JP4853581B2 - Inspection method and inspection apparatus using electron beam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection method and device, capable of performing the inspection at a higher speed, using an electron beam. <P>SOLUTION: An electron beam 36 from an electron gun 1 is converged by an objective lens 9 and decelerated by a retarding voltage impressed to a sample 13; the sample 13 is scanned by the electron beam, while being moved; secondary electrons 33 generated from the sample 13 are accelerated by the retarding voltage to make a nearly parallel beam which is deflected by an E&times;B deflector 18, arranged between the objective lens 9 and the sample 13 and has a secondary electron generating body 19 irradiated; and second secondary electrons 20 are generated from the secondary electron generating body 19, and second detected by a charged particle detector 21. The output signal detected is stored as an image signal, and the image stored is compared in an operation section 29 and a defect determining section 30 to thereby determine defects. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an inspection method and an inspection apparatus using an electron beam, and more particularly to an inspection method and an inspection apparatus using an electron beam suitable for inspecting a pattern of a circuit or the like on a wafer in the process of manufacturing a semiconductor device.

  As a sample observation apparatus using an electron beam, there is a scanning electron microscope (hereinafter referred to as SEM), and a length measuring scanning electron microscope (hereinafter referred to as length measurement SEM) as one of inspection apparatuses for semiconductor devices. There is. However, a normal SEM or length measurement SEM is suitable for observing a limited field of view at a high magnification, but is not suitable for searching for a defect on a wafer. This is because, in order to search for such a defect, it is necessary to inspect a very wide area, that is, the entire surface area of the wafer, but when such a large area is inspected by the above-described SEM or length measurement SEM. Takes a very long time. Therefore, these SEMs are not practical for use as an inspection apparatus synchronized with the manufacturing tact in the process of manufacturing a semiconductor device.

  As an apparatus for solving such a problem, an inspection apparatus using an electron beam for detecting a defect on a wafer using image comparison is known. This device uses a high-current electron beam, continuously moves the sample stage while irradiating the sample with the electron beam, uses a high acceleration voltage, and decelerates the electron beam to the sample. It has the characteristics that a retarding voltage for preventing electrification is applied and that charged particles generated in the sample by irradiation with an electron beam are detected after passing through the objective lens (TTL method). According to this, there is a possibility that the defect inspection of the mask or wafer pattern as a sample can be performed more efficiently than the conventional SEM. An example of this related technique is described in Japanese Patent Laid-Open No. 5-258703.

JP-A-5-258703

  According to a so-called TTL (Through The Lens) method in which charged particles emerging from a sample are detected through an objective lens, the distance between the objective lens and the sample can be shortened. As a result, the objective lens can be used with a short focal point, the electron beam aberration is small, and high-resolution images can be acquired. However, on the other hand, the improvement in the inspection speed is hindered, and if the height of the sample is further changed, the rotation of the electron beam is greatly changed, resulting in a non-negligible problem that the obtained image is rotated. In addition, there is a disadvantage that a change in detection efficiency of charged particles when the retarding voltage is changed can have an influence that cannot be ignored.

  A first object of the present invention is to provide an inspection method and an inspection apparatus using an electron beam capable of increasing the inspection speed.

  A second object of the present invention is to provide an inspection method and an inspection apparatus using an electron beam with little image rotation.

  A third object of the present invention is to provide an inspection method and an inspection apparatus using an electron beam with little change in the detection efficiency of charged particles.

The scanning electron microscope of the present invention comprises an electron source that generates an electron beam,
An acceleration electrode for applying a voltage for accelerating the electron beam;
An objective lens for focusing the electron beam on the sample;
A detector for detecting charged particles obtained by irradiating the sample with the electron beam;
An electrode provided between the objective lens and the sample;
And means for setting a voltage generated between the sample and the electrode by the electrode according to the sample.

An inspection apparatus of the present invention includes an electron source that generates an electron beam,
An acceleration electrode for applying a voltage for accelerating the electron beam;
An objective lens for focusing the electron beam on the sample;
A detector for detecting charged particles obtained by irradiating the sample with the electron beam;
An electrode provided between the objective lens and the sample;
Means for setting a voltage generated between the sample and the electrode by the electrode according to the sample;
A storage unit for storing an image signal generated based on the signal obtained by the detector;
An arithmetic unit that compares the image signal with a second image signal corresponding to the image signal;
A defect determination unit for determining a defect from the comparison result of the calculation unit;
It is characterized by having.

  According to the present invention, first, it is possible to provide an inspection method and an inspection apparatus using an electron beam that can increase the inspection speed.

  Second, it is possible to provide an inspection method and an inspection apparatus using an electron beam with little image rotation.

  Third, it is possible to provide an inspection method and an inspection apparatus using an electron beam with little change in detection efficiency of charged particles.

The longitudinal cross-sectional view which shows the concept of a structure of the test | inspection apparatus using the electron beam which shows the Example based on this invention. The block diagram which shows the flow of the general manufacturing process of a semiconductor device. Schematic of the image which observed an example of the circuit pattern on the semiconductor wafer in a manufacture process by SEM. The correlation diagram which shows the relationship between sample stage settling time and an electron beam deflection width. The correlation diagram which shows the relationship between secondary electron detection efficiency and a retarding voltage.

〔Example〕
FIG. 2 is a block diagram showing a flow of a semiconductor device manufacturing process. As can be seen from the figure, in manufacturing the semiconductor device, a large number of pattern forming steps 51 to 55 are repeated on the wafer of the semiconductor device, and each pattern forming step is roughly formed by film formation 56, resist coating 57, The process includes steps of photosensitivity 58, development 59, etching 60, resist removal 61, and cleaning 62. If the manufacturing conditions are not optimized in each step, the circuit pattern of the semiconductor wafer cannot be formed normally. Therefore, automatic visual inspection steps 63 and 64 are provided between the steps, and the circuit pattern is inspected.

  FIG. 3 shows an outline of an image obtained by observing a circuit pattern on a semiconductor wafer in a manufacturing process with a scanning electron microscope (SEM). FIG. 3A shows a pattern that has been processed normally, and FIG. 3B shows a pattern in which a processing defect has occurred. For example, when an abnormality occurs in the step of film formation 56 in FIG. 2, particles adhere to the surface of the semiconductor wafer and become an isolated defect A in FIG. Further, if the conditions such as the focus and the exposure time are not optimal at the time of light exposure after resist application, there are places where the amount and intensity of light irradiating the resist are excessive or insufficient, and short C in FIG. Or breakage E, pattern thinning or chipping D. If there is a defect on the mask or reticle at the time of exposure, the same pattern shape abnormality is likely to occur. In addition, when the etching amount is not optimized, and when a thin film or particles generated during the etching are present, the opening defect G including the short C, the protrusion B, and the isolated defect A also occurs. At the time of cleaning, abnormal oxidation is likely to occur at the corners of the pattern and other locations due to the condition of running out of water during drying, and a thin film residue F that is difficult to observe with an optical microscope is generated. Therefore, in the wafer manufacturing process, it is necessary to optimize the processing conditions so that these defects do not occur, and it is necessary to detect the occurrence of an abnormality at an early stage and feed back to this step.

  In order to detect the defects as described above, for example, an automatic appearance inspection is performed after the step of development 59 in FIG. 2 and after the step of resist removal 61. The inspection apparatus using the electron beam according to the present invention is used for this inspection.

  FIG. 1 is a longitudinal sectional view showing an outline of the configuration of an inspection apparatus using an electron beam according to an embodiment of the present invention.

In FIG. 1, the electron gun 1 includes an electron source 2, an extraction electrode 3, and an acceleration electrode 4. An extraction voltage V ₁ is applied between the electron source 2 and the extraction electrode 3 by the extraction power source 5, whereby an electron beam 36 is extracted from the electron source 2. The acceleration electrode 4 is maintained at the ground potential, and an acceleration voltage Vacc is applied between the acceleration electrode 4 and the electron source 2 by the acceleration power source 6, so that the electron beam 36 is accelerated by the acceleration voltage Vacc. The accelerated electron beam is crossed by a first converging lens 8 connected to the lens power source 7 between the first converging lens 8 and the objective lens 9 which is a second converging lens connected to the lens power source 7. And is converged by the objective lens 9 onto a sample 13 such as a semiconductor wafer on the sample stage 12 that is horizontally movable by a stage driving device (not shown) and a position monitor length measuring device 11. The That is, the sample 13 is irradiated with the focused electron beam. Although not shown, the above configuration is housed in a container that maintains a vacuum so as to be suitable for irradiation with an electron beam.

  A negative voltage as a retarding voltage for decelerating the electron beam 36 is applied to the sample 13 by the variable decelerating power supply 14, and the electrode 34 provided between the sample 13 and the objective lens 9 is applied to the sample 13. A positive direction voltage is applied, and thus the electron beam 36 is decelerated by the retarding voltage. Usually, the electrode 34 is at ground potential, and the retarding voltage can be arbitrarily changed by adjusting the variable deceleration power supply 14.

  A diaphragm 15 is disposed between the first converging lens 8 and the crossover 10. This diaphragm 15 blocks excess electrons and further serves to determine the aperture angle of the electron beam 36. An electron beam scanning deflector 16 is disposed between the crossover 10 and the objective lens 9, and has a function of deflecting the electron beam 36 so as to scan the sample 13 with the converged electron beam 36. The electron beam scanning deflector 16 is provided in the objective lens 9 so that the fulcrum of deflection and the center of the magnetic pole gap of the objective lens 9 substantially coincide with each other, thereby reducing deflection distortion. be able to. A blanking deflector connected to the scanning signal generator 24 that deflects and blanks the electron beam 36 at a position where the crossover 10 is formed between the diaphragm 15 and the electron beam scanning deflector 16. 17 is arranged.

  In order to blank the electron beam 36, if a point other than the crossover 10 is deflected as a fulcrum, the electron beam irradiation position on the sample 13 is moved during the deflection. In addition, if blanking is performed when the electron beam is a parallel beam, there is an electron beam that cannot be blocked by the diaphragm 15 during blanking, and the adjacent region that is not desired to be irradiated is slightly irradiated. In this way, during the period from the start of blanking to the completion, portions that are not preferably irradiated with an electron beam are irradiated with an electron beam. On the other hand, in the embodiment of the present invention, since the electron beam 36 is deflected with the crossover 10 as a fulcrum at the time of blanking, the electron beam irradiation position on the sample 13 does not change. Does not occur.

  When the sample 13 is irradiated with the focused electron beam 36 and scanned, secondary electrons and reflected electrons, which are charged particles, are generated from the sample 13. Of these, the secondary electrons 33 are defined as having an energy of 50 eV or less. The retarding voltage for the electron beam 36 that irradiates the sample 13 acts as an accelerating voltage because the positive and negative directions are reversed with respect to the generated secondary electrons. Therefore, since the generated secondary electrons 33 are accelerated by the retarding voltage, the directions are almost aligned and become substantially parallel beams, so that E × B (e-cross • between the sample 13 and the objective lens 9 is arranged. B) The light enters the deflector 18. The E × B deflector 18 includes a deflection electric field generator for generating a deflection electric field for deflecting the secondary electrons 33, and cancels the deflection due to the deflection electric field of the electron beam irradiating the sample 13, and is a deflection orthogonal to the deflection electric field. A deflection magnetic field generator for generating a magnetic field is included. This deflection magnetic field has a deflection effect on the secondary electrons 33 in the same direction as the deflection electric field. Therefore, the deflection electric field and the deflection magnetic field generated by the E × B deflector 18 deflect the accelerated secondary electrons 33 without adversely affecting the electron beam that irradiates the sample 13. In order to maintain this deflection angle substantially constant, the deflection electric field and the deflection magnetic field generated by the E × B deflector 18 can be changed in conjunction with the change of the retarding voltage. Since the E × B deflector 18 generates a deflection electric field and a deflection magnetic field, it may be called a deflection electric field and a deflection magnetic field generator.

  The secondary electrons 33 deflected by the deflection electric field and the deflection magnetic field of the E × B deflector 18 impact or irradiate the conductive secondary electron generator 19. The secondary electron generator 19 is disposed between the objective lens 9 and the E × B deflector 18 around the axis of the electron beam, and has a conical shape that expands toward the electron gun 1 along the axis. Has been. The secondary electron generator 19 is made of CuBeO, and has a secondary electron generation capability that is about five times the number of incident electrons. The second secondary electrons 20 (which have energy of 50 eV or less) generated from the secondary electron generator 19 are detected by the charged particle detector 21 and converted into an electric signal.

  The height of the sample 13 is measured in real time by the optical sample height measuring device 22, and the measurement result is fed back from the correction control circuit 23 to the lens power supply 7, whereby the focal length of the objective lens 9 is dynamically corrected. The The electron beam sample irradiation position is detected by the position monitor length measuring device 11, and the result is fed back from the correction control circuit 23 to the scanning signal generator 24, whereby the electron beam sample irradiation position is controlled. .

  The sample 13 is continuously moved in the Y direction of the XY coordinates by a stage driving device (not shown), while the scanning of the sample 13 by the electron beam 36 is repeatedly performed in the X direction by scanning and blanking alternately. When the sample 13 finishes moving continuously from the start position to the end position, the sample 13 is moved in the X direction by an amount corresponding to the scanning width of the electron beam, and then the continuous movement of the sample 13 in the −Y direction is resumed. During the continuous movement, scanning of the sample 13 in the X direction by the electron beam 36 and blanking are repeated alternately. By repeating such an operation, scanning of the entire surface of the sample 13 by the electron beam 36 is completed. In order to make the irradiation of the sample 13 with the electron beam 36 temporally and spatially uniform, the electron beam 36 is deflected for blanking so that the electron beam 36 is not directed to the sample 13 during the blanking period of each scan. Deflection and blanking using the device 17.

  The electric signal of the second secondary electrons 20 detected by the charged particle detector 21 is amplified by the amplifier 25 and digitized by the A / D converter 26. The digitized signal is stored in the storage units 27 and 28 as an image signal. Specifically, first, the secondary electron image signal of the first inspection region is stored in the storage unit 27. Next, the secondary electron image signal of the second inspection area of the adjacent same circuit pattern is stored in the storage unit 28 and simultaneously compared with the secondary electron image signal of the first inspection area of the storage unit 27. Further, the secondary electron image signal in the third inspection area is overwritten and stored in the storage unit 27 and is simultaneously compared with the image in the second inspection area in the storage unit 28. This process is repeated to store and compare image signals for all inspection areas. The image signal stored in the storage unit 28 is displayed on the monitor 32.

  The image comparison is performed in the calculation unit 29 and the defect determination unit 30. That is, with respect to the secondary electron image signals stored in the storage units 27 and 28, based on the defect determination conditions that have already been obtained, the calculation unit 29 calculates various statistics, specifically the average and variance of image density values. Statistics, difference values between neighboring pixels, rungless statistics, co-occurrence matrix, etc. are calculated. After these processes are executed, the processed image signal is transferred to the defect determination unit 30 and compared to extract a difference signal, and a defect is determined with reference to the defect determination conditions already obtained and stored. The signal and other signals are separated.

  In addition, the secondary electron image signal of the inspection region of the standard circuit pattern is stored in the storage unit 27 in advance, and the secondary electron image signal of the inspection region of the circuit pattern of the sample 13 is stored in the storage unit 28, You may make it compare with the memory | storage image signal of the memory | storage part 27. FIG. That is, first, an inspection region and inspection conditions for a non-defective semiconductor device are input from the control unit 31 in advance, a non-defective product inspection is executed based on the data, and a secondary electron image signal in a desired region is taken into the storage unit 27. Remember. Next, the sample 13 to be inspected is inspected by the same method, and the secondary electron image is taken into the storage unit 28 and stored. At the same time, only a defect is detected by comparing this with a non-defective secondary electron image stored in the storage unit 27 after alignment. At this time, as a non-defective semiconductor device, a non-defective part of the sample 13 or a non-defective wafer or chip different from the sample 13 is used. For example, in the sample 13, when the circuit pattern is formed, there may be a defect such that the lower layer pattern and the upper layer pattern are formed with misalignment. If the comparison target is a circuit pattern on the same wafer or the same chip, a defect that has occurred on the entire wafer as described above is overlooked, but a good image signal is stored in advance, and the image signal of the sample 13 is stored. By comparing the above, it is possible to detect a defect that has occurred as a whole as described above. An operation command and condition setting for each part of the inspection apparatus are performed from the control unit 31. Therefore, conditions such as an acceleration voltage, a deflection width (scanning width) and a deflection speed (scanning speed) of the electron beam, a moving speed of the sample stage, and an output signal capturing timing of the detector are input to the control unit 31 in advance.

  Next, the difference between an inspection apparatus using an electron beam according to the present invention and a normal scanning electron microscope (SEM) will be described particularly from the viewpoint of high speed.

  The SEM is an apparatus for observing a very limited region, for example, a region of several tens of μm square over time with high magnification. Even a length-measuring scanning electron microscope (length-measuring SEM), which is one of semiconductor inspection apparatuses, only observes and measures only a plurality of points on a wafer at a high magnification. On the other hand, an electron beam inspection apparatus based on image comparison, which is an object of the present invention, is an apparatus that searches for a defect on a sample such as a wafer. Therefore, since a very wide area must be inspected all over, the speed of inspection is extremely important.

In general, the S / N ratio in an electron beam image is correlated with the value of the square root of the number of irradiated electrons per unit pixel of the electron beam that irradiates the sample. The defect to be detected on the sample is a minute defect that is desirable to be inspected by pixel comparison. From this viewpoint, when the resolution required for the inspection apparatus is about 0.1 μm from the size of the pattern to be inspected. From the inventors' experience, the S / N ratio of the raw image before image processing is preferably 10 or more, and more preferably 18 or more.
In order to make such a minute defect a detection target, it is desirable that the pixel size is about 0.1 μm. On the other hand, inspection time required for inspection of the circuit pattern of the wafer, considering the tact of the manufacturing process, is approximately 200 sec / cm ² or so, the time required only to the image acquisition about the inspection time half 100 sec / cm ² Degree. From these values, the required time per pixel is 10 nsec, and the required number of electrons per pixel is about 6000, which corresponds to an electron beam current of 100 nA.

Considering the above matters, in the embodiment of the present invention, the electron beam current for irradiating the sample is 100 nA, the pixel size is 0.1 μm, the spot size of the electron beam on the sample is 0.08 μm, the sample stage The continuous moving speed of 12 is set to 10 mm / sec. Under these conditions, the same area of the sample is scanned only once with the electron beam, thereby enabling a high-speed inspection of about 200 sec / cm ^2. Yes. In the conventional SEM and length measurement SEM, the electron beam current irradiating the sample is about several pA to several hundred pA, so the inspection time per 1 cm ² is several hundred hours. Is not practical.

  In the embodiment of the present invention, a diffusion replenishment type thermal field emission electron source (Zr / O / W) is used as the electron source 2 of the electron gun 1 so that a high-current electron beam can be obtained and high-speed inspection can be performed. It is used. Furthermore, the required time per pixel of 10 nsec corresponds to a sampling time of 100 MHz, and therefore the charged particle detector 21 needs to have a high-speed response speed corresponding thereto. The charged particle detector 21 is composed of a PIN type semiconductor detector so as to satisfy this condition.

  In the case of a sample with low or no conductivity, the sample is charged by being irradiated with an electron beam. This amount of charge depends on the acceleration voltage of the electron beam and can be solved by lowering the energy. However, since an electron beam inspection apparatus based on image comparison uses a high-current electron beam of 100 nA, if the acceleration voltage is lowered, aberration (expansion in the radial direction of the electron beam) increases due to the space charge effect. It becomes difficult to obtain an electron beam spot size on the sample of 08 μm, and therefore a reduction in resolution is unavoidable. In the embodiment of the present invention, the acceleration voltage Vacc is set to a constant value of 10 kV in order to prevent a decrease and change in resolution due to the space charge effect and stably obtain an electron beam spot size of 0.08 μm on the sample. .

  The quality of the image depends greatly on the energy of the electron beam that illuminates the sample, and the energy varies with the type of sample. The energy is increased for a sample that is difficult to be charged or a sample for which the edge of the circuit pattern is particularly desired by enhancing the contrast of the image, and the energy is decreased for a sample that is easily charged. For this reason, it is necessary to find and set the optimum electron beam irradiation energy every time the type of sample to be inspected changes.

  In the embodiment of the present invention, the optimum irradiation energy of the electron beam for irradiating the sample is set by changing the negative voltage applied to the sample 13 without changing the acceleration voltage Vacc, that is, the retarding voltage. This retarding voltage can be changed by the variable deceleration power supply 14.

  Conventionally, charged particles generated from the sample 13 have been detected through the objective lens 9. As described above, this is called a TTL (Through The Lens) method. According to the TTL method, the resolution can be increased by operating the objective lens with a short focal point. On the other hand, in the embodiment of the present invention, charged particles generated from the sample are detected under the objective lens 9, specifically, between the objective lens 9 and the sample 13. For this reason, the focal length of the objective lens 9 is longer than that of the TTL method. That is, in the normal TTL method, the focal length of the objective lens is about 5 mm (short focus), whereas in the embodiment of the present invention, the value is set to 40 mm (long focus). Therefore, according to the embodiment of the present invention, it is possible to increase the deflection width of the electron beam 36 performed for obtaining the image of the sample 13, that is, the scanning width by the electron beam. For example, the beam deflection width of the TTL method is about 100 μm, whereas in the embodiment of the present invention, it is set to 500 μm.

  As described above, when the sample 13 finishes moving continuously from the start point position to the end point position, the sample 13 is moved by an amount corresponding to the scanning width of the sample by the electron beam 36 and starts to move again. This movement causes a time during which the inspection cannot be performed until the sample stage is set.

  FIG. 4 shows the relationship between the integrated value (unit: sec) of the settling time of the sample stage 12 and the deflection width (unit: μm) of the electron beam 36. From this figure, it can be seen that there is an extreme difference in the integrated value of the sample stage settling time depending on whether the deflection width is 100 μm or 500 μm. That is, according to the embodiment of the present invention, the sample stage settling time can be shortened, and the inspection speed can be improved accordingly.

  Since the surface of the sample 13 is not a perfect plane, the height of the sample changes when the region to be inspected moves. Therefore, it is necessary to constantly focus on the sample 13 by changing the excitation of the objective lens 9. In the conventional TTL system, it is necessary to perform strong excitation so that the objective lens works at a short focal point. However, in the strong excitation objective lens, the image is rotated due to the horizontal rotation of the electron beam with the change in the height of the sample, so that correction is necessary. On the other hand, in the embodiment of the present invention, the objective lens 9 is weakly excited so as to be operated at a long focal point. For example, when I is the current value of the objective lens (unit A), N is the number of turns of the coil of the objective lens, and E is the energy of the electron beam (unit eV), excitation is about IN / √E = 9. For this reason, as the height of the sample 13 changes, even if the focus is finely adjusted, the rotation of the electron beam 36 and the rotation of the image occur only to a degree that can be substantially ignored, so that the correction becomes unnecessary.

  FIG. 5 shows the relationship between secondary electron detection efficiency (unit%) and retarding voltage (unit kV). Curve (1) in the figure is according to the embodiment of the present invention, and curve (2) is according to the TTL system. As already mentioned, the retarding voltage should be varied depending on the type of sample. In addition, the retarding voltage has an effect of accelerating secondary electrons. In FIG. 5, when the retarding voltage is changed, the secondary electron detection efficiency changes greatly in the case of the TTL method, whereas it does not change much in the embodiment of the present invention. In the case of the TTL method, secondary electrons generated from the sample are converged through the magnetic field of the objective lens, but the convergence position in the axial direction is changed by changing the retarding voltage. This is the main cause of greatly changing the secondary electron detection efficiency. In the embodiment of the present invention, since the secondary electrons 33 do not pass through the magnetic field of the objective lens 9, the influence is small. Therefore, in the embodiment of the present invention, the rotation of the image is small and the fluctuation of the secondary electron detection efficiency is small, so that the inspection image is stabilized.

  As described above, since the secondary electrons 33 generated from the sample 13 are accelerated by the retarding voltage to become a substantially parallel beam, the collection rate of the secondary electrons 33 is improved. The collimated secondary electrons 33 are further deflected by an angle, for example, 5 °, by the deflection electric field and the deflection magnetic field of the E × B deflector 18 to impact the secondary electron generator 19, thereby further 2 secondary electrons 20 are generated in large quantities. As described above, the detection efficiency of the secondary electrons is greatly improved by the collimated beam and the impact of the secondary electron generator 19.

  The scanning of the sample 13 by the electron beam 36 deflects the electron beam 36 in the X direction while continuously moving the sample 13 in the Y direction. However, the scanning and blanking are not repeated alternately, but the scanning may be deflected reciprocally. Good. In this case, the deflection speed (scanning speed) at the time of forward deflection and the deflection speed (scanning speed) at the time of return deflection are made the same. In this way, the blanking deflector 17 can be omitted, and the blanking time can be saved. In this case, however, the following should be noted. The first part and the last part of the reciprocating deflection of the electron beam 36 of the sample 13 are concentrated and irradiated by the electron beam 36 in a short time. That is, for example, in the case of scanning from the left to the right in the X direction, the movement of the electron beam in the X direction stops at the end of the irradiation region and waits for the sample 13 to move in the Y direction by the scanning width. The next column is moved from right to left in the X direction and scanned. While waiting for the movement in the Y direction, the end of the sample 13 is continuously irradiated in the Y direction. For this reason, in the case of a sample having a very short time constant of the charging phenomenon, the brightness of the image becomes non-uniform when the image is acquired. Therefore, in order to make the irradiation amount of the electron beam 36 almost the same over the entire surface of the sample 13, the deflection speed is controlled so that the deflection speed of the electron beam 36 is higher at the scanning end portion than at the scanning center portion. Good.

  In the above description, the secondary electrons 33 generated from the sample 13 are used for image formation. However, the same effect can be obtained by using the backscattered electrons scattered from the sample by the irradiation of the electron beam 36. Can be obtained.

  DESCRIPTION OF SYMBOLS 1 ... Electron gun, 2 ... Electron source, 4 ... Acceleration electrode, 6 ... Acceleration power source, 8 ... 1st converging lens, 9 ... Objective lens, 10 ... Crossover, 11 ... Length measuring device for position monitor, 12 ... Sample stage 13 ... Sample, 14 ... Variable deceleration power source, 15 ... Aperture, 16 ... Electron beam scanning deflector, 17 ... Blanking deflector, 18 ... ExB deflector, 19 ... Secondary electron generator, 20 ... Second secondary electrons, 21 ... charged particle detector, 22 ... optical sample height measuring device, 23 ... correction control circuit, 24 ... scanning signal generator, 29 ... calculating unit, 30 ... defect determining unit, 31 ... Control unit, 33 ... secondary electrons, 36 ... electron beam.

Claims (8)

An electron source that generates an electron beam;
An acceleration electrode for applying a voltage for accelerating the electron beam;
An objective lens for focusing the electron beam on the sample;
A detector for detecting charged particles obtained by irradiating the sample with the electron beam;
An electrode provided between the objective lens and the sample;
A scanning electron microscope comprising: means for setting a voltage generated between the sample and the electrode by the electrode according to the sample. The scanning electron microscope according to claim 1,
A scanning electron microscope, wherein a voltage is applied to the electrode. The scanning electron microscope according to claim 1,
A scanning electron microscope comprising a power source for applying a voltage to the sample. The scanning electron microscope according to claim 3,
A scanning electron microscope, wherein a voltage generated between the sample and the electrode is set by setting a voltage to be applied to the sample. An electron source that generates an electron beam;
An acceleration electrode for applying a voltage for accelerating the electron beam;
An objective lens for focusing the electron beam on the sample;
A detector for detecting charged particles obtained by irradiating the sample with the electron beam;
An electrode provided between the objective lens and the sample;
Means for setting a voltage generated between the sample and the electrode by the electrode according to the sample;
A storage unit for storing an image signal generated based on the signal obtained by the detector;
An arithmetic unit that compares the image signal with a second image signal corresponding to the image signal;
A defect determination unit for determining a defect from the comparison result of the calculation unit;
An inspection apparatus comprising: The inspection apparatus according to claim 5, wherein
An inspection apparatus that applies a voltage to the electrode. The inspection apparatus according to claim 5, wherein
An inspection apparatus comprising a power source for applying a voltage to the sample. The inspection apparatus according to claim 7,
An inspection apparatus, wherein a voltage generated between the sample and the electrode is set by setting a voltage to be applied to the sample.

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