Plasma processing device

Abstract

In order to provide a plasma processing device which generates an axially-symmetric electric field distribution under various conditions and enables uniform processing without actively losing microwave energy other than through plasma generation, this plasma processing device is configured as below.　The plasma processing device further comprises a septum polarizer for propagating, to a processing chamber, a microwave having been propagated via a circulator. One port of the circulator is connected to one port of the septum polarizer and the other port of the septum polarizer via an impedance matching unit. The other port of the circulator is connected to a high frequency power source via an impedance matcher. The one port of the septum polarizer is a port that converts the propagated microwave to a right-hand circular polarization wave. The other port of the septum polarizer is a port that converts the propagated microwave to a left-hand circular polarization wave. The impedance matching unit has specified dimensions so that the impedance matching of the propagated microwave is achieved.

Description

Plasma processing equipment

[0001] The present invention relates to a plasma processing apparatus.

[0002] In the manufacture of semiconductor devices, plasma processing equipment is often used for various processes such as etching, film deposition, and cleaning. To achieve the desired processing results, various factors, including pressure and gas species, are adjusted. From the viewpoint of yield, proper control of the plasma distribution within the processing chamber is one of the important factors for achieving uniform processing across the entire wafer surface.

[0003] In the past, in the case of a plasma processing apparatus that uses microwaves to generate plasma, for example, when the TE11 mode, which is the fundamental mode of a cylindrical waveguide, is introduced into the processing chamber as linearly polarized waves, the spatial distribution of electric field strength becomes non-axially symmetric, which can result in non-uniform processing. As a countermeasure, Patent Document 1 proposes a method in which the polarization plane is rotated by using a circularly polarized wave generating means, thereby making the electric field distribution in the processing chamber axially symmetric.

[0004] Japanese Patent Application Laid-Open No. 2006-179477

[0005] In a method using a circularly polarized wave generating means, the influence of reflected waves from the processing chamber, whose characteristics vary depending on the process conditions, can cause the circularly polarized wave input to the processing chamber to be mixed with a reverse-rotation component, resulting in an axially elliptically polarized wave, which can degrade the uniformity of the plasma distribution. For this reason, Patent Document 1 also proposes a method of suppressing the effect on uniformity by providing a dummy load to absorb the reflected waves. However, with the method using a dummy load, the reflected portion of the energy that would normally be used to generate plasma is converted into heat, increasing power loss, and there is a concern that a larger power supply will be required to compensate for this.

[0006] An object of the present invention is to provide a plasma processing apparatus that generates an axially symmetric electric field distribution under a wide range of conditions and enables uniform processing without actively losing microwave energy other than through plasma generation.

[0007] The present invention has the following configuration to achieve the above object. The plasma processing apparatus includes a processing chamber in which a sample is plasma-processed, a high-frequency power supply that supplies high-frequency microwave power, a magnetic field forming mechanism that forms a magnetic field in the processing chamber, and a sample stage on which the sample is placed. The plasma processing apparatus further includes a septum polarizer that propagates microwaves propagated through a circulator into the processing chamber, one port of the circulator being connected to one port of the septum polarizer and the other port of the septum polarizer via an impedance matching unit, the other port of the circulator being connected to the high-frequency power supply via a matching box. The one port of the septum polarizer is a port that converts the propagated microwave into a right-handed circularly polarized wave, and the other port of the septum polarizer is a port that converts the propagated microwave into a left-handed circularly polarized wave. The impedance matching unit includes a rectangular waveguide, and the width dimension of the rectangular waveguide and the waveguide length dimension of the rectangular waveguide are specified so that the propagated microwave is impedance-matched.

[0008] According to the present invention, it is possible to provide a plasma processing apparatus that generates an axially symmetric electric field distribution under a wide range of conditions and enables uniform processing without actively losing microwave energy other than through plasma generation.

[0009] 1A and 1B are schematic diagrams illustrating the configuration of a plasma processing apparatus according to an embodiment of the present invention, a mode converter, and a circular polarizer according to an embodiment of the present invention.

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] FIG. 1 shows a plasma processing apparatus according to an embodiment of the present invention. Microwaves having a frequency of 2.45 GHz are generated by a microwave source 1 such as a magnetron and transmitted through a rectangular waveguide 2, an isolator 3, and a matching box 4 to a mode converter 5. The microwaves transmitted to the mode converter 5 are further radiated into a cylindrical cavity 7 via a cylindrical waveguide (also called a "circular polarizer") 6, generating plasma in a processing chamber 9 separated by a microwave introduction window 8 below the cylindrical cavity 7. A gas introduction system and a vacuum exhaust system (not shown) are connected to the processing chamber 9, and the interior of the processing chamber 9 is maintained at a gas atmosphere and pressure suitable for processing. A stage 11 is provided within the processing chamber 9 for placing a wafer 10, which is the object to be processed. The microwaves incident on the cylindrical waveguide 6 are converted into circularly polarized waves in TE11 mode as they pass through the cylindrical waveguide 6, are radiated into the cylindrical cavity 7, pass through the microwave introduction window 8, and radiate microwave power into the processing chamber 9.

[0012] At the same time, an electromagnetic coil (not shown) is provided to surround the cylindrical cavity 7 and the processing chamber 9, creating a magnetic field strength surface of 875 gauss, which induces electron cyclotron resonance in the processing chamber 9, thereby forming plasma in the material gas supplied from the gas introduction system described above.

[0013] FIG. 2 shows the details of the mode converter 5. The two openings 20 and 21 of the T-shaped circulator 12, which is closest to the power supply and has a bias magnetic field application unit (e.g., microwave ferrite with a bias magnetic field applied by a permanent magnet) on the waveguide, are connected to the openings of the two E-corners 13a. As can be seen from FIG. 2, the two E-corners 13a are arranged symmetrically. Two E-corners 13b are connected to the bottom of the E-corner 13a in a folded-back manner, and two E-corners 14 are connected to be sandwiched between the E-corners 13a and 13b. The E-corners 13a, 13b, and 14 are collectively referred to as the impedance matching unit.

[0014] A cylindrical waveguide 6 is connected to the lower part (processing chamber side) of the E-corner 14. Inside the cylindrical waveguide 6, a tapered, sloped septum (partition) 15 made of metal is provided. A circular polarizer (cylindrical waveguide) equipped with such a septum (partition) is called a septum polarizer 16. The diagram on the lower left of Figure 2 is a side view of the septum polarizer 16 so that the shape of the "sloped septum" can be seen.

[0015] Furthermore, two ports (openings) 22 and 23 at the bottom (processing chamber side) of the E-corner 14 are independently connected to two ports (openings) 24 and 25 at the top (power supply side) of the septum polarizer 16 .

[0016] The circulator 12 does not necessarily have to be T-shaped, and may be Y-shaped or the like. Furthermore, the bias magnetic field application unit described above can use an electromagnet (electromagnetic coil) instead of a permanent magnet, allowing the sense of circular polarization, described below, to be electrically switched. It is desirable to select a microwave ferrite material with as low a loss as possible at the frequency to be used. However, since there are already circulators on the market with an insertion loss of approximately 0.1 dB at a frequency of 2.45 GHz, which is sufficiently low loss for practical use, it is sufficient to select one from these.

[0017] Furthermore, in this embodiment, the mode converter 5 has a symmetrical structure, but as long as impedance matching is achieved between the circulator 12 and the septum polarizer 16, the waveguide lengths of the E-corners 13a and 13b can be determined arbitrarily. Under similar constraints, H-corners, bends, coaxial cables, etc. may be used instead of the E-corners 13a and 13b.

[0018] Here, we will explain septum polarizers. Septum polarizers are known as a means of generating circularly polarized waves, and are described, for example, on page 111 of "The Fundamentals of Circularly Polarized Antennas" (by Takeshi Fukusako, Corona Publishing, 2018). While only a stepped septum is described there, in applications other than broadband applications, a simpler shape, such as a sloped septum, can simplify the shape optimization process in the design. Of course, the septum shape can also be stepped or have other shapes, as needed.

[0019] The septum polarizer has the property that the sense of circular polarization (the direction of rotation of the electric field, right-handed or left-handed) can be determined depending on which of the two ports separated by the septum is used to introduce the microwave. In this embodiment, the polarizer is configured to convert the traveling wave FW from the circulator 12 into a right-handed circularly polarized wave. However, the polarizer may be configured to convert the traveling wave into a left-handed circularly polarized wave by inverting either the circulator 12 or the sloped septum 15. The dimensions of each part of the septum polarizer 16 can be determined using known dimensions or electromagnetic field simulation software such as HFSS (full-wave 3D electromagnetic field software).

[0020] The septum polarizer also has the property that the sense of the microwave from the cylindrical waveguide determines which of the ports separated by the septum the microwave propagates to. In this embodiment, the section below the cylindrical cavity 7 has an axially symmetrical structure, so the sense of the reflected wave RW from the processing chamber is inverted relative to the forward wave FW, and the reflected wave RW propagates along the other path, not the path of the forward wave FW. Note, however, that the sense of the circularly polarized wave is defined based on the wave's traveling direction. Furthermore, in general plasma processing apparatuses, the periphery of the processing chamber often has an axially symmetrical structure for uniform processing, and the premise of the axially symmetrical structure described above is not particularly limited to this embodiment.

[0021] Incidentally, the generation of elliptically polarized waves, which was a problem in the prior art, was caused by the reflected microwave RW from the processing chamber 9 being converted into a circularly polarized wave with the opposite sense inside the mode converter 5 and then re-entering, whereby the circularly polarized waves with different senses are mixed and propagated toward the processing chamber. However, in this embodiment, as shown in Figure 2, the reflected microwave RW propagating from the processing chamber to the circulator 12 returns to the power supply side without being re-reflected inside the mode converter 5 (see "Top view of mode converter" in the upper right of Figure 2).

[0022] The microwaves returning to the power supply side are pushed back by the matching box 4 and propagate again as traveling waves FW along the path shown in the figure. Therefore, waves of a different sense than desired are not propagated to the processing chamber side, and deterioration of the uniformity of the electric field distribution due to mixing of waves of different senses does not occur. Furthermore, the components of the mode converter 5 do not include elements such as dummy loads that actively lose microwave energy, and all have sufficiently low loss for practical use, so that the energy can be effectively used to generate plasma.

[0023] However, this assumes that sufficient impedance matching is achieved between the circulator 12 and the septum polarizer 16. This is because if mismatching causes reflection within the impedance matching sections such as the E-corners 13a, 13b, and 14, the microwave will propagate directly in the case of the reflected wave RW, or via the circulator 12 to the other port above the septum polarizer 16 in the case of the traveling wave FW, generating a circularly polarized wave in the opposite sense. To avoid this, in this embodiment, impedance matching is achieved for the operating frequency of 2.45 GHz by adjusting the width and length of the rectangular waveguide in the E-corner 14.

[0024] In this embodiment, the same effect can be obtained even when a static magnetic field with an axially symmetric distribution is applied to the processing chamber 9, for example, as in an ECR plasma processing apparatus, with a strength sufficient to cause electron cyclotron resonance. In this case, the anisotropy of the dielectric constant of the magnetized plasma causes the reflection characteristics from the processing chamber to change depending on the sense of circular polarization. Although the magnitude of the reflection may change depending on the sense, the fact remains that when the traveling wave FW is right-handed circularly polarized, the reflected wave RW is left-handed circularly polarized, and vice versa, regardless of the anisotropy. Therefore, the uniformity effect of this embodiment can also be obtained in an ECR plasma processing apparatus.

[0025] Further advantages of this embodiment include that there is virtually no response time because the system configuration is simple without using a feedback control system, and that there is no need for moving parts such as an electric field sensor for monitoring the axial ratio of the circularly polarized wave (an index of the degree of sense mixing) or an actuator for adjusting the characteristics of the mode converter 5.

[0026] 1...microwave source, 2...rectangular waveguide, 3...isolator, 4...matching box, 5...mode converter, 6...cylindrical waveguide, 7...cylindrical cavity, 8...microwave introduction window, 9...processing chamber, 10...wafer, 11...mounting table, 12...circulator, 13a, 13b...E corner, 14...E corner, 15...septum, 16...septum polarizer, FW...traveling wave, RW...reflected wave.

Claims

1. A plasma processing apparatus comprising a processing chamber in which a sample is plasma-processed, a high-frequency power supply that supplies high-frequency microwave power, a magnetic field forming mechanism that forms a magnetic field in the processing chamber, and a sample stage on which the sample is placed, further comprising a septum polarizer that propagates the microwaves propagated via a circulator into the processing chamber, one port of the circulator being connected to one port of the septum polarizer and the other port of the septum polarizer via an impedance matching unit, the other port of the circulator being connected to the high-frequency power supply via a matching unit, the one port of the septum polarizer being a port that converts the propagated microwaves into right-handed circularly polarized waves, and the other port of the septum polarizer being a port that converts the propagated microwaves into left-handed circularly polarized waves, the impedance matching unit comprising a rectangular waveguide, a width dimension of the rectangular waveguide and a length dimension of the rectangular waveguide that are defined so as to match impedance of the propagated microwaves; 2. The plasma processing apparatus according to claim 1, wherein ferrite is disposed in the waveguide of said circulator.

3. A plasma processing apparatus according to claim 1, wherein an electromagnet is disposed in the waveguide of said circulator.

4. A plasma processing apparatus according to claim 1, wherein the traveling wave propagated from said circulator is propagated to said one port of said septum polarizer.

5. A plasma processing apparatus according to claim 1, wherein the interior of said septum polarizer is separated by a metal septum.

6. The plasma processing apparatus according to claim 1, wherein the microwaves are microwaves of 2.45 GHz.

Images