JP3791095B2 - Circuit pattern inspection method and inspection apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for manufacturing a substrate having a fine circuit pattern such as a semiconductor device or a liquid crystal, and more particularly to a pattern inspection technique for a semiconductor device or a photomask. It is related with the technology which carries out comparative inspection using.
[0002]
[Prior art]
  A semiconductor wafer inspection will be described as an example.
[0003]
  A semiconductor device is manufactured by repeating a process of transferring a pattern formed on a photomask on a semiconductor wafer by lithography and etching. In the manufacturing process of a semiconductor device, the quality of lithography processing, etching processing, and other conditions, and the occurrence of foreign matter greatly affect the yield of the semiconductor device. Therefore, in order to detect abnormalities and defects early or in advance, the semiconductor in the manufacturing process A method for inspecting a pattern on a wafer has been conventionally performed.
[0004]
  As a method for inspecting defects present in patterns on a semiconductor wafer, a defect inspection apparatus that irradiates a semiconductor wafer with white light and compares the same kind of circuit patterns of a plurality of LSIs using an optical image has been put into practical use. The outline of the inspection method is described in "Monthly Semiconductor World" August 1995, pp96-99. Further, in the inspection method using an optical image, as described in Japanese Patent Laid-Open No. 3-167456, an optically illuminated region on the substrate is imaged by a time delay integration sensor, and the image is input in advance. By detecting the image deterioration at the time of image acquisition and correcting it at the time of image detection as described in Japanese Patent Publication No. 6-58220. A method for performing a comparative inspection with an optical image is disclosed. When a semiconductor wafer in the manufacturing process is inspected by such an optical inspection method, residues and defects of a pattern having a silicon oxide film or a photosensitive photoresist material on the surface through which light is transmitted cannot be detected. Moreover, the etching residue which is below the resolution of the optical system and the non-opening defect of the minute conduction hole could not be detected. Furthermore, a defect generated at the bottom of the step of the wiring pattern could not be detected.
[0005]
  As described above, defect detection by optical images has become difficult due to miniaturization of circuit patterns, complicated circuit pattern shapes, and diversification of materials, so electron beam images with higher resolution than optical images are used. A method for comparing and inspecting circuit patterns has been proposed. When comparing circuit patterns with electron beam images, it is necessary to obtain images much faster than observation with a scanning electron microscope (hereinafter referred to as SEM) in order to obtain a practical inspection time. There is. It is necessary to ensure the resolution of the image acquired at high speed and the SN ratio of the image.
[0006]
  J. Vac. Sci. Tech. B, Vol. 9, No. 6, pp. 3005-3009 (1991), J. Vac. Sci. Tech. B, Vol. 10, No.6, pp. 2804-2808 (1992), and Japanese Patent Laid-Open No. 5-258703 and USP 5,502,306, an electron beam having an electron beam current 100 times or more (10 nA or more) of a normal SEM Irradiates a conductive substrate (X-ray mask, etc.), detects any secondary electrons, reflected electrons, or transmitted electrons generated, and automatically detects defects by comparing and inspecting the image formed from the signals. A method is disclosed.
[0007]
  In addition, as a method of inspecting or observing a circuit board having an insulator with an electron beam, Japanese Patent Application Laid-Open No. 59-155941 and “Electron, Ion Beam Handbook” (Nikkan Kogyo Shimbun) pp622-623 have the effect of charging. In order to reduce this, a method for acquiring a stable image by low-acceleration electron beam irradiation of 2 keV or less is disclosed. Further, Japanese Patent Laid-Open No. 2-15546 discloses a method of irradiating ions from the back of a semiconductor substrate, and Japanese Patent Laid-Open No. 6-338280 discloses that the surface of the semiconductor substrate is irradiated with light to cancel the charge on the insulator. A method is disclosed.
[0008]
  In addition, it is difficult to obtain a high-resolution image due to the space charge effect with an electron beam with a large current and low acceleration. As a method for solving this problem, Japanese Patent Application Laid-Open No. 5-258703 discloses a high resolution just before the sample. A method is disclosed in which an accelerated electron beam is decelerated and irradiated on a sample as a substantially low accelerated electron beam.
[0009]
  As a method for acquiring an electron beam image at a high speed, there is a method of continuously irradiating an electron beam onto a semiconductor wafer on a sample table while continuously moving the sample table, and Japanese Patent Application Laid-Open Nos. 59-160948 and 5- This is disclosed in Japanese Patent No. 258703. In addition, as a secondary electron detector that has been used in conventional SEMs, a scintillator (aluminum-deposited phosphor), a light guide, and a photomultiplier tube are used. Since light emission by the phosphor is detected, the frequency response is poor and it is inappropriate for high-speed electron beam image formation. In order to solve this problem, Japanese Patent Laid-Open No. 5-258703 discloses a detection means using a semiconductor detector as a detection device for detecting a high-frequency secondary electron signal.
[0010]
[Problems to be solved by the invention]
  When a circuit pattern in the manufacturing process of a fine-structured semiconductor device is inspected using the above-described conventional optical inspection method, an optical distance that is optically transmissive material and depends on the optical wavelength and refractive index used for the inspection is sufficient. Residues such as small silicon oxide films and photosensitive resist materials cannot be detected, and it is difficult to detect etching residues that are linear and whose short side width is less than the resolution of the optical system, or non-opening defects of minute conduction holes. Met.
[0011]
  On the other hand, observation and inspection using SEM have the following two problems. One is that the conventional method of forming an electron beam image by SEM requires a very long time. Therefore, when a circuit pattern is inspected over the entire surface of a semiconductor wafer, a very long time is required. Accordingly, it has been necessary to acquire an electron beam image at a very high speed in order to obtain a practical throughput in the manufacturing process of the semiconductor device. In addition, it is necessary to secure the SN ratio of the electron beam image acquired at high speed and to maintain a predetermined accuracy.
[0012]
  Another problem is that when the material constituting the circuit pattern to be inspected is formed of an insulating material such as a photosensitive resist or a silicon oxide film, the insulating material and the conductive material are different. When formed in a mixed manner, it has been difficult to obtain an image having a stable luminance by inspection with an electron beam and to obtain a predetermined inspection accuracy. This is because, when a material is irradiated with an electron beam, secondary electrons are generated from that portion. However, since the irradiated current value is not equal to the secondary electron current value, the material is charged when the inspection object is an insulator. When charging occurs, the secondary electron generation efficiency from that part and the trajectory of the secondary electrons after the generation are affected, and the brightness of the image changes. At the same time, the image reflects the actual circuit pattern shape. Will be distorted. This charged state is sensitive to the irradiation condition of the electron beam, and if the electron beam irradiation speed and irradiation range are changed, the same circuit pattern at the same location will have an image with completely different contrast.
[0013]
  As described in the above prior art, in order to detect defects that cannot be detected by the optical inspection method, an electron beam is irradiated on a conductive substrate in Japanese Patent Application Laid-Open Nos. 59-160948 and 5-258703. As a method for acquiring an image for comparative inspection, a method for inspecting a sample substrate by irradiating a finely focused electron beam at high speed is disclosed. However, this prior art does not describe a method for adjusting the inspection condition for a material such as an insulator. Another conventional technique, Japanese Patent Application Laid-Open No. 59-155941, discloses a technique for observing a substrate having an insulator, by decelerating the primary electron beam applied to the sample substrate and reducing the irradiation energy, for example, 2 keV. The following method is described. However, this conventional technique is a method of continuously irradiating an electron beam on a certain local area and acquiring an image after the local area has been stably charged. It is not suitable for inspecting large areas. In addition, even if the charging in the local region is stable, it is difficult to control another region to be compared to the same charged state, and it is difficult to inspect a wide region such as a semiconductor wafer. .
[0014]
  When a sample is slowly irradiated with a thinly focused electron beam with low electron beam current and signal detection is performed over a long period of time as in conventional SEM, detection per unit pixel is required to obtain the SN ratio required for comparative inspection. The signal detected in time is integrated to obtain an image signal of the unit pixel. As described above, since the state of charging changes with time depending on the irradiation time, the image signal changes during integration, and it is difficult to obtain a stable contrast. As a method for inspecting a circuit board having such an insulating material, the inventors of the present invention have sufficiently shortened the detection time of the secondary electron signal in order to obtain stable contrast, and caused contrast fluctuations due to the above-described processing such as integration. It has been found that there is an effect of eliminating the influence of change with time due to charging. In addition, the present inventors used a thick electron beam of about 50 nm to 10 nm as a sample at a higher speed than the electron beam image based on the contour information of the shape acquired with an electron beam narrowed down to 5 nm to 10 nm as in the conventional SEM. By irradiating and acquiring an image instantly, it was found that a contrast electron beam image generated by the secondary electron generation efficiency of the sample material is more suitable. In this way, an SN ratio that scans a thick electron beam at a high speed as compared with the prior art, acquires an electron beam image of light and dark contrast caused by the material instantly, and this electron beam image can sufficiently cope with the image comparison inspection.ofIt is an object of the present invention to ensure resolution.
[0015]
[Means for Solving the Problems]
  In the present invention,A substrate having a fine circuit pattern such as a semiconductor device often has an insulating material as well as a conductive film. The above-mentioned purpose of detecting a minute defect on a fine pattern at high speed by irradiating a circuit pattern having an insulating material with an electron beam.By the following methodAchievementTo do. That is, the first chip of the semiconductor wafer on which a plurality of chips are formed is scanned with an electron beam so that blanking is performed when swinging back, so that an area corresponding to the first chip is 1 Scanning only once, detecting secondary electrons generated from the first chip by the one-time scanning, forming an electron beam image of the first chip from the detected signal, By scanning the second chip with an electron beam so as to perform blanking when turning back, the region corresponding to the second chip is scanned only once, and the scanning is performed only once. To detect secondary electrons generated from the second chip, form an electron beam image of the second chip from the detected signal, and the electron beam image of the first chip and the second chip. By comparing with the electron beam image of , Inspecting said plurality of chips.
[0016]
  According to the study by the present inventors, when a large amount of electron beam is irradiated non-uniformly on a local region of the substrate surface including an insulator, the contrast varies greatly depending on time and place, but compared with the potential around the region to be inspected on the substrate. Then, when the specimen is irradiated uniformly with the electron beam at the same potential, and the secondary electrons generated in a very short time are detected, an electron beam image with stable contrast can be obtained even with an insulating material. I found out that I can. This is because even in a transient state where the sample is charged by irradiating an electron beam, it is possible to acquire a signal with little fluctuation in the secondary electron generation rate due to time by detecting secondary electrons instantaneously in a very short time. Because. In addition, the present inventors used a thick electron beam of about 50 nm to 10 nm as a sample at a higher speed than the electron beam image based on the contour information of the shape acquired with an electron beam narrowed down to 5 nm to 10 nm as in the conventional SEM. By irradiating and acquiring an image instantaneously, it was found that a contrast electron beam image generated by the secondary electron generation efficiency of the sample material is more suitable for detecting defects. Since the generation efficiency of secondary electrons differs depending on the material and film thickness of the ground pattern and surface pattern on which the circuit pattern is formed, if an electron beam image with a large contrast between the pattern generated by this material and the ground pattern is acquired, the pattern Or it becomes easy to detect the defect of a foundation | substrate. The secondary electron generation efficiency of each material constituting the circuit pattern varies depending on the condition of irradiation with the electron beam. The secondary electron generation efficiency varies depending on the state of charging. Therefore, by optimizing the irradiation conditions or charging conditions that increase the contrast between the surface pattern and the underlying material depending on the material, an electron beam image suitable for detecting defects corresponding to various combinations of materials can be obtained. It becomes possible to form. As a method for this, there is a method of forming an electron beam image by detecting secondary electrons generated by irradiating an electron beam once in a very short time, and depending on the material, the electron beam is irradiated several times and the brightness of the material is reduced. There is a method for detecting secondary electrons generated in a state where the contrast is increased in a very short time. Also, depending on the combination of materials and methods of irradiating an electron beam once or several times, detecting secondary electrons in a very short time while there is little transient change in potential due to charging, and materials There is a method of obtaining an electron beam image by irradiating a sample substrate with an electron beam or other charged particle beam in advance and detecting secondary electrons in a very short time after the charged state is stabilized and the contrast of light and dark is increased. I found out. In both methods, the electron beam is uniformly irradiated to the inspection area in the same potential state, that is, the same charged state as compared with the potential around the substrate inspection area, so that the contrast of the acquired image becomes substantially uniform even in different inspection areas. When the electron beam images are comparatively inspected, fluctuations in contrast do not become false detections.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an inspection method and an apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.
[0018]
(Example 1)
  FIG. 1 shows the configuration of a circuit pattern inspection apparatus 1 according to the first embodiment of the present invention. The circuit pattern inspection apparatus 1 includes an inspection chamber 2 in which the chamber is evacuated, and a preliminary chamber (not shown in the present embodiment) for transporting the sample substrate 9 into the inspection chamber 2. Is configured to be evacuated independently of the examination room 2. The circuit pattern inspection apparatus 1 includes a control unit 6 and an image processing unit 5 in addition to the inspection room 2 and the spare room. The inspection chamber 2 is roughly divided into an electron optical system 3, a secondary electron detection unit 7, a sample chamber 8, and an optical microscope unit 4. The electron optical system 3 includes an electron gun 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 reflecting plate 17, and an ExB deflector 18. ing. Of the secondary electron detector 7, a secondary electron detector 20 is disposed above the objective lens 16 in the examination room 2. The output signal of the secondary electron detector 20 is amplified by a preamplifier 21 installed outside the examination room 2 and converted into digital data by the AD converter 22. The sample chamber 8 includes a sample stage 30, an X stage 31, a Y stage 32, a rotary stage 33, a position monitor length measuring device 34, and a substrate height measuring device 35 to be inspected. The optical microscope section 4 is installed in the vicinity of the electron optical system 3 in the room of the examination room 2 and at a position far away from each other so as not to affect each other, and the distance between the electron optical system 3 and the optical microscope section 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. The image processing unit 5 includes a first image storage unit 46, a second image storage unit 47, a calculation unit 48, and a defect determination unit 49. The captured electron beam image or optical image is displayed on the monitor 50. Operation commands and operation conditions of each part of the apparatus are input / output from the control unit 6. In the control unit 6, conditions such as the acceleration voltage at the time of electron beam generation, the electron beam deflection width, the deflection speed, the signal acquisition timing of the secondary electron detector, the sample stage moving speed, etc. are arbitrarily or arbitrarily selected according to the purpose. It is input so that it can be set. The control unit 6 uses the correction control circuit 43 to monitor the position and height deviation from the signals of the position monitor length measuring device 34 and the inspected substrate height measuring device 35, and generates a correction signal from the result. Then, a correction signal is sent to the objective lens power supply 45 and the scanning deflector 44 so that the electron beam is always applied to the correct position.
[0019]
  In order to obtain an image of the substrate 9 to be inspected, the substrate 9 to be inspected is irradiated with a finely focused electron beam 19 to generate secondary electrons 51, which are scanned by the electron beam 19 and the stages 31, 32. By detecting in synchronization with the movement, an image of the surface of the substrate 9 to be inspected is obtained. As described in the subject of the present invention, in the automatic inspection of the present invention, it is essential that the inspection speed is high. Therefore, unlike an ordinary SEM, an electron beam having an electron beam current of the pA order is scanned at a low speed, and multiple scans and superposition of each image are not performed. Further, in order to suppress charging of the insulating material, it is necessary to scan the electron beam once or several times at a high speed. In this embodiment, therefore, an image is formed by scanning only a large current electron beam of, for example, 100 nA, which is about 100 times or more that of a normal SEM, only once. The scanning width is 100 μm, and one pixel is 0.1 μm^□And one scan was performed in 1 μs.
[0020]
  The electron gun 10 uses a diffusion supply type thermal field emission electron source. By using this electron gun 10, a stable electron beam current can be ensured as compared with a conventional tungsten (W) filament electron source or a cold field emission electron source. An image is obtained. Further, since the electron beam current can be set large by the electron gun 10, high-speed inspection as described later can be realized. The electron beam 19 is extracted from the electron gun 10 by applying a voltage between the electron gun 10 and the extraction electrode 11. The electron beam 19 is accelerated by applying a high negative potential to the electron gun 10. As a result, the electron beam 19 travels in the direction of the sample stage 30 with energy corresponding to the potential, is converged by the condenser lens 12, and is further narrowed down by the objective lens 16 to be XY stages 31, 32 on the sample stage 30. The substrate 9 to be inspected (a substrate having a fine circuit pattern such as a semiconductor wafer, a chip or a liquid crystal or a mask) mounted thereon is irradiated. The blanking deflector 13 is connected to a signal generator 44 for generating a scanning signal and a blanking signal, and the condenser lens 12 and the objective lens 16 are connected to a lens power source 45, respectively. A negative voltage can be applied to the substrate 9 to be inspected by a high voltage power source 36. By adjusting the voltage of the high voltage power source 36, the primary electron beam is decelerated, and the electron beam irradiation energy to the substrate 9 to be inspected can be adjusted to an optimum value without changing the potential of the electron gun 10.
[0021]
  Secondary electrons 51 generated by irradiating the inspection substrate 9 with the electron beam 19 are accelerated by a negative voltage applied to the substrate 9. An ExB deflector 18 is disposed above the substrate 9 to be inspected, and the secondary electrons 51 accelerated thereby are deflected in a predetermined direction. The amount of deflection can be adjusted by the voltage applied to the ExB deflector 18 and the strength of the magnetic field. The electromagnetic field can be varied in conjunction with a negative voltage applied to the sample. The secondary electrons 51 deflected by the ExB deflector 18 collide with the reflecting plate 17 under a predetermined condition. The reflecting plate 17 has a conical shape integrally with a shield pipe of a deflector of an electron beam (hereinafter referred to as a primary electron beam) irradiated on a sample. When the accelerated secondary electrons 51 collide with the reflecting plate 17, second reflecting electrons 52 having energy of several V to 50 eV are generated from the reflecting plate 17.
[0022]
  The secondary electron detector 7 has a secondary electron detector 20 inside the evacuated inspection chamber 2, and a preamplifier 21, an AD converter 22, an optical conversion means 23, a transmission means 24 outside the inspection room 2, It comprises an electric conversion means 25, a high voltage power supply 26, a preamplifier drive power supply 27, an AD converter drive power supply 28, and a reverse bias power supply 29. As already described, the secondary electron detector 20 of the secondary electron detector 7 is disposed above the objective lens 16 in the examination room 2. The secondary electron detector 20, the preamplifier 21, the AD converter 22, the optical conversion means 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 second secondary electrons 52 generated by colliding with the reflecting plate 17 are guided to the detector 20 by this attractive electric field. The secondary electron detector 20 is a second secondary electron 52 generated when the secondary electron 51 generated while the electron beam 19 is irradiated on the substrate 9 to be inspected is then accelerated and collides with the reflecting plate 17. Is detected in conjunction with the scanning timing of the electron beam 19. The output signal of the secondary electron detector 20 is amplified by a preamplifier 21 installed outside the examination room 2 and converted into digital data by the AD converter 22. The AD converter 22 is configured to immediately convert an analog signal detected by the semiconductor detector 20 into a digital signal after being amplified by the preamplifier 21 and transmit the digital signal to the image processing unit 5. Since the detected analog signal is digitized and transmitted immediately after detection, a signal having a higher speed and a higher SN ratio can be obtained.
  A substrate 9 to be inspected is mounted on the XY stages 31 and 32, and a method of scanning the electron beam 19 two-dimensionally with the XY stages 31 and 32 stationary at the time of performing the inspection and an X at the time of performing the inspection. A method of scanning the electron beam 19 in a straight line in the X direction by continuously moving the Y stages 31 and 32 in the Y direction at a constant speed can be selected. When inspecting a specific relatively small area, the former stage is inspected with the stationary stage, and when inspecting a relatively large area, the stage is continuously moved at a constant speed and inspected. It is. When the electron beam 19 needs to be blanked, it can be controlled so that the electron beam 19 is deflected by the blanking deflector 13 so that the electron beam does not pass through the diaphragm 14.
[0023]
  As the position monitor length measuring device 34, a length measuring device based on laser interference is 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. Similarly, data such as the number of rotations of the motors of the X stage 31, the Y stage 32, and the rotary stage 33 is also transferred from each driver to the control unit 6, and the control unit 6 receives these data. It is possible to accurately grasp the area and position where the electron beam 19 is irradiated based on the correction, and the correction control circuit 43 corrects the displacement of the irradiation position of the electron beam 19 in real time as necessary. It has become. In addition, the region irradiated with the electron beam can be stored for each substrate to be inspected.
[0024]
  The optical height measuring device 35 uses an optical measuring device that is a measuring method other than an electron beam, such as a laser interference measuring device or a reflected light measuring device that measures changes at the position of reflected light. The height of the substrate 9 to be inspected mounted on the Y stage 31 or 32 is measured in real time. In this embodiment, the inspected substrate 9 is irradiated with the elongated white light that has passed through the slit through the transparent window, the position of the reflected light is detected by the position detection monitor, and the amount of change in height from the position variation is detected. The calculation method was used. Based on the measurement data of the optical height measuring device 35, the focal length of the objective lens 16 for narrowing down the electron beam 19 is dynamically corrected, and the electron beam 19 always focused on the non-inspection area can be irradiated. It is like that. It is also possible to measure the warpage and height distortion of the inspected substrate 9 before electron beam irradiation, and to set the correction conditions for each inspection area of the objective lens 16 based on the data. It is.
[0025]
  The image processing unit 5 includes a first image storage unit 46, a second image storage unit 47, a calculation unit 48, a defect determination unit 49, and a monitor 50. The image signal of the inspected substrate 9 detected by the secondary electron detector 20 is amplified by a preamplifier 21, digitized by an AD converter 22, converted into an optical signal by an optical converter 23, and an optical fiber 24. And converted into an electric signal again by the electric converter 25 and stored in the first image storage unit 46 or the second storage unit 47. The arithmetic unit 48 performs alignment of the stored image signal with the image signal of the other storage unit, normalization of the signal level, various image processing for removing the noise signal, and compares both image signals. Calculate. The defect determination unit 49 compares the absolute value of the difference image signal calculated by the calculation unit 48 with a predetermined threshold value. If the difference image signal level is larger than the predetermined threshold value, the defect determination unit 49 determines that the pixel is defective. Judge as a candidate and display the position, number of defects, etc. on the monitor 50
  The overall configuration of the circuit pattern inspection apparatus 1 has been described so far, and the configuration and operation of the secondary electron 51 detection means will be described in more detail. When the primary electron beam 19 enters the solid, the primary electron beam 19 enters the inside and excites electrons in the shell at each depth to lose energy. In addition, a phenomenon occurs in which reflected electrons, in which the primary electron beam is scattered backward, proceed toward the surface while exciting the electrons in the solid. Through these multiple processes, the electrons in the shell cross the surface barrier and become secondary electrons from the solid surface and exit into the vacuum with energy of several V to 50 eV. The shallower the angle formed between the primary electron beam and the solid surface, the smaller the ratio between the distance of the primary electron beam and the distance from the position to the solid surface, and secondary electrons are more likely to be emitted from the surface. Therefore, the generation of secondary electrons depends on the angle between the primary electron beam and the solid surface, and the amount of secondary electron generation is information indicating the unevenness and material of the sample surface.
[0026]
  FIG. 2 shows a main configuration diagram of the electron optical system 3 for detecting the secondary electrons 51 and the secondary electron detector 7. The primary electron beam 19 is irradiated onto the sample substrate 9 to generate secondary electrons 51 on the surface of the sample substrate 9. The secondary electrons 51 are accelerated by a negative high voltage applied to the sample substrate 9. In this example, the negative voltage applied to the sample substrate 9 was set to 3.5 keV. The secondary electrons 51 are accelerated, converged and deflected by the objective lens 16 and the ExB deflector 18, and collide with the reflecting plate 17. The reflector 17 has a conical shape with a taper of 30 degrees integrated with a shield pipe for preventing the voltage applied to the detector from affecting the primary electron beam. The material is CuBeO, which has a secondary electron multiplication effect as a structure that emits secondary electrons about 5 times the number of irradiated electrons on average. When the accelerated secondary electrons 51 collide, second secondary electrons 52 having energy of several V to 50 eV are generated from the reflector 17. The second secondary electrons 52 are attracted to the front surface of the secondary electron detector 20 by the attraction electric field generated by the secondary electron detector 20 and the suction electrode 53 attached to the secondary electron detector 20. In this embodiment, the secondary electrons 51 generated on the surface of the sample substrate 9 are deflected by the ExB deflector 18 to the secondary electron detector 20 side by about 5 degrees, so the voltage and magnetic field applied to the ExB deflector 18, The electrode spacing is 35 V and 1.0 × 10 respectively when the negative high voltage applied to the sample substrate 9 is 3.5 keV.^-6The condition was T (Tesla), 10 mm. This electromagnetic field can be variably set in conjunction with a negative high voltage applied to the sample substrate 9. With the above configuration and conditions, secondary electrons 51 generated on the surface of the sample substrate 9 due to small angle deflection of about ~ 5 degrees, acceleration by -3.5 keV voltage applied to the sample substrate 9, and convergence by the objective lens are ExB When passing through the deflector 18, 95% or more can pass, and the reflector 17 multiplies the 95% secondary electrons 51 by about 5 times to generate the second secondary electrons 52. We were able to.
[0027]
  As the secondary electron detector 20, a PIN type semiconductor detector is used in this embodiment. PIN type semiconductor detectors are faster in response than normal PN type semiconductor detectors, and can detect high-frequency secondary electron signals with a sampling frequency of ~ 100MHz by applying a reverse bias voltage from a reverse bias voltage power supply. did it. The PIN-type semiconductor detector 20 and the preamplifier 21, AD converter 22, and light converting means 23, which are detection circuits, were floated to 6 keV, and the suction electrode 53 was set to 0V. The effective size of PIN type semiconductor detector 20 is 4mm.^□It is. The second secondary electrons 52 generated in the reflector 17 are attracted to the PIN semiconductor detector 20 by the attractive electric field, enter the PIN semiconductor detector 20 in a high energy state, and have a constant energy in the surface layer. After disappearing, electron-hole pairs are generated and converted into electric signals as current. The PIN type semiconductor detector 20 used in this example has a very high signal detection sensitivity, and considering the energy loss in the surface layer, the second secondary electron 52 incident upon being accelerated to 6 keV by the attractive electric field is The electric signal is amplified about 1000 times. This electric signal is further amplified by the preamplifier 21, and this amplified signal (analog signal) is converted into a digital signal by the AD converter 22. Here, a 12-bit AD converter 22 having a clock frequency of 100 MHz was used. Then, the output of the AD converter 22 was provided with an optical conversion means 23, a transmission means 24, and an electrical conversion means 25 for each bit, and transmitted in parallel. According to this configuration, each transmission means only needs to have the same transmission speed as the clock frequency of the AD converter 22. Now, the signal converted into the optical digital signal by the optical conversion means 23 is transmitted to the electrical conversion means 25 by the optical transmission means 24, where it is converted again from the optical digital signal to the electrical signal and sent to the image processing unit 5. . The reason for the transmission after the conversion to the optical signal is that the components from the PIN type semiconductor detector 20 to the optical conversion means 23 are floated to a positive high potential by the high voltage power supply 26. The configuration of the embodiment can convert a high potential level signal into a ground level signal. In this embodiment, the light converting means 23 converts a light emitting element that converts an electrical signal into an optical signal, the transmission means 24 converts an optical fiber cable that transmits the optical signal, and the electrical converting means 25 converts the optical signal into an electrical signal. A light receiving element was used. Since the optical fiber cable is made of a highly insulating material, a high potential level signal can be easily converted to a ground potential level signal. Further, since digital signals are optically transmitted, there is no signal degradation at the time of optical transmission. As a result, it is possible to obtain an image with less influence of noise as compared with a conventional technique for optically transmitting an analog signal. With these configurations, when the incident current of the second secondary electrons 52 to the PIN semiconductor detector 20 is 100 nA, a high-frequency secondary electron signal with a sampling frequency of 100 MHz can be detected with a signal SN ratio of 50 or more. I can do it now.
[0028]
  In the above embodiment, the semiconductor detector 20 is applied with the reverse bias voltage by the reverse bias voltage power supply 29, but may be configured not to apply the reverse bias voltage. In this embodiment, a PIN type semiconductor detector is used as the semiconductor detector 20, but other types of semiconductor detectors such as a Schottky type semiconductor detector and an avalanche type semiconductor detector may be used. Further, MCP (microchannel plate) can be used as a detector if conditions such as responsiveness and sensitivity are satisfied.
[0029]
  Next, the operation when the circuit pattern inspection apparatus 1 inspects a semiconductor wafer subjected to pattern processing in the manufacturing process as the sample 9 to be inspected will be described. First, although not shown in FIG. 1, the semiconductor wafer is loaded into the sample exchange chamber by the transfer means of the semiconductor wafer 9. Therefore, the semiconductor wafer 9 is mounted on the sample holder, held and fixed, evacuated, and transferred to the inspection chamber 2 for inspection when the sample exchange chamber reaches a certain degree of vacuum. In the examination room 2, the sample holder is placed on the sample stage 30, the XY stages 31, 32, and the rotary stage 33, and is held and fixed. The set semiconductor wafer 9 is arranged at predetermined first coordinates under the optical microscope unit 4 by moving the X-Y stages 31 and 32 in the X and Y directions based on predetermined inspection conditions registered in advance. An optical microscope image of the circuit pattern formed on the semiconductor wafer 9 is observed by the monitor 50 and compared with an equivalent circuit pattern image at the same position stored in advance for position rotation correction, and the position of the first coordinate A correction value is calculated. Next, the circuit moves to a second coordinate where a circuit pattern equivalent to the first coordinate exists at a certain distance from the first coordinate, and an optical microscope image is similarly observed, and the circuit stored for position rotation correction is stored. Compared with the pattern image, the position correction value of the second coordinate and the rotational deviation amount with respect to the first coordinate are calculated. The rotation stage 33 rotates by the calculated rotation deviation amount, and the rotation amount is corrected. In this embodiment, the rotational deviation amount is corrected by the rotation of the rotary stage 33. However, the rotational deviation can be corrected by a method of correcting the scanning deflection position of the electron beam based on the calculated rotational deviation amount without the rotary stage 33. . In this optical microscope image observation, a circuit pattern that can be observed not only with an optical microscope image but also with an electron beam image is selected. Also, for future position correction, the first coordinate, the amount of displacement of the first circuit pattern by optical microscope image observation, the second coordinate, the amount of displacement of the second circuit pattern by optical microscope image observation Stored and transferred to the control unit 6.
[0030]
  Furthermore, an image obtained by an optical microscope is used to observe the circuit pattern formed on the semiconductor wafer 9 to be inspected, and the position of the circuit pattern on the semiconductor wafer 9 and the distance between the chips, or the memory cell The repeated pitch of the repeated pattern is measured in advance, and the measured value is input to the control unit 6. Further, the chip to be inspected on the semiconductor wafer 9 to be inspected and the area to be inspected in the chip are set from the image of the optical microscope, and input to the control unit 6 in the same manner as described above. The image of the optical microscope can be observed at a relatively low magnification, and when the surface of the semiconductor wafer 9 to be inspected is covered with, for example, a silicon oxide film, it can be transmitted through to the ground and observed. This is because the arrangement of the chips and the layout of the circuit patterns in the chips can be easily observed, and the inspection area can be easily set.
[0031]
  When the preparatory work such as predetermined correction work and inspection area setting by the optical microscope unit 4 is completed as described above, the semiconductor wafer 9 is moved under the electron optical system 3 by the movement of the X stage 31 and the Y stage 32. The When the semiconductor wafer 9 is disposed under the electron optical system 3, the correction work performed by the optical microscope unit 4 and the work similar to the setting of the inspection area are performed using the electron beam image. Acquisition of the electron beam image at this time is performed by the following method. Based on the coordinate values stored and corrected in the alignment using the optical microscope image, the electron beam 19 is scanned two-dimensionally in the XY direction by the scanning deflector 44 in the same circuit pattern as observed by the optical microscope unit 4. Is irradiated. By the two-dimensional scanning of the electron beam, the secondary electrons 51 generated from the site to be observed are detected by the configuration and operation of each part for detecting the secondary electrons, thereby obtaining an electron beam image. 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, so the resolution and resolution are higher than optical images, and high-precision alignment and position correction are possible. Rotation correction can be performed. When the sample 9 is irradiated with the electron beam 19, the portion is charged. In order to avoid the influence of the charging during the inspection, the circuit pattern for irradiating the electron beam 19 in the pre-inspection preparatory work such as position rotation correction or inspection area setting is selected in advance as the circuit pattern existing outside the inspection area. Alternatively, an equivalent circuit pattern in a chip other than the chip to be inspected can be automatically selected from the control unit 6. As a result, the inspection image is not affected by the irradiation with the electron beam 19 by the pre-inspection preparatory work at the time of inspection.
[0032]
  Next, an inspection is performed. The conditions of the electron beam 19 applied to the semiconductor wafer 9 to be inspected at the time of inspection were obtained by the following method. First, in general, the SN ratio in an electron beam image has a correlation with the square root of the number S of irradiated electrons per unit pixel of the electron beam irradiated on the sample. When comparing and inspecting images, the SN ratio of the electron beam image needs to be a value that can detect the signal amount of the normal part and the defective part, and the minimum SN ratio needs to be 10 or more, preferably 50 or more is required. As described above, the S / N ratio of the electron beam image has a correlation with the square root of the number of irradiation electrons S per unit pixel of the electron beam irradiated on the sample. Therefore, in order to obtain the S / N ratio of 10, at least 100 per single pixel. More than one electron is required, and in order to obtain an SN ratio of 50, at least 2500 electrons must be irradiated.
[0033]
The main purpose of applying the circuit pattern inspection method of the present invention is to detect a minute defect that cannot be detected by the optical pattern inspection method as described above. That is, the difference between images in a minute pixel is detected. It was necessary to recognize. In order to achieve this, in this embodiment, the pixel size is set to 0.1 μm. Therefore, from the minimum required number of electrons per single pixel and the above pixel size, the required electron beam dose per unit area is 0.16 μC / cm²Preferably 4μC / cm²It becomes. If we try to obtain this amount of electron irradiation with the electron beam current of ordinary SEM (several pA to several hundreds pA), for example, 1 cm with an electron beam current of 20 pA²0.16μC / cm in the area²It takes 8000 seconds to irradiate 4 electrons, and 4μC / cm²It takes 200,000 seconds to irradiate the electrons. However, the required inspection speed for inspection of circuit patterns, for example, inspection of semiconductor wafers is 600 s / cm.²Below, preferably 300s / cm²If the inspection time is longer than this, the practicality of inspection becomes extremely low in semiconductor manufacturing. Therefore, in order to satisfy these conditions and irradiate the sample with the necessary electron beam within a practical inspection time, the electron beam current must be at least 270 pA (1.6 μC / cm², 600s / cm²) Or more, preferably 13nA (4μC / cm², 300s / cm²) It is necessary to set above. Therefore, in the circuit pattern inspection method of this embodiment, an electron beam image is formed by a single scan using a high-current electron beam of 13 nA or more.
[0034]
And, it is necessary from the point of inspection speed to form an electron beam image by a single scan using an electron beam of about 100 times larger current (270 nA or more, preferably 13 nA or more) compared with a normal SEM. In addition to the above, it has been found by the present invention that the underlying film or surface pattern is particularly necessary for inspecting a circuit pattern formed of an insulating material for the following reasons.
[0035]
  When an electron beam image of a circuit pattern having an insulating material is acquired by a normal SEM, an electron beam image different from the actual shape is obtained due to the effect of charging, and the contrast is often completely different depending on the field magnification. This is because the weak electron beam current (several pA to several hundred pA) is repeatedly scanned locally or when the field magnification is changed, the electron dose exceeds the electron dose required for image formation for focus and astigmatism correction. This is because by locally scanning the electron beam, the electron beam irradiation amount is concentrated and irradiated at one place, and the charging of the portion becomes uneven. As a result, since the quality of the electron beam image of the pattern formed of the insulating material is completely different depending on the field of view, such an image cannot be applied to the inspection for comparing the electron beam images. Therefore, a circuit pattern having an insulating material can be inspected in the same manner as a circuit pattern made of a conductive material, so that a single scan is performed using a high-current electron beam that is approximately 100 times more than a normal SEM. An electron beam image was formed. That is, in this example, the electron beam irradiation amount to the sample per unit area and per unit time is constant, and the electron dose necessary to form an image quality sufficient to perform a comparative inspection, The electron beam image was acquired by scanning the electron beam once at a scanning speed suitable for the practicality of the inspection method for a semiconductor wafer or the like. Then, as described above, an electron beam image of a circuit pattern having an insulating material was obtained by a single scan using a high-current electron beam about 100 times or more compared to a normal SEM. It is confirmed that the charge amount and image contrast differ depending on the material and structure of the various circuit patterns that make up the circuit, and that similar image contrast can be obtained between equivalent patterns of the same type of material.
I confirmed. Although scanning with a high-current electron beam is performed only once in the present embodiment, there may be several scans within a range in which the above-described operation is substantially realized.
[0036]
  3 (a), 3 (b), and 3 (c) schematically show the efficiency of secondary electron generation and the degree of charging when an electron beam is applied to a point P on the sample. In FIG. 3A, the vertical axis indicates the relative intensity of the primary electron beam irradiated on the sample, and the horizontal axis indicates time and distance. In FIG. 3B, the vertical axis represents the relative degree of charging of the sample, and the horizontal axis represents time. In FIG. 3C, the vertical axis indicates the relative amount of secondary electrons generated, and the horizontal axis indicates time. When the sample is irradiated with an electron beam by the inspection method of the present invention described so far, the electron beam scans and passes through the point P at high speed. A portion having a relatively high intensity of the electron beam passes through the point P during 10 ns. In this embodiment, since the scanning speed of the electron beam is set to 100 MHz / pixel, this 10 ns corresponds to one pixel. In this embodiment, one pixel is 0.1 μm.^□Therefore, this 10 ns corresponds to 0.1 μm. At the upper point P of the sample, when the sample is irradiated with an electron beam at the timing shown in FIG. 3A, the sample is charged as shown in FIG. The degree of charging and the degree of discharge over time vary depending on the material of the sample. In the case where the sample is an insulator, the charge remains even after the electron beam passes, and there are some samples that do not discharge unless a long time has passed. As shown in FIG. 3C, secondary electrons are generated from the moment when the primary electron beam is irradiated onto the sample. Since the amount of secondary electrons generated depends on the secondary electron generation efficiency determined for each material and the degree of charging shown in FIG. 3B, for example, the second scan shown in FIG. When the amount of secondary electrons is generated and the degree of charging in the second scan is different from that in the first time, the amount of secondary electrons generated is also different.
[0037]
  Next, irradiation conditions that affect the contrast of the electron beam image will be described. The contrast of the electron beam image is formed by the amount of secondary electrons generated and detected by the electron beam irradiated on the sample. For example, the difference in brightness is caused by the difference in the amount of secondary electrons generated due to the difference in materials. . 4A and 4B are graphs showing the influence of the electron beam irradiation condition on the contrast, FIG. 4A shows the case where the irradiation condition is appropriate, and FIG. 4B shows the irradiation condition. Indicates an inappropriate case. The vertical axis represents the degree of charging having a large correlation with the brightness of the image, and the horizontal axis represents the electron beam irradiation time. A solid line A indicates a case where a photoresist is used for the sample, and a dotted line B indicates a case where a wiring material is used for the sample.
[0038]
  As shown in FIG. 4A, in the time region C in which the irradiation time is short, the brightness fluctuation of each material is small, and in the time region D in which the irradiation time is relatively large, the change in the brightness due to the irradiation time becomes large. In particular, in the time region E in which the irradiation time is long, the brightness fluctuation due to the irradiation time again decreases. Further, as shown in FIG. 4B, when the irradiation condition is not appropriate, even in the time region C where the irradiation time is short, the brightness fluctuation with respect to the irradiation time is large, and it is difficult to obtain a stable image. Therefore, in order to acquire a high-speed and stable electron beam image, it is important to acquire the image under the irradiation conditions shown in FIG.
[0039]
  Examples of the irradiation condition of the electron beam to the sample include an electron beam irradiation amount per unit area, an electron beam current value, an electron beam scanning speed, and an electron beam irradiation energy applied to the sample. Therefore, it is necessary to obtain optimum values for these parameters for each shape and material of the circuit pattern. For this purpose, it is necessary to freely adjust and control the irradiation energy of the electron beam applied to the sample. Therefore, as described above, in this embodiment, a negative voltage for decelerating primary electrons is applied to the semiconductor wafer 9 as a sample by the high voltage power source 36, and the irradiation energy of the electron beam 19 is appropriately adjusted by adjusting this voltage. It is configured to be adjustable. As a result, when the acceleration voltage applied to the electron gun 10 is changed, the axis change of the electron beam 19 occurs and various adjustments are required. In the present embodiment, the same adjustment is made without performing such adjustments. An effect can be obtained.
[0040]
  Next, a scanning method of the electron beam 19 for forming an electron beam image for performing the inspection of the present invention will be described. In a normal SEM, an electron beam is scanned two-dimensionally with a stage stationary, and an image of a certain area is formed. According to this method, when inspecting the entire wide area, in addition to the time required to scan and scan the electron beam for each image acquisition area, the time obtained by adding stage acceleration / deceleration / position settling as the movement time It takes. Therefore, it takes a long time for the entire inspection time. Therefore, in the present invention, while moving the stage continuously in one direction at a constant speed, the electron beam is scanned in one direction at a high speed in a direction orthogonal to or intersecting the stage moving direction, thereby The acquired inspection method was used. Thereby, the electron beam acquisition time for one scanning width of the predetermined distance is only the time for the stage to move the predetermined distance.
[0041]
  FIG. 5A shows an example of a method in which the electron beam 19 scans when the Y stage 32 moves continuously at a constant speed in the Y direction by the above method. When scanning the electron beam 19 by the scanning deflector 44, the semiconductor wafer 9 as a sample is irradiated with the electron beam only in one direction indicated by the solid line, and the semiconductor wafer 9 is irradiated during the back-turning of the electron beam indicated by the broken line. By blanking so that the electron beam 19 is not irradiated, the electron beam can be uniformly and spatially irradiated on the semiconductor wafer 9. Blanking is performed by deflecting the electron beam 19 by the blanking deflector 13 so that it does not pass through the diaphragm 14.
[0042]
  FIG. 5B shows a method in which the electron beam 19 reciprocates at a constant speed as an example of another scanning method. When the electron beam 19 is scanned from one end to the other end at a constant speed, the XY stages 31 and 32 are sent by one pitch, and the electron beam is scanned in the opposite direction to the original end at a constant speed. In the case of this method, the time for returning the electron beam can be omitted.
[0043]
  The area or position where the electron beam is irradiated is detailed by measuring data from the position monitor length measuring device 34 installed on the XY stages 31 and 32 to the control unit 6 every moment. To be grasped. In this embodiment, a laser interferometer is employed. Similarly, the variation in the height of the region or position irradiated with the electron beam 19 is grasped in detail by measuring data from the optical height measuring device 35 being transferred to the control unit 6 every moment. Based on these data, deviations in the electron beam irradiation position and focus position are calculated, and these deviations are automatically corrected by the correction control circuit 43. Therefore, a highly accurate and precise electron beam operation method is ensured.
[0044]
  By the electron beam 19 scanning method described above, the entire surface of the semiconductor wafer 9 as a sample or a predetermined inspection region is irradiated with an electron beam, and secondary electrons 51 are generated according to the above-described principle. 51 and 52 are detected. A good-quality image can be obtained by the configuration and operation of the above-described units. For example, by irradiating the reflector 17 with the above-described configuration and method, a secondary electron multiplication effect of about 20 times can be obtained, and the influence of aberration on the primary electron beam can be suppressed more than the conventional method. Can do. Further, by adjusting the electromagnetic field applied to the ExB deflector with the same configuration, the second secondary obtained by irradiating the reflector 17 with the reflected electrons generated from the surface of the semiconductor wafer 9 in the same manner as the secondary electrons. The electrons 52 can be easily detected. Further, by adjusting and controlling the electric field and magnetic field of the ExB deflector 18 in conjunction with the negative high voltage applied to the sample, secondary electrons can be detected efficiently even under irradiation conditions that differ from sample to sample. In addition, by detecting the secondary electrons using the semiconductor detector 20, digitizing the detected image signal immediately after detection, and then transmitting the light, the effect of noise generated in various conversions / transmissions is reduced, and SN Image signal data with a high ratio can be obtained. In the process of forming an electron beam image from the detected signal, the image processing unit 5 applies a detection signal corresponding to the time to the desired pixel at the electron beam irradiation position designated by the control unit 6 according to the signal level. The brightness gradation value is sequentially stored in the first storage unit 46 or the second storage unit 47. By associating the electron beam irradiation position with the amount of secondary electrons associated with the detection time, an electron beam image of the sample circuit pattern is formed two-dimensionally. In this way, a high-quality electron beam image with high accuracy and high SN ratio can be acquired. In this embodiment, an inspection method and apparatus for detecting secondary electrons generated from a sample have been described. However, backscattered electrons and reflected electrons are generated simultaneously with secondary electrons from the sample. These secondary charged particles as well as secondary electrons can be detected as electron beam image signals in the same manner.
[0045]
  When the image signal is transferred to the image processing unit 5, the electron beam image of the first region is stored in the first storage unit 46. The calculation unit 48 performs alignment of the stored image signal with the image signal of the other storage unit, normalization of the signal level, and various image processing for removing the noise signal. Subsequently, the electron beam image of the second region is stored in the second storage unit 47, and the same circuit pattern is used for the electron beam image of the second region and the first electron beam image while performing the same calculation process. And the image signal of the place is compared and calculated. The defect determination unit 49 compares the absolute value of the difference image signal calculated by the calculation unit 48 with a predetermined threshold value. If the difference image signal level is larger than the predetermined threshold value, the defect determination unit 49 determines that the pixel is defective. The candidate is determined, and the position, the number of defects, and the like are displayed on the monitor 50. Next, an electron beam image of the third region is stored in the first storage unit 46, and stored in the second storage unit 47 in advance while performing the same calculation.
It is compared with the electron beam image in the second region, and a defect is determined. Thereafter, by repeating this operation, image processing is executed for all inspection regions.
[0046]
  By obtaining a high-accuracy and high-quality electron beam image by the above-described inspection method and performing a comparative inspection, it is possible to detect a minute defect generated on a fine circuit pattern in an inspection time according to practicality. In addition, by acquiring an image using an electron beam, light is transmitted by the optical pattern inspection method, and a pattern formed of a silicon oxide film or a resist film, which cannot be inspected, and foreign matter / defects of these materials are detected. Can be inspected. Furthermore, even when the material forming the circuit pattern is an insulator, the inspection can be performed stably.
[0047]
(Example 2)
  In this embodiment, an application example in which a semiconductor wafer is inspected using the circuit pattern inspection apparatus 1 and method of the present invention will be described. FIG. 6 shows a semiconductor device manufacturing process. As shown in FIG. 6, the semiconductor device repeats a number of pattern forming steps. The pattern forming process is roughly composed of steps of film formation, photosensitive resist application, photosensitivity, development, etching, resist removal, and cleaning. If the manufacturing conditions for processing are not optimized in each step, the circuit pattern of the semiconductor device formed on the substrate cannot be formed normally. FIG. 7A and FIG. 7B schematically show circuit patterns formed on the semiconductor wafer in the manufacturing process. FIG. 7A shows a normally processed circuit pattern, and FIG. 7B shows a pattern in which a processing defect has occurred. For example, when an abnormality occurs in the film forming process of FIG. 6, particles are generated and adhere to the surface of the semiconductor wafer, resulting in an isolated defect or the like in FIG. Also, if the conditions such as the focus of the exposure apparatus for exposure and the exposure time are not optimal at the time of exposure, there are places where the amount or intensity of the light irradiated by the resist is excessive or insufficient, and FIG. It becomes short inside, disconnection, and pattern thinning. If there is a defect in the mask / reticle at the time of exposure, the same pattern shape abnormality occurs at the same location for each shot which is a photosensitive unit. In addition, when the etching amount is not optimized and a thin film or particles generated during the etching, a short circuit, a protrusion, an isolated defect, an opening defect, or the like occurs. At the time of cleaning, fine particles are generated due to dirt on the cleaning layer, detached film, and reattachment of foreign matter, and the thickness of the oxide film is likely to be uneven on the surface due to water draining conditions during drying.
[0048]
  Therefore, by applying the circuit pattern inspection method and the apparatus 1 of the first embodiment to the semiconductor device manufacturing process, the occurrence of abnormality can be detected with high accuracy and at an early stage, and countermeasures for abnormality can be taken in the process. This makes it possible to optimize the processing conditions so that these defects do not occur. For example, when a circuit pattern inspection process is performed after the development process, and a defect or disconnection in the photoresist pattern is detected, it is estimated that the exposure condition or focus condition of the exposure apparatus in the photosensitive process is not optimal, and the focus condition Alternatively, these conditions are immediately improved by adjusting the exposure amount. In addition, by examining the defect distribution to determine whether or not these defects are common to each shot, defects in the photomask / reticle used for pattern formation are estimated, and inspection / replacement of the photomask / reticle is performed. Will be implemented as soon as possible. The same applies to other processes, and by applying the circuit pattern inspection method and apparatus of the present invention and carrying out the inspection process, various defects are detected, and abnormalities in each manufacturing process are detected depending on the contents of the detected defects. The cause is presumed.
[0049]
  In this way, by implementing the circuit pattern inspection method and the apparatus 1 in-line in the semiconductor device manufacturing process, it is possible to detect variations in various manufacturing conditions and occurrences of abnormalities within the inspection real time, so a large number of defects are generated. It can be prevented in advance. In addition, by applying the circuit pattern inspection method and apparatus, the non-defective product acquisition rate of the entire semiconductor device can be predicted from the degree and occurrence frequency of detected defects, and the productivity of the semiconductor device can be improved. become.
[0050]
(Example 3)
  In the third embodiment of the present invention, as shown in FIG. 8, the objective lens 16 in the electron optical system 3 is installed above the secondary electron detector 20, and the configuration of the other inspection devices is the same as that of the first embodiment. The configuration was the same as the example. FIG. 8 shows an enlarged partial view of the inside of the inspection room 2 of this circuit pattern inspection apparatus. The operation of the configuration of the third embodiment will be described below. The sample substrate 9 is irradiated with the electron beam 19 by the same method as in the first embodiment. A negative high voltage is applied to the sample substrate 9 as in the first embodiment. In this example, the negative voltage for primary electron deceleration applied to the sample substrate 9 was set to -3.5 keV. Due to the electron beam irradiation, secondary electrons 51 are generated from the surface of the sample substrate 9 by the action described above. Since the secondary electrons 51 generated on the surface of the sample substrate 9 are rapidly accelerated to 3.5 keV by the negative voltage applied to the sample substrate 9, the directions of the secondary electrons 51 generated on the substrate surface 9 are aligned. Since the spread of the accelerated secondary electrons 51 when colliding with the reflector 17 is as small as several millimeters, the detection efficiency does not decrease even if the secondary electrons 51 are not converged by the objective lens 16. Therefore, even in the configuration of the present embodiment in which the objective lens 16 is disposed at a position where only the primary electron beam 19 is converged, the second secondary electrons 52 generated by the collision of the accelerated secondary electrons 51 with the reflecting plate 17 are generated. Since it can be detected and converted into a signal with high efficiency, a high-quality electron beam image can be acquired. According to this embodiment, the focal length of the objective lens 16 is longer than that of the first embodiment. As a result, even if the primary electron beam 19 is largely deflected compared to the first embodiment, the resolution or Accuracy can be maintained. Other configurations and operations are the same as those in the first embodiment, and are omitted here.
[0051]
(Example 4)
  In the fourth embodiment, the shape of the reflector 17 is curved, and the others are configured in the same manner as in the first embodiment. FIG. 9 is an enlarged partial view showing the structure of the reflecting plate portion. In this embodiment, since the shape of the reflector 17 integrated with the shield pipe is curved, the electron beam 19 is irradiated to the sample substrate 9, and the secondary electrons 51 generated on the surface of the sample substrate 9 are Accelerated by the negative high voltage applied to, deflected by the ExB deflector 18, and when irradiating the reflector 17, the angle at which the second secondary electrons 52 are generated changes depending on the position of the reflector 17 As a result, the semiconductor detector 20 can easily capture the second secondary electrons 52 generated at any location on the reflector 17. Accordingly, when the secondary electrons 51 accelerated by the ExB deflector 18 are deflected, the selection range of the deflection angle is widened and the generation angle of the secondary electrons 51 generated on the surface of the sample substrate 9 is high. Since a signal can be detected efficiently, a high-quality electron beam image can be obtained. Other configurations and operations are the same as those in the first embodiment, and are omitted here.
[0052]
(Example 5)
  As a fifth embodiment, there is provided a method and apparatus for inspecting a sample substrate by irradiating a second charged particle beam to charge the substrate to be inspected and stabilizing the potential of a member forming a circuit pattern of the substrate to be inspected. The configuration will be described below.
[0053]
  FIG. 10 shows the configuration of the circuit pattern inspection apparatus 1 of the fifth embodiment. The circuit pattern inspection apparatus 1 includes an inspection chamber 2 in which the chamber is evacuated, a first preliminary chamber (not shown in the present embodiment) for transporting a sample into the inspection chamber 2, and a second charged particle A second preliminary chamber 100 for irradiating a line, a control unit 6, and an image processing unit 5. The first preliminary chamber (not shown) and the second preliminary chamber 100 are Are configured to be evacuated independently. The second preliminary chamber 100 includes an electron gun 101, a lens 102, and a large angle deflection coil 103. The inspection chamber 2 is roughly divided into an electron optical system 3, a secondary electron detection unit 7, a sample chamber 8, and an optical microscope (not shown). The electron optical system 3 includes an electron gun 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 reflecting plate 17, and an ExB deflector 18. ing. Of the secondary electron detector 7, a secondary electron detector 20 is disposed above the objective lens 16 in the examination room 2. The output signal of the secondary electron detector 20 is amplified by a preamplifier 21 installed outside the examination room 2 and converted into digital data by the AD converter 22. The sample chamber 8 includes a sample stage 30, XY stages 31 and 32, a rotary stage 33, a position monitor length measuring device 34, and a substrate height measuring device 35 to be inspected. The optical microscope (not shown) is installed in the vicinity of the electron optical system 3 in the examination room 2 and at a position that is not far apart from each other, and the distance between the electron optical system 3 and the optical microscope. Is known. The captured electron beam image or optical image is displayed on the monitor 50. Operation commands and operation conditions of each part of the apparatus are input / output from the control unit 6. In the control unit 6, conditions such as the acceleration voltage at the time of electron beam generation, the electron beam deflection width, the deflection speed, the signal acquisition timing of the secondary electron detector, the sample stage moving speed, etc. are arbitrarily or arbitrarily selected according to the purpose. It is input so that it can be set. The control unit 6 uses the correction control circuit 43 to monitor the position and height deviation from the signals of the position monitor length measuring device 34 and the inspected substrate height measuring device 35, and generates a correction signal from the result. Then, a correction signal is sent to the objective lens power supply 45 and the scanning deflector 44 so that the electron beam 19 is always irradiated to the correct position. The image processing unit 5 includes image storage units 46 and 47, a calculation unit 48, and a defect determination unit 49. The electron beam image signal detected by the secondary electron detection unit 7 is stored in the image storage unit, subjected to various calculations, compared with other adjacent electron beam images, and only defective portions are extracted.
[0054]
  Hereinafter, the second preliminary chamber 100 will be described in detail. The electron gun 101 and the lens 102 installed in the preliminary chamber 100 are in the vicinity of the electron optical system 3 in the examination room 2 but far enough so as not to affect each other. The substrate to be inspected 9 is loaded into a first preliminary chamber (not shown) which is a sample exchange chamber by the substrate transport means. Therefore, the substrate to be inspected is mounted on the sample holder, held and fixed, and then evacuated. When the first preliminary chamber, ie, the sample exchange chamber, reaches a certain degree of vacuum, the substrate to be inspected together with the sample holder is in the second preliminary chamber. Transferred to chamber 100. The second preliminary chamber 100 is evacuated in advance. In the second preliminary chamber 100, a preliminary irradiation electron beam 104 is irradiated onto the substrate 9 to be inspected from the electron gun 101. The electron gun 101 having a large light source and a large current is suitable. In this embodiment, an oxide cathode that emits thermoelectrons by heating a low work function oxide used in a CRT monitor with a heater is used. It was. The electron lens 102 is installed to limit the irradiation area of the preliminary irradiation electron beam 104 from the electron gun 101 to some extent, and the preliminary irradiation electron beam 104 has a diameter of several centimeters to several millimeters on the substrate 9 to be inspected. It can be narrowed down to. The large-angle deflector 103 is capable of deflecting at a very wide angle as used in a CRT monitor such as a television, and the deflector 103 allows the substrate to be inspected to be a semiconductor wafer, such as 8 inches or 12 inches. Even with the above size, the preliminary irradiation electron beam 104 can be scanned on the substrate 9 to be inspected to every corner of the sample. At this time, the current of the pre-irradiation electron beam 104, the number of scans, and the scan speed are kept constant so that the electron beam dose is uniform in terms of time and space. The irradiation energy of the preliminary irradiation electron beam 104 in the preliminary chamber 100 is the same as the irradiation energy of the electron beam 19 irradiated in the inspection chamber 2 inspection electron optical system 3. During the irradiation of the electron beam 104 in the second preliminary chamber 100 described here, another substrate 9 ′ to be inspected is set in the adjacent inspection chamber 2, and the inspection is executed by the electron beam 19 from the electron gun 10. ing. In other words, the examination room 2 and the second spare room 100 can be operated independently. Since the irradiation of the preliminary irradiation electron beam 104 in the second preliminary chamber 100 can be processed in a time sufficiently shorter than the time required for the inspection, the pretreatment of the substrate 9 to be inspected in the second preliminary chamber 100 is performed. Even if it is performed, the time required for the entire examination is hardly increased.
[0055]
  By irradiating the inspection target substrate 9 with the preliminary electron beam 104, the inspection target substrate 9 is charged. As already described in the first embodiment, the charged state of the substrate 9 to be inspected changes depending on the time and energy of electron beam irradiation, and as a result, the contrast of the image changes. FIG. 11A and FIG. 11B show the influence of electron beam irradiation time on contrast. FIG. 11A shows the case where the photoresist (solid line A) and the wiring material (dotted line B) shown in FIG. 4A are used, and FIG. 11B shows the case where the photoresist (solid line A) is used for the sample. The case where a silicon oxide film (dotted line C) is used is shown. In the region F where the irradiation time is short, the brightness variation of each material is small, in the time region G where the irradiation time is relatively long, the change in brightness due to time is largely unstable, and in the time region H where the irradiation time is long. Again, the brightness variation with time decreases. Further, in the combination of the two samples in FIG. 11A, the time domain F has a larger brightness difference between the two materials, that is, the contrast D, but in the combination of FIG. The contrast E ′ increases. Since the inspection of the circuit pattern is a comparative inspection, it is advantageous for detecting a defect that the contrast between the base material forming the pattern and the surface material is large. It can be seen that, depending on the combination of materials for forming the circuit pattern, the irradiation time or charging state for obtaining an electron beam with stable brightness and high contrast is different. In the first embodiment, the inspection is performed in the irradiation time zone F in FIG. 11A. However, the substrate 9 to be inspected is uniformly charged by the irradiation of the preliminary irradiation electron beam 104 in this embodiment, so that the inspection is performed. Charge state in time domain H before
To be able to. Thereafter, the electron beam 19 is irradiated in the inspection room 2 to acquire an electron beam image, and the circuit pattern is inspected.
[0056]
  After the irradiation of the preliminary irradiation electron beam 104 in the second preliminary chamber 100 is completed, the substrate 9 to be inspected is placed on the sample stage 30, the XY stages 31 and 32, and the rotary stage 33 together with the sample holder. Is held and fixed. Since the subsequent inspection method is the same as that of the first embodiment, a description thereof will be omitted. By performing the inspection according to the present embodiment, for each combination of materials, an electron beam image under the optimum conditions for performing the comparative inspection, that is, the brightness is stable, and the electron beam image in which the contrast of the member forming the circuit pattern is large Could get. In addition, the inspection method described in the first embodiment can obtain a high-quality image with a large S / N ratio at high speed, and as a result, erroneously detect a non-defect portion even in an inspection using an insulating material or the like. It is possible to detect fine defects with high accuracy and high sensitivity.
[0057]
(Example 6)
  In the sixth embodiment, a configuration and method for irradiating the substrate 9 to be inspected with the preliminary irradiation electron beam 104 without providing the second preliminary chamber 100 for preliminary irradiation described in the fifth embodiment will be described. . The basic configuration is the same as that of the first embodiment, but a second electron source is added to the electron optical system 3. FIG. 12 shows a main configuration diagram of the inspection room 2 of the inspection apparatus 1. For details of the control unit 6, the image processing unit 5, the detection system, and the like, refer to the first embodiment. The electron beam emitted from the second electron gun 110 is introduced between the objective lens 16 and the condenser lens 12 of the electron optical system 3. The second electron gun 110 is normally set to a negative potential that is the same as the potential of the image forming electron gun. The electron beam 104 emitted from the second electron gun 110 is converged by the second condenser lens 111 and is
Further, the light is deflected in the direction of the substrate 9 to be inspected mounted on the sample stage by a deflector 112 for joining the optical axis of the electron optical system. As an example of this deflector 112, the principle of an electromagnetic deflector is shown in FIG. A coil is wound in the axial direction of the cylindrical ferromagnet, and a current flows. Therefore, there is a circumferential magnetic field in the ferromagnetic body. A small hole is opened in the side wall of the cylindrical ferromagnetic body, and the second electron beam is arranged to enter the small hole. Since the magnetic field in the ferromagnetic body leaks into the space in the small hole, the second electron beam passing therethrough is deflected and introduced onto the optical axis of the electron optical system. Thereafter, the light travels on the optical axis almost the same as the electron beam for image formation, and is irradiated onto the substrate to be inspected. However, since the second electron beam is different in image formation condition from the electron beam for image formation, the second electron beam is not focused on the substrate to be inspected.
[0058]
  A method of simultaneously irradiating the preliminary irradiating electron beam 104 and the image forming electron beam 19 traveling along substantially the same optical axis as described above, and an inspection method of irradiating at different timings are conceivable. Normally, if the irradiation is performed simultaneously, the secondary electron generated by irradiating the electron beam 19 for image formation and the secondary electron generated by the preliminary irradiation electron beam 104 cannot be distinguished and detected. Can't get. However, as shown in FIGS. 14A and 14B, when the diameter of the preliminary irradiation electron beam 14 is sufficiently larger than the diameter of the electron beam 19 for image formation, the preliminary irradiation electron beam 14 The generated secondary electrons are almost at the background signal level, and the formed electron beam image is almost formed from the image signal by the irradiation of the image forming electron beam 19. Therefore, by adjusting the condenser lens 111 of the second electron gun 110, the preliminary irradiating electron beam 104 is not focused on the surface of the substrate 9 to be inspected, and has a size of 10 μm or more. 14A and 14B show cross-sectional profiles of the beam of the second electron beam 104 and the image forming electron beam 19 irradiated on the substrate 9 to be inspected. In FIG. 14 (a), the image forming electron beam 19 is located at the center of the electron beam from the second electron gun 110. However, as shown in FIG. 14 (b), the centers of both do not coincide with each other. good. However, preferably, the image forming electron beam 19 is positioned within the range of the diameter of the electron beam from the second electron gun 110. This is to prevent the inspection deflecting time from increasing as a result of the necessity of increasing the operating range of the scanning deflector in order to cause both electron beams to scan the non-inspection area if they are far apart.
[0059]
  In addition, when irradiating the inspection substrate with the irradiation timing of the electron beam 104 from the image forming electron beam 19 and the second electron gun 110 being shifted, preliminary irradiation is performed at the time when the scanning of the image forming electron beam 19 is turned back. The electron beam 104 was irradiated. The image-forming electron beam 19 is raster-scanned one-dimensionally or two-dimensionally as necessary. For example, the electron beam is scanned from the left to the right of the image acquisition area with a straight line and then returned to the left again. Since an image signal is not acquired, secondary electrons generated by irradiating the preliminary irradiation electron beam 104 during the returning do not affect the image.
[0060]
  Also by the method of irradiating the electron beam from the second electron gun 110 as described above, it is an image after being charged and the potential is stabilized as described in the fifth embodiment, and has good contrast and stability. I was able to obtain the image.
[0061]
(Example 7)
  In the seventh embodiment, a description will be given of a method and an apparatus configuration in which the second electron source of the preliminary irradiation electron beam 104 described in the sixth embodiment is provided in the periphery of the opening where the image forming electron beam irradiation is performed. To do. The electron optical system portion in the seventh embodiment is shown in FIGS. 15 (a) and 15 (b). Other parts are the same as those in the fourth and sixth embodiments. As shown in FIG. 15A, the tip of the objective lens 16 has a truncated cone shape, and the electron gun 120 of the preliminary irradiation electron beam 104 is disposed in the space facing the substrate 9 to be inspected. The electron gun 120 is suitably a large light source and capable of obtaining a large current. Here, an oxide cathode that emits thermoelectrons by heating a low work function oxide used in a CRT monitor with a heater is used. The irradiation energy of the electron beam from the second electron gun 120 to the substrate 9 to be inspected is the same as that of the image forming electron beam 19. In addition, the electron gun 120 of the preliminary irradiating electron beam 104 has two or four independently operated elements arranged on the axis on which the stage continuously moves during image formation and symmetrically arranged twice or four times with respect to the center. It consists of an electron gun. FIG. 15B shows the arrangement of the electron gun 120, and shows a view when the lower surface of the objective lens 16 is viewed from the substrate 9 to be inspected. The plurality of electron guns 120 operate so as to irradiate the preliminary irradiation electron beam 104 at a position immediately before scanning of the electron beam for image formation according to the moving direction of the stage. For example, as shown in FIG. 15A, when the stage moves from left to right, the second electron gun 120 on the left side in FIG. 15B operates.
[0062]
  In this embodiment, even if the preliminary electron beam irradiation 104 and the image forming electron beam irradiation 19 are simultaneously performed by the following method, secondary electrons generated by the preliminary electron beam irradiation 104 do not adversely affect the electron beam image. You can FIG. 16 shows a schematic diagram of the method. Secondary electrons 51 generated from the inspected substrate 9 travel upward in the objective lens 16 by the acceleration electric field described in detail in the first embodiment. At this time, the secondary electrons are focused by the influence of the magnetic field of the objective lens. The position of the focal point in the lateral direction varies depending on where the secondary electrons are generated. For example, secondary electrons generated from the surface A point of the substrate to be inspected are focused on A ′, and secondary electrons generated from the point B are focused on B ′. Accordingly, the stop 121 is provided at the focal position of the secondary electrons, and the secondary electron detector 20 is disposed above the stop 121, so that the secondary electron generated from the vicinity of the center of the optical axis, that is, the place where the image forming electron beam 19 is irradiated. Secondary electrons can be selectively detected. Since the irradiation position of the preliminary electron beam 104 is several hundred μm away from the irradiation position of the image forming electron beam 19, secondary electrons generated by the preliminary irradiation electron beam 104 are not detected by being blocked by the diaphragm. Also in this example, as in the fifth or sixth example, it was possible to obtain an image with good contrast after the sample was charged in advance and the potential was stabilized.
[0063]
(Example 8)
  For example, in the manufacturing process of a semiconductor device, the substrate to be inspected may already have been irradiated with an SEM inspection or observation in addition to the circuit pattern inspection apparatus of the present invention. In such a case, a local part of the surface of the substrate to be inspected is charged before the circuit pattern inspection is performed. In the inspection methods according to the embodiments described so far, the locally charged region is As with other regions, it is difficult to uniformly charge, and thus the locally charged portion becomes an electron beam image with a specific contrast, and inspection may not be possible. In order to avoid such a situation, the surface charge may be neutralized before the inspection, and then the circuit pattern inspection according to each of the embodiments described so far may be performed.
[0064]
  In this embodiment, a second preliminary chamber 130 is added to the configuration of the circuit pattern inspection apparatus 1 described in the first embodiment, and plasma is irradiated onto the substrate to be inspected in the second preliminary chamber 130 before the inspection. The configuration. FIG. 17 shows a partial configuration of the inspection chamber 2 and the second preliminary chamber 130 of the present embodiment.
[0065]
  The second preliminary chamber 130 is provided with a gas inlet 134 and an electrode 132 for applying an electric field for ionizing the introduced gas, and a high frequency power supply 131 is connected thereto. The inspected substrate 9 mounted on the sample holder in the first preliminary chamber (not shown) is evacuated and then transferred to the second preliminary chamber 130 that has already been evacuated. Thereafter, a rare gas such as Ar or air having a pressure of several Pa or less is introduced into the second preliminary chamber 130, a high-frequency voltage is applied to the electrode 132, and these gases are ionized to form a plasma 133. The inspected substrate 9 is exposed to the plasma 133 for a certain period of time, and the charged portion is neutralized during that time. After performing this pretreatment, the substrate 9 to be inspected is transferred into the inspection chamber 2 and inspection is performed. Since the inspection method has already been described in detail in the first embodiment, it is omitted here. By the pretreatment described in the present embodiment, the local charging of the substrate 9 to be inspected is neutralized immediately before the inspection, so when the electron beam image is acquired by irradiating the electron beam at the time of inspection, the substrate to be inspected Since all nine surfaces are uniformly charged and the electron beam image used for the comparison inspection has a uniform contrast, a highly accurate and stable inspection can be performed. During the plasma 133 irradiation in the preliminary chamber 130 described in the present embodiment, another inspection substrate 9 ′ is set in the adjacent inspection chamber and inspected. Since the time required for the pretreatment by plasma irradiation is sufficiently shorter than the time required for the inspection, there is almost no increase in the entire inspection time due to the pretreatment.
[0066]
  As mentioned above, about the structure of the typical apparatus of this invention, and the inspection method of a circuit pattern, the method of irradiating an electron beam, acquiring an electron beam image at high speed, and performing a comparison inspection, By irradiating a 2nd charged particle beam A method of inspecting after stabilizing the potential of the substrate to be inspected, a method of efficiently detecting secondary electrons generated from the substrate to be inspected to obtain an electron beam image of good quality, and a circuit pattern inspection of the present invention Although some embodiments of the method for improving the productivity of the manufacturing process of a semiconductor device or other substrate having a circuit pattern according to the invention have been described, a plurality of features listed in the claims are within the scope of the present invention. It is also possible for an inspection method and an inspection apparatus that combine the above.
[0067]
(Comparative example)
  In addition, the following is a list of solutions and solutions that are solved by the configurations described in the embodiments of the present application.
  In order to irradiate an electron beam at high speed, to detect a signal at high speed, and to ensure the SN ratio and resolution of the electron beam image, as described in the above prior art, the electron beam current is larger than that of a normal SEM. It is necessary to irradiate the substrate to be inspected with an electron beam. As described in the above prior art, it is difficult to obtain a high-resolution image due to the space charge effect with a large current and low acceleration electron beam. There is a method of irradiating the sample as a substantially low acceleration electron beam. In order to perform the deceleration of the primary electron beam, it is necessary to apply a negative voltage for deceleration to the sample substrate or the sample stage. When the sample substrate is irradiated with a primary electron beam decelerated by a negative voltage, secondary electrons having energy of about several tens of mV are generated from the substrate surface. An electric field generated by a negative voltage for deceleration acts on the secondary electrons, and the secondary electrons are accelerated to energy of several kV, so that it is difficult to collect high-speed secondary electrons to the detector. . As a method for collecting secondary electrons in the detector, a deflector (hereinafter referred to as a deflector) that deflects electrons by superimposing the amount of deflection due to electric and magnetic fields cancels each other for the primary electron beam. A method using an ExB deflector) has been proposed in the prior art. However, when the detector is located at a position deviated from the primary electron beam trajectory, it is necessary to largely deflect the secondary electrons with the ExB deflector in order to collect the secondary electrons at the detector. If too large, secondary electrons collide with the deflection plate itself of the ExB deflector and cannot be led to the detector. Further, when the deflection by the ExB deflector is strengthened, there is a problem that an aberration occurs in the primary electron beam, and it is difficult to narrow the electron beam finely on the sample substrate surface with an objective lens or the like.
[0068]
  Further, as described in the above prior art, there is a detecting means using a semiconductor detector as a detecting device for detecting a high-frequency secondary electron signal in order to form an electron beam image at high speed. The semiconductor detector includes a reverse-biased semiconductor detector having a high response speed, a preamplifier for amplifying the analog signal detected by the semiconductor detector, and means for optically transmitting the analog signal amplified by the preamplifier. The preamplifier is floated at a positive high potential. In this conventional method, an analog signal detected by a semiconductor detector is transmitted as it is by an optical transmission means. The optical transmission means includes a light emitting element that converts an electrical signal into an optical signal, and an optical fiber cable. And a light receiving element that converts an optical signal into an electric signal, noise generated in the light emitting element and the light receiving element is added to the original analog signal, and the SN ratio of the secondary electron signal is reduced. There was a problem.
[0069]
  The first object of the present invention is a circuit pattern that is difficult to detect in an optical image and formed of an insulating material, or a circuit pattern formed of a mixture of an insulating material and a conductive material. Another object of the present invention is to provide an inspection technique that can be inspected using an electron beam image.
[0070]
  The second object of the present invention is to obtain an electron beam image as a high-quality image with high speed, stability, high resolution, large contrast of light and darkness and large SN ratio in order to perform inspection using the electron beam image. In the comparative inspection, a defect generated on a fine circuit pattern is detected without error.
[0071]
  The third object of the present invention is to irradiate a sample with a relatively thick electron beam with a large current at high speed, and to instantaneously and efficiently detect the generated secondary electrons. It is to provide a technique for obtaining a stable electron beam image for an insulating material by forming a line image under conditions according to the material of the sample.
[0072]
  A fourth object of the present invention is to efficiently detect secondary electrons generated by irradiating a sample with an electron beam, or to provide means for detecting high-speed and high-frequency secondary electrons with a high SN ratio. To achieve the first, second, and third objectives.
[0073]
  The fifth object of the present invention is to solve the above first to fourth problems, provide a technique for inspecting a circuit pattern with high accuracy, and applying the inspection to a semiconductor device or other fine circuit pattern, An object of the present invention is to provide an inspection method that reflects the inspection result in the manufacturing conditions of the semiconductor device and the like, thereby improving the reliability of the semiconductor device and the like and contributing to reducing the defect rate.
[0074]
  the aboveIn order to realize this inspection method, it is effective to uniformly irradiate a substrate to be inspected with a high current electron beam at a high speed and detect a secondary electron signal corresponding to the spot almost simultaneously with the irradiation. I found out. In all inspection areas, the electron beam is irradiated uniformly for a moment during inspection, so the substrate potential due to charging is uniform at that moment, and the secondary electrons in that state are detected instantaneously to make transient charging. The influence of time fluctuation can be avoided. In addition, by controlling the energy of the electron beam applied to the sample, it is possible to set the ratio of the number of electrons incident on different samples depending on the material and the number of secondary electrons emitted from the sample to be approximately equal. Contrast is stabilized and damage to the sample circuit board can be avoided. That is, an image with stable contrast can be formed even in a circuit pattern having an insulating material. Controlling the energy of the electron beam irradiating the sample is possible by applying a negative potential to the sample or the sample stage, decelerating the primary electron beam directly above the sample, and variably controlling this applied voltage, so the degree of deceleration can be varied. It becomes possible.
[0075]
  As a means of automatically inspecting defects generated on the surface of a circuit pattern such as a semiconductor wafer at high speed, an electron beam is scanned at high speed in a direction perpendicular to the moving direction while continuously moving the sample stage in one direction. The secondary electrons are detected in real time during the movement of the sample stage to form an image, and this image is comparatively inspected. In order to realize this inspection method, the electron beam irradiation conditions differ depending on the material, but an image is formed by irradiating the electron beam once or several times at a high speed. In order to ensure the image quality of an electron beam image that can be used for comparative inspection by irradiating the electron beam once or several times, the following four means can be used. The first means is to ensure the SN ratio of the secondary electron signal that is the basis of the electron beam image necessary for the inspection by irradiating the sample with a high-density electron beam. The inspection is performed using an electron beam having an electron beam current value of 270 pA or more, preferably 13 nA or more. This current value is achieved by setting the square root of the number of irradiated electrons to be sufficiently larger than the SN ratio of the electron beam image necessary for the inspection. The second measure secures the resolution required for inspection of minute circuit patterns by squeezing the electron beam so that the diameter of the electron beam is sufficiently small on the sample when the sample is irradiated with a high-current electron beam. It is to be. As described in the prior art, in observation with an electron beam of a semiconductor or the like having an insulating material, it is desirable that the energy of the electron beam applied to the sample is low acceleration. In an electron beam with a large current and low acceleration, aberration due to the space charge effect occurs, and it is difficult to narrow the electron beam on the sample. Therefore, this problem can be solved by using the same means as described in the means for controlling the energy with which the sample is irradiated with the electron beam. That is, by generating an electron beam from the electron source at a high acceleration, the space charge effect is suppressed, and by applying a negative potential to the sample or the sample stage, the high acceleration electron beam is decelerated immediately before the sample and applied to the sample. By irradiating with an electron beam having substantially optimum low acceleration energy, it is possible to narrow down the diameter of the electron beam on the sample and secure the necessary resolution. The third means is to ensure the SN ratio of the electron beam image necessary for the inspection by efficiently guiding the secondary electrons generated on the surface to the detector. When the sample is irradiated with an electron beam by the second means, secondary electrons generated from the sample are accelerated by a negative potential electric field for decelerating the temporary electron beam. The accelerated secondary electrons are deflected by the ExB deflector and guided to the detector. The secondary electrons are irradiated to the metal piece provided between the optical path of the temporary electron beam and the detector. By deflecting and guiding the low-speed secondary electrons generated in the metal piece to the detector, it is not necessary to largely deflect the high-speed secondary electrons toward the detector, and the amount of deflection can be reduced. As a result, there are problems that occur when deflecting high-speed secondary electrons greatly, that is, loss of secondary electrons due to collision with the secondary electron deflector, degradation of resolution due to influence on the primary electron beam, etc. In addition, it is possible to obtain more secondary electrons than the number of electrons of the primary electron beam by using a material with high generation efficiency of secondary electrons for the metal piece, and as a result, the SN ratio of the image is improved. It becomes possible. A fourth means is to use a semiconductor detector as a detector to form an image with a high S / N ratio at high speed, and digitize and transmit an analog signal detected by the semiconductor detector. In addition, a means for converting the digitized signal into an optical signal, transmitting the optical signal by means such as an optical fiber, and converting the transmitted signal into an electric signal again is provided from the semiconductor detector to the optical conversion. The components up to the means are floated to a positive potential. Thereby, the analog signal detected by the semiconductor detector is digitized by the AD converter and then optically transmitted. By using a semiconductor detector, it becomes possible to ensure the responsiveness necessary for detecting secondary electrons at high speed, and by transmitting the digitized signal optically, the light emitting element of the photoelectric conversion means or Even if there is some noise in the light receiving element, it does not affect the discrimination of digital 1 or 0, so that the noise can be suppressed. In addition, by floating the semiconductor detector to the light conversion means at a positive potential, secondary electrons can be drawn into the semiconductor detector, and the circuit after the light conversion means can be operated at the ground potential. . Therefore, it is possible to detect the secondary electrons generated from the sample by irradiating the sample with an electron beam at high speed with little influence of noise.
[0076]
  With the various means described above, it is possible to obtain a stable image even on a circuit pattern having an insulating material under the condition of suppressing image contrast fluctuation due to charging, and an electron beam with high sensitivity, high speed and high SN ratio. An image can be formed.
[0077]
  The above is a method for obtaining an electron beam image before a potential change caused by charging occurs by irradiating an electron beam at a high speed only once or several times, which is effective for inspecting a circuit pattern having the above-described insulating material. Among the two means of obtaining an electron beam image after the charged state is stabilized by irradiating an electron beam or other charged particle beam, the former has been described. The means for the latter inspection method will be described below.
[0078]
  In order to stabilize the charged state before the latter inspection, there are two means. First, the first means is a preliminary chamber or the like different from the chamber to be inspected, and the substrate to be inspected is preliminarily irradiated with a second charged particle beam, for example, an electron beam, ion beam, plasma, electron shower or the like. Alternatively, it is a method of negatively charging. The second means transfers the substrate to be inspected to a chamber for inspecting, and irradiates the second electron beam at a position for forming an inspection image. In order to irradiate the region to be inspected before the inspection without affecting the inspection, (1) the first electron beam irradiation and the second electron beam irradiation for forming the inspection image. Irradiate with a time shift. (2) The first electron beam for forming the inspection image is raster-scanned on the inspected substrate, and the second electron beam is irradiated while the electron beam is turned back in the scanning. (3) Although the first electron beam and the second electron beam for forming the inspection image are coaxial and irradiate the substrate to be inspected simultaneously, the second electron beam is sufficiently larger than the diameter of the first electron beam. The current density is sufficiently smaller than the maximum current density of the first electron beam. As a configuration, one or a plurality of second electron beam sources are arranged in the periphery of the opening where the first electron beam for inspection image formation is irradiated, and each of them operates independently, and the first electron beam The second electron beam may be irradiated to the inspection area of the inspection substrate before the irradiation.
[0079]
  As a means for irradiating the second charged particle beam by a method other than the above, the charged particle beam is an ion beam, and an ion source is provided at the periphery of the opening where the first electron beam for image formation is irradiated. When the substrate to be inspected is inspected, an ion beam is irradiated onto the substrate to be inspected. The timing of irradiation is the same as when the second charged particle beam is an electron beam, or the first electron beam and the ion beam are irradiated with the time shifted, or the scanning of the first electron beam is reversed. There is no problem by irradiating in between.
[0080]
  Using the means described above, irradiate the substrate to be inspected with the second charged particle beam so that the surface of the substrate is uniformly charged, and then irradiate the first electron beam for forming the inspection image. This makes it possible to always form an electron beam image in a stable charged state with respect to a circuit pattern having an insulating material. Some insulating materials have a higher contrast with the underlying material when charged. In such a case, by controlling the irradiation conditions of the first electron beam for forming the inspection image, fluctuations in the electron beam image due to charging can be suppressed, but sufficient contrast is obtained for comparative inspection. Therefore, the method of irradiating the second charged particle beam according to the present invention is effective.
[0081]
  In the means for forming the electron beam image after stabilizing the charged state of the surface of the substrate to be inspected by the second charged particle beam, the conditions and means for irradiating the first electron beam are as described above. This is the same as the means for irradiating the first electron beam once or several times and forming an image before fluctuation due to charging occurs. The means for inspecting at a high speed and the means for making the image quality of the electron beam image a high signal-to-noise ratio and a high resolution at the time of the high-speed inspection are the same as those described above. Further, in the means for forming an electron beam image for inspection with the first electron beam after irradiating the second charged particle beam to stabilize the charge, the first electron beam and the second By controlling the irradiation energy of the charged particle beam, a means for adjusting the state of charging can be used in combination. When a charged particle beam other than the electron beam for image formation is irradiated at the same time or almost simultaneously with the electron beam, there is a possibility that a secondary electron signal which is originally not necessary for image formation is generated and detected. In this case, it is a means for forming an image of the circuit pattern to be inspected by secondary electrons, and a stop is disposed on the image surface of the sample surface, and the second generated from the region irradiated with the electron beam for forming the inspection image. By guiding only the secondary electrons to the secondary electron detector so that the aperture passes, unnecessary secondary electrons can be eliminated.
[0082]
  So far, various means for forming an electron beam image have been described among means for inspecting a substrate on which a fine circuit pattern is formed with an electron beam. A means for detecting defects generated on the circuit pattern from the electron beam image will be described below. The first region of the sample is irradiated with the first electron beam, secondary electrons generated from the sample surface are detected at high speed and high efficiency, and an image signal of the electron beam in the first region of the substrate to be inspected is obtained. Store in the first storage unit. At this time, if necessary, the second charged particle beam is irradiated before the first electron beam is irradiated. Similarly, an electron beam image of a second region of the sample having a circuit pattern equivalent to that of the first region is obtained and stored in the second storage unit, while the first and second regions are After performing detailed position adjustment on the image in the image processing unit, the images of the first and second regions are compared to obtain a difference image, and the absolute value of the brightness of the difference image is equal to or greater than a predetermined threshold value. A process such as determining a pixel as a defect candidate is performed. As another means, an electron beam image of a non-defective circuit pattern different from the board to be inspected is formed and stored in a first condition in a first storage unit, and the first area of the board to be inspected is stored in the first area. Irradiated with one electron beam, secondary electrons generated from the sample surface are detected at high speed and high efficiency, and an image signal of the electron beam in the first region of the substrate to be inspected is obtained and stored in the first storage unit The non-defective circuit pattern images are compared, and when the absolute value of the brightness of the difference image is larger than a predetermined threshold value, a defect is determined. Also in this case, the second charged particle beam is irradiated before the first electron beam is irradiated as necessary. In addition, since the first region and the second region of the substrate to be inspected are both irradiated with the first electron beam once or several times to form an image, the electron beam is not irradiated other than the image formation. As a means for performing this, a monitor for adjusting the focal position of the first electron beam is always irradiated with, for example, white light other than the electron beam, and the reflected light is monitored. Alternatively, prior to inspection, when setting sensitivity conditions and electron beam irradiation conditions according to the substrate to be inspected, an electron beam image is acquired in a region other than the inspection target region, and the inspection target region is always the first time during inspection. By means of managing so that the electron beam irradiation is performed, it is possible to prevent the region to be inspected of the inspected substrate from being locally charged, and to eliminate the cause of erroneous detection.
[0083]
  By carrying out the above inspection method, it is possible to inspect a circuit pattern on a substrate containing an insulating material with an electron beam at high speed and high sensitivity, and to automatically detect defects generated on the circuit pattern. An apparatus can be realized.
[0084]
  By using these methods and apparatuses to inspect a substrate having a circuit pattern, for example, a semiconductor device in a manufacturing process, a pattern generated by process processing that cannot be detected by a conventional technique for a semiconductor device in each process. Thus, it is possible to detect the shape defect or the defect at an early stage, and as a result, it becomes possible to reveal the problems that are latent in the process or the manufacturing apparatus conditions. As a result, it is possible to take measures against the cause of defects in the manufacturing process of various substrates including high-speed and high-accuracy semiconductor devices than before, and to ensure a high yield, that is, a non-defective product rate, and at the same time, are inspecting. Therefore, high-accuracy inspection is possible.
[0085]
【The invention's effect】
  A typical effect obtained by the present invention will be briefly described below.
[0086]
By inspecting a substrate such as a semiconductor device having a circuit pattern using the circuit pattern inspection apparatus of the present invention, it is formed of a silicon oxide film or a resist film that transmits light that could not be detected by a conventional optical pattern inspection. Circuit pattern inspection could be realized. Moreover, it is possible to inspect a circuit pattern having an insulating material, which has been difficult to obtain a stable image with a conventional SEM, with an inspection time that can be put to practical use in a manufacturing method of a semiconductor device or the like.
[0087]
  By applying this inspection to the substrate manufacturing process, defects that could not be detected by the above-described conventional technology, that is, abnormalities in the manufacturing apparatus, conditions, etc. can be discovered early and with high accuracy. Abnormality countermeasure processing can be taken, and as a result, the defect rate of semiconductor devices and other substrates can be reduced and productivity can be increased. In addition, by applying the above inspection, it is possible to quickly detect the occurrence of an abnormality, so it is possible to prevent a large number of defects from occurring, and as a result, the occurrence of defects itself can be reduced. The reliability of a semiconductor device or the like can be improved, the development efficiency of a new product or the like can be improved, and the manufacturing cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a device configuration of a circuit pattern inspection device.
FIG. 2 is a diagram showing a main configuration of an electron optical system and a secondary electron detection unit.
FIG. 3 is a diagram showing a correlation among electron beam irradiation, sample charging, and generation of secondary electrons.
FIG. 4 is a diagram for explaining the influence of electron beam irradiation conditions on contrast.
FIG. 5 illustrates an electron beam scanning method.
FIG. 6 is a diagram illustrating a semiconductor device manufacturing process flow.
FIG. 7 is a diagram for explaining a semiconductor device circuit pattern and a defect content;
FIG. 8 is a diagram illustrating the main configuration of an electron optical system according to a third embodiment.
9 is a diagram showing an enlarged partial configuration of an electron optical system of Example 4. FIG.
FIG. 10 is a diagram illustrating a device configuration of a circuit pattern inspection device according to a fifth embodiment.
FIG. 11 is a diagram for explaining the influence of electron beam irradiation time on contrast.
FIG. 12 is a diagram illustrating a main part configuration of an inspection apparatus according to a sixth embodiment.
FIG. 13 is a diagram illustrating the principle of a deflector according to a sixth embodiment.
14 is a view for explaining the shape of an electron beam in Example 6. FIG.
FIG. 15 is a diagram showing the main configuration of an electron optical system according to Example 7.
FIG. 16 is a diagram illustrating the operation of the seventh embodiment.
FIG. 17 is a diagram showing a main part configuration of an inspection apparatus according to an eighth embodiment.
[Explanation of symbols]
  1 ... Circuit pattern inspection equipment
  2 ... Inspection room
  3 ... Electronic optical system
  4 ... Optical microscope
  5 Image processing unit
  6 ... Control unit
  7 ... Secondary electron detector
  8 ... Sample chamber
  9 ... Board to be inspected
10 ... electron gun
11 ... Extraction electrode
12… Condenser lens
13 ... Blanking deflector
14 ... Aperture
15 ... Scanning deflector
16 ... Objective lens
17 ... Reflector
18 ... ExB deflector
19 ... electron beam
20 ... Secondary electron detector
21 ... Preamplifier
22 AD converter
23 ... Light conversion means
24: Optical transmission means
25 ... Electric conversion means
26 ... High voltage power supply
27… Preamplifier drive power supply
28… AD converter drive power supply
29… Reverse bias power supply
30 ... Sample stage
31 ... X stage
32 ... Y stage
33 ... Rotation stage
34… Position monitor length measuring device
35 ... Inspection board height measuring instrument
36 ... retarding power supply
40 ... White light source
41 ... Optical lens
42 ... CCD camera
43 ... Correction control circuit
44 ... Scanning signal generator
45 ... Objective lens power supply
46… First memory
47 ... Second memory part
48 ... Calculation unit
49 ... Defect judgment section
50 ... Monitor
51 ... Secondary electrons
52… Secondary secondary electrons
53… Suction electrode
54… Grounding electrode
100 ... Second spare room
101 ... electron source
102 ... Lens
103 ... Large angle deflector
104 ... Pre-irradiated electron beam
110 ... second electron source
111 ... Second condenser lens
112 ... deflector
120 ... second electron source
121 ... Aperture
130… Second spare room
131… High frequency power supply
132… Electrodes
133 ... Plasma
134… Gas inlet.

Claims (1)

A method for inspecting a semiconductor wafer on which a plurality of chips are formed,
The first chip on the semiconductor wafer is scanned only once in the region corresponding to the first chip by scanning the electron beam so as to perform blanking when swinging back,
Detecting secondary electrons generated from the first chip by the one-time scanning;
Forming an electron beam image of the first chip from the detected signal;
The second chip on the semiconductor wafer is scanned only once in the region corresponding to the second chip by scanning the electron beam so as to perform blanking when swinging back,
Detecting secondary electrons generated from the second chip by the one-time scanning;
Forming an electron beam image of the second chip from the detected signal;
A method for inspecting a semiconductor wafer, wherein the plurality of chips are inspected by comparing an electron beam image of the first chip and an electron beam image of the second chip.

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