Ion source extraction electrode system

Abstract

The present invention discloses an ion source extraction electrode system, comprising a plasma electrode and an extraction electrode group, wherein the extraction electrode group comprises a first ground electrode, a suppression electrode and a second ground electrode in the beam forward direction, wherein the first ground electrode and the second ground electrode are grounded, the suppression electrode is connected to a negative pressure, the plasma electrode is connected to a positive pressure, and the electric field between the plasma electrode and the first ground electrode is an extraction electric field, which is used to control the curvature and shape of the plasma extraction interface. Another ground electrode is introduced as a shielding ground electrode, which is used to shield and isolate the plasma electrode and the suppression electrode by electric field, stabilize the extraction electric field and the electric field of the electric field lens, and control the curvature and shape of the plasma extraction interface, thereby controlling the initial shape of the beam, thereby obtaining an ideal beam morphology.

Description

Technical Field

[0001] The invention relates to an extraction electrode system. Background Art

[0002] With the development of ion implanters, the continuous improvement of production capacity, and the wide application in more fields (semiconductor integrated circuits, single-crystal photovoltaic cells, and panel displays, etc.), new requirements have been put forward for the indicators of ion sources and beam extraction systems. While increasing the beam current, the width of the beam, the uniformity of the beam density, the controllability of the beam divergence angle (minimum aberration condition), and the stability of the ion source operation have become the current problems that need to be overcome.

[0003] Traditional large beam extraction systems are based on three-electrode systems, usually referred to as plasma electrodes, suppression electrodes, and ground electrodes. The main function of the suppression electrode is to suppress electrons from the downstream of the beam, and protect the ion source components at high potential from electron bombardment damage. Another function of the suppression electrode is to achieve an electric field lens effect by adjusting the voltage difference between the plasma electrode and the suppression electrode, and to control the extraction (ion acceleration process) and beam divergence angle of the beam. When the beam density is relatively low, the spatial electric field disturbance generated by the ion beam is basically negligible relative to the electric field formed between the electrodes, and the beam is also in a relatively balanced metastable state. However, as the beam density increases, the spatial electric field generated by the ion beam and the electrode field together form a complex integrated electric field. At this time, the optical properties of the beam (focusing, divergence, aberration) are completely dependent on this integrated electric field. Therefore, once a slight change in the plasma, beam, or electrode causes a sudden change in this integrated electric field, it cannot be reversed, and the beam is completely out of control. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the defect that the electric field of the extraction electrode system in the prior art is difficult to accurately control, and to provide an ion source extraction electrode system that can properly control the plasma extraction interface (plasma meniscus).

[0005] The present invention solves the above technical problems through the following technical solutions:

[0006] An ion source extraction electrode system is characterized in that it comprises a plasma electrode and an extraction electrode group, wherein the extraction electrode group comprises a first ground electrode, a suppression electrode and a second ground electrode in sequence in the beam advancing direction, wherein the first ground electrode and the second ground electrode are grounded, the suppression electrode is connected to a negative pressure, and the plasma electrode is connected to a positive pressure, and the electric field between the plasma electrode and the first ground electrode is an extraction electric field, and the extraction electric field is used to control the curvature and shape of the plasma extraction interface.

[0007] Preferably, the extraction electric field is adjusted by adjusting the distance between the first ground electrode and the plasma electrode.

[0008] Preferably, the first ground electrode is used to shield the plasma electrode with an electric field to stabilize the extraction electric field.

[0009] Preferably, the electric field between the first ground electrode and the suppression electrode is an electric field lens electric field, and the first ground electrode is used to electric field shield the suppression electrode to stabilize the electric field lens electric field.

[0010] Preferably, the divergence angle of the beam is controlled by adjusting the voltage of the suppression electrode to adjust the equivalent electric field lens parameters of the extraction electrode group.

[0011] Preferably, the extraction electrode group is integrally movable in the beam advancing direction.

[0012] Preferably, the distance between the first ground electrode and the suppression electrode is fixed, and the distance between the suppression electrode and the second ground electrode is fixed.

[0013] Preferably, the suppression electrode and the second ground electrode are fixed, and the first ground electrode is translatably movable in the beam advancing direction.

[0014] Preferably, the suppression electrode is used to prevent electrons from the downstream of the beam from passing through the openings of the extraction electrode group and the openings of the plasma electrode to enter the ion source.

[0015] Preferably, the shape of the plasma extraction interface is divergent, parallel or focused in the beam transmission direction.

[0016] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0017] The positive and progressive effect of the present invention is that: on the basis of the three electrodes in the prior art, another ground electrode is introduced as a shielding ground electrode, which is used to isolate the plasma electrode and the suppression electrode by electric field shielding, stabilize the extraction electric field and the electric field of the electric field lens, and control the curvature and shape of the plasma extraction interface, thereby controlling the initial shape of the beam, thereby obtaining an ideal beam morphology.

[0018] Even if the ion beam current changes instantaneously and the divergence angle fluctuates, the divergent beam will be blocked by the shielding ground electrode, preventing the suppression electrode from being irradiated by the beam, causing the suppression power supply to be overloaded and the beam extraction to be interrupted.

[0019] By adjusting the voltage of the suppression electrode, the equivalent electric field lens parameters of the extraction electrode group can be changed, thereby achieving control of the beam divergence angle.

[0020] Such an electrode extraction system has the advantage of single parameter corresponding adjustment for large beam current adjustment. The curvature and shape of the plasma extraction interface are mainly affected by the distance between the plasma electrode and the extraction electrode group, while the electric field lens effect of the extraction electrode group is only related to the voltage of the suppression electrode. When adjusting the beam current, this feature of independent optimization without the need for cyclic adjustment of multiple adjustment parameters provides a faster and simpler method for beam current optimization adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 FIG. 4 is a schematic diagram of an ion source extraction electrode system according to an embodiment of the present invention.

[0022] Figure 2 FIG. 1 is a schematic diagram of an ion beam being transmitted through an ion source extraction electrode system according to an embodiment of the present invention.

[0023] Figure 3 It is a schematic diagram of a plasma extraction interface that is a concave surface (beam focusing) according to an embodiment of the present invention.

[0024] Figure 4 It is a schematic diagram showing that the plasma extraction interface is substantially planar (beam is transmitted in parallel) according to an embodiment of the present invention.

[0025] Figure 5 It is a schematic diagram of a plasma extraction interface that is a convex surface (beam divergence) according to an embodiment of the present invention.

[0026] Figure 6 FIG. 1 is a schematic diagram of an electric field simulation of an ion source extraction electrode system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples.

[0028] Combine the following Figure 1-Figure 6, the technical solution of the present invention is described with a specific embodiment. The ion source extraction electrode system includes a plasma electrode 11 and an extraction electrode group 2. The plasma electrode is in close contact with the plasma 100 in the ion source cavity. Here, the plasma electrode 11 is arranged on the ion source cavity, and the potential of the plasma electrode determines the potential of the plasma. The extraction electrode group 2 includes a first ground electrode 21, a suppression electrode 22 and a second ground electrode 23 in the beam forward direction A. In this embodiment, two upper and lower electrodes with equal potential are used to form each electrode in the extraction electrode group. The material of the electrode is selected from high-temperature rare metal materials, such as tungsten and molybdenum. In the case where the electrode size gradually increases, considering the cost and weight factors, high-purity graphite material has also become the choice of electrode material. According to different practical application requirements, the electrode can also be a combination of high-temperature non-ferrous metals and graphite. There is an opening 10 in the center of the plasma electrode 11 for the beam to pass through. Similarly, the first ground electrode 21, the suppression electrode 22 and the second ground electrode 23 also form an opening 20 in the center for the beam to pass through. The ion source extraction electrode system described in this embodiment is applicable to electrodes with various opening shapes. For example, for a slit electrode opening, the extracted beam is in the shape of a long strip (a wide beam, a ribbon beam), and the long side of the beam is vertical. Figure 1 The short side of the beam is the direction perpendicular to A in the paper. For the circular hole electrode opening, the electrode opening shown is a circular symmetrical structure. This structure is also applicable to the mesh extraction electrode.

[0029] Among them, the first ground electrode 21 and the second ground electrode 23 are grounded, the suppression electrode is connected to negative pressure, the plasma electrode is connected to positive pressure, and the electric field between the plasma electrode 11 and the first ground electrode 21 is an extraction electric field, which is used to control the curvature and shape of the plasma extraction interface. The extraction electric field is adjusted by adjusting the distance between the first ground electrode 21 and the plasma electrode 11. The first ground electrode 21 is used to electric field shield the plasma electrode to stabilize the extraction electric field. In this technical solution, the grounding of the first ground electrode 21 ensures that its potential is fixed and is always at 0 volts. Compared with other electrodes controlled by power supplies, its voltage control is limited by the output power and maximum current of the power supply, and often encounters the problem of power supply overload, resulting in the power supply output voltage being out of control, thereby causing the beam state to be out of control and unable to recover. The technical solution of the present invention avoids this problem very well.

[0030] The electric field between the first ground electrode 21 and the suppression electrode 22 is an electric field lens electric field. The first ground electrode 21 is used to electrically shield the suppression electrode 22 to stabilize the electric field lens electric field. By adjusting the voltage of the suppression electrode 22, the equivalent electric field lens parameters of the extraction electrode group are adjusted to control the divergence angle of the beam. Figure 2, it is desired to obtain a beam 3 that is basically transmitted in parallel in the direction of beam advance, rather than a beam 31 with a large divergence angle, then it is necessary to adjust the voltage of the suppression electrode 22 so that the divergence angle is controlled within the ideal range. Specifically, the voltage adjustment of the suppression electrode can change the equivalent electric field lens parameters of the extraction electrode group, thereby achieving the control of the beam divergence angle. Because the divergence, collimation, and focusing characteristics of the beam mainly depend on the shape of the plasma emission surface (also known as the plasma meniscus), the extraction electrode group composed of the first ground electrode 21, the suppression electrode 22, and the second ground electrode 23 as the shielding ground electrode itself constitutes an electric field lens, so the electric field lens parameters can be changed by adjusting the suppression electrode voltage, thereby optimizing the beam optical characteristics.

[0031] Specifically, the extraction electrode group 2 can be translated as a whole in the beam advancing direction.

[0032] One way is that the distance between the first ground electrode 21 and the suppression electrode 22 is fixed, and the distance between the suppression electrode 22 and the second ground electrode 23 is fixed. Then, it is only necessary to translate the extraction electrode group as a whole to adjust the distance between the first ground electrode 21 and the plasma electrode 11, so as to control the curvature and shape of the plasma extraction interface.

[0033] Another way is that the suppression electrode 22 and the second ground electrode 23 are fixed, and the first ground electrode 21 is movable in the direction of beam advance. In this case, the curvature and shape of the plasma extraction interface can be adjusted by only moving the first ground electrode 21. Because in the ion implantation equipment, the ion source and the beam transmission system both work under vacuum, and generally the control equipment is set in the atmospheric environment, the fewer objects that need to be moved, the better the design is for the connection between the control equipment and the vacuum system.

[0034] In addition to controlling the divergence angle of the beam, the suppression electrode is used to prevent electrons from the downstream of the beam from passing through the openings of the extraction electrode group and the openings of the plasma electrode to enter the ion source.

[0035] Main references Figure 3-Figure 5 The shape of the plasma extraction interface is the divergence of the beam in the beam transmission direction ( Figure 5 convex), parallel ( Figure 4 ) or focus ( Figure 3concave surface). Specifically, since the first ground electrode 21 is maintained at a stable potential (0 volts), and the ion energy determines the potential of the plasma electrode 11, the ion beam extraction electric field between the two electrodes with a certain potential is adjusted by the distance between the two electrodes. The beam geometry characteristics (divergence, parallelism, focusing) of the extracted ion beam depend on the plasma density and the extraction electric field strength. Under a certain working plasma density, by adjusting the distance between the first ground electrode 21 and the plasma electrode 11, the extraction electric field can be adjusted, effectively changing the shape of the plasma emission surface (also known as the plasma meniscus) at the opening of the plasma electrode. By reducing the distance and increasing the electric field, the shape of the plasma emission surface will be concave, and the ion beam will show focusing characteristics; gradually increasing the distance, the shape of the emission surface changes from concave to flat, and the ion beam has a relatively parallel collimated beam characteristic; further increasing the distance, the shape of the emission surface begins to become convex, and the ion beam becomes divergent.

[0036] In a conventional three-electrode system, the voltages applied to different electrodes, such as the voltage of the plasma electrode (ion energy electron volt voltage) and the voltage of the suppression electrode (suppression voltage), are closely related to the plasma density. If one of the parameters changes, the other parameters need to be optimized accordingly. However, after inserting the first ground electrode 21, the influence of the voltage of the suppression electrode 22 on the extracted beam is effectively isolated, which greatly simplifies the beam optimization operation.

[0037] refer to Figure 6 , the electric field distribution of the extraction electrode system using this embodiment is simulated by IBSimu simulation of electric field (IBSimu software is a simulation software developed by the European JYFL laboratory, and the computing language is C++) beam simulation calculation. The horizontal axis is the reference distance from the ion source in the beam transmission direction, and the vertical axis is the electrode half-opening size (the size from the center of the beam to the edge of the electrode opening. If the opening is circular, this represents the opening circle radius. If it is a slit opening, the vertical axis represents the half-opening width of the slit). The leftmost side is the plasma 100 reaction zone. In the simulation calculation, a positive voltage of 9kV is applied to the plasma electrode 11, and -3kV is applied to the suppression electrode.

[0038] The present invention describes a large ion beam ion source extraction electrode system, which overcomes the problem of unstable electric field control of the ion source extraction electrode caused by large beam current, thereby greatly improving the operation stability of the ion source and simultaneously meeting the requirements of ultra-wide beam amplitude, uniformity, and small divergence angle.

[0039] Although the specific embodiments of the present invention are described above, those skilled in the art should understand that these are only examples, and the protection scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. An ion source extraction electrode system, characterized in that: It comprises a plasma electrode and an extraction electrode group, wherein the extraction electrode group comprises a first ground electrode, a suppression electrode and a second ground electrode in sequence in the beam forward direction, wherein the first ground electrode and the second ground electrode are grounded, the suppression electrode is connected to a negative pressure, the plasma electrode is connected to a positive pressure, and the electric field between the plasma electrode and the first ground electrode is an extraction electric field, and the extraction electric field is used to control the curvature and shape of the plasma extraction interface; adjusting the extraction electric field by adjusting the distance between the first ground electrode and the plasma electrode; The first ground electrode is used for electric field shielding the plasma electrode to stabilize the extraction electric field; The electric field between the first ground electrode and the suppression electrode is an electric field lens electric field, and the first ground electrode is used for electric field shielding the suppression electrode to stabilize the electric field lens electric field.

2. The ion source extraction electrode system according to claim 1, characterized in that: The equivalent electric field lens parameters of the extraction electrode group are adjusted by adjusting the voltage of the suppression electrode to control the divergence angle of the beam.

3. The ion source extraction electrode system according to claim 1, characterized in that: The extraction electrode group can be translated as a whole in the beam advancing direction.

4. The ion source extraction electrode system according to claim 3, characterized in that: The distance between the first ground electrode and the suppression electrode is fixed, and the distance between the suppression electrode and the second ground electrode is fixed.

5. The ion source extraction electrode system according to claim 1, characterized in that: The suppression electrode and the second ground electrode are fixed, and the first ground electrode is translatable in the beam advancing direction.

6. The ion source extraction electrode system according to any one of claims 1 to 5, characterized in that: The suppression electrode is used to prevent electrons from the downstream of the beam from passing through the openings of the extraction electrode group and the openings of the plasma electrode and entering the ion source.

7. The ion source extraction electrode system according to any one of claims 1 to 5, characterized in that: The shape of the plasma extraction interface is divergence, parallelism or focusing of the beam in the beam transmission direction.

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