Inspection method and inspection device by charged particle beam

The present invention relates to a substrate manufacturing technique for a semiconductor device, a liquid crystal, or the like having a fine circuit pattern, and more particularly to a pattern inspection technique for a semiconductor device, a photomask, or the like.

The semiconductor device is manufactured by repeating the steps of transferring a pattern formed by a photomask on a wafer by a lithography process and an etching process. In order to inspect such a pattern, a defective portion is identified by acquiring a SEM (Scanning electron microscope) image of the pattern. With the recent miniaturization of patterns, the difficulty of processing contact holes has increased, and the number of conduction defects generated inside contact holes has increased in particular, and highly sensitive defect detection technology is required.

The wafer cross-sectional view 400 shown in FIG. 4 illustrates these defects. Si substrate 404 with SiO₂A film 405 is formed, a contact hole is processed, and metal is embedded. Here, the normal part 401 and the continuity defect 402. In order to detect this defect, it is necessary to charge the wafer and acquire a potential contrast image in which the charging potential difference caused by the difference in electrical resistance between the normal part and the defect is expressed as the difference in the number of detected secondary electrons. There is.

The method of acquiring the potential contrast image and the principle of defect detection will be described. Some potential contrast images have the sample surface (1) positively charged and (2) negatively charged. The charging polarity suitable for inspection depends on the structure of the inspection wafer. The charging polarity can be changed depending on the inspection conditions. For example, there is a method of changing the incident energy of the electron beam (see, for example, Non-Patent Document 1).

Here, as another method, a case where the potential of the charge control electrode 407 installed facing the wafer is changed will be described. For both positive and negative charges, the incident energy of the electron beam 410 used on the wafer is controlled so that the emission efficiency of secondary electrons generated from the wafer is 1 or more (for example, 500 eV).

(1) In the case of positive charging: The potential of the charge control electrode 407 is set so that the electric field generated in the vicinity of the wafer accelerates the secondary electrons. That is, as shown in FIG. 5 (enlarged view of the beam irradiation region), a positive potential potential 501 is formed on the wafer. When the electron beam is applied to the normal portion 401 and the conduction defect portion 402, the generated secondary electrons 502 are accelerated by the potential 501, and the conduction defect portion 402 is positively charged. The normal part 401 is not charged because the charge is supplied from the substrate 404. Due to the positive charge of the conduction defect portion 402, the low energy component 503 of the secondary electrons is pulled back to the wafer, while the normal portion is not charged, so that all the secondary electrons are emitted by 504. As a result, a potential contrast of 505 is obtained, and dark conduction defects in the image can be detected (see, for example, Non-Patent Document 2 and Patent Document 1).

(2) In the case of negative charging: The potential of the charge control electrode 407 is set so that the electric field generated in the vicinity of the wafer decelerates the secondary electrons and pulls them back to the wafer. That is, as shown in FIG. 6 (enlarged view of the beam irradiation region), a negative potential potential 601 is formed on the wafer. When the normal portion 401 and the conduction defect portion 402 are irradiated with the electron beam, the generated secondary electrons 602 are pulled back to the wafer by the potential 601 and the conduction defect portion 402 is negatively charged. Due to the negative charge of the conduction defect portion 402, the secondary electrons 603 are accelerated and emitted without being pulled back by the negative potential potential 601. On the other hand, since the normal portion is not charged, all the secondary electrons 604 are pulled back to the wafer. As a result, the potential contrast image 605 is obtained, and it becomes possible to detect bright conduction defects in the image (see, for example, Patent Document 2).

<nplcit num="1"><text>L. Reimer: Scanning Electron Microscopy, Springer-Verlag, Berlin Heidelberg, 1998.</text></nplcit>

<nplcit num="2"><text>H. Nishiyama, et al .: SPIE 4344, p.12 (2001)</text></nplcit><patcit num="1"><text>Japanese Unexamined Patent Publication No. 2001-313322</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 11-121561</text></patcit>

<p> The charging potential described above can be changed by the potential of the charging control electrode 407. If the potential of the charge control electrode 407 is increased with the positive charge potential contrast, secondary electrons are likely to be emitted, so that the charge potential increases. In the case of negative charging, if the potential of the charge control electrode 407 is lowered, many secondary electrons are pulled back to the wafer, so that the charge potential is lowered. However, if the charging potential of the wafer is not optimally set at this time, the inspection sensitivity is lowered. The cause of the decrease in sensitivity will be described separately when the amount of charge (proportional to the absolute value of the charge potential) is large and when it is small.</p><p> (1) When the amount of charge is large: A charge leak occurs in the conduction defect, and the charge cannot be sufficiently charged, which may cause a false recognition as a normal part. Further, when the amount of charge is large, the orbits of the secondary electrons are greatly bent, which affects the secondary electron detection efficiency. As a result, distortion and brightness spots occur in the acquired image, and the defect detection accuracy is lowered.</p><p> (2) When the amount of charge is small: Since the difference in charge between the normal part and the defective part is small, the contrast is small and it becomes difficult to detect the defect.</p><p> As described above, for high-sensitivity inspection, it is necessary to provide sufficient contrast while suppressing charging. Conventionally, the conditions for that purpose have been set manually based on the experience of the operator. Therefore, it takes time to set, the reproducibility of the inspection is poor, and there is a problem in the inspection accuracy.</p><p> Therefore, the present invention establishes a method for setting conditions for optimizing the charged state of the object to be inspected without relying on the experience of the operator, and can acquire a potential contrast image having higher defect detection efficiency than before. It is an object of the present invention to provide an inspection technique using a possible charged particle beam.</p>

<p> In order to achieve the above object, the present inventors have determined the potential contrast image from the viewpoint of "finding a condition that minimizes the amount of charge while maintaining the contrast required for the inspection". We obtained a histogram and found that the shape was used.</p><p> Hereinafter, the basic configuration of the present invention will be described.</p><p> FIG. 7 shows the potential contrast image 703 and its histogram 704. Histogram 704 has two peaks 702 and 701 due to the pattern part (contact hole, wiring, etc.) and the other insulating part.</p><p> First, the image histogram is fitted by the sum of two Gaussian functions, (Equation 1) (i = 1, 2).</p><p><maths num="1"><img file="JP2005292076A_D0001.tif" /></maths> (Equation 1) However, x is the signal value and p (x) is the frequency of the signal value x.</p><p> At this time, the average of each Gaussian function is μ₁, Μ₂, Standard deviation σ₁, Σ₂And. Where | μ₁-μ₂| / (σ₁+ σ₂) Dependence on the inspection conditions (for example, the potential Vcc of the charge control electrode 407), and the condition of (Equation 2) is the optimum condition.</p><p><maths num="2"><img file="JP2005292076A_D0002.tif" /></maths> (Equation 2) Here, ε₁, Ε₂Can be changed by the judgment at that time, but the typical value is ε₁= 1, ε₂= 3.</p><p> Further, as the function used for fitting the histogram, a function having an isolated peak such as the Lorentz function (Equation 3) may be used in addition to the Gaussian function shown here.</p><p><maths num="3"><img file="JP2005292076A_D0003.tif" /></maths> (Equation 3) Since the evaluation of the histogram is important in this method, the signal value is corrected (auto brightness and contrast control) when the image is acquired by changing the electron irradiation conditions. must not.</p><p> In addition, although the case where there are two peaks in the histogram is shown here, when there are three or more peaks, it is necessary to do the same for adjacent peaks.</p><p> In the optimization of the inspection conditions, the case where the potential Vcc of the charge control electrode 407 is optimized will be described here as an example.</p><p> FIG. 8 shows negative charging potential contrast images 801 to 803 obtained by changing the potential of the charging control electrode 407 to -8440V, -8460V, and -8510V as inspection conditions, and histograms 804 to 806 thereof. The lower the potential of the charge control electrode 407, the lower the negative charge potential. When the amount of charge is small, the two peaks are not separated (histogram 804), so that the pattern portion is not clear (potential contrast image 801), which makes inspection difficult. On the other hand, when the amount of charge is large, the two peaks are separated (histogram 805), the pattern portion becomes clear (potential contrast image 802), and inspection becomes possible. However, if the amount of charge becomes too large (histogram 806, potential contrast image 803), the sensitivity will decrease. Therefore, the optimum conditions are determined by the following method. (1) The potential Vcc of the charge control electrode 407 installed facing the wafer is changed, the potential contrast is acquired, and the histogram is obtained. (2) Two peaks occur in the histogram due to the insulating part and the pattern part. (3) Equations (2) (ε) as conditions for separating these peaks.₁= 1, ε₂Applying = 3), Vcc = -8460V is the optimum condition as shown in Fig. 9. (4) As a result of actual inspection, as shown in Fig. 10, the number of defects detected is the largest under the optimum conditions (Vcc = -8460V), and under other conditions, defects are overlooked, so the number of defects detected. Is reduced.</p><p> As described above, the optimum inspection conditions can be determined. However, as the inspection conditions are changed, the residual charge may affect the potential contrast image. In that case, the charge may be alleviated by irradiating ultraviolet rays as needed. In addition, the image acquisition location may be changed each time the image is acquired.</p><p> The target types of defects are contact holes and line pattern conduction defects, which account for most of the defects.</p>

<p> According to the present invention, it is possible to establish a method for setting conditions for optimizing the charged state of an object to be inspected without relying on the experience of an operator, and to obtain a potential contrast image having higher defect detection efficiency than before. It is possible to realize an inspection technique using a possible charged particle beam.</p>

Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

(Example 1) FIG. 1 shows the configuration of the inspection device according to the first embodiment. The inspection device (inspection SEM) is provided with an inspection chamber 2 in which the chamber is evacuated and a spare chamber (not shown in this embodiment) for transporting the wafer 9 as a sample into the inspection chamber 2. This spare room is configured so that it can be evacuated independently of the inspection room 2. The inspection device is composed of a control unit 6 and an image processing unit 5 in addition to the inspection room 2 and the spare room. The inside of the examination room 2 is roughly divided into an electron optical system 3, a charge control unit, a detection unit 7, a sample room 8, and an optical microscope unit 4.

The electron optics system 3 is composed of an electron source 10, an electron beam extraction electrode 11, a condenser lens 12, a blanking deflector 13, a scanning deflector 15, an aperture 14, an objective lens 16, a reflector 17, and an E × B deflector 18. It is configured. Of the detection units 7, the detector 20 is arranged above the objective lens 16 in the examination room 2. The output signal of the detector 20 is amplified by the preamplifier 21 installed outside the examination room 2, and becomes digital data by the AD converter 22.

The charge control unit includes a charge control electrode 65 installed facing the stage, a charge control electrode control unit 66, and a charge control power supply 67.

The detector 7 includes a detector 20 in the vacuum-exhausted inspection room 2, a preamplifier 21 outside the inspection room 2, an AD converter 22, an optical converter 23, an optical fiber 24, an electric converter 25, and a high-voltage power supply 26. It consists of a preamplifier drive power supply 27, an AD converter drive power supply 28, and a reverse bias power supply 29. Of the detection units 7, the detector 20 is arranged above the objective lens 16 in the examination room 2. The detector 20, the preamplifier 21, the AD converter 22, the optical converter 23, the preamplifier drive power supply 27, and the AD converter drive power supply 28 are floated to a positive potential by the high voltage power supply 26.

The sample chamber 8 is composed of a sample table 30, an X stage 31, a Y stage 32, a rotating stage 33, a length measuring instrument 34 for a position monitor, and an optical height measuring instrument 35.

The optical microscope unit 4 is installed in the vicinity of the electron optical system 3 in the examination room 2 and at a position separated from each other to the extent that it does not affect each other, and the distance between the electron optical system 3 and the optical microscope unit 4 Is known. Then, the X stage 31 or the Y stage 32 reciprocates a known distance between the electron optical system 3 and the optical microscope unit 4. The optical microscope unit 4 includes a light source 40, an optical lens 41, and a CCD camera 42.

The operation commands and operating conditions of each unit of the device are input / output from the control unit 6. In the control unit 6, conditions such as the acceleration voltage when the electron beam is generated, the electron beam deflection width, the deflection speed, the signal capture timing of the detection device, the sample table moving speed, and the like are arbitrarily or selected according to the purpose. It is entered so that it can be done. The control unit 6 monitors the position and height deviation from the signals of the position monitor length measuring device 34 and the optical height measuring device 35 by using the correction control circuit 43, and generates a correction signal from the result. A correction signal is sent to the lens power supply 45 and the scanning deflector 44 so that the electron beam is always emitted to the correct position.

In order to acquire an image of the wafer 9, the wafer 9 is irradiated with a finely focused electron beam 19 to generate secondary electrons and backscattered electrons 51, which are scanned by the electron beam 19 and of stages 31 and 32. An image of the surface of the wafer 9 is obtained by detecting in synchronization with the movement.

A diffusion-supplied thermal field emission electron source is used as the electron source 10. By using this electron source 10, it is possible to secure a stable electron beam current as compared with the conventional, for example, tungsten (W) filament electron source and cold field emission type electron source, so that the potential with less brightness fluctuation can be secured. A contrast image is obtained. The electron beam 19 is extracted from the electron source 10 by applying a voltage between the electron source 10 and the extraction electrode 11. The acceleration of the electron beam 19 is achieved by applying a high voltage negative potential to the electron source 10.

As a result, the electron beam 19 travels in the direction of the sample table 30 with energy corresponding to its potential, is converged by the condenser lens 12, and is further narrowed down by the objective lens 16 to form the X and Y stages 31 on the sample table 30. The wafer 9 mounted on the 32 is irradiated. A scanning signal generator 44 that generates a scanning signal and a blanking signal is connected to the blanking deflector 13, and a lens power supply 45 is connected to each of the condenser lens 12 and the objective lens 16. A negative voltage (retarding voltage) can be applied to the wafer 9 by the retarding power supply 36. By adjusting the voltage of the retarding power supply 36, the primary electron beam can be decelerated, and the electron beam irradiation energy to the wafer 9 can be adjusted to an optimum value without changing the potential of the electron source 10.

The secondary electrons and backscattered electrons 51 generated by irradiating the wafer 9 with the electron beam 19 are accelerated by the negative voltage applied to the wafer 9. An E × B deflector 18 is arranged above the wafer 9, and the accelerated secondary electrons and backscattered electrons 51 are deflected in a predetermined direction. The amount of deflection can be adjusted by the voltage applied to the E × B deflector 18 and the strength of the magnetic field. Further, this electromagnetic field can be changed in conjunction with the negative voltage applied to the sample. The secondary electrons and backscattered electrons 51 deflected by the E × B deflector 18 collide with the reflector 17 under predetermined conditions. When the accelerated secondary electrons and backscattered electrons 51 collide with the backscattering plate 17, second secondary electrons and backscattered electrons 52 are generated from the backscattering plate 17.

The second secondary electrons and backscattered electrons 52 generated by colliding with the reflector 17 are guided to the detector 20 by this suction electric field. In the detector 20, the secondary electrons and backscattered electrons 51 generated while the electron beam 19 is irradiating the wafer 9 are subsequently accelerated and collide with the reflector 17, and the second secondary electrons and backscattered electrons generated are generated. The scattered electrons 52 are configured to be detected in conjunction 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 examination room 2, and becomes digital data by the AD converter 22. The AD converter 22 is configured to convert the analog signal detected by the detector 20 into a digital signal immediately after being amplified by the preamplifier 21 and transmit it to the image processing unit 5. Since the detected analog signal is digitized immediately after detection and then transmitted, a high-speed signal with a high SN ratio can be obtained. As the detector 20 here, for example, a semiconductor detector may be used.

Wafers 9 are mounted on the X, Y stages 31 and 32. A method of stationary the X, Y stages 31 and 32 to scan the electron beam 19 in two dimensions when the inspection is executed, and an X and Y when the inspection is executed One of the methods of scanning the electron beam 19 in a straight line in the X direction can be selected so that the stages 31 and 32 are continuously moved in the Y direction at a constant speed. When inspecting a specific relatively small area, the former method of stationary inspection is effective, and when inspecting a relatively large area, the method of continuously moving the stage at a constant speed is effective. Is. When it is necessary to blank the electron beam 19, the electron beam 19 is deflected by the blanking deflector 13 and can be controlled so that the electron beam does not pass through the diaphragm 14.

As the length measuring device 34 for the position monitor, a length measuring meter by laser interference was used in this embodiment. The positions of the X stage 31 and the Y stage 32 can be monitored in real time and transferred to the control unit 6. Further, data such as the rotation speeds of the motors of the X stage 31, Y stage 32, and rotation stage 33 are also configured to be transferred from each driver to the control unit 6, and the control unit 6 is configured to transfer these data. The area and position where the electron beam 19 is irradiated can be accurately grasped based on the above, and the position deviation of the irradiation position of the electron beam 19 is corrected by the correction control circuit 43 in real time as needed. It has become. In addition, the area irradiated with the electron beam can be stored for each wafer.

The optical height measuring instrument 35 uses an optical measuring instrument that is a measuring method other than the electron beam, for example, a laser interference measuring instrument or a reflected light measuring instrument that measures a change in the position of the reflected light. It is configured to measure the height of the wafer 9 mounted on the Y stage 31 and 32 in real time. In this embodiment, a method is used in which the wafer 9 is irradiated with white light emitted from the light source 37, the position of the reflected light is detected by a position detection monitor, and the amount of change in height is calculated from the change in position. Based on the measurement data of this optical height measuring instrument 35, the focal length of the objective lens 16 for narrowing the electron beam 19 is dynamically corrected, and the electron beam 19 always focused on the non-inspection region can be irradiated. It has become like. It is also possible to measure the warpage and height distortion of the wafer 9 in advance before irradiating the electron beam, and set the correction conditions for each inspection area of the objective lens 16 based on the data. ..

The image processing unit 5 includes an image storage unit 46, a computer 48, and a monitor 50. The image signal of the wafer 9 detected by the detector 20 is amplified by the preamplifier 21, digitized by the AD converter 22, converted into an optical signal by the optical converter 23, transmitted by the optical fiber 24, and electrically operated. After being converted into an electric signal again by the converter 25, it is stored in the image storage unit 46.

The electron beam irradiation conditions in image formation and various detection conditions of the detection system are set in advance when the inspection conditions are set, and are filed and registered in the database.

Next, the procedure of performing the inspection using the inspection apparatus shown in FIG. 1 will be described using the flow shown in FIG. 2A.

First, in step 201, a wafer cassette in which the wafer is placed on an arbitrary shelf is placed. In order to specify the wafer to be inspected from the monitor 50, the shelf number in the cassette in which the wafer is set is specified. Then, in step 202, various inspection conditions are input from the monitor 50. The inspection condition input contents include the electron beam current, the electron beam irradiation energy, the field of view (FOV) of one screen, the potential of the retarding power supply 36, the potential of the charge control electrode 65, and the like. Although it is possible to input individual parameters, usually, a combination of the above-mentioned various inspection parameters is stored in a database as an inspection condition file, and it is sufficient to select and input an inspection condition file according to the range.

When the automatic inspection is started in step 203, first, the wafer 9 set in step 204 is loaded from the sample exchange chamber 62 into the inspection apparatus. In the wafer transfer system, even if the diameter of the wafer 9 is different or the shape of the wafer is different such as the orientation flat type or the notch type, the holder for mounting the wafer 9 is changed to the size and shape of the wafer. It can be handled by exchanging them together. The wafer 9 is placed on a holder by a wafer loader including an arm, a preliminary vacuum chamber, etc. from a wafer cassette, held and fixed, and evacuated in the wafer loader together with the holder, and is already evacuated in the vacuum exhaust system. Transported to 2.

After the wafer is loaded, in step 205, the control unit 6 sets the electron beam irradiation conditions for each unit based on the input inspection conditions. Then, the stage 32 moves so that the first beam calibration pattern on the wafer holder is under the electron optics system, acquires a potential contrast image of the beam calibration pattern, and focuses / non-points from the potential contrast image. match. Then, it moves to a predetermined position on the wafer 9 to be inspected, acquires a potential contrast image of the wafer 9, and adjusts the contrast and the like. Here, if it becomes necessary to change the electron beam irradiation conditions and the like, it is possible to perform beam calibration again. In addition, the correlation between the height information and the focusing condition of the electron beam is obtained by the optical height measuring device 35, and the result of the wafer height detection is used without performing focusing every time the potential contrast image is acquired thereafter. It is also possible to automatically adjust to the focal condition.

In step 206, the set wafer 9 is moved by X, Y stages 31, 32 to observe the first coordinates for alignment in the light microscope unit 4. An optical microscope image of the alignment pattern formed on the wafer 9 is observed by the monitor 50, and the position correction value of the first coordinate is calculated by comparing with the same pattern image stored in advance. Next, move from the first coordinate by a certain distance to the second coordinate where a circuit pattern equivalent to the first coordinate exists, and the optical microscope image is observed in the same manner and compared with the circuit pattern image stored for alignment. Then, the position correction value of the second coordinate and the amount of rotation deviation with respect to the first coordinate are calculated.

As described above, when the predetermined correction work and the preparatory work such as the inspection area setting by the optical microscope unit 4 are completed, the wafer 9 is moved under the electro-optical system 3 by the movement of the X, Y stages 31 and 32. To. When the wafer 9 is arranged under the electron optics system 3, the same work as the alignment work performed by the optical microscope unit 4 is performed by the potential contrast image. The potential contrast image at this time is acquired by the following method. Based on the coordinate values memorized and corrected in the alignment by the optical microscope image, the electron beam 19 is two-dimensionally scanned in the XY direction by the scanning deflector 15 in the same circuit pattern as that observed in the optical microscope unit 4. Is irradiated. By two-dimensional scanning of this electron beam, secondary electrons and backscattered electrons 51 generated from the observed portion are detected by the configuration and action of each part for detecting emitted electrons, so that a potential contrast image is acquired. To. Since simple inspection position confirmation, alignment, and position adjustment have already been performed using an optical microscope image, and rotation correction has also been performed in advance, the resolution is higher than that of an optical image, and alignment and position correction are performed with high magnification and high accuracy. , Rotation correction can be performed. When the wafer 9 is irradiated with the electron beam 19, the portion is charged. In order to avoid the influence of the charge during the inspection, the circuit pattern that irradiates the electron beam 19 in the pre-inspection preparatory work such as the position rotation correction or the inspection area setting is selected in advance from the circuit pattern existing outside the inspection area. Alternatively, an equivalent circuit pattern on a chip other than the chip to be inspected can be automatically selected from the control unit 6. The alignment result performed in this way is transferred to each control unit. At the time of inspection, rotation and position coordinates are corrected by each control unit.

At step 207, the wafer is moved to a designated area. After that, as shown in FIG. 2B, the optimum inspection conditions are determined in the inspection condition optimization flow 200 (steps 208 to 220). Here, one of the inspection conditions, the potential Vcc of the charge control electrode 65, will be described as an example, but the same applies to other conditions such as electron beam energy and retarding potential. First, in step 208, the minimum value V1 of Vcc, the maximum value V2, and the step width ΔV to be changed are input. In step 210, the initial condition Vcc = V1 of Vcc is input, and in step 211, the image is acquired. Signal value correction (auto brightness and contrast) when acquiring images control) is not performed. Calculate the histogram of the image in step 213, and perform Gaussian fitting in (Equation 1). In step 214, the peak separation determination based on (Equation 2) is performed. If peak separation is not possible, change the Vcc value in step 215. If this Vcc value is within the range input in step 208 in step 216, the image is acquired again in step 211, and the above steps (211 to 216) are repeated. If the Vcc value is out of the range entered in step 208 in step 216, the range needs to be entered again in step 208. In this way, the inspection conditions are determined in step 220.

The result of actually executing these steps is shown. First, in step 208, V1 = -8530V, V2 = -8420V, and ΔV = 10V. The obtained images 801 to 803 and the histogram 804 are shown in FIG. These histograms are fitted by (Equation 1), and σ₁, Σ₂, Μ₁, Μ₂Is calculated and shown in Fig. 9. | Μ₁-μ₂| / (σ₁+ σ₂) Vcc dependency was obtained. From this result, the peak separation condition (ε) in (Equation 2)₁= 1, ε₂= 3) We were able to find Vcc = -8460V that satisfies (the area shown by the diagonal line in the figure).

Next, in step 221 the beam calibration is performed again in the same manner as in step 205. When the beam calibration is completed, the calibration is performed in step 222. Move to the second calibration pattern placed on the sample holder. The second calibration pattern matches the signal strength with the signal of the potential contrast image obtained by the inspection. The pattern is sufficiently low resistance (10)³Contact holes with Ω or less and sufficiently high resistance (10)²⁰It is a pattern in which contact holes (Ω or more) are machined. The potential contrast image of the pattern is used to calibrate the signal values of the sufficiently low resistance portion and the high resistance portion. An insulating portion without a pattern may be used as a sufficiently high resistance portion. Based on this result, the wafer is moved onto the wafer 9, a potential contrast image of a pattern portion on the wafer is acquired, and calibration is performed.

At step 223, the inspection is started. The defect image is acquired in step 224, and the image of the defect detected in step 225 is saved. When the inspection is complete, the wafer is unloaded in step 226 and finished in step 227.

With the above inspection method, it has become possible to solve the problems of inspection reproducibility and deterioration of defect detection sensitivity, which have been problems in the past, and it has become possible to perform highly reproducible and highly sensitive inspection.

Here, an example in which the potential of the charge control electrode 65 is automatically set among the inspection conditions has been described, but other conditions such as electron beam current, electron beam energy, retarding potential, and the like can also be set in the same manner.

In this embodiment, a Gaussian function is used to fit the histogram, but a function having an isolated peak such as a Lorentz function other than that function may be used.

When optimizing the inspection conditions, an image is acquired every time the inspection conditions are changed, but the influence of charging and contamination under the previous conditions may not be negligible. In that case, ultraviolet light irradiation may be performed in order to eliminate these effects. Alternatively, the image acquisition location may be changed each time the inspection conditions are changed.

If the image has shading, it is advisable to perform the inspection condition optimum flow 200 after performing the shading correction.

(Example 2) In this example, an example in which the electron beam energy E0 is optimized by the same method as in Example 1 will be described. Considering the damage of the wafer, the maximum value of E0 was set to 1.5 keV. In the inspection condition optimization flow 200 (Fig. 2B), E0 was set instead of Vcc, and V1, V2, and ΔV were set to 0 keV, 1.5 keV, and 0.25 keV, respectively. As a result, as shown in Fig. 11 | μ₁-μ₂| / (σ₁+ σ₂) E0 dependency was obtained. From this result, the peak separation condition (ε) in (Equation 2)₁= 1, ε₂We were able to find E0 = 1.0keV that satisfies = 3).

(Example 3) In this example, an example in which the electron beam current IP is optimized by the same method as in Example 1 will be described. In the inspection condition optimization flow 200 (Fig. 2B), IP was set to 0nA, 300nA, and 50nA for V1, V2, and ΔV, respectively, instead of Vcc. As a result, as shown in Fig. 12 | μ₁-μ₂| / (σ₁+ σ₂) IP dependency was obtained. From this result, the peak separation condition (ε) in (Equation 2)₁= 1, ε₂We were able to find IP = 100, 150, 200nA that satisfy = 3).

(Example 4) When the pattern density is low as shown in 1101 of FIG. 13, even if the contrast is good in appearance, when a histogram is drawn, as shown in FIG. 14, the peak caused by the pattern portion is SiO.₂It turned out that it was buried in the signal of the part. Therefore, the optimum conditions could not be determined by the method described in Example 1. Therefore, as shown in the upper right figure of FIG. 13, the area 1102 having the same area as the pattern set as the area is set between the extraction of the pattern area 1102 and the closest pattern. As shown in the lower right figure of FIG. 13, the region 1102 was extracted as the region 1105 within the half width of the peak in the signal profile 1104. As a result of drawing a histogram again after performing such image extraction (signal extraction processing), FIG. 15 was obtained. It was confirmed that the peak was separated into two. Further, the shading of the image may be removed before the signal extraction process.

Figure 3 shows the inspection condition optimum flow 300 that performs the above. In step 208, enter the minimum value V1 and maximum value V2 of Vcc, and the step size ΔV to be changed. In step 209, the value 0 is set to the numerical value N used for the subsequent shading removal and the execution determination of the signal extraction process 219. In step 210, the initial condition V1 of Vcc is input, and in step 211, the image is acquired. Signal value correction (auto brightness and contrast) when acquiring images control) is not performed. The N value determination condition is performed in step 212, and when N = 0, the histogram calculation of the image is performed in step 213, and the Gaussian fitting is performed in (Equation 1). In step 214, the peak separation determination based on (Equation 2) is performed. If peak separation is not possible, change the Vcc value in step 215. If this Vcc value is within the range input in step 208 in step 216, the image is acquired again in step 211, and the above steps (211 to 216) are repeated. If the Vcc value is out of the range input in step 208 in step 216, 1 is added to N in step 217, N = 1 is determined in step 218, and the process proceeds to steps 210, 211, and 212. Since N = 0 is not set in step 212, the process proceeds to step 219. In step 219, shading processing and signal extraction processing are performed. Using the result of the signal extraction process, step 213 is performed, and the peak separation condition determination in step 214 is performed. If the peaks have not been separated, the process proceeds to step 215. If peak separation is possible, the inspection conditions are determined in step 220. As described above, in the inspection methods shown in FIGS. 2A and 2B, the inspection conditions could be optimized by applying the inspection condition optimization flow 300 instead of the inspection condition optimization flow 200.

(Example 5) In this example, an example in which defect classification is performed using a review SEM will be described.

Figure 16 shows an example of the configuration of the review SEM. This device is composed of an electron optical system 321, a stage mechanism system 322, a wafer transfer system 323, a vacuum exhaust system 324, an optical microscope 325, a control system 326, an operation unit 327, and a charge control unit.

The electron optics system 321 is composed of an electron source 328, a condenser lens 329, an objective lens 330, a first detector 331, a second detector 332, a deflector 335, a reflector 336, and a wafer height detector 337. There is. The backscattered electrons 353 and the secondary electrons 354 generated by irradiating the wafer 351 with the electron beam 352 are detected by the first detector 331 and the second detector 332, respectively.

The stage mechanism system 322 includes an XY stage 338, a holder 339 for mounting a wafer as a sample, and a retarding power supply 340 for applying a negative voltage to the holder 339 and the wafer 351. A position detector by laser length measurement is attached to the XY stage 338.

The wafer transfer system 323 is composed of a cassette mounting unit 341 and a wafer loader 342, and the holder 339 moves back and forth between the wafer loader 342 and the XY stage 338 with the wafer 351 mounted.

The control system 326 is composed of a signal detection system control unit 343, a beam deflection correction control unit 344, an electro-optical system control unit 345, a wafer height sensor detection system 346, a mechanism and a stage control unit 347. The operation unit 327 is composed of an operation screen, an operation unit 348, an image processing unit 349, and an image / inspection data storage unit 350.

The charge control unit includes a charge control electrode 364 installed facing the stage, a charge control electrode control unit 365, and a charge control power supply 366.

Next, the operation of each part of FIG. 16 will be described with reference to the flow shown in FIG. First, in step 1501, the wafer cassette on which the wafer 351 is installed on an arbitrary shelf is placed on the cassette mounting portion 341 in the wafer transfer system 323. Next, in step 1502, from the operation screen 348, in order to specify the wafer 351 should review, cassette the wafer 351 is set to specify the door in the shelf number. In addition, in the review, the inspection is carried out by another inspection device, and the inspection result file is displayed from the operation screen and the operation unit 348 in order to perform the observation by the electron beam image based on the inspection result information including the position information such as defects. Select. In the selection, it is possible to read the inspection result file by communication via a network or the like, or to read the inspection result file from a recording medium. In either case, by specifying the inspection result file name, various data of the inspection result can be read into the data input unit 356 and converted by the data conversion unit 357 into the data format and coordinate system used in the review SEM. is there. Furthermore, the review condition file name is input from the operation screen and the operation unit 348. This review condition file is configured by combining various parameters for determining the content of the review. Complete the entry of the conditions required to perform the review and start the automated review sequence in step 1503.

When the review is started in step 1503, the set wafer 351 is first conveyed into the review device. In the wafer transfer system 323, the holder 339 on which the wafer 351 is placed is set to the size and shape of the wafer regardless of whether the diameter of the wafer to be inspected is different or the shape of the wafer is different such as the orientation flat type or the notch type. It can be handled by exchanging them together. The wafer to be inspected is placed on the holder 339 by a wafer loader 342 including an arm, a preliminary vacuum chamber, etc. from the cassette, held and fixed, and transported to the inspection chamber together with the holder.

In step 1504, when the wafer 351 is loaded, in step 1505, electron beam irradiation conditions are set in each part by the electron optics system control unit 345 based on the input review conditions. Then, an electron beam image of a predetermined position of the wafer 351 is acquired, and the focus / non-point is adjusted from the image. At the same time, the height of the wafer 351 is obtained from the wafer height detector 337, the correlation between the height information and the focusing condition of the electron beam is obtained, and the wafer is not focused every time the electron beam image is acquired thereafter. The height detection result automatically adjusts to the focusing condition. This has made it possible to acquire high-speed continuous electron beam images.

After the electron beam irradiation conditions and the focus / non-point adjustment are completed, alignment is performed by the two points on the wafer in step 1506.

After that, in step 1507, the pattern is moved to the pattern in the wafer, and the same inspection condition optimization flow 200 (FIG. 2B) or 300 (FIG. 3) as in Examples 1 and 4 is performed. Then perform beam calibration 1508 again.

In step 1509, the rotation and coordinate values are corrected based on the alignment result, and the position of the defect to be reviewed is moved based on various information of the inspection result file that has already been read.

After moving to the defect position, beam irradiation is performed in step 1510, and image acquisition is performed in step 1511. In step 1512, the acquired high-magnification image is stored in the image / data storage unit 350 as needed. It is possible to set in advance whether to save or not to save in the review condition file, and if necessary, to save multiple types of images by a plurality of detectors at the same time according to the settings. For example, it is possible to simultaneously store an image of secondary electrons detected by the second detector 332 and an image of backscattered electrons detected by the first detector 331.

In step 1512, at the same time as saving the image, the image processing unit 349 extracts the feature of the defect from the image information and automatically classifies the content of the defect. The classified result is coded into a numerical value from 0 to 255, for example, and the code number is written in the place corresponding to the defect classification code in the inspection result file. The above defect review operation is repeated in step 1516. When the above series of operations is completed for all the defects specified to be reviewed on one wafer, the inspection result file (file in which the classification result is written) of the wafer is automatically saved and specified in step 1513. First, the inspection result file is output. Then, in step 1514, the wafer is unloaded, and in step 1515, the review ends.

By using this method, it has become possible to 100% review and classify defects detected by inspection SEM.

In this embodiment, a Gaussian function is used to fit the histogram in the inspection condition optimization flow 200 or 300, but a function having an isolated peak such as a Lorentz function other than that function may be used.

If the image has shading, it is advisable to perform the inspection condition optimum flow 200 or 300 after performing the shading correction. Alternatively, a region where shading does not occur may be specified, and the inspection condition optimization flow 200 or 300 may be performed on that region.

When optimizing the inspection conditions, an image is acquired every time the inspection conditions are changed, but the influence of charging and contamination under the previous conditions may not be negligible. In that case, ultraviolet light irradiation may be performed in order to eliminate these effects. Alternatively, the image acquisition location may be changed each time the inspection conditions are changed.

(Example 6) In the inspection condition optimization flows 200 (Fig. 2B) and 300 (Fig. 3) of Examples 1 to 5, when the inspection conditions are changed, the step width of the condition change is changed a plurality of times to achieve high speed. An example in which various conditions can be set will be described. In this example, among the inspection conditions, the value Vcc of the charge control power supply 67 (inspection SEM) or 366 (review SEM) was optimized. First, the inspection condition optimization flow 200 or 300 was performed with the step size ΔV of the Vcc value set to 40V. The histogram of the image is fitted by (Equation 1) and shown in Fig. 18 | μ₁-μ₂| / (σ₁+ σ₂) Vcc dependency was obtained. Since the step size ΔV is large, (Equation 2) (ε)₁= 1, ε₁Although it was not possible to determine the conditions that satisfy = 3), we were able to find Vcc conditions 2002 and 2001 that were close to those conditions. Next, between these conditions, ΔV was set to a small value of 10V, and the inspection condition optimization flow was performed again. As a result, as shown in FIG. 19, conditions 2101 and 2102 satisfying (Equation 2) could be found. When two or more conditions were found, the average value of Vcc was regarded as the optimum condition. By adopting such a method, it has become possible to optimize the inspection conditions faster than using a small value for ΔV from the beginning.

(Example 7) When there are a plurality of types of patterns in the wafer, the inspection conditions may not be fixed to one. In this embodiment, the inspection condition determination method in that case will be described.

Patterns 1905 and 1906 are processed in regions 1903 and 1904 on the die 1902 of the wafer 1901 in FIG. 20, respectively. As a result of optimizing the inspection conditions for the potential Vcc of the charge control power supply 67 by the method of the inspection condition optimization flows 200 and 300, the inspection conditions became pattern-dependent. The optimum conditions were Vcc = -8460V for pattern 1905 and Vcc = -8440V for pattern 1906. In this case, a method of (1) using the average value of the inspection conditions and (2) changing the inspection conditions for each pattern and executing the test multiple times can be selected as necessary. In method (1), the sensitivity is slightly lowered because the inspection conditions deviate slightly from the optimum values, but there is an advantage that the inspection time is short because the entire surface is inspected under the same conditions. On the other hand, in method (2), the inspection conditions are optimized for each pattern, so highly sensitive inspection is possible, but the inspection time is long because it is necessary to inspect in two steps.

(Example 8) By using the data obtained by optimizing the inspection conditions as in Examples 1 to 7 and creating a database of the inspection conditions, it was possible to speed up the inspection condition setting.

An example of the database is shown in FIGS. 21 and 22. Figure 16 is a cross-sectional view of the pattern, 1601 is a Si substrate, 1602 is a pn junction, 1603 is a plug embedded in a contact hole, 1604 is a contact hole, and 1605 is SiO.₂Is. Here, the representative items that determine the pattern, the presence or absence of the plug 1603, the aspect ratio (of the contact hole 1604), and the presence or absence of the pn junction 1602 are classified. As a result, the inspection conditions could be summarized as shown in Fig. 23. Here, the inspection conditions are as follows (1) to (3). (1) Vac = -10kV, Vr = -9.5kV, Vcc = -5kV (2) Vac = -10kV, Vr = -8.5kV, Vcc = -8.7kV (3) Vac = -10kV, Vr = -8.5kV , Vcc = -8.8kV However, Vac is the potential of the electron source 10 and Vr is the potential of the retarding power supply 36, and Vcc is the potential of the charge control electrode 65.

Next, the wafer was inspected using this database. FIG. 18 shows the cross-sectional structure of the inspection wafer. When applied to the database FIG. 17, inspection condition (1) was selected because there was no plug embedding, low aspect ratio, and pn junction. As a result of the inspection under these conditions, it was possible to detect the conduction defect with high sensitivity. Since the inspection conditions are selected using the database, the inspection conditions can be optimized faster than using the inspection condition optimization flows 200 (Fig. 2B) and 300 (Fig. 3).

In the above-described embodiment, the condition is set for the inspection SEM, but other SEMs (for example, review SEM, CD-SEM) can also set the conditions in the same manner. Further, although the inspection device using the electron beam has been described in detail as an example, the basic idea of the present invention can be similarly applied not only to the electron beam but also to the inspection device using an ion beam or the like.

As described in detail above, according to the present invention, in the inspection of a partially completed substrate such as a semiconductor device having a circuit pattern, the setting of inspection conditions has conventionally relied on the experience of the operator, so that the defect detection result It is possible to solve the problem that the inspection conditions are not reproducible and high-sensitivity inspection conditions cannot always be set. In addition, by automating the inspection condition setting, it is possible to shorten the time until the condition setting. Further, since the optimum conditions can be set with high accuracy with good reproducibility, the defect detection sensitivity of the inspection device is improved, which makes it possible to monitor the semiconductor product with high sensitivity.

<figref num="1">The figure explaining the apparatus configuration of the inspection SEM used in the 1st Example of this invention.</figref><figref num="2A">The figure explaining an example of the inspection flow in 1st Example of this invention.</figref><figref num="2B">The figure explaining an example of the inspection condition optimization flow in FIG. 2A.</figref><figref num="3">The figure explaining another example of the inspection condition optimization flow in FIG. 2A.</figref><figref num="4">The figure explaining the potential contrast image acquisition principle.</figref><figref num="5">The figure explaining the principle of positive charge contrast image acquisition.</figref><figref num="6">The figure explaining the principle of acquiring a negative charge contrast image.</figref><figref num="7">The figure explaining the potential contrast image and the histogram thereof in this invention.</figref><figref num="8">The figure explaining the Vcc dependence of the potential contrast image and the histogram in this invention.</figref><figref num="9">The figure for determining the optimum inspection condition in this invention.</figref><figref num="10">The figure explaining the Vcc dependence of the defect detection number in this invention.</figref><figref num="11">The figure for determining the optimum electron beam incident energy E0 in the 2nd Example of this invention.</figref><figref num="12">The figure for determining the optimum electron beam current IP in the 3rd Example of this invention.</figref><figref num="13">The figure explaining the potential contrast image of the wafer which has few patterns and the image processing principle for optimizing the inspection condition in 4th Example of this invention.</figref><figref num="14">FIG. 13 is a diagram illustrating a histogram of a potential contrast image of a wafer having few patterns.</figref><figref num="15">FIG. 13 is a diagram illustrating a histogram after image processing a potential contrast image of a wafer having few patterns.</figref><figref num="16">The figure explaining the apparatus configuration of the review SEM used in the 5th Example of this invention.</figref><figref num="17">The figure which shows an example of the inspection method in 5th Example of this invention.</figref><figref num="18">The figure for determining the optimum Vcc value in the 6th Example of this invention.</figref><figref num="19">The figure for determining the Vcc value by the inspection condition optimization flow in the 6th Example of this invention.</figref><figref num="20">The figure which shows the wafer which processed the plurality of patterns in the 7th Example of this invention.</figref><figref num="21">The figure which shows the cross-sectional structure of the pattern in 8th Example of this invention.</figref><figref num="22">FIG. 21 is a diagram illustrating a database of inspection conditions.</figref><figref num="23">The figure which shows the cross-sectional structure of the inspection wafer in 8th Example of this invention.</figref>

Code description

2 ... Laboratory, 3 ... Electro-Optical System, 4 ... Optical Microscope, 5 ... Image Processing, 6 ... Control, 7 ... Detection, 8 ... Sample Chamber, 9 ... wafer, 10 ... electron source, 11 ... extraction electrode, 12 ... condenser lens, 13 ... blanking deflector, 14 ... aperture, 15 ... scanning deflection Instrument, 16 ... objective lens, 17 ... reflector, 18 ... E × B deflector, 19 ... electron beam, 20 ... detector, 21 ... preamp, 22 ... AD converter, 23 ... optical converter, 24 ... optical fiber, 25 ... electric converter, 26 ... high pressure power supply, 27 ... preamp drive power supply, 28 ... AD converter drive Power supply, 29 ... reverse bias power supply, 30 ... sample table, 31 ... X stage, 32 ... Y stage, 33 ... rotating stage, 34 ... position monitor length measuring instrument, 35. .. Optical height measuring instrument, 36 ... retarding power supply, 37 ... light source, 40 ... light source, 41 ... optical lens, 42 ... CCD camera, 43 ... correction control circuit , 44 ... scanning signal generator, 45 ... lens power supply, 46 ... image storage, 48 ... computer, 50 ... monitor, 51 ... secondary and backward scattered electrons, 52 ... second secondary electron and backscattered electron, 62 ... sample exchange chamber, 65 ... charge control electrode, 66 ... charge control electrode control unit, 67 ... charge control power supply, 321. .. Electron optics, 322 ... Stage mechanism, 323 ... Wafer transfer system, 324 ... Vacuum exhaust system, 325 ... Optical microscope, 326 ... Control system, 327 ... Operation unit , 328 ... electron source, 329 ... condenser lens, 330 ... objective lens, 331 ... first detector, 332 ... second detector, 335 ... deflector, 336 ... reflector, 337 ... wafer height detection system, 338 ... XY stage ... 339 ... holder, 340 ... retarding power supply, 341 ... cassette mounting part, 342. .. Wafer loader, 343 ... Signal detection system control unit, 344 ...Beam deflection correction control unit, 345 ... Electro-optical system control unit, 346 ... Wafer height sensor detection system, 347 ... Mechanism and stage control unit, 348 ... Operation screen and operation unit, 349 .. Image processing unit, 350 ... data storage unit, 351 ... wafer, 352 ... primary electron beam, 353 ... reflected electron, 354 ... secondary electron, 356 ... data input unit, 357 ... data conversion unit, 364 ... charge control electrode, 365 ... charge control electrode control unit, 366 ... charge control power supply, 401 ... normal part, 402 ... conduction defect, 403. .. Short defect, 404 ... Si wafer, 405 oxide film, 406 ... retarding power supply, 407 ... charge control electrode, 408 ... charge control electrode, 409 ... secondary electron, 410. .. Primary electron, 501 ... Positive potential potential, 502 ... Secondary electron, 503 ... Low energy component of secondary electron, 504 ... Secondary electron, 505 ... Potential contrast, 601 ... negative potential potential, 602 ... secondary electron, 603 ... secondary electron, 604 ... secondary electron, 605 ... potential contrast, 701 ... histogram due to oxide film Peak, 702 ... Graphite peak due to pattern part, 703 ... Potential contrast image, 704 ... histogram, 801 ... Potential contrast image, 802 ... Potential contrast image, 803 ... Potential contrast image, 804 ... histogram, 1101 ... potential contrast image, 1102 ... extracted pattern, 1103 ... extracted insulating film, 1104 ... signal profile, 1105 ... extracted pattern , 1601 ... Si substrate, 1602 ... pn junction, 1603 ... plug, 1604 ... contact hole, 1605 ... SiO.. Wafer, 352 ... Primary electron beam, 353 ... Backscattered electron, 354 ... Secondary electron, 356 ... Data input unit, 357 ... Data conversion unit, 364 ... Charge control electrode , 365 ... charge control electrode control unit, 366 ... charge control power supply, 401 ... normal part, 402 ... conduction defect, 403 ... short defect, 404 ... Si wafer, 405 oxide film , 406 ... retarding power supply, 407 ... charge control electrode, 408 ... charge control electrode, 409 ... secondary electron, 410 ... primary electron, 501 ... positive potential potential, 502 ... secondary electron, 503 ... low energy component of secondary electron, 504 ... secondary electron, 505 ... potential contrast, 601 ... negative potential potential, 602 ... secondary electron , 603 ... secondary electrons, 604 ... secondary electrons, 605 ... potential contrast, 701 ... histogram peak due to oxide film part, 702 ... histogram peak due to pattern part , 703 ... potential contrast image, 704 ... histogram, 801 ... potential contrast image, 802 ... potential contrast image, 803 ... potential contrast image, 804 ... histogram, 1101 ... potential Contrast image, 1102 ... extracted pattern, 1103 ... extracted insulating film, 1104 ... signal profile, 1105 ... extracted pattern, 1601 ... Si substrate, 1602 ... pn junction, 1603 ... plug, 1604 ... contact hole, 1605 ... SiO.. Wafer, 352 ... Primary electron beam, 353 ... Backscattered electron, 354 ... Secondary electron, 356 ... Data input unit, 357 ... Data conversion unit, 364 ... Charge control electrode , 365 ... charge control electrode control unit, 366 ... charge control power supply, 401 ... normal part, 402 ... conduction defect, 403 ... short defect, 404 ... Si wafer, 405 oxide film , 406 ... retarding power supply, 407 ... charge control electrode, 408 ... charge control electrode, 409 ... secondary electron, 410 ... primary electron, 501 ... positive potential potential, 502 ... secondary electron, 503 ... low energy component of secondary electron, 504 ... secondary electron, 505 ... potential contrast, 601 ... negative potential potential, 602 ... secondary electron , 603 ... secondary electrons, 604 ... secondary electrons, 605 ... potential contrast, 701 ... histogram peak due to oxide film part, 702 ... histogram peak due to pattern part , 703 ... potential contrast image, 704 ... histogram, 801 ... potential contrast image, 802 ... potential contrast image, 803 ... potential contrast image, 804 ... histogram, 1101 ... potential Contrast image, 1102 ... extracted pattern, 1103 ... extracted insulating film, 1104 ... signal profile, 1105 ... extracted pattern, 1601 ... Si substrate, 1602 ... pn junction, 1603 ... plug, 1604 ... contact hole, 1605 ... SiO.. Secondary electron, 410 ... Primary electron, 501 ... Positive potential potential, 502 ... Secondary electron, 503 ... Low energy component of secondary electron, 504 ... Secondary electron, 505 ... Potential contrast, 601 ... Negative potential potential, 602 ... Secondary electron, 603 ... Secondary electron, 604 ... Secondary electron, 605 ... Potential contrast, 701 .. The peak of the histogram due to the oxide film part, the peak of the histogram due to the 702 ... pattern part, 703 ... potential contrast image, 704 ... histogram, 801 ... potential contrast image, 802 ... Potential contrast image, 803 ... potential contrast image, 804 ... histogram, 1101 ... potential contrast image, 1102 ... extracted pattern, 1103 ... extracted insulating film part, 1104 ... signal profile , 1105 ... extracted pattern, 1601 ... Si substrate, 1602 ... pn junction, 1603 ... plug, 1604 ... contact hole, 1605 ... SiO.. Secondary electron, 410 ... Primary electron, 501 ... Positive potential potential, 502 ... Secondary electron, 503 ... Low energy component of secondary electron, 504 ... Secondary electron, 505 ... Potential contrast, 601 ... Negative potential potential, 602 ... Secondary electron, 603 ... Secondary electron, 604 ... Secondary electron, 605 ... Potential contrast, 701 .. The peak of the histogram due to the oxide film part, the peak of the histogram due to the 702 ... pattern part, 703 ... potential contrast image, 704 ... histogram, 801 ... potential contrast image, 802 ... Potential contrast image, 803 ... potential contrast image, 804 ... histogram, 1101 ... potential contrast image, 1102 ... extracted pattern, 1103 ... extracted insulating film part, 1104 ... signal profile , 1105 ... extracted pattern, 1601 ... Si substrate, 1602 ... pn junction, 1603 ... plug, 1604 ... contact hole, 1605 ... SiOPlug, 1604 ... contact hole, 1605 ... SiOPlug, 1604 ... contact hole, 1605 ... SiO₂, 1901 ... Wafer, 1902 ... Die, 1903 ... Machining Area, 1904 ... Machining Area, 1905 ... Pattern, 1906 ... Pattern.