made smaller than that of  FIG. 2A . The laser beam  19 , the cylindrical lens  20 , the relay lens  30 , and the wafer  1  are arranged in the same manner as that of  FIG. 2A , while the transmission diffraction grating  25  used in  FIG. 2A  is replaced with the transmission diffraction grating  26  having a larger pitch than that of the transmission diffraction grating  25 . 
         [0055]    Let it be assumed that the angle formed by the incidence laser beam  19  and the normal line of the diffraction grating is “α” and the angle (angle of diffraction) formed between the diffracted light and the normal line of the diffraction grating is “β”. In this case, the following relational expression can be used. 
         [0000]      Sin α±sin β= Nmλ   (Expression 1)
       N: number of grating members per mm   m: degree of diffraction (m=0, ±1, ±2, . . . )   λ: wavelength       
 
         [0059]    The transmission diffraction grating  26  illustrated in  FIG. 2B  includes a less number of grating members than that of the transmission diffraction grating  26  illustrated in  FIG. 2A , (that is, there is a large pitch between the grating members). If the angle of diffraction β gets smaller, the angle θ 2  formed between the high-order diffraction light and the normal line of the diffraction grating  26  becomes smaller than θ 1 . By performing oblique projection on the wafer  1  with the relay lens  30  designed with an NA (Numerical Aperture) for enabling to capture the high-order diffracted light, it is possible to illuminate the wafer  1  at a large incidence angle as compared to the case of  FIG. 2A . 
         [0060]    Accordingly, the image of the condensed laser beam  19  which has linearly been condensed by the cylindrical lens  20  is formed in the linear region  35  on the wafer  1 . Thus, if an image of condensed light with a width equal to or narrower than 1 to 2 μm can be formed, the linear region  35  to be formed on the wafer  1  can have a width equal to or narrower than 1 to 2 μm, regardless of the incidence angle of the illumination light onto the wafer  1 . It is possible to avoid diffusion of illumination light to a region, beyond an imaging range for inspection and thus having nothing to do with inspection. Therefore, the laser beam  11  output from the laser light source  10  can be irradiated with high efficiency onto a target range to be inspected on the wafer  1 , that is, on the imaging range for inspection. As a result, it is possible to improve the illumination brightness of the linear region having a narrow line width on the wafer  1 , thus enabling to perform high sensitive inspection. 
         [0061]    By changing the pitch of the diffraction pattern in the transmission diffraction grating, it is possible to change the incidence angle of the high-order diffracted light from the transmission diffraction grating onto the wafer  1 , without changing the positions of the illumination optical system  1100  and/or the beam irradiation unit  1110 . 
         [0062]      FIG. 3  illustrates a unit for changing the illumination elevation angle and the direction for the wafer  1 . The laser beam  19  entering the cylindrical lens  20  is parallel light, and has a cross sectional shape which is formed as an ellipse  18  by the anamorphic prism  14 . This cross sectional shape is in a plane perpendicular to the optical axis. The parallel light is linearly condensed  27  on the transmission diffraction grating  25  by the cylindrical lens  20 . Of the diffracted light generated by the laser beam  19  transmitting through the cylindrical lens  20 , the high-order diffracted light  28  is caused to enter the relay lens  30 , and an image of the illumination light  27  is formed with an equal magnification. This illumination light is linearly condensed on the transmission diffraction light  25  on the wafer  1  by the lenses  31  and  33  included in the relay lens  30 . In this configuration, it is possible to change the diffraction direction of the high-order diffraction light  28 , by rotating the transmission diffusion grating  27  using a non-illustrative driving unit as shown with an arrow  75 , at a grating normal line  70  as the rotational center. As a result, it is possible to control the illumination direction of the region  35  to which the illumination light is illuminated on the wafer  1 , within the range of the NA of the lenses  31  and  33  included in the relay lens  30 . 
         [0063]    In  FIG. 1  to  FIG. 3 , the descriptions have been made to the configuration in which the condensed position of the laser entering the cylindrical lens  20  is adjacent to the grating plane of the transmission diffraction grating  27 . However, it is possible to obliquely form a linear condensed light image on the wafer  1 , as long as an imaging relation is kept between the condensed position  27  and the wafer  1 , even if there is a certain distance equal to or greater than the depth of focus of the cylindrical lens  20  between the linearly-condensed position  27  by the cylindrical lens  20  and the transmission diffraction grating  25 , as illustrated in  FIG. 4 . Accordingly, the condensed position and the grating plane are spatially separated, thereby enabling to reduce the energy of the laser beam condensed on the grating plane and to restrain the damage on the grating plane of the transmission diffraction grating  25 . 
         [0064]    In  FIG. 1  to  FIG. 4 , the descriptions have been made to the example in which the transmission diffraction grating  25  is used as a diffraction grating.  FIG. 5  illustrates an example in which a reflection diffraction grating  29  is used in place of the transmission diffraction grating  25 . In the configuration illustrated in  FIG. 5 , the cylindrical lens  20  is arranged on the side of the plane where the diffraction grating of the reflection diffraction grating  29  is formed. In addition, the laser beam  19  which is formed as an ellipse by the anamorphic prism  14  and reflected on the mirror  15  is caused to enter the cylindrical lens  20 , without using the mirror  16  included in the configuration of  FIG. 1 , and is linearly condensed  27  near the reflection diffraction grating  29 . In the configuration, the high-order reflected light for use in illumination is condensed to obliquely form an image of condensed light near the reflection diffraction grating  29 , in the linear region  35  on the wafer  1 , using the lenses  31  and  33  included in the equal magnification relay system of the relay lens  30 . 
       Second Embodiment 
       [0065]      FIG. 6  illustrates a schematic configuration of a defect inspection device  2000  including an illumination optical system  2100  which obliquely illuminates above the wafer  1  without using the transmission diffraction gratins  25  and  26  described in the first embodiment or the reflection diffraction grating  29 . 
         [0066]    The constituent elements, except the illumination optical system  2100 , are the same as that of the defect inspection device  1000  described in  FIG. 1 . Thus, the same reference numerals as those of  FIG. 1  are given thereto, and will not be described again. 
         [0067]    In the illumination optical system  2100 , the laser beam  11  oscillated by the laser light source  10  is expanded into a predetermined beam diameter by the beam expander  12 , and it is expanded only in a particular direction by the anamorphic prism  14 , thereby being formed in an elliptic light flux. In this case, the particular direction implies a direction in which the condensing of light is performed on the wafer  1 . The laser beam  19  which is formed in an elliptic light flux is reflected on the mirrors  15  and  16 , and enters a beam irradiation unit  2110 . The laser beam  19  having an elliptic light flux and entered the beam irradiation unit  2110  enters the cylindrical lens  20  which is arranged with respect to the planar mirror  16 , as illustrated in  FIG. 7A . The laser beam  10  transmitted through the cylindrical lens  20  will be a narrow light flux one direction of which is condensed, to form a linearly condensed light image  92  (intermediate image). To obtain a narrower condensed width by reducing the aberration in the linear condensed light image  92 , it is preferred that the convex surface of the cylindrical lens  20  has an aspherical surface form. 
         [0068]    The light which has formed the linear condensed light image  92  enters a relay lens  30  having the lenses  31  and  33  and a zoom function, and the linear condensed light image  92  is obliquely formed in the linear region  35  on the wafer  1 . The linear region  35  on the wafer  1  is longitudinal in the X direction and narrow in the Y direction. The linear region  35 , to which the illumination light is irradiated on the wafer  1 , is longitudinal in the X direction. By setting the relay lens  30  in a manner that the surface of the wafer  1  and the linearly condensed light  35  are in a conjugate relationship, the linearly condensed light  92  formed by the cylindrical lens  20  is projected and illuminated in the linear region  35  on the wafer  1 . 
         [0069]    When there is set a large incidence angle of the condensed illumination light irradiated into the linear region  35  on the wafer  1  from the relay lens  30 , the incidence angle of the laser beam  19  entering the cylindrical lens  20  after reflected on the planar mirror  16  is large as well. In this case, to reduce the reflection loss on the surface of the cylindrical lens  20 , the polarization of the laser beam  19  entering the cylindrical lens  20  is selected as S polarization light or P polarization light, and an antireflection film (not illustrated) to be formed on the surface of the cylindrical lens  20  is necessarily optimized. The polarization light for restraining the surface reflection is assumed as incidence polarization light toward the cylindrical lens  20  where a non-illustrative antireflective film is formed. However, to visualize defects generated on the wafer  1 , it is necessary to be able to change the polarization state of the light between S/P/circular polarization in accordance with the defect type. A wavelength plate  32  is embedded into the relay lens  30 . The plate  32  is formed of a ½ wavelength plate, a ¼ wavelength plate, or a combination thereof, which is independently rotatable. 
         [0070]      FIG. 7A  and  FIG. 7B  illustrate a unit for changing an elevation angle of illumination light (illumination elevation angle) entering the wafer  1 . The planar mirror  16  and the cylindrical lens  20  form a light condensing unit  95 , and this unit has an integral structure.  FIG. 7A  illustrates a case of a large incidence angle θ 3  toward the wafer  1 , while  FIG. 7B  illustrates a case of a small incidence angle θ 4 . In  FIG. 7A , the light condensing unit  95  which is formed of the planar mirror  16  and the cylindrical lens  20  is mounted on a goniometer  90 . 
         [0071]    The elliptical light flux  19  entering the light condensing unit  95  after reflected on the planar mirror  15  is reflected on the planar mirror  16 , and enters the cylindrical lens  20 . The elliptical light flux  19  emitted from the cylindrical lens  20  is condensed in one direction, thereby forming the linearly condensed light image  92 . The goniometer  90  can rotate the light condensing unit  90 , at, as a rotation center, an intersection  94  between this linearly condensed light  92  and the optical axis of the elliptical light flux  19  emitted from the cylindrical lens  20 . The light having formed the linear condensed light image  92  enters the relay lens  30  including a zoom function, and is irradiated into the linear region  35  in the surface of the wafer  1  where the entire area of the linearly condensed light image  92  and the surface of the wafer  1  are in a conjugate relationship. 
         [0072]    In the configuration illustrated in  FIG. 7B , the light condensing unit  95  rotates (in a counter clockwise direction on the illustration sheet), thereby rotating a linearly condensed light image  92  as well. At this time, a beam of light forming the linearly condensed light image  92  is inclined in a direction that the angle formed with the Z axis gets large. As a result, the light transmitting through the zoom lens has the small incidence angle θ 4  on the wafer  1 . 
         [0073]    Because the linearly condensed light image  92  rotates, the linearly condensed light image  92  and the wafer  1  are not conjugate with each other, at the magnification same as the magnification of the relay lens  30  including the zoom function of  FIG. 7A . Thus, the magnification of the relay lens  30  including the zoom function (configuration for realizing the zoom function is not illustrated) is adjusted and reduced from the case of  FIG. 7A . This magnification is adjusted for projecting the linearly condensed light image  92  on the wafer  1 . As a result, the linearly condensed light image  92  and the wafer  1  can be in a conjugate relationship. 
         [0074]      FIG. 8  illustrates a configuration for mechanically forming a narrow form, for oblique projection on the wafer  1 , as the first modification of the second embodiment. The configuration of the optical system is the same as that illustrated in  FIG. 6 , and a slit plate  110  having a linear opening  113  is arranged in a position for linearly condensing light by the cylindrical lens  20 . The image of the opening  113  in the slit plate  110  is obliquely projected on the wafer  1  using the relay lens  30 . As a result, it is possible to restrain a change in the linearly illumination position or line width due to the fluctuation of the laser beam. 
         [0075]      FIG. 9A  illustrates a front view of a structure of the slit plate  110 , while  FIG. 9B  is a side view of the slit plate. A substrate  111  of the slit plate  110  is formed of synthesis silica through which ultraviolet light transmits. A reflecting film or an absorbing film is formed for a light shielding unit  112 , while any of these films is not formed for the slit-like formed opening  113  (width W, length L). Candidates of the reflection film  113  formed for the light shielding unit  112  include a dielectric multilayer and a metal film such as aluminum, while a candidate of the absorbing film is chromium oxide. The opening width W of the opening  113  illustrated in  FIG. 9A  is in a range from 2 to 1 μm. Thus, it is possible to form an opening pattern using a photolithography process and an etching process. 
         [0076]      FIG. 10A  illustrates a unit for forming the linearly condensed light image  92  to be projected on the wafer  1  using the relay lens  30  or the relay lens  30  having the zoom function, as the second modification of the second embodiment. The parallel light  19  which is elliptically formed is caused to enter a concave cylindrical mirror  120 , and this reflected light is caused to enter a convex cylindrical lens  125 , thereby forming the linearly condensed light image  92 . The convex cylindrical lens  125  is formed to have the convex surface radius which is approximately one half of the radius of the reflecting surface of the concave cylindrical mirror  120 . As a result, it is possible to condense the beams of light in directions orthogonal to the concave cylindrical mirror  120  and the plane of incidence of the convex cylindrical lens  125 . As a result, the longitudinal direction of the linearly condensed light image  92  is not expanded more than necessary, thus avoiding a reduction in the illumination efficiency. 
         [0077]    As shown in  FIG. 10B  at least one of the concave surface of the concave cylindrical mirror  120  and the convex surface of the cylindrical lens  125  has an aspherical form. As a result, it is possible to reduce the aberration in the formation position of the linearly condensed light image, thus attaining a very small width of condensing light. An alternative solution for that is wavefront correction in a manner that the aberration is reduced with another optical element, even if the concave surface or the convex surface is not formed to have an aspherical form. For example, the planar mirror  15  of  FIG. 6  has an aspherical form, or one surface of a parallel plate (not illustrated) has an aspherical form. 
       Third Embodiment 
       [0078]    Descriptions will now be made to an example in which the present invention is applied to a surface inspection device which detects surface defects or foreign matters attached on the surface on a wafer (bear wafer) where no pattern is formed thereon, using  FIG. 11A . In  FIG. 11A , the same constituent elements as those of  FIG. 1  descried in the first embodiment are identified with the same reference numerals as those in  FIG. 1 . 
         [0079]    The surface inspection device illustrated in  FIG. 11A  includes the illumination optical system  1100 , a detecting optical system  3200 , a stage unit  3300 , an image processing unit  3400 , a mechanism control unit  3500 , an entire control unit  3600 , a storage unit  3610 , and a display unit  3620 . 
         [0080]    In the above configuration, the illumination optical system  1100  has the same configuration as that of the first embodiment. An image of light, which is linearly condensed on the surface of the transmission diffraction grating  25  by the cylindrical lens  20 , is obliquely projected and formed in a linear region  3035  on the surface of a wafer  3001  through the relay lens  30 . 
         [0081]    The detecting optical system  3200  detects scattered light generated in the linear region  3056  on the surface of the wafer  3001 , on which the image of illumination light which is linearly condensed is obliquely projected. 
         [0082]    The wafer  3001  is chucked by a chuck  3302  of the stage unit  3300 . It includes a θ stage  3303 , an X stage  3304 , and a base plate  3305 . The θ stage  3303  lets the chuck  3302  rotate thereon. The X stage  3304  accepts the θ stage  3303  to be mounted thereon, and is movable in an X direction. The base plate  3305  accepts the X stage  3304  to be mounted thereon. The stage unit  3300  includes a sensor for detecting the rotational angle of the θ stage  3303  and a sensor for detecting the position of the X stage. These sensors are not illustrated. 
         [0083]    An image of illumination light which is linearly condensed is obliquely projected in the linear region  3035  of the surface of the wafer  3001 , in a state where the wafer  3001  is chucked by the chuck  3302 , rotated by the θ stage  3303 , and moved by the X stage  3304  at a constant speed in the X direction during rotation. 
         [0084]    The detecting optical system  3200  includes low angle scattered light detecting optical systems  3210  and  3240  and high angle scattered light detecting optical systems  3220  and  3230 . The low angle scattered light detecting optical systems  3210  and  3240  detect light scattered in a low angle direction as seen from the surface of the wafer  3001 , of scattered light generated in the linear region  3035  on the surface of the wafer  3001 . The high angle scattered light detecting optical systems  3220  and  3230  detect light scattered in a high angle direction as seen from the surface of the wafer  3001 . 
         [0085]    As illustrated in  FIG. 11B , the configuration of the low angle scattered light detecting optical system  3210  includes an objective lens  3211 , an image forming lens  3212 , a one-dimensional sensor  3213 , and a lens-barrel  3214 . The objective lens  3211  condenses light scattered in a direction of the low angle scattered light detecting optical system  3210 , of scattered light generated in the linear region  3035  on the surface of the wafer  3001 . The image forming lens  3212  forms an image of the scattered light in the linear region  3035  on the surface of the wafer  3001 , with the scattered light condensed by the objective lens  3211 . The one-dimensional sensor  3213  detects the image of the scattered light in the linear region  3035 , as formed by the image forming lens  3212 . The lens-barrel  3214  includes the entire elements. The low angle scattered light detecting optical system  3240  and the high angel scattered light detecting optical systems  3220  and  3230  also have the same configuration. 
         [0086]    An analog signal is obtained, upon detection of the image of the scattered light generated in the linear region  3035  on the surface of the wafer  3001 , by each of the low angle scattered light detecting optical systems  3210  and  3240  and the high angle scattered light detecting optical systems  3220  and  3230 . This obtained analog signal is input and amplified by the A/D conversion unit  3401  of the image processing unit  3400 , thereafter being converted into a digital signal (A/D conversion). The A/D converted signal is processed by a signal processing unit  3402  to obtain an image signal. The image signal is processed by a defect detecting unit  3403 , to detect defect candidates on the wafer  3001  and to extract feature amounts of the defects detected on the wafer  3001  including position information, size, length, and the brightness of the image. 
         [0087]    The detected position information of the defect candidates or the feature amount information are sent to the entire control unit  3600 . The processes by the entire control unit  3600  and the functions of the mechanism control unit  3500  are the same as the processes by the system control unit  1600  and the functions of the mechanism control unit  1500  explained in the first embodiment, and thus will not be described again. 
         [0088]    In a surface inspection device  3000  having the above configuration, the illumination optical system  1100  forms an image of condensed light with the laser beam  19  which is linearly condensed by the cylindrical lens  20  in the linear region  3035  on the wafer  3001 . Thus, it is possible to realize the width of the linear region  3035  for forming the image on the wafer  3001 , in a range from 1 to 2 μm or ever thinner than that, regardless of the incidence angle of the illumination light for the wafer  3001 , as long as an image of condensed light with a width from 1 to 2 μm or thinner can be formed by the cylindrical lens  20 . As a result, it is possible to avoid diffusion of illumination light to a region, having nothing to do with inspection and beyond the image range for inspection, and to efficiently irradiate the laser beam output from the laser light source  10  onto a region for inspection on the wafer  3001 , that is, the imaging range for inspection. As a result, it is possible to improve the illumination brightness of the linear region which has a narrow line width and to which the illumination light is irradiated, on the wafer  3001 . This enables high sensitive inspection. 
       Fourth Embodiment 
       [0089]    Descriptions will now be made to an example using  FIG. 12  in which the illumination optical system described in the second embodiment is applied to a surface inspection device  4000  which detects surface defects or foreign matters attached on a surface of the wafer (bear wafer)  3001  where no patter is formed on the surface. In  FIG. 12 , the same reference numerals are given to those constituent elements same as those of  FIG. 6  described in the second embodiment or those of  FIG. 11A  described in the third embodiment. 
         [0090]    The surface inspection device illustrated in  FIG. 12  includes the illumination optical system  2100 , the detecting optical system  3200 , the stage unit  3300 , an image processing unit  4400 , a mechanical control unit  4500 , an entire control unit  4600 , a storage unit  4610 , and a display unit  4620 . 
         [0091]    In the above configuration, the illumination optical system  2100  has the same configuration described in the second embodiment. The image of the illumination light  92  linearly condensed by the cylindrical lens  20  is obliquely projected and formed in the linear region  3035  on the surface of the wafer  3001  through the relay lens  30 . 
         [0092]    As described in the second embodiment, the planar mirror  16  and the cylindrical lens  20  of the illumination optical system  2100  are mounted on the goniometer  90 , at, as a rotation center, a position where the image of the illumination image  92  linearly condensed by the cylindrical lens  20  is formed. This is not illustrated in  FIG. 12 . 
         [0093]    The detecting optical system  3200  detects the light scattered in the linear region  3035  on the surface of the wafer  3001 , onto which the image of the linearly condensed illumination light is obliquely protected. 
         [0094]    The operations from the signal processing for a signal detected by the detecting optical system  3200  are the same as those described in the third embodiment, and thus will not be described again. 
         [0095]    Accordingly, the descriptions have specifically been made to the present invention of the present inventors. However, the present invention is not limited to the above embodiments, and various modifications are included. For example, a configuration part of some embodiment may be replaced with another configuration part of another embodiment, or a configuration part of some embodiment may be added to another configuration, without departing from the scope. A configuration part of each embodiment may be added to, deleted from, and replaced with another known configuration. 
       DESCRIPTION OF SYMBOLS 
       [0096]      1 , 3001  . . . wafer  2 , 3302  . . . chuck  3  . . . z stage  3303  . . . stage  5 , 3304  . . . x stage  7  . . . y stage  8 , 3305  . . . base plate  10  . . . laser light source  12  . . . beam expander  14  . . . anamorphic prism  20  . . . cylindrical lens  25  . . . transmission diffraction grating  29  . . . reflection diffraction grating  30  . . . relay lens  32  . . . wavelength plate  1200 , 3200  . . . detection optical system  40 , 3211  . . . objective lens  42  . . . spatial filter  44  . . . polarization filter  45 , 3212  . . . imaging lens  50 , 3213  . . . image sensor  1300 , 3300  . . . stage unit  1400 , 3400  . . . image processing unit  1600 , 2600 , 3600 , 4600  . . . system control unit  1500 , 2500 , 3500 , 4500  . . . mechanism control  110  . . . slit  120  . . . concave cylindrical mirror  125  . . . convex cylindrical mirror