Plasma generation unit, plasma processing apparatus, and plasma generation method

Abstract

To provide a plasma generation unit, a plasma processing apparatus, and a plasma generation method, capable of improving the degree of freedom of a shape of a plasma generation surface.SOLUTION: A plasma generation unit U comprises a dielectric body 4 into which a tip of an inner conductor 30 of a coaxial tube 3 for transmitting a micro wave output from a micro wave output section 1 is inserted, and generates a plasma wave using the micro wave transmitted by the coaxial tube 3. The dielectric body 4 has a shape and size inside which a micro wave having a predetermined wavelength output from the micro wave output section 1 is propagated to generate a standing wave. Using the generated standing wave, plasma is generated on a surface of the dielectric body 4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application discloses a plasma generating unit for generating plasma, a plasma processing apparatus including such a plasma generating unit, and a plasma generating method using such a plasma processing apparatus. [Background technology]

[0002] Plasma processing apparatuses are used that use microwaves to perform plasma processing on a processing object. For example, the inventors of the present application have proposed in Patent Document 1 a technology for generating surface wave-excited plasma, in which high-density plasma is generated in a reactor for generating surface waves, and which is suitable for processing large areas at a high processing speed. The method for generating surface wave-excited plasma proposed in Patent Document 1 has a structure in which a reactor having a slot antenna in a waveguide is provided with a quartz dielectric separating it from the reduced pressure side, and plasma is generated on the surface of the reactor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-348898 Summary of the Invention [Problem to be solved by the invention]

[0004] As proposed in Patent Document 1, in technical fields such as surface treatment of processing objects, there is a demand for a technology that improves the degree of freedom in the shape of the plasma generation surface, such as by expanding the plasma generation area.

[0005] The present application has been made in consideration of the above circumstances, and its main purpose is to disclose a plasma generating unit that can improve the degree of freedom in the shape of the plasma generating surface by propagating microwaves as standing waves within a dielectric.

[0006] Another object of the present invention is to provide a plasma processing apparatus and a plasma generating method using such a plasma generating unit. [Means for solving the problem]

[0007] In order to solve the above problems, the plasma generating unit disclosed in the present application is a plasma generating unit that includes a dielectric into which the tip of an inner conductor of a coaxial tube that transmits microwaves output from a microwave output unit is inserted, and that generates plasma by the microwaves transmitted by the coaxial tube, wherein the dielectric is formed in a shape and dimensions that allow standing waves to be generated inside when microwaves of a predetermined wavelength output from the microwave output unit propagate inside the dielectric, and the generated standing waves generate plasma on the surface of the dielectric.

[0008] In the plasma generating unit, the inner conductor is inserted so that its tip is positioned at a node of a standing wave generated in the dielectric.

[0009] In the plasma generating unit, the dielectric body is shaped like a rectangular parallelepiped, and the inner conductor is inserted so as to be parallel to the shortest side of the dielectric body.

[0010] In addition, in the plasma generating unit, the rectangular parallelepiped dielectric is characterized in that the lengths of the long and short sides of the surface into which the tip of the inner conductor is inserted are N times (N is a natural number greater than or equal to 2) the half wavelength of the microwave propagating inside.

[0011] In addition, in the plasma generating unit, the dielectric is formed using alumina having a length in the insertion direction of the inner conductor of 17 to 19 mm or quartz glass having a length of 30 to 32 mm, and the metal casing is characterized in that it has a cooling surface that contacts the dielectric and cools the dielectric in contact therewith.

[0012] In the plasma generating unit, the dielectric body is shaped like a rectangular parallelepiped, and the inner conductor is inserted so as to be parallel to the longest side of the dielectric body.

[0013] In addition, the plasma generating unit is characterized in that a plurality of the dielectric bodies are arranged with gaps therebetween.

[0014] The plasma generating unit is characterized by having a metal housing that covers the dielectric and has a plurality of openings formed therein.

[0015] Furthermore, the plasma processing apparatus disclosed in the present application comprises the plasma generating unit, the plasma generating unit having a metal casing that covers the dielectric and has a portion that is open, and further comprising a processing chamber that contains the dielectric covered by the metal casing, and is characterized in that surface wave plasma is generated by radiating microwaves from the opening of the metal casing into the processing chamber, which has been reduced in pressure to 30 to 300 Pa.

[0016] The plasma processing apparatus further comprises the plasma generating unit, the plasma generating unit having a metal casing that covers the dielectric and has a portion that is open, and further comprising a processing chamber that contains the dielectric covered by the metal casing, and is characterized in that volume wave plasma is generated by radiating microwaves from the opening of the metal casing into the processing chamber, which has been reduced in pressure to 20 Pa or less.

[0017] The plasma processing apparatus is also characterized in that it is designed so that the minimum value of the voltage standing wave ratio as viewed from the inner conductor into which the microwave is introduced is 1.5 or less.

[0018] Furthermore, the plasma generation method disclosed in the present application is a plasma generation method that uses a microwave output unit that outputs microwaves of a predetermined wavelength, a coaxial tube that transmits the microwaves output from the microwave output unit, and a dielectric into which the tip of an inner conductor of the coaxial tube is inserted, and generates plasma by the microwaves transmitted through the coaxial tube, characterized in that the microwaves of the predetermined wavelength output from the microwave output unit propagate through the dielectric, generating standing waves within the dielectric, and the generated standing waves generate plasma on the surface of the dielectric. [Effects of the Invention]

[0019] The plasma generating unit and the like disclosed herein generate standing waves that propagate through a dielectric using microwaves, thereby providing excellent effects such as increased freedom in designing the plasma generating surface, e.g., increasing the plasma generation area. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic diagram illustrating an example of a plasma processing apparatus disclosed herein; [Figure 2] 1 is a schematic cross-sectional view showing an enlarged view of a portion of a plasma generating unit disclosed in the present application. [Figure 3] 1 is a schematic perspective view showing an example of the structure of a dielectric and a peripheral portion provided in a plasma generating unit disclosed in the present application. FIG. [Figure 4] 1 is a schematic perspective view showing an example of the structure of a dielectric and a peripheral portion provided in a plasma generating unit disclosed in the present application. FIG. [Figure 5] FIG. 1 is a perspective view conceptually illustrating an example of the behavior of microwaves. [Figure 6] FIG. 1 is a perspective view conceptually illustrating an example of the behavior of microwaves. [Figure 7] 1 is a cross-sectional view schematically showing an example of the structure of a dielectric and a peripheral portion provided in a plasma generating unit disclosed in the present application. [Figure 8]1 is an explanatory diagram schematically illustrating an example of the relationship between an inner conductor, a dielectric, and a standing wave provided in a plasma generating unit disclosed in the present application. FIG. [Figure 9] FIG. 10 is an explanatory diagram showing some of the conditions for a simulation of the plasma generating unit disclosed herein. [Figure 10] 10 is an example of a simulation result of the electric field strength in the dielectric in the plasma generating unit disclosed in the present application. [Figure 11] FIG. 10 is an explanatory diagram showing some of the conditions for a simulation of the plasma generating unit disclosed herein. [Figure 12] 10 is an example of a simulation result of the electric field strength in the dielectric in the plasma generating unit disclosed in the present application. [Figure 13] FIG. 10 is an explanatory diagram showing some of the conditions for a simulation of the plasma generating unit disclosed herein. [Figure 14] 10 is an example of a simulation result of the electric field strength in the dielectric in the plasma generating unit disclosed in the present application. [Figure 15] 10 is an example of a simulation result of the electric field strength in the dielectric 4 in the plasma generating unit disclosed in the present application. [Figure 16] FIG. 10 is an explanatory diagram showing some of the conditions for a simulation of the plasma generating unit disclosed herein. [Figure 17] 10 is an example of a simulation result of the electric field strength in the dielectric in the plasma generating unit disclosed in the present application. [Figure 18] 10 is an example of a simulation result of the electric field strength in the dielectric in the plasma generating unit disclosed in the present application. [Figure 19] FIG. 10 is an explanatory diagram showing an example of simulation conditions for the plasma generating unit disclosed in the present application. [Figure 20] 10 is an example of a simulation result of the electric field strength in the dielectric in the plasma generating unit disclosed in the present application. [Figure 21] 10 is an example of a simulation result of the electric field strength in the dielectric in the plasma generating unit disclosed in the present application. [Figure 22]10 is an example of a simulation result of the electric field strength in the dielectric in the plasma generating unit disclosed in the present application. [Figure 23] 10 is an example of a simulation result of the electric field strength in the dielectric in the plasma generating unit disclosed in the present application. [Figure 24] FIG. 10 is an explanatory diagram showing some of the conditions for a simulation of the plasma generating unit disclosed herein. [Figure 25] 10 is an example of a simulation result of the electric field strength in the dielectric in the plasma generating unit disclosed in the present application. [Figure 26] 10 is a graph showing an example of the relationship between the number of teeth and the voltage standing wave ratio (VSWR) regarding a standing wave in a dielectric in a plasma generating unit disclosed in the present application. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments will be described with reference to the drawings. The plasma generating unit disclosed herein is a system that generates plasma using microwaves. The plasma generating unit performs processing such as surface treatment of a processing object by irradiating the generated plasma onto the processing object. The following description will be given with reference to the drawings, taking as an example a plasma processing apparatus E equipped with a plasma generating unit U shown in the drawings.

[0022] 1 is a schematic diagram illustrating an example of a plasma processing apparatus E disclosed herein. The plasma processing apparatus E includes a plasma generating unit U, which irradiates a processing object W with plasma to perform various surface treatments such as reduction treatment, addition of hydroxyl groups, ashing, etc., as well as plasma CVD, etching, and addition of water-repellent groups.

[0023] The plasma processing apparatus E includes a microwave output unit 1 that outputs microwaves and a waveguide 2 that transmits the microwaves output from the microwave output unit 1 to a plasma generating unit U. The plasma generating unit U includes components such as a coaxial tube 3 and a dielectric 4. The plasma processing apparatus E also includes components such as a processing chamber 5 that performs various processes using the plasma generated in the plasma generating unit U. The microwave output unit 1 includes a power supply and an oscillator such as a magnetron that generates microwaves using power applied from the power supply, and outputs the microwaves generated by the oscillator. The waveguide 2 is a transmission medium that transmits the microwaves output from the microwave output unit 1 to the plasma generating unit U. The coaxial tube 3 is connected to the waveguide 2 and functions as an antenna that transmits the microwaves into the dielectric 4 via an internal conductor 30 contained therein and outputs the microwaves within the dielectric 4. The dielectric 4 is formed in a shape such as a rectangular parallelepiped and is covered by a metal housing 40. A portion of the bottom surface of the metal housing 4 is open as an opening 400. Furthermore, the tip of the inner conductor 30 is inserted into the dielectric 4 as an antenna.

[0024] A transfer conveyor 50 for transferring the processing object W is disposed within the processing chamber 5. A carry-in gate 51 that opens and closes to transfer the processing object W onto the transfer conveyor 50 is provided on a wall of the processing chamber 5, and a carry-in conveyor 52 that transfers the processing object W to the transfer conveyor 50 via the carry-in gate 51 is provided outside the processing chamber 5. A carry-out gate 53 that opens and closes to transfer the processing object W from the transfer conveyor 50 is provided on a wall of the processing chamber 5 facing the carry-in gate 51, and a carry-out conveyor 54 that receives and transfers the processing object W transferred from the transfer conveyor 50 is provided outside the processing chamber 5. The processing chamber 5 is also provided with a gas supply unit 55 that supplies a processing gas for generating plasma into the processing chamber 5, and a gas exhaust unit 57 that is connected to a pressure reduction unit 56 such as a vacuum pump to exhaust gas from the processing chamber 5. From the gas supply unit 55, a gas containing oxygen, hydrogen, argon, nitrogen, carbon fluoride, water vapor, or a mixture of these gases as a main component is supplied as a processing gas.

[0025] FIG. 2 is a schematic cross-sectional view showing an enlarged portion of a plasma generating unit U disclosed herein. FIG. 3 is a schematic perspective view showing an example of the structure of the dielectric 4 and surrounding area provided in the plasma generating unit U disclosed herein. FIG. 4 is a schematic perspective view showing an example of the structure of the dielectric 4 and surrounding area provided in the plasma generating unit U disclosed herein. FIG. 2 is an enlarged view of the tip of the inner conductor 30 of the coaxial tube 3 provided in the plasma generating unit U provided in the plasma processing apparatus E illustrated in FIG. 1. FIG. 3 illustrates the dielectric 4 and coaxial tube 3 provided in the plasma generating unit U. FIG. 4 illustrates the dielectric 4, metal housing 40, and coaxial tube 3 provided in the plasma generating unit U.

[0026] The dielectric 4 and its surrounding structure will be further described with reference to Figures 1 to 4. The dielectric 4 is shaped like a rectangular parallelepiped, etc., and the tip of the inner conductor 30 of the coaxial waveguide 3 is inserted into it. The dielectric 4 is shaped like a rectangular parallelepiped, with the shortest length in the thickness (height) direction (t direction), and with the top surface having a rectangular, square, or other shape in plan view. The dielectric 4 is made of a material such as alumina with a dielectric constant of about 9.6 or quartz glass with a dielectric constant of about 3.6.

[0027] The inner conductor 30 of the coaxial waveguide 3 is tapered so that its outer diameter gradually decreases toward the tip. The inner conductor 30 is inserted to a depth such that its tip is located approximately halfway from the top surface of the dielectric 4 in the thickness direction. In the plasma processing apparatus E, the bottom surface of the dielectric 4 becomes a reduced-pressure space V by discharging gas from the processing chamber 5. In the configuration illustrated in FIGS. 1 to 4, the inner conductor 30 of the coaxial waveguide 3 is inserted at the center of gravity of the top surface of the dielectric 4. As will be described later, the plasma processing apparatus E disclosed herein may be configured so that the tip of the inner conductor 30 is inserted at a position other than the center of gravity of the top surface, as long as it is located at a node of a standing wave generated inside the dielectric 4.

[0028] The metal casing 40 is formed using a material such as aluminum. The outer shape of the metal casing 40 is formed in a substantially rectangular parallelepiped shape, and the inner shape is formed in a shape that closely fits the outer shape of the dielectric 4, covering the dielectric 4. Part or all of the bottom surface of the metal casing 40 is opened as an opening 400, exposing the bottom surface of the dielectric 4. The metal casing 40 has a supply port 401 and a discharge port 402 for a cooling medium such as water formed on the top surface, and a circulation path (not shown) that circulates the cooling medium supplied from the supply port 401 and discharges it from the discharge port 402 is formed inside the top surface. The dielectric 4 covered by such a metal casing 40 has an upper surface that closely fits the inner top surface of the metal casing 40, which functions as a cooling surface, and a lower surface that functions as a plasma generation surface.

[0029] 5 and 6 are perspective views conceptually illustrating an example of microwave behavior. These figures are based on "Figure 3: Electromagnetic Field Distribution in a Rectangular Cavity (Single Mode)" and "Figure 4: Electromagnetic Field Distribution in a Multimode Cavity (Half Position in the Height Direction)" in "Summary—Historical Background of Research and Development of Microwave Application to Materials Processing," by Hideoki Fukushima, edited by the Editorial Committee for Latest Microwave Energy and Applied Technology, published by Industrial Technology Service Center Co., Ltd., November 26, 2014, pp. 331-338. The plasma processing apparatus E disclosed herein outputs microwaves generated by a microwave output unit 1. The microwaves are output from the tip of the inner conductor 30 of the coaxial tube 3 via a waveguide 2, propagate through the dielectric 4, and become single-mode or multimode standing waves. Figures 5 and 6 conceptually illustrate standing waves generated in the dielectric 4, which is formed into a rectangular parallelepiped shape in a plan view. In the present application, the behavior illustrated in Fig. 5 will be described as a single-mode standing wave, and the behavior illustrated in Fig. 6 will be described as a multi-mode standing wave. When a dielectric 4 having a slope rather than a rectangular parallelepiped shape is used, the microwaves undergo diffuse reflection inside, and therefore do not form standing waves aligned vertically and horizontally as illustrated in Fig. 5 and Fig. 6. When a dielectric 4 having a curved surface such as a circle is used, the microwaves do not form standing waves aligned vertically and horizontally.

[0030] FIG. 7 is a cross-sectional view schematically illustrating an example of the structure of the dielectric 4 and its surroundings included in the plasma generation unit U disclosed herein. FIG. 7 also illustrates the behavior of microwaves within the dielectric 4 and the plasma generated by the microwaves. As illustrated in FIG. 7 , the insertion position of the tip of the inner conductor 30 inserted into the dielectric 4 is set at or near a node of a single-mode or multi-mode standing wave formed by the microwaves within the dielectric 4. By setting the insertion position of the tip of the inner conductor 30 in this manner, the microwaves efficiently propagate from the tip of the inner conductor 30 into the dielectric 4 and become a standing wave. The standing wave formed within the dielectric 4 forms plasma, such as surface wave plasma or volume wave plasma, on the lower surface (plasma surface) of the dielectric 4. Propagating microwaves into the dielectric 4 and forming a standing wave improves the degree of freedom in designing the plasma generation surface of the dielectric 4, making it possible, for example, to expand the area of ​​the plasma generation surface. Furthermore, the electric field intensity on the plasma generation surface can be made uniform for plasma generation surfaces designed in various shapes, thereby enabling the formation of homogeneous plasma.

[0031] Design examples of the shape of the dielectric 4 and the microwave wavelength for forming the standing waves shown in Figures 5 to 7 will be described below. In the following description, the thickness of the dielectric 4 is defined as t, the short side of the rectangular top surface into which the inner conductor 30 is inserted as a, and the long side as b (see Figure 4). Also, the wavelength in a vacuum is defined as λ0, the wavelength inside the dielectric 4 as λd, and the dielectric constant as ε.

[0032] When alumina with a dielectric constant ε=9.6 is used as the dielectric 4, the wavelength λd of the microwave (2.45 GHz) in the dielectric 4 is calculated as λd=39.3 mm using the following formula (1) assuming λ0=122 mm.

[0033] λd=λ0 / (ε^1 / 2) Equation (1)

[0034] Furthermore, the thickness t is preferably set to approximately half the microwave wavelength in the dielectric 4, which is the minimum thickness required for microwave propagation and the formation of a standing wave. From the calculation of λd=39.3 mm using the above formula (1), the optimum value for thickness t is 17 mm to 19 mm. Note that the inner conductor 30 is inserted so that its tip is positioned at a position half the thickness t of the dielectric 4, so the insertion depth of the inner conductor 30 is approximately 9 mm.

[0035] Similarly, when quartz glass with a dielectric constant ε=3.8 is used as the dielectric 4, λd=62.6 mm and t=30 mm to 32 mm. Note that if the thickness t is equal to or greater than the wavelength of the microwave, diffuse reflection occurs inside, preventing the formation of vertically and horizontally aligned standing waves. The insertion depth of the inner conductor 30 is approximately 15 mm.

[0036] The short side a and long side b of the rectangle forming the top surface of the dielectric 4 into which the tip of the inner conductor 30 is inserted are designed to be N times (N is a natural number) the half wavelength (λd / 2) of the microwave in the dielectric 4. That is, the microwave output section 1 outputs microwaves having a wavelength such that the short side a and long side b of the dielectric 4 are N times the half wavelength in the dielectric 4, thereby enabling the plasma generation unit U to form a standing wave in the dielectric 4. For example, when the microwave is 2.45 GHz and alumina is used as the dielectric 4, the short side a and long side b are designed to be approximately 39 mm, 78 mm, 117 mm, 156 mm, and so on.

[0037] Similarly, when quartz glass is used as the dielectric 4, the short side a and long side b of the dielectric 4 are designed to be 62 mm, 124 mm, 186 mm, 248 mm, . . .

[0038] FIG. 8 is an explanatory diagram schematically illustrating an example of the relationship between the inner conductor 30, the dielectric 4, and the standing wave included in the plasma generating unit U disclosed herein. FIG. 8 shows the general shape of the standing wave and the position of the inner conductor 30 when the lengths of the short side a and long side b of the alumina dielectric 4 are 39 mm, 78 mm, 117 mm, and 156 mm. The positions of the inner conductor 30 when the lengths of the short side a (or long side b) are 39 mm, 78 mm, 117 mm, and 156 mm are 30A, 30B, 30C, and 30D, respectively. As illustrated in FIG. 8, the plasma generating unit U disclosed herein is designed so that the tip of the inner conductor 30 is located at a node of the standing wave. Note that FIG. 8 illustrates a series of examples in which the tip of the inner conductor 30 is located at a node of the standing wave formed at the center of the dielectric 4. However, the tip of the inner conductor 30 may be located at a node of the standing wave that is off the center, as long as it is at a node of the standing wave.

[0039] A plasma generation method using the plasma processing apparatus E disclosed herein, configured as described above, will be described with reference to Figures 1 to 7. First, the processing object W is carried into the processing chamber 5 of the plasma processing apparatus E on the transport conveyor 50 by the carry-in conveyor 52. After the processing object W is carried in, the carry-in gate 51 and the carry-out gate 53 are closed, and the processing chamber 5 is sealed. Next, the gas in the processing chamber 5 is sucked in through the gas exhaust unit 57 by the decompression unit 56, and the processing chamber 5 is placed in a decompressed state.

[0040] After the processing chamber 5 is depressurized, a gas containing oxygen, hydrogen, argon, nitrogen, carbon fluoride, water vapor, or a mixture of these gases as its main components is supplied into the processing chamber 5 from the gas supply unit 55 as a processing gas.

[0041] After the processing chamber 5 is filled with the processing gas, the microwave output unit 1 outputs oscillated microwaves. The microwaves output from the microwave output unit 1 are transmitted through the waveguide 2 and sent to the coaxial tube 3. The microwaves are transmitted from the tip of the inner conductor 30 in the coaxial tube 3 to the dielectric 4, and form a single-mode or aligned multi-mode standing wave that spreads within the dielectric 4.

[0042] For example, when the plasma generating unit U generates surface wave plasma, the pressure inside the processing chamber 5 is reduced to approximately 30 to 300 Pa. In the plasma generating unit U, plasma is generated starting from the area with the highest electric field strength, becoming surface wave plasma. When the electron density in the plasma-generated area becomes high, no more microwave power is input to that area, so the plasma spreads and becomes surface wave plasma, resulting in a homogenized plasma overall. In particular, the plasma generating unit U disclosed herein generates surface wave plasma using standing waves generated in the dielectric 4, making it easy to generate homogenized plasma.

[0043] Furthermore, for example, when the plasma generating unit U generates volume wave plasma, the pressure inside the processing chamber 5 is reduced to approximately 20 Pa or less. When the pressure inside the processing chamber 5 is reduced to 20 Pa or less, plasma generated by a standing wave generated in the dielectric 4 provided in the plasma generating unit U diffuses inside the processing chamber 5 and becomes volume wave plasma.

[0044] Within the processing chamber 5, the processing object W placed on the transport conveyor 50 is transported by the transport conveyor 50 while being irradiated with plasma such as surface wave plasma or volume wave plasma generated on the underside of the dielectric 4. When the processing object W is transported by the transport conveyor 50, the plasma processing on the processing object W is completed. After the plasma processing is completed, the processing gas is discharged and outside air is supplied, and then the discharge gate 53 opens, and the processing object W is transferred from the transport conveyor 50 to the discharge conveyor 54 and is then transported by the discharge conveyor 54.

[0045] In this manner, the plasma processing apparatus E disclosed in the present application uses the plasma generating unit U to carry out the plasma generating method.

[0046] Furthermore, for example, when the plasma generating unit U generates volume wave plasma, the pressure inside the processing chamber 5 is reduced to approximately 20 Pa or less. When the pressure inside the processing chamber 5 is reduced to 20 Pa or less, plasma generated by standing waves generated in the dielectric 4 provided in the plasma generating unit U diffuses within the processing chamber 5 and becomes volume wave plasma. The plasma generating unit U disclosed herein is designed to optimize various dimensions and shapes, such as the overall dimensions of the dielectric 4 and the dimensions of the opening 400 in the metal housing 40. By optimizing various dimensions and shapes, the plasma generating unit U disclosed herein has a small minimum value of VSWR (Voltage Standing Wave Ratio) for microwave frequencies, such as 1.5 or less. Furthermore, for example, when the VSWR is 1.5, the reflectance is 4%. Even when generating such volume wave plasma, the microwaves propagate to the end of the dielectric 4 and become standing waves, which makes it easier to homogenize the electric field strength on the plasma surface of the dielectric 4 and improves the degree of freedom in the shape of the plasma generation surface that generates plasma, for example, making it possible to expand the area of ​​the generation surface.

[0047] In the case of the volume wave plasma described above, the smaller the reflection at the dielectric 4, the smaller the load on the isolator, and there is no need for a matching device to return the reflection from the oscillator side of the microwave output part 1 to the processing chamber 5. This is a particularly effective characteristic when a semiconductor oscillator is used to generate microwaves.

[0048] Next, the effects of the shape of the dielectric 4 and the metal housing 40 covering the dielectric 4 in the plasma generating unit U disclosed herein will be described using the results of simulations. The simulations were performed using HFSS (High Frequency Structure Simulator) manufactured by Ansys, Inc. The following simulations were performed under the following conditions: The dielectric 4 was made of alumina and had an optimal shape and dimensions for forming a standing wave. Similar results were obtained when the dielectric 4 was made of quartz glass. The conditions for the inner conductor 30 were set to optimize the tip position and insertion depth. First, as Simulation Example 1, Simulation Examples 1.1 to 1.3 were performed. In Simulation Example 1 (Examples 1.1 to 1.3), the effects of the metal housing 40 covering the dielectric 4 were confirmed by simulation under the conditions optimized for forming a standing wave as described above. The electric field strength was calculated when 1 W was input from the coaxial end face, and the maximum electric field strength level indicated by dark colors was 1000 V / m or 400 V / m. The electric field strength is the maximum value under those conditions. The following simulation examples are the results of simulating the electric field strength, and the plasma is indirectly estimated from the electric field strength.

[0049] <Simulation example 1.1> FIG. 9 is an explanatory diagram showing some of the simulation conditions for the plasma generating unit U disclosed herein. FIG. 10 shows an example of a simulation result of the electric field intensity within the dielectric 4 in the plasma generating unit U disclosed herein. FIG. 9(a) shows a side view of the dielectric 4 defined as a condition, and FIG. 9(b) shows a bottom view of the dielectric 4. Simulation Example 1.1 uses a dielectric 4 whose side and bottom surfaces are not covered with a metal housing 40 as an experimental condition. Note that, to maintain the same conditions except for not being covered with a metal housing 40, it is assumed that a metal housing 40 exists on the top surface, which functions as a cooling surface. The regions corresponding to the metal housing 40 on the side and bottom surfaces are defined as a reduced-pressure space V and are indicated by diagonal lines in the figure. The simulation result of the electric field intensity illustrated in FIG. 10 is a simulation result in which the electric field intensity at a position 2 mm below the bottom surface of the dielectric 4 is indicated by shading. As illustrated in FIG. 10, the standing wave extends to a position corresponding to the end of the dielectric 4. When the dielectric 4 is not covered with the metal housing 40, a peak of the electric field intensity appears in the center, but the electric field intensity is low overall.

[0050] <Simulation example 1.2> FIG. 11 is an explanatory diagram showing some of the simulation conditions for the plasma generating unit U disclosed herein. FIG. 12 shows an example of a simulation result of the electric field strength within the dielectric 4 in the plasma generating unit U disclosed herein. FIG. 11(a) shows a side view of the dielectric 4 defined as a condition, and FIG. 11(b) shows a bottom view of the dielectric 4. In Simulation Example 1.2, the upper and side surfaces of the dielectric 4 are covered with a metal housing 40, but the entire lower surface, as shown by the opening 400, is an experimental condition. Note that, for the simulation setup, the opening 400 is set to be in contact with the reduced pressure space V, which is indicated by the diagonal lines in the figure. The simulation result of the electric field strength shown in FIG. 12 shows that, compared to Simulation Example 1.1, the electric field is spread throughout the dielectric 4, the electric field strength is stronger in the center, and the overall electric field strength is more homogenized.

[0051] <Simulation example 1.3> FIG. 13 is an explanatory diagram showing some of the simulation conditions for the plasma generating unit U disclosed herein. FIG. 14 shows an example of a simulation result of the electric field strength within the dielectric 4 in the plasma generating unit U disclosed herein. FIG. 13(a) shows a side view of the dielectric 4 defined as a condition, and FIG. 13(b) shows a bottom view of the dielectric 4. Simulation example 1.3 uses a metal housing 40 that covers the top and side surfaces of the dielectric 4 and has a portion of its bottom surface exposed as a plasma surface, as shown by an opening 400. The exposed plasma surface of the metal housing 40 in Simulation example 1.3 is narrower and thinner than the plasma surface of the metal housing 40 in Simulation example 1.2. The simulation result of the electric field strength illustrated in FIG. 14 shows that the region of high electric field strength is spread across the entire plasma surface, compared to Simulation example 1.2.

[0052] From the simulation results of Simulation Example 1 above, the plasma generating unit U disclosed herein makes it possible to control the plasma generation area and electric field strength by limiting the dimensions of the opening 400 of the metal housing 40, i.e., the dimensions of the plasma generating surface that contacts the reduced pressure space V within the processing chamber 5.

[0053] <Simulation example 2> The plasma generating unit U disclosed herein is not limited to the above simulation example and can be implemented in various forms. Simulation results for other forms are shown below. FIG. 15 shows an example of a simulation result of the electric field strength within the dielectric 4 in the plasma generating unit U disclosed herein. FIG. 15(a) shows the electric field strength within the dielectric 4 from a side view, and FIG. 15(b) shows it from a bottom view. Simulation example 2 is an example in which the length is further extended using a long dielectric 4, and the simulation results of the electric field strength are shown in FIGS. 15(a) and 15(b). Simulation example 2 shows the results of a simulation performed using a long dielectric 4 with a short side a = 39 mm and a long side b = 494 mm. As shown in FIGS. 15(a) and 15(b), the plasma generating unit U disclosed herein resonates a standing wave within the dielectric 4, thereby generating homogenized plasma even in a long dielectric 4.

[0054] <Simulation example 3> As shown in Simulation Example 2, microwaves propagate to the end of the long dielectric 4 and become a standing wave. Simulation Example 3 is a configuration in which multiple dielectrics 4 are connected in series while taking into account the characteristics of such standing waves. FIG. 16 is an explanatory diagram showing some of the simulation conditions for the plasma generating unit U disclosed herein. FIG. 17 is an example of a simulation result of the electric field intensity within the dielectric 4 in the plasma generating unit U disclosed herein. FIG. 16(a) shows a side view of the dielectric 4 defined as a condition, and FIG. 16(b) shows an enlarged view of a portion of the dielectric 4 indicated by the circle in FIG. 16(a). Simulation Example 3 is a configuration in which multiple dielectrics 4 are connected in series, and the dielectrics 4 are arranged with gaps between them, as illustrated in FIG. 16. The simulation of Simulation Example 3 is the result of leaving a gap of 1 mm, with the space between them defined as a reduced-pressure space V. Even when multiple dielectrics 4 are arranged with a gap between them, by arranging the dielectrics 4 so that their lengths and nodes are located in the gaps and optimally designing the openings 400 of the metal housing 40, microwaves propagate to the tips of both dielectrics 4, resonating as a whole and forming standing waves, as shown in Fig. 17. In addition, tests using an actual device confirmed that operation is possible with a gap of 0.1 mm or less, and that a long plasma generation unit U can be realized by arranging multiple dielectrics 4.

[0055] <Simulation example 4> Simulation example 4 is a configuration in which a plurality of rectangular parallelepiped dielectrics 4 are arranged so that the propagation direction of the microwaves changes. FIG. 18 shows an example of a simulation result of the electric field intensity in the dielectric 4 in the plasma generating unit U disclosed in the present application. In simulation example 4 illustrated in FIG. 18, other rectangular parallelepiped dielectrics 4 are arranged at both ends of a long rectangular parallelepiped dielectric 4 so that the long side directions are perpendicular to each other, forming a U-shaped dielectric 4 as a whole. Even in the case of a bent dielectric 4 as shown in Example 4, by adjusting the length of the dielectric 4 and the wavelength of the microwave and arranging it so that the nodes are at the bending positions, it is possible to propagate the microwave to the end and form a standing wave.

[0056] <Simulation example 5> In Simulation Example 5, the position at which the inner conductor 30 of the coaxial waveguide 3 is inserted is shifted from the center of gravity of the dielectric 4. FIG. 19 is an explanatory diagram showing an example of simulation conditions for the plasma generating unit U disclosed herein. FIG. 20 shows an example of a simulation result of the electric field intensity in the dielectric 4 in the plasma generating unit U disclosed herein. FIG. 19 shows a side view of the dielectric 4 defined as a condition. As illustrated in FIG. 19, in the plasma generating unit U according to Simulation Example 5, the inner conductor 30 of the coaxial waveguide 3 is inserted near one end of the dielectric 4. As shown in FIG. 20, even when the inner conductor 30 is inserted near one end, microwaves propagate to the other end, forming a standing wave.

[0057] <Simulation example 6> Simulation example 6 is a configuration in which the inner conductor 30 of the coaxial waveguide 3 is inserted from the end of the dielectric 4 along the long side direction in Simulation example 5. FIG. 21 shows an example of a simulation result of the electric field strength within the dielectric 4 in the plasma generation unit U disclosed herein. FIG. 21(a) shows the electric field strength within the dielectric 4 as viewed from the side, and FIG. 21(b) shows the electric field strength within the dielectric 4 as viewed from below. As shown in FIG. 21, even when the inner conductor 30 is inserted from one end so as to be parallel to the long side direction, microwaves propagate to the other end, forming standing waves.

[0058] <Simulation example 7> Simulation Example 7 is a configuration in which the electric field strength is controlled by the shape of the opening 400 in the metal housing 40. FIG. 22 shows an example of a simulation result of the electric field strength within the dielectric 4 in the plasma generating unit U disclosed herein. FIG. 22(a) shows the electric field strength within the dielectric 4 from a bottom perspective, and FIG. 22(b) shows an enlarged portion of FIG. 22(a). The plasma generating unit U in Simulation Example 7 aims to control the electric field strength by the shape of the opening 400 in the metal housing 40 and start plasma generation at low power. In the plasma generating unit U, total reflection occurs from the plasma generating unit U until plasma generation starts, which places a strain on the isolator. Therefore, a characteristic that produces a high electric field even at low power is required. Specifically, as shown in FIG. 22, a small gap is provided at the peak of the standing wave, and discharge is set to start there. In a simulation under the conditions of Simulation Example 7 shown in Figure 22, the plasma generating unit U generates an electric field of 200 V / cm with an input of 50 W, which is sufficient to start a discharge even under a reduced pressure of 100 Pa. In the plasma generating unit U, plasma is generated starting from the location where the discharge starts, and the generated plasma spreads throughout. Even when a gap such as that shown in Figure 22 is provided, no deterioration in the voltage standing wave ratio (VSWR) was observed.

[0059] <Simulation example 8> Simulation example 8 is a configuration in which multiple sets of coaxial tubes 3, dielectrics 4, and metal housings 40 are arranged side by side. FIG. 23 shows an example of a simulation result of the electric field strength in the dielectric 4 in a plasma generating unit U disclosed herein. FIG. 23 is a bottom view of the dielectric 4. By arranging multiple plasma generating units U disclosed herein side by side, it is possible to generate plasma over a wide area. In the plasma generating unit U illustrated in FIG. 23, standing waves are generated in each of the multiple dielectrics 4, but mutual interference can be prevented by inserting a metal plate between the dielectrics 4.

[0060] <Simulation Example 9> Simulation Example 9 is a configuration in which multiple openings 400 are formed in the metal housing 40. FIG. 24 is an explanatory diagram showing some of the simulation conditions for the plasma generating unit U disclosed herein. FIG. 25 is an example of a simulation result of the electric field intensity within the dielectric 4 in the plasma generating unit U disclosed herein. FIG. 24(a) shows a side view of the dielectric 4 defined as a condition, and FIG. 24(b) shows a bottom view of the dielectric 4. Simulation Example 9 is a configuration in which four rectangular openings 400 are formed in the bottom surface of the metal housing 40, arranged in a matrix of two columns and two rows. Note that the vertical and horizontal dimensions of each opening 400 are different. Even when multiple openings 400 are formed in the bottom surface of the metal housing 40, standing waves are formed in the dielectric 4, as illustrated in FIG. 25, and plasma can be generated. The plasma generating unit U shown in Simulation Example 9 is capable of generating stable plasma that can adapt to fluctuations in the microwave wavelength by forming multiple openings 400 with different shapes and dimensions.

[0061] <Relationship between frequency and voltage standing wave ratio (VSWR)> Next, the relationship between frequency and VSWR in the plasma generating unit U disclosed herein will be described. FIG. 26 is a graph showing an example of the relationship between frequency and voltage standing wave ratio (VSWR) for a standing wave in the dielectric 4 of the plasma generating unit U disclosed herein. FIG. 26 shows the relationship between frequency and VSWR when a model is designed to have a minimum VSWR value of 1.5 or less in which a microwave with a frequency of 2.45 GHz is propagated through the dielectric 4 of the plasma generating unit U disclosed herein, as exemplified in Simulation Example 9. FIG. 26 shows the relationship between frequency and VSWR when the model is designed to have a minimum VSWR value of 1.5 or less. The horizontal axis represents the frequency of the microwave input to the dielectric 4, and the vertical axis represents the VSWR. By covering the dielectric 4 with a metal housing 40 and defining a portion of the metal housing 40 as an opening 400 to limit the plasma generation surface, it is possible to control not only the plasma generation region and electric field intensity but also the VSWR. In the simulation results shown in FIG. 26, the VSWR is suppressed to approximately 1.4 near 2.45 GHz. 26, it was confirmed that surface wave plasma was generated with a reflection rate of 18% (VSWR of 2.5) when the pressure in the processing chamber 5 was 120 Pa. It was also confirmed that volume wave plasma was generated with a reflection rate of 3% (VSWR of 1.4) when the pressure was 20 Pa.

[0062] As described above, in the plasma generating unit U disclosed herein, microwaves propagate through the dielectric 4, and the propagated microwaves generate standing waves. This allows the plasma generating unit U disclosed herein to achieve excellent effects, such as enabling the construction of a system that allows for increased freedom in designing the shape of the plasma generating surface, including an increased plasma generation area. Furthermore, the plasma generating unit U disclosed herein can propagate standing waves even when multiple dielectrics 4 are arranged closely together. Therefore, the plasma generating unit U disclosed herein allows for the generation of plasma over a large area by arranging the dielectrics 4 side by side, thereby achieving excellent effects.

[0063] The present invention is not limited to the above-described embodiments, and can be embodied in various other forms. Therefore, the above-described embodiments are merely illustrative in all respects and should not be interpreted as limiting. The technical scope of the present invention is defined by the claims and is not limited in any way by the text of the specification. Furthermore, all modifications and variations within the equivalent scope of the claims are within the scope of the present invention.

[0064] For example, in the above embodiment, a form applied to continuous processing in which plasma is irradiated onto the transported processing object W is shown, but the present invention is not limited to this and can be expanded into various forms, such as application to batch processing in which plasma is placed on a fixed mounting table and irradiated with plasma. [Explanation of symbols]

[0065] E. Plasma treatment equipment U Plasma Generation Unit W Processing target 1 Microwave output section 2 waveguide 3 coaxial tube 30 Inner conductor 4 Dielectrics 40 Metal Case 400 opening 401 Supply port 402 Outlet 5 Processing Room 50 Transport Conveyor 51 Loading Gate 52 Intake conveyor 53 Loading Gate 54 Discharge conveyor 55 Gas supply section 56 Pressure reducing section 57 Gas exhaust section V Decompression space

Claims

1. A plasma generating unit comprising a dielectric body into which a tip of an inner conductor of a coaxial tube that transmits microwaves output from a microwave output unit is inserted, the plasma generating unit generating plasma by the microwaves transmitted through the coaxial tube, the dielectric body is formed in a shape and size such that a standing wave is generated inside the dielectric body when microwaves having a predetermined wavelength output from the microwave output unit propagate therethrough, The generated standing wave generates plasma on the surface of the dielectric. A plasma generating unit characterized by:

2. 2. The plasma generating unit according to claim 1, The inner conductor is inserted so that its tip is positioned at a node of a standing wave generated in the dielectric. A plasma generating unit characterized by:

3. 3. The plasma generating unit according to claim 1 or 2, The dielectric has a rectangular parallelepiped shape, The inner conductor is inserted so as to be parallel to the shortest side of the dielectric. A plasma generating unit characterized by:

4. 4. The plasma generating unit according to claim 3, The dielectric body having a rectangular parallelepiped shape is The length of the long side and short side of the surface into which the tip of the inner conductor is inserted is N times (N is a natural number of 2 or more) the half wavelength of the microwave propagating inside. A plasma generating unit characterized by:

5. 5. The plasma generating unit according to claim 4, The dielectric material is The length of the inner conductor in the insertion direction is 17 to 19 mm and is formed using alumina or 30 to 32 mm and using quartz glass, The metal housing is a cooling surface that contacts the dielectric and cools the dielectric in contact therewith; A plasma generating unit characterized by:

6. 3. The plasma generating unit according to claim 1 or 2, The dielectric has a rectangular parallelepiped shape, The inner conductor is inserted so as to be parallel to the longest side of the dielectric. A plasma generating unit characterized by:

7. 3. The plasma generating unit according to claim 1 or 2, The dielectric is arranged in plurality with gaps between them. A plasma generating unit characterized by:

8. 3. The plasma generating unit according to claim 1 or 2, a metal housing that covers the dielectric and has a plurality of openings formed therein; A plasma generating unit characterized by:

9. A plasma generating unit according to claim 1, The plasma generating unit comprises: a metal housing that covers the dielectric and has an opening at one end; further comprising a processing chamber that accommodates the dielectric body covered with the metal housing; Microwaves are radiated from the opening of the metal housing into the processing chamber, the pressure of which has been reduced to 30 to 300 Pa, to generate surface wave plasma. A plasma processing apparatus characterized by:

10. A plasma generating unit according to claim 1, The plasma generating unit comprises: a metal housing that covers the dielectric and has an opening at one end; further comprising a processing chamber that accommodates the dielectric body covered with the metal housing; Microwaves are radiated from the opening of the metal housing into the processing chamber, which has been decompressed to 20 Pa or less, to generate volume wave plasma. A plasma processing apparatus characterized by:

11. The plasma processing apparatus according to claim 10, It is designed so that the minimum value of the voltage standing wave ratio seen from the inner conductor through which microwaves are introduced is 1.5 or less. A plasma processing apparatus characterized by:

12. A plasma generation method using a microwave output unit that outputs microwaves of a predetermined wavelength, a coaxial tube that transmits the microwaves output from the microwave output unit, and a dielectric body into which a tip of an inner conductor of the coaxial tube is inserted, in which plasma is generated by the microwaves transmitted through the coaxial tube, a microwave having a predetermined wavelength output from the microwave output unit propagates within the dielectric, generating a standing wave within the dielectric; The generated standing wave generates plasma on the surface of the dielectric. A plasma generation method comprising:

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