JP4380782B2 - Sample inspection equipment - Google Patents

Description

The present invention relates to a pattern inspection apparatus and a pattern inspection method for semiconductors, and more particularly to a pattern inspection apparatus and a pattern inspection method capable of inspecting semiconductors and the like at high speed.

The semiconductor device manufacturing process repeats a number of pattern forming steps. If the manufacturing conditions are not optimized in each step, abnormalities such as foreign matters and defects occur in the circuit pattern of the semiconductor device formed on the substrate. Therefore, in the manufacturing process, it is necessary to detect the occurrence of the abnormality at an early stage and feed back to the process.
In general, in a manufacturing process of a semiconductor device such as a VLSI, a large number of chips having the same circuit pattern are taken out from a single semiconductor substrate. Therefore, the same circuit pattern is detected between different chips in order to detect this pattern abnormality. A method of comparison is taken. In an inspection apparatus that inspects a circuit pattern of a semiconductor wafer using an electron beam, it takes a tremendous amount of time to scan the entire surface of the wafer with an electron beam. Japanese Patent Laid-Open No. 59-6537 discloses a method for comparing identical circuit patterns.

In this known example, the difference signal between the detection signals obtained for the same circuit pattern between different chips exceeds the certain reference value, and the pattern is determined to be abnormal. However, in this configuration, it is possible to determine that either one is abnormal, but it is not possible to determine which pattern is abnormal. In order to determine abnormality, a comparison with a pattern obtained with another chip is essential. For this purpose, all the image data of these two chips are stored in the image memory, moved to another chip, and irradiated with the same pattern corresponding to the electron beam for determination. Therefore, a large-capacity image memory is required, and there is a risk that the stability of the system will be lost over time until moving to another chip.
Further, in order to improve the throughput of the inspection time, it is necessary to irradiate a fine electron beam probe with a large current on the sample. For this purpose, the luminance of the electron source must be high, and a field emission electron source is essential as an electron source. However, in order to operate the field emission electron source stably, the degree of vacuum in the vicinity of the electron source needs to be 10 ⁻⁷ Pa or less. However, it is difficult to arrange a plurality of electron optical systems densely while keeping the degree of vacuum of the electron gun at a high vacuum in the configuration so far. For example, in the above known example, the vicinity of the electron source is evacuated from the sample chamber. In the conventional example described in Journal of Vacuum Science and Technology B14 (6), page 3776, the entire electron optical system is placed in one chamber as shown in FIG. Therefore, in such a configuration, the sample chamber must also be in an ultrahigh vacuum in order to evacuate the vicinity of the electron source to an ultrahigh vacuum. However, wafers coated with chemicals such as resist have a large amount of released gas, and the structure of the stage that controls the movement of the wafer becomes complicated.
It is practically impossible to make the sample chamber into an ultra-high vacuum, and usually the degree of vacuum can only be improved to about 10 ⁻⁵ Pa. Even if an ultra-high vacuum in the sample chamber can be realized, the degree of vacuum in the sample chamber decreases when the sample is replaced. Therefore, it takes, for example, one hour or more to evacuate the sample chamber after the replacement. Therefore, it is impossible to inspect a large number of wafers in a short time.
Further, when the electron gun chamber 101 and the sample chamber 103 are evacuated by separate vacuum pumps for each electron optical system as shown in FIG. 13, a large number of vacuum pumps must be arranged,
It is necessary to provide a large space for installing the vacuum pump. For example, in order to arrange the vacuum pump in the central electron optical system of FIG.
Furthermore, when the electron optical system is densely arranged in a normal detection means, it becomes difficult to keep secondary electrons and reflected electrons 302 obtained by irradiating the sample with an electron beam in the same electron optical system. End up. That is, as a means for detecting secondary electrons and reflected electrons 302 with a plurality of arranged electron optical systems, as shown in FIG. 15, a method of detecting by arranging the detector 13 on the back surface of the final lens is a Journal of Vacuum. As described in Science and Technology B14 (6), page 3775, this configuration makes it difficult to keep secondary electrons and reflected electrons 302 in the same electron optical system. Secondary electrons and reflected electrons 302 can be easily applied to the detector 13 in the system.
Will be sucked and accurate pattern inspection will not be possible. Japanese Patent Laid-Open No. 2-142045 discloses a method for detecting secondary electrons accelerated by applying a negative voltage to a sample after passing through an objective lens. However, a specific method for improving the detection efficiency of secondary electrons is described. The configuration is not stated.

JP 59-6537

Japanese Patent Laid-Open No. 2-142045

The present invention is characterized by the following configuration as means for solving the above-described problems. That is, at least three or more electron optical systems are arranged, and the detection signals obtained with the same circuit pattern between different chips are compared. If there are three or more images acquired simultaneously, the location of the pattern defect can be determined simultaneously. Furthermore, even when the same pattern is repeatedly present in the chip and images obtained successively by the respective electron optical systems are sequentially compared and compared, the throughput of the inspection time is proportional to the number of electron optical systems. Will improve.

In order to keep the degree of vacuum in the vicinity of the electron source 1 always high, in the present invention, three or more electron optical systems are arranged in one mirror body as shown in FIG. The configuration is such that the electron optical system can be densely arranged by evacuating the vicinity of the intermediate chamber 102 disposed between the electron source 1 and the sample chamber 103 with a common vacuum pump. That is, the vicinity of the plurality of electron sources 1 communicates with the vicinity of the sample chamber only through a fine opening through which an electron beam passes, and is evacuated independently of the vicinity of the sample chamber 103, thereby The degree of vacuum was always kept at a high vacuum.

Further, since secondary electrons and reflected electrons generated in a plurality of electron optical systems can be independently detected by each electron optical system, secondary electrons and reflected electrons 302 generated from the sample as shown in FIG.
Is accelerated in the direction toward the electron source side of the electron beam optical axis 9 and can be detected by a detector disposed on the electron source side from the objective lens without colliding with the counter electrode 19. The velocity in the vertical direction of the electron beam optical axis 9 of the secondary electrons and the reflected electrons 302 is constant from the time of emission of the sample, but by obtaining acceleration in the direction of the electron beam optical axis 9, the secondary electrons and the reflected electrons 302 The trajectory is directed toward the electron beam optical axis 9. Here, when the voltage U is applied between the sample 10 and the counter electrode 19 facing the sample 10, and the sample 10 is not inclined and is placed substantially parallel to the counter electrode 19, the sample 10 and the counter electrode 1 are placed.
Between 9, a parallel electric field is distributed on a substantially uniform sample. Therefore, assuming a parallel electric field, the distance R traveled in a direction parallel to the sample until electrons emitted in a direction substantially parallel to the sample surface reach the counter electrode.
If the distance between the sample and the electrode is L, and the energy of electrons emitted from the sample is eV,
R = 2L√ (eV / eU) (1)
It is represented by Actually, if the counter electrode 19 has an opening, a parallel electric field is not generated in the vicinity of the opening, but R can be approximated by the equation (1). Considering S as the scanning width of the primary electron beam on the sample, the region where the electrons emitted from the sample spread on the counter electrode is 2R + S. Therefore, R obtained by substituting the maximum energy of reflected electrons, that is, the energy of the primary electron beam, into the emitted electron energy of the equation (1) is Rmax, and the diameter D1 of the counter electrode is D1> 2Rmax + S (2)
Is selected, the reflected electrons and secondary electrons are not allowed to escape outside the counter electrode and can be collected in the same optical system. Further, R obtained by substituting 50 eV for eV in the equation (1) is set as Rse, and the diameter D2 of the opening of the counter electrode 19 is set to D2> 2Rse + S (3)
Is selected, all secondary electrons or reflected electrons having an energy of 50 eV or less pass through the opening of the counter electrode and travel toward the electron source side. When the scanning width S is sufficiently small, the equations (2) and (3)
S in the equation can be omitted. From the above, if the size of the counter electrode and the size of the opening of the counter electrode are set under the above-mentioned conditions, secondary electrons or reflected electrons generated from the sample can be efficiently detected without escaping to the adjacent optical system. Can do. Secondary electrons and reflected electrons 302 that have passed through the opening of the counter electrode are subjected to the action of the objective lens 4 after passing through the opening of the counter electrode. The detector 13 is disposed above the objective lens 4 and can detect almost all secondary electrons and reflected electrons 302 whose trajectories have been changed by the action of the objective lens. Secondary electrons and backscattered electrons 302
Can be detected efficiently without escaping secondary electrons or reflected electrons 302 to the adjacent optical system even under the condition that a plurality of electron optical systems are densely arranged. Also,
For example, a secondary electron or reflected electron 302 is deflected in the direction of the electron beam optical axis so that the secondary electron or the reflected electron 302 undergoes a deflection action while the primary electron beam 301 is hardly deflected. If it is arranged so as to pass after being accelerated to deflect toward the detector,
Secondary electrons and reflected electrons 302 can be detected more efficiently. In addition, an aperture stop that restricts the opening angle of the primary electron beam is arranged closer to the electron source than the detector so that secondary electrons or reflected electrons do not collide with the aperture stop.

Further, in the present invention, an electric field or a magnetic field generated in each electron optical system is applied within the same optical system as shown in FIG. 14 so that the electromagnetic field generated in each optical system does not affect the surrounding electron optical system. A shielding electrode 17 having a structure that can shield the electron beam path and can evacuate the electron beam path is disposed on the outer periphery of the electron optical system so that the bleeding electric field and magnetic field from the electron lens and detector are within the same optical system. I tried to close it.

With the above configuration, the pattern inspection apparatus of the present invention densely arranges three or more electron optical systems in the same lens body and determines pattern defects in real time, thereby improving inspection accuracy and electron optics. The inspection speed is increased in proportion to the number of systems. In addition, by constantly maintaining a high vacuum in the vicinity of three or more electron sources, the electron source can be stably operated even when the sample chamber is in a low vacuum state, for example, when the sample is replaced. Furthermore, the signals detected from the pattern can be independently and accurately detected within each electron optical system without deflecting the electron beam from other electron optical systems. Therefore, pattern inspection can be performed at high speed and accurately.

Hereinafter, the present invention will be described with reference to examples. The first embodiment of the present invention is applied to circuit inspection of a semiconductor pattern, and will be described with reference to FIGS.

In the manufacturing process of a semiconductor device, as shown in FIG. The pattern forming process is roughly constituted by steps of film formation, photosensitive resist application, photosensitivity, development, etching, resist removal, and cleaning. If the manufacturing conditions are not optimized in each step, the circuit pattern of the semiconductor device formed on the substrate cannot be formed normally. For example, when an abnormality occurs in the film forming process of FIG. 2, particles are generated and adhere to the wafer surface, resulting in isolated defects. Also, if the conditions such as the focus and exposure time are not optimal at the time of resist exposure, locations where the amount and intensity of light irradiating the resist are excessive and insufficient occur, resulting in short circuit, disconnection, and pattern thinning. If there is a defect on the mask or reticle at the time of exposure, a similar pattern shape abnormality is likely to occur. Further, when the etching amount is not optimized or a thin film or particles generated during the etching, a short circuit, a protrusion, an isolated defect, an opening defect or the like also occurs. During cleaning, abnormal oxidation is likely to occur at the corners of the pattern due to the condition of running out of water during drying. Therefore, in the wafer manufacturing process, it is necessary to optimize the processing conditions so that these defects do not occur, and it is necessary to detect the occurrence of abnormality at an early stage and feed back to the process. Therefore, in this embodiment, an example in which inspection is applied after resist exposure and development in the n-th pattern forming step will be described.

  Examples of inspection will be described in detail below. FIG. 1 shows a configuration diagram thereof.

The electron optical system is composed of a first electron optical system 51, a second electron optical system 52, and a third electron optical system 53, and these electron optical systems are installed in one mirror body 200. Can be arranged more densely. Since the configuration of each electron optical system is the same, in the following description, the display of each part will be described in a simplified manner. For example, the electron source has 1a, 1a,
Although there are three, b and 1c, the following will be described as the electron source 1. The electron optical system includes an electron source 1, an electron gun lens 2, a condenser lens 3, an objective lens 4, a blanking deflector 5, a scanning deflector 6,
The reflector 7 and the E × B deflector 8 are included. The sample chamber 102 is an XY stage 11,
It comprises a pallet 12 for holding a sample, a spacer 18 and a position monitor length measuring device 27. The detector 13 is above the objective lens 4, and the output signal of the detector 13 is a preamplifier 31.
Is converted into digital data by the AD converter 32. The image processing unit 105 includes an image storage unit 33, a calculation unit 37, and a defect determination unit 38. The captured electron beam image is displayed on the monitor 36. Operation commands and operation conditions of each part of the inspection apparatus are input / output from the control unit 104. Conditions such as an acceleration voltage at the time of generating an electron beam, an electron beam deflection width, a deflection speed, a sample stage moving speed, and a signal capturing timing of a detector are input to the control unit 104 in advance. Further, a correction signal is generated from the signal of the position monitor length measuring device 27, and the correction signal is sent from the correction control circuit 28 to the lens power source or the scanning signal generator 25 so that the electron beam is always irradiated to the correct position.

The primary electron beam emitted from the field emission electron source 1 is accelerated to a desired acceleration voltage by the electron gun lens 2 and then focused on the sample by the condenser lens 3 and the objective lens 4. Reflected electrons reflected from the sample or secondary electrons generated secondarily in the sample are detected by the detector 13, amplified by the preamplifier 31, AD converted by the AD converter 32, and then the image storage unit 33. And the image is displayed on the monitor 36. The control unit 10 performs deflection scanning of the primary electron beam.
4 is performed by controlling the primary electron beam with the scanning signal sent from the scanning signal generator 25.

Although a field emission electron source is used as the electron source 1, it is preferable to use a diffusion replenishment type thermal field emission electron source particularly for pattern circuit inspection. As a result, a comparative inspection image with little brightness fluctuation can be obtained, and the electron beam current can be increased, so that high-speed inspection is possible.
The electron lens of each electron optical system is controlled as follows. The primary electron beam is extracted from the electron source 1 by applying a voltage to the electron gun lens 2. The primary electron beam is accelerated by applying a high-voltage negative voltage to the electron source from the high-voltage power supply 21 for applying the electron source. As a result, the primary electron beam advances toward the sample stage 11 with energy corresponding to the potential, for example, 10 kV. XY
A negative voltage can be applied to the pallet 12 electrically insulated from the stage 11 via the spacer 18 by a high voltage power supply 29 for retarding, and the sample 10 held on the pallet 12 is also connected to the pallet 12. Set to the same potential. This high voltage power supply for retarding 2
By adjusting the voltage of 9, it becomes easy to adjust the electron beam irradiation energy to the sample 10 to an optimum value. The acceleration voltage supplied to the electron source 1 from the high voltage power supply 21 for applying the electron source and the voltage applied to the pallet 12 are made equal in each electron optical system, and the energy of the primary electron beam incident on the sample is made equal in the all electron optical system. I am doing so. On the other hand, the voltage applied to the extraction electrode in the electron gun lens 2 can be adjusted independently by each electron optical system, and is supplied from the electron gun power supplies 22a, 22b, and 22c, respectively, so that the emission current from the electron source is independent. Can be controlled. The primary electron beam that has passed through the electron gun lens 2 is a condenser lens power source 23a.
, 23b, 23c and the objective lens power supplies 24a, 24b, 24c are independently adjusted so that the primary electron beam is mounted on the XY stage 11 at an arbitrary magnification in each electron optical system ( The sample 10 which is a wafer or a chip) is focused and irradiated.

In order to acquire an image of the sample 10, the sample 10 is irradiated with a finely focused primary electron beam to generate secondary electrons, which are detected in synchronization with the scanning of the primary electron beam and the movement of the stage. An image of the sample surface is obtained. A high inspection speed is essential for the automatic inspection described in the present invention. Accordingly, the beam current of the pA order is not irradiated at a low speed unlike a normal SEM. Therefore, an image is formed by scanning once or several times, for example, a 100 nA high-current electron beam that is about 100 times or more that of a normal SEM. For example, 1000 × 1000 pixels are acquired in 10 msec for one image.

Comparison of patterns between chips can be performed in real time from an image obtained by irradiating the same pattern portion of different chips almost simultaneously using three electron optical systems. That is, in the image processing system 105, the first electron optical system 51 stored in the image storage unit 33a.
And the pattern image from the second electron optical system 52 stored in the image storage unit 33b and the pattern image from the third electron optical system 53 stored in the image storage unit 33c are compared on the circuit board. Defect determination is performed in real time. First, in the image processing system 105, the image storage unit 3
The pattern images stored in 3a and 33b are calculated by the calculation unit 37ab. For example, the calculation unit 37ab has a function of calculating a difference between both images, and stores an address of an image in which the difference between both images exceeds a certain threshold. For example, as shown in FIG. 1, it is determined that the address P and the address Q are defective. However, the comparison between the two images cannot determine which image is defective. Therefore, the pattern images stored in the image storage units 33b and 33c are almost simultaneously converted into the calculation unit 3
Calculation is performed with 7bc. For example, as shown in FIG. 1, it is assumed that a defect is displayed only at the position of Q. Since the defect always appears at the position Q in the image comparison including the image b, the defect determination unit 38 determines that the defect at the position Q is a defect included in the image 33b. Further, it is determined that the defect at the position P is a defect included in the image 33a. Thus, by acquiring the same pattern image between different chips almost simultaneously using three electron optical systems, pattern defect determination can be performed in real time. Here, three image comparisons have been described. However, even when four or more images are simultaneously compared, a defective image can be determined by a substantially similar algorithm.

Next, FIG. 3 shows a configuration of an image processing system 105 that sequentially compares the images obtained by the optical systems and detects defects. When the same pattern is repeatedly drawn in the chip as in the case of a semiconductor memory pattern, it is possible to detect defects by sequentially comparing images obtained for each optical system. In the image processing system 105, the image stored in the image storage unit 33 in each optical system and the delay circuit 3.
5 is compared with the image stored in the image storage unit 34 with a delay of one image. The calculation unit 37 has a function of calculating, for example, a difference between both images, and stores an address P of an image in which the difference between both images exceeds a certain threshold in the defect determination unit 38. When the address P matches the address stored as a defect in the previous comparison, the defect determination unit 38 determines that the defect at the address P is a defect included in the image stored in the image storage unit 33. It is configured to search for defects on the circuit board in this order. Even when detecting defects by comparing images sequentially in this way, the defect inspection speed of the pattern increases in proportion to the number of electron optical systems, and if many electron optical systems are arranged, the defect inspection time can be greatly shortened. Can do.

Next, a means by which the detection system operates independently in each electron optical system will be described. In the present invention, secondary electrons and reflected electrons 202 are accelerated in the direction of the electron beam optical axis 9 on the electron source 1 side so that the secondary electrons and reflected electrons 202 are moved in the direction perpendicular to the electron beam optical axis 9. Spread and prevent entry into adjacent optical systems. Sample 10 is set to a negative potential, and primary electron beam 201 is sample 1
It is decelerated rapidly just before 0. Reflected electrons reflected from the sample 10 or secondary electrons generated secondarily in the sample 10 are accelerated in the direction of the electron beam optical axis 9. If the primary electron beam 201 is decelerated from 10 kV to 500 eV on the sample, reflected electrons or secondary electrons are accelerated by a voltage of 9.5 kV applied between the sample 10 and the counter electrode 19. When the distance between the sample 10 and the counter electrode 19 is 5 mm, and the scanning width of the primary electron beam is 0.1 mm, the diameter of the counter electrode 19 is set to about 5 mm or more from the equation (2), and generated from the sample. All the secondary electrons or backscattered electrons have a trajectory inside the counter electrode, and can be prevented from entering the adjacent optical system. In addition, from the equation (3), by setting the diameter of the opening 47 to about 1.6 mm or more,
Reflected electrons or secondary electrons of 50 eV or less can pass through the inside of the opening 47.
After the reflected electrons or secondary electrons pass through the objective lens 4, they are deflected in the direction of the detector 15 by the E × B deflector 8 and directly detected by the detector 15. Alternatively, secondary electrons or reflected electrons 202 are accelerated in the direction of the electron beam optical axis 9 and then deflected in the direction of the reflecting plate 7 by the E × B deflector 8, and collide with the reflecting plate 7 to hit the second secondary. Electrons 203 are generated, and the second secondary electrons 203 are detected by the detector 13 set to a positive potential from the reflector 7.
Further, the position of the diaphragm 20 that restricts the sample irradiation angle of the primary electron beam is installed on the electron source side from the detector 13 or the detector 15, so that secondary electrons or reflected electrons are efficiently detected without colliding with the diaphragm 20. I try to do it.

Furthermore, means for operating each optical system independently by confining an electric field and a magnetic field generated in each electron optical system in the same optical system will be described. A shield electrode made of a conductor magnetic material is grounded on the outer peripheral portion of each electron optical system, and the electromagnetic field of the electron optical system is shielded within the same optical system. That is, the electron gun chamber 101 shields the electromagnetic field of the electron source 1 and the electron gun lens 2, and the intermediate chamber 102 shields the electromagnetic field of the condenser lens 3, the objective lens 4 and the scanning deflector 6. A shield electrode 17 is provided. Especially E
If the electromagnetic field of the × B deflector 8 and the detector 13 leaks to the adjacent optical system, electrons generated in the adjacent optical system are attracted, so that the E × B deflector 8 and the detector 13 are particularly attracted. It is configured to enhance the shielding effect of the nearby electromagnetic field. These shielding electrodes also have the effect of shielding external stray electromagnetic fields. The shape of the shielding electrode may be any shape as long as it has an electromagnetic field shielding effect and can evacuate the electron beam path to a high vacuum. For example, it may be a cylindrical mesh as shown in FIG. A cylinder as shown in FIG. 10 has a hole for evacuation. Furthermore, if the shielding electrode has a double structure or a multiple structure of more than that, and has a shape as shown in FIG. 11 in which the openings are staggered, the shielding effect is substantially reduced without substantially degrading the conductance of the vacuum exhaust. Can be further improved.

Next, means for constantly operating the electron source in a high vacuum will be described. In this embodiment, three or more electron optical systems are installed in one mirror body 200. However, the electron gun chamber 101 including the electron source 1, the electron source lens 2, the intermediate chamber 102, and the sample chamber 103 are separated from each other. Vacuum pumps 42, 4
3 and 44 are evacuated. Although it is desirable to evacuate each space independently, an electron beam path through which the primary electron beam 201 irradiating the sample 10 passes is necessary. That is, the electron gun chamber 101 and the intermediate chamber 102 are connected through the opening 46, and the intermediate chamber 102 and the sample chamber 103 are connected through the opening 47. Therefore, particularly when the primary electron beam 201 is emitted from the electron source 1, an electron beam passage including the opening 46 and the opening 47 is provided with an electron gun chamber 101 and an intermediate chamber in order to evacuate each space as independently as possible. 102, the intermediate chamber 102 and the sample chamber 103 or the electron gun chamber 101 and the sample chamber 103 have the largest conductance. With this configuration, for example, the degree of vacuum of about 10 ⁻⁷ Pa is always obtained in the electron gun chamber 101 by evacuating with an ultrahigh vacuum pump such as an ion pump. Sample 10
For replacement, the sample 10 is preliminarily evacuated in another space by a roughing pump before inserting the sample into the sample chamber 103. However, when the sample chamber 103 is inserted, the degree of vacuum of the sample chamber 103 is temporarily temporarily reduced. It will drop. Even in such a situation, if the electron gun chamber 101 and the sample chamber 103 can be evacuated almost independently, a decrease in the degree of vacuum in the sample chamber 103 has little effect on the electron gun chamber 101, and thus the primary electron beam 201 is emitted. The sample can be exchanged even in a running state. Further, each electron optical system is provided with a valve 41a,
If 41b, 41c, and 41d are installed and each valve is closed, the degree of vacuum of the electron gun does not change even when the sample is exchanged, so that the sample can be exchanged while the primary electron beam 201 is emitted. .

In this embodiment, instead of the detection means using the E × B deflector 8, the detection surface is arranged so as to be perpendicular to the electron beam optical axis 9 and straddle the electron beam optical axis, and a hole is formed in the electron beam passage. Reflected electrons and secondary electron detectors may be used.

In this embodiment, the E × B deflector 8, the reflector 7 and the detector 13 are placed between the objective lens 4 and the electron source 1. However, the E × B deflector 8, the reflector 7 and the detector 13 are arranged. Objective lens 4 and sample 1
Even if it is placed between 0, the object of this embodiment can be achieved.

In this embodiment, the sample 10 is set to a negative potential. However, even when the sample 10 is grounded, if the relative potential between the sample and the other electrode is set in the same manner as in this embodiment, The objective can be achieved.

In the present embodiment, the arrangement of the electron optical system is not particularly limited. For example, the electron optical systems may be arranged in a grid pattern, or the electron optical systems may be arranged in a line.

The second embodiment uses an electrostatic lens as an electron lens. The electrostatic lens can be made smaller than the magnetic lens, and a large number of electron optical systems can be arranged in a limited space. FIG. 4 is a side view of the electron optical system of this embodiment. Although only two electron optical systems are shown in the drawing, in actuality, it is composed of three or more electron optical systems. The present embodiment is for an optical system that decelerates the primary electron beam 201 immediately before incidence of the sample, and the detection system uses the secondary secondary electrons 202 generated by the secondary electrons or the reflected electrons 202 colliding with the reflector 7. It is configured to detect. The secondary electrons or reflected electrons 202 emitted from the sample 10 are accelerated and converged by the objective lens 4, and then collide with the reflecting plate 7 with a certain spread to generate the second secondary electrons 203. The secondary electrons 203 are detected by the detector 13. The detector 13 is set to a positive potential and generates a detector electric field that attracts secondary electrons to the detector. Here, the electrode configuration is, for example, a two-electrode electrostatic lens or condenser lens 3 as the electron gun lens 2.
The objective lens 4 uses a three-electrode lens. In this embodiment, the shielding electrodes 16 and 17 are also used as an electron lens support. Since the positions of the electron gun lens 2, the condenser lens 3, and the objective lens 4 can be defined so as to be in contact with the inner peripheral portion of the shielding electrode 16, each lens can be positioned on the electron beam optical axis 9 with high accuracy. It is possible. The field emission electron source 1 can be replaced by removing the flange having the insulator. . Use a flange that can be vacuum-sealed to a high vacuum, with a diameter of 34mm to 70mm.
Range.

Even if the electrode configuration of the electrostatic lens is not the above-described configuration, the electrostatic lens functions as an electron gun lens including an extraction electrode that emits electrons from the electron source 1 and an electrode that accelerates or decelerates the primary electron beam to an acceleration voltage. Any configuration may be used as long as it has a function as a condenser lens capable of adjusting the magnification of the electron optical system and a function as an objective lens for converging the primary electron beam on the sample. For example, one multistage lens having three or more electrodes may be configured to have both functions of a condenser lens and an objective lens or both functions of an electron gun lens and a condenser lens. In the third embodiment shown in FIG. 5, it is possible to make the electron optical system more compact by providing two functions of an electron gun lens and a condenser lens with a single three-electrode electron gun lens. FIG. 5 is a side view of the configuration of the electron optical system of the present embodiment, and FIG. 6 is a view of the electron gun chamber 101 and the intermediate chamber 102 of the present embodiment as viewed obliquely from above. In this embodiment, the detector 13 of the reflected electrons or secondary electrons 202 is arranged so that the detection surface is perpendicular to the electron beam optical axis 9 and straddles the electron beam optical axis 9, and a hole is formed in the electron beam passage. Something is used. Sample 1
A negative voltage is set to 0, and the reflected electrons or secondary electrons 202 are accelerated after the sample 10 is emitted and then detected. The shape of the detector 13 is, for example, an annular one or a plurality of detectors arranged symmetrically with respect to the electron beam optical axis 9. When a plurality of detectors are used, it is also possible to distinguish and detect the emission direction from the sample by selecting an acquisition signal from the detector.

In the fourth embodiment shown in FIG. 7, the electrode 441 on the most electron source side of the objective lens 4 is the mirror body 200.
The counter electrode 443 to the sample is set to a negative voltage having the same potential as that of the sample. Further, by adjusting the potential of the intermediate electrode 442, the primary electron beam is focused on the sample. In this configuration, secondary electrons and reflected electrons 202 are not affected by the electric field until reaching the counter electrode 443, and are accelerated in the direction of the electron source side of the electron beam optical axis 9 after passing through the counter electrode 443. If the diameter of the opening of the counter electrode 443 is made larger than the distance between the samples, for example, twice or more, most of the electrons are accelerated without colliding with the counter electrode 443 and detected by the detector 13. it can. In FIG. 17, the distance L between the counter electrode 443 and the sample 10 is L = 3 mm, the diameter of the counter electrode opening 2R = 6 mm, the sample 10 counter electrode is at the same potential, and +9.5 kV is applied to the intermediate electrode 442 with respect to the counter electrode 443 The potential distribution in this case is obtained by the difference method, and the result of calculating the secondary electron orbit under this potential distribution is shown. The potential distribution is as shown by the equipotential surface 444. The figure shows the trajectory of the secondary electrons 202 emitted at an angle of 10 ° from 0 ° to 90 ° with an initial energy of 50 eV. When the opening is made large, the equipotential surface bleeds into the sample side. As a result, the secondary electrons are accelerated upward before reaching the counter electrode, and all the secondary electrons including the electrons emitted almost in parallel to the sample do not collide with the counter electrode. Can be directed to.

FIG. 8 shows a top view of the electron source 1 of the present embodiment with the electron source 1 removed.
Are divided for each electron source and can be evacuated by a separate vacuum pump.
By closing the valve 41, each electron source can be brought into an atmospheric pressure state independently. With this function, the electron source 1 can be replaced while the other electron sources are kept in a high vacuum state.

In the first to fourth embodiments, the case where three or four sets of electron optical systems are mounted has been described. Of course, five or more sets of electron optical systems, for example, ten sets of electron optics are used. The object of the present invention can be easily achieved even in a configuration in which the system is mounted.

In the second to fourth embodiments, the actual shape of the electrostatic lens is such that the insulating portion cannot be seen from the electron beam passage. The shape was explained on a flat plate.
In the second to fourth embodiments, the condenser lens power supply 23 is used for convenience.
Although the objective lens power supply 24 is placed in the vacuum in the figure, it is actually installed outside the vacuum.

Further, in the present invention, the configuration in which a plurality of electron sources are kept in a high vacuum and the configuration in which each electron optical system can independently detect secondary electrons and reflected electrons in the electron optical system are an electron beam using an electron beam. The present invention can also be applied to various electron beam application apparatuses such as a drawing apparatus and a scanning electron microscope that measures pattern dimensions, with the same configuration. Furthermore, not only electron beams but also charged particle beam application devices including ion beams are generated secondary by charged particle irradiation in a configuration that maintains a plurality of charged particle sources in a high vacuum and each charged particle optical system. A configuration capable of detecting charged particles with high accuracy in the same charged particle optical system can be realized by a configuration similar to the present invention. In these cases, the present invention can be applied to an apparatus having two or more electron optical systems or charged particle optical systems.

As described above, the pattern inspection apparatus according to the present invention is useful for an inspection apparatus for inspecting a circuit pattern on a semiconductor wafer, and is applied to a pattern inspection apparatus intended to perform pattern inspection at high speed and accurately. Suitable for that.

It is a block diagram which shows the 1st Example of this invention. It is a figure which shows the analysis procedure of the 1st Example of this invention. It is a block diagram which shows another structure of the image processing system of the 1st Example of this invention. It is a block diagram which shows the 2nd Example of this invention. It is a block diagram which shows the 3rd Example of this invention. It is the figure which looked at the structure of the 3rd Example of this invention from diagonally upward. It is a block diagram which shows 4th Example of this invention. It is the figure which looked at the structure of 4th Example of this invention from the top. It is a figure which shows the structure of a shielding electrode. It is a figure which shows the structure of a shielding electrode. It is a figure which shows the structure of a shielding electrode. It is a figure which shows the prior art example in which the electron optical system was placed in one chamber. It is a figure which shows the prior art example which exhausts an electron gun chamber and a sample chamber with a separate vacuum pump. It is a figure which shows the outline of this invention. It is a figure which shows the prior art example which has arrange | positioned the detector on the back surface of the last stage lens. The figure which shows the structure which accelerates and detects a secondary electron or a reflected electron. It is a figure which shows the electric potential distribution of a counter electrode and an intermediate electrode, and the calculation result of a secondary electron orbit.

Claims (3)

Scanning the primary electron beam to the sample, a plurality of the electron optical system for detecting secondary electrons or reflected electrons generated by the scanning of the primary electron beam, a sample stage where the sample is placed, the in the sample inspection apparatus and a processes the signal by the secondary electrons or the reflected electron image processing unit to inspect the sample,
The plurality of electron optical systems includes:
An electron source for generating the primary electron beam;
An objective lens for the primary electron beam and the secondary electrons or the reflected electrons pass through,
A counter electrode disposed between the objective lens and the sample stage;
A detector disposed above the objective lens;
And a power source for applying a potential to accelerate the secondary electrons or the reflected electrons between the sample stage and the counter electrode,
The potential U, L a distance between the sample and the counter electrode, when the irradiation energy of the primary electron beam to be irradiated to the sample was eV, the counter electrode, 4L (eV / eU) have a ^1/2 or more of the diameter,
The plurality of electron optical systems are installed in a single lens body, and each of the plurality of electron optical systems includes a shielding electrode that shields an electromagnetic field on the outer periphery.
A sample inspection apparatus. Scanning the primary electron beam to the sample, a plurality of the electron optical system for detecting secondary electrons or reflected electrons generated by the scanning of the primary electron beam, a sample stage where the sample is placed, the in the sample inspection apparatus and a processes the signal by the secondary electrons or the reflected electron image processing unit to inspect the sample,
The plurality of electron optical systems includes:
An electron source for generating the primary electron beam;
An objective lens for the primary electron beam and the secondary electrons or the reflected electrons pass through,
A counter electrode disposed between the objective lens and the sample stage;
A detector disposed above the objective lens;
And a power source for applying a potential to accelerate the secondary electrons or the reflected electrons between the sample stage and the counter electrode,
The potential U, L a distance between the sample and the counter electrode, the irradiation energy of the primary electron beam to be irradiated to the sample eV, if the scanning width of the primary electron beam was set to S, the counter electrode may have a opening of ^{4L (eV / eU) 1/2 +} S or more in diameter,
The plurality of electron optical systems are installed in a single lens body, and each of the plurality of electron optical systems includes a shielding electrode that shields an electromagnetic field on the outer periphery.
A sample inspection apparatus. Scanning the primary electron beam to the sample, a plurality of the electron optical system for detecting secondary electrons or reflected electrons generated by the scanning of the primary electron beam, a sample stage where the sample is placed, the in the sample inspection apparatus and a processes the signal by the secondary electrons or the reflected electron image processing unit to inspect the sample,
The plurality of electron optical systems includes:
An electron source for generating the primary electron beam;
An objective lens for the primary electron beam and the secondary electrons or the reflected electrons pass through,
A counter electrode disposed between the objective lens and the sample stage;
A detector disposed above the objective lens;
And a power source for applying a potential to accelerate the secondary electrons or the reflected electrons between the sample stage and the counter electrode,
The counter electrode may have a opening of at least twice the diameter of the distance between the counter electrode and the sample,
The plurality of electron optical systems are installed in a single lens body, and each of the plurality of electron optical systems includes a shielding electrode that shields an electromagnetic field on the outer periphery.
A sample inspection apparatus.

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