Patent Publication Number: US-2023158517-A1

Title: Shower head electrode assembly and plasma processing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2021-189273 filed on Nov. 22, 2021, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a shower head electrode assembly and a plasma processing apparatus. 
     BACKGROUND 
     In a plasma processing apparatus, a shower head that supplies a processing gas into a processing chamber from a plurality of gas flow paths is used. For example, Japanese Laid-open Patent Publication No. 2010-514160 discloses a shower head which includes a first member attached to a second member, the first and second members having first and second gas flow paths in fluid communication. It is disclosed that when the processing gas flows through the gas flow path in such a shower head, a total pressure drop occurs along the first and second gas flow paths, and a rate of total pressure drop along the second gas flow path is greater than a rate of total pressure drop along the first gas flow path. 
     SUMMARY 
     The present disclosure provides a technology for preventing abnormal discharge that occurs inside a shower head. 
     In accordance with an aspect of the present disclosure, there is provided a shower head electrode assembly of a plasma processing apparatus, comprising: an electrode having a plurality of first gas flow paths and having a surface exposed to plasma; and a backing member attached to the electrode and having a plurality of second gas flow paths which communicate with the plurality of first gas flow paths. Each of the plurality of second gas flow paths is a slit-shaped elongated hole, and is configured such that a length of the elongated hole in radial direction is longer than a length of the elongated hole in circumferential direction with respect to a central axis of the shower head electrode assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram showing a configuration example of a plasma processing system according to an embodiment. 
         FIGS.  2 A and  2 B  are longitudinal cross-sectional views enlarging a part of a shower head according to a reference example. 
         FIGS.  3 A and  3 B  are longitudinal cross-sectional views enlarging a part of a shower head according to the embodiment. 
         FIGS.  4 A and  4 B  are longitudinal cross-sectional views enlarging a part of a gas flow path according to the embodiment. 
         FIGS.  5 A and  5 B  are diagrams showing a part of a support surface of a backing member according to the embodiment. 
         FIGS.  6 A to  6 C  are diagrams showing a modification of a configuration of a first gas flow path and a second gas flow path according to the embodiment. 
         FIGS.  7 A and  7 B  are diagrams showing an example of a simulation result for an amount of decrease in pressure of a processing gas according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments for carrying out the present disclosure will be described with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals, and redundant description thereof may be omitted. 
     In the present specification, deviation is allowed in parallel, perpendicular, orthogonal, horizontal, vertical, up-down, left-right directions, etc., to the extent that the effects of the embodiments are not impaired. A shape of a corner is not limited to a right angle, and may be arcuately rounded. Parallel, perpendicular, orthogonal, horizontal, vertical, and circular may include substantially parallel, substantially perpendicular, substantially orthogonal, substantially horizontal, substantially vertical, and substantially circular. 
     Hereinafter, a configuration example of a plasma processing system will be described.  FIG.  1    is a diagram for explaining a configuration example of a capacitively coupled plasma processing apparatus. 
     The plasma processing system includes a capacitively coupled plasma processing apparatus  1  and a controller  2 . The capacitively coupled plasma processing apparatus  1  includes a plasma processing chamber  10 , a gas supply  20 , a power supply  30 , and an exhaust system  40 . Further, the plasma processing apparatus  1  includes a substrate support  11  and a gas introduction portion. The gas introduction portion is configured to introduce at least one processing gas into the plasma processing chamber  10 . The gas introduction portion includes a shower head  13 . The substrate support  11  is disposed in the plasma processing chamber  10 . The shower head  13  is disposed above the substrate support  11 . In one embodiment, the shower head  13  forms at least a part of a ceiling of the plasma processing chamber  10 . The plasma processing chamber  10  has a plasma processing space  10   s  defined by the shower head  13 , sidewalls  10   a  of the plasma processing chamber  10 , and the substrate support  11 . The plasma processing chamber  10  has at least one gas supply port for supplying at least one processing gas to the plasma processing space  10   s  and at least one gas exhaust port for exhausting gas from the plasma processing space. The plasma processing chamber  10  is grounded. The shower head  13  and the substrate support  11  are electrically insulated from a housing of the plasma processing chamber  10 . 
     The substrate support  11  includes a body portion  111  and a ring assembly  112 . The body portion  111  has a central region  111   a  for supporting a substrate W and an annular region  111   b  for supporting the ring assembly  112 . A wafer is an example of the substrate W. The annular region  111   b  of the body portion  111  surrounds the central region  111   a  of the body portion  111  in plan view. The substrate W is disposed on the central region  111   a  of the body portion  111 , and the ring assembly  112  is disposed on the annular region  111   b  of the body portion  111  so as to surround the substrate W on the central region  111   a  of the body portion  111 . Therefore, the central region  111   a  is also referred to as a substrate support surface for supporting the substrate W, and the annular region  111   b  is also referred to as a ring support surface for supporting the ring assembly  112 . 
     In one embodiment, the body portion  111  includes a base  1110  and an electrostatic chuck  1111 . The base  1110  includes a conductive member. The conductive member of the base  1110  can serve as a lower electrode. The electrostatic chuck  1111  is disposed on the base  1110 . The electrostatic chuck  1111  includes a ceramic member  1111   a  and an electrostatic electrode  1111   b  disposed in the ceramic member  1111   a . The ceramic member  1111   a  has the central region  111   a . In one embodiment, the ceramic member  1111   a  also has the annular region  111   b . Another member surrounding the electrostatic chuck  1111 , such as an annular electrostatic chuck or an annular insulating member, may have the annular region  111   b . In this case, the ring assembly  112  may be disposed on the annular electrostatic chuck or the annular insulating member, or may be disposed on both the electrostatic chuck  1111  and the annular insulating member. Further, at least one RF/DC electrode coupled to a radio frequency (RF) power supply  31  and/or a direct current (DC) power supply  32 , which will be described later, may be disposed in the ceramic member  1111   a . In this case, at least one RF/DC electrode serves as the lower electrode. If a bias RF signal and/or a DC signal, described below, is applied to at least one RF/DC electrode, the RF/DC electrode is also referred to as a bias electrode. Further, the conductive member of the base  1110  and at least one RF/DC electrode may serve as a plurality of lower electrodes. Further, the electrostatic electrode  1111   b  may serve as the lower electrode. Therefore, the substrate support  11  includes at least one lower electrode. 
     The ring assembly  112  includes one or more annular members. In one embodiment, the one or more annular members include one or more edge rings and at least one cover ring. The edge ring is made of a conductive material or an insulating material, and the cover ring is made of an insulating material. 
     Further, the substrate support  11  may include a temperature control module configured to control at least one of the electrostatic chuck  1111 , the ring assembly  112 , and the substrate to a target temperature. The temperature control module may include a heater, a heat transfer medium, a flow path  1110   a , or a combination thereof. Through the flow path  1110   a , a heat transfer fluid such as brine or gas flows. In one embodiment, the flow path  1110   a  is formed in the base  1110  and one or more heaters are disposed in the ceramic member  1111   a  of the electrostatic chuck  1111 . Further, the substrate support  11  may include a heat transfer gas supply configured to supply a heat transfer gas to a gap between a back surface of the substrate W and the central region  111   a . 
     The shower head  13  is configured to introduce at least one processing gas from the gas supply  20  into the plasma processing space  10   s . The shower head  13  includes at least one gas supply port  13   a , at least one gas diffusion chamber  13   b , and a plurality of gas flow paths. 
     The shower head  13  has an upper electrode  13 B having a surface exposed to plasma, and a backing member  13 A attached to the upper electrode  13 B from a back surface side of the upper electrode  13 B. The upper electrode  13 B and the backing member  13 A are disk-shaped. The upper electrode  13 B has a plurality of first gas flow paths  13 B h   1  and  13 B h   2 . The backing member  13 A has a plurality of second gas flow paths  13 A h . Specifically, two first gas flow paths  13 B h   1  and  13 B h   2  communicate with one second gas flow path  13 A h . The first gas flow paths  13 B h   1  and  13 B h   2  are also collectively referred to as a first gas flow path  13 B h . For example, the backing member  13 A may be formed with a flow path through which a heat transfer fluid such as brine or gas flows, and may have a function of cooling the shower head  13 . The backing member  13 A is also referred to as a cooling plate. 
     The processing gas supplied to the gas supply port  13   a  passes through the gas diffusion chamber  13   b , passes through the plurality of second gas flow paths  13 A h  and the plurality of first gas flow paths  13 B h , and is introduced into the plasma processing space  10   s . In addition to the shower head  13 , the gas introduction portion may include one or more side gas injectors (SGI) attached to one or more openings formed in the sidewall  10   a . 
     The gas supply  20  may include at least one gas source  21  and at least one flow controllers  22 . In one embodiment, the gas supply  20  is configured to supply at least one processing gas to the shower head  13  from respective gas sources  21  through respective flow controllers  22 . Each flow controller  22  may include, for example, a mass-flow controller or a pressure controlled flow controller. Further, the gas supply  20  may include one or more flow modulation devices which modulate or pulse the flow rate of at least one processing gas. 
     The power supply  30  includes the RF power supply  31  coupled to the plasma processing chamber  10  via at least one impedance matching circuit. The RF power supply  31  is configured to supply at least one RF signal (RF power) to at least one lower electrode and/or at least one upper electrode. Therefore, plasma is formed from at least one processing gas supplied to the plasma processing space  10   s . Therefore, the RF power supply  31  may serve as at least a part of a plasma generating portion configured to generate plasma from one or more processing gases in the plasma processing chamber  10 . Further, by supplying a bias RF signal to at least one lower electrode, a bias potential is generated in the substrate W, and ion components in the formed plasma can be drawn into the substrate W. 
     In one embodiment, the RF power supply  31  includes a first RF generating portion  31   a  and a second RF generating portion  31   b . The first RF generating portion  31   a  is coupled to at least one lower electrode and/or at least one upper electrode via at least one impedance matching circuit, and configured to generate a source RF signal (source RF power) for plasma generation. In one embodiment, the source RF signal has a frequency within a range of 10 MHz to 150 MHz. In one embodiment, the first RF generating portion  31   a  may be configured to generate a plurality of source RF signals having different frequencies. The generated one or more source RF signals are supplied to at least one lower electrode and/or at least one upper electrode. 
     The second RF generating portion  31   b  is coupled to at least one lower electrode via at least one impedance matching circuit, and configured to generate a bias RF signal (bias RF power). The frequency of the bias RF signal may be the same as or different from the frequency of the source RF signal. In one embodiment, the bias RF signal has a frequency lower than the frequency of the source RF signal. In one embodiment, the bias RF signal has a frequency in a range of 100 kHz to 60 MHz. In one embodiment, the second RF generating portion  31   b  may be configured to generate a plurality of bias RF signals having different frequencies. The generated one or more bias RF signals are supplied to at least one lower electrode. Further, in various embodiments, at least one of the source RF signal and the bias RF signal may be pulsed. 
     Further, the power supply  30  may include the DC power supply  32  coupled to the plasma processing chamber  10 . The DC power supply  32  includes a first DC generating portion  32   a  and a second DC generating portion  32   b . In one embodiment, the first DC generating portion  32   a  is connected to at least one lower electrode and configured to generate a first DC signal. The generated first DC signal is applied to at least one lower electrode. In one embodiment, the second DC generating portion  32   b  is connected to at least one upper electrode and configured to generate a second DC signal. The generated second DC signal is applied to at least one upper electrode. 
     In various embodiments, at least one of the first and second DC signals may be pulsed. In this case, a sequence of voltage pulses is applied to at least one lower electrode and/or at least one upper electrode. The voltage pulses may have rectangular waveforms, trapezoidal waveforms, triangular waveforms, or a combination thereof. In one embodiment, a waveform generating portion for generating a sequence of voltage pulses from a DC signal is connected between the first DC generating portion  32   a  and at least one lower electrode. Therefore, the first DC generating portion  32   a  and the waveform generating portion constitute a voltage pulse generating portion. When the second DC generating portion  32   b  and the waveform generating portion constitute the voltage pulse generating portion, the voltage pulse generating portion is connected to at least one upper electrode. The voltage pulses may have a positive polarity or a negative polarity. Further, the sequence of voltage pulses may include one or more positive voltage pulses and one or more negative voltage pulses in one cycle. The first and second DC generating portions  32   a  and  32   b  may be provided in addition to the RF power supply  31 , and the first DC generating portion  32   a  may be provided instead of the second RF generating portion  31   b . 
     The exhaust system  40  may be connected to a gas outlet  10   e  provided at a bottom of the plasma processing chamber  10 , for example. The exhaust system  40  may include a pressure regulating valve and a vacuum pump. Pressure in the plasma processing space  10   s  is regulated by the pressure regulating valve. The vacuum pump may include a turbomolecular pump, a dry pump, or a combination thereof. 
     The controller  2  processes computer-executable instructions which cause the plasma processing apparatus  1  to perform various steps described in the present disclosure. The controller  2  may be configured to control each component of the plasma processing apparatus  1  to perform various processes described herein. In one embodiment, part or all of the controller  2  may be included in the plasma processing apparatus  1 . The controller  2  may include a processor  2   a   1 , a storage  2   a   2 , and a communication interface  2   a   3 . The controller  2  is implemented by, for example, a computer  2   a . The processor  2   a   1  may be configured to perform various control operations by reading a program from the storage  2   a   2  and executing the read program. This program may be stored in the storage  2   a   2  in advance, or may be acquired via a medium when necessary. The acquired program is stored in the storage  2   a   2 , and read from the storage  2   a   2  and executed by the processor  2   a   1 . The medium may be various storage media readable by the computer  2   a , or may be a communication line connected to the communication interface  2   a   3 . The processor  2   a   1  may be a central processing unit (CPU). The storage  2   a   2  may include a random access memory (RAM), a read only memory (ROM), a hard disk drive (HDD), a solid state drive (SSD), or a combination thereof. The communication interface  2   a   3  may communicate with the plasma processing apparatus  1  via a communication line such as a local area network (LAN). 
     Shower Head 
     Next, a configuration of the shower head (shower head electrode assembly)  13  according to the embodiment will be described in comparison with a shower head  113  according to a reference example.  FIG.  2 A  is a longitudinal cross-sectional view enlarging a part of the shower head  113  according to the reference example, and  FIG.  2 B  is a plan view of a part of a back surface of a upper electrode  113 B taken from the plane IIB-IIB of  FIG.  2 A .  FIG.  3 A  is a longitudinal cross-sectional view enlarging a part of the shower head  13  according to the embodiment, and  FIG.  3 B  is a plan view of a part of the back surface of the upper electrode  13 B from the plane IIIB-IIIB of  FIG.  3 A . 
     Reference Example 
     The shower head  113  according to the reference example shown in  FIGS.  2 A and  2 B  has the upper electrode  113 B having a front surface  113 BS 2  and a back surface  113 BS 1  which is an opposite surface thereto, and a backing member  113 A having a support surface  113 AS and attached to the upper electrode  113 B. The support surface  113 AS is a lower surface of the backing member  113 A and contacts the back surface (upper surface)  113 BS 1  of the upper electrode  113 B. The front surface  113 BS 2  is a lower surface of the upper electrode  113 B and is exposed to plasma. 
     In the shower head  113 , a plurality of first gas flow paths  113 B h  and a plurality of second gas flow paths  113 A h  communicate vertically and are provided on a plurality of concentric circles.  FIG.  2 B , which is a plan view taken from the plane IIB-IIB of  FIG.  2 A , shows the gas flow paths when the back surface  113 BS 1  side is viewed from a boundary between the support surface  113 AS and the back surface  113 BS 1 , and shows part of the gas flow paths provided on the plurality of concentric circles. Four first gas flow paths  113 B h  and four second gas flow paths  113 A h  provided on the concentric circle (on the same circumference) with respect to a center CT shown in  FIG.  2 B  will be described below as an example. The center CT is a point through which a central axis of the shower head  113  passes, and a central axis of the disk-shaped upper electrode  113 B and the backing member  113 A is common to the central axis of the shower head  113 . 
     The backing member  113 A is made of, for example, aluminum and has an alumite-treated surface, thereby having plasma resistance. The backing member  113 A has the plurality of second gas flow paths  113 A h  for supplying gas from the gas diffusion chamber  113   b  to the support surface  113 AS. The processing gas introduced into the gas diffusion chamber  113   b   passes through the plurality of second gas flow paths  113 A h  and is discharged toward the upper electrode  113 B. That is, the processing gas flows through the plurality of second gas flow paths  113 A h . Each of the plurality of second gas flow paths  113 A h  is a round hole. 
     The upper electrode  113 B is an electrode that supplies high-frequency power (RF power) to the plasma processing space  10   s . The upper electrode  113 B is made of, for example, silicon. The front surface  113 BS 2  of the upper electrode  113 B contacts the plasma processing space  10 S and is exposed to the plasma. The upper electrode  113 B has the plurality of first gas flow paths  113 B h  penetrating the front surface  113 BS 2  and the back surface  113 BS 1 . Each of the plurality of first gas flow paths  113 B h  is a round hole. 
     As shown in  FIG.  2 B , the four first gas flow paths  113 B h  and the four second gas flow paths  113 A h  are provided on a concentric circle (on the same circumference) with respect to the center CT and are separated from each other at equal intervals. Each of the four second gas flow paths  113 A h  is connected to each of the four first gas flow paths  113 B h  on a one-to-one basis. 
     The shower head  113  is structured to introduce the processing gas supplied to the gas diffusion chamber  113   b  into the plasma processing space  10   s  through the plurality of second gas flow paths  13 A h  and the plurality of first gas flow paths  113 B h . 
     In the shower head  113  having such a structure, abnormal discharge may occur near the boundary between the upper electrode  113 B and the backing member  113 A. That is, the pressure of the processing gas may not be sufficiently lowered due to decrease in conductance in the first gas flow path  113 B h  formed on the back surface  113 BS 1  of the upper electrode  113 B and/or in the second gas flow path  113 A h  formed on the support surface  113 AS of the backing member  113 A. At this time, the abnormal discharge occurs inside the shower head  113 , i.e., inside the second gas flow path  113 A h  and/or the first gas flow path  113 B h . Therefore, the upper electrode  113 B and/or the backing member  113 A may be damaged or consumed, or the supply of the processing gas may be disturbed. 
     Embodiment 
     On the other hand, the shower head  13  according to the present embodiment increases the conductance in the first gas flow path  13 B h  and the second gas flow path  13 A h  at the boundary between the upper electrode  13 B and the backing member  13 A to sufficiently lower the pressure of the processing gas. This prevents the abnormal discharge from occurring inside the shower head  13 , i.e., inside the first gas flow path  13 B h  and the second gas flow path  13 A h . A configuration example of the shower head  13  according to the present embodiment will be described with reference to  FIGS.  3 A and  3 B . 
     The shower head  13  according to the present embodiment has the upper electrode  13 B having a front surface  13 BS 2  and a back surface  13 BS 1  which is an opposite surface thereto, and the backing member  13 A having a support surface  13 AS and attached to the upper electrode  13 B. The support surface  13 AS is a lower surface of the backing member  13 A and contacts the back surface (upper surface)  13 BS 1  of the upper electrode  13 B. The front surface  13 BS 2  is a lower surface of the upper electrode  13 B and is exposed to the plasma. 
     In the shower head  13 , the plurality of first gas flow paths  13 B h   1  and  13 B h   2  and the plurality of second gas flow paths  13 A h  communicate vertically and are provided on a plurality of concentric circles.  FIG.  3 B , which is a plan view taken from the plane IIIB-IIIB of  FIG.  3 A , shows gas flow paths when the back surface  13 BS 1  side is viewed from a boundary between the support surface  13 AS and the back surface  13 BS 1 , and shows part of the gas flow paths provided on the plurality of concentric circles. Eight first gas flow paths  13 B h   1  and  13 B h   2  and four second gas flow paths  13 A h  provided concentrically with respect to the center CT shown in  FIG.  3 B  will be described below as an example. The center CT is a point through which the central axis of the shower head  13  passes, and the central axis of the disk-shaped upper electrode  13 B and the backing member  13 A is common to the central axis of the shower head  13 . 
     The backing member  13 A is made of, for example, aluminum and has an alumite-treated surface, thereby having plasma resistance. The backing member  13 A has the plurality of second gas flow paths  13 A h  for supplying gas from the gas diffusion chamber  13   b  to the support surface  13 AS. The processing gas introduced into the gas diffusion chamber  13   b  passes through the plurality of second gas flow paths  13 A h  and is discharged toward the upper electrode  13 B. That is, the processing gas flows through the plurality of second gas flow paths  13 A h . Each of the plurality of second gas flow paths  13 A h  is an elongated hole extending in the radial direction with respect to the center CT. In other words, each of the plurality of second gas flow paths  13 A h  is configured such that the length in the radial direction is longer than the length in the circumferential direction with respect to the center CT. 
     The upper electrode  13 B is an electrode that supplies high-frequency power (RF power) to the plasma processing space  10   s . The upper electrode  13 B is made of, for example, silicon. The back surface  13 BS 1  of the upper electrode  13 B contacts the backing member  13 A. The front surface  13 BS 2  of the upper electrode  13 B is in contact with the plasma processing space  10   s . That is, the front surface  13 BS 2  of the upper electrode  13 B forms the inner surface of the plasma processing space  10   s  and is exposed to the plasma. The upper electrode  13 B has the plurality of first gas flow paths  13 B h   1  and  13 B h   2   penetrating the front surface  13 BS 2  and the back surface  13 BS 1 . Each of the plurality of first gas flow paths  13 B h   1  and  13 B h   2  is a round hole. 
     As shown in  FIG.  3 B , four first gas flow paths  13 B h   1  and four first gas flow paths  13 B h   2  are provided on concentric circles with respect to the center CT and are separated from each other at equal intervals. Each of the four second gas flow paths  13 A h  is connected to each of the eight first gas flow paths  13 B h   1  and  13 B h   2  on a one-to-two basis. That is, two first gas flow paths  13 B h   1  and  13 B h   2  are connected to one second gas flow path  13 A h . Therefore, when one second gas flow path  13 A h  and two first gas flow paths  13 B h   1  and  13 B h   2  form one group, four groups (four second gas flow paths  13 A h  and eight first gas flow paths  13 B h   1  and  13 B h   2 ) are provided spaced apart from each other. 
       FIGS.  4 A and  4 B  are longitudinal cross-sectional views showing further enlarged gas flow paths below the gas diffusion chamber  13   b  of  FIG.  3 A .  FIG.  4 B  shows dimensions of the gas flow paths shown in  FIG.  4 A .  FIGS.  4 A and  4 B  are cross-sectional views taken along line IV-IV of  FIG.  5 A , which will be described later. 
     The first gas flow paths  13 B h   1  and  13 B h   2  of the upper electrode  13 B pass through the back surface  13 BS 1  and the front surface  13 BS 2  and communicate with the bottom of the second gas flow path  13 A h . Each of the first gas flow paths  13 B h   1  and  13 B h   2  has narrowed portions  13 B h   12  and  13 B h   22  at a connection portion (lower side of the bottom) with the second gas flow path  13 A h . Even when the front surface  13 BS 2  of the upper electrode  13 B is exposed to the plasma and worn out, the pressure on an outlet side (front surface  13 BS 2  side) of the first gas flow paths  13 B h   1  and  13 B h   2  can be made substantially constant by the narrowed portions  13 B h   12  and  13 B h   22 . 
     The first gas flow paths  13 B h   1  and  13 B h   2  are arranged side by side in the longitudinal direction of the second gas flow path  13 A h , which is an elongated hole. The first gas flow paths  13 B h   1  and  13 B h   2  are respectively provided at positions extending in the vertical direction along longitudinal side surface  13 A h   3  of the second gas flow path  13 A h . 
       FIG.  5 A  is a plan view of a part of the support surface  13 AS of the backing member  13 A according to the embodiment and  FIG.  5 B  is an enlarged view of one of the second gas flow paths  13 A h  shown in  FIG.  5 A . As shown in  FIG.  5 A , each of the plurality of second gas flow paths  13 A h  is a slit-shaped elongated hole, and is configured such that the length of the elongated hole in the radial direction is longer than the length in the circumferential direction with respect to the central axis of the shower head  13 .  FIG.  5 A  shows the second gas flow paths  13 A h  disposed on a first circumference, a second circumference, a third circumference, a fourth circumference, and so on in the circumferential direction. All imaginary lines passing through both longitudinal ends of the elongated hole of the second gas flow path  13 A h  pass through the center CT (see  FIG.  3 B ). The intervals between the elongated holes on the same circumference are equal to each other, and the intervals between the elongated holes on different circumferences become narrower as the distance from the center CT increases. 
     As shown in  FIGS.  4 A and  4 B , the second gas flow path  13 A h  is chamfered at an opening of a boundary surface  13 AR (surface opposite to the support surface  13 AS) of the backing member  13 A with the gas diffusion chamber  13   b , and at the support surface  13 AS. The chamfered portions are inclined surfaces  13 A h   1  and  13 A h   2  that are inclined outward with respect to the side surface  13 A h   3  of the second gas flow path  13 A h . The chamfered portion is formed over the entire circumference. In the second gas flow path  13 A h , the outer edge of the elongated hole, i.e., the outer circumference of the chamfered inclined surfaces  13 A h   1  and  13 A h   2  has a substantially elliptical shape. Further, in each of the second gas flow paths  13 A h , the inner edge of the elongated hole in plan view, i.e., a portion surrounded by the side surface  13 A h   3  of the second gas flow path  13 A h  has an elongated slit shape. 
     Although the chamfered portions are shown as flat inclined surfaces  13 A h   1  and  13 A h   2  in  FIGS.  4 A and  4 B , the inclined surfaces  13 A h   1  and  13 A h   2  may have a curved surface curved outward. Therefore, an opening of the elongated hole of the second gas flow path  13 A h  has no corners and has a gradual surface, thereby further suppressing occurrence of the abnormal discharge in the second gas flow path  13 A h . As a secondary effect, the alumite treatment (surface processing) of the backing member  13 A can be facilitated by eliminating the corners. 
     As shown in  FIG.  4 B , the diameter φ1 of the first gas flow paths  13 B h   1  and  13 B h   2  is, for example, 0.8 mm and the diameter φ2 of the narrowed portions  13 B h   12  and  13 B h   22  is, for example, 0.5 mm. 
     The thickness H 1  of the backing member  13 A is 7.0 mm and the thickness H 2  of the upper electrode  13 B is 20 mm. The length of the narrowed portions  13 B h   12  and  13 B h   22  is about ⅒ of the total length of 20 mm of the first gas flow paths  13 B h   1  and  13 B h   2  including the narrowed portions  13 B h   12  and  13 B h   22 . 
     As shown in  FIGS.  4 B and  5 B , the longitudinal width W 1  of the inner edge of the elongated hole of the second gas flow path  13 A h  is 5.0 mm, and the longitudinal width W 2  of the outer edge of the elongated hole is 8.0 mm. The transverse width D 1  of the inner edge of the elongated hole of the second gas flow path  13 A h  is 0.2 mm, and the transverse width D 3  of the outer edge of the elongated hole is 3.2 mm. The width D 2  of the chamfered portion is 1.5 mm in plan view. The amount of chamfering in the radial direction and the amount of chamfering in the circumferential direction of the elongated hole are the same, and are 1.5 mm in plan view. By equalizing the amount of chamfering in the radial direction and the amount of chamfering in the circumferential direction of the elongated hole, the chamfering process can be facilitated. However, the amount of chamfering in the radial direction and the amount of chamfering in the circumferential direction of the elongated hole may be different. Further, in the present embodiment, the amount of chamfering is the same over the entire circumference. 
     At least a part of each of the first gas flow paths  13 B h   1  and  13 B h   2  is disposed in a position that can be seen from the second gas flow path  13 A h  in plan view. The first gas flow paths  13 B h   1  and  13 B h   2  are not limited to being arranged at both ends of the elongated hole of the second gas flow path  13 A h , and can be arranged side by side in the longitudinal direction of the elongated hole. 
     Modification 
       FIGS.  6 A to  6 C  are diagrams showing a modification of the configuration of the second gas flow path  13 A h  and the first gas flow path  13 B h  according to the embodiment. In  FIGS.  6 A to  6 C , the longitudinal width W 1  of the inner edge of the second gas flow path  13 A h  is 15 mm, and the longitudinal width W 2  of the outer edge thereof is 18 mm. Other dimensions are the same as those shown in  FIG.  5 B . Therefore, the longitudinal width W 1  of the inner edge of the second gas flow path  13 A h  may be 5.0 mm or more and 15 mm or less. Further, the longitudinal width W 2  of the outer edge of the second gas flow path  13 A h  may be 8.0 mm or more and 18 mm or less. 
     By increasing the length of the second gas flow path  13 A h  in the longitudinal direction, the number of first gas flow paths  13 B h  which communicate with each of the second gas flow paths  13 A h  can be increased. In the case of  FIG.  6 A , two first gas flow paths  13 B h   1  and  13 B h   2  are communicated with one second gas flow path  13 A h . In the case of  FIG.  6 B , four first gas flow paths  13 B h   1  to  13 B h   4  are communicated with one second gas flow path  13 A h . In the case of  FIG.  6 C , seven first gas flow paths  13 B h   1  to  13 B h   7  are communicated with one second gas flow path  13 A h . The diameter φ of the first gas flow paths  13 B h   1  to  13 B h   7  is 0.5 mm. 
     In the shower head  13  described above, the processing gas supplied to the gas diffusion chamber  13   b  passes through the second gas flow path  13 A h . The processing gas branches and flows into two or more first gas flow paths  13 B h  communicating with the bottom surface of the second gas flow path  13 A h . This increases the conductance in the first gas flow path  113 B h  and the second gas flow path  13 A h  at the boundary between the backing member  13 A and the upper electrode  13 B, thereby sufficiently reducing the pressure of the processing gas. As a result, it is possible to prevent the abnormal discharge from occurring inside the shower head  13 , i.e., inside the first gas flow path  13 B h  and the second gas flow path  13 A h . 
     Simulation Result 
     A simulation was performed on the amount of decrease in the pressure of the processing gas in the first gas flow path  13 B h  and the second gas flow path  13 A h .  FIGS.  7 A and  7 B  are diagrams showing a result of simulating the amount of decrease in the pressure of the processing gas according to the embodiment in comparison with the reference example. 
       FIG.  7 A  shows a simulation result of the amount of decrease in the pressure of the processing gas in the reference example. In the reference example, the second gas flow path  113 A h  penetrates the backing member  113 A, and the first gas flow paths  113 B h   1  and  113 B h   2  that are vertically connected penetrate the upper electrode  113 B. 
     The diameter of the first gas flow path  113 B h   1  is larger than the diameter of the second gas flow path  113 A h , and the diameter of the first gas flow path  113 B h   2  is larger than the diameter of the first gas flow path  113 B h   1 . That is, the first gas flow path  113 B h   2  expands in diameter from the first gas flow path  113 B h   1  and opens to the plasma processing space  10   s . 
       FIG.  7 B  shows a simulation result of the amount of decrease in the pressure of the processing gas in the gas flow path in a configuration in which branching into two first gas flow paths  13 B h   1  and  13 B h   2  is performed at the bottom surface of the second gas flow path  13 A h  according to the present embodiment described with reference to  FIGS.  3  and  4   . 
     In both  FIGS.  7 A and  7 B , the pressure in the plasma processing chamber  10  was set at 17 mTorr (2.27 Pa). A total flow rate of the gas to be supplied was about 600 sccm, and the number of gas flow paths (gas holes) was  1000 . In the present embodiment, about 1000 second gas flow paths  13 A h , 1000 first gas flow paths  13 B h   1 , and 1000 first gas flow paths  13 B h   2  are provided. In the present embodiment, 2000 holes are opened in the plasma processing space  10   s . On the other hand, in the reference example, about 1000 circular holes formed by the second gas flow path  113 A h  and the first gas flow paths  13 B h   1  and  13 B h   2  communicating vertically are provided. In the reference example, 1000 holes are opened in the plasma processing space  10   s . 
     Simulation results of the pressures P 1  to P 4  of the processing gas are shown in the Tables of  FIGS.  7 A and  7 B . In the reference example, the pressure P 1  of the processing gas at the outlet of the first gas flow path  113 B h   2 , the pressure P 2  at the inlet of the first gas flow path  113 B h   2 , the pressure P 3  of the first gas flow path  113 B h   1  at the boundary between the backing member  113 A and the upper electrode  113 B, and the pressure P 4  at the inlet of the second gas flow path  113 A h  were calculated. For the pressures P 2  to P 4  other than the pressure P 1 , the pressures at a center, a middle, and an edge of each gas flow path were calculated. 
     In the present embodiment, the pressure P 1  of the processing gas at the outlet of the first gas flow paths  13 B h   1  and  13 B h   2 , the pressure P 2  at the outlet of the narrowed portion, the pressure P 3  of the first gas flow paths  13 B h   1  and  13 B h   2  at the boundary between the backing member  13 A and the upper electrode  13 B, and the pressure P 4  at the inlet of the second gas flow path  13 A h  were calculated. For the pressures P 2  to P 4  other than the pressure P 1 , the pressures at a center, a middle, and an edge of each gas flow path were calculated. 
     As a result, in the reference example, when the pressure at the inlet of the second gas flow path  113 A h  is 100% (total pressure), the amount of decrease in the total pressure along the second gas flow path  113 A h  is 26%, and the amount of decrease in the total pressure along the first gas flow path  113 B h  (the first gas flow paths  113 B h   1  and  113 B h   2 ) is 74%. All of the center, the middle, and the edge have approximately the same amount of decrease. That is, a ratio of the amount of decrease in the total pressure along the second gas flow path  113 A h  to the amount of decrease in the total pressure along the first gas flow path  113 B h  is 26%:74% = 0.4:1.0. 
     On the other hand, in the present embodiment, when the pressure at the inlet of the second gas flow path  13 A h  is 100% (total pressure), the amount of decrease in the total pressure along the second gas flow path  13 A h  is 47%, and the amount of decrease in the total pressure along the first gas flow path  13 B h  (the first gas flow paths  13 B h   1  and  13 B h   2 ) is 53%. All of the center, the middle, and the edge have approximately the same amount of decrease. That is, a ratio of the amount of decrease in the total pressure along the second gas flow path  13 A h  to the amount of decrease in the total pressure along the first gas flow path  13 B h  is 47%:53% = 0.9:1.0. 
     Therefore, the shower head  13  according to the present embodiment can sufficiently lower the pressure of the processing gas at the boundary between the backing member  13 A and the upper electrode  13 B as compared with the reference example. By lowering the pressure of the processing gas, the abnormal discharge can be prevented from occurring at the boundary between the backing member  13 A and the upper electrode  13 B. 
     In the shower head  13  according to the present embodiment, the ratio of the amount of decrease in the total pressure along the second gas flow path  13 A h  to the amount of decrease in the total pressure along the first gas flow path  13 B h  ranges from 0.6:1.0 to 1.2:1.0. According to this, the pressure of the processing gas can be lowered at the boundary between the backing member  13 A and the upper electrode  13 B, and the abnormal discharge can be prevented from occurring. 
     However, the ratio of the amount of decrease in the total pressure along the second gas flow path  13 A h  and the amount of decrease in the total pressure along the first gas flow path  13 B h  is more preferably 0.8:1.0 to 1.1:1.0 and still more preferably 0.9:1.0 to 1.0:1.0. According to this, the pressure of the processing gas can be lowered at the boundary between the backing member  13 A and the upper electrode  13 B, and the abnormal discharge can be prevented from occurring more reliably. 
     As described above, according to the shower head  13  and the plasma processing apparatus  1  of the present embodiment, the abnormal discharge occurring inside the shower head  13  can be prevented.