TWI742223B - Electron beam system and method, and scanning electron microscope - Google Patents

Abstract

Performance of a multi-electron-beam system can be improved by reducing Coulomb effects in the illumination path of a multi-beam inspection system. A beam-limiting aperture with multiple holes can be positioned between an electron beam source and a multi-lens array, such as in a field-free region. The beam-limiting aperture is configured to reduce Coulomb interactions between the electron beam source and the multi-lens array. An electron beam system with the beam-limiting aperture can be used in a scanning electron microscope.

Description

Electron beam system and method, and scanning electron microscope

The present invention relates to an electron beam system.

Previous electron beam inspection systems used a Schottky thermal field electron emitter to generate an electron beam. Around the transmitter is a suppressor electrode, which suppresses unwanted hot electrons from the handle of the transmitter from entering the primary beam. A voltage on the extractor electrode determines the electric field at the apex of the tip. The field at the tip determines the amount of current that can be drawn from the tip. A second electrode or anode after the extractor is usually used to accelerate the beam to the desired energy. The current distribution from the transmitter extends to several degrees. In an electron beam inspection system, a small source acceptance angle of less than 1 degree may require high resolution. In a scanning electron microscope (SEM), a jet aperture is usually used to block unused electrons. A second aperture located farther under the column can serve as a pupil aperture, which sets a numerical aperture (NA) of the objective lens. This design still has the problem of Coulomb effect.

Therefore, what is needed is an improved electron beam system.

In a first embodiment, an electron beam system is provided. The electron beam system includes: an electron beam source; a multi-lens array; and a beam limiting aperture, which defines a plurality of holes. The beam limiting aperture is arranged between the electron beam source and the multi-lens array. The beam limiting aperture is configured In order to reduce the Coulomb interaction between the electron beam source and the multi-lens array. The beam limiting aperture can be made of silicon, a metal or a metal alloy. The electron beam source may include an emitter, suppressor and extractor.

The beam limiting aperture can be arranged at a position between the electron beam source and the multi-lens array with a field less than 1V/mm. For example, the position between the electron beam source and the multi-lens array can be fieldless.

The beam limiting aperture can define at least 6 holes among the holes. The beam limiting aperture may define the apertures to each have a diameter from 1 μm to 100 μm. For example, the diameter of each of the holes may be 50 μm. The beam limiting aperture can define the apertures as having a pitch from 2 μm to 100 μm. For example, the pitch can be 100 μm. The beam limiting aperture can define the apertures to be each circular. The holes may be arranged in the beam limiting aperture in a polygonal configuration.

A scanning electron microscope may include the electron beam system of any of the design variants or the examples of the first embodiment.

A method is provided in a second embodiment. The method includes: generating an electron beam; extracting the electron beam; guiding the electron beam through a beam limiting aperture that defines a plurality of holes; The beam restricts a multi-lens array downstream of the aperture. The beam limiting aperture is configured to reduce Coulomb interaction between the electron beam source and the multi-lens array.

The electron beam is located in a region having a field of less than 1 V/mm when the electron beam passes through the beam limiting aperture. For example, the area can be a field-free area.

The electron beam passing through the multi-lens array can be focused to a diameter of 50 nm.

A third embodiment provides a system. The system includes an electron beam source, which is configured To generate an electron beam; a multi-lens array located upstream of a wafer; a beam limiting aperture, which defines a plurality of holes; and a detector, which is configured to detect from the wafer The electrons of the electron beam returning from a surface. The beam limiting aperture is arranged between the electron beam source and the multi-lens array. The beam limiting aperture is configured to reduce Coulomb interaction between the electron beam source and the multi-lens array.

The beam limiting aperture can be arranged at a position between the electron beam source and the multi-lens array with a field less than 1V/mm. For example, the position between the electron beam source and the multi-lens array can be fieldless.

100: electron beam system

101: Electron beam source

102: Extractor

103: beam limiting aperture

104: Multi-lens array

105: hole

106: anode

107: electron beam

108: thin beam

109: Launcher

110: Suppressor

111: Magnetic lens

112: Magnetic pole piece

113: Coil

114: component

200: System

201: Electron optical column/electronic column

202: electron beam source

203: Components

204: Wafer

205: component

206: Detector

207: Computer Subsystem

A-A: line

In order to fully understand the nature and objectives of the present invention, reference should be made to the following detailed description in conjunction with the accompanying drawings, in the drawings.

Fig. 1 is a block diagram of an embodiment of an electron beam system according to the present invention; Fig. 2 is a first electron beam histogram; Fig. 3 is a second electron beam histogram; Fig. 4 is a third electron beam Histogram; Fig. 5 is a fourth electron beam histogram; Fig. 6 is a fifth electron beam histogram; Fig. 7 is an embodiment of a system according to the present invention; and Fig. 8 is a method according to the present invention A flow chart;

Although the claimed subject matter will be described in terms of specific embodiments, other embodiments including embodiments that do not provide all the benefits and features stated herein are also within the scope of the present invention. Various structures, logics, program steps and electronics can be made without departing from the scope of the present invention Change. Therefore, the scope of the present invention is only defined with reference to the scope of the attached patent application.

The embodiments disclosed herein improve the performance of a multi-beam system by reducing the Coulomb effect in the illumination path of a multi-beam inspection system. A beam limiting aperture (BLA) can be used to block unused electrons from continuous downstream, such as to prevent charging and/or gas ionization. BLA can help reduce the Coulomb effect. As electrons travel through an electron optical column, the electrons interact with each other as described by Coulomb's law. This is because the electrons are charged particles. The cumulative effect of the number of electrons in the electron column and the length of time the electrons spend in the electron column determines the magnitude of the Coulomb effect. Introducing a BLA into the beam path near the electron source can remove electrons, so there are fewer electrons in the electron optical column in most electron paths. Since there are fewer electrons, the magnitude of the Coulomb effect can be reduced.

FIG. 1 is a schematic diagram of an embodiment of an electron beam system 100. The electron beam system 100 includes an electron beam source 101, a beam limiting aperture (BLA) 103 and a multi-lens array (MLA) 104. The electron beam source 101 may include an emitter 109, a suppressor 110, and an extractor 102.

The BLA 103 can be positioned close to the electron beam source 101 to reduce space charge effects. In one example, the BLA 103 is as close to the extractor 102 as possible in an electric field-free area. The BLA 103 may be slightly lower than one of the anodes 106 at ground potential.

BLA 103 can be made of silicon, a metal, a metal alloy, or another material that provides acceptable power and/or heat dissipation. The material of BLA 103 can resist melting or distortion caused by heat. The BLA 103 may be connected to the anode 106. The BLA 103 can have a thickness from 2 μm to 25 μm, although other sizes are also possible.

BLA 103 can be called a "pepper pot" BLA. The BLA 103 in FIG. 1 defines a plurality of holes 105 passing through the BLA 103. The BLA 103 may include from 1 hole 105 to 2,000 or 3,000 holes 103, including all ranges and values in between. In one case, BLA 103 6 or 7 holes 105 are defined. More or less holes 105 may be included in the BLA 103.

Each hole 105 may have a diameter ranging from 1 μm to 100 μm, including all values up to 0.5 μm and ranges therebetween. In one example, each hole 105 has a diameter of 50 μm. In another example, each hole 105 has a diameter from 1 μm to 10 μm, inclusive of all values up to 0.5 μm and ranges therebetween. The aperture 105 may be slightly too large relative to the size of the electron beam so that the illumination overfills the pupil aperture of the MLA 104. The BLA 103 can also serve as a shield to block part of the electron beam.

The holes 105 may be located in the BLA 103 to have a pitch from 2 μm to 100 μm, inclusive of all values up to 0.5 μm and ranges therebetween. In one example, the distance between the holes 105 in the BLA 103 is 100 μm.

The illustration of Fig. 1 (which is not drawn to the scale of the rest of Fig. 1) is an example of a front view of the BLA 103 taken along the line A-A. Each of the holes 105 may be circular, polygonal, or other shapes. The six holes 105 are arranged in a polygonal pattern (shown by a dashed line).

In another example, the BLA 103 defines 7 holes 105 in a polygonal configuration. In yet another example, BLA 103 defines approximately 1,000 holes 105. In one example of the BLA 103 used for inspection, the BLA 103 contains 331 holes 105.

It can be beneficial to arrange the holes 105 in the BLA 103 in a polygonal pattern because the holes 105 will be arranged in a manner close to a circle. Electro-optical devices used in an electron beam inspection system can be rotationally symmetrical. To optimize the area in the macroscopic electronic lens, it is desirable to have a pattern close to a circle.

As an electron beam 107 generated by the electron beam source 101 passes through the hole 105 of the BLA 103, the electron beam 107 is converted into a plurality of thin beams 108 by the BLA 103. Each hole 105 generates a thin beam 108. Each beamlet 108 may leave the BLA 103 with a diameter of approximately 50 nm. Electron beam system The design of 100 can provide a plurality of small beams 108 that are dispersed from each other. One of the remaining parts of the electron beam 107 is blocked by the BLA 103.

The MLA 104 includes a 2D lens array. An individual lens in the MLA 104 may have a plurality of holes along the optical axis or the third axis of that particular lens. In one example, there is a one-to-one mapping between the hole in the lens of the MLA 104 and one of the holes 105 in the BLA 103.

A multi-beam system is created by projecting and illuminating the MLA 104, which can be electrostatic. An electrostatic lens is formed by placing an electric field across an aperture of the MLA 104. Each individual lens forms an image of the electron beam source 101 at the virtual source plane, which is then reduced to a wafer. To illuminate the MLA 104, a large illumination angle from one of the sources may be required. For example, this illumination angle can be as high as two degrees, although other values are also possible.

The BLA 103 is located between the electron beam source 101 and the MLA 104. The BLA 103 may be located between the electron beam source 101 and the MLA 104 in an area or position less than 1V/mm or no field, which means that there may be a minimum lens effect of the hole 105 or even no lens effect. Therefore, the BLA 103 may not focus the beamlet 108. No field can mean 0V/mm, but can be other values close to 0V/mm under which a lens effect will not occur. Positioning the BLA 103 between the electron beam source 101 and the MLA 104 can reduce the Coulomb interaction in this area. In this way, the BLA 103 may not act as an optical component, which reduces the tolerance requirements. In one example, the electron beam current delivered to a wafer can be doubled, tripled, or quadrupled at a resolution from about 3 nm to 10 nm.

Electronic interaction and Coulomb interaction can cause problems. For example, these interactions can increase blurring caused by chromatic aberration or dispersion. It may not be possible to correct horizontal blur. The BLA 103 is configured to reduce the Coulomb interaction between the electron beam source 101 and the MLA 104. The separation of the thin beam 108 can further improve performance by reducing crosstalk.

In an item, the transmitter 109 at -V _E operation, the extractor 102 operating at -V _ext, suppressor 110 operates in the -V _S (e.g., -V _E -1000V), and the anode operated at 0V . A voltage can also be applied to the MLA 104. For example, -V _E from line to 6000V and 30,000V -V _ext lines -V _E plus from 3000V to 7000V.

A magnetic lens 111 located downstream of the MLA 104 with respect to the direction of the electron beam or the thin beam 108 has at least one coil 113 and a magnetic lens 111 of the pole piece 112. The element 114 adjusts the trajectory, focus, and/or size of the beamlet 108.

For example, the electron beam system 100 can be used in an SEM or other devices.

Figures 2 to 6 are simulated electron beam histograms based on Monte Carlo. Figure 3 shows a 250μm electron beam upstream of the BLA. Figure 4 shows the electron beam downstream of the BLA. Figure 5 shows the electron beam upstream of the MLA. Figure 6 shows the electron beam downstream of the MLA. Figure 7 shows an intermediate image of the electron beam. As disclosed in this article, the use of BLA reduces Coulomb blur, as shown by the simulations in Figs. 3-7. Compared with 49nm in the absence of BLA, the central electron beam blur is reduced from D2080=31nm. The total current is reduced from 16.1nA without BLA to 6.3nA with BLA. As seen in such simulations, BLA can provide improved performance that is twice as good as a system without BLA.

The embodiments described herein may include or may be implemented in a system, such as the system 200 of FIG. 7. The system 200 includes an output acquisition subsystem including at least one energy source and a detector. The output acquisition subsystem may be an output acquisition subsystem based on electron beams. For example, in one embodiment, the energy directed to the wafer 204 includes electrons, and the energy detected from the wafer 204 includes electrons. In this way, the energy source may be an electron beam source 202, which may include or be coupled to an electron beam system as disclosed herein. In one such embodiment shown in FIG. 7, the output acquisition subsystem includes an electronic optical column 201 coupled to a computer subsystem 207.

As also shown in FIG. 7, the electron optical column 201 includes an electron beam source 202 that is configured to generate electrons that are focused on the wafer 204 by one or more elements 203. The electron beam source 202 may include an emitter and one or more elements 203 may include, for example, a gun lens, an anode, a BLA, an MLA, a gate valve, a beam current selection aperture, an objective lens, and/ Or a scanning subsystem. The electron column 201 may include any other suitable elements known in the art. Although only one electron beam source 202 is illustrated, the system 200 may include multiple electron beam sources 202.

The electrons (eg, secondary electrons) returned from the wafer 204 can be focused to the detector 206 by one or more elements 205. The one or more elements 205 may include, for example, a scanning subsystem, which may be the same scanning subsystem included in the element 203. The electron column 201 may include any other suitable elements known in the art.

Although the electron column 201 is shown in FIG. 7 as being configured so that electrons are guided to the wafer 204 at an oblique angle of incidence and scattered from the wafer at another oblique angle, it should be understood that the electron beam can be guided to the wafer at any suitable angle. The circle is scattered from the wafer. In addition, the electron beam-based output acquisition subsystem can be configured to use multiple modes to generate images of the wafer 204 (for example, with different illumination angles, collection angles, etc.). The multiple modes of the output acquisition subsystem based on the electron beam can be different in any image generation parameters of the output acquisition subsystem.

The computer subsystem 207 can electronically communicate with the detector 206. The detector 206 can detect electrons returning from the surface of the wafer 204 to form an electron beam image of the wafer 204. The electron beam image can include any suitable electron beam image. The computer subsystem 207 can be configured to use the output of the detector 206 and/or the electron beam image to perform other functions or additional steps.

It should be noted that FIG. 7 is provided herein to roughly illustrate a configuration of an electron beam-based output acquisition subsystem. The configuration of the electron beam-based output acquisition subsystem described in this article can be changed to optimize the performance of the output acquisition subsystem, as is usually done when designing a commercial output acquisition system implement. In addition, an existing system can be used to implement the system described in this article (for example, by adding the functionality described in this article to an existing system). For some of these systems, the methods described in this article can be provided as optional functionality of the system (for example, in addition to other functionality of the system).

In one embodiment, the system 200 is an inspection system. For example, the electron beam output acquisition subsystem described in this article can be configured as an inspection system. In another embodiment, the system 200 is a defect re-inspection system. For example, the electron beam output acquisition subsystem described in this article can be configured as a defect re-detection system. In another embodiment, the system 200 is a metering system. For example, the electron beam output acquisition subsystem described in this article can be configured as a metering system. In particular, one or more of the parameters of the embodiment of the system 200 described herein and shown in FIG. 7 can be modified to provide different imaging capabilities depending on the application in which the parameters will be used. In one such example, the system 200 shown in FIG. 7 can be configured to have a higher resolution if it will be used for defect re-detection or metering rather than for inspection. In other words, the embodiment of the system 200 shown in FIG. 7 illustrates some general and various configurations of a system 200. The system 200 can be tailored in several ways to produce different imaging capabilities that are more or less suitable for different applications. The output acquisition subsystem.

In particular, the embodiments described herein can be installed on a computer node or computer cluster that is a component of an output acquisition subsystem or is coupled to the output acquisition subsystem, such as an electron beam Checker or defect re-inspection tool, a mask checker, a virtual checker or other device. In this way, the embodiments described herein can generate outputs that can be used in various applications including (but not limited to) wafer inspection, mask inspection, electron beam inspection and re-inspection, metrology, or other applications. The characteristics of the system 200 shown in FIG. 7 can be modified as described above based on the sample that will produce the output.

FIG. 8 is a flowchart of a method 300. An electron beam is generated 301, extracted 302, guided through a BLA 303, and guided through an MLA 304 downstream of the BLA with respect to a projection direction of the electron beam. BLA defines multiple holes. The BLA is configured to reduce the Coulomb interaction between the electron beam source and the multi-lens array. The electron beam may be located in an area less than 1V/mm or a field-free area when the electron beam passes through the BLA. The electron beam passing through the MLA can be focused to a diameter of, for example, 50 nm.

Each of the steps of the method can be performed as set forth herein. The method may also include any other steps that can be executed by the controller and/or computer subsystem or system described herein. These steps can be performed by one or more computer systems, which can be configured according to any of the embodiments described herein. In addition, the method described above can be executed by any of the system embodiments described herein.

Although the invention has been described with respect to one or more specific embodiments, it should be understood that other embodiments of the invention can be made without departing from the scope of the invention. Therefore, it is believed that the present invention is only limited by the scope of the attached patent application and its reasonable interpretation.

100: electron beam system

101: Electron beam source

102: Extractor

103: beam limiting aperture

104: Multi-lens array

105: hole

106: anode

107: electron beam

108: thin beam

109: Launcher

110: Suppressor

111: Magnetic lens

112: Magnetic pole piece

113: Coil

114: component

A-A: line

Claims (20)

An electron beam system, comprising: an electron beam source; a multi-lens array; a beam limiting aperture defining a plurality of holes, wherein the beam limiting aperture is arranged between the electron beam source and the multi-lens array, And wherein the beam limiting aperture is configured to reduce the beam blur between the electron beam source and the multi-lens array; a plurality of elements are located on the opposite side of the multi-lens array with respect to the electron beam source On the side, the elements are configured to adjust the focal length of the beamlets from the multi-lens array; and a magnetic lens is arranged between the multi-lens array and the elements. The electron beam system of claim 1, wherein the beam limiting aperture is arranged at a position between the electron beam source and the multi-lens array with a field less than 1V/mm. The electron beam system of claim 2, wherein the position between the electron beam source and the multi-lens array is fieldless. The electron beam system of claim 1, wherein the beam limiting aperture defines at least 6 holes among the holes. Such as the electron beam system of claim 1, wherein the electron beam source includes an emitter, a suppressor and Extractor. The electron beam system of claim 1, wherein the beam limiting aperture defines the apertures to each have a diameter from 1 μm to 100 μm. Such as the electron beam system of claim 6, wherein the diameter of each of the holes is 50 μm. The electron beam system of claim 1, wherein the beam limiting aperture defines the apertures as having a pitch from 2 μm to 100 μm. Such as the electron beam system of claim 8, wherein the pitch is 100 μm. Such as the electron beam system of claim 1, wherein the beam limiting aperture is made of silicon, a metal or a metal alloy. Such as the electron beam system of claim 1, wherein the beam limiting aperture defines the holes to be circular. Such as the electron beam system of claim 1, wherein the holes are arranged in the beam limiting aperture in a polygonal configuration. A scanning electron microscope comprising the electron beam system as claimed in claim 1. An electron beam method, comprising: generating an electron beam; extracting the electron beam; guiding the electron beam through a beam limiting aperture defining a plurality of holes; guiding the electron beam through one of the electron beams The projection direction is located in a multi-lens array downstream of the beam limiting aperture, wherein the beam limiting aperture is configured to reduce the beam blur between the electron beam source and the multi-lens array; the electron beam is guided through relative to The projection direction of the electron beam is located at a magnetic lens downstream of the multi-lens array; and the electron beam is guided through a plurality of elements located downstream of the magnetic lens with respect to the projection direction of the electron beam, wherein the The element is configured to adjust the focal length of the thin beam from the magnetic lens. The method of claim 14, wherein the electron beam is located in a region having a field less than 1 V/mm when the electron beam passes through the beam limiting aperture. Such as the method of claim 15, wherein the area is a field-free area. The method of claim 14, wherein the electron beam passing through the multi-lens array is focused to a diameter of 50 nm. An electron beam system, which includes: An electron beam source, which is configured to generate an electron beam; a multi-lens array, which is located upstream of a wafer; a beam limiting aperture, which defines a plurality of holes, wherein the beam limiting aperture is placed on the electron Between the beam source and the multi-lens array, and wherein the beam limiting aperture is configured to reduce the beam blur between the electron beam source and the multi-lens array; a plurality of elements are located relative to the multi-lens array On the opposite side of the electron beam source, the elements are configured to adjust the focal length of the thin beam from the multi-lens array; a magnetic lens arranged between the multi-lens array and the elements; and a The detector is configured to detect electrons from the electron beam returning from a surface of the wafer. The system of claim 18, wherein the beam limiting aperture is arranged at a position between the electron beam source and the multi-lens array having a field less than 1V/mm. The system of claim 19, wherein the position between the electron beam source and the multi-lens array is fieldless.

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