Abstract:
An inspection and measurement method and apparatus for semiconductor devices and patterns such as photomasks using an electron beam capable of measuring the potential of a sample with higher precision than conventional systems. When an S curve is observed in a semiconductor device to be inspected, fluctuations of the potential of the inspection sample surface are suppressed by optimizing the energy of a primary electron beam used for irradiation. When the surface potential of the semiconductor device is measured, a more precise measurement can be obtained without adverse effects from an insulation film surface. Further, the surface potential can be measured without installing a special apparatus for wafer surface potential measurement such as an energy filter, so the cost of the apparatus can be reduced.

Description:
CLAIM OF PRIORITY 
   The present application claims priority from Japanese application JP No. 2005-238105 filed on Aug. 19, 2005, the content of which is hereby incorporated by reference into this application. 
   FIELD OF THE INVENTION 
   The present invention relates to a method of manufacturing a fine circuit pattern formed on a substrate such as a semiconductor device or liquid crystal, and in particular relates to a method of pattern inspecting and measurement of a semiconductor device and photomask by an electron beam. 
   BACKGROUND OF THE INVENTION 
   A semiconductor device is manufactured by repeatedly performing a process which transfers a pattern formed on a photomask to a semiconductor wafer by lithography and etching. In this manufacturing process, the quality of lithography, etching and other steps, and the production of foreign matter, largely affect the yield of the semiconductor device, so in the semiconductor manufacturing field, it is important to have a method for early or prior detection when a fault occurs in the manufacturing process. In the prior art, a pattern inspecting and measurement apparatus employing an optical microscope was conventionally used, but in recent years, semiconductor devices have become more intricate while manufacturing processes have become more complex, so the use of electron microscopes is becoming more widespread. 
   One such appliance which uses an electron microscope is a circuit pattern inspection apparatus employing the Scanning Electron Microscopy (hereafter, SEM inspection apparatus). Many defects can be detected by this inspection apparatus such as electrical defects, adhesion of foreign matter, pattern shape defects, etc., and since an optical inspection apparatus cannot detect electrical defects, this special function of the SEM inspection apparatus is now attracting attention in the semiconductor manufacturing field. The detection of electrical defects in a semiconductor device by this SEM inspection apparatus is performed by charging a circuit pattern formed in a wafer surface, and using the contrast visualized by the charging. This is referred to as the voltage contrast method, and it is effective in detecting defective electrical properties of the semiconductor device. 
   Hereafter, the mechanism of forming a voltage contrast will be described using  FIG. 2 .  FIG. 2  is a schematic cross-sectional view of a wafer in a step for machining a contact hole on a Si wafer, and embedding a metal therein. There is a normal part  401  in which the metal and Si wafer are conducting, and a defective part  402  in which the metal and the Si wafer are not conducting due to a residual film from defective processing of the contact hole. In order to detect this defect, the wafer must be electrostatically charged, a voltage contrast image obtained by taking the potential difference produced by the electrical resistance difference of the normal part and defective part as a difference in the number of secondary electrons detected by a detector  411 , and the voltage contrast difference between the normal part and defective part measured. In the voltage contrast image, the wafer surface may be given a (1) positive charge or (2) negative charge according to the structure and inspecting conditions of the wafer to be inspected. The contrast of the pattern varies with the potential of the wafer. 
   To detect a defective electrical property using the aforesaid voltage contrast, and to detect a defect with high sensitivity, the wafer surface must be suitably charged. To obtain results which are highly reliable and reproducible, the electrostatic charge on the wafer surface must always be constant. Therefore, a method to measure the electrostatic charge on the wafer surface precisely is required. 
   Here, the potential measurement method by a conventional electron beam tester will be described. The schematic view of a prior art potential measurement method using an energy filter is shown in  FIG. 3A . In  FIG. 3A ,  92  is a deflector,  87  is a first grid,  88  is a second grid,  86  is a sample, and the sample  86  is irradiated by an electron beam  81 . The electron beam  81  can irradiate arbitrary points on the sample  86  due to the deflector  92 . A potential  82  of this sample  86  with respect to earth is unknown. It is attempted to measure this unknown potential  82  by secondary electrons. Secondary electron  93  emitted from the sample  86  are accelerated by the first grid  87  to which a potential  84  of +10 to +100 V is applied, and most pass through the first grid  87 . A potential  83  (energy filter potential) of, for example, −5 V is applied to the second grid  88 . Secondary electrons  95  which pass through the second grid  88  are detected by a secondary electron detector  89 . If the potential  83  applied to the second grid  88  is changed, for example to −30 to +30 V and the corresponding output of the secondary electron detector  89  is recorded on a XY recording waveform  91 , a curve like A of  FIG. 3B  will be obtained. In general, this is referred to as an S curve.  FIG. 3B  shows the analysis characteristics of the energy filter obtained by the aforesaid operation. The horizontal axis is the potential of the second grid  88 , and the vertical axis is the secondary electron detector output. Curves A, B are curves obtained for two different sample potentials. In both curves, the secondary electron detector output decreases as the potential of the second grid  88  becomes more negative. The curve A is shifted to the left-hand side compared with the curve B. This shows that the sample potential of curve A is a more negative potential. For the actual potential measurement, the output of the secondary electron detector  89  is set to the value shown by for example the arrow C, and the intersection points V A , V B  with the S curve are obtained. This difference (V A −V B ) becomes the variation amount of the sample potential  82 . If the curve A is for the case of a sample potential of 0, (V A −V B ) is the sample potential when B is measured (e.g., Scanning Electron Microscopy, Vol. 1, p. 375). To prevent the effect of fluctuation in the irradiation electric current of the primary electron beam, or the amount of secondary electron emission, there is also the method of differentiating the S curve shown in  FIG. 3B  by the second grid voltage, normalizing it, and calculating the variation amount of the sample potential  82  from the curve shift amount (e.g., JP 1986-239554 A). 
   SUMMARY OF THE INVENTION 
   The problem inherent in the prior art technique will be described using  FIG. 3 . Most of the secondary electrons emitted from the sample  86  are picked up the first grid  87  to which a positive electropositive potential was applied, the potential applied to the second grid  88  is changed, the S curve is obtained by recording the corresponding output of the secondary electron detector  89 , and the potential of the sample is computed from the S curve. This technique is used to measure the potential of interconnections on the semiconductor device. The potential of the interconnections is a fixed potential under given operating conditions. Since the effect of irradiation by the primary electron beam can be disregarded, a more precise potential can thus be measured. 
   However, for most semiconductor devices which are targets for inspecting measurement using an electron beam, there is an insulating film on the surface. If the surface potential of the semiconductor device is measured by the described method, the following problem occurs:
     (1) The electric charge of the surface regions of the insulating film is spatially re-distributed by irradiation with the primary electron beam, the surface potential changes, and the potential of the actual insulating film surface cannot be measured precisely.   

   The following secondary problems also occur:
     (2) To enhance the resolution of the SEM image, the primary electron beam is first accelerated to several keV, and then decelerated to about several hundred −1 keV by applying a retarding voltage to the wafer holder. This method is widely applied to inspecting and measurement apparatus using charged particles. Due to this, the secondary signal emitted from the surface of the semiconductor device is also accelerated by the retarding potential to several keV. However, to measure the potential of the wafer surface by the aforesaid energy filter, the secondary signal must be decelerated to several eV, so a strong electrostatic lens effect may occur which decreases the resolution of the primary electron beam. To avoid such an adverse effect, more grids have to be used, the energy of the secondary signal must be reduced gradually and the S curve then measured. Since the construction of the energy filter becomes more complex, the transmissivity of the secondary signal decreases and operating condition restrictions occur.   (3) Due to potential distortion of the grid vicinity, the resolution of the energy filter will decrease.   

   Thus, not only must an energy filter of complex construction be used, but also, the surface potential of the wafer cannot be measured with high precision. 
   The present invention therefore aims to provide an inspection and measurement apparatus and inspection and measurement method which can measure the potential of a sample with higher precision than the prior art technique. It also aims to provide an inspection and measurement apparatus which can measure potential by means of an easy construction. 
   In order to attain the aforesaid object, when the inventors observed the S curve for semiconductor devices used as inspection and measurement targets, they discovered that the variation of the potential of the test sample surface could be suppressed by optimizing the energy of the irradiating primary electron beam. Here, optimization of the energy of the primary electron beam means that the irradiation energy (landing energy: E Land ) of the primary electron beam is suppressed so that the secondary particle yield is 1 or a value near 1. Here, the secondary particle yield, when the primary charged particle beam irradiates the sample, is the number of secondary particles generated per unit primary particles. 
   Therefore, the test sample is irradiated with the primary electron beam, two S curves, i.e., the dependency of secondary particle (e.g., secondary electron or reflected electron) signal strength on sample charge control voltage, are observed, and the surface potential of the test sample is calculated from the difference of the charge control voltage of the S curve equivalent to a predetermined secondary particle signal strength. 
   When the S curves are observed, if the control electrode is installed above the sample and facing the sample to be inspected, the S curves can be acquired without using an apparatus of complex construction such as an energy filter and plural grids. Hence, it is possible to measure the potential of the sample surface. 
   Here, for convenience, the potential of the sample was calculated from the result of measuring the S curve, but even if the S curve is not measured, the surface potential of the sample can still be measured. This is because, among the data which constitute the S curve, two points are theoretically sufficient to calculate the surface potential of the sample. 
   According to the invention, when measuring the surface potential of a semiconductor device, a more precise potential measurement than before, which is almost unaffected by the potential of the insulating film surface, can now be performed. Also, since the surface potential can be measured without equipment specialized for wafer surface potential measurement such as an energy filter, the manufacturing cost for the apparatus can be reduced. 
   Further, since the surface potential of the sample can be measured with high precision, in an apparatus wherein charge control of the sample surface must be performed to control the quality of an image which is to be acquired, quality control of the acquired image is easy. This advantage is particularly useful in an inspection/measurement apparatus using a scanning electron microscope such as a critical dimension measurement SEM or SEM inspection apparatus. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagram describing an SEM inspection apparatus according to a first embodiment; 
       FIG. 2  is a diagram describing a voltage contrast image acquisition principle; 
       FIG. 3A  is a diagram describing an EB tester construction and principle; 
       FIG. 3B  is a diagram describing a principle whereby a sample potential is computed from an S curve; 
       FIG. 4A  is a diagram describing an SEM image of a semiconductor device; 
       FIG. 4B  is a diagram describing the result of measuring the variation of a secondary signal yield with an electron beam irradiation energy; 
       FIG. 5A  is a diagram describing the computation of the potential of an inspection region by an S curve; 
       FIG. 5B  is a diagram describing the computation of the potential of the inspection region by differentiating the S curve with respect to the Vcc potential and normalizing; 
       FIG. 6  is a diagram describing one example of flow charts for the inspection according to the first embodiment of the; 
       FIG. 7  is a detailed flow of the potential measurement portion in  FIG. 6 ; 
       FIG. 8  is a diagram describing SEM images in which different pattern density portion is existing, according to a second embodiment; 
       FIG. 9  is a diagram describing the construction of a length measurement SEM apparatus according to a third embodiment of the; 
       FIG. 10  is a diagram describing an example of a length measurement flow chart according to the third embodiment of the; and 
       FIG. 11  is a diagram describing the result of measuring the potential distribution on a wafer surface by the flow chart of  FIG. 7  according to fourth and fifth embodiments of the. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereafter, referring to the drawings, an inspection method and apparatus according to one embodiment will be described in detail. 
   Embodiment 1 
     FIG. 1  shows the schematic view of the inspection apparatus relating to a first embodiment. The apparatus of this embodiment is a scanning electron microscope having a sample surface potential measurement means and charge control means, and may be applied to an inspection SEM, review SEM and measurement SEM. The scanning electron microscope shown in  FIG. 1  is provided with a chamber  2  which is placed under vacuum, and a reserve chamber (in this embodiment, not shown) for transporting a wafer  9  as sample to the interior of the chamber  2 . This reserve chamber is constructed so that it can be placed under vacuum independently from the chamber  2 . In addition to the chamber  2  and the reserve chamber, the apparatus comprises a controller  6  and image processor  5 . The interior of the chamber  2  broadly comprises an electron optics system  3 , charge controller, detector  7 , sample chamber  8  and optical microscope  4 . In this embodiment, the chamber  2  means the whole vacuum vessel containing a sample chamber  8 , and the electron optics system  3 , charge controller, detector  7  and optical microscope  4  mentioned above operate inside the decompressed vacuum vessel. The sample chamber  8  is an enclosure wherein the sample stage is driven inside the chamber  2 . The region enclosed by the dotted line of  FIG. 1  corresponds to the sample chamber. The sample to be inspected may be a semiconductor wafer on which an interconnection pattern or circuit pattern is formed, a piece obtained by splitting off a part of a wafer, or a semiconductor chip on which a circuit is formed, but potential observations of samples other than semiconductor devices, such as a magnetic head, a recording medium or a liquid crystal panel can also be performed. 
   The electron optics system  3  comprises an electron source  10 , electron beam drawout electrode  11 , condenser lens  12 , blanking deflector  13 , scanning deflector  15 , aperture  14 , object lens  16 , reflector plate  17 , and ExB deflector  18 . In the detector  7 , a detector  20  is disposed above the object lens  16  in the chamber  2 . The output signal of the detector  20  is amplified by a preamplifier  21  installed outside the chamber  2 , and is converted to digital data by an A/D converter  22 . 
   The charge controller comprises a charge control electrode  65 , charge control electrode controller  66  and charge control power supply  67  which are installed facing the stage. 
   The detector  7  comprises the detector  20  in the chamber  2  which is placed under vacuum, preamplifier  21  outside the chamber  2 , AD converter  22 , optical transducer  23 , optical fiber  24 , electric transducer  25 , high voltage power supply  26 , preamplifier drive power supply  27 , AD converter drive power supply  28 , and reverse bias power supply  29 . In the detector  7 , the detector  20  is disposed above the object lens  16  in the chamber  2 . The detector  20 , preamplifier  21 , AD converter  22 , optical transducer  23 , preamplifier drive power supply  27  and AD converter drive power supply  28  are floated at an electropositive potential by the high voltage power supply  26 . 
   The sample chamber  8  comprises a sample stand  30 , X stage  31 , Y stage  32 , wafer holder  33 , position monitor length meter  34 , and optical height gauge  35 . 
   The optical microscope  4  is installed near the electron optics system  3  in the chamber  2  at a position sufficiently distant that they do not interfere with each other, and the distance between the electron optics system  3  and optical microscope  4  is known. The X stage  31  or Y stage  32  moves back and forth over the known distance between the electron optics system  3  and optical microscope  4 . The optical microscope  4  comprises a light source  40 , optical lens  41 , and CCD camera  42 . 
   Operating commands and operating conditions for each part of the apparatus are inputted and outputted from the controller  6 . The controller  6  has a database in which control parameters and operating conditions of the electron optics system, X stage  31 , Y stage  32  and other units are stored. Conditions such as the accelerating voltage when the electron beam is generated, electron beam deviation width, deviation rate, signal acquisition timing of detector and sample stand movement speed, are selected according to the purpose, and the parts of the apparatus are thereby controlled. The user may operate the apparatus by manual operation via a user interface, or may set the operating conditions beforehand by the controller  6  and operate the apparatus according to the setting. The controller  6  monitors position and height offsets from the signals of the position monitor length meter  34  and optical height gauge  35  using the correction control circuit  43 , generates corrected signals from the result, and sends the corrected signals to the lens power supply  45  or scanning deflector  44  so that the electron beam always irradiates the sample in the right position. 
   In order to acquire an image of the wafer  9 , this wafer  9  is irradiated with a finely focused beam  19 , and secondary electrons, reflected electrons or both  51  are generated, the image of the surface of the wafer  9  being obtained by detecting these in synchronism with the scanning of the electron beam  19 , and if required, the movement of the stages  31 ,  32 . 
   The electron source  10  is a Schottky type electron source. By using this electron source  10  compared with, for example, a tungsten (W) filament electron source or conventional cold field emission type electron source of the prior art, a stable electron beam current can be ensured, so a voltage contrast image with little brightness variation can be obtained. The electron beam  19  is drawn from the electron source  10  by applying a voltage between the electron source  10  and drawout electrode  11 . The electron beam  19  is accelerated by applying a high electronegative potential to the electron source  10 . 
   Due to this, the electron beam  19  proceeds towards the sample stage  30  with an energy corresponding to this potential, is converged by the condensing lens  12 , and is further focused by the objective lens  16  so as to irradiate the wafer  9  mounted on the X, Y stages  31 ,  32  on the sample platform  30 . The scanning signal generator  44  which generates a scanning signal and blanking signal is connected to the blanking deflector  13 , and the lens power supplies  45  are connected to the condenser lens  12  and objective lens  16 . The arrangement is such that a negative voltage (retarding voltage) can be applied by the retarding power supply  36  to the wafer  9 . Due to this, the primary electron beam is decelerated by adjusting the voltage of the retarding power supply  36 , and the electron beam irradiation energy delivered to the wafer  9  can be adjusted to the optimum value without varying the potential of the electron source  10 . 
   The secondary electrons or reflected electrons generated by irradiating the wafer  9  with the electron beam  19 , or both  51 , are accelerated by the negative voltage applied to the wafer  9 . An ExB deflector  18  is disposed above the wafer  9 , and the secondary electrons, reflected electrons or both which are thusly accelerated are deflected in a predetermined direction. The deflection amount can be adjusted by the voltage and magnetic field strength applied to the ExB deflector  18 . Also, this electromagnetic field can be varied in synchronism with the negative voltage applied to the sample. The secondary electrons, reflected electrons or both  51  deflected by the ExB deflector  18  collide with a reflection plate  17  under predetermined conditions. When the accelerated secondary electrons, reflected electrons or both  51  collide with the reflection plate  17 , second secondary electrons, reflected electrons or both  52  are emitted from the reflection plate  17 . 
   The second secondary electrons and posterior scattered electrons  52  generated due to collision with the reflection plate  17  are led to the detector  20  by this sucking electrical field. The detector  20  detects the second secondary electrons, reflected electrons or both  52  generated when the secondary electrons, reflected electrons or both  51 , which are generated when the electron beam  19  irradiates the wafer  9  and are accelerated to collide with the reflection plate  17 , in synchronism with the scanning timing of the electron beam  19 . The output signal of the detector  20  is amplified by the preamplifier  21  installed outside the chamber  2 , and converted to digital data by the AD converter  22 . The AD converter  22  immediately converts the analog signal detected by the detector  20  and amplified by the preamplifier  21  to a digital signal, and sends it to the image processor  5 . The detected analog signal is digitized and transmitted immediately after detection, so a high speed signal with a high SN ratio can be obtained. Here, the detector  20  may be for example a semiconductor detector. 
   The wafer  9  is mounted on the X, Y stages  31 ,  32 , and when scanning is performed, either the X, Y stages  31 ,  32  are held stationary while the electron beam  19  is scanned in 2 dimensions, or the X, Y stages  31 ,  32  are moved continuously at constant speed in the Y direction while the electron beam  19  is scanned in a straight line in the X direction. If a specific, relatively small region is to be scanned, the former method is used where the stages are held stationary for scanning, and if a relatively large region is to be scanned, it is effective to move the stages continuously at a constant speed for scanning. If the electron beam  19  must be blanked, control can be performed so that the electron beam  19  is deflected by the blanking deflector  13 , and does not pass through the aperture  14 . 
   In this embodiment, the position monitoring length measurement device  34  was a laser interference length measurement gauge. The positions of the X stage  31  and Y stage  32  can be monitored in real-time, and sent to the controller  6 . Data such as the rotation speeds of the X stage  31 , Y stage  32  and the motor of the wafer holder  33  are likewise sent to the controller  6  by the respective drivers. Based on this data, the controller  6  can precisely capture the region and position irradiated by the electron beam  19 , and if required, the positional offset of the irradiation position of the electron beam  19  can be corrected by the correction control circuit  43  in real-time. Further, the region irradiated by the electron beam can be stored for each wafer. 
   The optical height measurement gauge  35  uses an optical measurement apparatus which is a measurement system different from that of the electron beam, for example a laser interference measuring device or a reflected light measuring device which measures the variation at a reflected light position, so the height of the wafer  9  mounted on the X, Y stages  31 ,  32  can be measured in real-time. In this embodiment, the wafer  9  is irradiated with white light from the light source  37 , the position of the reflected light is detected by a position detecting monitor, and the height variation amount is computed from the positional variation. Based on the measurement data from this optical height measuring device  35 , the focal length of the objective lens  16  which finely converges the electron beam  19  can be corrected dynamically, and the electron beam  19  can be irradiated so that it is always focused on a region to be inspected. Also, the warp and height distortion of the wafer  9  can be measured beforehand prior to electron beam irradiation, and the correction conditions for the objective lens  16  can be set for each inspection region based on the data obtained by the warp and height distortion measurement. 
   The image processor  5  comprises an image storage unit  46 , computer  48  and monitor  50 . The computer  48  has software for computing the potential of the sample surface based on the detection result of the detector  7 , and software for defect inspecting of the sample by processing the detection result of the detector  7 , and it performs potential detection computations together with defect inspecting computational processing. Also, although not shown in the diagram, the monitor  50  is provided with an information input means so that the user can input information required by the apparatus control system, the monitor  50  and information input means together forming the user interface of the apparatus. The image signal of the wafer  9  detected by the detector  20  is amplified by the preamplifier  21 , and after digitization by the AD converter  22 , converted to an optical signal by an optical converter  23 , transmitted by an optical fiber  24 , and after re-conversion to an electrical signal by an electrical converter  25 , stored by the image storage unit  46 . 
   The electron beam irradiation conditions for forming the image and the detection conditions of the detection system are set beforehand when the test conditions are set, filed and recorded in a database. 
   Next,  FIG. 4A  shows an example of the SEM image obtained by the apparatus of this embodiment. The SEM image of  FIG. 4A  is an SEM image of a semiconductor device obtained from the secondary signal amount emitted by a semiconductor device  100  detected by the detector when the surface of the semiconductor device  100  is scanned by a primary electron beam having a certain irradiation energy (E Land ). The white areas are holes, and the other shaded region is an inter-layer insulation film. The average value of the secondary signal from this shaded region or part thereof is calculated, and the yield of the secondary signal is computed. E land  of the primary electron beam is varied by adjusting the voltage Vr applied to the wafer holder  33  ( FIG. 1 ) by the controller  68 , the yield of the secondary signal is computed by the same method, and the dependence of the secondary signal on E land  of the primary electron beam is calculated ( FIG. 4B ). E Land  (E 2 ) of the primary electron beam when the secondary signal is 1, is computed from the above dependence, and taken as E land  of the primary electron beam used for potential measurement of the wafer surface. 
   Next, a region identical to that of the semiconductor device  100  is scanned by the primary electron beam having the aforesaid E land , the potential of Vcc applied to the electrode  65  ( FIG. 1 ) is varied from the more positive side (in  FIG. 5 , the value of Vcc is varied from right to left), the output of the secondary electron detector  20  ( FIG. 1 ) corresponding to each Vcc value is recorded, and the S curve  41  ( FIG. 5 ) is acquired. Since the yield or the secondary signal is 1 or close to 1, the emitted secondary signal does not return to the wafer surface until a push-back field is generated on the wafer surface, and the effect of the potential of the device surface due to the measurement can be ignored. By comparing with a reference S curve  40  obtained under identical measurement conditions, the surface potential of the semiconductor device to be measured is computed (V B −V A ). Alternatively, computations such as differentiation and normalization are performed on the curves  40 ,  41  obtained by the measurement, and the aforesaid potential is computed from the peak shift amounts of the resulting curves  42 ,  43  (V D −V C ). 
   As described above, in the apparatus according to this embodiment, the surface potential of a sample can be measured more precisely, and almost unaffected by the surface potential of the semiconductor device itself. However, due to variation in the Vcc condition during measurement, it may be affected by the potential of the insulation film. In this case, the image acquisition position may be changed for each image acquisition. Also, if required, the electrostatic charge may be mitigated by irradiating with an ultraviolet light beam or another electron beam. 
   Next, the means for measuring the wafer surface potential using the apparatus shown in  FIG. 1  will be described referring to the flow chart of  FIG. 6 . 
   First, in a step  201 , a wafer cassette containing a wafer in any desired shelf, is positioned. The monitor displays an input request message to specify the wafer to be inspected, and the user specifies the shelf number of the cassette where the wafer is set by the information input means. Likewise, in a step  202 , the monitor displays various input request messages to input inspection conditions, and the user inputs various inspection conditions via the information input means. The inspection conditions which are input include the electron beam current, electron beam irradiation energy, FOV (Field of View) of one screen, potential of the retarding power supply  36  and potential of the electrostatic control electrode  65 . The individual parameters may be input, but normally a combination of these inspection parameters is entered into a database as an inspection condition file, inspection condition files being selected according to various ranges. 
   In a step  203  when Auto inspection is started, in a step  204 , the set wafer  9  is loaded into the apparatus from the sample load/unload chamber  62 . In the wafer transport system, even if the diameter of the wafer  9  is different, and even if the wafer shape is different such as orientation flat or notched, a holder for carrying the wafer  9  can be selected according to the wafer size and shape. This wafer  9  is transferred from the wafer cassette to the holder by a wafer loader comprising an arm and reserve vacuum chamber or the like, held fixed, placed under vacuum in the wafer loader together with the holder, and transferred to the chamber  2  which is already under vacuum in a vacuum pump system. 
   After the wafer is loaded, in a step  205 , the electron beam irradiation conditions for each part of the apparatus are set by the controller  6  based on the input inspection conditions. The apparatus parts comprise for example a position monitor length gauge  34 , optical height gauge  35 , lens power supply  45  and scanning deflector  44 , but also include all control parts required to control electron beam irradiation. The stage  32  is then moved so that the first beam correction pattern on the wafer holder is below the electron optical system, a voltage contrast image of the beam correction pattern is acquired, and focus/no-focus is adjusted by this voltage contrast image. This is then moved to a predetermined position on the wafer  9 , an SEM image of the wafer  9  is acquired, and brightness and contrast are adjusted. Here, if it is required to vary the electron beam irradiation conditions, another beam correction may be performed. Also, the correlation between height information from the optical height gauge  35  and the focal point conditions of the electron beam can be calculated, and the focal point conditions adjusted automatically from the wafer height detection result without adjusting the focus each time the voltage contrast image is acquired thereafter. 
   In a step  206 , to observe a first alignment coordinate by the optical microscope  4 , the set wafer  9  is moved by the X, Y stages  31 ,  32 . From the monitor  50 , an optical microscope image of the alignment pattern formed on the wafer  9  is observed and compared with an identical pattern image stored beforehand, and a position-corrected value of the first coordinate is computed. Next, it is moved a fixed distance from the first coordinate to a second coordinate to where there is an equivalent circuit pattern to that of the first coordinate, an optical microscope image is observed in the same way, compared with a circuit pattern image stored for alignment, and the position correction value of the second coordinate and rotation offset amount relative to the first coordinate are computed. 
   Hence, when preparations such as predetermined corrections by the optical microscope  4  and test region settings are complete, the wafer  9  is moved underneath the electron optical system  3  by moving the X, Y stages  31 ,  32 . When the wafer  9  is under the electron optical system  3 , the same procedure as that of the alignment procedure performed by the optical microscope  4  is performed by the SEM image. The SEM image in this case is acquired by the following method. The electron beam  19  is scanned in two-dimensions in the XY direction by the scanning deflector  15  to irradiate the same circuit pattern as that observed by the optical microscope  4  based on the stored, corrected coordinate values in the positioning by the optical microscope image. Due to this two-dimensional scanning of the electron beam, the secondary electrons, reflected electrons or both  51  emitted from the observed site are detected by the construction and action of the various parts which perform detection of emitted electrons, and an SEM image is thereby acquired. Since simple inspection position confirmation, positioning and position adjustment have already been performed using the optical microscope image, and a rotation correction has already been made, the positioning, position correction and rotation correction can be performed with higher resolution, higher magnification and higher precision than with an optical image. When the electron beam  19  irradiates the wafer  9 , the irradiation position is charged. To avoid the effect of this charge during inspecting, in pre-inspection preparations such as the aforesaid position rotation correction and inspection region setting, the circuit pattern irradiated by the electron beam  19  is pre-selected to be a circuit pattern outside the inspection region, or an equivalent circuit pattern of a chip or die outside the inspection region on the wafer is selected automatically by the controller  6 . The alignment results obtained by this procedure are sent to each controller. During inspecting, rotation or position coordinates are corrected by the controllers. 
   When the step  206  is complete, the X, Y stages are moved, and the specified region of the wafer is moved to the irradiation region of the primary electron beam (step  207 ). When the step  207  is complete, a step (step  200 ) for electrostatic charge potential measurement of the specified region is started.  FIG. 7  shows the details of the process performed in the step  200 . Hereafter, the flow chart  200  (steps  209 - 217 ) of the potential measurement of the specified region will be described. In the example describe in  FIG. 7 , the potential Vr of the holder  33  is varied under a probe current is restricted, however, the measurement under other measurement conditions could be taken into account in the same way. First, in the step  209 , the request for setting the voltage Vcc is displayed on the monitor  50 , and the user sets following values through via the information input means connected to the monitor  50 ; the voltage range (minimum value Vcc1, maximum value Vcc2), the increment width δVcc of the voltage Vcc applied to the Vcc electrode. To detect the secondary electron signal emitted from the wafer without it returning to the wafer, an electric field is normally formed to pick up the secondary signal. In the step  210 , the request for setting the retarding voltage Vr is displayed on the monitor  50 , and the user inputs the minimum value Vr1, maximum value Vr2 and increment unit amplitude δVr of Vr. In the step  211 , when the initial condition Vr=Vr1 is met, scanning of the primary electron beam is performed and an SEM image is acquired. Subsequently, the Vr is progressively varied with the step size δVr until the Vr reaches to Vr2 (step  212 ), and the SEM image is acquired for each Vr condition. Here, when the image is acquired, auto brightness and contrast control of the signal value are not performed. In the step  213 , the brightness and contrast of each image are analyzed, and in the step  214 , Vr(E Land   1 ) at which the secondary signal yield is 1 is computed by the computer  48 . In the step  215 , Vr computed by the computer  48  is sent to the retarding power supply controller via the controller  6 . Also, the initial value (Vcc1 or Vcc2) of the voltage Vcc set by the user is sent to the charged state control electrode controller  66 . These procedures permit setting of the retarding voltage and voltage applied to the control electrode  65 . Subsequently, in the step  216 , an SEM image is acquired, and brightness signal information acquired by the detector  20  is stored by the image processor  46 . In the step  217 , the voltage Vcc is varied with the increment unit δVcc, the voltage Vcc is reset while maintaining the voltage Vr constant, and an SEM image is acquired. This routine is repeated by the controller  6  until the voltage Vcc reaches its final value Vcc2. After SEM image acquisition is completed at Vcc2, the S curve is constructed in the step  218 . Here, in constructing the S curve, the calculation is performed by computing the average value of signals outside the pattern shown in  FIG. 4A . In the step  219 , the processing that the obtained S curve is compared with the reference data, and then the potential of the specified region is calculated is executed by the computing unit in the computer  48 . Also, in a case that adjustment of the potential of the wafer surface is needed before inspection, the charge/discharge procedure is performed by ultraviolet light or the electron source (step  220 ), an SEM image is again acquired, a new S curve is constructed (steps  216 - 218 ), and the variation of the wafer charge after processing is evaluated quantitatively by comparing with the data prior to charge/discharge (step  219 ). Here, the acquired S curve may also be differentiated and normalized in order to compute the potential of the specified region. 
   In the above description, the setting of Vr, Vcc in the steps  209 ,  210  was performed by the user inputting these values manually with viewing the monitor  50 , while the setting values of Vcc1, Vcc2, δVcc, and Vr1, Vr2, δVr could be stored in a database equipped in the controller  6  in advance, consequently the flow chart of  FIG. 7  is operated and controlled automatically by the controller  6 . As for the operation of the flow chart of  FIG. 7 , the controller  6  does not necessarily have a database, and can still function if it is provided with storage means (i.e., a memory or storage) storing parameters for the control or conditions inputted by the user. 
     FIG. 5A  shows the results of executing the steps in actual practice.  FIG. 5A  shows the results of measuring the S curves (respectively, curves  41 ,  40 ) before and after negative charging processing for the wafer surface of the semiconductor device, the shift amount (AB) of the both curves corresponds to the variation of potential of the wafer surface. Also, the results of differentiation and normalization of the curves  40 ,  41  are the curves  42 ,  43 . The difference of the values Vcc of the positions C, D of the two peaks corresponds to the variation of potential in the measured region. 
   Next, in the step  208 , inspection condition optimization is performed. Here, the contrast of the SEM images obtained at each Vcc in the aforesaid steps  215 - 217  are analyzed, and the Vcc value which gives the highest pattern contrast is taken as the inspection condition. If the irradiation energy of the primary electron beam used for the inspection is different from E Land   1 , SEM images for each Vcc value are newly acquired and contrast-analyzed in the inspection region, the Vcc which gives the highest contrast being taken as the inspection condition. 
   Next, in a step  221 , the beam correction of the step  205  is repeated. When the beam correction is complete, in a step  222 , calibration is performed. The beam is moved to a second correction pattern mounted on the sample holder. The aim of the second correction pattern is to make the signal strength coincide with the signal from the voltage contrast image obtained in the inspection. The correction pattern may be contact holes of sufficiently low resistance (10 3 ω or less), or a pattern in which contact holes of sufficiently high resistance (10 20 ω or more) have been formed. Using the voltage contrast image of this pattern, the signal values of the sufficiently low resistance part and high resistance part are corrected. The sufficiently high resistance part may be an insulating part without a pattern. In view of this result, the beam is moved on the wafer  9 , voltage contrast images of pattern positions on the wafer are acquired, and calibration is performed. 
   In a step  223 , the inspection is started. In a step  224 , SEM images of defects and the like are acquired, and in a step  225 , these SEM images are stored. When the inspection is complete, in a step  226 , the wafer is unloaded, and in a step  227 , the routine is terminated. 
   In the above inspection method, the potential of the wafer can be managed quantitatively for each inspection, the problems of inspection reproducibility and decreased defect detection sensitivity of the prior art can be resolved, and a high reproducibility, high sensitivity inspection can be performed. 
   When the surface potential is measured, an image is acquired each time Vcc is changed, but there are some cases when the effect of charge or contamination under the above conditions cannot be ignored. In this case, to eliminate these effects, ultraviolet light irradiation may be performed. Alternatively, each time the inspection conditions are changed, the position where the image is acquired may be changed. 
   If there is any shading of the image, the flow chart  200  for potential measurement of the specified region may be performed after applying a shading correction. 
   Embodiment 2 
   If there are plural types of patterns in the wafer, the potential of each pattern will be different even if a precharge is performed on the whole wafer prior to the inspection. In this embodiment, a method will be described for determining the inspection conditions in this case. 
   In a die  252  of a wafer  251  of  FIG. 8 , patterns  255 ,  256  were made, respectively. From measurements by the method of the flow chart  200  for potential measurement of a specific region, the electrostatic potentials of the regions  253 ,  254  were −5 V and −10 V, respectively. In this case, (1) the average value of the optimum inspection conditions (e.g., Vcc value) estimated for both regions was used, or (2) the measurement was performed plural times varying the inspection conditions for each pattern, these methods being selected as required. Method (1) has an advantage that the inspection time is short as the whole surface is inspected under the same conditions, even though the inspection conditions deviate slightly from the optimum value so the sensitivity decreased to some extent. On the other hand, Method (2) has an advantage that inspection can be performed with a high sensitivity as the inspection conditions are optimized for the different patterns, however, inspection time becomes long as the inspection should be carried out on two occasions. 
   Embodiment 3 
   In this embodiment, an example will be described where a pattern dimensional measurement was performed using a length measuring SEM. 
     FIG. 9  shows an example of the construction of the length measurement SEM of this embodiment. The apparatus comprises an electron optical system  301 , stage mechanism system  315 , wafer transport system  322 , vacuum discharge system  305 , optical microscope  325 , control system  331 , control unit  332 , and electrostatic controller. 
   The electron optical system  301  comprises an electron source  302 , condenser lens  303 , objective lens  312 , first detector  310 , second detector  307 , deflector  308 , reflecting plate  309 , and wafer height detector  313 . Reflected electrons  311  and secondary electrons  306  emitted by irradiating a wafer  316  with a primary electron beam  304  are detected by the first detector  310  and second detector  307 , respectively. 
   The stage mechanism system  315  comprises an XY stage  318 , holder  317  for mounting a wafer as a sample, and retarding power supply  319  for applying a negative voltage to the holder  317  and wafer  316 . A laser length measurement position detector is attached to the XY stage  318 . 
   The wafer transport system  322  comprises a cassette mounter  323  and wafer loader  324 , the wafer holder  317  moving back and forth between the wafer loader  324  and XY stage  317  with the wafer  316  mounted thereupon. 
   The control system  331  comprises a signal detection system controller  330 , beam deflection correction controller  329 , electron optical system controller  328 , wafer height sensor detection system  313 , and a mechanism and stage controller  326 . The control unit  332  comprises an operating screen and control panel  335 , image processor  336 , and image/measurement data storage unit  347 . 
   The electrostatic charge controller comprises an electrode  314  installed facing the stage, charging control electrode controller  320 , and charging control power supply  321 . 
   Next, the operation of each part of  FIG. 9  will be described referring to the flow chart of  FIG. 10 . 
   First, in a step  501 , the wafer cassette in which the wafer  316  is set at any desired position is placed in the cassette mounter  323  in the wafer transport system  322 . Next, in a step  502 , to specify the wafer  316  to be measured, the cassette shelf number on which the wafer  316  is set, is specified from the operation screen  335 . Also, the measurement condition file name is input from the operation screen and control panel  335 . This measurement condition file is built by combining various parameters for determining the measurement details. When input of the conditions required for measurement is complete, in a step  503 , the automatic measurement sequence is started. 
   In a step  503 , when the measurement is started, the set wafer  316  is first transported inside the length measurement apparatus. In the wafer transport system  322 , even when the diameter of the wafer to be measured is different, or the wafer shape is different from the orientation flat shape or notched shape, the holder  317  on which the wafer  306  is mounted may be selected according to the wafer size and shape. The wafer to be measured is mounted from the cassette onto the holder  317  by the wafer loader  324  which includes an arm and reserve vacuum chamber, held fixed, and transported to the test chamber together with the holder. 
   In a step  504 , the wafer  316  is loaded, and in a step  505 , the electron beam irradiation conditions and focus/no-focus are adjusted based on the input measurement conditions. The electron beam irradiation conditions for each part are set from the electron optical system controller  328 . In a step  506 , precharge (charge/discharge) is performed using ultraviolet light or an electron source. In a step  507 , alignment is performed using plural points on the wafer. The electron beam image at predetermined locations on the wafer  316  is acquired, and focus/no-focus is adjusted by the image. Also, the height of the wafer  316  is simultaneously calculated by the wafer height detector  313 , the correlation between the height information and the electron beam focusing conditions is calculated, and from the wafer height detection results, the focusing conditions are automatically adjusted without having to focus on each occasion in subsequent electron beam image acquisitions. Next, the potential of the specified region is measured according to the flow chart  200 , and precharge (charge/discharge) is repeated until the potential of the measurement region reaches the predetermined value. In a step  509 , the rotation and coordinate values are corrected based on the alignment results, and the wafer is moved to the measurement position based on the various wafer information already read. High-speed, continuous electron beam image acquisition can then be performed. 
   In a step  510 , after the wafer is moved to the measurement position, in a step  511  it is irradiated by the electron beam, and in a step  512 , image data acquisition is performed. In the step  512 , the acquired high magnification image is saved, if required, by the image/data storage unit  337 . If required, plural types of image from plural detectors can be saved simultaneously depending on the setting. For example, the image from secondary electrons detected by the second detector  307  and the image from reflected electrons detected by the first detector  310 , may be saved simultaneously. 
   In the step  512 , when the image data is saved, pattern dimensional data is extracted from the image information by the image processor  336 , and this result is saved automatically (step  514 ). If required, this result is displayed on the operation screen  335 . When the aforesaid sequence of operations has been completed for all measurement positions specified for one wafer, in the step  514 , the wafer measurement result file (classification results file) is saved automatically, and the measurement result file is output to a specified location. Subsequently, in a step  515 , the wafer is unloaded, and in a step  516 , measurement is terminated. 
   By using this method, pattern dimensions can be always be measured in a fixed charge state, and fine pattern dimensions can be measured at high speed with high precision. 
   In this embodiment, if there is any shading in the image, measurements may be performed after performing a shading correction. 
   When the surface potential is measured, the image is acquired each time the irradiation conditions are changed, but it may occur that the charge under previous conditions and the effect of contamination cannot be ignored. In this case, to eliminate these effects, ultraviolet light irradiation may be performed. Alternatively, the image acquisition position can be changed each time the irradiation conditions are changed. 
   Embodiment 4 
   The inspecting and measurement was accelerated by converting the inspection/measurement conditions to a database using data comprising potential measurements at each position on the wafer surface as shown in Embodiments 1-3. 
     FIG. 11  shows the surface potential distribution of a wafer  551  measured by the flow chart  200 . This distribution  552  may be obtained by measuring the surface potential by the flow chart  200  at several positions on the wafer surface, and predicting the potential distribution over the whole wafer surface from the obtained results. The potential measurement is carried out prior to performing inspecting and measurement, and the results are converted to a database, and stored in the data storage unit  337 . 
   Next, inspecting and measurement of the wafer is performed using this database. An SEM image is acquired by reading the potential at each inspecting and measurement position into the correction control circuit  43  or control system  331  from the distribution  552 , and adjusting the excitation current so that the secondary electron beam is focused at the inspecting and measurement position. Defect detection and dimensional measurement are performed from the obtained SEM image. 
   By using this method, inspecting and measurement can be performed so that the primary electron beam is always focused on the wafer surface, and high sensitivity defect detection, as well as high speed, high precision, fine pattern dimensional measurement, can thus be achieved. 
   The aforesaid embodiment can be applied to any inspecting and measurement device which uses a convergent charged particle beam such as an inspection SEM, review SEM and CD-SEM. 
   Embodiment 5 
   The inspecting and measurement was accelerated by converting the inspection/measurement conditions to a database using data comprising potential measurements at each position on the wafer surface as shown in Embodiments 1-3. 
     FIG. 11  shows the surface potential distribution of the wafer  551  measured by the flow chart  200 . This distribution  552  may be obtained by measuring the surface potential by the flow chart  200  at several positions on the wafer surface, and predicting potential distribution over the whole wafer surface from the obtained results. The potential measurement is carried out prior to performing inspecting and measurement, and the results are converted to a database, and stored in the data storage unit  337 . 
   Next, inspecting and measurement of the wafer is performed using this database. If the potential difference at each point in the wafer surface is relatively small, an SEM image is acquired by reading the potential at each inspecting and measurement position into the correction control circuit  43  or control system  331  from the distribution  552 , and adjusting the retarding voltage 36 or 319 so that the primary electron beam is focused at the inspecting and measurement position. Defect detection and dimensional measurement are performed from the obtained SEM image. 
   By using the aforesaid method, inspecting and measurement can be performed with the primary electron beam always focused on the wafer surface simply by adjusting the retarding voltage. Compared to the case where the excitation current of a magnetic field objective lens is adjusted to focus the primary electron beam, the response speed is relatively fast and feedback to the focus can be performed in real-time, so inspecting and measurement can be performed more rapidly. 
   The aforesaid embodiment can also be applied to any inspecting and measurement device which uses a convergent charged particle beam such as an inspection SEM, review SEM and CD-SEM. 
   As described above, defect detection can always be performed at the required potential in a wafer which has been partially completed with a semiconductor device having a circuit pattern, therefore defect detection sensitivity and reproducibility can be greatly enhanced. Further, in a measuring device such as a length measurement SEM, by measuring the potential distribution on the wafer surface by global charge or the like, and feeding back this data to the control system of the optical system, automatic measurement can be performed more rapidly with higher precision, and productivity in semiconductor manufactured goods can be monitored with higher sensitivity and higher precision.