Patent Publication Number: US-8537351-B2

Title: Inspection apparatus and inspection method

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/350,581, filed on Jan. 8, 2009 now U.S. Pat. No. 8,203,705, claiming priority of Japanese Patent Application No. 2008-003807, filed on Jan. 11, 2008, the disclosures of which Applications are incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method and apparatus for inspecting an object to be inspected. For example, the invention is suitable for an inspection method and a surface inspection apparatus for detecting a foreign matter, a defect, and the like in an object to be inspected such as a semiconductor wafer, a glass substrate or a ceramic substrate. 
     2. Description of the Related Art 
     In the case where a foreign matter or a defect exists in the surface of a semiconductor wafer, it exerts an influence on the yield of a semiconductor device. Consequently, a semiconductor wafer surface inspection has been being performed by a surface inspection apparatus. As conventional techniques for detecting a foreign matter and a defect existing in the surface of a wafer, techniques disclosed in U.S. Pat. No. 6,201,601 and Japanese Patent Application Laid-Open Publication No. 11-153549 (JP-A-11-153549) are known. 
     U.S. Pat. No. 6,201,601 discloses a surface inspection apparatus for irradiating a wafer with a perpendicular beam and an oblique beam from an illumination optical system using a laser as a light source, collecting scattered light from the wafer by a parabolic mirror, and detecting the collected light by a detector. Scattered light originating from the perpendicular beam and scattered light originating from the oblique beam is split from each other by intentionally introducing an offset between the two radiation beams, using two beams having different wavelengths, or switching the perpendicular radiation beam and the oblique radiation beam on and off alternately. A beam position error caused by a change in sample height is corrected by detecting specular reflection of the oblique radiation beam and changing the radiation direction in accordance with a result of detection of the specular reflection by a mirror. 
     JP-A-11-153549 discloses a method of inspecting the surface of an object to be measured, by emitting light from a light source via an optical system obliquely to the surface of an object to be measured, receiving scattered light reflected from the surface of the object to be measured, while making the object to be measured and the optical system displaced relative to each other, detecting a foreign matter on the surface of the object to be measured, and recording the coordinate position of the foreign matter. In the method, at the time of detecting a foreign matter on the surface of the object to be measured, height of the object to be measured is measured. By using a height signal of the object to be measured, the coordinate position of the foreign matter is corrected. 
     A control criterion for a foreign matter and a defect existing in a semiconductor wafer is becoming severer as the size of a semiconductor device is becoming smaller. In recent years, since even a foreign matter adhered to the rear face of a wafer and a rear-face state exert an influence on the yield of a semiconductor device, an inspection for a foreign matter and a defect existing not only in the main face of a wafer but also in the rear face is demanded. In such an inspection, a stage of an edge grip method of handling the main face and rear face of a wafer in a non-contact manner is used. However, since an internal space which makes the main face and rear face in non-contact state is provided and a wafer itself is held by its edges, a large deformation (deflection and warp) occurs in the wafer due to pressure fluctuations in the internal space accompanying self weight and rotation of the wafer. The deformation of the wafer makes both sensitivity of detection of a foreign matter and a defect and the coordinate precision significantly degrade. It is therefore necessary to detect a deformation state under operation and to correct the state in order to maintain the detection sensitivity and coordinate precision. 
     However, in the conventional techniques, detection of a wafer deformation state while detecting a foreign matter and a defect existing in the wafer is not considered. There is a problem such that it is not possible to determine whether or not the shape of a wafer is in a proper range in order to determine credibility of detection sensitivity and position coordinate precision of a surface inspection apparatus and in order to maintain the performance of detection sensitivity and position coordinate precision. In addition, since correction of the shape of a wafer against the detected deformation state of a wafer is not considered, deformation-following ability of an autofocus mechanism degrades. Due to a focus deviation and an irradiation position deviation of a perpendicular irradiation beam spot and an oblique irradiation beam spot formed on the surface of a wafer, detection sensitivity of a foreign matter and a defect and position coordinate precision degrade. When deformation of a wafer under inspection is conspicuous, a problem occurs such that a small foreign matter and a small defect cannot be detected. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an inspection apparatus and method capable of detecting a deformation state of an object to be inspected during an inspection. 
     Another object of the invention is to provide an inspection apparatus and method for detecting a deformation state of an object to be inspected during an inspection and properly correcting the deformation state of the object to be inspected in accordance with the detected deformation state. 
     A feature of the invention is detection of a deformation state of an object to be inspected while inspecting the object to be inspected. More concretely, for example, the invention provides an inspection apparatus including: a first light irradiating unit for irradiating an object to be inspected with light; a first detector for detecting scattered light from the object to be inspected; a second light irradiating unit for irradiating the object to be inspected with light; a second detector for detecting light reflected from the object to be inspected, of light of the second light irradiating unit; a stage for moving an object to be inspected, which moves the object to be inspected so as to change irradiation positions on the object to be inspected, of the light of the first light irradiating unit and the light of the second light irradiating unit; an inspection coordinate detector for outputting information of coordinates of a position irradiated with light of the second light irradiating unit; an elevation control circuit for outputting height information of the object to be inspected on the basis of a detection signal from the second detector; and a data processing unit for calculating a deformation state of the object to be inspected on the basis of both the information of the coordinates of a position irradiated with the light of the second light irradiating unit from the inspection coordinate detector and the height information from the elevation control circuit. 
     Another feature of the invention is to provide a gas port for correcting a shape at the time of detecting the deformation state of the object to be inspected while inspecting the object to be inspected. More concretely, for example, an inspection apparatus includes: a first light irradiating unit for irradiating an object to be inspected with light; a first detector for detecting scattered light from the object to be inspected; a second light irradiating unit for irradiating the object to be inspected with light; a second detector for detecting light reflected from the object to be inspected, of light of the second light irradiating unit; a stage for moving an object to be inspected, which moves the object to be inspected so as to change irradiation positions on the object to be inspected, of the light of the first light irradiating unit and the light of the second light irradiating unit; a gas supplying unit for supplying gas whose flow is controlled to the reverse face of the object to be inspected; an inspection coordinate detector for outputting information of coordinates of a position irradiated with light of the second light irradiating unit; an elevation control circuit for outputting height information of the object to be inspected on the basis of a detection signal from the second detector; and a data processing unit for calculating a deformation state of the object to be inspected on the basis of both the information of the position coordinates from the inspection coordinate detector and the height information from the elevation control circuit. 
     Another feature of the invention is to detect a deformation state of an object to be inspected while inspecting the object to be inspected, and to control flow of gas for correcting a shape in accordance with a detection result. More concretely, for example, an inspection apparatus includes: a first light irradiating unit for irradiating an object to be inspected with light; a first detector for detecting scattered light from the object to be inspected; a second light irradiating unit for irradiating the object to be inspected with light; a second detector for detecting light reflected from the object to be inspected, of light of the second light irradiating unit; a stage for moving an object to be inspected, which moves the object to be inspected so as to change irradiation positions on the object to be inspected, of the light of the first light irradiating unit and the light of the second light irradiating unit; a gas supplying unit for supplying gas whose flow is controlled to the reverse side of a surface to be inspected of the object to be inspected; an elevation control circuit for outputting height information of the object to be inspected on the basis of a detection signal from the second detector; a data processing unit for calculating a deformation state of the object to be inspected on the basis of both the information of the position coordinates from the inspection coordinate detector and the height information from the elevation control circuit; and a flow controller for controlling flow of gas supplied to the gas supplying unit on the basis of the calculated deformation state. 
     A further another feature of the invention is an inspection method for irradiating an object to be inspected with a light beam while scanning and for detecting scattered light from the object to be inspected, including: irradiating the object to be inspected with a second light beam different from the light beam; capturing height information of the object to be inspected by reflection light of the second light beam; controlling height of the object to be inspected to a predetermined position in accordance with the height information; and calculating a deformation state of the object to be inspected on the basis of information of the control to the predetermined position. 
     A further another feature of the invention is an inspection method for irradiating an object to be inspected with a light beam while scanning and for detecting scattered light from the object to be inspected, including: irradiating the object to be inspected with a second light beam different from the light beam while supplying gas whose flow is controlled to the reverse side of a surface to be inspected of the object to be inspected; capturing height information of the object to be inspected by reflection light of the second light beam; controlling height of the object to be inspected to a predetermined position in accordance with the height information; calculating a deformation state of the object to be inspected on the basis of information of the control to the predetermined position; and controlling flow of gas supplied to the reverse side of the surface to be inspected in accordance with the calculated deformation state. 
     In one mode of the invention, an inspection apparatus and an inspection method capable of detecting a deformation state of an object to be inspected during an inspection can be provided. 
     In another mode of the invention, an inspection apparatus and an inspection method capable of detecting a deformation state of an object to be inspected during an inspection and, according to the detected deformation state, correcting properly shape of the object to be inspected can be provided. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view showing a schematic configuration of a surface inspection apparatus as an embodiment of the invention. 
         FIG. 2  is a front view showing an internal configuration of an inspection unit in the surface inspection apparatus. 
         FIG. 3A  shows a chuck having an air gap forming part made by a plurality of steps, and  FIG. 3B  shows a chuck having an air gap forming part having a projected curve. 
         FIG. 4  is a diagram showing a schematic configuration of a gas supply system related to the invention. 
         FIG. 5  is a diagram showing a setting screen for controlling the gas supply system related to the invention. 
         FIG. 6  is a plan view showing a light irradiating unit related to the invention. 
         FIG. 7  is a top view showing a schematic configuration of a first detector related to the invention. 
         FIG. 8  is a front view showing a schematic configuration of a height position controller in the case of using a two-segmented sensor. 
         FIG. 9  is a diagram showing the relation between inspection plane height and sensor output in the case of using a two-segmented sensor. 
         FIG. 10  is a diagram showing a schematic configuration of a display screen for estimating a warp measurement result and a gas supply amount in the invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     An inspection method and inspection apparatus of the invention can be applied to, for example, a flat plate-shaped object to be inspected such as a semiconductor wafer, a glass substrate for a liquid crystal panel or a TFT module, and a sapphire substrate or ceramic substrate for use in a sensor, an LED, or the like. In the following embodiments, a surface inspection apparatus and a surface inspection method using a semiconductor wafer as an object to be inspected will be described as an example. 
     First Embodiment 
       FIG. 1  is a plan view showing a schematic configuration of a surface inspection apparatus as an embodiment of the invention. The surface inspection apparatus includes a plurality of load ports  100  having the function of mounting a wafer (object to be inspected)  1 , a carrying unit  200 , a pre-alignment unit  300 , an inspection unit  400 , and a data processing unit  500 . On the load port  100 , a wafer pod  110  for housing the wafer  1  is mounted. On all of the plurality of load ports  100 , wafer pods  110  for inspecting process can be mounted. A part of the plurality of load ports  100  can be used for separating and collecting a wafer  1  determined as defective. 
     The carrying unit  200  includes a carrying apparatus  210  for carrying the wafer  1 , and a Y-axis carrying unit  250 . The carrying apparatus  210  has a handling arm  220  of an edge grip type being driven on the basis of an instruction signal from the data processing unit  500  and handling the face and the rear face of the wafer  1  in a non-contact manner. The handling arm  220  includes, in an almost U-shaped fork, a fixed-side wall  230  and a grip block  240  disposed so as to face the fixed-side wall  230 . By pressing the end portion (edge) of the wafer  1  with the fixed-side wall  230  and the grip block  240 , the wafer  1  itself is gripped by the edge and carried among load ports  100   a  and  100   b , the pre-alignment unit  300 , and the inspection unit  400 . 
     The pre-alignment unit  300  includes a mounting stand  310  for supporting the end portion of the wafer  1  in three or four points and a sensor  320  for detecting the outer periphery of the wafer  1 . The mounting stand  310  on which the wafer  1  is mounted detects the outer periphery by the sensor  320  while rotating the wafer  1  and pre-aligns the position (almost the center position) of the wafer  1  and the notch position. By supporting the wafer  1  by the surrounding end portion, the surface reverse to the surface to be inspected of the wafer  1  can be pre-aligned in a non-contact manner. 
     Above the pre-alignment unit  300 , a receiving stand of a not-shown inverting unit is disposed. At the time of inspecting the rear face of the wafer  1  as a surface to be inspected, the wafer  1  is reversed by the unit. By the inverting unit, substrate carriage with the face or the rear face of the wafer  1  being set as a surface to be inspected can be performed. 
     The data processing unit  500  includes a controller  510 , an input device  520  such as a keyboard, a touch panel, or a mouse, a display device  530  such as a CRT or a flat panel display, an output device  540  such as a printer, and an external storage  550  for controlling an external medium. The controller  510  includes an arithmetic processing unit  511 , a storage  512  such as an HDD, and a control device  513 , and controls the entire surface inspection apparatus on the basis of an instruction from the input device  520 . Setting conditions, an inspection result, and the operation state of the inspection apparatus are displayed by the display device  530 . Their respective informations are outputted via the output device  540 . 
       FIG. 2  is a vertical cross-sectional view showing the internal configuration of the inspection unit  400  illustrated in  FIG. 1 . The inspection unit  400  includes a stage  410  for moving an object to be inspected, for scanning the wafer  1 , a first light emitting unit  600  for emitting a light beam (illumination beam)  658  such as a visible laser beam or an ultraviolet laser beam, a first detector  770  for detecting scattered light from the surface to be inspected of the wafer  1 , and a height position controller  900  (which will be described later) for controlling the surface to be inspected to a focus position. 
       FIG. 6  is a diagram showing a schematic configuration of the first light emitting unit  600 . The first light emitting unit  600  (irradiating mechanism) has a laser light source  651  for generating the light beam  658 , a shutter  652  for blocking the laser beam, an attenuator  653  for adjusting intensity of the light beam  658 , an optical axis correcting mechanism  654  for correcting an optical axis shift of the light beam  658 , an irradiation direction switching mechanism  655  for switching the irradiation direction of the light beam  658  to an oblique direction or a perpendicular direction, beam shaping mechanism  656   a  and  656   b  for shaping the cross-sectional shape of the light beam  658  to a predetermined shape, and mirrors  657   a  to  657   g  for changing the course of the light beam  658 . 
     The light beam  658  emitted from the laser light source  651  passes through the mirror  657   a  and is adjusted to energy density adapted for an inspection by the attenuator  653 . The light beam  658  passes through the optical axis correcting mechanism  654  for correcting an optical axis shift, and through the mirror  657   b , and is transmitted to the irradiation direction switching mechanism  655 . The irradiation direction switching mechanism  655  includes optical elements such as a mirror, a parallel plate glass, and a half mirror. By selecting any of the optical elements, the optical path of the light beam  658  can be changed. The optical path of the light beam  658  is changed to a first projection light optical system effecting perpendicular illumination when the mirror is selected, to a second projection light optical system effecting oblique illumination when the parallel plate glass is selected, and an optical path branched to the first and second projection light optical systems effecting composite irradiation of the perpendicular illumination and the oblique illumination when the half mirror is selected. 
     In the first projection light optical system effecting perpendicular illumination, by the irradiation direction switching mechanism  655 , the course is switched toward the beam shaping mechanism  656   b . The light beam  658  is shaped to a sectional shape adapted for the purpose of the inspection and, after that, emitted to the wafer  1  via the mirror  657   g  at a high elevation angle (using the wafer surface as a reference). 
     In the second projection light optical system effecting oblique illumination, after passing through the irradiation direction switching mechanism  655 , the course is switched by the mirror  657   c  toward the beam shaping mechanism  656   a . The light beam  658  is shaped to a sectional shape adapted for the purpose of the inspection and, after that, emitted to the wafer  1  via the mirrors  657   d ,  657   e , and  657   f  at a low elevation angle. The illumination angle (elevation angle) is controlled to a predetermined elevation illumination angle θi by an output unit  660  made of both the mirror  657   f  and an irradiation angle control mechanism (not shown). 
     In the composite irradiation of the perpendicular illumination and the oblique illumination, the branched optical beams  658  are applied to almost the same position in the wafer  1  via the two projection light optical systems. By different elevation illuminations from different elevation angles or composite illumination from a plurality of elevation angles, a characteristic amount (directivity) of a scattered light distribution with respect to the kind of a foreign matter and the kind of a defect is emphasized, and the performance of discriminating the kind of a foreign matter and the kind of a defect can be improved. 
       FIG. 7  shows an example of layout, seen from above, of a first detector  770  illustrated in  FIG. 2 . The first detector  770  is made of a group of PMTs (photomultipliers)  771  to  780  disposed at a plurality of elevation angles and azimuths, which are roughly divided in two groups in terms of elevation angle. 
     The PMTs  771  to  774  as a group of high-elevation detectors are disposed in positions of elevation angles larger (higher) than those of the PMTs  775  to  780  as a group of low-elevation detectors (using the wafer surface as a reference). The PMTs  771  to  774  in the group of the high-elevation detectors are disposed at elevation angles of about 30 degrees or larger (using the wafer surface as a reference), preferably, in the range of 35 degrees to 65 degrees in order to capture light scattered from crystal defects including a COP (Crystal Originated Particle) and OSF (Oxidation induced Stacking Fault) and from structural defects such as a scratch and a crack. 
     The four PMTs  771  to  774  in the group of the high-elevation detectors are disposed in a plurality of azimuths in angles of about 90 degrees in the circumferential direction so as to be able to efficiently capture scattered light in three modes of forward scattering, side scattering, and back scattering from a foreign matter kind or a defect kind. The number of azimuths is not limited to four. According to kinds of foreign matters and kinds of defects to be discriminated, the PMTs can be disposed in such azimuths that the characteristic amount (directivity) of each of scattered light distributions can be easily captured. 
     The elevation angles of the PMTs  775  to  780  as a group of low-elevation detectors are set to almost 30 degrees or less (using the wafer surface as a reference), preferably, in the range of 5 degrees to 20 degrees in order to receive mainly scattered light from foreign matters. The six PMTs  775  to  780  in the group of the low-elevation detectors are disposed in a plurality of azimuths at angle intervals of about 60 degrees in the circumferential direction so as to be able to efficiently capture both scattered light in three modes of forward scattering, side scattering, and back scattering from a foreign matter kind or a defect kind, and scattered light emitted in intermediate azimuths. The number of azimuths is not limited to six. According to kinds of foreign matters and kinds of defects to be discriminated, the PMTs may be disposed in azimuths at which the characteristic amount (directivity) of each of scattered light distributions can be easily captured. 
     The first detector  770  can detect total eight azimuths of the PMTs  775  to  780  in the low-elevation detector group and the PMTs  771  to  774  in the high-elevation detector group, and can efficiently detect the characteristic amount (directivity) of the scattered light distribution with respect to the azimuth. The PMTs  773  and  777  and the PMTs  771  and  780  are disposed at different elevation angles in almost the same azimuth so that the characteristic amount of the scattered light distribution with respect to the elevation angle can be detected. The characteristic amounts of distributions of scattered light from a foreign matter kind or a defect kind are captured by the PMTs disposed in the eight azimuths, and detection signals from the PMTs are computed, thereby enabling discrimination between a foreign matter and a defect and further the kind of the foreign matter or the defect to be performed. 
     Precision and processing speed of the discrimination between a foreign matter and a defect can be improved by the combination of the projection light optical system and the first detector  770 . For example, to detect a foreign matter, the combination of oblique illumination by the second projection light optical system and the PMTs  775  to  780  in the low-elevation detector group is preferable. On the other hand, to detect a defect, it is preferable to select perpendicular illumination of the first projection light optical system or oblique illumination of the second projection light optical system in accordance with the kind of the defect to be discriminated, and to combine the selected illumination with the PMTs  771  to  774  in the high-elevation detector group. 
     Further, to discriminate between a foreign matter kind and a defect kind at high speed, it is preferable to combine the composite irradiation of the first and second projection light optical systems and the composite detection of different elevation angles of the PMTs  771  to  774  in the high-elevation detector group and the PMTs  775  to  780  in the low-elevation detector group and to obtain the characteristic amount (directivity) of scattered light by arithmetic processing. 
     Referring again to  FIG. 2 , the stage  410  for moving an object to be inspected includes a chuck  411  on which the wafer  1  is mounted, retaining nails  412  for locking the wafer  1  by its end portion, a rotating mechanism  420  for rotating the chuck  411 , an elevating mechanism  430  for controlling the height of the wafer  1 , and a back-and-forth driving mechanism (linear driving mechanism)  440  for moving the wafer almost in parallel along with the chuck  411 , the rotating mechanism  420 , and the elevating mechanism  430 . 
     The rotating mechanism  420  comprises a rotating device (not shown) such as a spindle motor, and can detect an angle coordinate (θ coordinate) in the circumferential direction of the wafer  1  by a θ position detecting device (not shown) such as an internally-provided optical-reading-type rotary encoder. The back-and-forth driving mechanism  440  has therein a linear encoder of the optical-reading-type and can detect the position coordinate (r coordinate) in the radial direction of the wafer  1 . 
     By the rotating mechanism  420  and the back-and-forth driving mechanism  440 , the surface to be inspected of the wafer  1  is spirally or circularly scanned with the light beam  658  emitted from the first light emitting unit  600 . When a foreign matter or a defect exists in the scan path of the light beam  658 , scattered light according to the foreign matter or defect is emitted. By detecting the scattered light by the first detector  770 , the existence of the foreign matter or defect is detected. A signal of the scattered light detected by the first detector  770  is stored in the storage  512  in the data processing unit  500  so as to be associated with signals of the angle coordinate and the position coordinate from the rotary encoder and the linear encoder, which signals are outputted from an inspection coordinate detector  450 , and is subjected to arithmetic processing. On the basis of the intensity of the detected scattered light, the size of the foreign matter or defect is identified. On the basis of the coordinate signals from the inspection coordinate detector  450 , the coordinates of the foreign matter or defect in the wafer  1  are identified. 
     The chuck  411  has a recessed shape having a ring-shaped rim  413  along the shape of the wafer  1 . In the rim  413  disposed at the outer periphery, an inclined plane which is inclined downward to the inside of the chuck  411  is formed. The end portion (edge) of the wafer  1  itself is supported by the inclined plane of the rim  413 . By pressing the end portion on the side of the surface to be inspected of the wafer  1  by the retaining nail  412 , the wafer  1  is locked to the chuck  411 . Between the surface of the chuck  411  and the reverse face of the surface to be inspected of the wafer  1 , an internal space  414  via the rim  413  is formed. By the internal space  414 , the non-contact state between the reverse face of the surface to be inspected and the chuck  411  is maintained. By the edge grip mechanism, occurrence of adhesion of a foreign matter and a defect in the reverse face of the surface to be inspected is prevented, so that the surface inspection on the face and the rear face of the wafer  1  can be conducted. 
     In an almost center of the chuck  411 , a gas supply part  415  is disposed. The gas supply part  415  supplies gas such as N 2 , Ar, He, or air via a gas supply path  416  internally provided in both the chuck  411  and the rotating mechanism  420 . In the surface of the chuck  411 , ring-shaped air gap forming parts  417  each having a flat part in its top face are disposed in a position lower than the rim  413 . The plurality of air gap forming parts  417  are formed sparsely in the area of the surrounding part of the chuck  411  and densely toward the area of the center part. The disposition of the air gap forming parts  417  is adjusted so that the pressure distribution in the internal space  414  has a high pressure in the area of the center part of the wafer  1  and a low pressure in the surrounding area. A deflection or warp caused by the self weight of the wafer  1  can be corrected with a small gas flow. 
     A plurality of exhaust ports  418  for exhausting the gas in the internal space  414  to the rear surface side of the chuck  411  are provided near the rim  413  of the chuck  411 . 
     The gas supplied from the gas supply part  415  transmits pressure to the reverse face of the wafer  1  in accordance with the pressure distribution in the internal space  414  adjusted by the air gap forming parts  417  and is exhausted to the outside of the chuck  411  via the exhaust ports  418 . 
     Consequently, the inside in the internal space  414  surrounded by the wafer  1 , the chuck  411  body, and the rim  413  is maintained in a predetermined pressure distribution, an air gap of a predetermined amount is always formed between the air gap forming parts  417  and the wafer  1 , and a deflection and warp of the wafer  1  can be corrected. 
     In the chuck  411  of the embodiment, the pressure distribution is adjusted by the plurality of air gap forming parts  417 . A similar effect can be obtained by an air gap forming part  417  formed by a plurality of steps disposed so that the internal space  414  is widened toward the outside as shown in  FIG. 3A , or an air gap forming part  417  having a projected curved surface having a predetermined curvature as shown in  FIG. 3B . The shape of the air gap forming part  417  may be obtained by processing the chuck  411  body or generated by combining processed other elements. 
       FIG. 4  shows a schematic configuration of a gas control system  800  for supplying gas to the reverse face of the wafer  1 . The gas control system  800  supplies gas to the internal space  414  of the side grip mechanism to correct a deflection or warp of the wafer  1 . The gas control system  800  has a flow controller  801  such as an MFC (Mass Flow Controller) for controlling gas flow, a shutoff valve  802  such as an air valve for opening/closing a gas supply path, an electromagnetic valve  803  for controlling supply of compressed air for opening/closing the shutoff valve  802 , a filter  804  for removing dusts in the supply gas, and a pipe  805  for connecting the pipe elements. The pipe  805  is preferably subjected to internal polishing in order to suppress adhesion of a foreign matter to the reverse face of the inspection surface. 
     The gas control system  800  controls a gas supply timing and supply flow on the basis of an instruction from the controller  510 . 
     At the time of inspecting the wafer  1 , the carried wafer  1  is locked by the retaining nail  412  to the chuck  411 . After that, a whole close signal is transmitted from the controller  510  to the flow controller  801 , and a flow control valve (not shown) in the flow controller  801  is closed. 
     Subsequently, an open signal to the electromagnetic valve  803  is transmitted. The valve is opened to send the compressed air to the shutoff valve  802 , and the gas supply path is opened. After that, a flow setting signal is transmitted to the flow controller  801 , slow-up is performed while gradually increasing the opening of the flow control valve, and the flow is controlled to a predetermined flow. 
     When the inspection is finished, a close signal is transmitted to the electromagnetic valve  803  to close the electromagnetic valve  803  and exhaust the compressed air in the inside, and the shutoff valve  802  is closed. By closing the gas supply path, supply of gas is stopped. After that, locking of the retaining nail  412  is released, and the wafer  1  is carried out to the load port  100  by the carrying unit  200 . 
     It is desirable to use compressed air as the gas supplied to the internal space  414  from the view point of suppressing running cost. However, a gas whose purity and dew point are controlled, for example, N 2  or the like is desirable from the viewpoint of suppressing contamination on the reverse face of the inspection surface. 
       FIG. 5  shows a setting screen  820  for controlling the gas control system  800 . The setting screen  820  is displayed on the display device  530  of the data processing unit  500 , and the information of the setting screen  820  is registered on the storage  512 . 
     The setting screen  820  comprises a flow setting and displaying part  821  for setting and displaying flow of gas supplied, a kind selecting and displaying part  822  for selecting and displaying the kind of gas, a flow correcting and displaying part  823  for correcting and displaying the flow which changes according to the kind of gas, a slow-up setting and displaying part  824  for setting and displaying slow-up time until the flow reaches a predetermined flow, and a timing setting and displaying part  825  for setting and displaying timings of supplying and stopping the gas. 
     The flow correcting and displaying part  823  multiplies a set value of the flow setting and displaying part  821  by a coefficient determined according to the kind of gas, and outputs the resultant signal. For example, the MFC is corrected with N 2  gas and, generally, makes the flow controller  801  output a flow setting signal multiplied by a heat loss coefficient called a conversion factor. 
     The timing setting and displaying part  825  controls gas supply start with delay time of 0.5 to 5 seconds using the time point when the wafer  1  is locked to the chuck  411  as a base point. Using the time point when the surface inspection on the wafer  1  is finished and the rotational speed of the rotating mechanism  420  becomes a predetermined rotational speed or less as a base point, gas supply stop is controlled after delay time of 0.5 to 5 seconds. As long as the delay time for stabilizing the operation can be set, the base points of supply and stop of gas are not limited to the above. Any base points may be employed as long as the timings of supply and stop can be controlled. 
     Although the setting is made on the flow correcting and displaying part  823  via the input device  520  in the embodiment, the coefficient may be automatically changed when the gas kind is selected in the kind selecting and displaying part  822 . The setting display or selection display may be performed via the input device  520 , or it is also possible to use pressure-sensitive means or the like as the input means on the setting screen  820  and to enter the setting on the screen. 
       FIG. 8  is a schematic configuration diagram of the elements related to the height position controller  900 , extracted from the vertical cross section of the inspection unit  400  shown in  FIG. 2 . The height position controller  900  detects height information of the neighborhood of the inspection location in the wafer  1  corrected by the gas control system  800  and determines whether the correction is proper or not. Subsequently, the height position controller  900  controls vertical movement position of the inspection location which has been able to be corrected by the gas control system  800  to a predetermined height position. Further, the height position controller  900  calculates a warp state of the wafer  1  under the surface inspection and can check whether the correcting condition of the gas control system  800  is proper or not. 
     The height position controller  900  includes a second light emitting unit  920  for irradiating the inspection surface of the wafer  1  with light used for detecting a vertical movement position, a second detector  910  for detecting reflection light (specular reflection) of the second light emitting unit  920  and for outputting inspection surface height information (electric signal) of the wafer  1 , amplifiers  930   a  and  930   b  for amplifying the electric signal from the second detector  910 , an A/D converter  950  for converting analog signals from the amplifiers  930   a  and  930   b  to digital signals, the data processing unit  500  for processing the digital signals and for outputting an electric signal (control signal) which controls the inspection surface height, and an elevating mechanism control circuit  940  for driving the elevating mechanism  430  on the basis of the control signal from the data processing unit  500 . 
     The second detector  910  is constructed by a photoelectric conversion element. In the embodiment, a two-segmented sensor is used as the second detector  910 . It is sufficient for the second detector  910  to detect the position of reception of reflection light from the second light emitting unit  920 . A CCD or the like also can be used. 
     As the light source of the second light emitting unit  920 , a light source for emitting light of a wide band or white light is used. In some cases, a laser light source of a single wavelength or the like can hardly obtain reflection light due to the thickness of a film formed on the inspection surface of the wafer  1 . Due to the film thickness interference, reception of specular reflection of the second detector  910  is hindered, and an inconvenience occurs such that the vertical movement position of the inspection surface of the wafer  1  cannot be detected. Since the wavelength dependency of reflectance variously varies according to the film thickness and its substance, the light source of the second light emitting unit  920  of the present embodiment is a light source of a wide band (350 to 700 nm) for emitting light from UV light to a visible light range, or a light source for emitting light including wavelengths of a wide range such as white light. With the light source, even if specular reflection cannot be obtained at a specific wavelength, reflection light can be received from another wavelength, and the vertical movement position can be detected stably. As the white light source, for example, a white laser, a white light emitting diode, a xenon lamp, a mercury lamp, a metal halide lamp, a halogen lamp, or the like can be used. 
     Light emitted from the second light emitting unit  920  is applied near the light beam  658  of the first light emitting unit  600  and is applied ahead on the scan path in which the light beam  658  travels. It is preferable to determine the interval between the light and the light beam  658  in accordance with response speed of the elevating mechanism from the viewpoint of improving precision of height control. The interval can be controlled by an irradiation position control mechanism  960  provided for the second light emitting unit  920 . A deviation of the coordinates from the light beam  658  is computed by the data processing unit  500  and corrected to the irradiation coordinates of the second light emitting unit  920 . 
     Light emitted from the light source passes through the second light emitting unit  920  and is applied to the inspection surface of the wafer  1  corrected by the gas control system  800 . Therefore, the inspection surface of the wafer  1  is spirally or circularly scanned with the illumination light of the second light emitting unit  920  like the light beam  658 . While changing the coordinates in the wafer  1 , reflection light from the inspection surface accompanying irradiation of the illumination light is received by the second detector  910 , and height position information of the inspection surface at the coordinates is outputted as an electric signal. 
       FIG. 9  shows the relation between height of the inspection surface of the wafer  1  and output from the second detector  910 . As described above, it shows an example in which a two-segmented sensor is used as the second detector  910 . 
     The two-segmented sensor comprises an upper sensor  910   a  and a lower sensor  910   b . The two-segmented sensor changes a detection signal to be outputted, in accordance with the focus position of reflection light, which position varies according to the vertical movement position of the inspection surface of the wafer  1 . 
     Both of the sensors have an upwardly projected output curve with respect to the height of the inspection surface. An electric signal outputted from the upper sensor  910   a  becomes the maximum value on the high position side of the inspection surface of the wafer  1 , and that from the lower sensor  910   b  becomes the maximum value on the low position side. Therefore, the cross point between signals outputted from the upper sensor  910   a  and the lower sensor  910   b , that is, the position in which the output signals becomes the same is detected as the height of the inspection surface of the wafer  1  to be controlled. In the embodiment, predetermined height of the inspection surface to be controlled is set to the focus position. The light beam  658  of each of the first and second projection light optical systems is adjusted to form a predetermined beam spot at the predetermined height, and the second detector  910  is disposed so as to detect the predetermined height. 
     Electric signals of height position information outputted from the upper sensor  910   a  and the lower sensor  910   b  are amplified by the amplifiers  930   a  and  930   b , respectively, and transmitted to the A/D converter  950 . The analog electric signal of the analog height position information is converted by the A/D converter  950  to a digital electric signal. The electric signals are outputted to the data processing unit  500 . The data processing unit  500  performs arithmetic processing on the basis of the electric signals and detects a positional deviation (differential signal) from the predetermined height of the inspection surface. 
     Subsequently, the data processing unit  500  outputs a control signal for correcting the positional deviation to the elevating mechanism control circuit  940 . The elevating mechanism control circuit  940  drives the elevating mechanism  430  on the basis of the control signal to control the inspection surface to the predetermined height of the inspection surface. The elevating mechanism  430  has therein a driving device such as a pulse motor. The elevating mechanism control circuit  940  outputs a drive signal (pulse) to the elevating mechanism  430  until the detected positional deviation decreases to a predetermined value, to control the inspection surface to the predetermined height. 
     The drive signal outputted from the elevating mechanism control circuit  940  to the driving device is stored in the storage  512  of the data processing unit  500  so as to be associated with signals of the angle coordinate and the position coordinate of the inspection location in the wafer  1 , which are outputted via the inspection coordinate detector  450 . By arithmetic processing, a warp state of the wafer  1  is calculated. 
     For example, the travel distance of the vertical movement for one pulse of the drive signal can be obtained from specifications of mechanical elements related to the pulse motor and its driving. Therefore, by sequentially tracing the movement from the start point of the coordinates to the end point on the basis of the coordinates scanned by irradiation light of the second light emitting unit  920  and the output history of the corresponding drive signal, the distance (deviation amount) between the predetermined inspection surface height and an actual inspection location with respect to the coordinates is obtained. That is, the warp state of the wafer  1  can be obtained. 
     It is also possible to use an output from the A/D converter  950  as it is before being shifted to the correction of the predetermined height of the inspection surface, use a signal from the A/D converter  950  based on the upper sensor  910   a  as A, use a signal from the A/D converter  950  based on the lower sensor  910   b  as B, and obtain the distance by the following equation 1.
 
 H =α( A−B )/( A+B )  Equation 1
 
     (A+B) expresses the sum of reflection light received by the second detector  910 . By dividing (A−B) as the differential signal between the upper sensor  910   a  and the lower sensor  910   b  by (A+B), the influence due to a change in the light reception amount is reduced. α denotes a correction factor of the vertical movement amount. It is sufficient to preliminarily obtain a change amount with respect to the drive signal or the travel distance in accordance with the kind of the film and the film thickness. H denotes distance to the predetermined height of the inspection surface. The sign of H shows the positional relation of highness or lowness to the predetermined height. 
     The value of H computed by the data processing unit  500  is stored in the storage  512  of the data processing unit  500  so as to be associated with signals of the angle coordinate and the position coordinate of the inspection location in the wafer  1  outputted via the inspection coordinate detector  450  by a method similar to the above. By the processing of computing the H value corresponding to the coordinates, the warp state of the wafer  1  is calculated. In the case where a translucent film is formed on the inspection surface of the wafer  1 , there is a case that the interface under the film, that is, the Si surface is regarded as an inspection surface. In such a case, it is preferable to provide an offset value and perform a control with a signal to which the offset value signal is added (height detection correcting means). For example, in the calculating method, it is sufficient to add an output signal corresponding to the offset value to the positional deviation (difference signal). It is sufficient for calculating means to be described later to set the offset value in the term of the difference signal by setting α(A−B)/(A+B) in Equation 1 to α(A−B+C)/(A+B). 
       FIG. 10  shows outline of a display setting screen  1000  for displaying a warp state of the entire inspection surface of the wafer  1  detected by the height position controller  900 , analyzing the warp state, and simulating a correction supply gas amount. The display setting screen  1000  is displayed on the display device  530  of the data processing unit  500  and can be operated via the input device  520 . 
     In a left upper part of the screen, a result display function  1010  for indicating a numerical value of a warp obtained from measurement is disposed and, for example, the maximum warp amount, curvature radius, the direction of the warp, and the like are displayed. As the curvature radius, curvature radius in a designated direction sandwiched by two pointers  1020  is calculated and displayed. The profile of the warp amount in this direction is displayed by a shape display function  1030 . 
     By selecting an arbitrary position in the profile with a pointer  1120 , the coordinates of that point and its numerical value of the warp are displayed (point display function). 
     The direction of the warp indicates whether the shape of the warp is upwardly projected or downwardly projected. For example, upward projection is displayed as −, and downward projection is displayed as +. 
     In a left lower part, a warp state display function  1050  is disposed. To unify the positional relation of the wafer  1 , a base point  1040  such as a notch or orientation flat is disposed and displayed at a predetermined screen position. The image of the warp state is displayed so that the warp state of the plane of the wafer  1  can be recognized at a glance by 3D display, contour display, shade image display, color display, or the like. The display mode is not limited and can be selected by a display selection function  1060  including a display method other than the above-described display methods. 
     In a right upper part, a supply gas amount estimation function  1070  for examining setting conditions of the correction supply gas amount is disposed with respect to the measurement result of the warp state. The supply gas amount estimation function  1070  comprises a target setting function  1080  for setting a target value of a warp amount, and some condition setting functions  1090  for setting conditions such as rotational speed of the rotating mechanism  420  and shape of the air gap forming parts  417 . By entering an arbitrary numerical value via the input device  520  and clicking a processing instruction function  1100 , a correction supply gas amount for converging the warp amount to the target one is calculated. The estimated correction supply gas amount is displayed via a result display function  1110 . 
     The supply gas amount estimation function  1070  has two estimation modes. In one of the modes, for the whole wafer  1 , the warp amount is converged to a target value. In the other mode, the warp amount of an arbitrary designated place in the profile is converged to the target value. The estimation mode can be selected by an estimation mode selection function  1130 . The designated place in the profile can be instructed by a pointer  1140 . 
     The details of the process flow of the surface inspection apparatus in the embodiment will now be described. 
     The surface inspection on the inspection surface of the wafer  1  starts in response to an execution instruction to an inspection program on the display device  530 . The wafer  1  in the wafer pod  110  is handled by the carrying apparatus  210  in the carrying unit  200  and carried to the pre-alignment unit  300 . 
     In the case where the rear face of the wafer  1  is an inspection surface, the wafer  1  is mounted once on the inverting unit and turned upside down. The wafer  1  is mounted on the mounting stand  310  of the pre-alignment unit  300 . In the case where the face is the inspection surface, the wafer  1  is mounted as it is onto the mounting stand  310  of the pre-alignment unit  300 . 
     The wafer  1  mounted on the mounting stand  310  is subjected to coarse position correction (pre-alignment) in respect to both an almost center position in the wafer  1  and the position of the notch. Subsequently, the wafer  1  is handled again to the inspection unit  400  by the carrying apparatus  210 . The wafer  1  handled to the inspection unit  400  is mounted on the chuck  411  and locked to the chuck  411  by the retaining nail  412 . 
     Subsequently, under the setting conditions of the gas supply setting screen  820 , the controller  510  outputs an instruction signal to the gas control system  800  and supplies warp correction gas to the reverse face of the inspection surface of the wafer  1  via the gas supply path  416  and the gas supply part  415 . A warp or swell in the wafer  1  due to self weight is corrected by the warp correction gas. The stage  410  for moving an object to be inspected moves to an inspection start position while maintaining the state. 
     In response to an inspection start instruction from the controller  510 , the back-and-forth driving mechanism  440  for emitting the light beam  658  to an almost center of the wafer  1  preliminarily calculated and the elevating mechanism  430  via the height position controller  900  are controlled to perform a start point position correction in the surface inspection. 
     In parallel with the start point position correcting operation, the rotating mechanism  420  starts rotating the chuck  411  and accelerates increase in the rotational speed. By parallel process of the start point position correcting operation and the rotational speed accelerating operation, required time for the surface inspection is shortened, and the throughput is improved. 
     The controller  510  controls the rotating mechanism  420  so that the rotational speed reaches predetermined rotational speed in consideration of the timing of completion of the position correcting operation so that the two operations are completed almost synchronously. After the rotational speed reaches the predetermined rotational speed, the rotational speed is held almost constant. 
     By almost linearly moving the back-and-forth driving mechanism  440  in one-axis direction while irradiating the inspection surface of the wafer  1  rotated at high speed with the light beam  658 , the light beam  658  relatively moves spirally, swirly, or circularly to scan the inspection surface at high speed (scanning mechanism). On the other hand, the height position controller  900  emits illumination light of a second irradiation unit  720  ahead on the scan path in which the light beam  658  travels, captures height information of the inspection location in the wafer  1 , and controls the inspection location irradiated with the light beam  658  to the height of the focus position. 
     Scattered light generated from a foreign matter or a defect by the irradiation of the light beam  658  is received by the first detector  700  and analyzed together with the relative travel position information (r coordinate and θ coordinate) of the back-and-forth driving mechanism  440  and the rotating mechanism  420  outputted via the inspection coordinate detector  450  by the data processing unit  500 , and the size of the foreign matter or defect and the position coordinates in the wafer  1  are obtained. Similarly, the height information of the inspection location captured by the height position controller  900  is analyzed together with the relative travel position information (r coordinate and θ coordinate) of the back-and-forth driving mechanism  440  and the rotating mechanism  420  outputted via the inspection coordinate detector  450  by the data processing unit  500 , and the size of the warp or swell and the warp state in the wafer  1  are obtained. The information of the foreign matter, defect, and warp is stored in the storage  512  with the ID unique to the wafer  1 . 
     By the height position control to the focus position, in the perpendicular irradiation of the first projection light optical system, the beam spot diameter of the light beam  658  is maintained properly, and detection sensitivity is improved. In the oblique irradiation of the second projection light optical system, not only the detection sensitivity but also precision of the coordinates of the foreign matter or defect are improved. Further, in the projection light optical system using both the first and second projection light optical systems, the detection sensitivity is improved and, in addition, false information can be reduced. 
     The wafer  1  inspected is handled again by the carrying apparatus  210  and housed into the wafer pod  110  of the load port  100 . 
     Although a PMT (photomultiplier) is used for the first detector  700  in the embodiment, the invention is not limited to the PMT. Any photoelectric converting element for converting detected light to an electric signal, such as APD (Avalanche Photodiode), a CCD (Charge Coupled Device), an EM-CCD (Electron Multiplier CCD), a CMOS, or an APS (CMOS Active Pixel Sensor) can be used. 
     Description has been given using the surface inspection apparatus related to manufacture of a semiconductor device as an example and the semiconductor substrate (wafer) as an object to be inspected. However, the technique of the invention is not limited to a semiconductor substrate but can be used in the field in which a warp amount of a wafer rotating at high speed under inspection has to be detected in a real time manner. Irrespective of the material of the substrate, any plate-shaped substrate such as a glass substrate for use in a liquid crystal panel or a TFT module, or a sapphire substrate for use in a sensor or an LED can be used. The invention is not limited to the manufacturing process of a semiconductor device but can be widely applied to surface inspection apparatuses in various manufacturing processes of various sensors, hard disks, liquid crystal panel display devices, and the like. 
     Description Of Reference Numerals 
     
         
           1  wafer (object to be inspected) 
           100  load port 
           110  wafer pod 
           200  carrying unit 
           210  carrying apparatus 
           220  handling arm 
           230  fixed-side wall 
           240  grip block 
           250  Y-axis carrying unit 
           300  pre-alignment unit 
           310  mounting stand 
           320  sensor 
           400  inspection unit 
           410  stage for moving object to be inspected 
           411  chuck 
           412  retaining nail 
           413  rim 
           414  internal space 
           415  gas supply part 
           416  gas supply path 
           417  air gap forming part 
           418  exhaust port 
           420  rotating mechanism 
           430  elevating mechanism 
           440  back-and-forth driving mechanism 
           450  inspection coordinate detector 
           500  data processing unit 
           510  controller 
           511  arithmetic processing unit 
           512  storage 
           513  control device 
           520  input device 
           530  display device 
           540  output device 
           550  external storage 
           600  first light emitting unit 
           651  laser light source 
           652  shutter 
           653  attenuator 
           654  optical axis correcting mechanism 
           655  irradiation direction switching mechanism 
           656   a ,  656   b  beam shaping mechanisms 
           657   a  to  657   g  mirrors 
           658  light beam 
           660  output unit 
           710 ,  910  second detectors 
           720 ,  920  second light irradiation units 
           770  first detector 
           771  to  780  PMTs 
           800  gas control system 
           801  flow controller 
           802  shutoff valve 
           803  electromagnetic valve 
           804  filter 
           805  pipe 
           820  setting screen 
           821  flow setting and displaying part 
           822  kind selecting and displaying part 
           823  flow correcting and displaying part 
           824  slow-up setting and displaying part 
           825  timing setting and displaying part 
           900  height position controller 
           930   a ,  930   b  amplifiers 
           940  elevating mechanism control circuit 
           950  A/D converter 
           960  irradiation position control mechanism 
           1000  display setting screen 
           1010  result display function 
           1020 ,  1120 ,  1140  pointers 
           1030  shape display function 
           1040  base point 
           1050  warp state display function 
           1060  display selection function 
           1070  supply gas amount estimation function 
           1080  target setting function 
           1090  condition setting function 
           1100  process instruction function 
           1110  result display function 
           1130  estimation mode selection function