Plasma processing device

Abstract

This plasma processing device includes an introduction unit, a high-frequency power supply, a high-frequency supply line, a resonator, and a reflected-wave absorber. The introduction unit is disposed so as to introduce electromagnetic waves into a plasma generation region. The high-frequency supply line is electrically connected to the high-frequency power supply. The resonator has a power feed unit, a first end, a second end, and a waveguide. The power feed unit is an inlet for electromagnetic waves in the resonator and is connected to the high-frequency supply line. The waveguide extends between the first end and the second end for resonating electromagnetic waves therebetween, and is electromagnetically coupled to the introduction unit. The reflected-wave absorber is installed in the high-frequency supply line. The distance between the power feed unit and the first end along the propagation direction of the electromagnetic waves is greater than the distance along the propagation direction between the first end and a location at which the impedance on the load side when viewed from the location during plasma excitation in the resonator is equal to the characteristic impedance of the high-frequency supply line.

Description

Plasma processing apparatus

[0001] An exemplary embodiment of the present disclosure relates to a plasma processing apparatus.

[0002] In plasma processing of a substrate, a plasma processing apparatus is used. One type of plasma processing apparatus includes a chamber, a high-frequency power source, a resonator, an introduction unit, and a matcher. The high-frequency power source is coupled to the resonator. Electromagnetic waves from the resonator are supplied into the chamber from the introduction unit. The matcher is connected between the high-frequency power source and the resonator. Such a plasma processing apparatus is described in Patent Document 1 below.

[0003] Japanese Patent Application Laid-Open No. 2020-92031

[0004] The present disclosure provides a technique for suppressing the influence of abnormal discharge in a plasma processing apparatus.

[0005] In one exemplary embodiment, a plasma processing apparatus is provided. The plasma processing apparatus includes a chamber, an introduction unit, a high-frequency power source, a high-frequency supply line, a resonator, and a reflected wave absorber. The introduction unit is arranged to introduce electromagnetic waves into a plasma generation region in the chamber. The high-frequency supply line is electrically connected to the high-frequency power source. The resonator has a power supply unit, a first end, a second end, and a waveguide. The power supply unit is an entrance of electromagnetic waves in the resonator and is connected to the high-frequency supply line. The waveguide extends between the first end and the second end for resonating electromagnetic waves therebetween and is electromagnetically coupled to the introduction unit. The reflected wave absorber is installed on the high-frequency supply line. The distance between the power supply unit and the first end along the propagation direction of the electromagnetic wave is longer than the distance along the propagation direction between the location where the impedance seen from the load side becomes equal to the characteristic impedance of the high-frequency supply line and the first end in the resonator during plasma excitation.

[0006] According to one exemplary embodiment, it becomes possible to suppress the influence of abnormal discharge in the plasma processing apparatus.

[0007] Figure 3 shows a plasma processing apparatus according to one exemplary embodiment. Figure 4 shows the lower part of the resonator of the plasma processing apparatus according to one exemplary embodiment. Figure 3 shows an example of the relationship between the position in the propagation direction within the resonator and the return loss. Figure 4 shows a plasma processing apparatus according to another exemplary embodiment.

[0008] Various exemplary embodiments will be described in detail below with reference to the drawings. In each drawing, the same or corresponding parts will be denoted by the same reference numerals.

[0009] Figure 1 shows a plasma processing apparatus according to one exemplary embodiment. The plasma processing apparatus 1 shown in Figure 1 comprises a chamber 10, a substrate support section 12, an introduction section 16, a resonator 20, and a high-frequency power supply 24.

[0010] Chamber 10 provides a processing space 10s within it. In the plasma processing apparatus 1, the substrate W is processed in the processing space 10s. Chamber 10 is made of a metal such as aluminum and is grounded. Chamber 10 has a side wall 10a which is open at its upper end. Chamber 10 and side wall 10a may have a substantially cylindrical shape. The processing space 10s is provided inside the side wall 10a. The central axis of each of chamber 10, side wall 10a, and processing space 10s is axis AX. Chamber 10 may have a corrosion-resistant film on its surface. The corrosion-resistant film may be a ceramic film containing yttrium oxide, yttrium fluoride oxide, yttrium fluoride, yttrium oxide, or yttrium fluoride, etc.

[0011] The bottom of the chamber 10 provides an exhaust port 10e. An exhaust system is connected to the exhaust port 10e. The exhaust system may include a vacuum pump such as a dry pump and / or a turbomolecular pump and an automatic pressure control valve.

[0012] The substrate support portion 12 is provided within the processing space 10s. The substrate support portion 12 is configured to support the substrate W placed on its upper surface in a substantially horizontal manner. The substrate support portion 12 has a substantially disc shape. The central axis of the substrate support portion 12 is axis AX.

[0013] In one embodiment, the plasma processing apparatus 1 may further include an upper electrode 14. The upper electrode 14 is provided above the substrate support portion 12 via a processing space 10s. The upper electrode 14 is formed from a conductor such as a metal (e.g., aluminum) and has a substantially disc shape. The central axis of the upper electrode 14 is axis AX. The upper electrode 14, together with the shower plate 22 described later, constitutes an excitation electrode.

[0014] The introduction section 16 is provided to emit electromagnetic waves into the plasma generation region. In the plasma processing apparatus 1, the plasma generation region is the space within the processing space 10s and directly below the excitation electrode, i.e., directly below the shower plate 22. In the plasma processing apparatus 1, the electromagnetic waves emitted from the introduction section 16 into the plasma generation region excite the gas in the plasma generation region, thereby generating plasma. The electromagnetic waves emitted from the introduction section 16 into the plasma generation region may be high-frequency waves such as VHF waves or UHF waves. The introduction section 16 is formed from a dielectric material such as quartz, aluminum nitride, or aluminum oxide. In one embodiment, the introduction section 16 is provided at the lateral end of the processing space 10s and extends circumferentially around the axis AX. The introduction section 16 may have a ring shape.

[0015] The resonator 20 includes a power supply unit 20p and a waveguide 20w. The power supply unit 20p is the electromagnetic wave inlet for the waveguide 20w of the resonator 20. The electromagnetic wave is generated based on high-frequency power generated by a high-frequency power supply 24. The high-frequency power supply 24 may be configured to change the frequency of the high-frequency power it outputs. The high-frequency power supply 24 and the power supply unit 20p are electrically connected via a high-frequency supply line 40. The electromagnetic wave is input to the power supply unit 20p of the resonator 20 via the high-frequency supply line 40. The resonator 20 resonates the electromagnetic wave input to the power supply unit 20p within the waveguide 20w and propagates it to the introduction unit 16. The electromagnetic wave is introduced from the introduction unit 16 into the plasma generation region. In one embodiment, the resonator 20 may be located above the chamber 10 and on the upper electrode 14.

[0016] The high-frequency supply line 40 may include a coaxial connector 40c, which is a coaxial line. The coaxial connector 40c includes an inner conductor 40i and an outer conductor 40o. The outer conductor 40o has a cylindrical shape and surrounds the inner conductor 40i. The inner conductor 40i and the outer conductor 40o extend coaxially. The lower end of the inner conductor 40i is electrically connected to the power supply unit 20p. In one embodiment, the lower end of the inner conductor 40i is electrically connected to the wall of the resonator 20 that defines the upper part 20a from below. The lower end of the inner conductor 40i may also be electrically connected to the power supply unit 20p via an elastic body (e.g., a spring member) formed from a conductor (not shown). The outer conductor 40o is also electrically connected to the wall of the resonator 20 that defines the upper part 20a from above.

[0017] The plasma processing apparatus 1 further includes a circulator 25. The circulator 25 includes a first port 251, a second port 252, and a third port 253. The circulator 25 outputs high-frequency power (forward wave, incident wave) received at the first port 251 from the second port 252, and outputs high-frequency power (reflected wave) received at the second port 252 from the third port 253. A high-frequency power supply 24 is connected to the first port 251. The second port 252 is connected to the power supply unit 20p via a high-frequency supply line 40. A load 27 is connected to the third port 253. According to the plasma processing apparatus 1, the reflected wave of high-frequency power is returned to the load 27 by the circulator 25. Therefore, the return of the reflected wave to the high-frequency power supply 24 is suppressed. The plasma processing apparatus 1 may also include an isolator instead of the circulator 25, which outputs high-frequency power from the high-frequency power supply 24 to the power supply unit 20p via the high-frequency supply line 40 and outputs the reflected wave of the high-frequency power to the load 27.

[0018] In one embodiment, the plasma processing apparatus 1 may further include a shower plate 22. The shower plate 22 may be made of a metal such as aluminum. The introduction section 16 extends to surround the shower plate 22. The introduction section 16 and the shower plate 22 are arranged to close the opening at the upper end of the chamber 10. The shower plate 22 provides a plurality of gas holes 22h. The plurality of gas holes 22h extend in the thickness direction (vertical direction) of the shower plate 22 and penetrate the shower plate 22.

[0019] The shower plate 22 is located below the upper electrode 14. The shower plate 22 extends over the plasma generation region described above. The shower plate 22 and the upper electrode 14 define a gas diffusion space 14d between them. The central axis of the gas diffusion space 14d may be axis AX. Multiple gas holes 22h of the shower plate 22 are connected to the gas diffusion space 14d. The upper electrode 14 also provides an inlet 14h. The inlet 14h may extend along axis AX. The inlet 14h is connected to the gas diffusion space 14d. A gas supply unit 26 is connected to the gas diffusion space 14d. The gas output from the gas supply unit 26 is supplied to the processing space 10s via the inlet 14h, the gas diffusion space 14d, and the multiple gas holes 22h.

[0020] Hereinafter, Figure 2 will be referenced along with Figure 1. Figure 2 is a diagram showing the lower part of a resonator in a plasma processing apparatus according to one exemplary embodiment. Figure 2 is a cross-sectional view taken along the line II-II in Figure 1. The waveguide 20w of the resonator 20 may provide a cavity surrounded by walls. The walls of the waveguide 20w are formed from a material such as metal. The walls of the waveguide 20w may be formed from an aluminum alloy, copper, nickel, or stainless steel, and may be coated with a low-resistance material such as silver, gold, or rhodium.

[0021] The resonator 20 includes a first end 201 and a second end 202. The first end 201 and the second end 202 constitute one end and the other end of the waveguide 20w of the resonator 20. The waveguide 20w extends between the first end 201 and the second end 202 and is electromagnetically coupled to the introduction section 16.

[0022] In one embodiment, the wall of the resonator 20 may include an inner circumferential portion 20i and an outer circumferential portion 20o. The inner circumferential portion 20i extends around its central axis, axis AX, and has a substantially cylindrical shape. The outer circumferential portion 20o extends coaxially with the inner circumferential portion 20i around axis AX. The outer circumferential portion 20o may also have a substantially cylindrical shape.

[0023] The waveguide 20w may have a layered structure that alternately folds between an inner circumferential portion 20i and an outer circumferential portion 20o. The walls of the waveguide 20w may include a plurality of walls that extend radially and circumferentially between adjacent layers of the layered structure and between the inner circumferential portion 20i and the outer circumferential portion 20o. The plurality of walls may be annular plates.

[0024] Furthermore, the waveguide 20w may include an upper part 20a constituting the uppermost layer of the layer structure and a lower part 20b constituting the lowest layer of the layer structure. The layer structure may also include an intermediate part 20c between the upper part 20a and the lower part 20b. In this embodiment, the upper part 20a may provide a first end 201, i.e., the upper end, of the waveguide 20w at the outer periphery 20o. In this case, the first end 201 of the waveguide 20w extends circumferentially around the axis AX. Furthermore, the lower part 20b may provide a second end 202, i.e., the lower end, of the waveguide 20w at the outer periphery 20o. In this case, the second end 202 of the waveguide 20w extends circumferentially around the axis AX.

[0025] The resonator 20 provides a plurality of gaps 20g near or along the second end 202. The plurality of gaps 20g are arranged circumferentially around the axis AX. Electromagnetic waves resonating in the resonator 20 propagate electromagnetically to the introduction section 16 through the plurality of gaps 20g.

[0026] In one embodiment, the upper electrode 14 provides a plurality of slots 14s as a plurality of gaps 20g and includes a plurality of beams 14b. The plurality of slots 14s are positioned above the introduction section 16. The plurality of slots 14s electromagnetically couple the waveguide 20w and the introduction section 16 to each other. The plurality of slots 14s penetrate the upper electrode 14 along its thickness direction (vertical direction) and extend long in the circumferential direction. The plurality of slots 14s are spaced apart from each other and arranged along the circumferential direction around the axis AX. The plurality of slots 14s may be arranged at equal intervals. The plurality of beams 14b are arranged alternately with the plurality of slots 14s along the circumferential direction around the axis AX. The plurality of beams 14b connect the inner and outer portions of the upper electrode 14 to each other.

[0027] In the plasma processing apparatus 1, electromagnetic wave resonance occurs between the first end 201 and the second end 202 of the resonator 20. The electromagnetic waves that resonate in the resonator 20 are supplied to the introduction section 16 through a plurality of gaps 20g, i.e., a plurality of slots 14s. The electromagnetic waves supplied to the introduction section 16 are emitted from the introduction section 16 into the plasma generation region.

[0028] As shown in Figure 1, in the plasma processing apparatus 1, the distance between the power supply unit 20p and the first end 201 along the electromagnetic wave propagation direction (radial direction or opposite direction) is longer than the distance L50. The distance L50 is the distance along the propagation direction between the point in the resonator 20 where the impedance viewed from there towards the load side during plasma excitation is equal to the characteristic impedance of the high-frequency supply line 40 and the first end 201.

[0029] Figure 3 shows an example of the relationship between the position in the propagation direction within the resonator and the return loss. In Figure 3, graph G1 shows the return loss during normal discharge, and graph G2 shows the return loss during abnormal discharge. In Figure 3, L50 on the horizontal axis indicates the position at which the distance from the first end 201 is distance L50, and position Pi on the horizontal axis indicates the installation position in the plasma processing apparatus 1. As shown in Figure 3 and as described above, in the plasma processing apparatus 1, the distance between the power supply unit 20p (position Pi) and the first end 201 along the propagation direction is longer than distance L50.

[0030] As shown in graph G1, during normal discharge, there is almost no reflection at a distance L50 from the first end 201, and a certain return loss occurs when the power supply unit 20p is installed at position Pi. In the illustrated example, the return loss when the power supply unit 20p is installed at position Pi is about 16 dB, and the reflected wave power is about 2.5% of the incident wave power.

[0031] As shown in graph G2, when an abnormal discharge occurs, the return loss is greater when the power supply unit 20p is located at position Pi compared to when it is located at a distance L50 from the first end 201. In the illustrated example, the reflected wave power at a distance L50 from the first end 201 is about 16% of the incident wave power. In contrast, in the illustrated example, when the power supply unit 20p is located at position Pi, the return loss is reduced to 5 dB, and the reflected wave power becomes larger, at about 32% of the incident wave power.

[0032] As a result, the plasma processing apparatus 1, when an abnormal discharge occurs, increases the reflected wave power to self-match and reduce the power supplied to the plasma, thereby instantly stopping the abnormal discharge. In other words, if the plasma density is low relative to the plasma density at the top of the processing vessel (e.g., inside the chamber 10) under the desired plasma excitation conditions, the radial position from the resonator input (e.g., the power supply unit 20p) to the load side where the impedance is 50Ω becomes shorter than L50. Conversely, if it is high, it becomes longer than L50.

[0033] On the other hand, if an abnormal discharge occurs in the processing vessel, high-frequency power is consumed at the abnormal discharge generation site, so the average plasma density in the upper part of the processing vessel decreases. The position in the propagation direction of the resonator input where the impedance on the load side is 50Ω becomes shorter than L50. In the plasma processing apparatus 1, the position in the propagation direction of the resonator input is originally set to be longer than L50, so when an abnormal discharge occurs, the return loss decreases and the power supplied to the plasma decreases significantly in a self-matching manner.

[0034] The frequency matching function built into the high-frequency power supply 24 optimizes the frequency to minimize reflection. However, if the radial position of the resonator input is deviated from the matching position, reflection cannot be suppressed, and a state of high reflection is maintained. As a result, the abnormal discharge disappears instantaneously. Once the abnormal discharge disappears, the system automatically returns to the normal plasma excitation state. Thus, the plasma processing device 1 can instantly stop the abnormal discharge when it occurs, and instantly return to the original state after the abnormal discharge has stopped. Therefore, damage caused by abnormal discharge can be minimized. As a result, the plasma processing device 1 can suppress the effects of abnormal discharge.

[0035] In the above example, the distance between the power supply unit 20p and the first end 201 along the propagation direction was such that the reflected wave power of the high-frequency power from the high-frequency power supply 24 was approximately 2.5% of the incident wave power. However, in another example, the distance between the power supply unit 20p and the first end 201 along the propagation direction may be set so that the reflected wave power of the high-frequency power from the high-frequency power supply 24 is 5% or less of the incident wave power. In yet another example, the distance between the power supply unit 20p and the first end 201 along the propagation direction may be set so that the reflected wave power of the high-frequency power from the high-frequency power supply 24 is 10% or less of the incident wave power.

[0036] Furthermore, in the plasma processing apparatus 1, since the distance between the power supply unit 20p and the first end 201 is longer than the distance L50, a matching state is not achieved even at the frequency where reflection is minimized. However, the plasma processing apparatus 1 includes a circulator 25 or isolator that includes a first port 251 connected to the high-frequency power supply 24, a second port 252 connected to the high-frequency supply line 40, and a third port 253 connected to the load 27. Therefore, reflected waves can be absorbed by the load 27.

[0037] Hereinafter, a plasma processing apparatus according to another exemplary embodiment will be described with reference to Figure 4. Figure 4 is a diagram showing a plasma processing apparatus according to another exemplary embodiment.Hereinafter, the plasma processing apparatus 1A shown in Figure 4 will be described in terms of differences from the plasma processing apparatus 1.The plasma processing apparatus 1A further comprises a reactance variable circuit 50.The reactance variable circuit 50 is provided in the high-frequency supply line 40 between the coaxial connector 40c and the second port 252 of the circulator 25.

[0038] In the plasma processing apparatus 1A (or plasma processing apparatus 1), the position of the power supply unit 20p is set so that, for example, a few percent of reflection occurs during normal discharge in order to suppress abnormal discharge. However, when the plasma excitation conditions change, both the position of the resonator input unit (for example, the power supply unit 20p) where there is no reflection (for example, at a distance L50 from the first end 201) and the position of the resonator input unit where a few percent of reflection occurs change. In response to this, the plasma processing apparatus 1A is provided with a reactance variable circuit 50 between the resonator input unit and the circulator 25. The reactance of the reactance variable circuit 50 is adjusted so that a few percent of reflection occurs during normal discharge according to the plasma excitation conditions. As a result, abnormal discharge can be suppressed without changing the position of the resonator input unit, even when the plasma excitation conditions change.

[0039] Although various exemplary embodiments have been described above, the invention is not limited to the exemplary embodiments described above, and various additions, omissions, substitutions, and modifications may be made. Furthermore, it is possible to combine elements from different embodiments to form other embodiments.

[0040] For example, the plasma processing apparatus 1 may include a matching circuit connected between the high-frequency supply line 40 and ground. In this case, the matching circuit can be matched so that, for example, a few percent of reflection occurs during normal discharge, thereby being compatible with the function of reducing the power supplied to the plasma in a self-matching manner by increasing the reflected wave power during abnormal discharge in the plasma processing apparatus 1.

[0041] Herein, various exemplary embodiments included in this disclosure are described in [E1] to [E12] below.

[0042] [E1] A chamber, an introduction part arranged to introduce electromagnetic waves into a plasma generation region in the chamber, a high-frequency power source, a high-frequency supply line electrically connected to the high-frequency power source, a power supply part which is an inlet of the electromagnetic waves and is connected to the high-frequency supply line, a first end and a second end for resonating the electromagnetic waves therebetween, and a resonator having a waveguide extending between the first end and the second end and being electromagnetically coupled to the introduction part; a reflection wave absorber installed on the high-frequency supply line; provided, the distance between the power supply part and the first end along the propagation direction of the electromagnetic waves is longer than the distance along the propagation direction between a position where the impedance seen from the load side becomes equal to the characteristic impedance of the high-frequency supply line when plasma is excited in the resonator and the first end, a plasma processing apparatus.

[0043] [E2] The plasma processing apparatus according to E1, further comprising a circulator or an isolator including a first port connected to the high-frequency power source, a second port connected to the high-frequency supply line, and a third port connected to a load.

[0044] [E3] The plasma processing apparatus according to E1 or E2, wherein the distance between the power supply part and the first end along the propagation direction is set such that the reflected wave power of the high-frequency power from the high-frequency power source is 10% or less of the incident wave power of the high-frequency power.

[0045] [E4] The plasma processing apparatus according to any one of E1 to E3, further comprising a reactance variable circuit provided on the high-frequency supply line.

[0046] [E5] The plasma processing apparatus according to any one of E1 to E4, wherein the resonator includes: an inner circumferential portion extending around the central axis of the chamber and the resonator; an outer circumferential portion extending around the central axis; a waveguide having a layered structure that alternately folds between the inner circumferential portion and the outer circumferential portion; an upper portion located in the uppermost layer of the layered structure and providing the first end in the outer circumferential portion; and a lower portion located in the lowermost layer of the layered structure and providing the second end in the outer circumferential portion, and providing a plurality of slots along the second end for coupling the waveguide and the introduction portion to each other.

[0047] From the above description, it will be understood that the various embodiments of this disclosure are described herein for illustrative purposes and can be modified in various ways without departing from the scope and spirit of this disclosure. Accordingly, the various embodiments disclosed herein are not intended to limit the scope and spirit, and the true scope and spirit are shown by the appended claims.

[0048] 1, 1A... Plasma processing apparatus, 10... Chamber, 12... Substrate support section, 16... Inlet section, 20... Resonator, 20w... Waveguide, 20p... Power supply section, 201... First end, 202... Second end, 24... High-frequency power supply, 25... Circulator, 40... High-frequency supply line, 50... Variable reactance circuit.

Claims

1. A plasma processing apparatus comprising: a chamber; an introduction unit arranged to introduce electromagnetic waves into a plasma generation region within the chamber; a high-frequency power supply; a high-frequency supply line electrically connected to the high-frequency power supply; a resonator having a power supply unit which is an inlet for electromagnetic waves and connected to the high-frequency supply line, a first end and a second end for resonating the electromagnetic waves between them, and a waveguide extending between the first end and the second end and electromagnetically coupled to the introduction unit; and a reflected wave absorber installed on the high-frequency supply line, wherein the distance between the power supply unit and the first end along the propagation direction of the electromagnetic waves is longer than the distance between the first end and the point in the resonator where the impedance viewed from there toward the load side during plasma excitation is equal to the characteristic impedance of the high-frequency supply line.

2. The plasma processing apparatus according to claim 1, further comprising a circulator or isolator including a first port connected to the high-frequency power supply, a second port connected to the high-frequency supply line, and a third port connected to a load.

3. The plasma processing apparatus according to claim 1 or 2, wherein the distance between the power supply unit and the first end along the propagation direction is set such that the reflected wave power of the high-frequency power from the high-frequency power supply is 10% or less of the incident wave power of the high-frequency power.

4. The plasma processing apparatus according to claim 1 or 2, further comprising a reactance variable circuit provided in the high-frequency supply line.

5. The plasma apparatus according to claim 1 or 2, wherein the resonator comprises: an inner circumferential portion extending around the central axis of the chamber and the resonator; an outer circumferential portion extending around the central axis; a waveguide having a layered structure that alternately folds between the inner circumferential portion and the outer circumferential portion; an upper portion located in the uppermost layer of the layered structure and providing the first end in the outer circumferential portion; and a lower portion located in the lowermost layer of the layered structure and providing the second end in the outer circumferential portion, and providing a plurality of slots along the second end for coupling the waveguide and the introduction portion to each other.

Images