MARKED—UP SPEIFICATION
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`PLASMA TREATMENT DEVICE
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`[0001] Embodiments of the present disclosure relate to a plasma treatment device.
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`TECHNICAL FIELD
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`BACKGROUND
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`[0002] In the manufacture of a semiconductor device or the like, a plasma treatment is
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`performed on a workpiece by exposing the workpiece to plasma.
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`In such a plasma treatment,
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`from the viewpoint of reducing the processing time and reducing damage to the workpiece, it is
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`desirable to use plasma with high density and low electron temperature.
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`[0003] In order to generate plasma with high density and low electron temperature, there is a
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`method that uses a high-frequency wave in the very-high-frequency (VHF) band or the ultra-
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`high-frequency (UHF) band as electric power for plasma generation.
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`For example, Patent
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`Document 1 discloses a parallel plate-type plasma treatment device that generates plasma by
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`applying a high-frequency wave ranging from 20 MHz to 200 MHz to a cathode electrode that is
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`used as a lower electrode.
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`In addition, Patent Document 2 discloses a parallel plate-type plasma
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`treatment device that generates plasma by applying high-frequency power of 100 MHz to a
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`susceptor that is used as a lower electrode.
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`[Prior Art Documents]
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`[Patent Documents]
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`[0004] Patent Document 1: Japanese Unexamined Patent Application Publication No. 9-312268
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`Patent Document 2: Japanese Unexamined Patent Application Publication No. 2009-
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`021256
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`[0005] When high-frequency waves in the VHF band or the UHF band are applied to an
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`electrode, electromagnetic waves generated by the high-frequency waves propagate as surface
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`waves on the surface of the electrode. These surface waves interfere with each other to
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`generate a voltage intensity distribution on the surface of the electrode. This deteriorates the
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`uniformity of plasma density.
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`In particular, in a case where the plasma treatment device is
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`configured such that the surface waves propagate from the outer edge of the surface of a circular
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`electrode towards the center thereof, the surface waves interfere with each other in the vicinity of
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`the center of the surface of the electrode. Thus, the density of plasma generated radially inward
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`of the electrode surface is higher than the density of plasma generated radially outward of the
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`electrode surface.
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`In contrast, in the plasma treatment device disclosed in Patent Document 1,
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`in order to improve the uniformity of the plasma density, the distance between an upper
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`electrode and a lower electrode is reduced toward the outer edge by increasing the thickness of
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`the lower electrode toward the outer edge of the lower electrode.
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`[0006] However, in the device disclosed in Patent Document 1, the shape of the lower electrode
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`is fixed, which makes it difficult to flexibly control the density distribution of plasma according
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`to process conditions. Therefore, in this technical field, there is a demand for a plasma
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`treatment device capable of flexibly controlling the density distribution of plasma even when
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`high-frequency waves in the VHF band or the UHF band are used as high-frequency waves for
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`plasma generation.
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`SUMMARY
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`[0007] A plasma treatment device according to an aspect includes: a chamber body including a
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`chamber defined therein; a gas supply part configured to supply a processing gas into the
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`chamber; a stage disposed within the chamber; an upper electrode having a circular surface that
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`faces the stage via an internal space of the chamber; a conductor connected to the upper
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`electrode; a high-frequency power supply configured to generate a first high-frequency wave
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`having a frequency ranging from 100 MHz to 1,000 MHz, the high-frequency power supply
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`being coupled to the upper electrode via the conductor; a bias power supply configured to apply
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`a second high-frequency wave or a direct current (DC) bias We to the upper electrode, the
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`second high-frequency wave having a frequency lower than a frequency of the first high-
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`frequency wave; an annular insulating ring provided to extend along an outer edge of the circular
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`surface of the upper electrode; a waveguide through which electromagnetic wave generated
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`around the conductor based on the first high-frequency wave propagates, the waveguide being
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`connected to the annular insulating ring outside the upper electrode; and a controller configured
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`to control the second high-frequency wave or the DC bias We to be applied to the upper
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`electrode.
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`[0008] In the plasma treatment device according to one aspect, as the first high-frequency wave
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`are applied to the upper electrode through the conductor, the electromagnetic waves are
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`generated around the conductor. The electromagnetic waves pass through the waveguide and
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`the insulating ring and propagate along the annular surface of the upper electrode in the form of
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`surface waves directed towards the center of the upper electrode from the outer edge of the
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`annular surface of the upper electrode. The surface waves are gradually attenuated while
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`transmitting energy to plasma generated in the internal space of the chamber. The attenuation
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`coefficient of the surface waves depends on the thickness of a sheath formed between the plasma
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`and the annular surface of the upper electrode. The thickness of the sheath can be controlled by
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`the bias voltage applied to the upper electrode. For example, as the absolute value of a negative
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`bias voltage applied to the upper electrode increases, the thickness of the sheath is increased and
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`the attenuation coefficient of the surface waves is decreased.
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`In contrast, as the absolute value
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`of the negative bias voltage applied to the upper electrode decreases, the thickness of the sheath
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`is decreased and the attenuation coefficient of the surface waves is increased.
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`In the plasma
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`treatment device according to another aspect, by controlling the second high-frequency waves or
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`the DC bias We to be applied to the upper electrode by the control part, it is possible to
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`control the attenuation coefficient of the surface waves. Thus, it is possible to change, among
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`the surface waves that have been introduced from the outer edge of the upper electrode, a ratio of
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`energy of the surface waves reaching the center of the upper electrode in the radial direction.
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`Therefore, according to the plasma treatment device of an embodiment, it is possible to flexibly
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`control the density distribution of plasma in the radial direction.
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`[0009] In some embodiments, the chamber body may include a sidewall, and a choke part may
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`be provided in the sidewall. The choke part may be formed to extend in an annular shape
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`around a central axis of the chamber body and may be configured to suppress electromagnetic
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`waves propagating between the stage and the sidewall.
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`[0010] In some embodiments, m—the—pl—asma—treatment—deviee—aeeerdmg—te—Glmm—Z: the choke
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`part may include a first portion that extends in a radial direction of the chamber body and a
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`second portion that extends in a direction parallel to the central axis.
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`[0011] In some embodiments, a sum of a length of the first portion in the radial direction and a
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`length of the second portion in the direction parallel to the central axis may be set to a length that
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`is adapted to eliminate the electromagnetic waves propagating between the stage and the
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`sidewall.
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`[0012] In some embodiments, a plurality of sensors configured to detect parameters
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`corresponding to heat fluxes directed toward the upper electrode from the internal space may be
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`provided in the upper electrode. The plurality of sensors may be disposed at different positions
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`in the upper electrode in the radial direction, respectively, and the controller may be configured
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`to control the second high-frequency waves or the DC bias We based on detection results
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`obtained by the plurality of sensors.
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`[0013] In some embodiments, the upper electrode may include: a main body having a coolant
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`flow path formed therein; and a shower plate disposed under the main body and having the
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`annular surface, the shower plate having a plurality of gas discharge holes formed therein.
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`Each of the plurality of sensors may be configured to output an output signal corresponding to a
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`difference between a temperature of the main body and a temperature of the shower plate, and
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`the controller may be configured to control the second high-frequency waves or the DC bias
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`£ltage based on the output signal.
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`[0014] According to some embodiments of the present disclosure, it is possible to provide a
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`plasma treatment device capable of flexibly controlling the density distribution of plasma.
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`BRIEF DESCRIPTION OF DRAWINGS
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`[0015] FIG. 1 is a vertical cross-sectional view illustrating a plasma treatment device according
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`to an embodiment.
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`FIG. 2 is a view for explaining a propagation path of electromagnetic waves.
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`FIG. 3 is an enlarged view of a sensor.
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`FIG. 4 is a vertical cross-sectional view of a plasma treatment device according to
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`another embodiment.
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`FIG. 5 is a vertical cross-sectional view of a plasma treatment device according to
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`another embodiment.
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`FIG. 6 is a simulation result showing the relationship between the thickness of a sheath
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`and the distribution of electric field strength in the sheath.
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`FIG. 7 is a simulation result showing the relationship between the length of a choke part
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`and the intensity of transmitted waves.
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`DETAILED DESCRIPTION
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`[0016] Hereinafter, various embodiments of the present disclosure will be described in detail
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`with reference to the drawings. Throughout the drawings, the same or similar parts are denoted
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`by the same reference numerals and duplicate descriptions thereof will be omitted.
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`Further,
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`dimension ratios in the respective drawing do not necessarily coincide with actual dimension
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`ratios.
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`[0017] A plasma treatment device according to an embodiment will be described.
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`FIG. 1 is a
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`cross-sectional view schematically illustrating a plasma treatment device 10A according to an
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`embodiment. The plasma treatment device 10A includes a chamber body 12. The chamber
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`body 12 may be made of aluminum, and has an anodized surface. The chamber body 12
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`provides a chamber C defined therein. The chamber body 12 is grounded.
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`[0018] In an embodiment, the chamber body 12 may include a sidewall 12a, a bottom portion
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`12b, and a lid portion 12c. The sidewall 12a has a substantially cylindrical shape. A central
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`axis of the sidewall 12a coincides with a central axis Z of the chamber body 12. The bottom
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`portion 12b is connected to a lower end of the sidewall 12a. An exhaust port l2e is formed in
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`the bottom portion 12b. An exhaust device 14 such as a vacuum pump is connected to the
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`exhaust port l2e. The exhaust device 14 exhausts gas in the chamber body 12 such that an
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`internal pressure of the chamber body 12 becomes a predetermined pressure. The lid portion
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`12c is connected to an upper end of the sidewall 12a so as to close an opening formed in an
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`upper portion of the sidewall 12a.
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`[0019] A stage 20 is provided in a lower portion of the chamber C. A workpiece W is
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`supported on an upper surface of the stage 20.
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`[0020] The plasma treatment device 10A further includes an upper electrode 30. The upper
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`electrode 30 has a substantially disk shape. The upper electrode 30 is provided above the stage
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`20, and is arranged to face the stage 20 via an internal space S of the chamber C.
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`In an
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`embodiment, the upper electrode 30 may include a main body 32 and a shower plate 34.
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`[0021] The main body 32 has a substantially disk shape, and may be made of an aluminum alloy.
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`In an embodiment, a coolant flow path 32p may be formed inside the main body 32. A coolant
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`inlet pipe and a coolant outlet pipe are connected to the coolant flow path 32p. The coolant
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`inlet pipe and the coolant outlet pipe are connected to a chiller unit. Coolant is supplied from
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`the chiller unit to the coolant flow path 32p via the coolant inlet pipe and circulates so as to
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`return from the coolant flow path 32p to the chiller unit via the coolant outlet pipe. The upper
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`electrode 30 is configured to be controlled to have a predetermined temperature by circulating an
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`appropriate coolant such as cooling water or the like through the coolant flow path 32p.
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`[0022] The shower plate 34 is provided below the main body 32. The shower plate 34 has a
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`substantially shaped like a disk, and may be made of an aluminum alloy. A plurality of
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`through-holes 34h, namely a plurality of gas discharge holes are formed in the shower plate 34.
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`A surface 35 facing the upper surface of the stage 20 in the shower plate 34 is exposed in the
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`space S. The surface 35 includes an inner portion 35a and an outer portion 35b. The inner
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`portion 35a is a substantially circular region located above the stage 20. The outer portion 35b
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`is a region located outward of the stage 20 in the radial direction of the surface 35, and is an
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`annular region surrounding the outer side of the inner portion 35a. An outer edge 35c of the
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`surface 35 is positioned at the outermost periphery of the outer portion 35b.
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`[0023] A plurality of spacers 36 are provided between the shower plate 34 and the main body 32.
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`The shower plate 34 and the main body 32 are separated from each other in the direction of the
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`central axis Z via the plurality of spacers 36. A gas diffusion chamber 38 communicating with
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`the plurality of through-holes 34h is formed between the main body 32 and the shower plate 34.
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`The gas diffusion chamber 38 is connected to a gas supply part GS provided outside the chamber
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`body 12. The gas supply part GS includes a gas source, a flow rate controller, and a valve.
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`The gas source supplies a processing gas into the gas diffusion chamber 38 via the flow rate
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`controller and the valve. The processing gas supplied from the gas supply part GS to the gas
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`diffusion chamber 38 is supplied into the space S via the plurality of through-holes 34h.
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`[0024] An annular supporting portion 16 is formed in the upper portion of the sidewall 12a so as
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`to project radially inwards from the inner surface of the sidewall 12a. That is to say, an inner
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`diameter of a portion in which the supporting portion 16 of the sidewall 12a is formed is smaller
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`than that of a portion in which the supporting portion 16 is not formed. The supporting portion
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`16 may have an inclined surface l6t that is inclined so as to be oriented inward in the radial
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`direction as it goes upwards.
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`[0025] The plasma treatment device 10A further includes an insulating ring 40. The insulating
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`ring 40 is made of an insulator such as alumina. The insulating ring 40 is an annular body
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`extending around the central axis Z, and is supported on the supporting portion 16. The
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`insulating ring 40 extends along the outer edge 35c of the surface 35, and supports the upper
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`electrode 30 from below.
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`[0026] In an embodiment, the insulating ring 40 may have an inclined surface 40t that is inclined
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`so as to be oriented inward in the radial direction as it goes upwards. The inclined surface 40t
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`of the insulating ring 40 and the inclined surface l6t of the supporting portion 16 may have the
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`same inclination angle. The inclined surface 40t and the inclined surface l6t may be positioned
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`on the same straight line when viewed in the vertical cross section passing through the central
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`axis Z. O-rings are provided between the insulating ring 40 and the upper electrode 30 and
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`between the insulating ring 40 and the supporting portion 16, respectively. As a result, the
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`airtightness of the chamber C is secured.
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`[0027] The plasma treatment device 10A further includes a coaxial waveguide 42. The coaxial
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`waveguide 42 includes an inner conductor 42a and an outer conductor 42c. One end of the
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`inner conductor 42a is connected to the main body 32. The other end of the inner conductor
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`42a is connected to a high-frequency power supply 46 via a matcher 44. The high-frequency
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`power supply 46 is a power supply configured to generate first high-frequency waves for plasma
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`generation, which have a frequency ranging from 100 MHZ to 1000 MHZ. The first high-
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`frequency waves are applied to the upper electrode 30 via the matcher 44 and the inner
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`conductor 42a. The matcher 44 is configured to adjust a load impedance of the high-frequency
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`power supply 46.
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`[0028] The other end of the inner conductor 42a is also coupled to a bias power supply 48 via a
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`low-pass filter 47. The bias power supply 48 generates bias output waves that are supplied to
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`the upper electrode 30. The output waves generated by the bias power supply 48 are second
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`high-frequency waves having a frequency lower than that of the first high-frequency waves.
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`The second high-frequency waves are high-frequency waves having a positive or negative direct
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`current component, and may have a frequency of 500 kHz. The bias power supply 48 applies
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`the second high-frequency waves to the upper electrode 30 via the low-pass filter 47 and the
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`inner conductor 42a. That is to say, the second high-frequency waves are applied to the upper
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`electrode 30 while being superimposed on the first high-frequency waves. The bias power
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`supply 48 may apply a direct current (DC) bias We to the upper electrode 30 instead of the
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`second high-frequency waves.
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`[0029] Further, the outer conductor 42c of the coaxial waveguide 42 is connected to the lid
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`portion 12c. The inner conductor 42a and the outer conductor 42c constitute a portion of a
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`waveguide 42b to be described later.
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`[0030] The plasma treatment device 10 further includes the waveguide 42b. The waveguide
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`42b propagates electromagnetic waves generated around the inner conductor 42a to the space S
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`on the basis of the first high-frequency waves provided from the high-frequency power supply
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`46. The waveguide 42b may be made of an insulator. The waveguide 42b includes a first
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`portion 43a and a second portion 43b, which are continuous with each other. The first portion
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`43a extends between the inner conductor 42a and the outer conductor 42c. The second portion
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`43b extends between the upper electrode 30 and the lid portion 12c, and is connected to the
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`insulating ring 40 outside the upper electrode 30.
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`[0031] The plasma treatment device 10A further includes a control part 50. The control part 50
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`may include a computer device that may include a processor or a storage part. The control part
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`50 is connected to the bias power supply 48. The control part 50 sends a control signal to the
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`bias power supply 48 so as to control the bias voltage (second high-frequency waves or DC bias
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`voltage) provided from the bias power supply 48.
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`In addition to controlling the bias power
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`supply 48, the control part 50 may have a function of controlling each part of the plasma
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`treatment device 10A. For example, the control part 50 may supply control signals to the high-
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`frequency power supply 46, the exhaust device 14, and the gas supply part GS so as to control
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`the first high-frequency waves supplied to the upper electrode 30, the internal pressure of the
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`chamber body 12, and the type and flow rate of each gas supplied into the chamber body 12.
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`[0032] The function of the plasma treatment device 10A will be described with reference to FIG.
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`2. When the first high-frequency waves are applied from the high-frequency power supply 46
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`to the upper electrode 30, electromagnetic waves are generated around the inner conductor 42a.
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`The electromagnetic waves generated around the inner conductor 42a propagate towards the
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`insulating ring 40 while being reflected inside the waveguide 42b, as indicated by arrows in FIG.
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`2. The insulating ring 40 receives the electromagnetic waves propagated through the
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`waveguide 42b, and transmits the same to the space S. The electromagnetic waves transmitted
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`through the insulating ring 40 propagate as surface waves that are directed from the outer edge
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`35c of the surface 35 to the center of the surface 35 along a sheath formed between plasma
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`generated in the space S and the surface 35. That is to say, the surface waves propagate along
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`the surface 35 made of metal. As indicated by different lengths of arrows in FIG. 2, the surface
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`waves are gradually attenuated while transmitting energy to the plasma generated in the space S
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`as they go to the inner side of the surface 35 in the radial direction.
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`[0033] The attenuation coefficient of the surface waves depends on the thickness of the sheath.
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`The thickness of the sheath can be controlled by the bias voltage applied to the upper electrode
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`30. For example, the thickness of the sheath is increased as the absolute value of a negative
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`bias voltage applied to the upper electrode 30 increases. When the thickness of the sheath
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`increases, the attenuation coefficient of the surface waves decreases.
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`In contrast, the thickness
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`of the sheath is decreased as the absolute value of the negative bias voltage applied to the upper
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`electrode decreases. When the thickness of the sheath decreases, the attenuation coefficient of
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`the surface waves increases.
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`In the plasma treatment device 10A, the attenuation coefficient of
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`the surface waves may be changed by controlling the second high-frequency waves or the DC
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`bias We applied to the upper electrode 30 by the control part 50. Thus, it is possible to
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`change, among the surface waves that are being introduced from the outer edge 35c of the upper
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`electrode 30, a ratio of the energy of the surface waves reaching the center of the surface 35 in
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`the radial direction. As a result, the degree of interference of the surface waves can be adjusted,
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`which makes it possible to flexibly control the density distribution of the plasma in the radial
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`direction.
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`[0034] Referring to FIG. 1, the plasma treatment device 10A may further include a choke part 52.
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`The choke part 52 has a function of suppressing electromagnetic waves propagating between the
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`stage 20 and the sidewall 12a. That is to say, the choke part 52 suppresses generation of
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`unnecessary plasma between the stage 20 and the sidewall 12a. The choke part 52 may be
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`made of a material having high heat resistance, such as ceramics made of alumina, aluminum
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`nitride, or the like, or quartz, and has an annular shape centered at the central axis Z.
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`[0035] As illustrated in FIG. 1, the choke part 52 may include a first portion 52a extending along
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`the radial direction of the chamber body 12 and a second portion 52b extending along a direction
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`parallel to the central axis Z. The first portion 52a and the second portion 52b are continuous
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`with each other. The sum of a length of the first portion 52a of the choke part 52 in the radial
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`direction and a length of the second portion Q in the direction parallel to the central axis Z is
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`set to such a length as to remove the electromagnetic waves propagating between the stage 20
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`and the sidewall 12a.
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`Specifically, the sum of the length of the first portion 52a of the choke
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`part 52 in the radial direction and the length of the second portion 52b in the direction parallel to
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`the central axis Z is about 1/4 of the wavelength of the electromagnetic waves propagating inside
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`the choke part 52. By setting the length of the choke part 52 to about 1/4 of the wavelength of
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`the electromagnetic waves propagating inside the choke part 52, the impedance of the choke part
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`52 reaches an infinite value as viewed from the insulating ring 40. Thus, it is possible to
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`eliminate the electromagnetic waves propagating between the stage 20 and the sidewall 12a by
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`the choke part 52.
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`In some embodiments, in order to make a position of an end surface of the
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`choke part 52 coincide with a position of an electrical short-circuit surface, the length of the
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`choke part 52 may be designed to be slightly longer than 1/4 of the wavelength of the
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`electromagnetic waves propagating inside the choke part 52.
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`In some embodiments, the choke
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`part 52 may extend only in the radial direction, and the length of the choke part 52 in the radial
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`direction may be set to such a length as to eliminate the electromagnetic waves propagating
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`between the stage 20 and the sidewall 12a, namely about 1/4 of the wavelength of the
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`electromagnetic waves propagating inside the choke part 52.
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`In addition, an O-ring may be
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`provided between the choke part 52 and the sidewall 12a.
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`[0036] In an embodiment, the plasma treatment device 10A may further include a plurality of
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`sensors 60. The plurality of sensors 60 are provided at different positions in the radial direction
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`of the upper electrode 30.
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`In the embodiment illustrated in FIG. 1, two sensors 60a and 60b as
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`the plurality of sensors 60 are installed in the upper electrode 30. The sensor 60a is provided at
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`the center position of the upper electrode 30 in the radial direction, namely on the central axis Z.
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`The sensor 60b is provided radially outward of the sensor @ [[90a]]. The plurality of sensors
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`60 detect parameters corresponding to heat fluxes directed from the space S to the upper
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`electrode 30.
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`[0037] Ions and high-energy electrons in the plasma generated in the space S are incident on the
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`shower plate 34 and heat the shower plate 34. The heat fluxes generated when ions and
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`electrons are incident on the shower plate 34 are proportional to the density of the plasma
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`generated in the space S. Therefore, by detecting the distribution of the heat fluxes directed
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`from the space S to the upper electrode 30 using the plurality of sensors 60, it is possible to
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`estimate the density distribution of the plasma generated in the space S.
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`[0038] The plurality of sensors 60 acquire the parameters corresponding to the heat fluxes by
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`measuring a difference in temperature between the main body 32 and the shower plate 34.
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`Hereinafter, the plurality of sensors 60 will be described in detail with reference to FIG. 3.
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`3 is an enlarged cross-sectional view of the sensor 60b. The sensor 60a has the same
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`configuration as the sensor 60b.
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`[0039] Referring to FIG. 3, the sensor 60b includes a Peltier element 62. The Peltier element
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`62 includes a first electrode 62a and a second electrode 62b, and outputs a voltage corresponding
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`to a difference in temperature between the first electrode 62a and the second electrode 62b due to
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`the Seebeck effect. The first electrode 62a is in contact with the shower plate 34 via a metal
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`pipe 64. The metal pipe 64 may be made of a metal such as stainless steel. Therefore, the first
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`electrode 62a is thermally connected to the shower plate 34, and is electrically connected to the
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`shower plate 34 and the main body 32.
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`In order to obtain the temperature of the surface 35
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`more accurately, as illustrated in FIG. 3, the metal pipe 64 may be in contact with the shower
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`plate 34 at a position lower than a height position of the upper surface of the shower plate 34,
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`namely at a position close to the surface 35.
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`Further, an O-ring may be provided between an
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`upper portion of the metal pipe 64 and the main body 32.
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`[0040] The second electrode 62b is in contact with the main body 32 via an insulating pipe 66.
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`The insulating pipe 66 is made of an insulating material having high thermal conductivity, such
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`as aluminum nitride. Therefore, the second electrode 62b is thermally connected to the main
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`body 32, but is electrically insulated from the main body 32. A filling material 68 made of an
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`insulator having low thermal conductivity, such as epoxy resin, is filled between the metal pipe
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`64 and the insulating pipe 66. Thus, the metal pipe 64 and the insulating pipe 66 are
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`electrically and thermally insulated from each other.
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`[0041] Further, a metal rod 70 is connected to the second electrode 62b. The metal rod 70 is
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`made of a metal having high thermal conductivity, such as copper.
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`In an embodiment, a
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`concave portion is formed in a portion of the upper surface of the main body 32. The concave
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`portion may define a housing space HS that accommodates a portion of the plurality of sensors
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`60 and a voltage measurement circuit 78 (to be described later). The metal rod 70 extends to
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`the housing space HS through a through-hole TH formed in the main body 32. An upper
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`portion of the metal rod 70 is fastened to the main body 32 by a nut 74. An insulating washer
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`72 is provided between the nut 74 and the upper surface of the main body 32. The insulating
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`washer 72 is made of an insulator such as aluminum nitride. A crimping terminal 76 is
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`provided between the insulating washer 72 and the nut 74. The crimping terminal 76 is
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`electrically coupled to the second electrode 62b via the metal rod 70, but is electrically insulated
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`from the main body 32.
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`[0042] As illustrated in FIG. 1, the voltage measurement circuit 78 may be provided in the
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`housing space HS. The voltage measurement circuit 78 is electrically coupled to the crimping
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`terminal 76 of each of the plurality of sensors 60 via a wire 77. The voltage measurement
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`circuit 78 measures a voltage between the wire 77 and the main body 32, namely an output
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`voltage of the Peltier element 62. The voltage measurement circuit 78 sends an output signal
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`corresponding to an output voltage from each of the plurality of sensors 60 to the control part 50.
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`[0043] The control part 50 controls the bias power supply 48 on the basis of the output signal
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`from the voltage measurement circuit 78. For example, when the output voltage from the
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`sensor 60a is higher than that from the sensor 60b, the control part 50 estimates that the density
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`of plasma generated radially inward of the space S is higher than the density of plasma generated
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`radially outward of the space S. Therefore, in an exemplary embodiment, the control part 50
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`controls the bias power supply 48 such that the absolute value of the negative bias voltage to be
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`applied to the upper electrode 30 from the bias power supply 48 becomes smaller. Thus, the
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`sheath becomes thinner and the attenuation coefficient of the surface waves increases.
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`Therefore, among the surface waves supplied from the outer edge 35c of the surface 35, the ratio
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`of energy of the surface waves reaching the center position of the surface 35 in the radial
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`direction becomes smaller. As a result, the density of the plasma generated radially inward of
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`the space S is decreased, thus improving the in-plane uniformity of plasma.
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`In contrast, when
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`the output voltage from the sensor 60a is lower than that from the sensor 60b, the control part 50
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`estimates that the density of plasma generated radially inward of the space S is lower than the
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`density of plasma generated radially outward of the space S. Therefore, in this case, the control
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`part 50 controls the bias power supply 48 such that the absolute value of the negative bias
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`voltage to be applied to the upper electrode 30 from the bias power supply 48 becomes larger.
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`As a result, the sheath becomes thicker and the attenuation coefficient of the surface waves is
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`13
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`MARKED—UP SPEIFICATION
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`decreased. Therefore, among the surface waves supplied from the outer edge 35c of the surface
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`35, the ratio of energy of the surface waves reaching the center position of the surface 35 in the
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`radial direction becomes larger. As a result, the density of plasma generated radially inward of
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`the space S is increased, thus improving the in-plane uniformity of plasma density.
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`[0044] Next, a plasma treatment device according to another embodiment will be described. A
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`plasma treatment device 10B illustrated in FIG. 4 includes a plurality of sensors 80 that are
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`different from the plurality of sensors 60. Hereinafter, the plasma treatment device 10B will be
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`described with a focus on the differences from the plasma treatment device 10A illustrated in
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`FIG. 1, and redundant descriptions thereof will be omitted.
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`[0045] The plurality of sensors 80 is provided at different positions in the radial direction of the
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`upper electrode 30, respectively.
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`In the embodiment illustrated in FIG. 4, two sensors 80a and
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`80b as the plurality of sensors 80 are provided in the upper electrode 30. The sensor 80a is
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`provided at the center position of the upper electrode 30 in the radial direction, namely on the
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`central axis Z. The sensor 80b is provided radially outward of the sensor 80a. Each of the
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`sensor 80a and the sensor 80b includes a thermocouple 82 and a voltage measurement circuit 84.
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`The thermocouple 82 ha