Patent Publication Number: US-2023141688-A1

Title: Plasma source and plasma processing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2021-183650 filed on Nov. 10, 2021, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a plasma source and a plasma processing apparatus. 
     BACKGROUND 
     There is a plasma processing method for supplying reactive species of a gas from a remote plasma source to a reactor and performing wafer processing or cleaning in the reactor. For example, Japanese Patent Application Publication No. 2004-179426 discloses a method for performing cleaning in a reactor of a substrate processing apparatus by supplying reactive species of a fluorine-containing gas to the reactor from a remote plasma source installed in the substrate processing apparatus. The inner wall of the remote plasma source from which the reactive species of the fluorine-containing gas are supplied to the reactor is coated with fluororesin to reduce damage to the inner wall caused by the fluorine-containing gas and suppress generation of particles. 
     SUMMARY 
     The present disclosure provides a technology capable of effectively suppressing generation of particles. 
     One aspect of the present disclosure provides a plasma source comprising a metal member having an inlet and forming a wall that delimits an upstream flow of a processing gas supplied from the inlet, a ceramic member having an outlet and forming a wall that delimits a downstream flow of the processing gas discharged from the outlet, and a power supply device configured to supply a power for plasma generation into a chamber, wherein the chamber includes the metal member and the ceramic member, and is configured to discharge an activated gas generated by producing plasma from the processing gas to the outside of the chamber through the outlet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects and features of the present disclosure will become apparent from the following description of embodiments, given in conjunction with the accompanying drawings, in which: 
         FIG.  1    shows a configuration example 1 of a plasma source and a configuration example of a plasma processing apparatus according to an embodiment; 
         FIG.  2    shows a configuration example “a” of a conventional plasma source; 
         FIG.  3    shows a modification of a stress buffer according to an embodiment; 
         FIG.  4 A  shows a configuration example “b” of the conventional plasma source; 
         FIG.  4 B  shows a configuration example 2 of the plasma source according to the embodiment; and 
         FIG.  5    shows a configuration example 3 of the plasma source according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. Like reference numerals will be given to like parts throughout the drawings, and redundant description thereof may be omitted. 
     For example, there is a plasma processing method for processing a substrate that is a wafer using a processing gas or cleaning a reactor by supplying reactive species (activated gas) of a fluorine-containing gas such as NF 3  gas or the like from a remote plasma source (hereinafter, also referred to as “plasma source”) to the reactor. In this plasma processing method, fluorination progresses due to heat generated at a location where the fluorine-containing gas stagnates, such as a bent portion of a line of the plasma source, a line or an inner wall near an outlet for the activated gas, or the like. In a conventional plasma source, aluminum, for example, forming a chamber wall may be fluorinated to aluminum fluoride (AlF), and AlF may be peeled off from the wall and become particles. 
     In the case of forming an oxide film such as yttria (Y 2 O 3 ) or forming alumina (Al 2 O 3 ) by performing surface treatment such as alumite treatment (anodic oxidation treatment) or the like on the inner wall of the chamber, it is possible to reduce particles by suppressing fluorination of the chamber wall. However, the oxide film is also peeled off or cracked due to damage, and the fluorine-containing gas reaches aluminum forming the chamber wall. Accordingly, AlF or strips generated from the inner wall of the chamber may become particles and fall into the reactor. 
     Therefore, in the plasma source of the present embodiment, instead of performing conventional surface treatment to form an oxide film such as yttria or alumina, the location in the chamber that is likely to be fluorinated, e.g., the vicinity of the outlet for the reactive species (activated gas), is formed of an yttria sintered body. In other words, a chamber wall on a downstream side of a gas is likely to be fluorinated due to an increase in a residence time of a gas supplied into the chamber from an inlet for supplying a gas to a plasma source or an increase in a density of the gas, and thus, the chamber wall on the downstream side of the gas is formed of an yttria sintered body. Thus, the durability of the chamber wall is improved. Accordingly, fluorine components do not enter the inner wall of the chamber where fluorination is likely to occur, thereby suppressing the generation of particles from the chamber wall or the like due to damage and preventing particles from falling from the plasma source into the reactor. Hereinafter, a configuration example 1 of a plasma source and a plasma processing apparatus according to an embodiment will be described in detail with reference to  FIG.  1   . 
     Configuration Example 1 of Plasma Source and Plasma Processing Apparatus 
       FIG.  1    shows a configuration example 1 of a plasma source  2  and a configuration example of a plasma processing apparatus  1  including the plasma source  2  according to an embodiment. The plasma source  2  has a chamber  36  and a power supply  37 . The chamber  36  has a metal member  30  and a ceramic member  31 . In  FIG.  1   , the size relationship between the plasma source  2  and a reactor  10  is ignored. 
     (Chamber Structure) 
     The metal member  30  is made of a metal such as aluminum or the like, and has a substantially cylindrical shape. The inner space of the metal member  30  serves as a plasma generation space  30   s . The upper portion of the metal member  30  is closed and the lower portion thereof is opened. An inlet  28  for a processing gas is formed substantially at the center of the upper portion of the metal member  30 . The inlet  28  is connected to a gas supply device  24  through an opening/closing valve  29 . The metal member  30  constitutes a wall that delimits the upstream flow of the processing gas supplied from the inlet  28 . The processing gas is supplied from the gas supply device  24 . The supply and the stop of the supply of the processing gas are controlled by the opening/closing valve  29 , and the processing gas is introduced into the metal member  30  from the inlet  28 . The processing gas includes a cleaning gases, a film forming gas, an etching gas, or the like. 
     The power supply device  37  supplies a power for plasma generation into the chamber  36 . The power for plasma generation may be a radio frequency (RF) power having a frequency of 400 kHz, 13.56 MHz, or the like. The power supply device  37  is connected to a coil  33  wound around the metal member  30  and applies an RF power to the coil  33 . On the sidewall of the metal member  30 , a gap is formed in a circumferential direction at a height where the coil  33  is disposed, and an annular dielectric window  32  is fitted in the gap. An electromagnetic field generated by applying an RF power to the coil  33  passes through the dielectric window  32  and propagates to the plasma generation space  30   s  in the metal member  30 , thereby contributing to production of plasma from a gas. 
     Accordingly, plasma of the processing gas is produced in the plasma generation space  30   s . The inner wall of the metal member  30  is coated with an yttria sprayed film  30   a . Plasma electrolytic oxidation (PEO) may be performed on the wall of the metal member  30 . In any case, the plasma resistance can be improved. 
     The chamber  36  of the plasma source  2  of the present embodiment mainly includes two members, i.e., the metal member  30  that delimits the upstream flow of the processing gas and the ceramic member  31  that delimits the downstream flow thereof. In other words, the ceramic member  31  has an outlet  27  and constitutes a wall that delimits the downstream flow of the processing gas (activated gas) discharged from the outlet  27 . In the plasma source  2  of the present embodiment, the ceramic member  31  is formed of an yttria sintered body. 
     A configuration example “a” of a conventional plasma source  102  is shown in  FIG.  2   . In the configuration example “a” of the conventional plasma source  102 , the processing gas is introduced from an inlet  128  formed at an upper portion of a chamber  136  made of aluminum, and plasma is produced in the plasma generation space  30   s . In the vicinity of the outlet  127  (e.g., area A) on the downstream side of the gas that is likely to fluorinate due to an increase in the residence time of the gas or an increase in the density of the gas, fluorine components enter the chamber wall made of aluminum, thereby generating particles. Similarly, when a ceramic coating is thermally sprayed on the inner wall surface of the chamber  136 , the fluorine components enter the ceramic coating in the area A, for example, thereby generating particles. 
     Therefore, in configuration example 1 of the plasma source  2  of the present embodiment shown in  FIG.  1   , the wall that delimits the downstream flow of the processing gas near the outlet  27  is formed of an yttria sintered body. In other words, the chamber  36  of the present disclosure mainly includes the ceramic member  31  formed of an yttria sintered body and the metal member  30  made of aluminum. 
     Accordingly, the durability against fluorine is improved by providing an yttria sintered body only at the outlet  27  where the residence time of the gas increases or the density of the gas becomes high and the vicinity of the outlet  27  on the downstream side of the processing gas. In other words, since the sintered body having a dense structure compared to ceramic formed by thermal spraying is used for the ceramic member  31 , the durability against fluorine is further improved. However, yttria has low thermal conductivity, so that it is preferable to provide the ceramic member  31  formed of an yttria sintered body only at the portion where the gas stagnates in the chamber  36 . The metal member  30  made of aluminum defines the supply port  28  and its vicinity on the upstream side of the processing gas and the portion between the upstream side and the downstream side. 
     With this configuration, the chamber  36  includes the metal member  30  and the ceramic member  31 , and is configured to discharge the activated gas generated by producing plasma to the outside of the chamber  36  through the outlet  27 . Accordingly, it is possible to suppress the generation of particles due to the fluorination of the chamber wall on the downstream side of the gas. In addition, the chamber  36  can be easily cooled due to high thermal conductivity of the metal member  30 . 
     Since yttria has plasma resistance, it is preferable that the yttria sintered body is exposed on the inner wall of the ceramic member  31 . On the other hand, it is necessary to form a metal deposition film  31   b  on the outer wall of the ceramic member  31 . Since the ceramic member  31  is a dielectric material, the electromagnetic waves propagating in the plasma generation space  30   s  reach the atmosphere outside the chamber  36  if there is no deposition film  31   b . Hence, a metal such as aluminum, chromium, nickel, tantalum, or the like is deposited on the outer wall of the ceramic member  31 . The leakage of electromagnetic waves can be prevented by the deposition film  31   b.    
     The ceramic member  31  may be formed of an alumina (Al 2 O 3 ) sintered body, an yttrium fluoride (YF3) sintered body, a magnesium fluoride (MgF) sintered body, or a calcium fluoride (CaF) sintered body, instead of an yttria sintered body. Since, however, an alumina sintered body, a magnesium fluoride sintered body, and a calcium fluoride sintered body have lower resistance to fluorine plasma compared to the yttria sintered body, it is preferable to use an yttria sintered body for the ceramic member  31 . 
     The metal member  30  is not necessarily made of aluminum, and may be made of any material which can form a surface resistant to fluoride plasma processing. 
     The entire chamber  36  may be formed of an yttria sintered body. In this case, the deposition film  31   b  is formed on the entire outer wall of the ceramic member  31  except the dielectric window  32 . However, when the entire chamber  36  is made of ceramic such as an yttria sintered body or the like, the manufacturing cost of the plasma source  2  increases and, also, the cooling efficiency decreases in terms of thermal conductivity. Hence, it is preferable to limit the location where the ceramic member  31  is used. 
     In the chamber  36 , the fluorine components are likely to enter the location where the density of the fluorine-containing gas increases or the flow velocity of the fluorine-containing gas decreases, such as the location where the gas channel is narrowed or the gas stagnates. Therefore, it is preferable to provide the ceramic member  31  at least at the location where the fluorine components are likely to reach. 
     (Stress Buffer) 
     The metal member  30  and the ceramic member  31  are brazed to each other with a stress buffer  34  interposed therebetween. When the metal member  30  and the ceramic member  31  are directly bonded, cracks or the like may be generated in the joining portion between the metal member  30  and the ceramic member  31  or at the ceramic member  31  due to the temperature difference in the chamber  36  caused by thermal expansion. When cracks or the like are generated, the fluorine components enter the cracks, and particles are generated due to corrosion of the joining portion. Therefore, the metal member  30  and the ceramic member  31  are not directly bonded, and the annular stress buffer  34  is interposed between the metal member  30  and the ceramic member  31 . The stress buffer  34  is brazed in a circumferential direction to the outer wall near the lower end of the metal member  30  and the inner wall near the upper end of the ceramic member  31 . The brazing may be active metal brazing in which titanium and silver are mixed, for example. Further, metallization may be used for bonding the stress buffer  34  and the ceramic member  31  formed of an yttria sintered body. 
     The stress buffer  34  is preferably made of a material having a thermal expansion coefficient between the thermal expansion coefficient of the metal member  30  and the thermal expansion coefficient of the ceramic member  31 . For example, the stress buffer  34  is preferably made of a nickel-based metal having a composition of 29% Ni, 17% Co, and the balance F. Kovar (Registered Trademark) may be used as an example of such a metal. The stress buffer  34  can absorb stress caused by the thermal expansion difference between the metal member  30  and the ceramic member  31 , which makes it possible to prevent cracks from being generated at the metal member  30  or the ceramic member  31 . However, the stress buffer  34  may have a linear thermal expansion coefficient greater than or equal to that of the ceramic member  31  and smaller than or equal to that of the metal member  30 . 
     In the example of  FIG.  1   , the stress buffer  34  is a hollow spring-like member having an opening  34   a  with a U-shaped cross section. The opening  34   a  is opened in the same direction as the direction in which one of the inlet  28  and the outlet  27  is opened. 
     The structure of the stress buffer  34  shown in  FIG.  1    is an example, and the stress buffer  34  may be a plate-shaped member that is a modification of the stress buffer  34  shown in  FIG.  3    as long as a load is not applied to the ceramic member  31  and the joining portion between the metal member  30  and the ceramic member  31 . 
     (Plasma Processing Apparatus) 
     Referring back to  FIG.  1   , the plasma processing apparatus  1  includes the plasma source  2  and the reactor  10 . A connecting portion  38  has the outlet  27  of the plasma source  2  therein and is fitted into the opening/hole formed in/at the upper wall of the reactor  10 . Accordingly, the plasma source  2  is installed. In the plasma source  2 , plasma is produced from the processing gas, and the generated activated gas is discharged to the outside of the chamber  36  through the outlet  27  and supplied into the reactor  10 . At this time, the ceramic member  31  formed of an yttria sintered body is used to improve the corrosion resistance of the outlet  27  and its vicinity where the gas conductance increases and the residence time increases. Thus, even when a fluorine-containing gas is used for cleaning, for example, the fluorine-containing gas does not enter the yttria sintered body, thereby suppressing the generation of particles and preventing particles from falling into the reactor  10 . Although not shown, it is preferable to provide a valve in the connecting portion  38  to prevent backflow of a gas and to reduce the volume of the reactor  10 . 
     The reactor  10  includes a chamber body  12 . The chamber body  12  has a substantially cylindrical shape and defines a sidewall and a bottom wall of the reactor  10 . The chamber body  12  has an upper opening. The chamber body  12  is made of a metal such as aluminum or the like, and is grounded. 
     The sidewall of the chamber body  12  has a passage  12   p . The substrate W is transferred between the inside of the reactor and the outside of the reactor  10  through the passage  12   p . The passage  12   p  can be opened and closed by a gate valve  12   v . A gate valve  12   v  is disposed along the sidewall of the chamber body  12 . 
     The reactor  10  further includes an upper wall  14  made of a metal such as aluminum or the like. The upper wall  14  has a substantially disc shape, and closes the upper opening of the chamber body  12 . The upper wall  14  is grounded. 
     The bottom wall of reactor  10  has an exhaust port  16   a . The exhaust port  16   a  is connected to an exhaust device  16 . The exhaust device  16  includes a pressure controller such as an automatic pressure control valve, and a vacuum pump such as a turbo molecular pump. 
     The plasma processing apparatus  1  further includes a substrate support  18 . The substrate support  18  is disposed in the reactor  10 . The substrate support  18  is configured to support the substrate W placed thereon. The substrate W is placed on the substrate support  18  in a substantially horizontal state. The substrate support  18  may be supported by a support member  19 . The support member  19  extends upward from the bottom portion of the reactor  10 . The substrate support  18  and the support member  19  may be made of a dielectric such as aluminum nitride or the like. 
     The plasma processing apparatus  1  further includes a shower head  20 . The shower head  20  is made of a metal such as aluminum or the like. The shower head  20  has a substantially disc shape and has a diffusion space  30   d  therein. The shower head  20  is disposed above the substrate support  18  and below the upper wall  14 . The shower head  20  constitutes a ceiling that defines the inner space of the reactor  10 , and the upper wall  14  is disposed on the shower head  20 . 
     A plurality of gas holes  20   i  are formed through the diffusion space  30   d  in a vertical direction. The gas holes  20   i  are opened on the bottom surface of the shower head  20  to introduce a gas toward a processing space  30   e  between the shower head  20  in the reactor  10  and the substrate support  18 . Accordingly, the shower head  20  introduces the activated gas supplied from the plasma source  2  from the diffusion space  30   d  into the processing space  30   e  through the holes  20   i.    
     The outer circumference of the shower head  20  is covered with a dielectric member  13  such as ceramic. The outer circumference of the substrate support  18  is covered with a dielectric member  15  such as ceramic. When the RF power is not applied to the shower head  20 , the dielectric member  13  may be omitted. However, it is preferable to provide the dielectric member  13  in order to determine the area of the shower head  20  that functions as the counter electrode of the substrate support  18 . Further, it is preferable to provide the dielectric member  13  in order to make the ratio between the anode and the cathode of the electrode approximately equal. 
     An RF power supply  60  is connected to the substrate support  18  via a matching device  61 . The matching device  61  has an impedance matching circuit. The impedance matching circuit is configured to match an output impedance of the RF power supply  60  and a load impedance on a plasma side. The RF power supplied from the RF power supply  60  has a frequency of 60 MHz or less. The RF power may have a high frequency of 13.56 MHz, for example. The RF power may be applied to the shower head  20  by the RF power supply  60 . 
     In the plasma processing apparatus  1  configured as described above, the reactor  10  communicates with the chamber  36  and the activated gas is introduced from the outlet  27 . The activated gas is supplied to the processing space  30   e  through an inlet  13   a  of the shower head  20  and the diffusion space  30   d . The activated gas that has reached the processing space  30   e  is easily re-dissociated by the RF power from the RF power supply  60 , so that the substrate W can be processed using the activated gas. Alternatively, the activated gas may be directly supplied to the processing space  30   e  without providing the RF power supply  60 . 
     A controller (control device)  90  may be a computer having a processor  91  and a memory  92 . The controller  90  includes a calculation device, a storage device, an input device, a display device, a signal input/output interface, and the like. The controller  90  controls individual components of the plasma processing apparatus  1  including the plasma source  2 . In the controller  90 , an operator may use the input device to input commands to manage the plasma processing apparatus  1 . In addition, the controller  90  can visualize and display the operation status of the plasma processing apparatus  1  using the display device. The memory  92  of the controller  90  stores a control program and recipe data. The control program is executed by the processor  91  of the controller  90  to perform various processes in the plasma processing apparatus  1 . The processor  91  executes the control program and controls individual components of the plasma processing apparatus  1  based on the recipe data. Accordingly, the plasma processing apparatus  1  can perform cleaning, film formation, etching, and other various plasma processing using a fluorine-containing gas such as NF 3  gas, ClF 3  gas, or the like. 
     Other Configuration Examples of Plasma Source 
     Other configuration examples of the plasma source  2  will be described with reference to  FIGS.  4 A,  4 B, and  5   .  FIG.  4 A  shows a configuration example “b” of the conventional plasma source  102 , and  FIG.  4 B  shows a configuration example 2 of the plasma source  2  according to the embodiment.  FIG.  5    shows a configuration example 3 of the plasma source  2  according to the embodiment. 
     In configuration example “b” of the conventional plasma source  102  of  FIG.  4 A , the processing gas is introduced from the inlet  128  formed in the upper wall of the chamber  136  made of aluminum. The chamber  136  is configured such that a plurality of plasma generation channels R1 and R2 branched from the inlet  128  are formed. The plasma generation channels R1 and R2 are branched from the upstream side of the gas flow, and gases flow through an annular gas channel or two or more branched gas channels and join at the downstream side. 
     In configuration example “b” of the conventional plasma source  102 , the chamber  136  has an atmospheric space  30   p  in the plasma generation space  30   s . An RF power is applied to a plurality of coils  33   a  and  33   b  wound around the chamber  136 . The RF power applied to the coils  33   a  and  33   b  passes through dielectric windows  32   a  and  32   b  and is supplied to the plasma generation space  30   s  in the chamber  136  to produce plasma from the processing gas. 
     In the vicinity of the exhaust port  127  (e.g., area A) on the downstream side of the gas supplied from the inlet  128 , where the gas is likely to fluorinate due to an increase in the residence time of the gas or an increase in the density of the gas, fluorine components enter the wall of the chamber  136  made of aluminum, thereby generating particles. 
     Therefore, in configuration example 2 of the plasma source  2  of the present embodiment shown in  FIG.  4 B , the chamber  36  includes the ceramic member  31  formed of an yttria sintered body and the metal member  30  made of aluminum. Further, the ceramic member  31  that defines the downstream side of the processing gas supplied from the inlet  28  and discharged from the outlet  27  is formed of an yttria sintered body. Accordingly, the fluorine components do not enter the dense yttria sintered body, thereby suppressing the generation of particles. 
     The chamber  36  has the atmospheric space  30   p  in the plasma generation space  30   s . The ceramic member  31  is configured to form at least the joining portion of the plasma generating channels R1 and R2. The stress buffers  34  and  35  are disposed between the plasma generation channels R1 and R2 and the ceramic member  31 , respectively. The stress buffers  34  and  35  are brazed to the outer wall of the metal member  30  and the inner wall of the ceramic member  31  in the plasma generation channels R1 and R2, respectively. 
     In the configuration example 3 of the plasma source  2  of the present embodiment shown in  FIG.  5   , the chamber  36  of the present disclosure includes the metal member  30  made of aluminum and the ceramic member  31  formed of an yttria sintered body. The structure of the metal member  30  is the same as that in the configuration example 2 of the plasma source  2  of  FIG.  4 B . Further, similarly to the configuration example 2, the ceramic member  31  that delimits the downstream flow of the processing gas discharged from the outlet  27  is formed of an yttria sintered body. Accordingly, the generation of particles can be suppressed. 
     The plasma generation space  30   s  has therein the atmospheric space  30   p , and the ceramic member  31  is configured to form at least the joining portion of the plasma generation channels R1 and R2. The stress buffers  34  and  35  are disposed between the plasma generation channels R1 and R2 and the ceramic member  31 , respectively. The stress buffers  34  and  35  are brazed to the metal member  30  and the ceramic member  31  in the plasma generation channels R1 and R2. 
     The configuration example 3 is different from the configuration example 2 of the plasma source  2  shown in  FIG.  4 B  in that a plurality of plasma generation channels R3 and R4 of the ceramic member  31  are obliquely formed such that the ceramic member  31  has a Y-shaped vertical cross section and communicate with the plasma generation channels R1 and R2, respectively. Since the plasma generation channels R3 and R4 are formed obliquely, stepped portions or corner portions in the channels are reduced and the gas flow is improved, which makes the occurrence of turbulence or convection near the outlet  27  difficult. Accordingly, the deterioration of the ceramic member  31  due to fluorine components can be further suppressed, thereby further suppressing the generation of particles. 
     In addition, the configuration example 3 is different from the configuration example 2 of the plasma source  2  of  FIG.  4 B  in that the stress buffers  34  and  35  are brazed to the lower end of the metal member  30  and the upper end of the ceramic member  31 . In this case, openings  34   a  and  35   a  of the respective stress buffers  34  and  35  are opened in a direction perpendicular to the direction in which the inlet  28  and the outlet  27  are opened. However, the present disclosure is not limited thereto, and the openings  34   a  and  35   a  of the respective stress buffers  34  and  35  may be opened obliquely with respect to the direction in which the inlet  28  and the outlet  27  are opened. 
     As described above, in accordance with the plasma source  2  and the plasma processing apparatus  1  of the present embodiment, the corrosion resistance is improved by providing the ceramic member  31  formed of an yttria sintered body at the location where the residence time increases due to a high conductance on the downstream side of the gas flow, thereby effectively suppressing the generation of particles. 
     The plasma source and the plasma processing apparatus according to the embodiments of the present disclosure are considered to be illustrative in all respects and not restrictive. The above-described embodiments can be changed and modified in various forms without departing from the scope of the appended claims and the gist thereof. The above-described embodiments may include other configurations without contradicting each other and may be combined without contradicting each other. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosures. Indeed, the embodiments described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.