Title of Invention: SURFACE DEFECT INSPECTION METHOD AND APPARATUS Abstract: A surface defect inspection apparatus and method for irradiating a beam multiple times to a same region on a surface of an inspection sample, detecting each scattered light from the same region by detection optical systems individually to produce plural signals, and wherein irradiating the beam includes performing a line illumination of the beam on a line illumination region of the sample surface. The line illumination region is moved in a longitudinal direction at a pitch shorter than a length of the line illumination region in the longitudinal direction. Detailed Description: CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation of U.S. application Ser. No. 12/727,752, filed Mar. 19, 2010, which, in turn, is a continuation of U.S. application Ser. No. 12/109,548, filed Apr. 25, 2008 (now U.S. Pat. No. 7,710,557), and which application claims priority from Japanese Application JP 2007-115004 filed on Apr. 25, 2007 and Japanese Application JP 2007-156385 filed on Jun. 13, 2007, the contents of which are hereby incorporated by reference into this application. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface defect inspection method and a surface defect inspection apparatus for detecting a tiny foreign matter/defect on the surface of the semiconductor substrate and the like with high sensitivity at high speeds. On the manufacturing line of the semiconductor substrate or the thin film substrate, the inspection with respect to the defect and foreign matter on the surface of the semiconductor substrate or the thin film substrate is performed for the purpose of maintaining and further improving the product yield. For example, the sample of the semiconductor substrate prior to formation of the circuit pattern requires detection of the tiny defect or foreign matter with the size equal to or smaller than 0.05 μm on the surface. It is essential to periodically inspect whether or not the tiny defect or the foreign matter exists in the respective step of the manufacturing facility in order to improve the production yield. The generally employed inspection apparatus as disclosed in JP-A 9-304289 and 2000-162141, and U.S. Pat. No. 5,903,342 is structured to irradiate the laser beam of several tens μm focused on the surface of the sample so as to condense and detect the scattered light from the defect or the foreign matter. With the art for classifying the defect type has been disclosed in Japanese Unexamined Patent Application Publication No. 2001-255278 or U.S. Pat. No. 6,894,302, the scattered light from the defect is multi-directionally detected so as to identify the directionality of the scattered light. SUMMARY OF THE INVENTION A problem to be solved by the present invention will be described. The distribution of the scattered light caused by the defect with the size corresponding to 1/10 of the illumination wavelength becomes isotropic. So the SN ratio is improved by adding the multi-directionally detected signals, which makes it possible to detect the tiny defect. Meanwhile, the defect which causes the distribution of the scattered light to be anisotropic reduces the SN ratio by adding the multi-directionally detected signals, thus lowering the detection sensitivity. The surface defect inspection with respect to the semiconductor substrate is required to be performed with high sensitivity irrespective of the defect type. The tiny defect inspection is performed by adding the detection signals of the multi-directionally detected scattered lights, and the respective detected signals are individually processed so as to avoid the error failing to detect the anisotropic defect. The specific structures will be described hereinafter. According to the first aspect of the structure, in a surface defect inspection apparatus, a laser beam focused on a surface of an inspection sample is irradiated, a scattered light generated on the surface of the inspection sample is multi-directionally condensed, and the condensed scattered light is photoelectrically converted to inspect a defect which exists on the surface of the inspection sample. Multi-directionally detected detection signals are added to detect a tiny defect. Each of the multi-directionally detected detection signals is individually processed to detect an anisotropic defect. According to the second aspect of the structure, in a surface defect inspection apparatus, a laser beam focused on a surface of an inspection sample is irradiated, a scattered light generated on the surface of the inspection sample is multi-directionally condensed, and the condensed scattered light is photoelectrically converted to inspect a defect which exists on the surface of the inspection sample. The apparatus includes first plural photoelectric conversion elements for performing a multi-directional detection, and second plural photoelectric conversion elements for performing the multi-directional detection. The first plural photoelectric conversion elements are arranged each at a first elevation angle with respect to an inspection sample surface, and the second plural photoelectric conversion elements are arranged each at a second elevation angle higher than the first elevation angle. According to the third aspect of the structure, in a surface defect inspection apparatus, a laser beam focused on a surface of an inspection sample is irradiated, a scattered light generated on the surface of the inspection sample is multi-directionally condensed, and the condensed scattered light is photoelectrically converted to inspect a defect which exists on the surface of the inspection sample. The apparatus includes first plural photoelectric conversion elements for performing a multi-directional detection, and second plural photoelectric conversion elements for performing the multi-directional detection. The first plural photoelectric conversion elements are arranged each at a first elevation angle with respect to an inspection sample surface, the second plural photoelectric conversion elements are arranged each at a second elevation angle higher than the first elevation angle, and sensitivity of the first and the second plural photoelectric conversion elements is individually adjusted. According to the fourth aspect of the structure, in a surface defect inspection apparatus, a laser beam focused on a surface of an inspection sample is irradiated, a scattered light generated on the surface of the inspection sample is multi-directionally condensed, and the condensed scattered light is photoelectrically converted to inspect a defect which exists on the surface of the inspection sample. The apparatus includes first plural photoelectric conversion elements for performing a multi-directional detection, and second plural photoelectric conversion elements for performing the multi-directional detection. The first plural photoelectric conversion elements are arranged each at a first elevation angle with respect to an inspection sample surface, and the second plural photoelectric conversion elements are arranged each at a second elevation angle higher than the first elevation angle. The first and the second plural photoelectric conversion elements are allowed to set the threshold value capable of distinguishing the detection signal, that is, noise from the defect signal based on the level of the shot noise caused by the photoelectric conversion element. Another problem to be solved by the present invention will be described. Recently, the LSI wiring has been rapidly miniaturized to cause the size of the defect to be detected in the optical inspection to approach the limit of detection. According to the semiconductor roadmap, in the year 2007, the mass production of the LSI of 65 nm node has reportedly been about to start. The production requires the performance for detecting the defect with the size half the DRAM ½ pitch. It is known that the scattered light intensity I upon the laser irradiation to the defect establishes the relationship of I∞d̂6 (d: particle size of the defect). That is, as the defect size becomes smaller, the generated scattered light is rapidly reduced. The process for reducing the illumination wavelength, increasing the output of the laser, reducing the laser beam spot may be employed for intensifying the generated scattered light. The improvement in the detection sensitivity by reducing the wavelength will be described. Assuming that the illumination wavelength is set to λ, the scattered light intensity I establishes the relationship of I∞λ̂(−4). In other words, the generated scattered light may be intensified by reducing the illumination wavelength, which is effective for improving the detection sensitivity. However, reduction of the illumination wavelength generally increases the absorbing coefficient of the substance, thus increasing the rate of the temperature rise on the sample surface. The improvement in the detection sensitivity by increasing the laser output will be described. The scattered light intensity is substantially proportional to the laser output. So the scattered light may be intensified by making the laser output high. Likewise the case for reducing the illumination wavelength, the rate of the temperature rise on the sample surface may be increased. As a result, further improvement in the detection sensitivity to exceed the current level by increasing the output cannot be expected. The improvement in the detection sensitivity by reducing the illumination spot will be described. Reduction in the illumination spot may reduce the scattered light intensity from the wafer roughness (tiny surface roughness). The detection sensitivity may be improved in view of the noise reduction. However, the laser irradiation per unit area is increased by the reduced beam spot, thus increasing the rate of the temperature rise on the sample surface. It is difficult for a mere extension of the generally employed process to further improve the detection sensitivity as the sample is damaged by the temperature rise. It is therefore an object of the present invention to provide the surface defect inspection method and the surface defect inspection apparatus for improving the detection sensitivity while suppressing the temperature rise on the sample surface. In the present invention, the sample is subjected to a line illumination to increase the beam spot length to the feed pitch of the stage such that substantially the same region of the inspection sample is illuminated plural times in the single inspection to add the resultant plural scattered lights for improving the detection sensitivity. The line illumination may increase the state where two or more defects exist simultaneously in the illumination range. In the aforementioned case, the sensor with the plural pixels may be used for dividing the illumination range so as to individually detect the defects in the respective ranges. The plural scattered lights resulting from the single inspection are subjected to the appropriate processing such as the amplification and the noise elimination by the analog circuit. Then the scattered lights generated from substantially the same region of the inspection sample are added in the signal processor to improve the sensitivity of the defect detection. The summary of the present invention for solving the aforementioned problems will be described hereinafter. (1) A surface defect inspection method includes a step of irradiating a laser beam to the same region on the sample surface plural times, a step of detecting each scattered light from the same region individually, and a step of adding or averaging the detected plural signals. The defect determination is performed based on the added or the averaged signal. The detection sensitivity may be improved while suppressing the temperature rise on the sample surface. (2) In the step of irradiating the laser beam to the same region on the sample surface plural times of the surface defect inspection, the line illumination of the laser beam on the sample surface is performed, and the line illumination region is moved in the longitudinal direction at the pitch shorter than the length of the line illumination region in the longitudinal direction. As a result, the irradiation to the same region is performed plural times. This makes it possible to perform irradiation and detection to the same region plural times while maintaining the good throughput, thus improving the detection sensitivity. (3) A surface defect inspection apparatus includes a stage which holds the sample, an illumination optical system for linearly irradiating the laser beam to the illumination region on the sample surface, and a detection optical system for detecting the scattered light from the line illumination region on the sample surface. The stage is moved in the longitudinal direction of the line illumination region on the sample surface at the feed pitch shorter than the longitudinal length of the line illumination region. (4) The surface defect inspection apparatus for inspecting the sample includes a stage which holds the sample, an illumination optical system for irradiating the plural divided laser beams in array to the sample surface, and a detection optical system for detecting the scattered light from the plural illumination regions on the sample surface. The stage moves in the longitudinal direction of the line illumination region on the sample surface at the feed pitch shorter than the longitudinal length of the line illumination region. These and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing an embodiment (side view) of the present invention; FIG. 2 is a view showing an embodiment (plan view) of the present invention; FIG. 3 is a view showing an embodiment (plan view) of the present invention; FIG. 4 is an explanatory view of a signal processing circuit; FIG. 5 is an explanatory view of a signal processing circuit; FIG. 6 is a view representing the intensity distribution of the scattered light from the tiny defect; FIG. 7 is an explanatory view of a signal processing circuit; FIG. 8 is an explanatory view of the process for adjusting the sensitivity of the photomultiplier tube; FIG. 9 is an explanatory view of the process for setting the threshold value; FIG. 10 is an explanatory view with respect to the process shown in FIG. 9; FIG. 11 is an explanatory view of the inspection flow; FIG. 12 is an explanatory view showing an example of GUI; FIG. 13 is an explanatory view of the defect classification processing circuit; FIG. 14 is an explanatory view of the defect classification; FIG. 15 is a view schematically showing the structure of the inspection apparatus according to the present invention; FIG. 16 is an explanatory view which shows the imaging system in detail; FIG. 17 is a view schematically showing the illumination optical system and the detection optical system which exist at different elevation angles; FIG. 18 is a view schematically showing the detection optical systems each in the different azimuth direction; FIG. 19 is an explanatory view representing the inspection method for performing the illumination to the same defect plural times; FIG. 20 is an explanatory view of the definition of SN ratio; FIG. 21 is an explanatory view representing the detection of the scattered light from the defect in separated way using the photodiode array when plural defects exist on the beam spot; FIG. 22 is an explanatory view showing the relationship between the position through which the defect passes and the generated scattered light intensity when the illumination intensity distribution is Gaussian distribution; FIG. 23 is an explanatory view showing the relationship between the position through which the defect passes and the generated scattered light intensity when the illumination intensity distribution is uniform; FIG. 24 is an explanatory view of the illumination optical system for dividing the laser beam from the single light source into plural sections, and performing the long illumination by arraying those sections in the radial direction; FIGS. 25A and 25B show the process for adding the signals when the photodiode array is employed in the detection optical systems disposed in the plural azimuth directions; FIGS. 26A and 26B show the process for adding the signal when the photodiode array and PMT are employed in the detection optical systems disposed in the plural azimuth directions; FIGS. 27A and 27B show the detection light intensity when the sensitivity of the light receiving section is different; FIGS. 28A and 28B show the process for correcting the sensor sensitivity based on the detection information prior to the rotation; FIG. 29 is an explanatory view representing the coordinate merge process of the signal detected plural times with respect to the same defect; FIGS. 30A and 30B show the difference between the generally employed scanning method and the scanning method according to the present invention; FIG. 31 is a flowchart showing the process for detecting the defect in the inspection apparatus; and FIG. 32 is a view showing an example of GUI. DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described. FIGS. 1 to 3 show an example of an apparatus for detecting the defect/foreign matter on the semiconductor wafer before forming the circuit pattern. FIG. 1 is a side view, FIG. 2 is a plan view of a low angle detection system, and FIG. 3 is a plan view of a high angle detection system. The apparatus shown in FIG. 1 includes an illumination optical system 101, a detection optical system 102 and a wafer stage 103. The illumination optical system 101 includes a laser light source 2, an attenuator 3, a beam expander 4, wavelength plates 5, 6, and a condensing lens 8. The laser beam from the laser light source 2 has its light intensity adjusted to the required value by the attenuator 3. The beam radius of the laser is expanded by the beam expander 4, and the polarization direction of the illumination is set by the wavelength plates 5, 6. The condensing lens 8 performs condensing and illumination to the detection area on a wafer 1. Mirrors 7a, 7b are employed for changing the illumination optical path when required. The wavelength plates 5 and 6 are employed to set the polarization of the illumination to S polarization, P polarization and circular polarization. Preferably the illumination elevation angle θi ranges from 5° to 25°. The attenuator 3 includes a half-wave plate and a polarization beam splitter. The polarized angle of the beam from the laser light source (linear polarization) is inclined by the half-wave plate to change the intensity of light passing through the PBS (Polarized Beam Splitter). As the half-wave plate rotates, the polarized axis is changed to adjust the light intensity. The detection optical system 102 includes a low angle detection system and a high angle detection system formed of scattered light detection lenses 9a, 9c, 12a, 12c, analyzers 10a, 10c, 13a, 13c, and photoelectric conversion elements 11a, 11c, 14a, 14c, respectively such that the scattered light from the foreign matter/defect on the detection area is substantially condensed on the light receiving surfaces of the photoelectric conversion elements 11, 14 by the scattered light detection lenses 9, 12. Each of the photoelectric conversion elements 11, 14 generates an electric signal in proportion to the received scattered light intensity so as to be processed in the signal processing circuit (not shown). As a result, the foreign matter/defect is detected to obtain such information as the size and location. The photoelectric conversion elements 11, 14, for example, the TV camera, the CCD linear sensor, the TDI sensor and the photomultiplier tube, receive the scattered light condensed by the detection optical system 102 so as to be photoelectrically converted. The analyzers 10, 13 are employed for detecting only the component in the specific direction contained in the scattered light. Preferably, the detection elevation angle (center angle) θ1 of the low angle detection system is set to the value ranging from 15° to 35°, and the detection elevation angle (center angle) θ2 of the high-angle detection system is set to the value ranging from 45° to 70° The wafer stage 103 includes a chuck 15 for holding the wafer 1, a rotating mechanism 17 for rotating the wafer 1, and a direct feed mechanism 16 for directly feeding the wafer 1 in the radial direction. The wafer 1 is subjected to the rotation scanning and the direct feed movement in the horizontal direction by the wafer stage 103 to allow the detection of the foreign matter/defect in the entire region of the wafer 1 and classification of the defect. FIG. 2 is a plan view of the low angle detection system, which allows the multi-directional detection. In FIG. 2, 9a-9f denote scattered light detection lenses, 10a-10f denote analyzers, 11a-11f denote photoelectric conversion elements. The embodiment allows the 6-direction detection. Each output of the respective photoelectric conversion elements 11 is subjected to such calculation as addition, subtraction, and division in accordance with the usage. Preferably each detection azimuth (center angle) is set to 20° to 50° (φ1), −20° to −50° (φ2), 70° to 110° (φ3), −70° to 110° (φ4), 130° to 160° (φ5), and −130° to −160° (φ6) with respect to the illumination direction, respectively. FIG. 3 is a plan view of the high angle detection system similar to the one shown in FIG. 2, which allows the multidirectional detection. In FIG. 3, 12a-12d denote scattered light detection lenses, 13a-13d denote analyzers, 14a-14d denote photoelectric conversion elements. The embodiment allows the 4-direction detection. Each output of the respective photoelectric conversion elements 14 is subjected to such calculation as addition, subtraction, and division in accordance with the usage. Preferably each detection azimuth (center angle) is set to ±10°(φ7), 80° to 110° (φ8), −80° to −110° (φ9), and 180°±10° (φ10) with respect to the illumination direction, respectively. FIG. 4 shows an example of the signal processing performed in the low angle detection system which employs the photomultiplier tube as the photoelectric conversion element 11. The photomultiplier tube 11a-11f requires application of the high voltage supplied from a high voltage DC power source 19. The output of the photomultiplier tube 11 is subjected to the current-voltage conversion and the required voltage amplification by the amplifier circuit 18a-f, which is then added by an adder circuit 20. At this time, the amplifier circuit 18 adjusts the amplification factor for correcting the difference in sensitivity of the photomultiplier tube 11. The output of the adder circuit 20 has the DC component and the unnecessary noise eliminated by the band-pass filter 21 so as to be subjected to the digital conversion by an AD conversion circuit 22. The output of the AD conversion circuit 22 is compared with a threshold value by a comparison circuit 23. When the output exceeds the threshold value, the AD conversion value and the R·θ coordinate are loaded in a defect memory 26. The threshold value is set to a latch 24 from the CPU (not shown) via an interface 25. The content of the defect memory 26 is read from the CPU (not shown) so as to be used for displaying the defect map and classifying the defect. FIG. 5 shows an example of the signal processing in the high angle detection system, the content of which is the same as the one shown in FIG. 4. In FIG. 5, 14a-14d denote photoelectric conversion elements, 27a-27d denote the amplifier circuits, 28 denotes an adder circuit, 29 denotes the band-pass filter, 30 denotes an AD conversion circuit, 31 denotes a comparison circuit, 32 denotes a latch, 33 denotes an interface, 34 denotes the defect memory. FIG. 6 shows an example of a scattered light intensity distribution 35 which is caused by the tiny defect upon illumination with the P polarization. When the dimension of the defect is approximately ⅕ of the illumination wavelength or shorter, the scattered light intensity distribution becomes isotropic as shown in FIG. 6. In this case, the respective detection signals become substantially the same value (S). A shot noise (N) occurs upon the photoelectric conversion in the photomultiplier tube 11. The shot noise (N) output from each photomultiplier tube 11 is random, and the SN ratio of the output signal from the photomultiplier tube 11 becomes S/N. Referring to FIGS. 4 and 5, when all the detection signals are added and averaged, the shot noise is averaged to become 1/√6. Then the S/N ratio of the detection signal is increased by √6 times. Each individual processing for the photomultiplier tube 11 makes it possible to detect the tiny defect. When the addition/averaging is performed in the case where the scattered light intensity distribution is biased like scratch to be detected only in the single photomultiplier tube 11, the detection signal becomes 1/6, and the shot noise becomes 1/√6, thus reducing the S/N ratio to 1/√6 compared with the process for each of the photomultiplier tube 11 individually. In order to avoid the aforementioned disadvantage, a first embodiment is provided as shown in FIG. 7. The circuit which is the same as the processing circuit shown in FIG. 4 is added for each of the photomultiplier tubes 11a-11f. In FIG. 7, 18a-18f denote the amplifier circuits, 21a-21f denote the band-pass filter, 22a-22f denote an AD conversion circuit, 24a-24f denote latches. The output of the comparison circuit 23a-23f are subjected to the logic OR operation. When any one of the value exceeds the threshold value, the outputs of the all the AD conversion circuits 22 and the R·θ coordinate are loaded in the defect memory 26. This makes it possible to prevent the error failing to detect the anisotropic defect with the directionality in the scattered light intensity distribution. FIG. 8 shows an embodiment for correcting the difference in sensitivity of the photomultiplier tube 11a-11f. A power unit 39a-39f are structured to adjust the high application voltage in accordance with the input voltage. The power unit of the type of C4900 produced by Hamamatsu Photonics may be employed as one of the exemplary power units. The voltage value is written into the latch 37a-37f via the interface 40 to convert the value into the voltage value by the DA conversion circuit 38a-38f so as to be applied to the power unit 39a-39f. This makes it possible to supply the high application voltage to the photomultiplier tube 11. The change in the voltage value written into the latch 37a-37f allows the sensitivity of the photomultiplier tube 11 to be adjusted from the CPU. The adjustment of the amplification factor by the amplification circuit 18a-18f may be performed together with the aforementioned operation to allow the easy correction of the difference in the sensitivity. The intensity and distribution of the scattered light on the wafer surface varies depending on the space frequency/degree of the roughness thereon. When the scattered light intensity on the wafer surface detected by the photomultiplier tube 11a-aaf are set to Su, the shot noise generated thereby becomes √Su. In the case where the scattered light intensity on the wafer surface detected by the photomultiplier tube 11a-11f vary depending on each of the photomultiplier tubes 11a-11f, the resultant shot noise will vary. It is necessary to change the threshold value for detecting the defect. An embodiment to cope with the aforementioned problem and the detailed process will be described referring to FIGS. 9 and 10, respectively. In FIGS. 9 and 10, an output signal 45a from the amplifier circuit 18a is separated into a wafer signal 46a and a defect signal 47a which contains the shot noise using the band-pass filter 21a and the lowpass filter 41a. The wafer signal 46a which has passed through the lowpass filter 41a is used for setting the threshold value. The signal derived from the wafer signal 46a is subjected to the digital signal conversion by the AD conversion circuit 42a, and is formed into the threshold value Vth by the calculation circuit 43a so as to be set in the latch 44a. The shot noise 47a is subject to the digital conversion by the AD con version circuit 22a, and is sent to a comparison circuit 23a. The wafer signal also is sent to the comparison circuit 23a. The shot noise is proportional to the square root of the wafer signal Su, and the threshold value Vth is calculated through the following equation (1): Vth=k·√(Su·Δf) where k denotes the constant and Δf denotes a frequency band of the circuit. In FIG. 10, left side graph shows the out put signal 45a, in which y-axis Vo denotes output signal, and x-axis denotes time (t). Upper right side graph shows the wafer signal 46a, in which y-axis Vn denotes wafer signal, and x-axis denotes time (t). Lower right side graph shows the defect signal 47a, in which y-axis Vs denotes defect signal, x-axis denotes time (t). FIG. 11 shows an example of the inspection routine. The inspection recipe is loaded to set the required parameter in the apparatus. The wafer is loaded and inspected to input the defect data from the defect memory. When the inspection ends, the wafer scan (rotation and the single axis feed) is stopped so as to unload the wafer. Thereafter, the defect map is displayed on the GUI screen as required. FIG. 12 shows an example of the GUI. A GUI screen 48 includes at least a defect map 49 displayed after the end of the inspection, and a defect map display sensor selector screen 50. FIG. 13 shows an example of distinguishing the defect. The detection signal VL of the low angle detection system flows from Ad conversion circuit 22, and the detection signal VH of the high angle detection system flows from Ad conversion circuit 30. The ratio of the detection signal VL of the low angle detection system to the detection signal VH of the high angle detection system is calculated by a processing circuit 51, and the calculation result is written into the defect memory. The detailed process will be described referring to FIG. 14. The calculation results are plotted on the graph having an x-axis as VL and the y-axis as VH. On the graph, the concave defect (COP, scratch and the like) is observed in an area 53 above the threshold curve 52, and the convex defect is observed in an area 54 below the threshold curve 52. The threshold curve 52 is set to allow the appropriate distinguishing between the concave defect and the convex defect (defect type). Referring to FIG. 14, each of the defects in the area below the dotted line 52 is the convex defect, and each of the defects in the area above the dotted line 52 is the concave defect. In most of the cases, the concave defect has been existed in the Si wafer, and the convex defect is likely to be caused in the apparatus. The number of the convex defects larger than that of the concave defects in spite of the same defect density tends to indicate the problem in the manufacturing apparatus. The above explanation has been made when the photomultiplier tube 11 is used as the photoelectric conversion element. However, the relationship between the shot noise and the defect detection signal is kept unchanged when the CCD is used as the photoelectric conversion element. Accordingly, the aforementioned description is applicable to the case where the element other than the photomultiplier tube 11 is used as the photoelectric conversion element. The detection signals of the multi-directionally detected scattered lights are added to detect the tiny defect, and to prevent the error failing to detect the anisotropic defect by performing the individual process for each of the detection signals. The obtained defect data are automatically analyzed to make a determination whether the defect has been caused by the problem of the apparatus, or it has already existed on the substrate. An example of the embodiment according to the invention for solving the aforementioned problem will be described referring to FIG. 15. FIG. 15 schematically shows the structure including an illumination optical system 2-101, a detection optical system 2-102, a wafer stage 2-103, and a circuit/signal processor. The illumination optical system 2-101 includes a laser light source 2-2, a beam expander 2-3, a homogenizer 2-4, mirrors 2-5, 2-6, and a cylindrical lens 2-7. A laser beam 2-100 irradiated from the laser light source 2-2 allows the beam radius to be adjusted to the required size by the beam expander 2-3, and converted by the homogenizer 2-4 into the uniform illumination distribution. It is further subjected to the line illumination in the inspected region on the wafer 2-1 by the cylindrical lens 2-7. The laser light source for generating ultraviolet or extra ultraviolet laser beams may be employed as the laser light source 2. The homogenizer 2-4 is used for making the illumination intensity uniform. However, the diffraction optical element and the fly eye lens may be used to make the illumination intensity uniform. The illumination may be performed without using the homogenizer 2-4. The illumination without using the homogenizer suppresses the attenuation of the laser beam intensity, thus allowing the illumination with the high intensity. The cylindrical lens 2-7 is used for the line illumination. However, the anamorphic optical system formed of plural prisms may be used to change the beam radius on the plane perpendicular to the optical axis with respect to only one direction such that the condensing lens is used for the line illumination to the sample. The use of the anamorphic optical system is effective in view of easy adjustment of the optical axis. The detection optical system 2-102 includes an imaging system 2-8 and a photodiode array 2-9. FIG. 16 illustrates the detection optical system 2-102 in detail. The detection optical system 2-102 includes a condensing lens 2-21, an image intensifier 2-22, an imaging lens 2-23 and a photodiode array 2-9. The light scattered from the beam spot 2-20 is condensed by the condensing lens 2-21. The scattered light is amplified by the image intensifier 2-22 so as to be imaged on the photodiode array 2-9 through the imaging lens 2-23. The image intensifier 2-22 is used for amplifying the weak scattered light to be detectable. However, instead of the image intensifier, the sensor with high gain, for example, EM-CCD, the multi-anode PMT and the like may be employed. The use of the aforementioned sensor is effective in view of downsizing the apparatus. The photodiode array 2-9 is used for receiving the scattered light to be photoelectrically converted. However, TV camera, CCD linear sensor, TDI, photodiode array, multi-anode PMT, and the like may be employed. For example, the use of the 2D sensor allows the wide region to be inspected at one time. The photodiode array 2-9 generates the electric signal corresponding to the received light intensity so as to be subjected to the required process by the analog circuit 2-51 including amplification, noise process, and analog-digital conversion. The signal processor 2-52 adds plural optical signals scattered from substantially the same region and performs the defect determination to display the defect map by the map output section 2-54 via a CPU 2-53. The wafer stage 2-103 is formed of a chuck (not shown) for holding the wafer 2-1, a rotating stage 2-10 for rotating the wafer, and a parallel stage 2-11 for moving the wafer in the radial direction. The wafer stage 2-103 performs the rotation scan and the parallel scan to spirally illuminate the entire sample surface. The stage control section 2-55 controls the rotating speed and the parallel advancing speed so as to illuminate the desired region. As a feature of the present invention, the line illumination is performed to the sample surface, and the sample is moved in substantially the same direction as the longitudinal direction of illumination while being rotated. As a result, the entire sample surface may be spirally illuminated to allow the surface defect inspection based on the detected scattered light. FIG. 15 shows the example where the single illumination optical system and the single detection optical system are employed. However, plural illumination optical systems and detection optical systems may be employed likewise the case shown in FIG. 17 including an oblique illumination optical system 2-101a for illuminating the sample from the low elevation angle, a perpendicular illumination optical system 2-101b for illuminating the sample from substantially the perpendicular direction, a low angle detection optical system 2-102a for detecting the sample at the low elevation angle, and a high angle detection optical system 2-102b for detecting the ample at the higher elevation angle compared with the low angle detection optical system. The oblique illumination optical system 2-101a includes the laser light source 2-2, the beam expander 2-3, the homogenizer 2-4, the mirrors 2-5, 2-6a, and a cylindrical lens 2-7a. Likewise, the perpendicular illumination optical system 2-101b includes the laser light source 2-2, the beam expander 2-3, the homogenizer 2-4, a mirror 2-6b, and a cylindrical lens 2-7b. The aforementioned structures allow any of the components of the embodiment shown in FIG. 15 to be omitted and replaced. In this case, the mirror 2-5 is structured to change the advancing direction of the laser beam 2-100, and the optical system is switchable between the oblique illumination optical system 2-101a and the perpendicular illumination optical system 2-102b in need. The oblique illumination optical system may be selected to improve the detection sensitivity, and the perpendicular illumination optical system is selected to improve the capability of classifying the defect. Accordingly, the desired system may be selected depending on the usage. The low angle detection optical system 2-102a includes an imaging system 2-8a and a photodiode array 2-9a. Likewise, the high angle detection optical system 2-102b includes an imaging system 2-8b and a photodiode array 2-9b. The imaging system 2-8a includes the condensing lens, the image intensifier, and the imaging lens (not shown). The imaging system 2-8b has the same structure. The aforementioned structures allow any of the components of the embodiment shown in FIG. 15 to be omitted and replaced. Each of the photodiode arrays 2-9a and 2-9b generates the electric signal corresponding to the received light intensity so as to be subjected to the required process by the analog circuits 2-51a and 2-51b including amplification, noise process, and analog-digital conversion. Then the signal processor 2-52 adds the plural optical signals scattered from substantially the same region, and performs the defect determination such that the defect map is displayed by the map output section 2-54 via the CPU 2-53. In the embodiment, substantially the same location is detected at the different elevation angle at substantially the same time. Any of the optical system selected from the low angle detection optical system and the high angle detection optical system may be used for the inspection by adjusting the sensitivity of the respective sensors such that the dynamic range of the detected particle size is widened. The use of the combination of the illumination optical system and the detection optical system makes it possible to improve the accuracy in the defect classification. For example, as for the convex defect, the low angle detection optical system is capable of detecting the large scattered light upon the oblique illumination. As for the concave defect, the high angle detection optical system is capable of detecting the large scattered light upon the perpendicular illumination. Referring to FIG. 17, the example where the detection optical systems exist in the different elevation angle directions. However, plural detection optical systems may be provided in the different azimuth directions as shown in FIG. 18. FIG. 18 is a view of the embodiment according to the present invention when seen from above, which shows a wafer 2-1, the illumination optical system 2-101, and detection optical systems 2-102c to 2-102h. The detection optical systems 2-102c to 2-102h are formed of the corresponding imaging systems 2-8c to 2-8h, and the respective photodiode arrays 2-9c to 2-9h. The detection signal is subjected to the required process by the analog circuit including amplification, noise processing and analog-digital conversion. The signal processor adds the plural optical signals scattered from substantially the same region and performs the defect determination. Then the defect map (not shown) is displayed by the map output section via the CPU. With respect to the structure of the detection optical system, each of the imaging systems 2-8c to 2-8h is formed of the condensing lens, the image intensifier, and the imaging lens (not shown), respectively. The use of the detection optical system which exists at plural azimuths allows the detection optical system capable of detecting more scattered lights from the defect while suppressing the noise to be selected by performing the inspection when the angular property of the scattered light caused by the size/configuration of the defect, film type of the sample, and surface roughness. This makes it possible to improve the detection sensitivity. Referring to FIG. 18, six detection optical systems are arranged in different azimuth directions. However, the number of the detection optical systems does not have to be limited to six, but may be arbitrarily set to be arranged in the arbitral azimuth direction. The plural detection optical systems do not have to be arranged at substantially the same elevation angle. Furthermore, the detector does not have to be arranged in substantially the same azimuth direction. In the present invention, the line illumination and the scanning allow the illumination to the same defect plural times. The generally employed inspection method will be described first, and then the inspection method according to the present invention will be described hereinafter. The stage advances in parallel at substantially the constant speed in the radial direction (R direction) while rotating. It is assumed that the advancing distance in the radial direction in the cycle of the single rotation is referred to as the feed pitch. The rotation/parallel advancement allows the spiral scan on the entire sample surface. However, the length of the beam spot in the radial direction is substantially the same as the feed pitch length. In most of the case, the illumination to the single defect is performed only once. In the present invention, the line illumination is performed, and the beam spot length is made longer than the pitch length to illuminate the same defect plural times. Referring to FIG. 19, the defect 2-25 is illuminated four times in the condition where the length of the beam spot 2-20 is four times longer than that of the feed pitch 2-26. The illumination performed plural times will be described referring to FIG. 19. At a time point t1, the first illumination is performed to the defect 2-25. At a time point t2, the wafer rotates at the single round. The beam spot advances in the radial direction by the distance substantially corresponding to the feed pitch 2-26 to illuminate the defect 2-25 again. Then at the time points t3 and t4, the wafer rotates at the single round, respectively to illuminate the defect 2-25. Referring to FIG. 19, the defect 2-25 may be illuminated four times, and the detected light is added by the analog circuit or the signal processor. The number of times for illumination is not limited to four, but may be arbitrarily set so long as it is plural times. The improvement in the detection sensitivity by adding the plural scattered lights in the present invention will be described. The improvement in the detection sensitivity will be described in reference to the SN ratio defined in FIG. 20. Referring to FIG. 20, the y-axis of the graph denotes the detected light intensity, and x-axis denotes the time (t). The sample surface is constantly illuminated even if no defect exists on the beam spot so as to continuously detect the scattered light 2-30 generated in accordance with each size of concavity and convexity of the wafer roughness. Assuming that the average intensity of the scattered lights from the wafer roughness is set to N0, the detected light intensity fluctuates at the amplitude of √N0 owing to fluctuation on the sensor light receiving surface caused by the photoelectric conversion, thus generating the noise. The defect which exists on the beam spot generates the scattered light 2-31. Assuming that the intensity of the scattered light from the defect is set to S0 having the value N0 as the standard, the SN ratio is defined as “S0/√N0”. The scattered light from the same defect is added n times to increase the scattered light intensity from the defect from S0 to n×S0, and the scattered light intensity from the wafer roughness from N0 to n×N0. That is, the SN ratio becomes “n×S0/√(n×N0)”, and the detection sensitivity is intensified by √n times. It is effective to illuminate the same defect plural times by increasing the beam spot to be longer than the feed pitch, that is, generating the line illumination. Instead of increasing the beam spot length, the feed pitch length may be decreased to allow the same defect to be illuminated plural times. In this case, however, the throughput is reduced. Referring to FIG. 21, the photodiode array is used to divide the beam spot to be detected such that each scattered light from the two or more simultaneously illuminated defects may be detected individually. The photodiode array having four light receiving sections 2-35a, 2-35b, 2-35c, and 2-35d will be described. When the defects 2-25a and 2-25b are simultaneously illuminated on the beam spot 2-20, they may be divided by the imaging system 2-8 with respect to the light receiving sections 2-35a and 2-35d of the photodiode array 2-9. The divided beam spot is detected to allow the noise from the wafer roughness to be reduced, resulting in the effect expected to improve the detection sensitivity. In the inspection method according to the present invention, the substantially the same region is illuminated with the line illumination plural times, and the plural scattered lights are added to improve the detection sensitivity. The detection sensitivity may be improved without decreasing the illumination wavelength to be short, or without using the process for increasing the laser output and reducing the beam spot. That is, the embodiment of the present invention is capable of improving the detection sensitivity while suppressing the damage to the sample. In the illumination optical system, the laser beam intensity distribution generally has a Gaussian distribution. In the present invention, however, the illumination may be performed with the uniform intensity distribution. In the case where the intensity distribution of the beam spot 2-20a has a Gaussian distribution 2-40a as shown in FIG. 22, the scattered light 2-41a is generated by illuminating the defect 2-25a on the beam spot 2-20a, and the scattered light 2-41b which is larger than the scattered light 2-41a is generated by illuminating the defect 2-25b. In the right side drawing of FIG. 22, y-axis is detected light intensity, and x-axis is time (t). In the case where the intensity distribution of the beam spot 2-20b has the uniform distribution 2-40b on the beam spot 2-20b as shown in FIG. 23, the scattered light 2-41c resulting from illumination to either the defect 2-25a or 2-25b on the beam spot 2-20b has substantially the same size. In the right side drawing of FIG. 23, y-axis is detected light intensity, and x-axis is time (t). The wafer stage which is rotated at high speeds during the inspection generates oscillation both in height and radial directions. So the fluctuation in the sample height and heave occur at high frequency. There may be often the case where the positional relationship between the defect and the beam spot displaces. However, the fluctuation in the detected scattered light intensity resulting from the displacement of the illumination position may be suppressed by allowing the illumination intensity to have the uniform distribution. This makes it possible to improve the repeatability and stability with respect to the defect detection sensitivity and coordinate accuracy. In the illumination optical system, the line illumination is performed using the beam expander and the cylindrical lens. However, the Wallaston prism may be used to divide the laser beam so that the divided laser beams are arrayed in the radial direction for illumination, thus making the beam spot long enough to illuminate the sample surface. The process for dividing the laser beam will be described referring to FIG. 24. Generally, the laser beam 2-100 from the laser light source 2 is linearly-polarized. After passing through the beam expander 2-3 and the homogenizer 2-4, the laser beam is circularly polarized by the quarter-wave plate 2-42a so as to be divided into two linearly-polarized beams which is orthogonal with each other at the Wallaston prism 2-43. The divided laser beam is circularly polarized by the quarter-wave plate 2-42b again such that the sample surface is illuminated by the condensing lens 2-44 on the beam spots 2-20c and 2-20d. In this way, the long beam spot may be generated by illuminating the sample on the plural arrayed beam spots. The distance between the thus divided two beam spots may be arbitrarily adjusted, which allows the illumination by overlapping or separating the beam. This makes it possible to adjust the number of illuminations to substantially the same region. The intensity of the divided laser beam allows the adjustment of the ellipticity of the circular polarization/azimuth of elliptic long axis by controlling the angle defined by the oscillating direction of the linearly polarized laser beam 2-100 and the phase lag axis of the quarter-wave plate 2-42a. Illumination intensity of the beam spots 2-20c and 2-20d divided by the Wallaston prism 2-43 may be arbitrarily adjusted by controlling the ellipticity/azimuth of elliptic long axis. This makes it possible to expand the dynamic range of the detectable defect (to be described later). The beam spots 2-20c and 2-20d may be set to substantially the same intensity values or different intensity values. In the embodiment shown in FIG. 24, the laser beam is divided into two. However, the laser beam may be
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