JP6576712B2 - Microwave plasma generator - Google Patents

Description

  The present invention relates to a microwave plasma generation apparatus that generates plasma using microwaves.

  Surface wave plasma using microwaves has the advantage of being able to generate high-density plasma in a wide space area, so it can be used for various purposes such as cleaning, modification, and film formation on the surface of resin parts, resin films, and semiconductors. Used for processing. For example, as described in Patent Documents 1 and 2, a conventional microwave plasma generation apparatus includes a waveguide, a slot antenna, and a dielectric plate. The slot antenna is disposed in the opening of the waveguide. A plurality of slots are formed in the slot antenna. The dielectric plate is stacked on the slot antenna. The microwave transmitted by the waveguide passes through the slot of the slot antenna, enters the dielectric plate, and propagates on the surface of the dielectric plate. Microwave plasma is generated by ionizing the gas in the vacuum chamber by the strong electric field of the propagating microwave.

  In order to suppress the mixing of impurities and increase the purity of the treatment, it is desirable to perform the microwave plasma treatment as low pressure as possible. However, according to the conventional microwave plasma generation apparatus, it is difficult to generate a stable microwave plasma under a low pressure, and the processing pressure can be reduced only to about 5 Pa. In addition, the dielectric plate plays a role of generating plasma by propagating microwaves on the surface. However, since the dielectric plate is exposed in the vacuum vessel, when the film is formed by plasma CVD (Chemical Vapor Deposition) or the like, the components of the film are likely to adhere to the surface of the dielectric plate. Thereby, a plasma density will fall. In addition, the attached film components may generate heat due to the propagated microwave, and the dielectric plate may break.

JP 2009-224269 A JP-A-2005-197371 International Publication No. 2014/103604 JP 2009-146837 A

  In order to solve the above-mentioned problem, the present inventor has developed a microwave plasma generation apparatus in which a dielectric plate is not exposed in a vacuum vessel (see Patent Document 3). FIG. 5 shows the configuration of the microwave plasma generation apparatus described in Patent Document 3. As shown in FIG. 5, the microwave plasma generation device 9 includes a first waveguide 90, a third waveguide 91, and a second waveguide 92 in order from the right. The first waveguide 90, the third waveguide 91, and the second waveguide 92 are all made of aluminum. The third waveguide 91 is disposed between the first waveguide 90 and the second waveguide 92. The third waveguide 91 is filled with a third dielectric 910 made of quartz as shown by a dotted line in FIG. The second waveguide 92 has a slot antenna 920. The slot antenna 920 is disposed as the front wall of the second waveguide 92. The slot antenna 920 is formed with a slot 921 penetrating in the front-rear direction. The second waveguide 92 is filled with a second dielectric 922 made of alumina, as shown by a one-dot chain line in FIG.

  As indicated by arrows in FIG. 5, the microwave propagates in the order of the first waveguide 90, the third waveguide 91, and the second waveguide 92. The microwave propagating through the second waveguide 92 passes through the slot 921 of the slot antenna 920 and propagates through the front surface of the slot antenna 920. At this time, the gas in the vacuum vessel is ionized by the strong electric field of the microwave, and microwave plasma is generated in front of the slot antenna 920.

  In the microwave plasma generation apparatus 9, the second dielectric 92 having a refractive index larger than that of air is filled in the second waveguide 92. Thereby, the wavelength of the microwave propagating through the second waveguide 92 becomes shorter than the wavelength when propagating through the air, and the portion where the electric field strength increases in the second waveguide 92 increases. Therefore, more slots 921 can be formed in the slot antenna 920 than in the prior art. This increases the electric field strength on the front surface of the slot antenna 920, so that it is easier to generate microwave plasma under a lower pressure than in the past.

  Further, according to the microwave plasma generation apparatus 9 shown in FIG. 5, it is not necessary to dispose a dielectric plate on the front side of the slot antenna 920. In other words, the microwave plasma generation apparatus 9 does not have a dielectric plate exposed in the vacuum vessel. For this reason, even if it uses for a film-forming process, the problem that the component of a film adheres to the surface of a dielectric plate does not arise.

  However, the microwave plasma generator shown in FIG. 5 is not sufficient in that microwave plasma can be stably generated at a lower pressure. Specifically, when generating plasma under a low pressure of about several Pa, it was necessary to first generate the plasma at about several tens to 100 Pa and then reduce the pressure to the target low pressure. .

  This invention is made | formed in view of such a situation, and makes it a subject to provide the microwave plasma production | generation apparatus which can produce | generate the stable microwave plasma also under low pressure.

  (1) In order to solve the above-described problem, a microwave plasma generation apparatus of the present invention is a microwave plasma generation apparatus that generates microwave plasma by ionizing a gas in a vacuum vessel, and is a first apparatus that transmits microwaves. A waveguide, a tube wall portion made of a magnetic material, a slot antenna formed with a plurality of slots through which the microwave propagating through the tube passes, and at least the tube inside the tube A second dielectric disposed so as to cover the slot, and extending in one direction; and a surface on the plasma generation side of the slot antenna disposed outside the second waveguide A magnet for forming a magnetic field in which electron cyclotron resonance is generated at the slot position, and is interposed between the first waveguide and the second waveguide, and the second waveguide is disposed inside the tube. Refractive than dielectric Characterized in that it and a third waveguide having a small third dielectric.

  In the microwave plasma generation apparatus of the present invention, the second dielectric is disposed inside the second waveguide. Thereby, the wavelength of the microwave propagating in the second waveguide is shorter than the wavelength when propagating in the air. As described above, when the wavelength of the microwave is shortened, the portion where the electric field strength increases in the second waveguide increases. For this reason, many slots can be formed in the slot antenna. When the slot interval is reduced and a large number of slots are formed, the electric field strength per unit area of the slot antenna increases. Further, when the slots are formed densely, the microwaves passing through the adjacent slots complement each other, so that the electric field strength of the entire surface of the slot antenna can be increased.

  Usually, when microwaves are propagated to media having different refractive indexes, the microwaves are reflected at the boundaries of the media. In this regard, in the microwave plasma generation apparatus of the present invention, the third waveguide is interposed between the first waveguide and the second waveguide. The refractive index of the third dielectric in the third waveguide is smaller than the refractive index of the second dielectric in the second waveguide. Therefore, the microwave transmitted from the first waveguide is transmitted to the second waveguide after the wavelength is once converted in the third waveguide. By performing wavelength conversion in two steps (or more), compared to the case where microwaves are directly transmitted from the first waveguide to the second waveguide, the wavelength is incident on the second waveguide. Microwave reflection can be suppressed. Thereby, it can suppress that the energy of a microwave falls. For example, when there is no filler in the first waveguide and microwaves are transmitted through the air, the third dielectric has a refractive index greater than the refractive index of air and the second dielectric is refracted. What is smaller than the rate may be adopted.

  As described above, in the microwave plasma generation apparatus of the present invention, since the electric field strength on the surface of the slot antenna can be increased, even when the second waveguide is elongated, it is substantially uniform in the longitudinal direction. Microwave radiation is possible. Further, the second waveguide can be reduced in size by reducing the cross-sectional area in the short direction of the second waveguide. In this case, interference with other members and apparatuses necessary for reforming and film formation is suppressed. Therefore, for example, the microwave plasma generation apparatus of the present invention can be easily incorporated into a processing apparatus that includes a device for supplying and transporting a member to be processed and continuously performs a reforming process and a film forming process.

In addition, the plasma generation unit of the microwave plasma generation apparatus of the present invention has a magnet outside the second waveguide. Thereby, a magnetic field is formed at the slot position on the surface of the slot antenna on the plasma generation side, and ECR plasma can be generated while generating electron cyclotron resonance (ECR). Electrons in the microwave plasma perform a clockwise turning motion with respect to the direction of the magnetic field in accordance with the cyclotron angular frequency _ωce . On the other hand, the microwave propagating in the microwave plasma excites a clockwise circular polarization called an electron cyclotron wave. When the electron cyclotron wave propagates forward and its angular frequency ω matches the cyclotron angular frequency ω _ce , the electron cyclotron wave is attenuated and wave energy is absorbed by the electrons. That is, ECR occurs.

In order to generate ECR, the microwave frequency f [MHz] and the magnetic flux density B [mT] at the slot position must satisfy the following equation (i).
ω _ce = 2πf = eB / m _e (i)
[In formula (i), e is an elementary charge, and _me is the mass of an electron. ]
When formula (i) is expanded, B = f / 28. For example, when the microwave frequency is 2.45 GHz, a magnetic flux density of 87.5 mT is required at the slot position. When the microwave frequency is 915 MHz, a magnetic flux density of 32.7 mT is required at the slot position.

  Electrons whose energy has been increased by ECR collide with surrounding neutral particles while being restrained by the lines of magnetic force. Thereby, neutral particles are ionized one after another. Electrons generated by ionization are also accelerated by ECR and further ionize neutral particles. In this way, a high density ECR plasma is generated.

  Thus, according to the microwave plasma generation apparatus of the present invention, stable plasma can be obtained even under a low pressure of 1 Pa or less, and even under a very low pressure of 0.5 Pa or less by increasing the plasma density using ECR. Can be generated. In addition, it is not necessary to generate plasma at several tens to 100 Pa in advance, and plasma can be generated in a state where the inside of the vacuum vessel is at a desired low pressure. Therefore, according to the microwave plasma generation apparatus of the present invention, high-purity processing can be performed by reducing the pressure in the vacuum vessel.

  Incidentally, if a magnet is disposed in the vicinity of the waveguide, the electromagnetic field inside the waveguide may be disturbed. For example, Patent Document 4 describes a microwave plasma processing apparatus including permanent magnets 25a to 25d. Among these, the permanent magnets 25a and 25b are disposed along the longitudinal direction of the waveguide 15a with the waveguide 15a interposed therebetween. The magnetic poles of the permanent magnets 25a and 25b are unknown, but the material of the waveguide 15a is an aluminum alloy (paragraph [0028] in Patent Document 4). For this reason, it is considered that the magnetic fields of the permanent magnets 25a and 25b act on the inside of the waveguide 15a, change the electromagnetic field in the waveguide 15a, and affect the propagation of microwaves.

  On the other hand, according to the microwave plasma generation apparatus of the present invention, the wall portion (tube wall portion) of the second waveguide is formed of a magnetic material. By forming a magnetic circuit with the magnet and the wall portion of the second waveguide, it is possible to suppress the magnetic lines of force from entering the inside of the second waveguide and to increase the magnetic field on the surface of the slot antenna. .

  (2) Preferably, in the configuration of (1) above, the inside of the tube of the second waveguide and the inside of the tube of the third waveguide are in a vacuum.

  For example, when only the inside of the tube of the second waveguide is evacuated, the second waveguide such as a vacuum seal between the slot antenna and the second dielectric, a vacuum seal between the slot antenna and the tube wall, etc. It is necessary to vacuum seal the members constituting the. Furthermore, a vacuum seal between the second waveguide and the third waveguide is required. However, it is complicated to perform vacuum sealing for each member, and vacuum sealing may be difficult in terms of dimensions. Moreover, since the second waveguide is at a high temperature, it is necessary to take measures against heat of the vacuum seal. In this regard, according to the present configuration, by making the inside of the second waveguide tube and the third waveguide tube all vacuum, it is not necessary to perform vacuum sealing for each member, and heat countermeasures for the vacuum seal Is also unnecessary.

  (3) Preferably, in the configuration of the above (1) or (2), the pressure of the gas in the vacuum vessel may be 0.05 Pa or more and 20 Pa or less.

  According to this structure, since the inside of a vacuum vessel will be in a high vacuum state, mixing of an impurity will be suppressed and the purity of a process can be raised. Moreover, the generated microwave plasma can be expanded.

  (4) Preferably, in any one of the constitutions (1) to (3), the second dielectric is a kind selected from quartz, alumina, zirconia, aluminum nitride, and magnesium oxide.

  Quartz, alumina, zirconia, aluminum nitride, and magnesium oxide are difficult to absorb microwaves. In other words, it is preferable because there is little loss of the microwave that becomes the plasma source.

  Further, it is sufficient that the third dielectric has a refractive index smaller than that of the second dielectric. For this reason, the third dielectric may be appropriately selected in consideration of the combination with the second dielectric. For example, when quartz is used as the second dielectric, polytetrafluoroethylene or the like may be used as the third dielectric. When alumina is used as the second dielectric, quartz or the like may be used as the third dielectric.

  (5) Preferably, in any one of the configurations (1) to (4), a cross section in a short direction of the second waveguide has a rectangular shape, and the slot antenna has an H of the second waveguide. It is good to have a configuration arranged on the surface.

  (6) Preferably, in any one of the configurations (1) to (5), the first waveguide is an upstream first waveguide disposed upstream of the second waveguide. A downstream first waveguide disposed on the downstream side, and the upstream first waveguide and the downstream first waveguide are symmetrical with respect to the second waveguide. It is preferable that the third waveguide is disposed between the at least one upstream first waveguide and the second waveguide.

  The microwave plasma generation apparatus of the present invention may have a configuration in which the downstream second waveguide is not disposed as the first waveguide, that is, only the upstream first waveguide is disposed. However, the tube length can be adjusted by connecting the waveguide also to the downstream side of the second waveguide and disposing a terminal adjusting member such as a plunger there as in this configuration. Here, the upstream first waveguide and the downstream first waveguide are arranged in a symmetrical L shape with the second waveguide interposed therebetween. For this reason, the microwave plasma generator can be attached to the vacuum vessel by passing the first waveguide (the upstream first waveguide and the downstream first waveguide) through one partition of the vacuum vessel. . Thereby, compared with the form which arrange | positions an upstream 1st waveguide, a plasma production | generation part, and a downstream 1st waveguide linearly, attachment becomes easy and can attain space saving. In addition, if the upstream first waveguide, the downstream first waveguide, the plasma generator, the third waveguide, and the partition are unitized, the microwave plasma generator can be easily used in various processing devices. Can be incorporated.

  (7) Preferably, in the configuration of (6), the downstream first waveguide may have a termination adjusting member that changes a termination position.

  According to this configuration, the electric field strength at the slot position can be adjusted by extending and contracting the tube length by the terminal adjusting member. Thereby, the microwave easily propagates from the slot, and stable plasma can be generated.

It is sectional drawing which looked at the microwave plasma processing apparatus provided with the microwave plasma generation apparatus of 1st embodiment from upper direction. It is a front view of the same microwave plasma generator. It is III-III sectional drawing of FIG. It is a left view of the microwave plasma generation apparatus of 2nd embodiment. It is a perspective view of the conventional microwave plasma generator. It is a graph which shows the measurement result of the electron density with respect to the output of a microwave.

  Hereinafter, embodiments of the microwave plasma generation apparatus of the present invention will be described.

<First embodiment>
[Configuration of microwave plasma generator]
First, the configuration of the microwave plasma generation apparatus of this embodiment will be described. FIG. 1 shows a cross-sectional view of a microwave plasma processing apparatus provided with the microwave plasma generation apparatus of the present embodiment as viewed from above. FIG. 2 shows a front view of the microwave plasma generation apparatus. FIG. 3 is a cross-sectional view taken along the line III-III in FIG. As shown in FIGS. 1 to 3, the microwave plasma processing apparatus 8 includes a vacuum vessel 80 and a microwave plasma generation apparatus 1.

  The vacuum vessel 80 is made of aluminum steel and has a rectangular parallelepiped box shape. Two waveguide insertion holes 81U and 81D are formed in the partition wall 83 on the rear side of the vacuum vessel 80. The upstream first waveguide 10U of the microwave plasma generation apparatus 1 is inserted into the waveguide insertion hole 81U. The downstream first waveguide 10D of the microwave plasma generating apparatus 1 is inserted into the waveguide insertion hole 81D. A gas supply hole 82 is formed in the right wall of the vacuum vessel 80. A gas supply pipe for supplying gas to the inside of the vacuum vessel 80 is connected to the gas supply hole 82. An exhaust hole (not shown) is formed in the lower wall of the vacuum vessel 80. A vacuum exhaust device for discharging the gas inside the vacuum vessel 80 is connected to the exhaust hole.

  The microwave plasma generation apparatus 1 includes an upstream first waveguide 10U, a downstream first waveguide 10D, a plasma generation unit 20, an upstream third waveguide 30U, and a downstream third waveguide. A tube 30D.

  The upstream first waveguide 10U is made of aluminum and has a tubular shape with a rectangular cross section. The upstream first waveguide 10U has an L shape when viewed from above. The upstream end of the upstream first waveguide 10U is connected to a microwave transmission unit (not shown). The microwave transmission unit includes a microwave power source, a microwave oscillator, an isolator, a power monitor, and an EH matching device. The downstream end of the upstream first waveguide 10U is connected to the upstream third waveguide 30U.

  The downstream first waveguide 10D is made of aluminum and has a tubular shape with a rectangular cross section. The downstream first waveguide 10D has an L shape (inverted L shape) symmetrical to the upstream first waveguide 10U with the plasma generation unit 20 in between when viewed from above. The upstream end of the downstream first waveguide 10D is connected to the downstream third waveguide 30D. A plunger 11 is disposed on the downstream side of the downstream first waveguide 10D. The plunger 11 is movable in the front-rear direction, and the front surface of the plunger 11 forms the end of the downstream first waveguide 10D. The plunger 11 is included in the concept of the termination adjusting member of the present invention.

  The plasma generation unit 20 is disposed in the vacuum vessel 80 and includes a main body unit 21 and a pair of magnet units 22a and 22b. The main body 21 has a housing 40, a second waveguide 41, and three cooling plates 42. The housing 40 is made of iron plated with Ni and has a rectangular parallelepiped shape. The housing 40 has a recess 400. The recess 400 has a C-shaped cross section and extends in the left-right direction. The three cooling plates 42 are each made of stainless steel and extend in the left-right direction. The three cooling plates 42 are arranged one on each of the upper, lower and rear sides of the recess 400.

  The second waveguide 41 is disposed in the recess 400 and extends linearly in the left-right direction. The second waveguide 41 has a tube wall portion 43, a slot antenna 44, and a second dielectric 45. The tube wall portion 43 is made of iron plated with Ni. The slot antenna 44 is made of iron and has a rectangular plate shape. The slot antenna 44 is disposed on the H surface of the second waveguide 41. The slot antenna 44 forms the front wall of the second waveguide 41. The slot antenna 44 has a plurality of slots 440 penetrating in the front-rear direction. The plurality of slots 440 each have a long hole shape extending in the left-right direction, and are arranged in two upper and lower rows. The slot 440 is arranged corresponding to the antinode position of the standing wave of the microwave. A space having a rectangular cross section is formed by the tube wall portion 43 and the slot antenna 44. The second dielectric 45 is filled in the space. The second dielectric 45 is made of alumina and has a rectangular parallelepiped shape. The second dielectric 45 covers the slot 440 from the rear.

  The pair of magnet portions 22 a and 22 b are arranged one above the other on the front surface of the main body portion 21 so as to sandwich the slot antenna 44. The upper magnet portion 22a extends linearly in the left-right direction. The magnet part 22a has a permanent magnet 50a and two cooling pipes 51a and 52a. The permanent magnet 50a is composed of ten permanent magnets connected linearly in the left-right direction. Each of the ten permanent magnets is a samarium cobalt magnet and has a rectangular parallelepiped shape. The ten permanent magnets have N poles on the lower side and S poles on the upper side. The NS direction of the permanent magnet 50 a is parallel to the front surface of the slot antenna 44. The lower surface of the permanent magnet 50a is covered with an aluminum cover member 53a. The cooling pipes 51a and 52a are arranged so as to sandwich the permanent magnet 50a in the front-rear direction. The cooling liquid flows in the cooling pipes 51a and 52a. The configuration of the lower magnet portion 22b is the same as the configuration of the magnet portion 22a. That is, the magnet portion 22b extends linearly in the left-right direction, and includes a permanent magnet 50b and two cooling pipes 51b and 52b. The permanent magnet 50b is composed of ten permanent magnets connected linearly. The ten permanent magnets have N poles on the upper side and S poles on the lower side. The NS direction of the permanent magnet 50 b is parallel to the front surface of the slot antenna 44. The upper surface of the permanent magnet 50b is covered with an aluminum cover member 53b. The cooling pipes 51b and 52b are arranged so as to sandwich the permanent magnet 50b in the front-rear direction. The cooling liquid flows in the cooling pipes 51a and 52b.

  A magnetic field is formed on the front surface (the surface on the plasma generation side) of the slot antenna 44 by the permanent magnets 50a and 50b. At the position of the slot 440, the magnetic flux density at a point spaced 10 mm forward from the front surface of the slot antenna 44 is 87.5 mT.

  The upstream third waveguide 30U is made of aluminum and has a short tubular shape with a rectangular cross section. The upstream third waveguide 30 </ b> U is disposed between the upstream first waveguide 10 </ b> U and the plasma generation unit 20. The upstream end of the upstream third waveguide 30U is connected to the downstream end of the upstream first waveguide 10U. The downstream end of the upstream third waveguide 30 </ b> U is connected to the upstream end of the second waveguide 41. The third dielectric 31 is filled in the upstream third waveguide 30U. The third dielectric 31 is made of quartz and has a rectangular parallelepiped shape. The right end of the third dielectric 31 is in contact with the second dielectric 45. The refractive index of the third dielectric 31 (quartz) is an intermediate value between the refractive index of the inside (air) of the upstream first waveguide 10U and the refractive index of the second dielectric 45 (alumina).

  The downstream third waveguide 30D is made of aluminum and has a short tubular shape with a rectangular cross section. The downstream third waveguide 30 </ b> D is disposed between the downstream first waveguide 10 </ b> D and the plasma generation unit 20. The upstream end of the downstream third waveguide 30 </ b> D is connected to the downstream end of the second waveguide 41. The downstream end of the downstream third waveguide 30D is connected to the upstream end of the downstream first waveguide 10D. The configuration of the downstream third waveguide 30D is the same as the configuration of the upstream third waveguide 30U. That is, the third dielectric 31 is filled in the downstream third waveguide 30D. The left end of the third dielectric 31 is in contact with the second dielectric 45. As shown in FIGS. 1 and 2, the inside of the tube in the section V from the upstream third waveguide 30U to the downstream third waveguide 30D is evacuated. Seal members (not shown) are arranged at the upstream end of the upstream third waveguide 30U and the downstream end of the downstream third waveguide 30D.

[Operation of microwave plasma generator]
Next, the operation of the microwave plasma generation apparatus 1 will be described. First, the vacuum evacuation device is operated, the gas inside the vacuum vessel 80 is discharged, and the inside of the vacuum vessel 80 is brought into a reduced pressure state. Next, a predetermined gas is supplied into the vacuum container 80 from the gas supply pipe, and the pressure in the vacuum container 80 is set to a predetermined pressure. Subsequently, the microwave power source of the microwave transmission unit is turned on, and a microwave having a frequency of 2.45 GHz is oscillated from the microwave oscillator. The oscillated microwave propagates in the upstream third waveguide 30U through the upstream first waveguide 10U as shown by the white arrow in FIG. The third dielectric 31 made of quartz is filled in the upstream third waveguide 30U. For this reason, the wavelength of the microwave is converted and shortened in the upstream third waveguide 30U. Subsequently, the microwave propagates in the second waveguide 41 of the plasma generation unit 20. The second waveguide 41 is filled with a second dielectric 45 made of alumina. For this reason, the wavelength of the microwave is further shortened in the second waveguide 41. The microwaves that have passed through the second waveguide 41 propagate to the downstream first waveguide 10D through the downstream third waveguide 30D.

  In the second waveguide 41, the microwave propagates through the slot 440 of the slot antenna 44 and propagates through the front surface of the slot antenna 44. Due to this strong microwave electric field, the gas in the vacuum chamber 80 is ionized, and microwave plasma is generated in front of the slot antenna 44. Electrons in the generated microwave plasma perform a clockwise turning motion with respect to the direction of the magnetic field lines according to the cyclotron angular frequency. On the other hand, the microwave propagating through the microwave plasma excites the electron cyclotron wave. The angular frequency of the electron cyclotron wave is a magnetic flux density of 87.5 mT and matches the cyclotron angular frequency. This causes ECR. Electrons whose energy has been increased by ECR collide with surrounding neutral particles while being restrained by the lines of magnetic force. Thereby, neutral particles are ionized one after another. Electrons generated by ionization are also accelerated by ECR and further ionize neutral particles. In this way, ECR plasma P is generated in front of the slot antenna 44. As a result, the workpiece (not shown) that has been previously disposed in front of the slot antenna 44 is processed.

[Function and effect]
Next, the effect of the microwave plasma generation apparatus of this embodiment is demonstrated. In the microwave plasma generating apparatus 1, a second dielectric 45 is disposed inside the second waveguide 41. Thereby, the wavelength of the microwave propagating in the second waveguide 41 is shorter than the wavelength when propagating in the upstream first waveguide 10U. As a result, a large number of slots 440 can be formed in the slot antenna 44, so that the electric field strength of the entire front surface of the slot antenna 44 increases. An upstream third waveguide 30U is interposed between the upstream first waveguide 10U and the second waveguide 41. The refractive index of the third dielectric 31 in the upstream third waveguide 30U is smaller than the refractive index of the second dielectric 45. Therefore, the microwave transmitted from the upstream first waveguide 10U is transmitted to the second waveguide 41 after the wavelength is once converted in the upstream third waveguide 30U. By performing wavelength conversion in two stages, compared to the case where microwaves are directly transmitted from the upstream first waveguide 10U to the second waveguide 41, the wavelength is changed when entering the second waveguide 41. Microwave reflection can be suppressed. Thereby, it can suppress that the energy of a microwave falls.

  As described above, in the microwave plasma generating apparatus 1, since the electric field strength on the front surface of the slot antenna 44 is large, the long second waveguide 41 can radiate a substantially uniform microwave in the longitudinal direction. it can. Further, the second waveguide 41 can be reduced in size by reducing the cross-sectional area of the second waveguide 41 in the short direction. That is, the plasma generation unit 20 can be reduced in size. In this case, interference with other members and apparatuses necessary for reforming and film formation is suppressed. Therefore, for example, the microwave plasma generation apparatus 1 can be easily incorporated into a processing apparatus that includes a device that supplies and conveys a member to be processed and continuously performs a reforming process and a film forming process.

  The plasma generation unit 20 has a pair of permanent magnets 50 a and 50 b arranged with the slot antenna 44 interposed therebetween. As a result, a magnetic field is formed on the front surface of the slot antenna 44, and the ECR plasma P can be generated. For this reason, according to the microwave plasma generator 1, the stable ECR plasma P can be generated even under a low pressure of 1 Pa or less, and even under an extremely low pressure of 0.5 Pa or less. In addition, it is not necessary to generate plasma at several tens to 100 Pa in advance, and ECR plasma P can be generated in a state where the inside of the vacuum vessel 80 is at a desired low pressure. Therefore, according to the microwave plasma generation apparatus 1, the pressure in the vacuum vessel 80 can be lowered and high-purity processing can be performed.

  The tube wall 43 of the second waveguide 41 is made of iron with Ni plating, and the slot antenna 44 is made of iron. That is, both the tube wall portion 43 and the slot antenna 44 are made of a magnetic material. Therefore, as indicated by a dotted arrow in FIG. 3, a magnetic circuit is formed by the permanent magnet 50a-slot antenna 44-tube wall portion 43 and permanent magnet 50b-slot antenna 44-tube wall portion 43. Thereby, it is possible to suppress the magnetic lines of force from entering the second waveguide 41 and to increase the magnetic field in front of the slot antenna 44. Further, the pair of permanent magnets 50 a and 50 b are arranged so that the N poles face each other, and the NS direction is arranged in the vertical direction, in other words, parallel to the surface direction of the slot antenna 44. Thereby, the magnetic field in front of the slot antenna 44 can be strengthened while reducing the influence of the magnetic field on the inside of the second waveguide 41. In addition, the tube wall portion 43 has high surface conductivity and is easy to form a magnetic circuit, and is excellent in corrosion resistance.

  Cooling pipes 51a and 52a are arranged on both sides of the permanent magnet 50a in the thickness direction. Cooling pipes 51b and 52b are disposed on both sides in the thickness direction of the permanent magnet 50b. Thereby, the temperature rise of permanent magnet 50a, 50b is suppressed, and the fall of magnetism can be suppressed. A cooling plate 42 is also disposed around the second waveguide 41. Thereby, the temperature rise inside the second waveguide 41 is suppressed.

  In the permanent magnet 50a, the rear surface close to the slot antenna 44 is in contact with the cooling pipe 51a, and the lower surface is covered with a cover member 53a. In the permanent magnet 50b, the rear surface close to the slot antenna 44 is in contact with the cooling pipe 51b, and the upper surface is covered with a cover member 53b. In this way, the permanent magnets 50a and 50b are protected against the generated ECR plasma P.

  In the microwave plasma generating apparatus 1, a waveguide (downstream third waveguide 30 </ b> D, downstream first waveguide 10 </ b> D) is also connected to the downstream side of the second waveguide 41. The downstream first waveguide 10D has a plunger 11 for adjusting the terminal position. The electric field intensity at the slot 440 position can be adjusted by moving the plunger 11 in the front-rear direction and adjusting the length of the downstream first waveguide 10D. Thereby, the microwave easily propagates from the slot 440, and stable plasma can be generated. Further, the inside of the tube in the section V from the upstream third waveguide 30U to the downstream third waveguide 30D is vacuum. Accordingly, between the members constituting the second waveguide 41 (between the slot antenna 44 and the second dielectric 45, between the slot antenna 44 and the tube wall portion 43, etc.) It is not necessary to perform a vacuum seal between the upstream third waveguide 30U and the downstream third waveguide 30D, and no heat countermeasures for the vacuum seal are required.

  The upstream first waveguide 10U and the downstream first waveguide 10D are arranged in a symmetrical L shape with the second waveguide 41 interposed therebetween as viewed from above. For this reason, the microwave plasma generator 1 can be attached to the vacuum vessel 80 by passing the upstream first waveguide 10U and the downstream first waveguide 10D through the partition wall 83 of the vacuum vessel 80. Thereby, compared with the form which arrange | positions the upstream 1st waveguide 10U, the plasma production | generation part 20, and the downstream 1st waveguide 10D linearly, attachment becomes easy and it aims at space saving. it can. Further, the upstream first waveguide 10U, the upstream third waveguide 30U, the plasma generation unit 20, the downstream third waveguide 30D, the downstream first waveguide 10D, and the partition wall 83 are unitized. In other words, the microwave plasma generation apparatus 1 can be easily incorporated into various processing apparatuses.

<Second embodiment>
The difference between the microwave plasma generation apparatus of this embodiment and the microwave plasma generation apparatus of the first embodiment is that the upstream first waveguide and the downstream first waveguide are inclined downward in the middle. It is a point. Therefore, the difference will be mainly described here. The configuration of the upstream first waveguide and the configuration of the downstream first waveguide are the same. Therefore, here, the configuration of the upstream first waveguide will be described.

  FIG. 4 shows a left side view of the microwave plasma generation apparatus of the present embodiment. In FIG. 4, members corresponding to those in FIG. As shown in FIG. 4, the upstream first waveguide 10 </ b> U is disposed so as to be inclined downward after passing through the partition wall 83 on the rear side of the vacuum vessel. The inclination angle α of the upstream first waveguide 10U with respect to the horizontal plane is 25 °. The upper wall of the upstream first waveguide 10U has a chamfered portion 100U that is chamfered and gently inclined near the boundary between the horizontal portion and the inclined portion.

  According to this embodiment, it is possible to irradiate ECR plasma at an optimum angle with respect to the workpiece W to be processed. Further, since the plasma generation unit 20 can be brought closer to the workpiece W, space saving can be achieved. Further, by arranging the chamfered portion 100U near the boundary between the horizontal portion and the inclined portion, it is possible to suppress the reflection of microwaves by the wall surface of the inclined portion. Therefore, the microwave energy is unlikely to decrease.

<Other forms>
The embodiment of the microwave plasma generation apparatus of the present invention has been described above. However, the embodiment is not limited to the above embodiment. Various modifications and improvements that can be made by those skilled in the art are also possible.

  The sizes of the first waveguide, the plasma generation unit, and the third waveguide are not particularly limited. In the above embodiment, the downstream third waveguide and the downstream first waveguide are also arranged on the downstream side of the second waveguide. However, the waveguide on the downstream side of the second waveguide is not always necessary. For example, the microwave plasma generation apparatus may be configured by an upstream first waveguide, an upstream third waveguide, and a plasma generation unit. In this case, the end of the second waveguide may be a metal wall. In the above embodiment, the upstream first waveguide and the downstream first waveguide are arranged in an L shape when viewed from above. However, the arrangement form of the upstream first waveguide and the downstream first waveguide is not particularly limited. For example, at least one of the upstream first waveguide and the downstream first waveguide and the plasma generation unit may be arranged linearly. As in the second embodiment, at least one of the upstream first waveguide and the downstream first waveguide may be inclined. In this case, the inclination angle is not particularly limited. When the downstream first waveguide is disposed, the downstream first waveguide does not have to have a termination adjusting member. That is, the terminal end of the downstream first waveguide may be a fixed end. The configuration of the termination adjusting member is not particularly limited.

  In the above embodiment, iron plated with Ni is adopted as the material of the second waveguide (tube wall portion). However, the material of the second waveguide may be a magnetic material, and the type thereof is not particularly limited. As the magnetic material, for example, iron, nickel, stainless steel, and alloys using these are suitable. In the above embodiment, an iron slot antenna is employed. However, the material of the slot antenna may be metal, and may be aluminum, stainless steel, brass, etc. in addition to iron.

  The shape, type, number, arrangement form, and the like of the magnet that forms a magnetic field on the surface of the slot antenna on the plasma generation side are not particularly limited as long as ECR can be generated. For example, an electromagnet may be used instead of a permanent magnet. The magnet has a magnetic flux density B [mT] at a position 10 mm away from the surface of the slot antenna in the vertical direction at the position where the slot is formed so that B ≧ f / 28 (f is the frequency [MHz] of the microwave). It is desirable to be arranged at the same time. In the above embodiment, magnets are arranged on both sides of the slot antenna along the longitudinal direction of the slot antenna. However, the magnet may be arranged only on one side of the slot antenna. When magnets are arranged on both sides of the slot antenna, they should be arranged so that the same magnetic poles face each other. By doing so, the magnetic field on the surface of the slot antenna can be strengthened while reducing the influence of the magnetic field on the inside of the second waveguide. In the above embodiment, the pair of permanent magnets is arranged so that the N poles face each other, but may be arranged so that the S poles face each other.

  In the above embodiment, a cooling pipe is disposed in the vicinity of the permanent magnet in order to suppress the temperature rise of the permanent magnet. However, the configuration, number, arrangement, etc. of the cooling means for the permanent magnet are not particularly limited. For example, a cooling plate or the like may be arranged instead of the cooling pipe or in combination with the cooling pipe. Moreover, in the said embodiment, in order to suppress the temperature rise inside a 2nd waveguide, the cooling plate was arrange | positioned around the 2nd waveguide. However, the cooling means for the second waveguide is not always necessary. When the cooling means for the second waveguide is arranged, the configuration, number, arrangement form, etc. are not particularly limited.

  The number, shape, arrangement, and the like of the slots formed in the slot antenna are not particularly limited. The arrangement of the slots may be one row or two or more rows. The number of slots may be odd or even. Further, the slots may be arranged in a zigzag shape by changing the arrangement angle of the slots.

  The material of the second dielectric and the third dielectric is not particularly limited. In any case, a material having a low dielectric constant and hardly absorbing microwaves is desirable. For example, quartz, alumina, zirconia, aluminum nitride, magnesium oxide and the like are suitable. Here, as the third dielectric, one having a refractive index smaller than that of the second dielectric is selected. The refractive index of the third dielectric is preferably a value between the refractive index inside the first waveguide and the refractive index of the second dielectric. In the above embodiment, the second dielectric is disposed in the entire space in the second waveguide. However, the second dielectric is only required to be disposed so as to cover at least the slot, and is not necessarily disposed in the entire internal space.

  In the above embodiment, a microwave having a frequency of 2.45 GHz is used. However, the frequency of the microwave is not limited to the 2.45 GHz band, and any frequency band may be used as long as it is a frequency band of 300 MHz to 100 GHz. Examples of the frequency band in this range include 8.35 GHz, 1.98 GHz, and 915 MHz.

What is necessary is just to determine the pressure in a vacuum vessel suitably according to a process. The microwave plasma generation apparatus of the present invention can generate microwave plasma under a relatively low pressure of 0.05 Pa to 20 Pa. A suitable pressure in the vacuum vessel is 0.1 Pa or more and 4 Pa or less. By making a high vacuum state of 4 Pa or less, mixing of impurities can be suppressed and the purity of the treatment can be increased. What is necessary is just to determine the gas to supply suitably according to a process. For example, argon (Ar), helium (He), neon (Ne), krypton (Kr), xenon (Xe), or other rare gas, nitrogen (N ₂ ), oxygen (O ₂ ), hydrogen (H ₂ ), or the like Can be mentioned. The gas to be supplied may be one type or two or more types.

  Next, the present invention will be described more specifically with reference to examples.

<Generation of microwave plasma under low pressure>
[Example 1]
Using the microwave plasma processing apparatus 8 of the first embodiment, the generation state of microwave plasma under a pressure of 0.4 Pa was confirmed. The reference numerals of members in the following processing correspond to FIG.

First, the vacuum evacuation device was operated, the gas inside the vacuum vessel 80 was discharged from the exhaust hole, and the internal pressure of the vacuum vessel 80 was set to 8 × 10 ⁻³ Pa. Next, argon gas was supplied into the vacuum vessel 80 from the gas supply hole 82, and the internal pressure of the vacuum vessel 80 was set to 0.4 Pa. Subsequently, the microwave power source is turned on, and the oscillated microwave (frequency 2.45 GHz) having an output of 1.6 kW is supplied to the upstream first waveguide 10U, the upstream third waveguide 30U, and the plasma generation unit 20. Then, it was transmitted to the downstream third waveguide 30D and the downstream first waveguide 10D, and the generation state of the microwave plasma in front of the slot antenna 44 was visually confirmed. As a result, it was confirmed that microwave plasma was stably generated.

  As described above, it is confirmed that the microwave plasma generation apparatus of the present invention can generate a stable microwave plasma under a low pressure of 1 Pa or less without generating the microwave plasma at a pressure of several tens of Pa in advance. It was done.

[Comparative Example 1]
A conventional microwave plasma generation apparatus (see FIG. 5) provided with no permanent magnet was placed in the vacuum vessel, and microwave plasma was generated under the same conditions as in Example 1. The reference numerals of members in the following processing correspond to FIG.

First, the vacuum evacuation device was operated to discharge the gas in the vacuum vessel, and the pressure in the vacuum vessel was set to 8 × 10 ⁻³ Pa. Next, argon gas was supplied into the vacuum vessel, and the pressure was set to 0.4 Pa. Subsequently, a microwave (frequency: 2.45 GHz) with an output of 1.6 kW is transmitted to the first waveguide 90, the third waveguide 91, and the second waveguide 92, and the microwave in front of the slot antenna 920 is transmitted. The generation state of the wave plasma was visually confirmed. However, no plasma was generated.

<Electron density of microwave plasma>
A microwave plasma was generated in the same manner as in Example 1 while changing the output of the microwave, and the electron density of the microwave plasma at a position 10 mm away from the slot forward was measured. A Langmuir probe was used to measure the electron density. The probe electrode has a thickness of 0.2 mm and a length of 5 mm. A variable voltage was applied to the probe electrode, and the change in the current flowing through the electrode was measured. FIG. 6 shows the measurement result of the electron density with respect to the microwave output. In FIG. 6, “1.00E + 08”, “1.00E + 09”, “1.00E + 10” on the vertical axis of the graph are “1.00 × 10 ⁸ ”, “1.00 × 10 ⁹ ”, “1. 00 × 10 ¹⁰ ”. As shown in FIG. 6, when the microwave output was 1.0 to 2.0 kW, an electron density of 10 ⁸ cm ⁻³ or more was realized.

  The microwave plasma generation apparatus of the present invention can be used for various processes such as cleaning, modification, and film formation on a substrate. For example, it is useful for forming a transparent conductive film used for touch panels, displays, LED (light emitting diode) illumination, solar cells, electronic paper, and the like.

1: microwave plasma generator, 8: microwave plasma processing apparatus, 10U: upstream first waveguide, 10D: downstream first waveguide, 11: plunger (terminating member), 20: plasma generator , 21: body part, 22a, 22b: magnet part, 30U: upstream third waveguide, 30D: downstream third waveguide, 31: third dielectric, 40: housing, 41: second guide Wave tube, 42: cooling plate, 43: tube wall, 44: slot antenna, 45: second dielectric, 50a, 50b: permanent magnet, 51a, 52a, 51b, 52b: cooling pipe, 53a, 53b: cover member 80: vacuum vessel, 81U, 81D: waveguide insertion hole, 82: gas supply hole, 83: partition wall, 100U: chamfered portion, 400: recessed portion, 440: slot, P: ECR plasma, V: section, W: work.

Claims (7)

A microwave plasma generation apparatus for generating microwave plasma by ionizing a gas in a vacuum vessel,
A first waveguide for transmitting microwaves;
A tube wall portion made of a magnetic material, a slot antenna formed with a plurality of slots through which the microwave propagating inside the tube is formed, and disposed inside the tube so as to cover at least the slot An elongated second waveguide extending in one direction, and the outside of the second waveguide and the slot with the plasma generation side of the slot antenna as the front disposed in front of the antenna, a plasma generator having a magnet, a to form a magnetic field electron cyclotron resonance to the slot position on the surface of the plasma generation side of the slot antenna is produced,
A third waveguide having a third dielectric interposed between the first waveguide and the second waveguide and having a refractive index smaller than that of the second dielectric inside the tube;
A microwave plasma generation apparatus comprising: The third waveguide is disposed in the vacuum vessel;
Microwave plasma generating device of claim 1 wherein the tube inside the tube interior and said third waveguide of the second waveguide is a vacuum.   The microwave plasma generation apparatus according to claim 1 or 2, wherein the pressure of the gas in the vacuum vessel is 0.05 Pa or more and 20 Pa or less.   4. The microwave plasma generation apparatus according to claim 1, wherein the second dielectric is one type selected from quartz, alumina, zirconia, aluminum nitride, and magnesium oxide. 5.   5. The micro of claim 1, wherein a cross section of the second waveguide in a short direction has a rectangular shape, and the slot antenna is disposed on an H surface of the second waveguide. Wave plasma generator. The first waveguide has an upstream first waveguide disposed on the upstream side of the second waveguide, and a downstream first waveguide disposed on the downstream side,
The upstream first waveguide and the downstream first waveguide are arranged in a symmetrical L shape across the second waveguide,
The microwave plasma generating apparatus according to any one of claims 1 to 5, wherein the third waveguide is interposed at least between the upstream first waveguide and the second waveguide. .   The microwave plasma generation apparatus according to claim 6, wherein the downstream first waveguide has a termination adjusting member that changes a termination position.

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