Ion grid structure in ion beam etching

Abstract

This invention provides an ion grid structure for ion beam etching, comprising: a screen grid and at least one grid located on the side of the screen grid away from the discharge chamber; the screen grid is in contact with a dielectric; and at least one of the grids is in contact with the dielectric. By using a dielectric as the grid framework of the ion grid structure, this invention improves the mechanical strength of the ion grid structure and enhances its stability and reliability by providing the dielectric for all the mechanical strength of the grid.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to an ion grid structure used in ion beam etching. Prior Art

[0002] In the semiconductor industry, ion beam etching (IBE) systems are increasingly being used in the manufacturing processes of many semiconductor devices, such as sensors and memory devices. Some manufacturing processes even rely on IBE.

[0003] The working principle of IBE is that the working gas in the ion source chamber is excited to generate plasma under low-pressure conditions using radio frequency electromagnetic waves and other means. The ions in the plasma are extracted and accelerated by the ion grid, and the electrons generated by the neutralizer and the ions in the ion beam are combined to form neutral particles. Finally, the particle beam reaches the substrate surface and the bombardment of the accelerated particles is used to achieve the purpose of physical etching.

[0004] How to improve the reliability and stability of the ion grid structure in ion beam etching is a technical problem that needs to be solved in this field. Summary of the Invention

[0005] In light of this, this Summary is provided to briefly introduce the concepts that will be described in detail in the Detailed Description section below. This Summary is not intended to identify key features or essential features of the claimed technical solution, nor is it intended to limit the scope of the claimed technical solution.

[0006] The object of the present invention is to provide an ion grid structure for ion beam etching, which can increase the intensity of the ion beam drawn through the grid and improve the efficiency of ion beam etching.

[0007] To achieve the above object, the present invention has the following technical solutions: An embodiment of the present invention provides an ion grid structure for ion beam etching, comprising: A screen grid and at least one grid located on one side of the screen grid away from the discharge chamber; The screen grid is in contact with the dielectric; At least one of the grids is in contact with the dielectric.

[0008] In one possible implementation, the grid includes: An accelerating grid is located on a side of the screen grid away from the discharge chamber.

[0009] In one possible implementation, the distance between the screen grid and the acceleration grid is less than or equal to a first preset threshold; The thickness of the screen grid is less than or equal to a second preset threshold.

[0010] In one possible implementation, the grid includes: A deceleration grid is located on the side of the acceleration grid away from the screen grid.

[0011] In one possible implementation, the grid includes: An extraction grid is located between the screen grid and the acceleration grid.

[0012] In one possible implementation, the grid includes: A focusing grid is located between the extraction grid and the acceleration grid.

[0013] In a possible implementation, the dielectric on the same side of the grid includes at least one.

[0014] In a possible implementation, the dielectrics on different sides of the grid include at least one.

[0015] In a possible implementation, the acceleration gate is located inside the dielectric.

[0016] In a possible implementation, the dielectric material is a material having a breakdown voltage greater than or equal to a third preset threshold.

[0017] In a possible implementation, the dielectric material is an insulating material.

[0018] In a possible implementation, the mechanical strength of the dielectric is greater than or equal to a fourth preset threshold.

[0019] In a possible implementation, the first preset threshold includes 3 mm, and the second preset threshold includes 5 mm.

[0020] In a possible implementation, the dielectric material includes aluminum oxide, aluminum nitride and / or quartz.

[0021] In a possible implementation, the third preset threshold includes 0.1 kV / mm.

[0022] In one possible implementation, the ion beam current intensity extracted from a single hole of the ion grid structure includes: Wherein, I1 is the ion beam current intensity extracted from a single hole of the ion grid structure, ε0 is the dielectric constant in a vacuum, e is the charge number carried by the ion beam, M is the atomic mass of the ion beam, V is the extraction voltage, lg is the distance between the screen grid and the acceleration grid, ts is the thickness of the screen grid, and ds is the aperture of the screen grid.

[0023] In a possible implementation, the screen grid and the grid are made of conductive material.

[0024] In a possible implementation, the electrical conductivity of the screen grid and the grid is greater than a first preset value.

[0025] In a possible implementation, the hardness of the screen grid and the grid is greater than a second preset value.

[0026] In a possible implementation, the thermal expansion coefficients of the screen grid and the grid are less than a third preset value.

[0027] In a possible implementation, the screen grid is made of molybdenum or graphite.

[0028] In a possible implementation, the screen grid is connected to a positive voltage; the acceleration grid is connected to a negative voltage.

[0029] In a possible implementation, the retarding fence is grounded.

[0030] In a possible implementation, the voltage of the extraction grid is smaller than the voltage of the screen grid and larger than the voltage of the acceleration grid.

[0031] In a possible implementation, the voltage of the focusing grid is smaller than the voltage of the extraction grid, and larger than the voltage of the acceleration grid.

[0032] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: An embodiment of the present invention provides an ion grid structure for ion beam etching, comprising: a screen grid and at least one grid located on a side of the screen grid away from a discharge chamber; the screen grid in contact with a dielectric; and at least one of the grids in contact with the dielectric. By providing a dielectric as the grid framework of the ion grid structure, the dielectric provides the mechanical strength of the grid, thereby improving the mechanical strength of the ion grid structure and enhancing its stability and reliability. Simple diagram description

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without making any further efforts. The above and other features, advantages, and aspects of various embodiments of the present invention will become more apparent with reference to the following detailed description in conjunction with the drawings. Throughout the drawings, identical or similar reference numerals represent identical or similar elements. It should be understood that the drawings are schematic, and that the elements and components are not necessarily drawn to scale. Figure 1 shows a schematic diagram of a conventional ion source discharge structure; Figure 2 shows a schematic diagram of a conventional extracted ion beam density distribution; Figure 3 shows a schematic diagram of a conventional ion beam etching ion grid structure; Figure 4 shows a schematic diagram of key parameters of the ion grid structure in a conventional ion beam etching; FIG5 is a schematic diagram showing key parameters of an ion grid structure in ion beam etching provided by an embodiment of the present invention. Implementation Method

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the drawings.

[0035] Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0036] As previously described, in the semiconductor industry, ion beam etching (IBE) systems are increasingly being used in the manufacturing processes of many semiconductor devices, such as sensors and memory devices. Some manufacturing processes even rely on IBE.

[0037] The working principle of IBE is that the working gas in the ion source chamber is excited to generate plasma under low-pressure conditions using radio frequency electromagnetic waves and other means. The ions in the plasma are extracted and accelerated by the ion grid, and the electrons generated by the neutralizer and the ions in the ion beam are combined to form neutral particles. Finally, the particle beam reaches the substrate surface and the bombardment of the accelerated particles is used to achieve the purpose of physical etching.

[0038] How to increase the intensity of the ion beam drawn through the grid to improve the efficiency of ion beam etching is a technical problem that needs to be solved in this field.

[0039] To address the above technical issues, embodiments of the present invention provide an ion grid structure for ion beam etching, comprising: a screen grid and at least one grid located on a side of the screen grid away from a discharge chamber; the screen grid in contact with a dielectric; and at least one of the grids in contact with the dielectric. By providing a dielectric as the grid framework of the ion grid structure, the dielectric provides all of the mechanical strength of the grid, thereby improving the mechanical strength of the ion grid structure and enhancing its stability and reliability.

[0040] As semiconductor device critical dimensions shrink and device fabrication becomes more complex, the requirements for IBE etching processes are becoming increasingly stringent. Furthermore, the stability and yield of semiconductor devices are directly related to the uniformity of IBE etching within the silicon wafer sample size. This uniformity is determined by the performance of the IBE ion source, specifically the structural parameters of the IBE grid design.

[0041] The current common ion source structure (see Figure 1) generates an inductively coupled plasma (ICP) by applying a radio frequency (RF) current to a helical antenna within a discharge chamber. Initially, the generated plasma is primarily distributed within the elliptical region shown in Figure 1. Under low-pressure conditions, the motion of the plasma within the ion source chamber approximately follows the bipolar diffusion equation, and the radial distribution of the plasma density exhibits a Gaussian distribution (see Figure 2). The plasma density is highest at the center of the coil and decreases radially with increasing distance from the center. This poses significant challenges to the uniformity required by the IBE etching process. The ion grid, in addition to extracting ions from the ion chamber, also ensures the generation of a uniform ion beam, making it a key component for achieving IBE etching and ensuring process uniformity.

[0042] Refer to Figure 3, which is a schematic diagram of an ion grid structure in traditional ion beam etching. The ion grid structure can be divided into a screen grid and an acceleration grid, wherein the acceleration grid is located on the side of the screen grid away from the discharge chamber. In order to ensure the uniformity of the etching process, the aperture of the grid corresponding to the center of the coil can be set smaller, and the aperture of the grid corresponding to the area away from the center of the coil can be set larger, thereby achieving the task of drawing out a uniform ion beam.

[0043] Among them, the screen grid is the grid layer closest to the plasma in the chamber and generally operates at a positive potential; while the acceleration grid generally operates at a negative potential. Its main purpose is twofold: 1) to provide an extraction voltage for positive ions; 2) to generate a larger electrostatic potential barrier to prevent the electrons generated by the neutralizer from flowing back into the ion chamber.

[0044] Generally, the ion source grid of IBE operates at a relatively low voltage, mainly considering the possibility of ion damage to the wafer. However, a large ion beam current density is required to ensure the etching rate and a uniform ion beam distribution is required to ensure etching uniformity. Current theoretical research shows that the maximum ion beam current intensity that can be drawn out by a single hole is: Wherein, referring to FIG4 , FIG4 is a schematic diagram showing key parameters of an ion grid structure in a conventional ion beam etching, where 1 is a screen grid and 2 is an acceleration grid.

[0045] I1 is the ion beam current intensity extracted from a single hole in the grid structure, ε0 is the dielectric constant in vacuum, e is the charge carried by the ion beam, M is the atomic mass of the ion beam, V is the extraction voltage, that is, the voltage difference between the screen grid and the acceleration grid, lg is the distance between the screen grid and the acceleration grid, ts is the thickness of the screen grid, and ds is the aperture of the screen grid.

[0046] By analyzing the theoretical formula (1), it can be seen that the ion beam intensity can be increased by increasing the extraction voltage and the screen grid aperture and reducing the grid pitch and screen grid thickness.

[0047] If the ion beam intensity is to be increased by increasing the extraction voltage, for the etching process, the screen grid voltage is generally a fixed value, and its value determines the energy of the particles that finally bombard the wafer surface; and the greater the negative value of the acceleration grid voltage, the greater the ion bombardment energy it receives. Whether it is to protect the acceleration grid or to reduce impurity particles, its value is determined not to be too large; therefore, the ion beam intensity cannot be significantly increased by increasing the extraction voltage.

[0048] If we want to increase the ion beam intensity by reducing the grid pitch, although reducing the grid pitch can effectively increase the extracted ion beam current, the minimum grid pitch is limited by the breakdown voltage of air. Therefore, the ion beam intensity cannot be significantly increased by reducing the grid pitch.

[0049] If the ion beam intensity is to be increased by reducing the screen grid thickness, the grid thickness determines the mechanical strength of the grid, thus affecting the stability of the grid operation, especially for grids made of special materials, such as graphite grids, which are difficult to make too thin due to the material properties. Therefore, in this case where the screen grid thickness cannot be reduced to increase the extraction current, a three-layer grid mode is generally chosen to increase the extraction current.

[0050] Therefore, in an embodiment of the present invention, in order to further improve the ion beam extraction capability of the ion grid structure, see FIG5 , which is a schematic diagram of key parameters of an ion grid structure in ion beam etching provided by an embodiment of the present invention.

[0051] The ion grid structure provided in embodiments of the present invention may include a screen 1 and at least one grid located on a side of the screen 1 that is away from the discharge chamber. It should be noted that the embodiments of the present invention do not specifically limit the number of grids, and those skilled in the art may determine the number based on actual circumstances.

[0052] The screen 1 is in contact with the dielectric 3; at least one of the grids is in contact with the dielectric 3. That is, the present invention provides the dielectric 3 as the grid skeleton of the ion grid structure, so that the mechanical strength of the grid is borne by the dielectric 3, thereby improving the mechanical strength of the ion grid structure and enhancing the stability and reliability of the ion grid structure.

[0053] In one possible implementation, the grid may be, for example, an accelerating grid 2; the accelerating grid 2 is located on a side of the screen grid 1 away from the discharge chamber, the screen grid 1 contacts one side of the dielectric 3; the accelerating grid 2 contacts the dielectric 3; the distance between the screen grid 1 and the accelerating grid 2 is less than or equal to a first preset threshold; and the thickness of the screen grid 1 is less than or equal to a second preset threshold.

[0054] That is, in the embodiment of the present invention, the dielectric 3 can be set as the grid skeleton of the ion grid structure, so that the mechanical strength of the grid is borne by the dielectric, and thus the thickness of the screen grid 1 is no longer a constraint on the mechanical strength of the grid. At the same time, the component on the grid that withstands the smallest ion bombardment is also the screen grid 1, which is about a dozen eV ion bombardment. Therefore, the design allows the thickness of the screen grid 1 to be very thin; at the same time, the breakdown voltage of the dielectric 3 is relatively large, which allows the distance between the screen grid 1 and the acceleration grid 2 to be smaller than in a gas environment. By reducing the thickness of the screen grid 1 and the distance between the screen grid 1 and the acceleration grid 2, the ion grid structure has a stronger ion beam extraction capability.

[0055] According to current research, the breakdown voltage of air is about 3kV / mm, while the breakdown voltage of dielectrics such as ceramics is about 14kV / mm. Therefore, the presence of dielectrics can theoretically allow the distance between grids to be smaller than in a gas environment.

[0056] In one possible implementation, the grid provided by the embodiment of the present invention may include: The deceleration grid (not shown in the figure) located on the side of the acceleration grid 2 away from the screen grid 1 is used to decelerate the ion beam to prevent the energy of the ion beam that eventually bombards the wafer from being too high.

[0057] In one possible implementation, the grid provided by the embodiment of the present invention may include: The extraction grid (not shown in the figure) located between the screen grid 1 and the acceleration grid 2 serves to extract the ion beam from the discharge ion chamber.

[0058] In one possible implementation, the grid provided by the embodiment of the present invention may include: A focusing grid (not shown) located between the extraction grid and the acceleration grid 2 serves to focus the beam. When a small beam spot is required, the focusing grid can be used to focus the beam.

[0059] In an embodiment of the present invention, at least one of the extraction grid, focusing grid, acceleration grid 2, and deceleration grid may be in contact with the dielectric 3, and may be in contact with the interior of the dielectric or on the surface of the dielectric. The remaining grids may not be in contact with the dielectric 3. This embodiment of the present invention does not specifically limit this, and may be specifically set by those skilled in the art according to actual circumstances.

[0060] In the embodiment of the present invention, the dielectrics on the same side of the grid may include at least one, i.e., one or more, and the dielectrics on different sides of the grid may also include at least one, i.e., one or more. The embodiment of the present invention does not make specific limitations here, and the specific settings can be made by those skilled in the art according to actual conditions.

[0061] For example, the dielectric between screen grid 1 and accelerator grid 2 is on the same side of the grid, and can be made of a variety of materials, such as aluminum oxide or quartz. The dielectric between screen grid 1 and accelerator grid 2, and the dielectric between accelerator grid 2 and retarder grid, are on different sides of the grid (in this case, different sides of accelerator grid 2), and can be made of a variety of materials, such as aluminum oxide or quartz.

[0062] In one possible implementation, the accelerating gate 2 provided by an embodiment of the present invention can be located inside the dielectric 3. This prevents the grid spacing from becoming a limiting factor affecting the mechanical strength of the grid. Since the accelerating gate 2 is placed inside the dielectric 3, the dielectric 3 also protects the accelerating gate 2 to a certain extent, allowing the accelerating gate's voltage to vary within a wider range, thereby better ensuring the grid's withstand voltage.

[0063] In a possible implementation, the material of the dielectric 3 provided in the embodiment of the present invention is a material having a breakdown voltage greater than or equal to a third preset threshold, thereby ensuring the withstand voltage value of the grid.

[0064] Optionally, the material of the dielectric 3 may include an insulating material, and the mechanical strength of the dielectric 3 may be greater than or equal to a fourth preset threshold, that is, the dielectric may be an insulating material with high mechanical strength, so as to improve the mechanical strength of the grid structure while ensuring insulation between each grid.

[0065] Specifically, the first preset threshold provided in the embodiment of the present invention includes 3 mm, and the second preset threshold includes 5 mm, that is, the distance between the screen grid 1 and the acceleration grid 2 can be designed to be 1 / 3 of the air dielectric grid pitch, and the screen grid can be designed as a very thin grid covering the dielectric 3.

[0066] Optionally, the material of the dielectric 3 provided in the embodiment of the present invention may include aluminum oxide, aluminum nitride and / or quartz. The third preset threshold includes 0.1 kV / mm, that is, the dielectric material is mainly selected from dielectric materials with a higher breakdown voltage.

[0067] At the same time, the screen grid 1 and the acceleration grid 2 provided in the embodiment of the present invention are made of conductive materials.

[0068] Optionally, the electrical conductivity of the screen grid 1 and the grid is greater than a first preset value; the hardness of the screen grid 1 and the grid is greater than a second preset value; and the thermal expansion coefficient of the screen grid 1 and the grid is less than a third preset value. In other words, the screen grid 1 and the grid selected in this embodiment of the present invention are materials with good electrical conductivity, high hardness, and a low thermal expansion coefficient.

[0069] For example, the material of the screen grid 1 may include molybdenum or graphite, but the specific material of the screen grid is not limited. It should be noted that the material of the screen grid cannot be copper to avoid possible contamination caused by copper.

[0070] Screen grid 1 is connected to a positive voltage; accelerating grid 2 is connected to a negative voltage. The retarding grid is grounded. The voltage of the extraction grid is less than that of screen grid 1 and greater than that of accelerating grid 2. The voltage of the focusing grid is less than that of the extraction grid and greater than that of accelerating grid 2.

[0071] An embodiment of the present invention provides an ion grid structure for ion beam etching, comprising: a screen grid and at least one grid located on a side of the screen grid away from a discharge chamber; the screen grid in contact with a dielectric; and at least one of the grids in contact with the dielectric. By providing a dielectric as the grid framework of the ion grid structure, the dielectric provides the mechanical strength of the grid, thereby improving the mechanical strength of the ion grid structure and enhancing its stability and reliability.

[0072] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0073] The above description is merely a preferred embodiment of the present invention. Although the present invention has been disclosed above in terms of preferred embodiments, this is not intended to limit the present invention. Anyone skilled in the art can utilize the methods and techniques disclosed above to make numerous possible variations and modifications to the present invention, or to create equivalent embodiments with equivalent variations, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

[0074] 1: Screen 2: Acceleration grid 3: Dielectric ds: screen aperture I1: ion beam intensity lg: distance between screen grid and the acceleration grid M: ion beam atomic mass ts: gate thickness V: output voltage

Claims

1. An ion grid structure for ion beam etching, characterized in that it comprises: A screen grid and at least one grid located on the side of the screen grid away from the discharge chamber; The ion grid includes an accelerating grid located on the side of the screen grid away from the discharge chamber and an extraction grid located between the screen grid and the accelerating grid. The accelerating grid, together with the screen grid, provides the extraction voltage for positive ions. The screen grid is in contact with a dielectric, and the accelerating grid is in contact with the dielectric. The mechanical strength of the ion grid structure is borne solely by the dielectric, such that the distance between the screen grid and the accelerating grid is reduced to less than or equal to a first preset threshold, and the thickness of the screen grid is reduced to less than or equal to a second preset threshold, thereby increasing the intensity of the ion beam extracted from a single aperture of the ion grid structure. At least one of the grids is in contact with the dielectric. The accelerating grid is located inside the dielectric. The voltage of the extraction grid is less than the voltage of the screen grid but greater than the voltage of the accelerating grid.

2. The structure as described in claim 1, wherein, The grid includes a deceleration grid located on the side of the acceleration grid away from the screen grid.

3. The structure as described in claim 1, wherein, The grid includes a focusing grid located between the lead-out grid and the acceleration grid.

4. The structure as described in any one of claims 1 to 3, wherein, The dielectric on the same side of the grid includes at least one type.

5. The structure as described in any one of claims 1 to 3, wherein, The dielectric on different sides of the grid includes at least one type.

6. The structure as described in claim 1, wherein, The dielectric material is a material whose breakdown voltage is greater than or equal to a third preset threshold.

7. The structure as described in claim 6, wherein, The dielectric material is an insulating material.

8. The structure as described in claim 6, wherein, The mechanical strength of the dielectric is greater than or equal to a fourth preset threshold.

9. The structure as described in claim 1, wherein, The first preset threshold includes 3mm, and the second preset threshold includes 5mm.

10. The structure as described in claim 1, wherein, The dielectric material includes aluminum oxide, aluminum nitride, and / or quartz.

11. The structure as described in claim 7, wherein, The third preset threshold includes 0.1 kV / mm.

12. The structure as described in claim 1, wherein, The intensity of the ion beam extracted from a single aperture of the ion grid structure includes: ; where I1 is the intensity of the ion beam extracted from a single aperture of the ion grid structure, is the dielectric constant in vacuum, e is the charge number of the ion beam, M is the atomic mass of the ion beam, V is the extraction voltage, lg is the distance between the screen grid and the accelerating grid, ts is the grid thickness of the screen grid, and ds is the aperture of the screen grid.

13. The structure as described in claim 1, wherein, The screen and the grid are made of conductive material.

14. The structure as described in claim 13, wherein, The conductivity of the screen and the grid is greater than a first preset value.

15. The structure as described in claim 13, wherein, The hardness of the screen and the grid is greater than a second preset value.

16. The structure as described in claim 13, wherein, The coefficient of thermal expansion of the screen and the grid is less than a third preset value.

17. The structure as described in claim 1, wherein, The screen grid is connected to a positive voltage; the acceleration grid is connected to a negative voltage.

18. The structure as described in claim 2, wherein, The deceleration gate is grounded.

19. The structure as described in claim 3, wherein, The voltage of the focusing gate is less than the voltage of the lead-out gate, but greater than the voltage of the acceleration gate.

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