JP5016799B2 - Inspection equipment using charged particle beam - Google Patents

Description

  The present invention relates to an apparatus used for evaluation of fine elements processed on a wafer and defect inspection, and in particular, evaluation or defect inspection of an arbitrary part on an unfinished wafer in the process of manufacturing a semiconductor device or the entire wafer surface. The present invention relates to an inspection apparatus using a charged particle beam.

  A semiconductor device is manufactured by repeating a process of transferring a pattern formed by a photomask on a wafer by lithography and etching. Further, ion implantation is performed between the respective steps to form a pn junction or the like. In the manufacturing process of these semiconductor devices, the lithography process, the etching process, the ion implantation process, and the other quality greatly affect the yield of the semiconductor devices. Therefore, it is important to detect the occurrence of defects and the type thereof at an early stage or in advance and feed back to manufacturing conditions to improve the yield.

  Of the above-mentioned defect detections, particularly important are the via hole non-conducting defect, the short defect, and the failure of the pn junction processed at the bottom of the via hole in the initial stage of the manufacturing process. Measurement of the resistance value at a desired voltage is indispensable for discriminating types of these defects. Also, in order to elucidate the cause of the defect, it was important to measure the resistance value over a wide range of voltages. Conventional techniques for measuring them include the following two techniques.

  One is a method using a nano probe (JP-A-8-160109: Patent Document 1). This is to measure the current-voltage characteristics by bringing a sharpened W needle (tip radius of curvature approximately 0.1 μm) into direct contact with the measuring unit, applying a voltage to the measuring unit, and measuring the flowing current. It is. However, with the recent miniaturization of the pattern, the size of the part to be measured has become the same as or smaller than that of the W needle, making measurement very difficult. As a means corresponding to this, it is conceivable to reduce the radius of curvature of the tip of the W needle. However, in that case, the tip becomes very soft, and the tip is deformed simultaneously with the contact with the measurement unit, which is not a practical method. In addition, there are the following three points as problems. (1) When the needle and the measuring part are different materials, particularly when at least one is a semiconductor, a Schottky junction is formed, and an electric resistance depending on the voltage is generated at that part, so that accurate measurement cannot be performed. (2) Since the measurement speed is slow, it is not suitable for the entire wafer inspection. (3) The wafer is contaminated due to contact between the needle and the sample, and is not suitable for in-line inspection.

  The other one uses a SEM (Scanning Electron Microscope). JP-A-5-258703 (Patent Document 2), JP-A-11-121561 (Patent Document 3), Proceedings of the 61st JSAP Academic Lecture Meeting, p671, 3p-K -4 (Non-Patent Document 1) and Proceedings of SPIE Vol. 4344 (2001) P12 (Non-Patent Document 2).

  The above-mentioned Japanese Patent Application Laid-Open No. 5-258703 compares a potential contrast image of a pattern processed on a wafer acquired using an SEM with a potential contrast image of an adjacent pattern, and determines a portion having a different potential contrast (brightness) as a defect. Judging and detecting it. The inspection is fast and suitable for wafer entire surface inspection, but the difference in the brightness of the potential contrast image only shows the difference in electrical resistance. From this result, quantitative data could not be obtained. . In addition, depending on the direction of the pn junction, the junction becomes high resistance due to charging, so that it is difficult to determine a defective conduction.

  JP-A-11-121561 discloses control of emission of secondary electrons by a control electrode on the front surface of a wafer, charging the wafer surface positively or negatively, and discriminating a defective portion from a potential contrast image at that time. It is. However, the control of secondary electron emission by this control electrode is disclosed in Japanese Patent Application Laid-Open No. 59-155941 (Patent Document 4).

  In the above Japanese Patent Laid-Open No. 11-121561, for example, in a potential contrast image when the control electrode is adjusted to be positively charged, the low resistance portion is a bright portion and the high resistance portion is a dark portion. If it is negatively charged, the contrast is reversed. Inspection is high-speed and suitable for wafer entire surface inspection, but the contrast of this potential contrast image only shows the magnitude of the resistance, the correspondence between the brightness of the image and the resistance value is not quantitatively shown, and the calculation of the resistance value is Can not. Therefore, for example, it is impossible to confirm whether or not the reverse bias resistance value of the pn junction is normal. In addition, there is a description that the junction direction of the pn junction is specified by using the positive and negative charged states. However, when the electron beam irradiation becomes a highly charged state, breakdown occurs in the junction and the resistance value is reduced. Because it is greatly reduced, inspection becomes impossible.

  Further, in Japanese Patent Laid-Open No. 11-121561, since the charging voltage cannot be measured, this cannot be avoided. Furthermore, the electrical resistance could be calculated by measuring the leakage current, but the inspection took time and could not be measured at high speed.

No.2, p671, 3p-K-4, and Proceedings of SPIE Vol. 4344 (2001) P12 calculate electrical resistance from signal value of potential contrast image. Is. This is impossible in Japanese Patent Laid-Open Nos. 5-258703 and 11-121561. However, this method is a study in a positively charged state, and there is no description regarding negatively charged state. Further, even in positive charging, the resistance value under a specific voltage can only be calculated, and the voltage is unknown. Therefore, the resistance-voltage characteristic of the element cannot be obtained, and it is difficult to determine the type of defect. In addition, since the charging voltage cannot be controlled and measured, the pn junction breakdown that should not occur cannot be avoided.
JP-A-8-160109 JP-A-5-258703 Japanese Patent Laid-Open No. 11-121561 JP 59-155941 A The 61st JSAP Scientific Lecture Proceedings No.2, p671, 3p-K-4 Proceedings of SPIE Vol. 4344 (2001) P12

  In the case of a nanoprober, the measurement target may be smaller than the tip of the needle, and there is a problem of contact resistance between the needle and the sample. Therefore, accurate electrical resistance cannot be estimated depending on the sample. Further, since the inspection time is long, the entire wafer inspection is impossible.

  Most apparatuses using SEM perform relative evaluation of the resistance value from the signal value of the potential contrast image. There was also a method of determining the electrical resistance from the signal value of the potential contrast image, but since both are inspections under a specific charging voltage, breakdown may occur due to high charging, and the defect detection sensitivity may decrease. there were. Also, it was impossible to calculate the electrical characteristics (resistance-voltage) of the element and to determine the type of defect. In addition, some devices calculate the resistance value by measuring leakage current, but this is also an inspection under a specific charging voltage, and it takes time to inspect, making high-speed inspection impossible. Was virtually impossible.

  The object of the present invention is to enable defect detection under a controlled charging voltage and to calculate the resistance-voltage characteristics of the device, and to distribute the distribution of electrical characteristics over the entire wafer surface and the distribution by defect type. The object is to provide a sample inspection technique required in a short time.

  In order to solve the above problems, the present inventors decided to use an SEM having a charging voltage measuring function. Here, an electron beam will be described as an example, but an electron beam is not necessarily required as long as it is a charged particle beam. Necessary techniques are resistance value, measurement of charging voltage, and control of charging voltage.

  First, an electron beam is irradiated onto a wafer (sample) whose element is processed, and a secondary electron and a backscattered electron generated therefrom are detected to obtain a signal of a potential contrast image. Since the signal depends on the resistance value, the resistance value of the element can be calculated. If the charging voltage at this time is measured, it becomes the voltage applied to the element. The charging voltage can be controlled by feeding back the measured charging voltage to the electron beam irradiation conditions.

  The electron beam conditions are the irradiation area of the beam, the beam energy, and the potential distribution between the wafer and the electrodes around the wafer, and the charging voltage can be changed by changing these conditions. The present inventors have found for the first time that by combining these methods, it is possible to calculate a resistance value in a state in which the charging voltage is controlled and to calculate a resistance-voltage relationship.

  In summary, the inspection apparatus using a charged particle beam according to the present invention includes a sample stage on which a sample is placed, an objective lens for irradiating a predetermined region of the sample on the sample stage with a primary charged particle beam, and A measurement unit for measuring the charging voltage of the region irradiated with the primary charged particle beam, a control unit for determining the irradiation condition of the primary charged particle beam for determining the charging voltage, and secondary electrons generated from the sample and the rear A detector for detecting scattered electrons, a storage unit for storing a signal of a potential contrast image of a region to be inspected using a signal from the detector, and a potential contrast image by a signal from the storage unit An image processing unit to be formed, and an arithmetic unit that calculates the relationship between the electrical resistance and the voltage of the part of the sample from the potential contrast image signal.

Hereinafter, the principle of the inspection technique of the present invention will be described.
(1) Method of calculating resistance value from potential contrast image signal When an electron beam is incident on a wafer, secondary electrons and backscattered electrons are emitted. Depending on the amount of these emitted electrons, the electron beam irradiation region is charged positively or negatively. For details, see the reference; L. Reimer, “Scanning Electron Microscopy,” Springer-Verlag Berlin Heidelberg, 1998. The number of emitted electrons changes depending on the degree of charging, and a potential contrast image is obtained. There are positively charged potential images (PVC, positive voltage contrast) and negatively charged images (NVC, negative voltage contrast). A method using these will be described below.
・ PVC
Refer to Proceedings of SPIE Vol. 4344 (2001) P12 for details of the method for calculating the resistance value from the positively charged potential contrast image. This will be briefly described below. FIG. 2 shows the incident electron beam energy EPE dependence of the electron emission efficiency, which is the ratio of the number of emitted electrons (the sum of the number of secondary electrons and the number of backscattered electrons) to the number of incident electrons.

  EPE when the electron emission efficiency was 1 was defined as E1 and E2. When the electron emission efficiency is larger than 1, the electron beam irradiation region is positively charged. When the electron emission efficiency is lower than 1, the electron beam irradiation region is negatively charged. When EPE is between E1 and E2, the electron emission efficiency is greater than 1, and the electron beam irradiation region is positively charged. This positive charge serves to pull back secondary electrons once emitted. Since backscattered electrons are sufficiently high in energy and are not pulled back, backscattered electrons are ignored in the following discussion.

  This will be described with reference to FIG. Here, as shown in the left figure, a description will be given using a wafer in which a SiO 2 film 303 is formed on a Si substrate 302 and via holes 301 and 305 in which Si plugs are embedded are processed. Between the via hole 305 and the Si substrate 302, there is a SiO2 residual film 304. In order to decelerate an incident electron beam having high energy, −Vr (<0) [V] is applied to the wafer as a retarding voltage 19. Here, the case where the electron beam 34 is irradiated to the via hole 301 is considered. Since the electron emission efficiency is greater than 1, positive charges are accumulated in the via hole 301.

  However, since the via hole 301 is connected to the Si substrate 302, the resistance value is sufficiently small and electrons are supplied from the ground, so that the positive charge is immediately neutralized and is not charged. Therefore, all generated secondary electrons are emitted as in 307. When the remaining film 304 is present, the resistance is high, so that the supply of electrons from the ground is small, and the via hole is positively charged. Positive charging is a barrier for secondary electrons with negative charge. Therefore, the potential distribution of the space becomes like 306, secondary electrons having low kinetic energy are pulled back, and secondary electrons 308 emitted without being pulled back decrease. As a result, the signal of the potential contrast image has a large low resistance portion and a small high resistance portion.

This discussion is performed using the energy diagram and the right diagram of FIG. The vertical axis is the distance from the wafer, and the horizontal axis is the energy. Before the electron beam irradiation, the vacuum level of the via hole is 309, and the potential distribution formed in front thereof is 311. When the electron beam is irradiated to the sufficiently low resistance via hole 301, the energy distribution 314 of the generated secondary electrons is continuously distributed from the vacuum level 309 to the high energy side. At this time, since the via hole has a sufficiently low resistance, it is not charged and the vacuum level 309 and the potential 311 do not change. Therefore, since there is no potential barrier for secondary electrons, the energy distribution 316 of the emitted secondary electrons is equal to the energy distribution 314 of the secondary electrons. on the other hand. When the electron beam is irradiated to the high resistance via hole 305, the via hole 305 is positively charged, so that the vacuum level is lowered as in 310. The position of the generated secondary electrons 315 also decreases by the charging voltage. Then, the potential distribution becomes 312 and the potential barrier 313 is formed. Due to this barrier, the secondary electrons once generated are pulled back, and only the remaining secondary electrons 317 are emitted. As a result, the signal of the potential contrast image has a large low resistance portion and a small high resistance portion.
・ NVC
When the EPE is large to some extent, for example, when the EPE is E3 in FIG. 2, if the electron emission efficiency is σ, then σ <1, and the electron beam irradiation region is negatively charged. This negative charging reduces EPE, EPE approaches E2, and the electron emission efficiency approaches 1. When the resistance is sufficiently large, the electron emission efficiency is stabilized at 1, that is, the charging voltage is stabilized at E2-E3 [V]. When the resistance is small, a leakage current is generated, so that the voltage is stabilized before becoming E2-E3 [V], and the electron emission efficiency is smaller than 1 and larger than σ. As described above, the number of emitted electrons is high at a high resistance, and the number of emitted electrons is reduced at a low resistance. That is, in the signal of the potential contrast image, the high resistance portion is large and the low resistance portion is small.

  Even when the electron emission efficiency is larger than 1, it is possible to make a negative charge state. In this method, as shown in FIG. 15, a charge control electrode 38 is provided on the front surface of the wafer, and a charge control voltage 39 is applied to bring the wafer to a negative potential. In this way, the low energy component of the secondary electrons cannot pass through the charge control electrode 38 and is pulled back to the wafer, so that the electron emission efficiency can be reduced. As a result, the number of electrons emitted from the low resistance portion is reduced. On the other hand, since the high resistance portion is negatively charged by the pulled-back electrons, the potential is reduced to about the charging control voltage 39. At this time, since the energy of the secondary electrons increases, the number of electrons passing through the charge control electrode 38 increases. That is, in the signal of the potential contrast image, the high resistance portion is large and the low resistance portion is small. However, since the drawn back electrons are spread, it takes time until the high resistance portion is negatively charged. In order to shorten the time, it is effective to apply a magnetic field perpendicularly to the wafer and narrow the drawn electrons.

When these phenomena are handled quantitatively, the relationship shown in FIG. 4 is established between the resistance and the number of detected electrons. The horizontal axis represents the product of the resistance R and the beam current IP applied to the sample, and the vertical axis represents the signal of the potential contrast image. In the case of PVC, the curve is 401, and in the case of NVC, the curve is 402. In the case of NVC, this is the result that we have clarified for the first time in the present invention. The areas where the brightness changes are both 0 <log (R · IP) <3. In this way, it is possible to calculate the resistance value from the signal of the potential contrast image.
(2) Method of Measuring Charging Voltage The charging voltage is measured by measuring the energy of secondary electrons or backscattered electrons using, for example, an energy filter (sometimes referred to as an energy analyzer). This is because when the wafer is charged positively or negatively, the energy of secondary electrons and backscattered electrons also changes by the charging voltage. Details of energy filters are described in the reference; L. Reimer, “Scanning Electron Microscopy,” Springer-Verlag Berlin Heidelberg, 1998, P197. One example is a metal mesh plate that serves as an energy filter in front of a detector that detects secondary and backscattered electrons. When a voltage is applied to a metal mesh that is an energy filter and the voltage is changed, the probability that secondary electrons and backscattered electrons pass through the metal mesh changes. By measuring the change using a detector, the charging voltage of the wafer can be measured.

  Details of the measurement principle are shown in FIG. Here, a method for obtaining the charging voltage by measuring the energy of secondary electrons will be described, but the same applies to the case of backscattered electrons. This figure is an energy diagram showing the state of secondary electron emission. The horizontal axis is the distance from the wafer, and the vertical axis is the energy. The position of the wafer is 0 distance. Before charging, the vacuum level is 309, and the potential distribution formed on the front surface of the wafer is 311.

  Since a negative voltage called a retarding voltage is normally applied to the wafer, the vacuum level 309 is higher than 0 eV. Then, secondary electrons 314 are generated by electron beam irradiation, and secondary electrons 316 are emitted in vacuum. However, in the figure, all secondary electrons display the energy distribution. When the electron emission efficiency is smaller than 1 and negatively charged, the vacuum level of the wafer rises from 309 to 320 and the potential distribution becomes 321. If it is positively charged, the opposite is true.

The energy distribution of secondary electrons generated in a negatively charged state is 323, and the secondary electrons emitted into the vacuum are 324. The energy filter obtains the charging voltage by measuring the energy of the secondary electrons 316 and 324 emitted into the vacuum. When a voltage is applied to the energy filter, a potential barrier 322 is formed. If the voltage value is low, it becomes a barrier against secondary electrons, and the detected electrons 325 and 326 start to decrease. FIG. 18 shows the energy filter voltage and the number of electrons passing through the filter and detected by the detector. The voltage value at which the signal starts to decrease is equal to the charging voltage. In this case, the charging voltage is −2, −10, and −15V. Although an example of negative charging has been described here, the same applies to the case of positive charging. In this way, the charging voltage can be measured.
(3) Method of changing and controlling charging voltage By changing the electron beam irradiation conditions (beam irradiation area, beam energy, potential distribution in the vicinity of the wafer), the charging voltage can be changed. For example, when an electron beam with an incident energy of 500 eV is used, the charging voltage is changed as shown in FIGS. 5 and 6 by changing the irradiation area (FOV) of the beam and the electric field in the vicinity of the wafer. It turns out that is possible. The range of the charging voltage value indicates that the charging voltage varies in the electron beam irradiation range.

  As another example, as shown in FIG. 15, a charging control electrode 38 capable of applying a charging control voltage 39 is provided on the front surface of the wafer, and the charging voltage can be changed by changing the potential in the vicinity of the wafer. I also understood that. If a positive voltage is applied to the charge control electrode 38 with respect to the wafer, secondary electrons are likely to be emitted, and the charge voltage increases. If a negative voltage is applied to the charge control electrode 38 with respect to the wafer, secondary electrons are pulled back, and the charge voltage decreases. FIG. 16 shows an actual measurement example. As shown here, it was found that the charging voltage can be controlled by changing the charging control voltage 39, Vcc.

  As described above, the charging voltage can be controlled by grasping the tendency of increase / decrease in charging and changing the charging voltage when the electron beam irradiation conditions are changed. For example, when it is desired to set a certain region to 10V, even if it is charged to 20V by electron beam irradiation, the charging voltage can be reduced by weakening the electric field in the vicinity of the wafer. By sending such a command to the electron beam irradiation control unit, charging control can be performed.

  As described above, by combining the means (1), (2), and (3), it is possible to calculate the resistance-voltage characteristic and measure the resistance value in a state where the charging voltage is controlled to a desired value.

  A typical effect obtained by the present invention will be briefly described below. By inspecting a partially completed substrate such as a semiconductor device having a circuit pattern by using the inspection method and apparatus of the present invention, it is possible to achieve desired charging of a minute portion in a non-contact manner, which is impossible with a conventional inspection apparatus. It became possible to measure the electrical resistance in voltage and the voltage dependence of electrical resistance. As a result, the type of defect can be determined.

  By applying this inspection to the substrate manufacturing process, it is possible to quickly take an abnormality countermeasure process in the substrate manufacturing process, and as a result, the defect rate of semiconductor devices and other substrates can be reduced and productivity can be increased. As a result, since the occurrence of defects itself can be reduced, the reliability of semiconductor devices and the like can be increased, the development efficiency of new products and the like can be improved, and the manufacturing cost can be reduced.

Example 1
In this example, a method for measuring the resistance-voltage characteristics of a sample at high speed without contact and determining the type of defect will be described. A cross-sectional structure of the wafer used here is shown in FIG. This includes a Si substrate 701, a SiO2 film 702, a via hole 703 in which a poly-Si plug is embedded, an n diffusion layer 704 immediately below the via hole, and a pn junction 706 formed by the diffusion layer 704. In addition, a defective conduction defect 705 partially exists.

  The configuration of the semiconductor device inspection apparatus in this embodiment is shown in FIG. The semiconductor device inspection apparatus 1 is roughly composed of an electron optical system 2, a stage mechanism system 3, a wafer transfer system 4, a vacuum exhaust system 5, an optical microscope 6, a control system 7, and an operation unit 8.

  The electron optical system 2 includes an electron gun 9 for emitting an electron beam 34, a condenser lens 10 for converging the electron beam 34 on the wafer 18, an objective lens 11, and an electron beam 34 for blanking (irradiating the wafer). Blanking control electrode 13, deflector 14 for scanning electron beam 34 on wafer 18, wafer height sensor 15 for detecting the height of the wafer, and emitted electrons (secondary electrons) generated on wafer 18. And a detector 12 for detecting backscattered electrons) 35, and an energy filter 36 installed in front of the detector. In order to acquire a potential contrast image of the wafer 18, the wafer 18 is irradiated with a finely focused electron beam 34 to generate emitted electrons 35, which are detected in synchronization with scanning of the electron beam 34.

  The stage mechanism system (sample stage) 3 includes an XY stage 16, a holder 17 (with a beam calibration pattern) for placing a wafer, and a retarding power source 19 for applying a negative voltage to the wafer 18. Yes. A position detector by laser length measurement is attached to the XY stage 16. The wafer transfer system 4 includes a wafer cassette 20 and a wafer loader 21, and the wafer holder 17 moves between the wafer loader 21 and the XY stage 16 with the wafer 18 placed thereon. Further, the wafer loader 21 is configured to be evacuated independently of the inspection chamber 2 so that the wafer can be transferred without bringing the inspection chamber 2 already in a vacuum to atmospheric pressure.

Although not shown in FIG. 1, the vacuum exhaust system 5 is generally composed of a rotary pump, a turbo molecular pump, and an ion pump.
The optical microscope 6 is installed in the examination room 2. By using the XY stage 16, the wafer is moved from the electron optical system 2 and can be observed by the optical microscope 6.

  The control system 7 includes a signal detection system control unit 22 that detects a signal from the detector 12, a blanking control unit 23, a beam deflection control unit 24, an electron optical system control unit 25, a wafer height sensor detection system 26, and a stage control unit. 27, an energy filter control unit 40. Here, the conditions such as the acceleration voltage of the electron beam, the deflection width, the deflection speed, the signal capture timing of the detector 12, the moving speed of the XY stage 16, the voltage applied to the energy filter 36, etc. are arbitrarily or selected depending on the purpose. It is input so that it can be set. Further, the position and height deviations are monitored from the signals of the position detector attached to the XY stage 16 and the wafer height sensor 15, and a correction signal is generated from the result, so that the electron beam is always irradiated to the correct position. It also serves to send a correction signal to each control unit.

  The operation unit 8 includes an operation screen for the apparatus, a captured electric potential contrast image, an optical image, an operation screen for displaying the measured electrical characteristics, a test result display unit 28, and a calculation unit for issuing commands to the image processing unit and the control system 7. 29, a potential contrast image / inspection data storage unit 30, a data input unit 32 for exchanging data from the external server 31, and a data conversion unit 33.

  Next, a method when an inspection is performed using the inspection apparatus shown in FIG. 1 will be described. First, a wafer cassette in which wafers are placed on an arbitrary shelf is placed on the wafer cassette 20 in the wafer transfer system 4 of FIG. In order to designate a wafer to be inspected from the operation screen 28, a cassette shelf number on which the wafer is set is designated.

  Then, various inspection conditions are input from the operation screen 28. The inspection condition input content includes an electron beam current, an electron beam irradiation energy, a field of view size (FOV, Field of view), a retarding voltage, and the like. Although it is possible to input individual parameters, usually a combination of the above various inspection parameters is stored in a database as an inspection condition file according to the resistance range and voltage range to be detected, and the inspection conditions according to these ranges Just select and enter the file. Database creation is performed as follows.

  By setting the resistance range, an equation of 0 <log (R · IP) <3 (as described in the means for solving the problem, if the resistance value to be measured is R, the beam current IP satisfying this equation is satisfied. Is used to determine the beam current IP range. Depending on the setting of the voltage range, the electric field, potential, and FOV range in the vicinity of the wafer are determined using the results shown in FIGS. When these condition inputs are completed, the inspection is started.

  When the automatic inspection is started, first, the set wafer 18 is transferred into the inspection apparatus 1. In the wafer transfer system 4, a holder 17 for placing the wafer 18 is mounted on the wafer even when the diameter of the wafer 18 to be inspected is different or the shape of the wafer is different, such as an orientation flat type or a notch type. It is possible to respond by exchanging according to the size and shape. The wafer 18 to be inspected is placed on the holder 17 from a wafer cassette 20 by a wafer loader 21 including an arm, a preliminary vacuum chamber, etc., held and fixed, and evacuated in the wafer loader 21 together with the holder. It is transported to a vacuumed laboratory.

  When the wafer is loaded, the electron beam irradiation condition is set to each part by the electron optical system control unit 25 based on the inputted inspection condition. Then, the stage 16 moves so that the first beam calibration pattern on the wafer holder 17 is under the electron optical system, and a potential contrast image of the beam calibration pattern is acquired by the image processing unit. Adjust the focus and astigmatism.

  Then, it moves to a predetermined location on the wafer 18 to be inspected, acquires a potential contrast image of the wafer 18, and adjusts the contrast and the like. Here, when it becomes necessary to change the electron beam irradiation conditions or the like, the beam calibration can be performed again. At the same time, the height of the wafer 18 is obtained from the height sensor 15, and the wafer height detection system 26 obtains the correlation between the height information and the in-focus condition of the electron beam. Without any adjustment, the focus condition is automatically adjusted based on the result of the wafer height detection. As a result, high-speed continuous potential contrast images can be acquired.

  For alignment, a pattern previously formed for alignment, an optical microscope image for alignment, a potential contrast image, and pattern position information are registered. This data can be read when inputting the inspection conditions.

  The set wafer 18 is moved by the XY stage 16 in order to observe the first coordinates for alignment by the optical microscope unit 6. An optical microscope image of the alignment pattern formed on the wafer 18 is observed by the monitor 28, and compared with the same pattern image stored in advance, a position correction value of the first coordinate is calculated. Next, move to a second coordinate where a circuit pattern equivalent to the first coordinate exists at a certain distance from the first coordinate, and the optical microscope image is similarly observed and compared with the circuit pattern image stored for alignment Then, the position correction value of the second coordinate and the rotational deviation amount with respect to the first coordinate are calculated.

  When the preparatory work such as predetermined correction work and inspection area setting by the optical microscope unit 6 is completed as described above, the wafer 18 is moved under the electron optical system 2 by the movement of the XY stage 16. When the wafer 18 is placed under the electron optical system 2, an operation similar to the alignment operation performed by the optical microscope unit 6 is performed using the potential contrast image. Acquisition of the potential contrast image at this time is performed by the following method.

  Based on the coordinate values stored and corrected in the alignment by the optical microscope image, the electron beam 34 is scanned two-dimensionally in the XY directions by the scanning deflector 14 in the same circuit pattern as observed by the optical microscope unit 6. Is irradiated. By the two-dimensional scanning of the electron beam, the emitted electrons 35 generated from the observation site are detected by the configuration and operation of each part for detecting the emitted electrons, thereby obtaining a potential contrast 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 electron beam 34 is irradiated on the wafer 18, the portion is charged. In order to avoid the influence of charging during inspection, a circuit pattern that irradiates the electron beam 34 in the pre-inspection preparatory work such as position rotation correction or inspection area setting is selected in advance. Alternatively, an equivalent circuit pattern in a chip other than the chip to be inspected can be automatically selected from the control system 7.

  In addition, means for irradiating with ultraviolet rays may be used to relieve charging. Thereby, the influence which irradiated with the electron beam 34 by the said pre-inspection preparatory work at the time of an inspection does not reach an inspection image.

  The alignment result thus performed is transferred to each control unit. At the time of inspection, the rotation and position coordinates are corrected by each control unit.

  When the alignment is completed, the second calibration pattern placed on the sample holder 17 is moved. The second calibration pattern matches the signal scale of the graph of FIG. 4 with the signal of the potential contrast image obtained by inspection. The pattern is a pattern in which a sufficiently low resistance via hole and a sufficiently high resistance via hole are processed.

  The signal values of the sufficiently low resistance portion and high resistance portion are calibrated using the potential contrast image of the pattern. An insulating part having no pattern may be used as the sufficiently high resistance part. Based on this result, the wafer moves onto the wafer 18, acquires a potential contrast image of a pattern portion on the wafer, and performs brightness adjustment, that is, calibration.

  When the calibration is completed, an inspection is performed based on the electron irradiation conditions already input to the control system 7. FIG. 8 shows the via hole resistance distribution converted from the potential contrast image signal obtained at that time using FIG. 4 and the via hole charging voltage distribution measured by the energy filter. The measurement of the charging voltage will be described more specifically. The charging voltage measuring function here uses an energy filter.

  A primary electron beam is irradiated onto a wafer (sample) on which the device is processed, and the energy of secondary electrons and backscattered electrons generated therefrom is measured. Since the value changes by the amount of voltage applied to the element having the irradiation region of the primary electrons on the sample, the voltage can be calculated. By acquiring this image every time the beam current, beam energy, FOV, and potential distribution between the wafer and the electrodes around the wafer are changed, the voltage dependency of the resistance can be calculated for each via hole.

  As a result, as shown in FIG. 9, the resistance value of the via hole was roughly classified into three (result 901, result 902, and result 903).

  The result 901 shows that the resistance-voltage characteristic is equal to that predicted from the impurity doping conditions, and that the pn junction is normal. The result 902 shows that both forward bias and reverse bias have high resistance, and a conduction failure defect has occurred. The result 903 was found to have a very low resistance and a leak defect. In addition, the result 904 has a large reverse bias resistance value, so it looks normal at first glance, but it is also found that the breakdown voltage is low and may cause a leak defect in the future.

  In addition, it is possible to estimate a defective portion in the impurity doping process from the resistance-voltage characteristics. Such a result cannot be understood unless the resistance value is obtained with a voltage within a relatively wide range.

  When moving to the next inspection region, either a method of moving the scanning region of the electron beam 34 by stopping the XY stage 16 or a method of moving the XY stage 16 can be selected. When inspecting a specific relatively small area, the former method in which the stage is stationary is effective, and when inspecting a relatively wide area, the method in which the stage is moved is effective. When moving the inspection region, when it is necessary to blank the electron beam 34, the blanking deflector 13 deflects the electron beam 34 so that the wafer is not irradiated with the electron beam.

  The image processing is performed in real time and the voltage dependence of the resistance value is measured while performing the inspection of the designated area. Then, the inspection result is displayed on the operation unit 28, and the data is output to the outside via the data conversion unit 33. In this way, when the inspection is completed over the entire wafer or partially, a conduction defect distribution and leak defect distribution within the wafer can be obtained as shown in FIG. Thereafter, the wafer is unloaded and the inspection is completed.

  Here, in order to change the charging voltage, the irradiation area of the beam, the beam energy, and the potential distribution between the wafer and the electrode around the wafer were changed. Other than that, it is possible to change the charging voltage by irradiating the electron beam over a wide range before the inspection. Further, in this embodiment, an electron beam is used to charge the wafer surface, but the same measurement can be performed using an ion beam instead.

(Example 2)
In the second embodiment, the resistance value of each element at a desired charging voltage is measured using the inspection apparatus described in the first embodiment, and when the resistance value is different from a predetermined value, Recognize as a defect and display the position of the defect. For controlling the charging voltage, information on the charging voltage measured using the energy filter 36 is sent to the calculation unit 29, the electron beam irradiation conditions for obtaining the desired charging voltage are determined by the calculation unit 29, and the information is transmitted to the control unit. This is done by sending 7. If the setting of the electron beam irradiation conditions is not successful and the charging voltage does not reach a desired value, this method is repeated again. Since the detailed description of the apparatus is described in the first embodiment, it will be omitted.

  Using this method, for example, a refresh defect inspection of a pn junction processed into a DRAM can be performed. The pn junction was determined to be defective when the resistance value when 3 V was applied thereto was 10 14 Ω or less. The wafer having a pn junction processed at the bottom of the via hole is inspected by the above method, the resistance value at a charging voltage of 3V is calculated, a via hole having a power of 10 14 or less is made a refresh defect, and the defect density distribution in the wafer is calculated. As shown in FIG.

(Example 3)
In the third embodiment, a pn junction inspection of the CMOS processed on the wafer was performed using the inspection apparatus described in the first embodiment. By performing resistance-voltage measurement, it is possible to determine the direction of the pn junction, the continuity defect, and the leak defect. An example of the inspection result is shown in FIG. A pn junction whose wafer surface is an n diffusion layer is 1201, a pn junction whose wafer surface is a p diffusion layer is 1202, a conduction defect is 1203, and a leak defect is 1204. Further, if the inspection is performed under the condition that the charging voltage is controlled and breakdown does not occur, it is possible to make the determination simply by looking at the signal change in the potential contrast images of NVC and PVC. FIG. 13 shows the result.

Example 4
In the fourth embodiment, the apparatus described in the first embodiment is used, and a potential contrast image signal of an element having a known resistance value is obtained before or before acquiring a potential contrast image signal for inspection. An inspection method and apparatus for acquiring and calibrating a relationship between a signal of a potential contrast image and a resistance value.

  First, the inspection wafer 18 is loaded into the inspection apparatus, and pre-registered electron beam irradiation conditions are set. As shown in FIG. 14, a standard sample 37 whose resistance value is known in advance is attached to the sample stage 17. Before starting the inspection, a potential contrast image of this standard sample is obtained, and the relationship between the electric resistance and the signal of the potential contrast image is obtained. Thereafter, the inspection was started, and the resistance value was calculated from the obtained potential contrast image using the relationship. This method enabled more accurate resistance measurement.

(Example 5)
The fifth embodiment uses the apparatus described in the first embodiment and uses a charge control electrode 38 installed on the front surface of the wafer 18 in order to change the charging voltage. As shown in FIG. 15, a voltage can be applied to the charge control electrode. When the voltage Vcc was applied to the wafer, the charging voltage value was as shown in FIG. This method makes it possible to easily and continuously change the charging voltage from positive to negative or from negative to positive. In order to change the charging voltage at high speed, a method of applying a magnetic field perpendicular to the wafer is effective.

(Example 6)
In the sixth embodiment, a defect is detected by performing a comparative inspection using the inspection apparatus described in the first embodiment. First, in the first region, the resistance value of each element in a desired charging voltage was measured, or the resistance value of each element in a desired charging voltage range was measured. Next, the resistance value was similarly measured in the second region. By comparing the resistance values of the first region and the second region, it was possible to determine a different portion and recognize that portion as a defect.

  The present invention is as follows when the embodiments are summarized.

  According to a first aspect of the present invention, there is provided a step of scanning a region of the wafer surface on which an element is formed with a charged particle beam, and irradiation with a charged particle beam in order to set the charging voltage in the region to one or a plurality of desired values. A step of changing conditions, a step of measuring a charging voltage to confirm whether or not the charging voltage is equal to the desired value, and secondary electrons generated from the region after the charging voltage is set to the desired value And backscattered electrons are detected, a signal for forming a potential contrast image of the region is stored from the signal, and an electric resistance value is calculated from the signal of the potential contrast image and the charged particle beam current value.

  Further, a step of scanning the region of the wafer surface on which the element is formed with a charged particle beam, and detecting secondary electrons and backscattered electrons generated from the region by the charged particle beam, and detecting the potential contrast of the region from the signal A step of storing a signal for forming an image, a step of calculating an electric resistance value from the signal of the potential contrast image and a charged particle beam current value, a step of measuring a charging voltage of the region, and all these steps. This is achieved by changing the irradiation condition of the charged particle beam and determining the relationship between the resistance and voltage of the element.

  In addition, the charged particle beam irradiation conditions are beam current, beam energy, irradiation area, and potential distribution between the wafer and the electrodes around the wafer. When changing the irradiation conditions, one or more of them are used. It can also be achieved by changing. Furthermore, the potential contrast signal can be detected with high accuracy by performing the scanning until the charged state is stabilized.

  Furthermore, as a pre-process of the step of storing the signal for forming the potential contrast image, it is achieved by scanning and charging a charged particle beam in a region wider than the signal acquisition region of the potential contrast image.

Structure when determining the resistance value is accomplished by these relationships are calibrated using voltage contrast image of a known device, using the measurement results of the resistance values, to determine the type of defect in the substrate It is to have done. The inspection method of the present invention is an inspection method for determining the junction direction, leakage defect, and continuity defect of an element in which a pn junction is formed by acquiring a potential contrast image in a positively and negatively charged state. To provide . Test method of the present invention, the charged particle beam is a test method which is characterized in that an electron beam. Test method of the present invention, when the electrical resistance to be measured is R, the electron beam current value IP of the used is inspection method characterized by the range of 0 <log (R · IP) <3.

  According to a second aspect of the present invention, there is provided a sample table on which a sample is placed, an objective lens for irradiating a sample on the sample table with a primary charged particle beam, and a charging voltage for measuring a charging voltage in a region irradiated with the charged particle beam. A measurement system, a control unit that changes the irradiation condition of the charged particle beam in order to set the charging voltage to a desired value, a detector that detects secondary electrons and backscattered electrons generated from the sample, and the detection A potential contrast image storage unit for storing a signal of a potential contrast image of a region to be inspected using a signal from the instrument, and an arithmetic unit for calculating an electrical resistance of a part of the sample from the potential contrast image signal; And an inspection apparatus using a charged particle beam.

  According to a third aspect of the present invention, there is provided a sample table on which the sample is placed, an objective lens for irradiating the sample on the sample table with a primary charged particle beam, and detection for detecting secondary electrons and backscattered electrons generated from the sample. A voltage contrast system for measuring a charging voltage of a region irradiated with a charged particle beam, and a potential contrast for storing a signal of a potential contrast image of a region to be inspected using a signal from the detector Each time the irradiation condition of the image storage unit and the charged particle beam is changed, the charging voltage is obtained, and at the same time, the electric resistance of the part of the sample is calculated from the potential contrast image signal, and the resistance-voltage relationship in each part is determined. An inspection apparatus using a charged particle beam, comprising: an arithmetic unit. In order to change the charging voltage, a charging control electrode capable of applying a voltage to the front surface of the wafer is provided. Further, in order to change the charging voltage at a high speed, this can be achieved by applying a magnetic field in the vertical direction to the wafer.

It is an apparatus block diagram of a test | inspection apparatus. It is a figure which shows the incident electron beam energy dependence of electron emission efficiency. It is a figure which shows the electric potential distribution of the wafer vicinity accompanying beam irradiation, the mode of secondary electron emission, and the mode of potential barrier formation. It is a figure which shows the resistance dependence of the signal of a potential contrast image. It is a figure which shows the electric field dependence of a charging voltage. It is a figure which shows the observation area | region (FOV) dependence of a charging voltage. It is a figure which shows the cross-section of a wafer. It is a figure which shows the resistance value distribution and charging voltage distribution of the via hole which were obtained in Example 1. FIG. It is a figure which shows the voltage dependence of the resistance value of the via hole obtained in Example 1. FIG. It is a figure which shows the distribution in a wafer of the conduction defect defect density and leak defect density which were obtained in Example 1. FIG. FIG. 6 is a diagram showing the in-wafer distribution of refresh defect density obtained in Example 2. It is a figure which shows the voltage dependence of the resistance value of the via hole obtained in Example 3. FIG. It is a figure which shows the charging voltage dependence of the signal of the potential contrast image obtained in Example 3. FIG. It is a figure which shows the sample stand with a resistance standard sample used in Example 4. FIG. FIG. 6 is a diagram illustrating a structure of a charge control electrode used in Example 5. It is a figure which shows the charging control voltage dependence of the charging voltage obtained in Example 5. FIG. It is a figure which shows the principle of the charging voltage measurement using an energy filter. It is a figure which shows the example of a charging voltage measurement using an energy filter.

Explanation of symbols

1: inspection apparatus, 2: electron optical system, 3: stage mechanism system, 4: wafer transfer system, 5: vacuum exhaust system, 6: optical microscope, 7: control system, 8: operation unit, 9: electron gun, 10 : Condenser lens, 11: objective lens, 12: detector, 13: blanking control electrode, 14: deflector, 15: height sensor, 16: XY stage, 17: wafer holder, 18: wafer, 19: retarding power supply 20: Wafer cassette, 21: Wafer loader, 22: Signal detection system control unit, 23: Blanking control unit, 24: Beam deflection control unit, 25: Electro-optical system control unit, 26: Height sensor detection system, 27: Stage control unit, 28: operation screen / inspection result display unit, 29: calculation unit, 30: data storage unit, 31: external server, 32: data input unit, 33: data conversion unit, 34: electron beam, 3 5: emitted electrons (secondary electrons and backscattered electrons), 36: energy filter, 37 resistance standard sample, 38: charge control electrode, 39: charge control voltage, 40: energy filter control unit, 301: via hole (low resistance) , 302: Si substrate, 303: SiO2 film, 304: SiO2 residual film, 305: Via hole (high resistance), 306: Potential distribution, 307: Secondary electron, 308: Secondary electron, 309: Vacuum level before charging 310: Vacuum level when positively charged, 311: Potential distribution before charging, 312: Potential distribution when positively charged, 313: Potential barrier, 314: Energy distribution of secondary electrons (before charging), 315: Energy distribution of secondary electrons (positive charge), 316: Energy distribution of secondary electrons released into the vacuum over the potential barrier Before charging) 317: Energy distribution of secondary electrons released into the vacuum over the potential barrier (positive charging), 320: Vacuum level when negatively charged, 321: Potential distribution when negatively charged, 322 : Potential barrier by energy filter, 323: energy distribution of secondary electrons, 324: energy distribution of secondary electrons emitted into the vacuum over the potential barrier, 325: energy distribution of secondary electrons that passed through the energy filter ( 326: energy distribution of secondary electrons that passed through the energy filter (negative charging), 401: negative charging, 402: positive charging, 701: p-Si substrate, 702: SiO 2 layer, 703: via hole embedded with a poly-Si plug, 704: n diffusion layer, 705: SiO 2 residual film, 06: pn junction, 901: normal pn junction, 902: conduction failure defect, 903: pn junction defect, 904: leak defect, 1201: normal pn junction (surface is n diffusion layer), 1202: normal pn junction (The surface is a p-diffusion layer) 1203: Conduction defect, 1204: Leak defect.

Claims (9)

A sample stage on which the sample is placed;
An objective lens for irradiating a predetermined region of the sample on the sample stage with a primary charged particle beam;
A scanning unit that scans a predetermined region of the sample with the primary charged particle beam;
A detector for detecting secondary electrons and backscattered electrons generated from the sample;
A measuring unit that measures a charging voltage in the predetermined region from a detected secondary electron signal intensity or backscattered electron signal intensity using a charged particle beam in which a current amount of the primary charged particle beam is adjusted to a predetermined value; ,
A control unit for adjusting a current amount of the primary charged particle beam so that a desired charged potential is formed in a predetermined region of the sample;
An image processing unit that forms a potential contrast image with a signal from the detector using the primary charged particle beam in which the amount of current is adjusted to a predetermined value;
A calculation unit for obtaining an electric resistance at an irradiation position of the charged particle beam from the charging voltage and the potential contrast image signal;
An inspection apparatus using a charged particle beam. In the inspection apparatus using the charged particle beam according to claim 1,
An inspection apparatus using a charged particle beam, comprising an electrode capable of applying a voltage to a sample surface as the measurement unit. In the inspection apparatus using the charged particle beam according to claim 1,
An inspection apparatus using a charged particle beam, wherein a magnetic field is applied to the sample in the vertical direction as the measurement unit. In the inspection apparatus using the charged particle beam according to claim 1 ,
An inspection apparatus using a charged particle beam, wherein the current amount has a function of adjusting a signal intensity detected by the detector within a region where the signal intensity changes with respect to a positive charging voltage and a negative charging voltage of the sample. . In the inspection apparatus using the charged particle beam according to claim 1 ,
An inspection apparatus using a charged particle beam having a function of adjusting an irradiation condition of the charged particle beam by adjusting an irradiation area of the charged particle beam instead of the amount of current . In the inspection apparatus using the charged particle beam according to claim 1 ,
In the scanning step, the charged particle beam having a function of scanning the charged particle beam over a region wider than the acquisition region of the secondary electron signal or the backscattered electron signal and charging the sample is used. Inspection device. In the inspection apparatus using the charged particle beam according to claim 1 ,
When the secondary electron signal or the backscattered electron signal intensity is displayed as a potential contrast image, the predetermined value of the current amount has a function to be determined in a region where the brightness of the potential contrast image changes. Inspection device using charged particle beam. In the inspection apparatus using the charged particle beam according to claim 1 ,
The semiconductor element is formed by irradiating the sample on which the semiconductor element is formed with the charged particle beam, calculating a resistance value of the predetermined region, and measuring a relationship between the calculated resistance value and the charging voltage. Inspection apparatus using a charged particle beam, characterized by inspecting a leak defect or a conduction defect. In the inspection apparatus using the charged particle beam according to claim 1 ,
A function of determining the current value of the charged particle beam under the condition of 0 <log (R · IP) <3, where R is the resistance value at the irradiation position of the charged particle beam and IP is the current value. Inspection apparatus using charged particle beam characterized by having.

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