Multiple electron beam irradiation device and multiple electron beam irradiation method

Abstract

A multiple electron beam irradiation device according to one embodiment of the present invention is characterized by comprising: an emission source that emits an electron beam in a divergence direction; a first condenser lens that refracts the electron beam traveling in the divergence direction in a focusing direction and forms substantially parallel beams; a molded aperture array substrate in which a plurality of first openings are formed and a portion of each of the electron beams that have become substantially parallel beams passes through the plurality of first openings, thereby forming multiple electron beams; and a two-stage multipole lens array in which each lens has a quadrupole or higher multipole arranged on the trajectory of an assigned beam of the multiple electron beams.

Description

Multi-electron beam irradiation device and multi-electron beam irradiation method

[0001] This application claims priority from JP2023-125752 (application number) filed in Japan on August 1, 2023. The entire contents of JP2023-125752 are incorporated herein by reference.

[0002] One aspect of the present invention relates to a multi-electron beam irradiation apparatus and a multi-electron beam irradiation method, for example, to an apparatus for correcting variations in the shape of the multi-electron beams and variations in the convergence angle at an intermediate image plane position of an electron source image of the multi-electron beams caused by aberrations or the like.

[0003] In recent years, with the increasing integration and capacity of large-scale integrated circuits (LSIs), the circuit line widths required for semiconductor elements have become increasingly narrow. Furthermore, improving yield is essential for the manufacture of LSIs, which incur significant manufacturing costs. However, as exemplified by 1-gigabit-class DRAMs (Dynamic Random Access Memory), the patterns that make up LSIs are now on the order of submicrons to nanometers. As the dimensions of LSI patterns formed on semiconductor wafers have become increasingly miniaturized in recent years, the dimensions that must be detected as pattern defects have also become extremely small. Therefore, high-precision image capture is necessary to inspect defects in ultra-fine patterns transferred onto semiconductor wafers.

[0004] In the inspection device, for example, a substrate to be inspected is scanned with multiple primary electron beams using electron beams, multiple secondary electron beams emitted from the substrate to be inspected are separated from the trajectories of the multiple primary electron beams, and the multiple secondary electron beams are detected by a detector to capture a pattern image.

[0005] Here, it is desirable that the multiple primary electron beams have the same shape, size, and focusing angle on the sample surface. However, there is a problem that variations in these occur due to field curvature aberration and astigmatism caused by electromagnetic lenses and the like along the way. It is desirable to reduce these variations as much as possible.

[0006] Here, it is disclosed that a two-stage stigmator is used to refract the entire multi-beams at once, thereby correcting both astigmatism and linear distortion (see, for example, Patent Document 1).

[0007] Japanese Patent Application Laid-Open No. 2022-159159

[0008] Therefore, one aspect of the present invention provides an apparatus and method that can correct astigmatism of multiple electron beams on a sample surface and reduce variations in focal position.

[0009] A multi-electron beam irradiation device according to one aspect of the present invention is characterized by comprising: an emission source that emits electron beams in divergent directions; a first condenser lens that refracts the electron beams traveling in the divergent direction in a converging direction to form a substantially parallel beam; a shaping aperture array substrate having a plurality of first openings formed therein, and in which portions of the electron beams that have become substantially parallel beams pass through the plurality of first openings to form a multi-electron beam; and a two-stage multipole lens array, in which each lens has a multipole element with a quadrupole or higher number that is positioned on the trajectory of a beam of the multi-electron beams that it is responsible for.

[0010] A multi-electron beam irradiation method according to one aspect of the present invention includes emitting an electron beam in a diverging direction from an emission source; using a first condenser lens, refracting the electron beam traveling in the diverging direction in a converging direction to form a substantially parallel beam; using a shaping aperture array substrate having a plurality of first openings, portions of the electron beam that has become a substantially parallel beam pass through the plurality of first openings to form a multi-electron beam; and using a two-stage multipole lens array, each lens having a multipole element with a quadrupole or higher number arranged on the trajectory of a beam of the multi-electron beam that it is responsible for, correcting the position of the electron source image in two orthogonal directions for each beam.

[0011] According to one aspect of the present invention, it is possible to correct astigmatism of multiple electron beams on a sample surface and reduce variations in focal position.

[0012] FIG. 1 is a configuration diagram showing the configuration of a pattern inspection apparatus according to the first embodiment. FIG. 2 is a conceptual diagram showing the configuration of a shaping aperture array substrate according to the first embodiment. FIG. 3 is a diagram showing an example of a plurality of chip regions formed on a semiconductor substrate according to the first embodiment. FIG. 4 is a diagram for explaining image acquisition processing according to the first embodiment. FIG. 5 is a diagram showing an example of the configuration from a radiation source to an intermediate image plane position of a multi-primary electron beam in a comparative example 1 of the first embodiment. FIG. 6 is a diagram showing an example of a method of correction using a one-stage stigmator in a comparative example 2 of the first embodiment. FIG. 7 is a diagram showing an example of a method of isotropic astigmatism correction using a two-stage multipole lens according to the first embodiment. FIG. 8 is a diagram showing an example of the configuration of a multipole lens array according to the first embodiment. FIG. 9 is a diagram showing another example of a method of isotropic astigmatism correction using a two-stage multipole lens according to the first embodiment. FIG. 10 is a diagram showing another example of a method of image plane formation at an arbitrary position using a two-stage multipole lens according to the first embodiment. FIG. 11 is a diagram showing an example of a configuration in which two-stage multipole lenses are arranged when object surfaces do not coincide according to the first embodiment. FIG. 12 is a diagram showing an example of the range of magnification adjustment when object surfaces do not coincide according to the first embodiment. 1 is a diagram showing an example of a configuration in which two stages of multipole lenses are arranged when the image plane is shifted in the x and y directions in embodiment 1. FIG. 2 is a diagram showing an example of a range of magnification adjustment when the image plane is shifted in the x and y directions in embodiment 1. FIG. 3 is a diagram showing an example of a range of focal lengths when the image plane is shifted in the x and y directions in embodiment 1. FIG. 4 is a diagram for explaining the operation of an angle-limiting aperture array in embodiment 1. FIG. 5 is a diagram showing an example of each configuration from an electron source to an intermediate image plane after astigmatism correction in modification 1 of embodiment 1. FIG. 6 is a diagram showing an example of each configuration from an electron source to an intermediate image plane after astigmatism correction in modification 2 of embodiment 1. FIG. 7 is a diagram showing an example of each configuration from an electron source to an intermediate image plane after astigmatism correction in modification 3 of embodiment 1. FIG. 8 is a flowchart showing an example of main steps of a method for adjusting a multistage lens array in embodiment 1. FIG. 9 is a diagram showing an example of the configuration within a comparison circuit in embodiment 1. FIG. 10 is a diagram showing an example of the configuration of an inspection device in embodiment 2. FIG. 11 is a diagram showing an example of a beam shaped by a shaping aperture array substrate in embodiment 2. FIG. 12 is a diagram showing an example of an arrangement of multipole lenses in each embodiment.

[0013] In the following embodiments, a multi-electron beam inspection apparatus will be described as an example of a multi-electron beam irradiation apparatus. However, the multi-electron beam irradiation apparatus is not limited to an inspection apparatus, and may be, for example, a drawing apparatus or the like.

[0014] [First Embodiment] Fig. 1 is a configuration diagram showing the configuration of a pattern inspection apparatus according to a first embodiment. In Fig. 1, an inspection apparatus 100 that inspects a pattern formed on a substrate is an example of a multi-electron beam inspection apparatus. The inspection apparatus 100 is an example of a multi-electron beam irradiation apparatus. The inspection apparatus 100 is an example of a multi-electron beam image acquisition apparatus. The inspection apparatus 100 includes an image acquisition mechanism 150 and a control system circuit 160 (control unit). The image acquisition mechanism 150 includes an electron beam column 102 (electron lens barrel), an inspection chamber 103, a detection circuit 106, a chip pattern memory 123, a stage driving mechanism 142, and a laser length measurement system 122. The electron beam column 102 contains an electron gun 201, a condenser lens 202 (first condenser lens) (pre-condenser lens), a shaping aperture array substrate 203, a multi-stage lens array 210, an angle limiting aperture array substrate 211, a condenser lens 205 (second condenser lens) (post-condenser lens), a collective deflector 212, a limiting aperture substrate 213, an electromagnetic lens 206, an E×B separator 214 (separator), an electromagnetic lens 207 (objective lens), deflectors 208 and 209, a deflector 218, deflectors 225 and 226, an electromagnetic lens 224, and a multi-detector 222.

[0015] The primary electron optical system 151 (illumination optical system) is composed of the electron gun 201, the condenser lens 202, the shaping aperture array substrate 203, the multistage lens array 210, the angle limiting aperture array substrate 211, the condenser lens 205, the collective deflector 212, the limiting aperture substrate 213, the electromagnetic lens 206, the E×B separator 214 (separator), the electromagnetic lens 207, and the deflectors 208 and 209. The secondary electron optical system 152 (detection optical system) is composed of the electromagnetic lens 207, the E×B separator 214, the deflector 218, the deflectors 225 and 226, and the electromagnetic lens 224.

[0016] The multi-detector 222 has a plurality of detection elements arranged in an array (grid).

[0017] The multi-stage lens array 210 is configured by a two-stage multipole lens array (plurality of lens arrays), each of which has a multipole of quadrupole or more arranged on the trajectory of a beam of the multiple primary electron beams 20 that it is responsible for.

[0018] The angle limiting aperture array substrate 211 has a plurality of passage holes (second openings) formed at positions where the multiple primary electron beams 20 pass through.

[0019] A stage 105 movable at least in the X and Y directions is disposed within the inspection chamber 103. A substrate 101 (sample) to be inspected is disposed on the stage 105. The substrate 101 includes an exposure mask substrate and a semiconductor substrate such as a silicon wafer. When the substrate 101 is a semiconductor substrate, multiple chip patterns (wafer dies) are formed on the semiconductor substrate. When the substrate 101 is an exposure mask substrate, multiple chip patterns are formed on the exposure mask substrate. The chip patterns are composed of multiple graphic patterns. The chip patterns formed on the exposure mask substrate are transferred onto the semiconductor substrate multiple times by exposure, thereby forming multiple chip patterns (wafer dies) on the semiconductor substrate. The substrate 101 is disposed on the stage 105, for example, with its pattern-forming surface facing upward. A mirror 216 is disposed on the stage 105 to reflect laser light for laser measurement irradiated from a laser measurement system 122 disposed outside the inspection chamber 103. A mark 111 is disposed on the stage 105 at the same height as the surface of the substrate 101. The mark 111 has, for example, a cross pattern formed thereon.

[0020] Furthermore, the multi-detector 222 is connected to a detection circuit 106 outside the electron beam column 102. The detection circuit 106 is connected to a chip pattern memory 123.

[0021] In the control system circuit 160, a control computer 110 that controls the entire inspection apparatus 100 is connected via a bus 120 to a position circuit 107, a comparison circuit 108, a reference image creation circuit 112, a stage control circuit 114, a lens control circuit 124, a blanking control circuit 126, a deflection control circuit 128, a multi-stage lens array control circuit 130, an E×B separator control circuit 132, a storage device 109 such as a magnetic disk drive, a monitor 117, a memory 118, and a printer 119. The deflection control circuit 128 is also connected to DAC (digital-to-analog converter) amplifiers 144, 146, 147, and 149, and a DC power supply 148. The DAC amplifier 146 is connected to a deflector 208, and the DAC amplifier 144 is connected to the deflector 209. The DC power supply 148 is connected to a deflector 218. The DAC amplifier 147 is connected to a deflector 225. The DAC amplifier 149 is connected to the deflector 226 .

[0022] The chip pattern memory 123 is also connected to the comparison circuit 108. The stage 105 is driven by a drive mechanism 142 under the control of the stage control circuit 114. The drive mechanism 142 is configured with a drive system, such as a three-axis (X-Y-θ) motor that drives the stage 105 in the X, Y, and θ directions of a stage coordinate system, thereby enabling the stage 105 to move in the X, Y, and θ directions. These X, Y, and θ motors (not shown) can be, for example, step motors. The stage 105 can move horizontally and in rotational directions by the motors for the X, Y, and θ axes. The movement position of the stage 105 is measured by a laser length measurement system 122 and supplied to the position circuit 107. The laser length measurement system 122 measures the position of the stage 105 based on the principle of laser interferometry by receiving light reflected from a mirror 216. In the stage coordinate system, for example, the X, Y, and θ directions of the primary coordinate system are set relative to a plane perpendicular to the optical axis of the multi-primary electron beams 20.

[0023] The condenser lens 202 , the condenser lens 205 , the electromagnetic lens 206 , the electromagnetic lens 207 , and the electromagnetic lens 224 are controlled by the lens control circuit 124 .

[0024] The multi-lens array 210 is controlled by a multi-lens array control circuit 130 .

[0025] The collective deflector 212 is composed of two or more electrodes and is controlled by the blanking control circuit 126 for each electrode via a DAC amplifier (not shown). The deflector 209 is composed of four or more electrodes and is controlled by the deflection control circuit 128 for each electrode via a DAC amplifier 144. The deflector 208 is composed of four or more electrodes and is controlled by the deflection control circuit 128 for each electrode via a DAC amplifier 146. The deflector 225 is composed of four or more electrodes and is controlled by the deflection control circuit 128 for each electrode via a DAC amplifier 147. The deflector 226 is composed of four or more electrodes and is controlled by the deflection control circuit 128 for each electrode via a DAC amplifier 149.

[0026] The deflector 218 (bender) is configured, for example, in the shape of a cylinder curved in an arc by a plurality of electrodes having four or more poles, and each electrode is controlled by the deflection control circuit 128 via the DC power supply 148. Alternatively, the deflector 218 may be configured to be configured by a plurality of flat electrodes having four or more poles, and each electrode may be controlled by the deflection control circuit 128 via the DC power supply 148.

[0027] The E×B separator 214 is controlled by the E×B separator control circuit 132 .

[0028] A high-voltage power supply circuit (not shown) is connected to the electron gun 201, and an acceleration voltage is applied from the high-voltage power supply circuit between a filament (not shown) and an extraction electrode (not shown) inside the electron gun 201. In addition, a voltage is applied to a predetermined extraction electrode (Wehnelt) and the cathode is heated to a predetermined temperature, whereby a group of electrons emitted from the cathode are accelerated and emitted as an electron beam 200.

[0029] 1 shows the configuration necessary for explaining the first embodiment. The inspection device 100 may also include other configurations that are normally required.

[0030] 2 is a conceptual diagram showing the configuration of the shaping aperture array substrate in the embodiment 1. In FIG. 2, the shaping aperture array substrate 203 has a two-dimensional lateral (x direction) m １ Column x vertical (y direction) n １ Step (m １ , n １ The shaping aperture array substrate 203 has holes (apertures) 22 (where n is an integer of 2 or more) formed at a predetermined arrangement pitch in the x and y directions. The example in FIG. 2 shows a case where 5 × 5 holes (apertures) 22 are formed. Each hole 22 is formed as a circle with the same outer diameter. Alternatively, they may be rectangular with the same dimensions. Multiple primary electron beams 20 are formed by portions of the electron beam 200 passing through these multiple holes 22. The shaping aperture array substrate 203 is an example of a multi-beam forming mechanism that forms multiple primary electron beams 20.

[0031] The image acquisition mechanism 150 uses multiple electron beams to acquire an image of the graphic pattern to be inspected from the substrate 101 on which the graphic pattern is formed. The operation of the image acquisition mechanism 150 in the inspection device 100 will be described below.

[0032] An electron gun 201 (an example of an electron source) emits an electron beam 200 in a diverging direction. The emitted electron beam can be considered to be emitted from a virtual electron source near the tip of the cathode, which is the electron emitter of the electron gun 201. This region is called, for example, a virtual light source or virtual electron source. The image obtained downstream of the electron gun and projected by the lens of this virtual light source or virtual electron source is called an electron source image. The electron beam 200 emitted from the electron gun 201 and traveling in a diverging direction is subjected to a focusing force by a condenser lens 202. An electromagnetic lens or an electrostatic lens is used as the condenser lens 202. The electron beam 200, which has become a substantially parallel beam, then illuminates the entire shaping aperture array substrate 203. For simplicity, an example is shown in which a single-stage condenser lens 202 is placed immediately after the electron gun 201. If necessary, the single-stage condenser lens 202 may be replaced by a lens group consisting of multiple stages of lenses. The size of the electron source image can also be adjusted by adjusting the focal length of each lens in the lens group. The lenses constituting the lens group include either or both of electromagnetic lenses and electrostatic lenses. The electron gun structure also includes a structure including an electrode group that further accelerates and focuses electrons emitted from the cathode after they are extracted by an extraction electrode. As shown in FIG. 2 , a plurality of holes 22 (first openings) are formed in the shaping aperture array substrate 203, and the electron beam 200 illuminates an area including all of the plurality of holes 22. Portions of the electron beam 200 irradiated at the positions of the plurality of holes 22 pass through the plurality of holes 22 in the shaping aperture array substrate 203, respectively, to form the multiple primary electron beams 20. By forming a substantially parallel beam using the condenser lens 202, the multiple primary electron beams 20 can travel substantially parallel to each other. This makes it easier to align the positions of the multiple openings in the downstream multistage lens array 210 and / or the multiple openings in the angle-limiting aperture array substrate 211 with the passing positions of the multiple primary electron beams 20. In other words, it is possible to eliminate or reduce errors in the formation positions of the openings in the components through which the multiple primary electron beams 20 pass.

[0033] The formed multiple primary electron beams 20 are refracted by a multistage lens array 210, and the position of the electron source image in two orthogonal directions for each beam is corrected. The multiple primary electron beams 20 that have passed through the multistage lens array 210 have their divergence angle or convergence angle limited by an angle-limiting aperture array substrate 211, thereby correcting variations in the convergence angle at the image plane 19 (intermediate image plane) position. The image plane 19 (intermediate image plane) position is determined so that the position of the electron source image after passing through the downstream optical system coincides with the sample surface. This makes it possible to eliminate the influence of the field curvature of the downstream optical system.

[0034] The multi-primary electron beams 20 that have passed through the angle-limiting aperture array substrate 211 are refracted by the condenser lens 205 to form an intermediate image of the electron source image and a crossover. Here, the crossover refers to the beam distribution at a position where the centers of the aberration-free trajectories of the multi-primary electron beams 20 converge at one point. The positions of the angle-limiting aperture array substrate 211 and the condenser lens 205 may be reversed. In such a case, the multi-primary electron beams 20 that have passed through the multistage lens array 210 are refracted by the condenser lens 205, and form an intermediate image and a crossover after passing through the angle-limiting aperture array substrate 211.

[0035] The multi-primary electron beams 20 that have passed through the condenser lens 205 are refracted by an electromagnetic lens 206 to further form an intermediate image, and proceed to an E×B separator 214 that is disposed at the height of the intermediate image plane (image plane conjugate position: I.I.P.) of the electron source image of each beam of the multi-primary electron beams 20. The multi-primary electron beams 20 then pass through the E×B separator 214 and proceed to an electromagnetic lens 207. Furthermore, by disposing a limiting aperture substrate 213 with limited passage holes near the crossover position of the multi-primary electron beams 20, scattered beams can be blocked. Furthermore, by deflecting the entire multi-primary electron beams 20 collectively with a collective deflector 212 and blocking the entire multi-primary electron beams 20 with the limiting aperture substrate 213, the entire multi-primary electron beams 20 can be blanked.

[0036] When the multiple primary electron beams 20 are incident on the electromagnetic lens 207, the electromagnetic lens 207 forms an image of the multiple primary electron beams 20 on the substrate 101. In other words, the electromagnetic lens 207 irradiates the substrate 101 with the multiple primary electron beams 20.

[0037] The multi-primary electron beams 20, which have been focused on the surface of the substrate 101 (sample) by the electromagnetic lens 207, are deflected collectively by the deflectors 208 and 209, and each beam is irradiated onto a respective irradiation position on the substrate 101. In this way, the primary electron optical system 151 illuminates the substrate 101 with the multi-primary electron beams 20.

[0038] When a desired position on the substrate 101 is irradiated with the multi-primary electron beams 20, a bundle of secondary electrons including reflected electrons (multi-secondary electron beams 300) is emitted from the substrate 101 due to the irradiation of the multi-primary electron beams 20. A secondary electron beam corresponding to each beam of the multi-primary electron beams 20 is emitted.

[0039] The multiple secondary electron beams 300 emitted from the substrate 101 pass through the electromagnetic lens 207 and proceed to the E×B separator 214 .

[0040] The E×B separator 214 separates the multiple secondary electron beams 300 from the orbit of the multiple primary electron beams 20 .

[0041] The EXB separator 214 has two or more magnetic poles (electromagnetic deflection poles) using coils and two or more electrodes (electrostatic deflection electrodes). For example, two opposing magnetic poles and two opposing electrodes shifted in phase by 90° are arranged. The arrangement is not limited to this. For example, a structure in which the electrodes also function as magnetic poles may be arranged, with four or eight electrodes / magnetic poles. The EXB separator 214 deflects the multiple secondary electron beams 300 to produce a separating effect. The EXB separator 214 generates a directional magnetic field using multiple magnetic poles. Similarly, it generates a directional electric field using multiple electrodes. Specifically, the EXB separator 214 generates an electric field E and a magnetic field B in perpendicular directions on a plane perpendicular to the direction in which the central beam of the multiple primary electron beams 20 travels (the central axis of the orbit). The electric field exerts a force in the same direction regardless of the direction of electron travel. On the other hand, the magnetic field exerts a force according to Fleming's left-hand rule. Therefore, the direction of the force acting on the electrons can be changed depending on the direction of electron travel. The force FE due to the electric field and the force FB due to the magnetic field cancel each other out on the multi-primary electron beams 20 entering the E×B separator 214 from above, causing the multi-primary electron beams 20 to travel straight downward. On the other hand, the force FE due to the electric field and the force FB due to the magnetic field act in the same direction on the multi-secondary electron beams 300 entering the E×B separator 214 from below, causing the multi-secondary electron beams 300 to bend obliquely upward by being deflected in a predetermined direction, and to separate from the trajectory of the multi-primary electron beams 20.

[0042] The multi-secondary electron beams 300, which have been bent obliquely upward and separated from the multi-primary electron beams 20, are guided to the multi-detector 222 by the secondary electron optical system 152. Specifically, the multi-secondary electron beams 300, which have been separated from the multi-primary electron beams 20, are deflected by the deflector 218, whereby they are further bent, and proceed to the electromagnetic lens 224. The multi-secondary electron beams 300 are then projected onto the multi-detector 222 while being refracted in the focusing direction by the electromagnetic lens 224 at a position away from the trajectories of the multi-primary electron beams 20. The multi-detector 222 (multi-secondary electron beam detector) detects the multi-secondary electron beams 300 which have been separated from the trajectories of the multi-primary electron beams 20. In other words, the multi-detector 222 detects the refracted and projected multi-secondary electron beams 300. The multi-detector 222 has a plurality of detection elements (for example, a diode-type two-dimensional sensor, not shown). Each beam of the multi primary electron beams 20 collides with a detection element corresponding to each secondary electron beam of the multi secondary electron beams 300 on the detection surface of the multi detector 222, generating electrons and generating secondary electron image data for each pixel. The intensity signal detected by the multi detector 222 is output to the detection circuit 106.

[0043] 3 is a diagram showing an example of a plurality of chip regions formed on a semiconductor substrate in the first embodiment. In the example of FIG. 3, a case where the substrate 101 is a semiconductor wafer is shown as an example. A plurality of chips (wafer dies) 332 are formed in a two-dimensional array in an inspection region 330 of the substrate 101. A mask pattern for one chip formed on an exposure mask substrate is transferred onto each chip 332 by an exposure device (stepper) (not shown), reduced to, for example, 1 / 4.

[0044] 4 is a diagram for explaining the image acquisition process in embodiment 1. As shown in Fig. 4, the area of ​​each chip 332 is divided into a plurality of stripe areas 32 with a predetermined width in the y direction, for example. If the substrate 101 is a mask substrate, a pattern formation area (inspection area) formed on the mask is divided into a plurality of stripe areas 32 with a predetermined width in the y direction, for example.

[0045] The scanning operation by the image acquisition mechanism 150 is performed, for example, for each stripe region 32. For example, while moving the stage 105 in the -x direction, the scanning operation of the stripe region 32 proceeds relatively in the x direction. Each stripe region 32 is divided into a plurality of rectangular regions 33 in the longitudinal direction. The movement of the beam to the target rectangular region 33 is performed by collective deflection of the entire multi-primary electron beam 20 by two-stage deflectors 208 and 209 (electrostatic deflectors).

[0046] The example of FIG. 4 shows, for example, a case of 5×5 arrays of multi-primary electron beams 20. An irradiation area 34 that can be irradiated by one irradiation of the multi-primary electron beams 20 is defined as (x-direction size obtained by multiplying the inter-beam pitch in the x-direction of the multi-primary electron beams 20 on the surface of the substrate 101 by the number of beams in the x-direction) × (y-direction size obtained by multiplying the inter-beam pitch in the y-direction of the multi-primary electron beams 20 on the surface of the substrate 101 by the number of beams in the y-direction). The irradiation area 34 is the field of view of the multi-primary electron beams 20. Each primary electron beam 10 constituting the multi-primary electron beam 20 is irradiated within a sub-irradiation area 29 surrounded by the inter-beam pitch in the x-direction and the inter-beam pitch in the y-direction where the beam is located, and scans (performs a scanning operation) within the sub-irradiation area 29. Each primary electron beam 10 is responsible for one of the mutually different sub-irradiation areas 29. Each primary electron beam 10 irradiates the same position within the assigned sub-irradiation area 29. The two-stage deflectors 208 and 209 deflect the multi-primary electron beams 20 collectively, thereby scanning the surface of the substrate 101 on which the pattern is formed with the multi-primary electron beams 20. In other words, the movement of the primary electron beam 10 within the sub-irradiation region 29 is achieved by collective deflection of the entire multi-primary electron beams 20 by the two-stage deflectors 208 and 209. By repeating this operation, one primary electron beam 10 is sequentially irradiated within one sub-irradiation region 29.

[0047] The width of each stripe region 32 is preferably set to the same size as the irradiation region 34 in the y direction or narrower by a scan margin. In the example of FIG. 4 , the irradiation region 34 is shown to be the same size as the rectangular region 33. However, this is not limiting. The irradiation region 34 may be smaller or larger than the rectangular region 33. Each primary electron beam 10 constituting the multi-primary electron beam 20 is irradiated into the sub-irradiation region 29 in which it is located, and scans (scans) the sub-irradiation region 29. After scanning one sub-irradiation region 29, the irradiation position is moved to an adjacent rectangular region 33 in the same stripe region 32 by collective deflection of the entire multi-primary electron beam 20 by the two-stage deflectors 208 and 209. This operation is repeated to sequentially irradiate the stripe region 32. After scanning one stripe region 32 is completed, the irradiation region 34 moves to the next stripe region 32 by moving the stage 105 and / or collectively deflecting the entire multi-primary electron beam 20 using the two-stage deflectors 208 and 209. As described above, scanning operations and secondary electron images are performed for each sub-irradiation region 29 by irradiating each primary electron beam 10. By combining the secondary electron images for each sub-irradiation region 29, a secondary electron image of the rectangular region 33, a secondary electron image of the stripe region 32, or a secondary electron image of the chip 332 is constructed. In actual image comparison, the sub-irradiation region 29 within each rectangular region 33 is further divided into a plurality of frame regions 30, and frame images 31 serving as measurement images for each frame region 30 are compared. The example in FIG. 4 shows a case where the sub-irradiation region 29 scanned by one primary electron beam 10 is divided into four frame regions 30, for example, by dividing the sub-irradiation region 29 into two in each of the x and y directions.

[0048] Furthermore, when the substrate 101 is irradiated with the multiple primary electron beams 20 while the stage 105 is continuously moving, a tracking operation is performed by collective deflection using the two-stage deflectors 208 and 209 so that the irradiation positions of the multiple primary electron beams 20 follow the movement of the stage 105. Therefore, the emission positions of the multiple secondary electron beams 300 change from moment to moment relative to the central axis of the orbit of the multiple primary electron beams 20. Similarly, when scanning the sub-irradiation region 29, the emission positions of each secondary electron beam change from moment to moment within the sub-irradiation region 29. For example, the two-stage deflectors 225 and 226 collectively deflect the multiple secondary electron beams 300 so that each secondary electron beam whose emission position has changed in this way is irradiated into the corresponding detection region of the multi-detector 222. In other words, the deflectors 225 and 226 fix the position of the multi secondary electron beams 300 on the detection surface of the multi-detector 222, which changes due to scanning using the multi primary electron beams 20, by deflecting the multi secondary electron beams back. This allows each secondary electron beam to be detected by the corresponding detection element of the multi-detector 222. The deflectors 225 and 226 are not limited to two-stage deflectors, and may be configured as a single-stage deflector.

[0049] 5 is a diagram showing an example of the configuration from the radiation source to the intermediate image plane position of the multiple primary electron beams in Comparative Example 1 of Embodiment 1. In Comparative Example 1 of Embodiment 1, an electron beam emitted from an electron gun 301 serving as a radiation source is refracted by a condenser lens 302 into a substantially parallel beam and proceeds to a shaping aperture array substrate 303. Then, multiple primary electron beams are formed by portions of the electron beam passing through a plurality of holes in the shaping aperture array substrate 303. The formed multiple primary electron beams pass through an electrostatic lens array 310 and are refracted by a condenser lens 305 to form an intermediate image and a crossover of the electron source image.

[0050] Here, aberrations such as field curvature occur due to the reduction optical system further downstream of the optical system shown in FIG. 5 . This can cause deviations in the image positions of the electron source images on the object plane 311 of each beam on the sample surface. Deviations in the image positions on the sample surface result in variations in the size of each beam on the sample surface. Therefore, it is desirable to shift the intermediate image planes of the peripheral beams downstream (e.g., to intermediate image plane position 319b) from the intermediate image plane position 319a of the central beam depending on their distance from the axis to compensate for the field curvature caused by the downstream reduction optical system. Therefore, in Comparative Example 1, an electrostatic lens array 310 is provided to correct the position of the intermediate image plane of each beam.

[0051] However, astigmatism occurs in the condenser lenses 302 and 305 and the downstream optical system. This causes a shift in the image plane position in the x and y directions. This shift is larger for more peripheral beams. Therefore, even if there is no astigmatism, there will be variations in the size of each beam image in the x and y directions at the intermediate image plane positions 319a and 319b. For example, even if the central beam has a nearly circular shape, the peripheral beams will have a flattened shape.

[0052] As described above, it is desirable for all of the multiple primary electron beams to form an image on the sample surface without astigmatism. However, there is a problem in that astigmatism and field curvature caused by lenses such as condenser lenses along the way can cause variations in the image plane position. Therefore, it is desirable to correct these variations at the intermediate image plane positions of each beam of the multiple electron beams. However, it is difficult to correct astigmatism with the electrostatic lens array 310 of Comparative Example 1.

[0053] FIG. 6 is a diagram illustrating an example of a method of correction using a single-stage stigmator in Comparative Example 2 of Embodiment 1. FIG. 6 illustrates the limitations of correction for one beam using a single-stage stigmator (multipole lens 40-1). With a single-stage stigmator, when astigmatism occurs between the x and y trajectories of the object plane, a virtual object plane 11 that coincides in the x and y directions can be formed, and the image plane position can be aligned in the x and y directions. However, the image plane position after correction is determined by the distance kxd from the object plane to the stigmator in the x direction and the distance kyd from the object plane to the stigmator in the y direction. Therefore, it is difficult to align the image plane to an arbitrary position. Note that if the condenser lens 202 generates astigmatism, it can be considered that a virtual quadrupole lens exists at the position of the condenser lens 202. However, this virtual quadrupole lens has a fixed focal length, so the degrees of freedom are not increased. Therefore, the above situation remains unchanged.

[0054] Therefore, in the first embodiment, a multistage lens array 210 consisting of two stages of a plurality of multipole lens arrays each having a quadrupole or higher multipole element is used to individually correct the position of the electron source image in two orthogonal directions for each beam. To explain the effects of the invention, in each embodiment, including this embodiment, an approximation is made that the astigmatism effect of the condenser lens 202 for the beam to be described is further focused in the x-direction in addition to the effect of obtaining a parallel beam. This effect is obtained by placing a quadrupole lens at the position of the condenser lens 202 and adjusting the conditions for the focal length of the condenser lens 202 and the focal length of this quadrupole lens. Furthermore, a thin lens approximation is made for the quadrupole lens and the condenser lens 202. This allows the function of each lens to be expressed by a matrix. A specific description is given below.

[0055] FIG. 7 is a diagram showing an example of a method for isotropic astigmatism correction using a two-stage multipole lens in the first embodiment. The trajectories in the x and y directions are not strict and are merely intended to illustrate the effect of each lens. FIG. 7 shows a case where a two-stage multipole lens array is used as the multistage lens array 210. FIG. 7 shows the lens action of two-stage multipole lenses 40-1 and 40-2 for one primary electron beam in a two-stage multipole lens array 40 corresponding to multiple primary electron beams 20. The two-stage multipole lenses 40-1 and 40-2 are composed of multipoles with a quadrupole or higher number, and form a quadrupole field. FIG. 7 shows an example of a diverging trajectory of an electron beam emitted from an object surface. In the first embodiment, the primary electron beam emitted from the object plane is refracted by the front condenser lens 202 to become a substantially parallel beam that is substantially parallel to the central axis of the orbit (optical axis) of the central beam of the multiple primary electron beams 20, and proceeds to the two-stage multipole lenses 40-1 and 40-2.

[0056] FIG. 8 is a diagram showing an example of the configuration of a multipole lens array according to the first embodiment. In FIG. 8 , each multipole lens array 40 is configured with three electrode substrates, for example, an upper electrode substrate 12, a middle electrode substrate 14, and a lower electrode substrate 18. A plurality of passage holes 17 are formed in the three electrode substrates, through which the multiple primary electron beams 20 pass. At least the surfaces of the upper electrode substrate 12 and the lower electrode substrate 18 are made of a conductive material, and a ground potential (GND) is applied. A plurality of electrodes 16 are disposed in the plurality of passage holes 17 in the middle electrode substrate 14, each of which forms a quadrupole or higher multipole element surrounding the passage hole 17. In other words, in the multipole lens array 40, each lens has a quadrupole or higher multipole element. The substrate body of the middle electrode substrate 14 is insulated from each electrode. Here, it is preferable that the multipole elements at each position are arranged so that, for example, the phases of the eight electrodes are equally spaced relative to the electrodes arranged on a line extending radially from the center of the central beam passage hole 17. However, this is not a limitation. For example, the multipole elements at each position may be arranged so that, for example, the phases of the eight electrodes are equally spaced relative to the electrodes arranged in the x-direction or y-direction. Furthermore, electrostatic multipoles may be used as the multipoles. Alternatively, magnetic multipoles may be used as the multipoles. Furthermore, the multiple electrodes 16 may be arranged on either the top or back surface of the middle electrode substrate 14. In the example of FIG. 8, eight electrodes 16a to 16h are arranged on the top surface of the middle electrode substrate 14. An independent control potential is applied to each of the eight electrodes 16a to 16h. Therefore, a maximum of eight independent potentials equal to the number of beams times eight poles can be applied. This allows the focal length of each multipole lens in a single multipole lens array to be independently controlled. Therefore, it is possible to perform correction appropriate for each electron beam that constitutes the multi-electron beam. Here, the quadrupole lens acts as a convex lens in one direction and a concave lens in the orthogonal direction, and a positive focal length fq is defined, and the focal length of the convex lens is defined as fq and the focal length of the concave lens is defined as -fq.

[0057] The example in Figure 7 shows a case where the object plane is misaligned between the x and y trajectories. In the example in Figure 7, the astigmatic primary electron beam emitted from the x-direction object plane and the y-direction object plane proceeds through two multipole lenses 40-1 and 40-2. The primary electron beam is then refracted by the first-stage multipole lens 40-1, for example, in a diverging direction in the x direction, and converging in the y direction. The second-stage multipole lens 40-2 then refracts the primary electron beam by, for example, a converging direction in the x direction, and converging in the y direction. This allows the x-direction and y-direction trajectories to be aligned with the trajectories from a virtual object plane 11 that coincides in the x and y directions, even when the object plane is misaligned between the x and y trajectories. The position of the object plane 11 is determined so that the image plane formed by the downstream optical system coincides with the sample plane.

[0058] This makes it possible to correct the curvature of field while correcting the astigmatism.

[0059] As a result, the intermediate image plane positions in the x and y directions can be matched to desired positions while correcting astigmatism. As described above, by arranging the two-stage multipole lens array 40, astigmatism and field curvature can be corrected individually for the multiple primary electron beams 20.

[0060] FIG. 9 is a diagram showing an example of a method for isotropic astigmatism correction using a two-stage multipole lens according to the first embodiment. FIG. 10 is a diagram showing another example of a method for forming an image plane at an arbitrary position using a two-stage multipole lens according to the first embodiment. FIGS. 9 and 10 show a case where a two-stage multipole lens array is used as the multistage lens array 210. FIGS. 9 and 10 show the lens action of two-stage multipole lenses 40-1 and 40-2 for one primary electron beam in a two-stage multipole lens array 40 corresponding to multiple primary electron beams 20. The two-stage multipole lenses 40-1 and 40-2 are composed of multipoles with a quadrupole or higher number and form a quadrupole field. FIGS. 9 and 10 show an example of a focusing trajectory of an electron beam. In the first embodiment, the primary electron beam emitted from the object plane is refracted by the front condenser lens 202 to become a substantially parallel beam that is substantially parallel to the central axis of the orbit (optical axis) of the central beam of the multiple primary electron beams 20, and proceeds to the two-stage multipole lenses 40-1 and 40-2.

[0061] In the examples of Figures 9 and 10, if the primary electron beam on the convergent trajectory is not corrected by the two-stage multipole lenses 40-1 and 40-2, the image plane in the x direction and the image plane in the y direction will be misaligned. However, the primary electron beam on the convergent trajectory is refracted, for example, in a diverging direction in the x direction by the first-stage multipole lens 40-1, and conversely, in a converging direction in the y direction by the second-stage multipole lens 40-2. Subsequently, the primary electron beam is refracted, for example, in a converging direction in the x direction and conversely, in a diverging direction in the y direction by the second-stage multipole lens 40-2. As a result, when the object plane is misaligned between the x trajectory and the y trajectory, an image plane 19 can be formed at any position that coincides in the x and y directions while correcting astigmatism. Similarly, when the object plane is coincident between the x trajectory and the y trajectory, an image plane 19 can be formed at any position that coincides in the x and y directions while correcting astigmatism.

[0062] As described above, by arranging the two-stage multipole lens array 40, the image plane positions that coincide in the x and y directions for the multiple primary electron beams 20 can be adjusted to any position. Note that it is preferable to determine the image formation positions in the x and y directions of the electron source images of each beam of the multiple primary electron beams 20 so that the image formation positions of each beam coincide on the surface of the substrate 101. In other words, it is preferable to correct the positions so that the field curvature of the downstream optical system is corrected.

[0063] FIG. 11 is a diagram showing an example of a configuration in which two stages of multipole lenses are arranged in the case where there is astigmatism in the condenser lens according to the first embodiment, and one electron beam is incident on a focused trajectory in the x direction and a parallel trajectory in the y direction. FIG. 12 is a diagram showing an example of the range of magnification adjustment according to the first embodiment. The example in FIG. 11 shows a case where there is astigmatism in the condenser lens. In FIG. 11, the multistage lens array 210 according to the first embodiment is located at a distance d from the condenser lens 202, which is located at a distance ηd from the object plane 11, and the first stage of multipole lens 40-1 is located at a distance d from the condenser lens 202, which is located at a distance ηd from the object plane in the y direction (and the Y object plane). The second stage of multipole lens 40-2 is located at a distance d. The image plane 19 is located at a distance λd from the second stage of multipole lens 40-2.

[0064] FIG. 13 is a diagram showing an example of a configuration in which two stages of multipole lenses are arranged when the image plane is shifted in the x and y directions in the first embodiment. FIG. 14 is a diagram showing an example of the range of magnification adjustment when the image plane is shifted in the x and y directions in the first embodiment. FIG. 15 is a diagram showing an example of the range of focal length when the image plane is shifted in the x and y directions in the first embodiment. The example in FIG. 14 shows a case in which the image plane is shifted in the x and y directions. In FIG. 13, in the multistage lens array 210 in the first embodiment, the first stage of multipole lens 40-1 is arranged at a distance d from the condenser lens 202, which is positioned at a distance ηd from the object plane 11. The second stage of multipole lens 40-2 is arranged at a distance d. The position at a distance λxd from the second stage of multipole lens 40-2 is the x-direction image plane 19, and the position at a distance λyd is the y-direction image plane 19b.

[0065] As described above, for the shaped multiple primary electron beams 20, the image plane positions of the electron source images in two orthogonal directions for each beam are individually corrected by the multistage lens array 210. This makes it possible to individually correct the variations in the image formation position on the sample surface for each beam at the intermediate image plane position of each beam (variations in size for each beam on the sample surface). In other words, by arranging the two-stage multipole lens array 40, although magnification anisotropy occurs in the x and y directions, it is possible to form an image with astigmatism correction at any position as long as the coefficient λ is within a predetermined range. The multiple primary electron beams 20 that have passed through the multistage lens array 210 proceed to the angle-limiting aperture array substrate 211. Next, the variations in the focusing angle are corrected.

[0066] FIG. 16 is a diagram illustrating the operation of the angle-limiting aperture array substrate of the first embodiment. In FIG. 16, the upper diagram shows a case where angle limitation is performed downstream of the multistage lens array 210. The lower diagram of FIG. 16 shows a case where angle limitation is performed upstream of the multistage lens array 210, for example, by a shaping aperture array substrate. The larger the convergence angle of each beam on the substrate 101 surface, the larger the beam current can be obtained. However, a larger convergence angle increases aberrations. Therefore, it is desirable to determine the convergence angle so that a large beam current can be obtained within the desired dimensional range on the substrate 101 surface. For this reason, the angle-limiting aperture substrate 211 is used to limit the convergence angle. However, since the image magnification and angular magnification are inversely proportional in the paraxial approximation, forming images with different magnifications in the x and y directions results in different convergence angles in each direction on the sample surface for electron beams that had an isotropic angular distribution upon incidence on the optical system. Therefore, the angle-limiting aperture substrate 211 can be provided to adjust the convergence angle to match the aberrations dependent on the convergence angle. An example is shown in FIG. 16. When imaging with different magnifications in the x and y directions, the convergence angle becomes large for trajectories with small magnifications. Therefore, the convergence angle is limited by an angle-limiting aperture. By placing the angle-limiting aperture close to the lens, the effect on the beam distribution at the imaging position can be suppressed. Alternatively, the angle-limiting aperture can be used to deform the angular distribution at the time of incidence into the optical system. It is desirable to determine the shape of the angle-limiting aperture so that an isotropic convergence angle distribution is obtained for each beam on the sample surface.

[0067] Specifically, the angle-limiting aperture array substrate 211 is disposed at a position away from the image plane 19 on the upstream side. In the example of FIG. 1 , for example, the angle-limiting aperture array substrate 211 is disposed between the multistage lens array 210 and the condenser lens 205. However, the present invention is not limited to this. The angle-limiting aperture array substrate 211 may be disposed between the condenser lens 205 and the image plane 19. In other words, the angle-limiting aperture array substrate 211 may be disposed at a position before the multiple primary electron beams 20 reach the image plane 19 after being refracted in the focusing direction. Since the divergence angle or focusing angle is limited when each beam has a wide beam diameter before forming the intermediate image plane, the diameter size of the multiple passage holes of the limiting aperture array 211 can be made sufficiently larger than the beam size at the image plane position. Therefore, blockage due to contamination or the like can be suppressed or reduced. The angle-limiting aperture array substrate 211 limits the divergence angle or focusing angle of each electron beam by allowing the multiple primary electron beams 20, which have passed through the multistage lens array 210, to pass through the multiple passage holes. If each beam is diverging, the angle of divergence can be limited, and if each beam is focusing, the angle of focusing can be limited. This makes it possible to correct variations in the convergence angle for each beam at the position of the image plane 19.

[0068] FIG. 17 is a diagram showing an example of the configuration from the electron source to the intermediate image plane after astigmatism correction in Modification 1 of Embodiment 1. In Modification 1 of Embodiment 1, as shown in FIG. 17 , a multipole lens array 40 is separately disposed downstream of the multistage lens array 210 to deflect the multiple primary electron beams 20 in the focusing direction instead of the condenser lens 205. The multipole lens array 40, instead of the condenser lens 205, functions as a deflector array that deflects the multiple primary electron beams 20 passing through the multistage lens array 210 in the focusing direction. In this case, the multipole lens array 40, instead of the condenser lens 205, generates a dipole field to focus each primary electron beam to one point. In other words, potentials with reversed positive and negative polarities are applied to the opposing electrodes of the multipole element. As a result, the primary electron beam passing through the multipole element is deflected in the direction of the positive potential of the electric field formed. In order to correct for variations in the shape (and size) of the electron source image at the image plane 19, the multipole lens array in the multistage lens array 210 has each multipole forming a quadrupole field, but the dipole field and quadrupole field can be applied in parallel.

[0069] 17, the angle limiting aperture array substrate 211 is disposed on the trajectory of the multi-primary electron beams 20 after they have been refracted in the convergence direction. The other configurations are the same as those in FIG.

[0070] 18 is a diagram showing an example of the configuration from the electron source to the intermediate image plane after astigmatism correction in Modification 2 of Embodiment 1. In Modification 2 of Embodiment 1, as shown in FIG. 18, a multipole lens array 40 is arranged downstream of the angle-limiting aperture array substrate 211 to deflect the multi-primary electron beams 20 in the focusing direction instead of the condenser lens 205. The other configurations are the same as those in FIG. 1. The multipole lens array 40 instead of the condenser lens 205 functions as a deflector array that deflects the multi-primary electron beams 20 that have passed through the multistage lens array 210 in the focusing direction. In this case as well, it is sufficient to make each multipole of the multipole lens array 40 generate only a dipole field.

[0071] FIG. 19 is a diagram showing an example of the configuration from the electron source to the intermediate image plane after astigmatism correction in Modification 3 of Embodiment 1. In Embodiment 1, a condenser lens 202 is used to form a substantially parallel beam, but the parallelism may deviate from the allowable degree. Therefore, in Modification 3 of Embodiment 1, as shown in FIG. 19 , for example, the first-stage multipole lens array 40 of the multistage lens array 210 is used to deflect at least one primary electron beam of the multiple primary electron beams 20 to form a substantially parallel beam. Therefore, for example, the first-stage multipole lens array 40 also functions as a deflector array in parallel with its original function described above. The dipole field and the quadrupole field can be applied in parallel. However, the multipole lens array functioning as a deflector array is not limited to the first stage. One multipole lens array of the multistage lens array 210 may generate a dipole field so that each beam of the multiple primary electron beams 20 becomes a parallel beam.

[0072] Alternatively, it is also preferable to separately arrange a multipole lens array 40 between the shaping aperture array substrate 203 and the multistage lens array 210. The multipole lens array 40 arranged separately from the multistage lens array 210 generates a dipole field so that each beam of the multiple primary electron beams 20 becomes a parallel beam. In this case, the multipole lens array 40 functions as a deflector array.

[0073] In the above example, the two-stage multipole lens array 40 constituting the multistage lens array 210 is constituted by an electrostatic multipole lens array constituted by electrostatic multipoles, or a magnetic multipole lens array constituted by magnetic multipoles, or a combination of an electrostatic multipole lens array constituted by electrostatic multipoles and a magnetic multipole lens array constituted by magnetic multipoles.

[0074] As described above, the two-stage multipole lens array 40 and the angle-limiting aperture array substrate 211 can reduce variations in the shape of each beam and variations in the focusing angle, or can reduce variations in the position of the image plane 19 (intermediate image plane) of each beam and variations in the focusing angle.

[0075] FIG. 20 is a flowchart illustrating an example of the main steps of the method for adjusting a multistage lens array according to the first embodiment. First, the lenses of the entire inspection apparatus 100, including the multistage lens array 210, are driven under initial conditions determined by simulation or past measurement experience (S102). Then, the beam array shape at different focal positions is measured (S104). From the measurement results, the residual astigmatism, field curvature, beam size, and focusing half angle are determined (S106). Then, it is determined whether the obtained results satisfy the desired conditions (S108). If the obtained results do not satisfy the desired conditions, lens conditions capable of correcting the astigmatism and variations in the image plane position are determined (S110). If the obtained results satisfy the desired conditions, the adjustment is completed, and the inspection process proceeds. The lens conditions are changed to the determined conditions (S112). Then, the process returns to S104, and steps S104 to S112 are repeated until the obtained results satisfy the desired conditions.

[0076] After adjusting the lenses of the entire inspection device 100 including the multistage lens array 210 as described above, the inspection device 100 inspects the substrate 101 .

[0077] In the scanning process, the image acquisition mechanism 150 scans the object (here, the substrate 101) with the multi-primary electron beams 20. Here, the image acquisition mechanism 150 scans the stripe region 32 with the multi-primary electron beams 20 for each stripe region 32. As described above, the primary electron optical system 151 irradiates the object (here, the substrate 101) with the multi-primary electron beams 20. The multi-secondary electron beams 300 emitted as a result of the irradiation of the substrate 101 with the multi-primary electron beams 20 are guided to the multi-detector 222 (detector array) by the secondary electron optical system 152. The guided multi-secondary electron beams 300 are then detected by the multi-detector 222 (detector array). The detected multi-secondary electron beams 300 may include reflected electrons. Alternatively, the reflected electrons may diverge while moving through the secondary electron optical system and not reach the multi-detector 222. A secondary electron image is acquired based on the signals of the detected multi-secondary electron beams 300. Specifically, secondary electron detection data (measurement image data: secondary electron image data: inspection image data) for each pixel in each sub-irradiation area 29 detected by the multi-detector 222 is output to the detection circuit 106 in the order of measurement. Within the detection circuit 106, an A / D converter (not shown) converts the analog detection data into digital data, which is stored in the chip pattern memory 123. The acquired measurement image data is then transferred to the comparison circuit 108 together with information indicating each position from the position circuit 107.

[0078] FIG. 21 is a block diagram showing an example of the configuration of a comparison circuit according to the first embodiment. In FIG. 21 , the comparison circuit 108 includes storage devices 50, 52, and 56, such as magnetic disk devices, a frame image creation unit 54, an alignment unit 57, and a comparison unit 58. Each of the "units" (such as the frame image creation unit 54, the alignment unit 57, and the comparison unit 58) includes a processing circuit, which may include an electrical circuit, a computer, a processor, a circuit board, a quantum circuit, or a semiconductor device. The "units" may share a common processing circuit (the same processing circuit). Alternatively, they may use different processing circuits (separate processing circuits). The input data or calculation results required for the frame image creation unit 54, the alignment unit 57, and the comparison unit 58 are stored in a memory (not shown) or in memory 118.

[0079] In the comparison step, the comparison circuit 108 compares the acquired secondary electron image with a predetermined reference image. Specifically, for example, the operation is as follows.

[0080] The measurement image data (beam image) transferred to the comparison circuit 108 is stored in the storage device 50 .

[0081] The frame image creation unit 54 then creates a frame image 31 for each of a plurality of frame regions 30 obtained by further dividing the image data of the sub-irradiation regions 29 acquired by the scanning operation of each primary electron beam. The frame regions 30 are then used as unit regions of the image to be inspected. It is preferable that the frame regions 30 are configured so that their margins overlap each other to prevent any missing parts of the image. The created frame images 31 are stored in the storage device 56.

[0082] On the other hand, the reference image creation circuit 112 creates a reference image corresponding to the frame image 31 for each frame area 30 based on the design data that is the basis of the multiple figure patterns formed on the substrate 101. Specifically, it operates as follows: First, it reads out the design pattern data from the storage device 109 through the control computer 110, and converts each figure pattern defined in the read design pattern data into binary or multi-value image data.

[0083] As described above, the figures defined in the design pattern data are, for example, rectangles or triangles as basic figures, and the figure data stored defines the shape, size, position, etc. of each pattern figure using information such as the coordinates (x, y) at the reference position of the figure, the length of the sides, and a figure code that serves as an identifier for distinguishing the type of figure, such as a rectangle or a triangle.

[0084] When the design pattern data that constitutes such graphic data is input to the reference image creation circuit 112, it is expanded into data for each graphic, and the graphic code and graphic dimensions that indicate the graphic shape of the graphic data are interpreted.Then, it is expanded into binary or multi-valued design pattern image data as a pattern to be arranged in a grid with a predetermined quantized dimension as a unit, and output.In other words, the design data is read, the inspection area is virtually divided into grids with a predetermined dimension as a unit, and the occupancy rate of the graphic in the design pattern is calculated for each grid, and n-bit occupancy data is output.For example, it is preferable to set one grid as one pixel.And, 1 / 2 for one pixel. ８ If a resolution of (= 1 / 256) is to be given, a small area of ​​1 / 256 is allocated for the area of ​​the figure placed within the pixel, and the occupancy rate within the pixel is calculated. This results in 8-bit occupancy data. The grid (inspection pixel) can be aligned with the pixel of the measurement data.

[0085] Next, the reference image creation circuit 112 applies filtering to the design image data of the design pattern, which is image data of the graphic, using a predetermined filter function. This makes it possible to match the design image data, which is image data on the design side with image intensity (grayscale value) in digital values, with the image generation characteristics obtained by irradiation with the multiple primary electron beams 20. The image data for each pixel of the created reference image is output to the comparison circuit 108. The reference image data transferred to the comparison circuit 108 is stored in the storage device 52.

[0086] Next, the alignment unit 57 reads out the frame image 31 to be the image to be inspected and the reference image corresponding to the frame image 31, and aligns the two images in units of sub-pixels, which are smaller than pixels. For example, the alignment may be performed using the least squares method.

[0087] The comparison unit 58 then compares the secondary electron image of the substrate 101 placed on the stage 105 with a predetermined image. Specifically, the comparison unit 58 compares the frame image 31 with the reference image for each pixel. The comparison unit 58 compares the two for each pixel in accordance with predetermined judgment conditions, and judges whether or not there is a defect, such as a shape defect. For example, if the difference in gradation value for each pixel is greater than the judgment threshold value Th, it is judged to be a defect. The comparison result is then output. The comparison result may be output to the storage device 109 or memory 118, or may be output from the printer 119.

[0088] In addition to the die-to-database inspection described above, it is also suitable to perform die-to-die inspection, which compares measurement image data obtained by capturing images of the same pattern at different locations on the same substrate. Alternatively, inspection may be performed using only the own measurement image.

[0089] As described above, according to the first embodiment, it is possible to reduce the variation in the shape and / or size of the multi-electron beams on the sample surface, and the variation in the focusing angle.

[0090] [Embodiment 2] In the first embodiment, the angle-limiting aperture array substrate 211 is disposed downstream of the multi-stage lens array 210, but the method of angle limitation is not limited to this. In the second embodiment, a configuration will be described in which angle limitation is also performed when shaping the multiple primary electron beams 20.

[0091] Fig. 22 is a diagram showing an example of the configuration of an inspection device in embodiment 2. Fig. 22 is the same as Fig. 1 except that the angle-limiting aperture array substrate 211 is omitted. Points other than those particularly described below may be the same as embodiment 1.

[0092] In the second embodiment, the shaping aperture array substrate 203 forms multiple primary electron beams 20 and limits the divergence angle or convergence angle of each primary electron beam, thereby making it possible to omit the angle-limiting aperture array substrate 211 at the subsequent stage.

[0093] Here, the formed multiple primary electron beams 20 may have astigmatism as described above. Therefore, when the beam is shaped by the shaping aperture array substrate 203, the beam shape due to such astigmatism may be corrected.

[0094] FIG. 23 shows an example of a beam shaped by the shaping aperture array substrate in the second embodiment. For example, when forming an image with a magnification of 1 in the x direction and 0.5 in the y direction, the angular magnification of the multistage lens array 210 is set to 1 in the x direction and 2 in the y direction. To align the focusing angle on the image plane 19 side equivalent to an opening with a diameter of 2r formed on the angle-limiting aperture array substrate 211, the focusing angle on the shaping side is limited to x direction:y direction = 1:0.5. To achieve this, the opening on the shaping aperture array substrate 203 is set to an ellipse with a major axis:minor axis ratio of 2:1. Note that the size may vary depending on the position. When determining the dimensions of the aperture, it is practical to assume that the angular distribution of the electron beam passing through the multistage lens array 210 is the desired one, trace the trajectory in reverse by simulation to determine the distribution at the shaping aperture array position, and then determine the shape of the aperture to provide that distribution. Alternatively, the marks 111 may be provided at different heights, and the beam convergence angle may be determined from the dependence of the beam distribution obtained by irradiating the marks 111 with an electron beam on the height of the marks 111, and may be determined so as to obtain a desired distribution.

[0095] As described above, according to the second embodiment, it is possible to limit the angle as well as to shape the beam, thereby correcting variations in the focusing angle on the image plane 19. Note that, like the first embodiment, the multistage lens array 210 can correct variations in the shape of the electron source image on the image plane 19 or variations in the image plane position (variations in size on the sample surface).

[0096] In the above description, a series of "circuits" includes processing circuits, which may include electrical circuits, computers, processors, circuit boards, quantum circuits, or semiconductor devices. Furthermore, each "circuit" may use a common processing circuit (the same processing circuit). Alternatively, different processing circuits (separate processing circuits) may be used. The program that runs the processor may be recorded on a recording medium such as a magnetic disk drive, a magnetic tape drive, a floppy disk, or a ROM (read-only memory). For example, the position circuit 107, the comparison circuit 108, and the reference image creation circuit 112 may be composed of at least one of the processing circuits described above. In this description, it is assumed that the absolute value of the focal length of the quadrupole lens or circular lens used can take any value other than zero. In practice, there are limitations on the focal length that can be achieved due to physical limitations such as discharge in the case of electrostatic lenses and magnetic pole saturation in the case of magnetic lenses. Furthermore, the quadrupole component of a condenser lens is also subject to limitations due to the desired magnification and lens arrangement. It is recommended that these limitations be taken into account when optimizing the device design.

[0097] The above describes the embodiments with reference to specific examples. However, the present invention is not limited to these specific examples. For example, in this description, the intermediate image plane is adjusted so that its position is the same in the x and y directions. However, as shown in FIG. 13 , it can also be adjusted to a different position so as to cancel out astigmatism in the downstream optical system. Furthermore, although the focal length of each lens constituting the lens array can be controlled independently, when the condition for the independence of the adjustment range is relaxed, it is also possible to divide the lenses constituting the lens array into at least two or more groups, with independent focal lengths between different groups and a common focal length within the same group.

[0098] Figure 24 shows an example of the arrangement of a multipole lens in each embodiment. For example, when the distribution of field curvature and astigmatism is axially symmetric, as shown in Figure 24, the rotational phase of the electrodes of the multipole lens can be changed depending on the direction from the central axis, and the number of power supplies can be reduced by dividing the multipole lens into two or more groups based on the radial distance and sharing a power supply that applies a potential to corresponding electrodes within the same group so that the focal lengths are equal. In the example of Figure 24, the power supply can be shared for electrodes assigned the same number. Furthermore, when only a quadrupole field is generated, a common power supply can be used by applying the same potential to opposing electrodes, such as electrode 1 and electrode 5.

[0099] Furthermore, although descriptions of the device configuration, control method, and other parts not directly necessary for explaining the present invention have been omitted, the required device configuration and control method can be appropriately selected and used.

[0100] In addition, all other multi-electron beam irradiation devices and multi-electron beam irradiation methods that include the elements of the present invention and that can be appropriately modified by those skilled in the art are included in the scope of the present invention.

[0101] The present invention relates to a multi-electron beam irradiation apparatus and a multi-electron beam irradiation method, which can be used, for example, in an apparatus for correcting variations in the shape of the multi-electron beams and variations in the convergence angle at an intermediate image plane position of an electron source image of the multi-electron beams caused by aberrations or the like.

[0102] 10 Primary electron beam 11 Object plane 12 Upper electrode substrate 14 Middle electrode substrate 16 Electrode 17 Passage hole 18 Lower electrode substrate 19 Image plane 20 Multi-primary electron beam 22 Hole 29 Sub-irradiation area 30 Frame area 31 Frame image 32 Stripe area 33 Rectangular area 34 Irradiation area 40 Multipole lens array 40-1, 40-2 Multipole lenses 50, 52, 56 Storage device 54 Frame image creation unit 57 Alignment unit 58 Comparison unit 62 Upper electrode substrate 64 Middle electrode substrate 66 Electrode 67 Passage hole 18 Lower electrode substrate 100 Inspection device 101 Substrate 102 Electron beam column 103 Inspection chamber 105 Stage 106 Detection circuit 107 Position circuit 108 Comparison circuit 109 Storage device 110 Control computer 111 Mark 112 Reference image creation circuit 114 Stage control circuit 117 Monitor 118 Memory 119 Printer 120 Bus 122 Laser length measurement system 123 Chip pattern memory 124 Lens control circuit 126 Blanking control circuit 128 Deflection control circuit 130 Multistage lens array control circuit 132 E×B separator control circuit 142 Stage drive mechanism 144, 146, 147, 148, 149 DAC amplifier 150 Image acquisition mechanism 151 Primary electron optical system 152 Secondary electron optical system 160 Control system circuit 200 Electron beam 201 Electron gun 202, 205 Condenser lens 203 Shaping aperture array substrate 206, 207 Electromagnetic lens 208 Deflector 209 Deflector 210 Multi-stage lens array 211 Angle limiting aperture array substrate 212 Collective deflector 213 Limiting aperture substrate 214 E×B separator 216 Mirror 218 Deflector 222 Multi-detector 224 Electromagnetic lens 225, 226 Deflector 300 Multi-secondary electron beam 301 Electron gun 302, 305 Condenser lens 303 Shaping aperture array substrate 310 Electrostatic lens array 311 Object plane 319 Image plane 330 Inspection area 332 Chip 341 Beam size limiting aperture array substrate

Claims

1. A multi-electron beam irradiation device comprising: an emission source which emits an electron beam in a diverging direction; a first condenser lens which refracts the electron beam proceeding in the diverging direction in a converging direction to form a substantially parallel beam; a shaped aperture array substrate in which a plurality of first openings are formed, and in which a portion of the electron beam which has become the substantially parallel beam passes through the plurality of first openings to form a multi-electron beam; and a two-stage multipole lens array in which each lens has a multipole element of quadrupole or more arranged on the trajectory of a beam which it is responsible for among the multi-electron beams.

2. A multi-electron beam irradiation device as described in claim 1, further comprising an angle-limiting aperture array substrate on which a plurality of second openings are formed, and in which the multi-electron beams that have passed through the two-stage multipole lens array pass through the plurality of second openings, thereby limiting the divergence angle or convergence angle of each electron beam.

3. A multi-electron beam irradiation device according to claim 1, wherein said shaping aperture array substrate forms said multiple electron beams and limits the divergence angle or convergence angle of each electron beam.

4. A multi-electron beam irradiation device according to claim 1, wherein one of said two-stage multipole lens arrays generates a dipole field so that each beam of said multiple electron beams becomes a parallel beam.

5. A multi-electron beam irradiation device as described in claim 1, further comprising a multi-pole lens array disposed between the shaped aperture array substrate and the two-stage multi-pole lens array, for generating a dipole field so that each beam of the multi-electron beam becomes a parallel beam.

6. A multi-electron beam irradiation apparatus according to claim 1, further comprising a second condenser lens for refracting the multi-electron beams having passed through the two-stage multipole lens array in a focusing direction.

7. A multi-electron beam irradiation apparatus according to claim 1, characterized in that an electrostatic multipole element is used as the multipole element.

8. A multi-electron beam irradiation apparatus according to claim 1, characterized in that a magnetic multipole is used as the multipole.

9. A multi-electron beam irradiation device as described in claim 1, characterized in that the two-stage multipole lens array is composed of a combination of an electrostatic multipole lens array composed of electrostatic multipoles and a magnetic multipole lens array composed of magnetic multipoles.

10. A multi-electron beam irradiation apparatus according to claim 1, further comprising a deflector array for deflecting the multi-electron beams having passed through the two-stage multipole lens array in a focusing direction.

11. A multi-electron beam irradiation method comprising: emitting an electron beam from an emission source in a diverging direction; using a first condenser lens to refract the electron beam traveling in the diverging direction in a converging direction to form a substantially parallel beam; using a shaped aperture array substrate having a plurality of first openings, a portion of the electron beam that has become the substantially parallel beam passes through the plurality of first openings to form a multi-electron beam; and using a two-stage multipole lens array, each lens having a multipole with four or more elements arranged on the trajectory of a beam it is responsible for among the multi-electron beams, to correct the position of the electron source image in two orthogonal directions for each beam.

12. A multi-electron beam irradiation method as described in claim 11, characterized in that an angle-limiting aperture array substrate having a plurality of second openings is used, and the multi-electron beams that have passed through the two-stage multipole lens array pass through the plurality of second openings to limit the divergence angle or convergence angle of each electron beam.

13. A method for irradiating multiple electron beams according to claim 11, wherein the step of forming multiple electron beams includes forming the multiple electron beams and limiting a divergence angle or a convergence angle of each electron beam.

14. A method for irradiating multiple electron beams according to claim 11, wherein one of the two-stage multipole lens arrays generates a dipole field so that each beam of the multiple electron beams becomes a parallel beam.

15. A multi-electron beam irradiation method as described in claim 11, characterized in that a dipole field is generated using a multipole lens array arranged between the shaped aperture array substrate and the two-stage multipole lens array, so that each beam of the multi-electron beam becomes a parallel beam.

16. A method for irradiating multiple electron beams according to claim 11, further comprising the step of refracting the multiple electron beams having passed through the two-stage multipole lens array in a focusing direction using a second condenser lens.

Images