TWI908017B - Plasma confinement system, plasma processing device and etching method - Google Patents

Abstract

This invention discloses a plasma confinement system, a plasma processing apparatus, and an etching method. The plasma confinement system, used in a plasma processing apparatus, includes: a plasma confinement ring with an evacuation channel, one end of which is connected to an etching area and the other end to an venting area; and an impedance matching element through which the plasma confinement ring can be grounded. This invention enables the plasma confinement ring to have an appropriate capacitance to ground according to process requirements, improving plasma confinement performance at high RF power.

Description

Plasma confinement system, plasma processing device and etching method

This invention relates to the field of semiconductor equipment technology, specifically to a plasma confinement system, a plasma processing device, and an etching method.

Dry etching processes utilize plasma to etch wafers. This process takes place within a reaction chamber of a plasma processing apparatus. During processing, a process gas is introduced into the reaction chamber, and then radio frequency power is applied to the introduced process gas via upper and lower electrodes to generate plasma. The plasma contains a large number of active particles, including electrons, ions, excited atoms, molecules, and free radicals. These active particles can undergo various physical and chemical reactions with the wafer surface, altering the wafer's morphology and completing the etching process.

To increase the mean free diameter of the plasma and remove reaction byproducts from the reaction chamber, a high degree of vacuum is maintained within the chamber by a vacuum unit located at its bottom. The plasma within the reaction chamber diffuses with the gas flow. Although most of the plasma remains in the etched area between the upper and lower electrodes, some plasma diffuses outside the etched area and flows into the vacuum line, causing corrosion or erosion, reducing the lifespan of the plasma treatment equipment, increasing maintenance frequency, and affecting efficiency.

Currently, a plasma confinement ring is typically placed below the etching region within the reaction chamber to contain the plasma, thus preventing it from entering the downstream evacuation line. However, in the prior art, plasma leakage is still possible. For example, when there is a need to increase the aspect ratio of the etching, it is necessary to increase the power to increase the etching rate and etching depth. This can lead to an increase in the velocity of the plasma hitting the plasma confinement ring, making the ring ineffective in confining the plasma, and allowing it to pass through the ring and enter the downstream region.

The purpose of this invention is to provide a plasma confinement system, a plasma processing device, and an etching method that can make the plasma confinement ring have a suitable capacitance to ground according to the process requirements, thereby improving the plasma confinement performance.

To achieve the above objectives, the present invention employs the following technical solution:

A plasma confinement system for a plasma processing apparatus, characterized in that it comprises: a plasma confinement ring having an evacuation channel, one end of which is connected to an etching region and the other end to an venting region; an impedance matching element, through which the plasma confinement ring can be grounded.

Preferably, the plasma limiting system further includes a grounding ring, and the impedance matching element is connected between the plasma limiting ring and the grounding ring to enable the plasma limiting ring to be grounded.

Preferably, the impedance of the impedance matching element is adjustable.

Preferably, the impedance matching element includes a variable capacitor or a variable inductor, and the impedance is adjusted by the variable capacitor or the variable inductor.

Preferably, it also includes an insulating ring disposed between the plasma limiting ring and the grounding ring.

A plasma processing apparatus includes a reaction chamber and a substrate located within the reaction chamber for supporting a wafer, and further includes: a plasma confinement ring disposed around the substrate, having a venting channel, one end of the venting channel being connected to an etching region above the substrate, and the other end being connected to an exhaust region; an impedance matching element, through which the plasma confinement ring is grounded.

Preferably, the plasma treatment apparatus further includes: a grounding ring configured to surround the base and located below the plasma limiting ring for supporting the plasma limiting ring, and an insulating ring disposed between the plasma limiting ring and the grounding ring.

Preferably, the thickness of the insulating ring is 3mm-12mm.

Preferably, an insulating ring is provided between the plasma limiting ring and the grounding ring, the insulating ring including an inner insulating ring and an outer insulating ring adapted to the inner limiting ring and the outer limiting ring.

Preferably, the insulation ring has a channel extending through the ring body to accommodate the connection wire of the impedance matching element.

Preferably, the insulating ring is made of any one or more of ceramic, Teflon, polyetherimide, polyetheretherketone, or glass fiber.

Preferably, the impedance matching element is connected between the plasma limiting ring and the grounding ring to ground the plasma limiting ring.

Preferably, the plasma confinement ring includes an inner confinement ring and an outer confinement ring, and an annular grid is provided between the inner confinement ring and the outer confinement ring. The gaps between the inner confinement ring, the outer confinement ring and the annular grid form an air extraction channel.

It also includes a grounding ring configured to surround the base and located below the plasma limiting ring for supporting the plasma limiting ring. The grounding ring includes an inner grounding ring and an outer grounding ring adapted to the inner limiting ring and the outer limiting ring, and the inner grounding ring and the outer grounding ring are connected by circumferentially evenly distributed radial branches.

There are multiple impedance matching elements, and the connection points of each impedance matching element and the plasma limiting ring are evenly distributed in the corresponding circumferential positions.

Preferably, both the inner limiting ring and the outer limiting ring are connected to the impedance matching element.

Preferably, the impedance of the impedance matching element is adjustable.

Preferably, the impedance matching element includes a variable capacitor or a variable inductor, and the impedance is adjusted by the variable capacitor or the variable inductor.

Preferably, the plasma treatment apparatus further includes a controller connected to the impedance matching element, the controller being able to adjust the impedance of the impedance matching element.

Preferably, the controller adjusts the impedance of the impedance matching element according to the radio frequency power of the ionized gas.

An etching method comprising: loading a wafer onto a substrate of any of the aforementioned plasma processing apparatus; performing an etching process on the wafer using the plasma processing apparatus.

Compared with conventional technology, this invention has the following advantages:

1. By grounding the plasma confinement ring through an impedance matching element, the plasma confinement ring can have a suitable capacitance to ground according to the process requirements, thereby improving the plasma confinement performance;

2. With the adjustable impedance matching element design, it can better adapt to different process requirements and has better flexibility;

3. By dynamically linking the impedance matching components with the RF power, the impedance of each impedance matching component can be dynamically adjusted according to the RF power. This effectively restrains the plasma while minimizing the impact intensity of the plasma on the plasma confinement ring, preventing the plasma confinement ring from being damaged too quickly and extending its service life.

4. By setting an insulating ring with a certain thickness between the plasma limiting ring and the grounding ring, the breakdown resistance between the plasma limiting ring and the grounding ring is further improved, avoiding instability of the RF circuit and affecting the process.

To make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described below in conjunction with the drawings. The described embodiments should not be regarded as a limitation of the present invention. All other embodiments obtained by a person of ordinary skill in the art without making progressive work are within the scope of protection of the present invention.

In the following description, the terms "some embodiments" and "one or more embodiments" refer to a subset of all possible embodiments. However, it is understood that "some embodiments" and "one or more embodiments" may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

In the following description, the terms "first/second/third" are used only to distinguish between similar objects and do not represent a specific ordering of the objects. Understandably, "first/second/third" may be interchanged in a specific order or sequence where permissible, so that the embodiments of the invention described herein can be implemented in a sequence other than that shown or described.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art field to which this invention pertains. The terms used herein are for the purpose of describing embodiments of the invention only and are not intended to limit the invention.

Figure 1 illustrates a capacitively coupled plasma processing apparatus, which includes a vacuum-ejectable reaction chamber 1. A spray head 2 for introducing reaction gas into the reaction chamber 1 is located above the interior of the reaction chamber 1, and a base 3 for supporting a wafer W is located below the spray head 2. An etching region A is formed between the spray head 2 and the base 3. Typically, the spray head 2 serves as the upper electrode, and the base 3 serves as the lower electrode. At least one radio frequency (RF) power source applies RF energy to at least one of the upper and lower electrodes via an impedance matching network, generating an RF electric field between the upper and lower electrodes. This ignites and dissociates the reaction gas in the etching region A into plasma. The plasma reaching the upper surface of the wafer W can then perform etching and other processing on the wafer W. During the manufacturing process, the radio frequency power of the ignition plasma needs to be adjusted to control the etching rate and etching depth, depending on the different requirements of the etching depth-to-width ratio. The higher the applied radio frequency power, the greater the etching rate and etching depth. The lower part of the reaction chamber 1 is the exhaust area B, which is connected to the vacuum pump 6. The vacuum pump 6 is used to extract the process waste gas generated after the etching reaction from the reaction chamber 1.

Between the etching zone A and the venting zone B, a plasma confinement ring 04 is also provided around the base 3 to confine the plasma in the etching zone A, preventing it from spreading into the venting zone B below and thus corroding the reaction chamber walls, pipelines, etc. in the venting zone B. Below the plasma confinement ring 04, an insulated grounding ring 05 is provided. This grounding ring 05 is grounded to support the plasma confinement ring 04 and to provide an RF loop for the RF field in the reaction chamber 1. As shown in Figure 2, in some embodiments, there is a gap between the plasma confinement ring 04 and the grounding ring 05, and a capacitive structure is formed between the plasma confinement ring 04 and the grounding ring 05 during the manufacturing process; at the same time, the plasma will continuously bombard the plasma confinement ring 04 during the manufacturing process, increasing the potential of the plasma confinement ring 04, so that there is a potential difference between it and the grounding ring 05. The greater the RF power applied between the upper and lower electrodes, the more plasma is generated and the faster it moves. The stronger the plasma bombardment on the plasma confinement ring 04, the greater the potential difference between the plasma confinement ring 04 and the grounding ring 05. This leads to several problems: on the one hand, the possibility of plasma escaping and leaking from the plasma confinement ring 04 increases; on the other hand, the high-intensity plasma bombardment can easily cause the plasma confinement ring 04 to be consumed and damaged too quickly. Furthermore, the excessive potential difference between the plasma confinement ring 04 and the grounding ring 05 may further lead to a breakdown between them, resulting in more serious consequences such as structural damage within the reaction chamber 1.

To address this technical problem, the conventional technique is to reduce the distance between the opposite surfaces of the plasma confinement ring 04 and the grounding ring 05, thereby increasing the capacitance formed between them and reducing the potential difference. Because the larger the capacitance between the plasma confinement ring 04 and the grounding ring 05, the smaller the impedance to ground of the plasma confinement ring 04 (hereinafter referred to as impedance), and the thicker the plasma sheath layer above it, the more difficult it is for the plasma to pass through the plasma confinement ring 04, resulting in a better plasma confinement effect. However, at the same time, the thicker the plasma sheath layer, the stronger the impact of the plasma on the plasma confinement ring 04, making it more prone to damage. The conventional method is not ideal. Firstly, the capacitance between the two elements is too small to produce a satisfactory plasma confinement effect. Secondly, due to the rough surface from machining, the contact between the plasma confinement ring 04 and the grounding ring 05 is uneven. When the distance between them is reduced, discharge is more likely to occur at some sharp points. The capacitance breakdown between the two causes instability in the RF circuit, affecting the manufacturing process. On the other hand, when the RF power is high, the plasma confinement ring 04 always maintains a relatively small impedance to ground, which will cause the plasma to continuously bombard the plasma confinement ring 04 with high intensity, thereby causing the plasma confinement ring 04 to be damaged too quickly and shortening its service life.

This invention addresses this technical problem by providing a plasma confinement system and a plasma processing device. Its working principle involves grounding the plasma confinement ring via an impedance matching element. Furthermore, the impedance of the plasma confinement ring can be adjusted according to process requirements to meet its capacitance to ground, achieving a satisfactory plasma confinement effect. Simultaneously, it avoids excessive capacitance to ground, preventing excessive plasma impact on the plasma confinement ring and extending its service life. Moreover, by providing a thicker insulation layer between the plasma confinement ring and the grounding ring, it further prevents discharge breakdown between them.

The plasma limiting system of the present invention will now be described in detail with reference to Figures 3-7. As shown in Figures 3 and 4, the plasma limiting system includes:

A plasma confinement ring 4 is disposed within the reaction chamber 1, surrounding the base 3. It is equipped with an exhaust channel, the two ends of which are connected to the etching area A and the exhaust area B, respectively. This channel confines the plasma within the etching area A, effectively serving as a channel for discharging process waste gas from the etching area A to the exhaust area B. Figure 5 shows a top view of the plasma confinement ring 4 in one embodiment, which includes an inner confinement ring 41 surrounding the outer periphery of the base 3, an outer confinement ring 42 surrounding the inner confinement ring 41, and an annular grid 43 located between the inner confinement ring 41 and the outer confinement ring 42. The annular grid 43 includes a set of concentrically arranged limiting rings 431 with increasing radii between the inner limiting ring 41 and the outer limiting ring 42, and a plurality of limiting radial strips 432 arranged radially along the inner limiting ring 41 to connect the inner limiting ring 41, the outer limiting ring 42, and each limiting ring 431. Optionally, the limiting radial strips 432 are evenly distributed circumferentially. The gaps between the inner limiting ring 41, the outer limiting ring 42, and the annular grid 43 constitute multiple drawstrings. The top of each evacuation channel is connected to the etching area A, and the bottom is connected to the exhaust area B. The exhaust area B is connected to the vacuum pump 6. The vacuum pump 6 uses the evacuation channels to draw in the process waste gas generated after the etching reaction and discharge it outside the cavity. When the plasma flowing with the process waste gas passes through the evacuation channels, it will collide with the annular grid 43 and be neutralized and annihilated, thereby confining the plasma in the etching area A and preventing the plasma from bombarding the side wall of the chamber in the evacuation area B and corroding the evacuation pipeline.

A grounding ring 5 surrounds the reaction chamber 1 of the base 3 and is disposed below the plasma confinement ring 4. It is used to support the plasma confinement ring 4 and provide an RF loop for the RF field within the reaction chamber 1. Figure 6 shows a top view of the grounding ring 5 in an embodiment, which includes an inner grounding ring 51 surrounding the outer periphery of the base 3 and an outer grounding ring 52 surrounding the inner grounding ring 51, as well as multiple grounding wires 53 connected to the inner grounding ring 51 and the outer grounding ring 52 at their respective ends. Each grounding wire 53 is evenly distributed circumferentially. The inner grounding ring 51 and the outer grounding ring 52 are adapted to the shape and size of the inner confinement ring 41 and the outer confinement ring 42, respectively.

The impedance matching element 7 is connected to the plasma confinement ring 4. The plasma confinement ring 4 is grounded through the impedance matching element 7 to adjust the impedance of the plasma confinement ring 4, thereby meeting the requirements of the plasma confinement ring 4 to ground capacitance in the manufacturing process, achieving good plasma confinement performance, and avoiding excessive plasma impact on the plasma confinement ring 4 due to excessive capacitance to ground, thus improving the service life of the plasma confinement ring. The grounding method of the impedance matching element 7 includes two methods: direct grounding and indirect grounding. Figure 3 shows an embodiment of direct grounding, in which the plasma confinement ring 4 is directly grounded through the impedance matching element 7; Figure 4 shows an embodiment of indirect grounding, in which the plasma confinement ring 4 is connected to the grounding ring 5 through the impedance matching element 7, and then grounded through the grounding ring 5.

Preferably, in some embodiments, there are multiple impedance matching elements 7, and each impedance matching element 7 is uniformly distributed circumferentially with each connection point of the plasma limiting ring 4 or with each connection point of the plasma limiting ring 4 and the grounding ring 5, so that the circumferential impedance of the plasma limiting ring 4 is uniformly distributed.

Preferably, in some embodiments, both the inner limiting ring 41 and the outer limiting ring 42 are connected to the impedance matching element 7, which enables the radial impedance of the plasma limiting ring 4 to be uniformly distributed.

In some embodiments, the impedance matching element 7 is a passive impedance matching element, such as a circuit composed of a fixed capacitor and an inductor, whose impedance is not adjustable during use, but can be configured according to specific process requirements. Preferably, in some embodiments, the impedance of the impedance matching element 7 is adjustable, which can better adapt to the needs of different processes on the same equipment. That is, the resistance value of the impedance matching element 7 can be adjusted to adapt when different processes are performed on the same equipment, providing better flexibility. Furthermore, in some embodiments, the impedance matching element 7 includes a variable capacitor or a variable inductor, which adjusts the impedance. More preferably, in some embodiments, the impedance matching element 7 is connected to a controller (not shown), which can adjust the impedance of the impedance matching element 7 according to specific process or process parameters, such as the RF power of the plasma ignition. Optionally, the RF power is inversely proportional to the impedance of the impedance matching element 7. The principle is that when the RF power is higher, more plasma is generated in the reaction chamber 1, and the plasma movement speed is faster, increasing the possibility of plasma escaping and leaking from the plasma confinement ring 4. At this time, the controller adjusts to reduce the impedance of the impedance matching element 7, increasing the thickness of the plasma sheath layer on the surface of each component of the plasma confinement ring 4, thus enhancing the plasma confinement performance. When the RF power is lower, the plasma generated in the reaction chamber 1 is relatively reduced, and the plasma movement speed is lower. As the plasma flow slows down, it is no longer necessary to maintain the previous strength of plasma restraint. At this time, the controller adjusts and increases the impedance of the impedance matching element 7, thereby reducing the thickness of the plasma sheath layer above the plasma restraint ring 4. The impact of the plasma on the plasma restraint ring 4 weakens, thus minimizing the impact intensity of the plasma on the plasma restraint ring 4 while effectively restraining the plasma, preventing the plasma restraint ring 4 from being damaged too quickly, and extending its service life.

Preferably, in order to improve the breakdown resistance between the plasma limiting ring 4 and the grounding ring 5, in some embodiments, as shown in FIG7, an insulating ring 8 is also provided between the plasma limiting ring 4 and the grounding ring 5. The shape of the insulating ring 8 is adapted to the plasma limiting ring 4 and the grounding ring 5, and it includes an inner insulating ring (not shown) and an outer insulating ring (not shown) adapted to the inner limiting ring 41 and the outer limiting ring 42. It is readily understood that the insulating ring is provided with an opening that matches the venting channel of the restraint ring to avoid obstructing the venting. In some embodiments, the insulating ring 8 is made of any one or more of ceramic, Teflon, polyetherimide, polyetheretherketone, or glass fiber. Furthermore, in some embodiments, the insulating ring 8 has a thickness of 3mm-12mm, which provides good breakdown resistance without affecting the component layout design within the reaction chamber 1; preferably, its thickness is 6mm. In some embodiments, the insulating ring 8 has a channel 81 inside for accommodating the connection wires of the impedance matching element 7; the grounding ring 5 also has a corresponding channel 54 inside for accommodating the connection wires of the impedance matching element 7, thus avoiding affecting the electromagnetic environment within the chamber.

Additionally, the present invention provides a plasma processing apparatus, comprising: a reaction chamber; a substrate located within the reaction chamber for supporting a wafer; any of the above-described plasma confinement systems;

Preferably, in some embodiments, a controller as described above is also included, which is associated with the radio frequency power of the ignition plasma. The controller is connected to each impedance matching element 7 of the plasma limiting system and is capable of dynamically adjusting the impedance of each impedance matching element 7 according to the radio frequency power.

In addition, this invention provides an etching method, comprising: loading a wafer onto a substrate of any of the above-described plasma processing apparatus; performing an etching process on the wafer using the plasma processing apparatus.

It is readily understood that the present invention is also applicable to other plasma processing devices that have plasma constraint requirements.

The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and scope of the present invention are included within the scope of protection of the present invention.

04 Plasma Confinement Ring 05 Grounding Ring 1 Reaction Chamber 2 Spray Head 3 Base 4 Plasma Confinement Ring 41 Inner Confinement Ring 42 Outer Confinement Ring 43 Circular Grid 431 Single Confinement Ring 432 Confinement Wire 5 Grounding Ring 51 Inner Grounding Ring 52 Outer Grounding Ring 53 Grounding Wire 54 Channel 6 Vacuum Pump 7 Impedance Matching Component 8 Insulating Ring 81 Channel A Etching area B Area W Wafer

To more clearly illustrate the technical solutions of the embodiments of this invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without any further effort. Figure 1 is a schematic diagram of a plasma etching apparatus in the prior art; Figure 2 is a partial cross-sectional schematic diagram of a plasma confinement ring and a grounding ring in the prior art; Figure 3 is a schematic diagram of one embodiment of the plasma confinement system of the present invention; Figure 4 is a schematic diagram of one embodiment of the plasma confinement system of the present invention; Figure 5 is a top view of one embodiment of the plasma confinement ring of the present invention; Figure 6 is a top view of one embodiment of the grounding ring of the present invention; Figure 7 is a front cross-sectional view of the plasma confinement ring, insulating ring, and grounding ring of the present invention.

4. Plasma limiting ring 41. Inner limiting ring 42. Outer limiting ring 43. Circular grid 5. Grounding ring 51. Inner grounding ring 52. Outer grounding ring 53. Grounding wire 7. Impedance matching element

Claims (18)

A plasma confinement system for a plasma processing apparatus includes: a plasma confinement ring having an evacuation channel, one end of which is connected to an etching region and the other end to an exhaust region; and an impedance matching element, through which the plasma confinement ring can be grounded for adjusting the impedance of the plasma confinement ring. The plasma limiting system as claimed in claim 1 further includes a grounding ring, wherein the impedance matching element is connected between the plasma limiting ring and the grounding ring to enable the plasma limiting ring to be grounded. The plasma limiting system as described in claim 1 or 2, wherein the impedance of the impedance matching element is adjustable. The plasma limiting system as described in claim 3, wherein the impedance matching element includes a variable capacitor or a variable inductor, and the impedance is adjusted by the variable capacitor or the variable inductor. The plasma limiting system as described in claim 2 further includes an insulating ring disposed between the plasma limiting ring and the grounding ring. A plasma processing apparatus includes a reaction chamber and a base located within the reaction chamber for supporting a wafer. The apparatus further includes: a plasma confinement ring surrounding the base, having an evacuation channel at one end connected to an etching area above the base and at the other end connected to an exhaust area; and an impedance matching element, through which the plasma confinement ring is grounded for adjusting the impedance of the plasma confinement ring. The plasma processing apparatus as described in claim 6 further includes: a grounding ring configured to surround the base and located below the plasma restraining ring for supporting the plasma restraining ring, and an insulating ring disposed between the plasma restraining ring and the grounding ring. The plasma treatment apparatus as described in claim 7, wherein the thickness of the insulating ring is 3mm-12mm. The plasma treatment apparatus as described in claim 8, wherein the insulating ring has a channel penetrating the ring body for accommodating the connection wire of the impedance matching element. The plasma treatment apparatus as described in claim 9, wherein the insulating ring is made of any one or more of ceramic, Teflon, polyetherimide, polyetheretherketone, or glass fiber. The plasma processing apparatus as claimed in claim 10, wherein the impedance matching element is connected between the plasma limiting ring and the grounding ring to ground the plasma limiting ring. The plasma treatment apparatus as described in any of claims 7 to 11, wherein the plasma confinement ring includes an inner confinement ring and an outer confinement ring, an annular grid is provided between the inner confinement ring and the outer confinement ring, and the gaps between the inner confinement ring, the outer confinement ring and the annular grid form an air extraction channel; and further includes a grounding ring configured to surround the base and be located within the plasma confinement ring. The lower part is used to support the plasma limiting ring. The grounding ring includes an inner grounding ring and an outer grounding ring adapted to the inner limiting ring and the outer limiting ring. The inner grounding ring and the outer grounding ring are connected by radials that are evenly distributed in the circumferential direction. There are multiple impedance matching elements, and the connection points of each impedance matching element and the plasma limiting ring are evenly distributed in the circumferential direction. The plasma treatment apparatus as claimed in claim 12, wherein both the inner limiting ring and the outer limiting ring are connected to the impedance matching element. The plasma treatment apparatus as described in claim 6 or 7, wherein the impedance of the impedance matching element is adjustable. The plasma treatment apparatus as described in claim 14, wherein the impedance matching element includes a variable capacitor or a variable inductor, and the impedance is adjusted by the variable capacitor or the variable inductor. The plasma treatment apparatus as described in claim 15 further includes a controller connected to the impedance matching element, the controller being capable of adjusting the impedance of the impedance matching element. The plasma treatment apparatus as claimed in claim 16, wherein the controller adjusts the impedance of the impedance matching element according to the radio frequency power of the ionized gas. An etching method comprising: mounting a wafer onto a base of a plasma processing apparatus as described in any one of claims 6 to 17; and etching the wafer using the plasma processing apparatus.