Abstract:
A defect inspection tool includes an illumination optical system for irradiating light to a surface of an object, and a detection optical system for detecting light scattered from the surface of the object which is irradiated. The detection optical system include an analyzer, a photoelectric converting device for receiving the scattering light passed through the analyzer, a member for saving a database prepared through an actual measurement or a calculation in correspondence with a condition of the illumination optical system, that of the detection optical system, a kind of an object to be inspected, and a rotation angle of the analyzer, and a member for adjusting an angle of the analyzer by selecting an angle of the analyzer from a database saved in the member for saving on a basis of an inspection recipe after receiving the inspection recipe to the defect inspection tool.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation application of U.S. application Ser. No. 11/940,483, filed Nov. 15, 2007, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    (1) Field of the Invention 
         [0003]    The present invention relates to a defect inspection tool and a defect detection method, and more specifically to a foreign substance and defect inspection tool for inspecting a minute foreign substance and a minute defect present on the surface of a semiconductor substrate or the like with high sensitivity and high speed, and a defect detection method. 
         [0004]    (2) Description of the Related Arts 
         [0005]    In a manufacturing line for a semiconductor substrate, a thin-film substrate, or the like, to maintain and improve the yield ratio of the product, a defect and a foreign substance present on the surface of the semiconductor substrate, the thin-film substrate, or the like are inspected. For example, for a sample such as a semiconductor substrate before circuit pattern formation, it is required to detect a minute defect and foreign substance of 0.05 μm or less in size on the surface. With conventional inspection tools, for example, as in Japanese Patent Application Laid-Open Publication No. H9-304289) and U.S. Pat. No. 5,903,342, to detect such a minute defect and such a minute foreign substance, a laser beam condensed into several tens of micrometers in size is irradiated to a sample surface, and scattering light from the defect and the foreign substance is condensed and detected. 
       SUMMARY OF THE INVENTION 
       [0006]    In a defect inspection for a semiconductor substrate, inspection objects include, in addition to a bare Si wafer, a wafer with various films formed on the surface thereof. For a sample formed with a metal film in particular, scattering light generated by surface roughness thereof is large, thus making it difficult to detect a minute defect and a minute foreign substance. 
         [0007]    Therefore, it is an object of the present invention to provide a defect inspection tool and a defect detection method capable of detecting a minute defect and a minute foreign substance regardless of scattering light generated by roughness of a sample surface. 
         [0008]    Main configuration of one aspect of the invention includes: a laser light source; an illumination optical system for controlling light emitted from the laser light source; a sample support for holding a sample to be inspected; and a detection optical system for, when light emitted from the illumination optical system is irradiated to a surface of the sample to be inspected, detecting first scattering light scattered from an object including a foreign substance and defect present on the surface and second scattering light scattered from surface roughness the surface has. The detection optical system includes: a condensing part for condensing the first and second scattering light; a photoelectric converter for converting these condensed scattering light into an electrical signal; and an analyzer for suppressing the second scattering light inputted to the photoelectric converter. 
         [0009]    Insertion of the analyzer in an optical path of the detection optical system at such an angle that the scattering light generated by the roughness becomes minimum suppresses the scattering light generated by the roughness, thereby permitting detection of a minute defect and a minute foreign substance. 
         [0010]    As described above, the invention can achieve an inspection while suppressing scattering light from roughness by the analyzer, thus permitting a detection of a minute foreign substance and a minute defect even in a sample formed with a metal film and large roughness. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    These and other features, objects and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings wherein: 
           [0012]      FIG. 1  is a diagram showing one embodiment of the present invention; 
           [0013]      FIG. 2  is a diagram showing another embodiment of the present invention; 
           [0014]      FIG. 3  is a diagram illustrating a relationship between the orientation of a detection optical system and the analyzer angle; 
           [0015]      FIG. 4  is a diagram illustrating a relationship between film materials and the analyzer angle; 
           [0016]      FIG. 5  is a diagram illustrating a relationship between the film materials and the analyzer angle; 
           [0017]      FIG. 6  is a diagram illustrating one embodiment of an analyzer rotating mechanism; 
           [0018]      FIG. 7  is a diagram illustrating an inspection flow; 
           [0019]      FIG. 8  is a diagram illustrating another inspection flow; and 
           [0020]      FIG. 9  is a diagram showing one example of a GUI. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Hereinafter, the embodiments of the present invention will be described with reference to the accompanying drawings. 
       First Embodiment 
       [0022]      FIG. 2  shows one example of a tool for detecting a defect and a foreign substance on a semiconductor wafer according to the invention.  FIG. 2  shows a case where a defect and a foreign substance on the semiconductor wafer before circuit pattern formation is detected. As schematic configuration, this tool is composed of an illumination optical system  101 , detection optical systems  102 , and a wafer stage  103 . Two detection optical systems  102   a  and  102   b  are shown in  FIG. 2 . Note that the number of detection optical systems provided may be one or more. 
         [0023]    The illumination optical system  101  is composed of a laser light source  2 , an attenuator  3 , a beam expander  4 , a wavelength plate  5 , and a condensing lens  7 . A laser beam emitted from the laser light source  2  is adjusted to a required light amount by the attenuator  3 , the beam diameter is expanded by the beam expander  4 , and the polarization direction of illumination is set by the wavelength plate  5  to illuminate a detection area  8  of a wafer  1  while condensing light thereon by the condensing lens  7 . Numerals  6   a  and  6   b  denote mirrors for changing the illumination optical path, and they are used when necessary. The wavelength plate  5  sets illuminating polarized light to S-polarized light, P-polarized light, or circular polarized light. 
         [0024]    The detection optical system  102  is composed of a scattering light detecting lens  9  and a photoelectric conversion element  12 . Scattering light from a foreign substance and a defect present in the detection area is condensed on the light receiving surface of the photoelectric conversion element  12  by the scattering light detecting lens  9 . The photoelectric conversion element  12  generates an electrical signal of a magnitude proportional to the amount of scattering light received, and a signal processing circuit (not shown) performs signal processing to thereby detect a foreign substance and a defect and then detect the magnitude and position thereof. The photoelectric conversion element  12  is used for receiving this scattering light condensed by the detection optical system  102  and then performing photoelectric conversion thereon. Examples of such a photoelectric conversion element  12  include a TV camera, a CCD linear sensor, a TDI sensor, and a photoelectric multiplier tube. 
         [0025]    The wafer stage  103  is composed of a chuck (not shown) for holding the wafer  1 , a rotating mechanism  14  for rotating the wafer  1 , and a straight feed mechanism  13  for feeding the wafer  1  straight in the radial direction. Horizontal rotational scanning and straight movement of the wafer  1  on the wafer stage  103  permits detection of a foreign substance and a defect over the entire region of the wafer  1  and also permits magnitude measurement thereof. 
         [0026]    The attenuator  3  is composed of a ½ wavelength plate and a polarized beam splitter (PBS). The attenuator  3  changes, by the ½ wavelength plate, the polarization direction of a beam (linear polarized light) emitted from the laser light source to change the amount of light passing through the PBS. Rotating the ½ wavelength plate changes the polarization direction, thereby permitting adjustment of the amount of light. 
         [0027]    The detection optical systems  102  can be oriented multidirectionally, and outputs of photoelectric conversion elements  12   a  and  12   b  are subjected to addition, subtraction, division, or the like in accordance with purposes. 
         [0028]    When a metal film or the like is formed on the surface of the wafer  1 , the photoelectric conversion element  12  receives, in addition to scattering light from a foreign substance and a defect, scattering light from roughness of the sample surface. Thus, an analyzer  15  is inserted in an optical path of the detection optical system  102  and its angle is set so that the scattering light from the roughness becomes minimum. The angle setting is achieved by measuring the scattering light from the roughness, and this angle is fixed after set. 
         [0029]      FIG. 3  shows a relationship between the analyzer angle and the detected angle of orientation where the horizontal axis defines a detected angle of orientation φ°, the vertical axis defines an analyzer angle α° at which scattering light from roughness becomes minimum, and a detected angle of elevation θ 0  is changed from 15 degrees to 60 degrees. Here, the detected angle of orientation forms an angle ranging from 0 to 180 degrees clockwise or counterclockwise, with respect to a cross line formed by orthogonal crossing of a plane including the travel direction of light that has passed through the illumination optical system and the surface of the wafer stage. The analyzer angle forms an angle through which the analyzer rotates in the positive or negative direction, with an arbitrarily determined line as an origin. The angle of elevation forms an angle of up to 90 degrees from the surface of the wafer stage as an origin. 
         [0030]    As shown in  FIG. 3 , the analyzer angle varies depending on the detected angle of orientation φ° and the detected angle of elevation θ 0  of the detection optical system  102 . Further, the analyzer angle also varies depending on the polarization direction (S, P, or circular) of illumination. 
         [0031]      FIG. 4  is a graph showing the analyzer angle for materials (Cu, W, and Al) of a film formed on the surface of the wafer  1 . The vertical and horizontal axes are the same as those in  FIG. 3 . Illumination condition is as follows: a wavelength of 355 nm, S polarized light, an illumination angle of elevation (θi) of 20 degrees, and a detected angle of elevation (θo) of 15 degrees. 
         [0032]      FIG. 5  shows the amount of scattering light from roughness at a detected angle of elevation (θo) of 15 degrees and a detected angle of orientation (φ) of 40 degrees under the same illumination condition as that of  FIG. 4 . The horizontal axis denotes the analyzer angle, and the vertical axis denotes the amount of scattering light from roughness, and they are normalized so that a maximum value for each material becomes “1”. The values are shown for the film materials Al, W, and Cu, and the analyzer angle at which scattering light from roughness becomes minimum varies depending on a complex refractive index of the film material. As can be understood from  FIGS. 4 and 5 , the optimum analyzer angle varies depending on the detected angle of elevation (θ 0 ), the detected angle of orientation (φ), the complex refractive index of the film material, and the illumination condition (illumination angle of elevation θi and polarization direction). 
       Second Embodiment 
       [0033]    As described above, the optimum analyzer angle varies depending on the condition such as the detected angle of elevation (θ 0 ), the detected angle of orientation (φ), and the like.  FIG. 1  shows one embodiment for this case. Tool configuration and an illumination optical system are the same as those of  FIG. 2 . One or more detection optical systems may be provided, as is the case with that of  FIG. 1 . An analyzer  10  to be inserted in the detection optical system is configured to be rotatable, and the rotation of the analyzer  10  is controlled by a rotating mechanism  11 . This configuration permits constantly inspecting a foreign substance and a defect under optimum detection condition by controlling the angle (α) of the analyzer  10  even in a case where the detected angle of elevation (θ 0 ), the detected angle of orientation (φ), the complex refractive index of the film material, and the illumination condition (illumination angle of elevation θi and polarization direction) vary. 
         [0034]      FIG. 6  shows one embodiment of the mechanism  11  for controlling the rotation of the analyzer  10 . The analyzer  10  is fixed inside the rotating mechanism with a ring  16 . The rotating mechanism is rotated by a pulse motor  17  via gears  18   a  and  18   b . The rotation angle of the analyzer  10  is controlled through calculation of the resolution (the numbers of pulses per rotation) of the pulse motor  17  and the gear ratio between the gears. The origin of the rotating mechanism lies at a point where a cog  19  fitted to the rotating mechanism crosses a photoelectric switch  20 . The rotating mechanism  11  is mounted on a linear motion stage  21 , and so structured as to be capable of escaping from the optical path under inspection condition where the analyzer  10  is not required. Methods of determining the angle (α) of the analyzer  10  are based on:
   (1) angle at which the scattering light from the roughness becomes minimum, and   (2) angle at which the ratio (S/N) between a defect detection signal and a roughness detection signal becomes maximum.     
         [0037]    For the case (1) above, as in an inspection flow shown in  FIG. 7 , after the angle is adjusted so that the roughness signal becomes the minimum at the time when the wafer is loaded, the wafer is inspected. In addition, at the time when a recipe is downloaded, the angle can also be adjusted by calculating the rotation angle based on the inspection condition and the complex refractive index of the film material. In the recipe, the intensity of laser light, the angle of polarization (S, P, and circular), the analyzer angle, and the like are inputted. The angle can also be adjusted by calculating the rotation angle based on the inspection condition, the orientation of the detection optical system  102 , and the complex refractive index of the film material, previously preparing a database on rotation angles, and then inputting from the database the analyzer angle that agrees with the inspection condition at the time when the inspection recipe is downloaded.  FIG. 8  shows an inspection flow in this condition. In the database, a list of materials and the analyzer in correspondence with each other is inputted. 
         [0038]    For the case (2) above, a database based on the inspection condition and the complex refractive indexes of the material can be prepared for each orientation of the detection optical system  102  through actual measurement or calculation, and then the analyzer angle can be adjusted after the recipe is downloaded, as in the inspection flow shown in  FIG. 8 . 
         [0039]      FIG. 9  shows one example of a GUI. The GUI screen  31  is essentially composed of: a defect map  32  displayed after an inspection is ended; a sub window  33  for inputting a material before an inspection; and a sub window  34  for displaying an analyzer angle for each detection optical system. The defect map is displayed based on a defect signal and defect position coordinates downloaded at the inspection. Inputting a material can be achieved by either direct inputting or pull-down selection. The sub window  34  for analyzer angle display permits confirmation of the presence or absence of erroneous setting of the analyzer angle.