Patent Publication Number: US-2021193443-A1

Title: Baffle unit and substrate processing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is based upon and claims priority to Japanese Patent Application No. 2015-229510 filed on Dec. 15, 2019, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a baffle unit and a substrate processing apparatus. 
     BACKGROUND 
     In a substrate processing apparatus that applies desired processing, such as etching, to substrates, a baffle unit through which a gas flows is provided. 
     Patent Document 1 describes a baffle plate assembly including a baffle plate on which multiple slots are arrayed in the radial direction. 
     RELATED ART DOCUMENT 
     Patent Document 
     [Patent Document 1] Japanese National Publication of International Patent Application No. 2007-525825 
     SUMMARY 
     In one aspect, the present disclosure provides a baffle unit and a substrate processing apparatus that suppress damage to the baffle unit. 
     In order to solve the problem, according to one aspect, there is provided a baffle unit that includes an inner ring, an outer ring disposed outside the inner ring, and a connecting portion connecting the inner ring with the outer ring. The connecting portion includes multiple openings arranged in a radial direction of the baffle unit and in a circumferential direction of the baffle unit, each of the multiple openings being arcuate and extending in the circumferential direction; multiple rigid portions each being disposed between the adjacent openings of the multiple openings that are adjacent to each other on a same concentric circle of the baffle unit; and multiple walls each being formed between the adjacent openings of the multiple openings that are adjacent to each other in the radial direction. Each of the multiple walls connects a rigid portion of the multiple rigid portions with another rigid portion of the multiple rigid portions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating a schematic configuration of a substrate processing apparatus according to an embodiment; 
         FIG. 2  is a partially enlarged plan view illustrating an example of a baffle plate according to the embodiment; 
         FIG. 3  is a diagram schematically illustrating deformation of the baffle plate according to the embodiment, in which an inner ring and an outer ring are shifted in the height direction; 
         FIG. 4  is an example of a cross-sectional perspective view illustrating a cross-sectional shape of a wall section and direction of deformation of the wall; 
         FIG. 5  is a partially enlarged plan view illustrating an example of a baffle plate according to a first reference example; 
         FIG. 6  is a partially enlarged plan view illustrating an example of a baffle plate according to a second reference example; and 
         FIG. 7  is a diagram schematically illustrating deformation of the baffle plate according to the second reference example, in which an inner ring and an outer ring are shifted in the height direction. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In the following, embodiments for carrying out the present disclosure will be described with reference to the drawings. In each drawing, elements having identical features are given the same reference symbols and overlapping descriptions may be omitted. 
     Substrate Processing Apparatus 
     A substrate processing apparatus  1  according to an embodiment will be described with reference to  FIG. 1 .  FIG. 1  is a cross-sectional view illustrating an example of the substrate processing apparatus  1  according to the present embodiment. 
     The substrate processing apparatus  1  includes a chamber  10 . The chamber  10  provides an interior space  10   s  therein. The chamber  10  includes a chamber body  11 . The chamber body  11  has a generally cylindrical shape. The chamber body  11  is formed of, for example, aluminum. A corrosion resistant film is provided on the inner wall surface of the chamber body  11 . The film may be formed of ceramic such as aluminum oxide or yttrium oxide. 
     A passage  11   p  is formed in the side wall of the chamber body  11 . A substrate W is transferred between the interior space  10   s  and the exterior of the chamber  10  through the passage  11   p.  The passage  11   p  is opened and closed by a gate valve  11   g  provided along the side wall of the chamber body  11 . 
     On the bottom of the chamber body  11 , a support  13  is provided via a bottom plate  12  formed of aluminum or the like. The support  13  is formed of an insulating material. The support  13  is generally cylindrical in shape. The support  13  extends upward from the bottom of the chamber body  11  in the interior space  10   s.  At the upper portion of the support  13 , a support platform  14  is disposed. The support platform  14  is configured to support the substrate W in the interior space  10   s.    
     The support platform  14  includes a lower electrode  18  and an electrostatic chuck  20 . The support platform  14  may further include an electrode plate  16 . The electrode plate  16  is formed of a conductor such as aluminum, and is generally disc-shaped. The lower electrode  18  is disposed on the electrode plate  16 . The lower electrode  18  is formed of a conductor such as aluminum, and is generally disc-shaped. The lower electrode  18  is electrically connected to the electrode plate  16 . 
     The electrostatic chuck  20  is provided on the lower electrode  18 . A substrate W is placed on the upper surface of the electrostatic chuck  20 . The electrostatic chuck  20  has a body and an electrode. The body of the electrostatic chuck  20  is generally disc-shaped, and is formed of a dielectric material. The electrode of the electrostatic chuck  20  is a film-like electrode provided within the body of the electrostatic chuck  20 . The electrode of the electrostatic chuck  20  is connected to a direct-current (DC) power supply  20   p  via a switch  20   s.  When voltage from the DC power supply  20   p  is applied to the electrode of the electrostatic chuck  20 , electrostatic attracting force is generated between the electrostatic chuck  20  and the substrate W. By the electrostatic attractive force, the substrate W is held by the electrostatic chuck  20 . 
     An edge ring  25  is disposed on a periphery of the lower electrode  18  to surround the edge of the substrate W. The edge ring  25  improves in-plane uniformity of plasma processing applied to the substrate W. The edge ring  25  may be formed of silicon, silicon carbide, quartz, or the like. 
     A flow passage  18   f  is provided within the lower electrode  18 . A heat exchange medium (e.g., refrigerant) is supplied to the flow passage  18   f  from a chiller unit (not illustrated) provided outside the chamber  10  through a pipe  22   a.  The heat exchange medium supplied to the flow passage  18   f  is returned to the chiller unit via a pipe  22   b.  In the substrate processing apparatus  1 , the temperature of the substrate W placed on the electrostatic chuck  20  is adjusted by heat exchange between the heat exchange medium and the lower electrode  18 . 
     The substrate processing apparatus  1  is provided with a gas supply line  24 . The gas supply line  24  supplies heat transfer gas (e.g., He gas) from a heat transfer gas supply mechanism to a gap between the upper surface of the electrostatic chuck  20  and the bottom surface of the substrate W. 
     The substrate processing apparatus  1  further includes an upper electrode  30 . The upper electrode  30  is provided above the support platform  14 . The upper electrode  30  is supported on the top of the chamber body  11  via a member  32 . The member  32  is formed of an insulating material. The upper electrode  30  and the member  32  occlude the top opening of the chamber body  11 . 
     The upper electrode  30  may include a top plate  34  and a support  36 . The lower surface of the top plate  34  is exposed to the interior space  10   s,  and defines the interior space  10   s.  The top plate  34  may be formed of a low resistance conductor or semiconductor with low Joule heat generation. The top plate  34  has multiple gas discharge holes  34   a  penetrating the top plate  34  in a thickness direction of the top plate  34 . 
     The support  36  removably supports the top plate  34 . The support  36  is formed of an electrically conductive material such as aluminum. Inside the support  36 , a gas diffusion chamber  36   a  is provided. The support  36  has multiple gas holes  36   b  extending downward from the gas diffusion chamber  36   a.  The multiple gas holes  36   b  communicate with the multiple gas discharge holes  34   a,  respectively. A gas inlet  36   c  is formed in the support  36 . The gas inlet  36   c  is connected to the gas diffusion chamber  36   a.  A gas supply line  38  is connected to the gas inlet  36   c.    
     Valves  42 , flow controllers  44 , and gas sources  40  are connected to the gas supply line  38 . The gas sources  40 , the valves  42 , and the flow controllers  44  constitute a gas supply section. Each of the valves  42  may be an open/close valve. Each of the flow controllers  44  is a mass flow controller or a pressure-controlled flow controller. Each of the gas sources  40  is connected to the gas supply line  38  via a corresponding open/close valve of the valves  42  and a corresponding flow controller of the flow controllers  44 . 
     In the substrate processing apparatus  1 , a shield  46  is removably provided along the inner wall surface of the chamber body  11 . The shield  46  prevents reaction by-products from adhering to the chamber body  11 . Also, a shield  47  is removably provided along the outer periphery of the support  13  and support platform  14 . The shield  47  prevents reaction by-products from adhering to the support  13  and support platform  14 . The shields  46  and  47  are, for example, made of quartz (SiO 2 ). A cylindrical member  48  formed of an insulator having corrosion resistance is disposed below the shield  47 . 
     A baffle unit  49  is provided between the outer side wall of the support  13  and the inner side wall of the chamber body  11 . The baffle unit  49  includes a baffle plate  100  and a cylindrical member  150 . 
     The baffle plate  100  is a disc-shaped member having a circular hole, into which the support  13  is inserted, in the center of the baffle plate  100 . The baffle plate  100  has an inner ring  110 , an outer ring  120  and a connecting portion  130 . The inner ring  110  is an annular member provided around the outer periphery of the support  13 . The inner ring  110  is disposed on the bottom plate  12  and below the shield  47 . The outer ring  120  is an annular member provided around the outer circumferential side of the inner ring  110 . The connecting portion  130  connects the inner ring  110  and the outer ring  120 , and multiple openings (see  FIG. 2 , below) through which gas can flow are formed in the connecting portion  130 . The baffle plate  100  is integrally formed from a material containing Si, such as Si or SiC, or a material containing aluminum. 
     The cylindrical member  150  is a generally cylindrical member extending in a height direction (i.e., axial direction, which is a vertical direction in  FIG. 1 ). The upper portion of the cylindrical member  150  is connected to the shield  46 . The lower portion of the cylindrical member  150  is connected to the outer ring  120  of the baffle plate  100 . The cylindrical member  150  may be formed of a material containing Si, such as Si or SiC, or a material containing aluminum. 
     It is described that the configuration of the baffle unit  49  is such that the inner ring  110 , the outer ring  120 , and the connecting portion  130  are integrally formed as the baffle plate  100  and the cylindrical member  150  is formed separately from the baffle plate  100 . However, the configuration of the baffle unit  49  is not limited thereto. The baffle plate  100  and the cylindrical member  150  may be integrally formed as a baffle unit  49 . The baffle unit  49  may only consist of the plate-like baffle plate  100  without including the cylindrical member  150 . 
     An exhaust port  11   e  is provided below the baffle unit  49  and at the bottom of the chamber body  11 . An exhaust device  50  is connected to the exhaust port lie through an exhaust pipe (not illustrated). The exhaust device  50  includes a pressure regulating valve and a vacuum pump such as a turbomolecular pump. 
     The substrate processing apparatus  1  includes a first radio frequency power supply  62  and a second radio frequency power supply  64 . The first radio frequency power supply  62  is a power source that generates first radio frequency power. The first radio frequency power has a frequency suitable for generating a plasma. The frequency of the first radio frequency power is, for example, a frequency in the range of 27 MHz to 100 MHz. The first radio frequency power supply  62  is connected to the lower electrode  18  via a matcher  66  and the electrode plate  16 . The matcher  66  includes circuitry for causing the output impedance of the first radio frequency power supply  62  to match impedance of the load side (lower electrode  18  side). The first radio frequency power supply  62  may be connected to the upper electrode  30  via the matcher  66 . The first radio frequency power supply  62  constitutes an exemplary plasma generator. 
     The second radio frequency power supply  64  is a power source that generates second radio frequency power. The second radio frequency power has a frequency lower than the frequency of the first radio frequency power. In a case in which the second radio frequency power is used in conjunction with the first radio frequency power, the second radio frequency power is used as radio frequency power for biasing to draw ions into the substrate W. The frequency of the second radio frequency power is, for example, a frequency in the range of 400 kHz to 13.56 MHz. The second radio frequency power supply  64  is connected to the lower electrode  18  via a matcher  68  and the electrode plate  16 . The matcher  68  includes circuitry for causing the output impedance of the second radio frequency power supply  64  to match impedance of the load side (lower electrode  18  side). 
     It should be noted that a plasma may be generated using the second radio frequency power, without using a first radio frequency power. That is, a plasma may be generated using only single radio frequency power. In such a case, the frequency of the second radio frequency power may be greater than 13.56 MHz, for example 40 MHz. In this case, the substrate processing apparatus  1  may not include the first radio frequency power supply  62  and the matcher  66 . The second radio frequency power supply  64  constitutes an exemplary plasma generator. 
     In the substrate processing apparatus  1 , gas is supplied from the gas supply to the interior space  10   s  to produce a plasma. Also, as the first radio frequency power and/or the second radio frequency power are supplied, a radio frequency electric field is generated between the upper electrode  30  and the lower electrode  18 . The generated radio frequency electric field generates a plasma. 
     The substrate processing apparatus  1  includes a power supply  70 . The power supply  70  is connected to the upper electrode  30 . The power supply  70  applies voltage to the upper electrode  30  to draw positive ions that are present in the interior space  10   s  into the top plate  34 . 
     The substrate processing apparatus  1  may further include a controller  80 . The controller  80  may be a computer including a processor, a storage device such as a memory, an input device, a display device, an input/output interface of a signal, or the like. The controller  80  controls each part of the substrate processing apparatus  1 . An operator can perform input operations of commands to manage the substrate processing apparatus  1 , by using the input device of the controller  80 . The controller  80  can also display an operation status of the substrate processing apparatus  1  on the display device. Further, a control program and recipe data are stored in the storage device. The control program is executed by the processor to cause the substrate processing apparatus  1  to perform various processes. The processor executes the control program, and controls each part of the substrate processing apparatus  1  in accordance with the recipe data. 
     Next, the baffle plate  100  will be further described with reference to  FIG. 2 .  FIG. 2  is a partially enlarged plan view illustrating an example of the baffle plate  100  according to the present embodiment. 
     The baffle plate  100  includes the annular inner ring  110 , the annular outer ring  120  disposed outside the inner ring  110  in the radial direction, and the connecting portion  130  connecting the inner ring  110  and the outer ring  120 . The inner ring  110  and the outer ring  120  are formed concentrically. Multiple arcuate openings  131 A to  131 M, each extending circumferentially, are formed in the connecting portion  130 . The openings  131 A to  131 M are arranged in the radial direction and in the circumferential direction. Each of the openings  131 A to  131 M is formed into an arc-shaped slot hole in which the central axis of the slot is an arc. 
     On the baffle plate  100 , the multiple (two or more) openings  131 A to  131 M are formed, when seen from the radial direction. Note that the respective openings ( 131 A to  131 M) arranged in the radial direction in  FIG. 2  are denoted by  131 A,  131 B, . . . ,  131 M, from a side closer to the central axis of the baffle plate  100  toward the outer circumference of the baffle plate  100 . 
     Further, on one concentric circle of the baffle plate (connecting portion  130 ), multiple (two or more) openings ( 131 A,  131 B, . . . , or  131 M) are formed, seen from the circumferential direction. In the present embodiment, the same reference symbol is assigned to openings disposed on the same concentric circle of the baffle plate (connecting portion  130 ). That is, multiple (at least two or more) openings  131 A are formed on a concentric circle of the connecting portion  130  that is concentric with the inner ring  110  and that is located closest to the inner ring  110 . Similarly, the multiple openings  131 B, the multiple openings  1310 , . . . , and the multiple openings  131 M are formed on other concentric circles concentric with the inner ring  110  respectively. 
     A rigid portion  132 A is formed between adjacent openings  131 A and  131 A arranged on the same concentric circle. Similarly, between openings  131 B to  131 M and their respective adjacent openings  131 B to  131 M on the same concentric circles, rigid portions  132 B to  132 M are formed, respectively. Here, the rigid portions  132 A to  132 M are more rigid and less deformable than walls  133 A to  133 L to be described below. 
     Further, because the openings  131 A to  131 M are arranged in the baffle plate  100  in the radial direction, an arcuate wall  133 A extending in the circumferential direction concentric with the inner ring  110  is formed between the openings  131 A and  131 B adjacent in the radial direction. Similarly, between the opening  131 B and the opening  131 C adjacent in the radial direction, between the opening  131 C and the opening  131 D adjacent in the radial direction, . . . , and between the opening  131 L and the opening  131 M adjacent in the radial direction, arcuate walls  133 B to  133 L, which extend in the circumferential direction concentric with the inner ring  110 , are formed, respectively. Here, the walls  133 A to  133 L are less rigid and more deformable than the rigid portions  132 A to  132 M. 
     The cross-sectional shape of the walls  133 A to  133 L, cut along a plane whose normal is the circumferential direction (a plane perpendicular to the extending directions of the walls  133 A to  133 L), is generally rectangular, as illustrated in  FIG. 4  below. Specifically, the cross-sectional shape of each of the walls  133 A to  133 L is longer (greater) in the vertical direction (i.e., height direction, or thickness direction of the baffle plate  100 ) as compared to the lateral direction (i.e., radial direction, or a direction in which the walls  133 A to  133 L are arranged). 
     Further, the openings  131 B formed in the circumferential direction are arranged such that each of the openings  131 B is shifted by a certain amount in the circumferential direction of the baffle plate  100 , with respect to an adjacent opening  131 A of the openings  131 A. Specifically, if the length of an arc between the centers of two adjacent openings  131 A is referred to as a “pitch of the openings  131 A”, the opening  131 A and the opening  131 B adjacent to the opening  131 A are mutually shifted by approximately half the pitch of the opening  131 A in the circumferential direction of the baffle plate  100 . Similarly, if the lengths of respective arcs between the centers of adjacent openings  131 B,  131 C, . . . , and  131 M are referred to as “pitches of the openings  131 B,  131 C, . . . , and  131 M”, the openings  131 C to  131 M are positioned in the circumferential direction such that the openings  131 C to  131 M are each shifted by approximately half the pitches of the openings  131 B to  131 L in the circumferential direction of the baffle plate  100 , relative to the openings  131 B to  131 L adjacent to the openings  131 C to  131 M respectively. Similarly, the rigid portions  132 B formed in the circumferential direction are arranged such that each of the rigid portions  132 B is shifted by half the pitch of the openings  131 A in the circumferential direction of the baffle plate  100 , relative to the adjacent rigid portion  132 A. Similarly, the rigid portions  132 C to  132 M formed in the circumferential direction are arranged such that each of the respective rigid portions  132 C to  132 M are shifted by half the pitches of the openings  131 B to  131 L in the circumferential direction of the baffle plate  100 , relative to the adjacent rigid portions  132 B to  132 L formed in the circumferential direction. In other words, lines on each of which the rigid portions  132 A,  132 C,  132 E,  132 G,  1321 ,  132 K, and  132 M are linearly arranged in the radial direction, and lines on each of which the rigid portions  132 B,  132 D,  132 F,  132 H,  132 J, and  132 L are linearly arranged in the radial direction, are formed on the connecting portion  130 . 
     Because of the above-described structure, the arcuate wall  133 A is formed so as to connect the rigid portion  132 A with the rigid portion  132 B. Similarly, the arcuate walls  133 B to  133 L are formed so as to connect the rigid portions  132 B to  132 L with the rigid portions  132 C to  132 M, respectively. 
     In addition, the walls  133 A to  133 L, which are easily deformable, are formed such that the circumferential length (i.e., arc length) of each of the walls  133 A to  133 L is equal to each other. For example, as illustrated in  FIG. 2 , let the circumferential length of the wall  133 A be “L 1 ”, and let the circumferential length of the wall  133 L be “L 2 ”. In this case, a relationship of “L 1 =L 2 ” is established. 
     In other words, the region bounded by a line, on which the rigid portions  132 A,  132 C,  132 E,  132 G,  1321 ,  132 K, and  132 M in odd numbers counted from the radially inner side are aligned, and by a line on which the rigid portions  132 B,  132 D,  132 F,  132 H,  132 J,  132 L, and  132 L in even numbers counted from the radially inner side are aligned, is a deformable region in which the walls  133 A to  133 L, which are easily deformed, are disposed. The deformable region has a rectangular shape, in a plan view of the baffle plate  100 . 
     Furthermore, the rigid portions  132 A to  132 M, which are not deformed easily, are formed such that the circumferential widths (i.e., arc lengths) of the rigid portions  132 A to  132 M increase toward the outside. For example, as illustrated in  FIG. 2 , let the circumferential width of the rigid portion  132 B be “W 1 ” and let the circumferential width of the rigid portion  132 L be “W 2 ”. In this case, a relationship of “W 1 &lt;W 2 ” is established. In other words, the circumferential widths of the rigid portions  132 A to  132 M are adjusted such that the circumferential length of each of the walls  133 A to  133 L is equal. 
     Note that a hole  134  may be formed in each of the rigid portions  132 A to  132 M. Further, the hole  134  may be formed in the shape of an arc-shaped slot hole. By forming the holes  134  in the rigid portions  132 A to  132 M, an aperture ratio of the baffle plate  100 , which is a ratio of an opened portion in the baffle plate  100 , is increased, and pressure loss can be reduced. 
     As illustrated in  FIG. 1 , the inner ring  110  of the baffle plate  100  is secured to the bottom plate  12  provided at the center of the bottom of the chamber  10 . In contrast, the outer ring  120  of the baffle plate  100  is secured to the shield  46  that is disposed on the upper portion of the side wall of the chamber  10  via the cylindrical member  150 . Accordingly, difference in a height direction (i.e., vertical direction) may occur between the inner ring  110  and the outer ring  120  of the baffle plate  100 , due to a stacking tolerance of the chamber  10 , thermal expansion, or the like. 
       FIG. 3  schematically illustrates deformation of the baffle plate  100  according to the present embodiment, when the inner ring  110  and the outer ring  120  are mutually shifted in the vertical direction.  FIG. 4  is an example of a cross-sectional view illustrating a cross-sectional shape and directions of deformation of the walls  133 A to  133 L. 
     When the inner ring  110  and the outer ring  120  are mutually shifted by the difference H in the vertical direction, the walls  133 A to  133 L receive a torsional deformation force (indicated by black-coated arrows in  FIG. 4 ) rather than a deformation force in the height direction (indicated by an outline arrow in  FIG. 4 ). The difference H in the vertical direction between the inner ring  110  and the outer ring  120  is absorbed, as each of the walls  133 A to  133 L is torsionally deformed to a small degree. Further, by making the circumferential length of each of the walls  133 A to  133 L equal, concentration of deformation when the walls  133 A to  133 L are deformed can be suppressed. Accordingly, even if the inner ring  110  and the outer ring  120  are mutually shifted by the difference H in the vertical direction, damage of the baffle plate  100  can be prevented. 
     Here, the baffle plate  100  according to the present embodiment will be described by comparing with baffle plates  200  and  300  according to reference examples. 
       FIG. 5  is a partially enlarged plan view illustrating an example of the baffle plate  200  according to a first reference example. The baffle plate  200  according to the first reference example has an inner ring  210 , an outer ring  220 , and a connecting portion  230 . In the connecting portion  230 , openings (slot hole)  231  each extending in the radial direction are formed. Thus, in the baffle plate  200 , walls  232  each extending in the radial direction are formed. In such a configuration, if the inner ring  210  and the outer ring  220  of the baffle plate  200  are mutually shifted by a difference H in the vertical direction, both ends of each of the walls  232  are mutually shifted by approximately H/2 in the vertical direction, and a deformation amount in the vertical direction per wall  232  is greater than that in the baffle plate  100  according to the present embodiment. Also, the direction of deformation of the wall  232  is a vertical direction of a rectangle of the cross-section of the wall  232  (i.e., direction indicated by the outline arrow in  FIG. 4 ). Therefore, the baffle plate  200  according to the first reference example may be damaged because of occurrence of height difference between the inner ring  210  and the outer ring  220 . 
       FIG. 6  is a partially enlarged plan view illustrating an example of the baffle plate  300  according to a second reference example. The baffle plate  300  according to the second reference example has an inner ring  310 , an outer ring  320 , and a connecting portion  330 . In the connecting portion  330 , openings  331  each extending in the circumferential direction are formed. A rigid portion  332  is formed between the adjacent openings  331 . Walls  333  are formed such that each of the walls  333  connects the rigid portions  332  disposed at its both ends. Here, in the baffle plate  300  of the second reference example, the circumferential length (width) of each of the rigid portions  332  is substantially the same. For example, the circumferential width W 3  of the rigid portion  332  at the inner ring side and the circumferential width W 4  of the rigid portion  332  at the outer ring side are substantially the same. In other words, in the baffle plate  300  of the second reference example, the circumferential length of the wall  333  of an arcuate shape increases toward the outside of the baffle plate  300 . For example, the circumferential length L 3  of the wall  333  at inner ring side is shorter than the circumferential length L 4  of the wall  333  at the outer ring side. 
       FIG. 7  is a diagram schematically illustrating deformation of the baffle plate  300  according to the second reference example when the inner ring  310  and the outer ring  320  are mutually shifted in the vertical direction. As illustrated in  FIG. 6 , because the circumferential length of the wall  333  located at the inner side of the baffle plate  300  differs from that located at the outer side of the baffle plate  300 , the wall  333  located at the outer side is more deformable than the wall  333  located at the inner side. Therefore, if the inner and outer rings  310  and  320  are mutually shifted by a difference H in the vertical direction, the amount of deformation in the wall  333  located at the outer side becomes significantly large. Therefore, the baffle plate  300  according to the second reference example may be damaged due to occurrence of height difference between the inner ring  310  and the outer ring  320 . 
     In contrast, as the baffle unit  49  (the baffle plate  100 ) according to the present embodiment can suppress concentration of deformation, even if a height difference (i.e., difference in the vertical direction) H occurs between the inner ring  110  and the outer ring  120 , damage of the baffle plate  100  can be prevented. 
     Further, in the baffle unit  49  (the baffle plate  100 ) according to the present embodiment, because deformation of each of the walls  133 A to  133 L can be reduced, even if a material containing Si, such as Si or SiC, having higher stiffness than a metallic material (for example, aluminum) is used as a material of the baffle unit  49 , the difference H in the vertical direction between the inner ring  110  and the outer ring  120  can be absorbed, thereby preventing damage to the baffle plate  100 . Accordingly, the substrate processing apparatus  1  according to the present embodiment can use a material containing Si, such as Si, SiC, or SiO 2 , as a material for the shields  46  and  47  and the baffle unit  49 . If an aluminum material having a protective film (for example, Y 2 O 3 ) formed on the surface is used as a material of the shields  46  and  47  and the baffle unit  49 , during plasma processing of a substrate W, an element (Y) derived from the protective film is generated by the plasma, and the element (Y) derived from the protective film may affect the processing of the substrate W. In contrast, if a material containing Si, such as Si, SiC, or SiO 2 , is used as a material of the shields  46  and  47  and the baffle unit  49 , influence on the processing of the substrate W can be reduced. 
     Also, in the baffle unit  49  (baffle plate  100 ) according to the present embodiment, both the inner and outer ends of the baffle unit  49  can be secured. This facilitates ensuring electrical conductivity between the baffle unit  49  and the bottom plate  12 . 
     Also, in the baffle unit  49  (baffle plate  100 ) according to the present embodiment, it is preferable that a shape of the cross-section of each of the walls  133 A to  133 L that is cut along a plane whose normal is the circumferential direction (a plane perpendicular to the extending directions of the walls  133 A to  133 L) is rectangular. This makes it easier to deform the walls  133 A to  133 L in a torsional direction. In addition, it is preferable that the aspect ratio of the cross-section of each of the walls  133 A to  133 L that is cut along a plane whose normal is the circumferential direction (a plane perpendicular to the extending directions of the walls  133 A to  133 L), which is a ratio of the height (length in the vertical direction) of the cross section to the width (length in the horizontal direction) of the cross section, is equal to or greater than 1. Thus, because the radial width of the opening  131  can be increased to increase the aperture ratio of the baffle plate  100 , pressure loss can be reduced. 
     Although the embodiment and the like of the substrate processing apparatus  1  have been described, the present disclosure is not limited to the above-described embodiment and the like. Various modifications and enhancements can be made within the scope of the gist of the present disclosure as claimed.