Immersion Magnetic Lens Electron Gun and its Optical Axis Alignment Method

Abstract

This application relates to an immersion magnetic lens electron gun, comprising: an electron beam source, an electron gun anode, and a magnetic lens. The magnetic lens has an optical axis through-hole at its center and an anode mounting groove at its top. The electron gun anode is positioned within the anode mounting groove, with its bottom and sidewalls attached to the inner wall of the anode mounting groove. The upper edge of the sidewall of the electron gun anode extends outwards, suitable for fixed connection with the electron microscope housing. The electron beam source is positioned above the electron gun anode to emit an electron beam downwards. By providing a mounting groove at the top of the magnetic lens and placing the electron gun anode, with its structure tightly fitted to it, within the mounting groove, alignment accuracy is ensured during installation, facilitating alignment between the electron beam source and the electron gun anode. Adjustment components operated by personnel in the art facilitate alignment between the electron gun anode and the magnetic lens, further optimizing the alignment position. Based on the position of the electron beam spot on the fluorescent screen and the characteristics of the microscopic image, the electron optical components are finely adjusted from top to bottom to achieve overall system alignment.

Description

Technical Field

[0001] This application relates to the semiconductor field, and more particularly to an immersion magnetic lens electron gun and a method for aligning its optical axis. Background Technology

[0002] With the advancement of integrated circuit manufacturing technology, the density and difficulty of defect detection during manufacturing have increased significantly, necessitating more precise and efficient defect detection methods. Electron beam inspection utilizes a high-energy electron beam to bombard the surface of the object under inspection, collecting signals such as secondary electrons and backscattered electrons. This electron imaging can reveal information such as the surface morphology and chemical composition of the sample, offering high resolution and the ability to specifically detect electrical defects. Therefore, electron beam defect inspection equipment has become an important means of monitoring yield in integrated circuit silicon wafer manufacturing.

[0003] Currently, the main methods to improve the electron beam defect detection rate are to increase the image signal-to-noise ratio and reduce the detection time per unit area. In existing technologies, the electron beam emitted from the electron gun is divergent, and most of the electron beam is blocked at the anode of the gun. Therefore, the downstream beam current is significantly weakened, resulting in a reduction in the probe beam current and affecting the imaging quality.

[0004] Using a high-current, high-brightness electron gun can significantly increase the probe beam current. High-current, high-brightness electron guns are usually immersed Schottky field emission electron guns, which can emit an electron beam current 10 times that of ordinary electron guns. However, the unique open magnetic field of Schottky field emission electron guns greatly increases the difficulty of optical axis alignment. There is a lack of a high-current, high-brightness electron gun that is easy to align with the optical axis. Summary of the Invention

[0005] In view of this, this application proposes an immersion magnetic lens electron gun, including an electron beam source, an electron gun anode, and a magnetic lens; the magnetic lens has an optical axis through hole at its center and an anode mounting groove at its top; the electron gun anode is disposed in the anode mounting groove, the bottom and sidewalls of the electron gun anode are attached to the inner wall of the anode mounting groove, and the upper edge of the sidewalls of the electron gun anode extends outward for fixed connection with the electron microscope housing; the electron beam source is disposed above the electron gun anode for emitting an electron beam downward.

[0006] In one possible implementation, the electron gun anode includes an anode plate; the bottom of the anode plate is horizontal, the sidewalls are vertical, and the height of the outer edge of the anode plate is higher than its middle height, with an anode hole at the center.

[0007] In one possible implementation, the electron gun anode further includes an anode grating; the anode grating is disposed at the center of the anode plate and its structure matches the anode aperture.

[0008] In a possible implementation, the electron gun anode further includes an anode grating; the anode grating is disposed within the through-hole of the optical axis of the magnetic lens, and is located at the bottom of the through-hole of the optical axis or near the bottom position of the through-hole of the optical axis.

[0009] In a possible implementation, the magnetic lens further includes an adjusting member; an adjusting hole is formed in the side wall of the magnetic lens, and the adjusting hole communicates with the anode mounting groove; the adjusting member is matched with the structure of the adjusting hole, one end extends into the anode mounting groove and abuts against the anode plate, and the other end extends outside the magnetic lens. By adjusting the adjusting member, the magnetic lens can move in the horizontal plane.

[0010] In a possible implementation, the anode plate is a cylinder with a notch at the top, and its horizontal cross-section is in a "U" shape.

[0011] In a possible implementation, it further includes a lower condenser assembly and a fluorescent screen; the lower condenser assembly is disposed below the magnetic lens for focusing the electron beam; the fluorescent screen is disposed below the lower condenser assembly.

[0012] On the other hand, the above-mentioned immersion magnetic lens electron gun is calibrated by using the optical axis alignment method of the immersion magnetic lens electron gun; the electron gun anode includes an anode plate; the bottom of the anode plate is horizontal, the side wall is vertical, and the height of the outer edge of the anode plate is higher than the height of the middle part thereof, and an anode hole is provided at the center; it further includes a fluorescent screen; the fluorescent screen is disposed below the magnetic lens for displaying the electron beam spot; the anode plate is installed in the anode mounting groove, and by continuously adjusting the voltage of the anode plate and simultaneously adjusting the horizontal position and tilt angle of the electron beam source until the position of the electron beam spot remains stationary, the electron beam source is aligned with the anode plate.

[0013] In one possible implementation, the electron gun anode further includes an anode plate and an anode grating; the bottom of the anode plate is horizontal, the sidewalls are inclined from top to bottom towards the center or are vertical, and the height of the outer edge of the anode plate is higher than its middle height, with an anode hole at the center; the anode grating is disposed in the optical axis through-hole of the magnetic lens, located at the bottom of the optical axis through-hole or near the bottom of the optical axis through-hole; the magnetic lens further includes an adjustment member; an adjustment hole is formed on the sidewall of the magnetic lens, the adjustment hole communicating with the anode mounting groove; the structure of the adjustment member matches the adjustment hole, one end extends into the anode mounting groove and abuts against the anode plate, and the other end extends out of the outer side of the magnetic lens, adjusting the adjustment member allows the magnetic lens to move in the horizontal plane; a first constant current is applied to the magnetic lens, the current value of the first constant current is continuously adjusted, and the adjustment member is adjusted simultaneously to change the horizontal position of the magnetic lens until the center position of the electron beam spot remains stationary, and the edge of the electron beam spot can concentrically scale with the change of the first constant current, at which point the electron beam source is aligned with the magnetic lens.

[0014] In one possible implementation, a lower-level focusing component is also included; the lower-level focusing component is disposed between the magnetic lens and the fluorescent screen; a second constant current is applied to the lower-level focusing component, and the horizontal position of the lower-level focusing component is adjusted by adjusting the current value of the first constant current, until the electron beam spot center is stationary, and the electron beam source is aligned with the lower-level focusing component.

[0015] The beneficial effects of this application are as follows: By providing a mounting groove on the top of the magnetic lens and placing the electron gun anode, which fits tightly with the magnetic lens, in the mounting groove, alignment accuracy is ensured during installation, facilitating alignment between the electron beam source and the electron gun anode. Furthermore, through the adjustment mechanism operated by an expert in the field, the magnetic lens can be finely adjusted horizontally, further optimizing the alignment between the electron gun anode and the magnetic lens. Then, based on the position of the electron beam spot on the fluorescent screen and the characteristics of the microscopic image, the electron optical components are finely adjusted step by step from top to bottom to achieve overall system alignment.

[0016] Other features and aspects of this application will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0017] The accompanying drawings, which are included in and form part of this specification, illustrate exemplary embodiments, features, and aspects of this application together with the specification and serve to explain the principles of this application.

[0018] Figure 1 A schematic diagram of the structure of an immersion magnetic lens electron gun according to an embodiment of this application is shown. Detailed Implementation

[0019] Various exemplary embodiments, features, and aspects of this application will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0020] It should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application or to simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0021] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0022] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0023] Furthermore, to better illustrate this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented without certain specific details. In some instances, methods, means, components, and circuits well-known to those skilled in the art have not been described in detail in order to highlight the main points of this application.

[0024] Figure 1 A schematic diagram of the structure of an immersion magnetic lens electron gun according to an embodiment of this application is shown.

[0025] like Figure 1 As shown, the immersion magnetic lens 130 electron gun includes: an electron beam source 100, an electron gun anode, and a magnetic lens 130. The magnetic lens 130 has an optical axis through hole at its center and an anode mounting groove at its top. The electron gun anode is placed in the anode mounting groove, and the bottom and sidewalls of the electron gun anode are attached to the inner wall of the anode mounting groove. The upper edge of the sidewall of the electron gun anode extends outward, which is suitable for fixed connection with the electron microscope housing. The electron beam source 100 is placed above the electron gun anode to emit an electron beam downward.

[0026] In this implementation, a mounting groove is provided on the top of the magnetic lens 130, and the electron gun anode, whose structure fits tightly with it, is placed in the mounting groove. This ensures alignment accuracy during installation and facilitates alignment between the electron beam source 100 and the electron gun anode. Furthermore, by operating the adjustment component 120, an expert can finely adjust the magnetic lens 130 in the horizontal direction, further optimizing the alignment between the electron gun anode and the magnetic lens 130. Then, based on the position of the electron beam spot on the fluorescent screen 190 and the characteristics of the microscopic image, the electron optical components are finely adjusted step by step from top to bottom to achieve overall system alignment.

[0027] Preferably, the electron beam source 100 of this application adopts a Schottky field emission electron gun, and the magnetic lens 130 is an immersion magnetic lens 130.

[0028] In one possible implementation, the electron gun anode includes an anode plate 110 and an anode grating 150. The bottom of the anode plate 110 is horizontal, the sidewalls are vertical, and the height of the outer edge of the anode plate 110 is higher than the height of its middle part. An anode hole is provided at the center.

[0029] In one possible implementation, the electron gun anode also includes an anode grating 150, which can be disposed at the center of the anode plate 110 and whose structure matches the anode hole.

[0030] In another possible implementation, the anode grating 150 is disposed within the optical axis through-hole of the magnetic lens 130, located at the bottom of the optical axis through-hole or near the bottom of the optical axis through-hole.

[0031] In the above possible implementations, the anode grating 150 can be designed as an integral part of the anode plate 110, that is, the anode grating 150 is fixedly installed at the anode hole, or it can be set separately, that is, the anode grating 150 is set in the optical axis through hole at the center of the magnetic lens 130, and the position of the anode grating 150 is located at the bottom of the optical axis through hole or near the bottom of the optical axis through hole.

[0032] More specifically, the magnetic lens 130 includes a ferromagnetic housing and a coil 140. The horizontal cross-section of the ferromagnetic housing is U-shaped, with a vertical column at the center. The optical axis through hole vertically penetrates the column, and the height of the column is lower than the side wall of the ferromagnetic housing. The coil 140 is arranged around the side wall of the column. The mounting groove is the area on the inner wall of the magnetic housing and above the column, which is used to place the anode plate 110.

[0033] Furthermore, the ferromagnetic outer shell and the external structure of the anode plate 110 are both cylindrical, and the radial distance between the upper inner edge of the magnetic lens 130 and the outer edge of the anode plate 110 is equal and parallel to each other.

[0034] In a possible implementation, the magnetic lens 130 further includes an adjusting member 120. An adjusting hole is provided on the side wall of the magnetic lens 130, and the adjusting hole communicates with the anode mounting groove. The adjusting member 120 is matched with the structure of the adjusting hole. One end extends into the anode mounting groove and abuts against the anode plate 110, and the other end extends outside the magnetic lens 130. By adjusting the adjusting member 120, the magnetic lens 130 can move in the horizontal plane.

[0035] In this implementation, the adjusting member 120 is an adjusting set screw, which is matched with the adjusting hole provided on the ferromagnetic outer shell. The anode plate 110 is fixed on the outer shell. By screwing the adjusting set screw, the adjusting set screw drives the magnetic lens 130 to move in the horizontal direction, facilitating the centering of the magnetic lens 130 and the anode plate 110.

[0036] Specifically, the number of adjusting holes is multiple, and the adjusting set screws correspond to them one by one.

[0037] Preferably, the number of adjusting holes is an even number, and they are arranged at equal intervals in the radial direction of the ferromagnetic outer shell. The adjusting holes arranged at equal intervals in the radial direction facilitate adjusting the ferromagnetic outer shell from multiple angles, effectively improving the accuracy of optical axis centering, and at the same time improving the adjusting efficiency of the centering of the ferromagnetic outer shell and the anode plate 110.

[0038] In a possible implementation, the anode plate 110 is a cylinder with a notch at the top, and its horizontal cross-section is in a "U" shape.

[0039] In a possible implementation, it further includes a lower condenser assembly and a fluorescent screen 190. The lower condenser assembly is arranged below the magnetic lens 130 for focusing the electron beam, and the fluorescent screen 190 is arranged below the lower condenser assembly.

[0040] It should be particularly noted that the specific components of the lower condenser assembly are not limited. Those skilled in the art can replace them according to different samples to be scanned specifically. The lower condenser assembly in this application is a prior art and has not been improved. Therefore, only a specific embodiment will be given in the following text, and the rest will not be elaborated.

[0041] In this possible implementation, more specifically, the lower condenser assembly includes a secondary condenser lens 160, an objective lens 180 aperture stop, and an objective lens 180; the secondary condenser lens 160, the objective lens grating 170, and the objective lens 180 are sequentially arranged in the vertical direction between the magnetic lens 130 and the fluorescent screen 190 from top to bottom.

[0042] The lower condenser lens assembly can increase the scanning field of view. Adjust the objective lens 180 aperture stop at the horizontal position to complete the centering of the objective lens 180 aperture stop.

[0043] On the other hand, the immersion magnetic lens 130 electron gun is calibrated using the optical axis alignment method of the immersion magnetic lens 130 electron gun. The electron gun anode includes an anode plate 110, the bottom of which is horizontal and the sidewalls are vertical. The height of the outer edge of the anode plate 110 is higher than the height of its middle part. An anode hole is opened at the center. The anode plate 110 also includes a fluorescent screen 190, which is located below the magnetic lens 130 and is used to display the electron beam spot. The anode plate 110 is installed in the anode mounting groove. By continuously adjusting the voltage of the anode plate 110, the horizontal position and tilt angle of the electron beam source 100 are adjusted simultaneously until the position of the electron beam spot remains unchanged, and the electron beam source 100 is aligned with the anode plate 110.

[0044] The anode plate 110 and the magnetic lens 130 are aligned during assembly due to their shape design. The radial distances between the outer edge of the anode plate 110 and the inner edge of the upper end of the magnetic lens 130 are equal and parallel. The anode plate 110 is stably installed within the mounting groove of the magnetic lens 130, using the magnetic lens 130 as a base. This design automatically defines the installation position during installation. When high voltage is applied to the anode plate 110 and the voltage value is continuously adjusted, if the anode plate 110 and the electron beam source 100 are not aligned, the position of the electron beam spot in the fluorescent screen 190 will shift according to the voltage change. The tilt angle or horizontal position of the electron beam source 100 is adjusted until the position of the electron beam spot no longer changes, thus aligning the anode plate 110 and the electron beam source 100.

[0045] In one possible implementation, the electron gun anode further includes an anode plate 110 and an anode grating 150. The bottom of the anode plate 110 is horizontal, and its sidewalls are inclined or vertical from top to bottom towards the center. The height of the outer edge of the anode plate 110 is higher than its middle height, and an anode hole is formed at the center. The anode grating 150 is disposed in the optical axis through-hole of the magnetic lens 130, located at the bottom of the optical axis through-hole or near the bottom of the optical axis through-hole. The magnetic lens 130 also includes an adjustment member 120, and an adjustment hole is formed on the sidewall of the magnetic lens 130. The adjustment hole is connected to the anode mounting groove for adjustment. The structure of component 120 matches that of the adjustment hole. One end extends into the anode mounting groove and abuts against the anode plate 110, while the other end extends out of the outer side of the magnetic lens 130. By adjusting component 120, the magnetic lens 130 can move in the horizontal plane. A first constant current is applied inside the magnetic lens 130. The current value of the first constant current is continuously adjusted, and the adjustment part is adjusted at the same time to change the horizontal position of the magnetic lens 130 until the center position of the electron beam spot remains stationary and the edge of the electron beam spot can concentrically expand and contract with the change of the first constant current. At this point, the electron beam source 100 and the magnetic lens 130 are aligned.

[0046] In this implementation, a first constant current is applied as an excitation within the magnetic lens 130. By continuously varying the first constant current, the electron beam moves in a circular motion along the axis, contracting or diverging. The electron beam spot on the fluorescent screen 190 scales and expands. If the anode plate 110 and the magnetic lens 130 are not properly aligned, the position of the electron beam spot will keep changing when the first constant current is varied. When the fine-tuning adjustment component 120 is adjusted so that the magnetic lens 130 moves in the horizontal direction, the outer edge of the electron beam spot scales and expands concentrically with the center, thus ensuring the alignment accuracy between the anode plate 110 and the magnetic lens 130.

[0047] In one possible implementation, a lower-level focusing component is also included. The lower-level focusing component is disposed between the magnetic lens 130 and the fluorescent screen 190. A second constant current is applied in the lower-level focusing component. By adjusting the current value of the first constant current, the horizontal position of the lower-level focusing component is adjusted until the center of the electron beam spot is stationary, and the electron beam source 100 is aligned with the lower-level focusing component.

[0048] In this implementation, as described above, the lower-level focusing assembly includes a secondary converging lens 160, an objective grating 170, and an objective lens 180 arranged from top to bottom between the magnetic lens 130 and the fluorescent screen 190. A second constant current is applied to the secondary converging lens 160, and the current value of the first constant current is continuously changed. If the secondary converging lens 160 is not aligned with the electron beam source 100, the center of the electron beam spot on the fluorescent screen 190 will move horizontally. The secondary converging lens 160 is horizontally adjusted until the position of the electron beam spot remains unchanged, thus completing the alignment of the secondary converging lens 160 with the electron beam source 100.

[0049] After adding a lower-level condenser assembly, the scanning field of view increases to a certain extent, causing the image edges and four corners to become blurred. As shown in the figure, the shape of the scanning field of view is mostly square, with 402 being the line of equal sharpness, forming a symmetrical shape. At a large field of view, the four corners are more prone to blurring. If the objective lens 180° aperture and the electron beam source 100 are not properly aligned, the image sharpness will no longer be symmetrical. Based on the scanning electron microscope image, the position of the objective lens 180° aperture is adjusted horizontally until the edge sharpness is symmetrical about the image center, thus completing the alignment of the objective lens 180° aperture and the electron beam source 100.

[0050] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. An immersed magnetic lens electron gun, characterized by, The electron gun anode is arranged in the anode mounting groove, the bottom and the side wall of the electron gun anode are attached to the inner wall of the anode mounting groove, the side wall of the electron gun anode extends outward, and is suitable for being fixedly connected with the electron microscope shell; The magnetic lens further comprises an adjusting member; The side wall of the magnetic lens is provided with an adjusting hole, and the adjusting hole is communicated with the anode mounting groove; The electron gun anode comprises an anode plate; The bottom of the anode plate is horizontal, the side wall is vertical, the height of the outer edge of the anode plate is higher than the middle part, an anode hole is arranged at the center, and the anode hole corresponds to the optical axis through hole; The adjusting member is matched with the structure of the adjusting hole, one end of the adjusting member extends into the anode mounting groove and abuts against the anode plate, the other end extends out of the outer side of the magnetic lens, the adjusting member is adjusted, and the magnetic lens can move in the horizontal plane. The electron gun anode further comprises an anode grating; The anode grating is arranged at the center of the anode plate and is matched with the structure of the anode hole. The electron gun anode further comprises an anode grating; 2. The immersed magnetic lens electron gun of claim 1, wherein, The anode grating is arranged in the optical axis through hole of the magnetic lens and is located at the hole bottom of the optical axis through hole or a position close to the bottom of the optical axis through hole. The anode plate is a cylinder with a notch at the top and a horizontal section in the shape of a "n" character.

3. The immersed magnetic lens electron gun of claim 1, wherein, Further comprising a lower light focusing assembly and a fluorescent screen; The lower light focusing assembly is arranged below the magnetic lens and is used for focusing the electron beam; 4. The immersed magnetic lens electron gun of any of claims 2-3, wherein, The fluorescent screen is arranged below the lower light focusing assembly.

5. The immersed magnetic lens electron gun of any of claims 1-3, wherein, An optical axis centering method of the immersion type magnetic lens electron gun is adopted to calibrate the immersion type magnetic lens electron gun of claim 1; The electron gun anode comprises an anode plate; The bottom of the anode plate is horizontal, the side wall is vertical, the height of the outer edge of the anode plate is higher than the middle part, and an anode hole is arranged at the center; 6. A method of optical axis centering of an immersed magnetic lens electron gun, characterized in that Further comprising a fluorescent screen; The fluorescent screen is arranged below the magnetic lens and is used for displaying the electron beam spot; The anode plate is installed into the anode mounting groove, the voltage of the anode plate is continuously adjusted, the horizontal position and the inclination angle of the electron beam source are adjusted at the same time, until the position of the electron beam spot remains unchanged, the electron beam source is centered with the anode plate; The electron gun anode further comprises an anode grating; The anode grating is arranged in the optical axis through hole of the magnetic lens and is located at the hole bottom of the optical axis through hole or a position close to the bottom of the optical axis through hole; The magnetic lens further comprises an adjusting member; The side wall of the magnetic lens is provided with an adjusting hole, and the adjusting hole is communicated with the anode mounting groove; The adjusting member is matched with the structure of the adjusting hole, one end of the adjusting member extends into the anode mounting groove and abuts against the anode plate, the other end extends out of the outer side of the magnetic lens, the adjusting member is adjusted, and the magnetic lens can move in the horizontal plane. ​ ​ ​ A first constant current is applied in the magnetic lens, the current value of the first constant current is continuously adjusted, and the adjusting member is adjusted to change the horizontal position of the magnetic lens, until the center position of the electron beam spot is fixed, and the edge of the electron beam spot can be concentrically scaled with the change of the first constant current, the electron beam source is aligned with the magnetic lens.

7. The optical axis centering method of an immersed magnetic lens electron gun according to claim 6, characterized in that, Further comprising a lower light condensing assembly; The lower light condensing assembly is arranged between the magnetic lens and the fluorescent screen. A second constant current is applied in the lower light condensing assembly, the current value of the first constant current is adjusted, and the horizontal position of the lower light condensing assembly is adjusted, until the center of the electron beam spot is fixed, and the electron beam source is aligned with the lower light condensing assembly.

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