Plasma processing apparatus and focus ring for plasma processing apparatus

Abstract

A focusing ring comprises: a ring-shaped main body and an extension part located inside the main body and extending inwardly, the ring-shaped main body has a center; the main body has a horizontal bottom surface, an inner sidewall and an outer sidewall and an upper surface; the upper surface of the main body is connected to the upper surface of the extension part by a first transition surface which is downwardly inclined, the lower surface of the extension part comprises a second transition surface which is downwardly inclined and connected to the inner sidewall of the main body, wherein the distance from the inside of the second transition surface to the center is less than the radius of the wafer to be processed. By providing an inclined second transition surface on the lower surface of the extension part, the material thickness is increased in the area where the transition surface exists, and the position of the transition surface is selected so that the area of the upper surface of the extension part which is quickly etched corresponds to the area below which the material thickness is increased, ultimately greatly extending the effective working time of the extension part and greatly improving the overall service life of the focusing ring.

Description

Technical Field

[0001] This utility model relates to a focusing ring for a plasma processing device, and in particular to the specific shape and dimensions of the focusing ring to significantly improve its service life. Background Technology

[0002] Etching uniformity is one of the key technical parameters of plasma etching, directly affecting the performance and reliability of integrated circuits. With technological advancements, the requirements for etching uniformity in etching processes have become increasingly stringent, especially regarding the uniformity of wafer edge etching. Etching uniformity is influenced by plasma density and the height of the sheath layer on and around the wafer. To improve plasma etching uniformity, a focusing ring made of silicon or silicon carbide is typically placed on the wafer support substrate. This focusing ring is closely attached to and surrounds the wafer, and a support ring made of insulating material (alumina) is placed below it. An edge electrode is also placed between the focusing ring and the support ring. Radio frequency power is supplied separately and independently to the lower electrode and the edge electrode in the substrate. By adjusting the power supplied to the edge electrode, the height and distribution of the sheath layer on the focusing ring can be adjusted. To prevent the radio frequency electromagnetic field generated by the edge electrode from affecting the inward lower electrode and the wafer center region, and to prevent corrosive etching gases from passing through the gap between the substrate and the focusing ring to reach the edge electrode, the inner side of the support ring usually includes an upward extension to shield the edge electrode. While this structure can operate effectively and improve etching uniformity, its long-term stability is poor, especially in high aspect ratio etching applications where radio frequency power can reach tens of thousands of watts. This results in extremely high energy from downward ion bombardment, causing rapid corrosion and consumption of the focusing ring surface exposed to the plasma. During operation, the focusing ring's consumption rate varies across different locations. The areas with the fastest corrosion rate render the focusing ring unusable, while areas with slower corrosion rates still have a significant amount of material remaining, necessitating ring replacement. Ultimately, this leads to a very short effective lifespan for the focusing ring, resulting in substantial resource waste.

[0003] The statements herein provide only background information relating to this invention and do not necessarily constitute prior art. Summary of the Invention

[0004] The purpose of this invention is to provide a focusing ring suitable for use in a plasma processing apparatus around a wafer to be processed. The focusing ring includes: an annular main body and an extension portion located inside the main body and extending inwards. The annular main body has a center. The main body has a horizontal bottom surface, an inner sidewall, an outer sidewall, and an upper surface. The upper surface of the main body is connected downwards to the upper surface of the extension portion via a first transition surface. The lower surface of the extension portion includes a second transition surface, which is connected downwards to the inner sidewall of the main body. The distance from the inner side of the second transition surface to the center is less than the radius of the wafer to be processed. By providing an inclined second transition surface on the lower surface of the extension portion, the material thickness in the area where the transition surface exists increases. The position of the transition surface is chosen so that the area on the upper surface of the extension portion that is rapidly etched corresponds to the area below where the material thickness increases, ultimately significantly extending the effective working time of the extension portion and greatly improving the overall service life of the focusing ring.

[0005] The lower surface of the extension may include a combination of a plane and a second transition surface, or it may include only a second transition surface; both can achieve the purpose of this invention. Attached Figure Description

[0006] Figure 1 This is a partial structural schematic diagram of a plasma processing device provided by this utility model.

[0007] Figure 2a , 2b This is a comparison chart of the corrosion rates of the focusing ring of this utility model and the focusing ring of the prior art.

[0008] Figure 3 This is a schematic diagram of the positioning notch on the wafer.

[0009] Figure 4 This is a schematic diagram of another embodiment of the focusing ring of this utility model.

[0010] Figure 5 This is a schematic diagram of another embodiment of the focusing ring of this utility model. Detailed Implementation

[0011] The following is based on Figures 1-3 The preferred embodiments of this utility model will be described in detail below.

[0012] like Figure 1As shown, this utility model provides a partially enlarged view of the base inside a plasma processing device. The plasma processing device generally includes a reaction chamber, with a gas spray head positioned at the top. The gas spray head is connected to an external gas source (not shown) and is used to deliver reactive gas into the reaction chamber. The gas spray head serves as the upper electrode of the reaction chamber and is positioned opposite to the lower electrode assembly. The lower electrode assembly supports the wafer W to be processed. The lower electrode assembly includes a lower electrode 202, an adhesive layer 201 sequentially disposed above the lower electrode, and an electrostatic chuck 200 above the adhesive layer. The wafer W to be processed is supported on the electrostatic chuck 200. An radio frequency power supply is applied to the upper electrode or the lower electrode assembly, generating a radio frequency electric field between the upper and lower electrodes. This field dissociates the reactive gas into plasma, forming a plasma processing region between the upper and lower electrodes. The plasma contains a large number of active particles such as electrons, ions, excited-state atoms, molecules, and free radicals. These active particles can react with the surface of the wafer W to complete the etching process. An exhaust device is also provided below the reaction chamber 1 to discharge reaction byproducts and maintain a vacuum environment in the reaction chamber. The lower electrode assembly includes a support ring 20 located around the lower electrode and a focusing ring 10 above the support ring. The support ring 20 can be made of ceramic (such as alumina). The inner side of the support ring 20 includes an upwardly extending cylindrical inner wall to shield the edge electrode 30 on the upper surface of the support ring. The edge electrode extends downward through the support ring 20 via a power supply wire 31 to receive radio frequency power. The focusing ring 10 includes a main body 10a and an extension 10b located inside the main body 10a. The upper surface S10 of the main body 10a is connected to the upper surface S12 of the extension via a downwardly inclined transition surface a1. The lower surface of the extension includes a straight surface C11 connected to the inner surface b3 of the main body via a downwardly inclined second transition surface b1. The angle between the second transition surface and the horizontal plane is greater than 30 degrees and less than 60 degrees. The bottom surface C10 of the main body is connected to the stepped surface S14 located on the outer side wall of the main body through the outer side wall b2. The stepped surface S14 is connected to the upper surface S10 through the side wall a2 of the main body. The stepped surface S14 can be adapted to the cover ring shape outside the focusing ring, so that the cover ring and the focusing ring fit together, preventing the corrosive gas above from diffusing directly downwards and reaching the non-corrosion-resistant parts below the cover ring to form contaminants.

[0013] The side walls a2, b2, and b3 of the main body are basically perpendicular to the horizontal plane, while the upper surface S10, the step surface S14, the upper surface S12 of the extension, and part of the lower surface area of ​​the extension are parallel to the horizontal plane.

[0014] The upper end of the cylindrical inner wall of the support ring is also in close contact with the elastic sealing ring 40 to prevent the processing gas from diffusing downwards into the gap below the elastic sealing ring 40 and causing a discharge phenomenon. The upper and lower surfaces of the extension 10b are basically horizontal, and the thickness is selected to be less than 2mm. The smaller thickness can reduce the leakage of the edge electrode RF power to the wafer center region, thereby ensuring that the RF power emitted by the edge electrode 30 is mainly fed to the upper focusing ring, so that the plasma concentration and sheath thickness around the wafer can be adjusted independently.

[0015] like Figure 2a , 2b The diagram shows the interface after the focusing ring 10 is etched during plasma etching. Figure 2a As shown, the focusing ring includes a main body 10a and an extension 10b located inside the main body. With long-term operation of the etching process, the material on the upper surface of the focusing ring is etched downwards. The upper surface S10 is planar, so it is etched downwards uniformly. At the junction of the upper surface S10 and the transition surface a1, due to the tendency of the sheath height to change at this point, more ions converge and bombard this area, resulting in faster etching. The area of ​​the upper surface S12 of the extension not covered by the wafer W is bombarded by ions from the vertical direction above, as well as by ions ejected from the inclined transition surface a1, thus being etched at the fastest speed. The difference in etching rates at these locations leads to the formation of [a specific etch rate] on the surface of the focusing ring. Figure 2a The curve of the upper surface of the focusing ring shown in L0 illustrates this. It can be seen that the area between the upper surface S12 of the extension and the transition surface a1 almost completely etches through the extension, rendering the focusing ring unusable and requiring replacement. Other areas are only partially etched. Therefore, in existing technologies, to ensure etching effectiveness, the focusing ring must be etched much earlier than the transition surface a1. Figure 2a The surface morphology of the focusing ring shown is replaced when it is examined. For example... Figure 2b As shown, by providing a second transition surface b1 on the lower surface of the extension 10b, the material thickness in the area of ​​the focusing ring with the fastest etching rate is significantly increased without affecting the original function of the focusing ring in distributing the radio frequency electric field and airflow. Ultimately, after prolonged use, the surface of the focusing ring achieves the pattern shown in L1, maintaining its basic functions. The rapidly etched area, namely the outer region of the upper surface S12 of the extension, no longer becomes a bottleneck for extending the focusing ring's lifespan. The focusing ring only needs to be replaced when all parts of the ring have been extensively etched. Therefore, the focusing ring structure provided by this invention can significantly increase the lifespan of the focusing ring, reduce the frequency of replacement, and consequently reduce the number of maintenance operations required for the plasma processing chamber.

[0016] like Figure 3As shown, in semiconductor processing, a small notch is created at the edge of the wafer W to position the wafer at its rotation angle within the semiconductor processing system. The innermost position of this notch is point P shown in the figure. In a plasma processing system, the focusing ring below this notch is directly exposed to the plasma and is rapidly etched. Therefore, this invention… Figure 1 The innermost diameter (D2) of the second transition surface b1 shown needs to be smaller than the wafer diameter D1 (300 mm), and ideally it needs to be a few millimeters smaller. The outermost side of the transition surface, which is also the inner side of the main body b3, should ideally be basically the same as the outer diameter of the wafer, or slightly smaller than the wafer diameter, such as 299.5~300 mm.

[0017] like Figure 4 As shown, the focusing ring in this utility model can also have a groove 11 opened on the bottom surface C10 of the main body, and then fill the groove 11 with silicone or other thermally conductive elastic materials to efficiently transfer the heat on the focusing ring 10 to the support ring 20 in a vacuum environment. The support ring then transfers the heat downward to the base with a cooling system in the lower electrode assembly, and finally achieves temperature control of the focusing ring.

[0018] like Figure 5 The image shown is another embodiment of this utility model, which differs from the basic structure of the focusing ring. Figure 1 The main difference is that the lower surface of the focusing ring extension only includes a second transition surface b1' directly connected to the outer wall of the main body, without a horizontal bottom surface C11. This structure can also achieve the purpose of this invention.

[0019] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present invention. After reading the above content, various modifications and substitutions to the present invention will be obvious to those skilled in the art. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A focusing ring adapted to be disposed around a wafer to be processed in a plasma processing apparatus, the focusing ring comprising: The annular main body and the extension located inside the main body and extending inward, the annular main body having a center; The main body has a horizontal bottom surface, an inner side wall, an outer side wall, and an upper surface; The upper surface of the main body is connected to the upper surface of the extension via a first transition surface that slopes downward. The lower surface of the extension includes a second transition surface that slopes downward and is connected to the inner wall of the main body. The distance from the inner side of the second transition surface to the center of the circle is less than the radius of the wafer to be processed.

2. The focusing ring as described in claim 1, characterized in that, The angle between the second transition surface and the horizontal plane is greater than 30 degrees and less than 60 degrees.

3. The focusing ring as described in claim 1, characterized in that, The lower surface of the extension includes a straight surface parallel to the upper surface of the extension and a second transition surface located outside the straight surface.

4. The focusing ring as described in claim 1, characterized in that, The outer wall of the main body of the focusing ring has a downwardly recessed stepped surface, which is lower than the upper surface of all extensions.

5. The focusing ring as described in claim 1, characterized in that, The bottom surface of the main body includes a groove for filling with thermally conductive silicone.

6. The focusing ring as described in claim 1, characterized in that, The second transition surface makes the outer thickness of the extension greater than the inner thickness of the extension.

7. The focusing ring as described in claim 6, characterized in that, The thickness of the material on the inner side of the extension is less than or equal to 1 mm, and the thickness on the outer side of the extension is greater than 2 mm.

8. A plasma processing apparatus, the plasma processing apparatus comprising the following electrode assembly, characterized in that, The lower electrode assembly includes a base and an adhesive layer and an electrostatic clamp on the base, wherein the focusing ring of claim 1 is arranged around the electrostatic clamp.

9. The plasma treatment apparatus as described in claim 8, characterized in that, The focusing ring includes a support ring below it, and the upper surface of the support ring is used to support the bottom surface of the focusing ring; The inner side of the support ring includes an upwardly extending portion, and the lower surface morphology of the upwardly extending portion of the support ring matches and closely fits the extension portion of the focusing ring, so that the edge electrode located between the focusing ring and the support ring is shielded.

10. The plasma treatment apparatus as described in claim 8, characterized in that, An elastic sealing ring is included between the extension and the outer wall of the electrostatic chuck.

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