Patent Publication Number: US-2021183685-A1

Title: Edge ring and substrate processing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Japanese Patent Application No. 2019-226533 filed on Dec. 16, 2019, the entire disclosures of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to an edge ring and a substrate processing apparatus. 
     BACKGROUND 
     In plasma processing on a substrate, an edge ring may be arranged along the outer periphery of the substrate arranged in a chamber having a predetermined degree of vacuum. By arranging the edge ring, the plasma processing can be performed uniformly across the surface of the substrate. 
     In addition, the plasma processing on the substrate is performed in a state where the substrate and the edge ring mounted on an electrostatic chuck are adsorbed to the electrostatic chuck by an electrostatic attraction force. Furthermore, to improve heat transfer between the substrate and the electrostatic chuck and heat transfer between the edge ring and the electrostatic chuck, a heat transfer gas such as He gas is supplied to a space between the electrostatic chuck and the substrate and to a space between the electrostatic chuck and the edge ring. 
     In the related art, an edge ring made of silicon carbide (SiC) (hereinafter, sometimes referred to as an “SiC edge ring”) is known. Due to high plasma resistance of the SiC edge ring, the frequency of replacement of the edge ring can be reduced. 
     Examples of related art include JP-A-2010-251723. 
     SUMMARY 
     The disclosure is directed to an edge ring that is replaced less frequently and capable of suppressing leakage of a heat transfer gas. 
     The edge ring according to an aspect of the disclosure has an annular first member and an annular second member. The first member has a recess on a lower surface and is made of a first material having plasma resistance. The second member is arranged in the recess of the first member and is made of a second material having a rigidity lower than that of the first material. 
     Using the edge ring according to the disclosure for the plasma processing reduces the frequency of replacement of the edge ring and suppresses the leakage of a heat transfer gas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a configuration example of a substrate processing apparatus; 
         FIG. 2  is a diagram illustrating an example of an edge ring and a wafer; and 
         FIG. 3  is a diagram illustrating a configuration example of the edge ring. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the technique of the disclosure will be described with reference to the drawings. In the following embodiments, the same components are designated by the same reference numerals. 
     &lt;Configuration of Substrate Processing Apparatus&gt; 
     In  FIG. 1 , a substrate processing apparatus  100  has a chamber  10  made of, for example, aluminum or stainless steel. The chamber  10  is grounded for safety. 
     A disc-shaped susceptor  11  is horizontally arranged in the chamber  10 . The susceptor  11  is arranged on a lower surface of an electrostatic chuck  25  on which a semiconductor substrate (hereinafter, also referred to as a “wafer W” in some cases) as a substrate to be processed and an edge ring ER are mounted. In addition, the susceptor  11  also functions as a lower electrode to which a radio frequency (RF) power is supplied. The susceptor  11  is made of, for example, aluminum and is supported by a cylindrical support portion  13  extending vertically upwards from the bottom of the chamber  10  via an insulating cylindrical holding member  12 . 
     An exhaust passage  14  is formed between the side wall of the chamber  10  and the cylindrical support portion  13 , an annular baffle plate  15  is arranged at the inlet or midway of the exhaust passage  14 , an exhaust port  16  is provided at the bottom of the chamber  10 , and an exhaust device  18  is connected to the exhaust port  16  via an exhaust pipe  17 . The exhaust device  18  has a vacuum pump and decompresses a processing space provided by the chamber  10  to a predetermined degree of vacuum. In addition, the exhaust pipe  17  has an automatic pressure control valve (APC), which automatically controls the pressure inside the chamber  10 . Moreover, a gate valve  20  that opens and closes a loading/unloading port  19  for the wafer W is provided to the side wall of the chamber  10 . 
     Radio frequency power supplies  21 - 1  and  21 - 2  are electrically coupled to the susceptor  11  via matching units  22 - 1  and  22 - 2 . The radio frequency power supply  21 - 1  supplies a radio frequency power to the susceptor  11  for plasma generation. It is preferable that the radio frequency power supply  21 - 1  supplies a radio frequency power of 27 to 100 MHz to the susceptor  11  and supplies a radio frequency power of, for example, 40 MHz to the susceptor  11 . In addition, the radio frequency power supply  21 - 2  supplies a radio frequency power to the susceptor  11  to attract ions to the wafer W. It is preferable that the radio frequency power supply  21 - 2  supplies a radio frequency power of 400 KHZ to 40 MHz to the susceptor  11  and supplies a radio frequency power of, for example, 3 MHz to the susceptor  11 . The matching unit  22 - 1  matches the output impedance of the radio frequency power supply  21 - 1  with the input impedance of the susceptor  11  side, and the matching unit  22 - 2  matches the output impedance of the radio frequency power supply  21 - 2  with the input impedance of the susceptor  11  side. 
     A shower head  24  as an upper electrode having a ground potential is arranged on the ceiling of the chamber  10 . 
     The electrostatic chuck  25  arranged on the upper surface of the susceptor  11  attracts the wafer W and the edge ring ER mounted on the electrostatic chuck  25  by an electrostatic attraction force. The electrostatic chuck  25  has a disc-shaped central portion  25   a , an annular outer peripheral portion  25   b , and a disc-shaped base portion  25   f  having a diameter larger than that of the central portion  25   a , and the central portion  25   a  projects upwards with respect to the outer peripheral portion  25   b . The lower surfaces of the central portion  25   a  and the outer peripheral portion  25   b  and the upper surface of the base portion  25   f  are adhered to each other to form the electrostatic chuck  25 . A wafer W is mounted on the upper surface of the central portion  25   a , and an edge ring ER that annularly surrounds the central portion  25   a  is mounted on the upper surface of the outer peripheral portion  25   b . In addition, the central portion  25   a  is formed by interposing an electrode plate  25   c  configured with a conductive film between a pair of dielectric films, while the outer peripheral portion  25   b  is formed by interposing electrode plates  25   d  and  25   e  configured with a conductive film between a pair of dielectric films. That is, the electrode plates  25   c ,  25   d , and  25   e  are provided inside the electrostatic chuck  25 . The electrode plate  25   c  is provided in a region corresponding to the wafer W inside the electrostatic chuck  25 . The electrode plates  25   d  and  25   e  are provided in a region corresponding to the edge ring ER inside the electrostatic chuck  25 . A DC power supply  26  is electrically connected to the electrode plate  25   c . A DC power supply  28  is electrically connected to the electrode plate  25   d . A DC power supply  29  is electrically connected to the electrode plate  25   e . Then, the electrostatic chuck  25  attracts and holds the wafer W by the Coulomb force or the Johnson-Rahbek force generated by the DC voltage applied to the electrode plate  25   c  from the DC power supply  26 . The electrostatic chuck  25  attracts and holds the edge ring ER by the Coulomb force or the Johnson-Rahbek force generated by the DC voltage applied to the electrode plates  25   d  and  25   e  from the DC power supplies  28  and  29 . That is, in a case where  FIG. 1  is viewed in plan view, inside the electrostatic chuck  25 , an electrode (first electrode) that electrostatically attracts the wafer W is provided such that the first electrode at least partially overlaps with the wafer W. An electrode (second electrode) that electrostatically attracts the edge ring ER is provided such that the second electrode at least partially overlaps with the edge ring ER. The second electrode may include two or more electrode parts. 
     As described above, the wafer W is mounted on the upper surface of the central portion  25   a  of the electrostatic chuck  25 , and the edge ring ER that annularly surrounds the central portion  25   a  is mounted on the upper surface of the outer peripheral portion  25   b  of the electrostatic chuck  25 . That is, the edge ring ER is arranged on the electrostatic chuck  25  so as to surround the periphery of the wafer W. In addition, the lower surface of the electrostatic chuck  25  and the upper surface of the susceptor  11  are in contact with each other. Therefore, the susceptor  11  and the electrostatic chuck  25  are formed as a stage on which the wafer W and the edge ring ER are mounted. 
     An annular cooling medium chamber  31  extending in the circumferential direction is provided inside the susceptor  11 . A cooling medium (for example, cooling water) having a predetermined temperature is circulated and supplied to the cooling medium chamber  31  via pipes  33  and  34  from a chiller unit  32 , and the processing temperature of the wafer W on the electrostatic chuck  25  is controlled by the temperature of the cooling medium. 
     Furthermore, the heat transfer gas (for example, He gas) from a heat transfer gas supply unit  35  is supplied to a space between the upper surface of the electrostatic chuck  25  and the lower surface of the wafer W and to a space between the upper surface of the electrostatic chuck  25  and the lower surface of the edge ring ER via a gas supply pipe  36  and gas introduction holes  101 ,  102 , and  103 . The gas supply pipe  36  is arranged to penetrate the susceptor  11  and the base portion  25   f  of the electrostatic chuck  25 . In addition, the gas introduction holes  101  and  102  connected to the gas supply pipe  36  are provided in the central portion  25   a  of the electrostatic chuck  25 , and the gas introduction hole  103  connected to the gas supply pipe  36  is provided in the outer peripheral portion  25   b  of the electrostatic chuck  25 . In the outer peripheral portion  25   b  of the electrostatic chuck  25 , the two electrode plates of the electrode plate  25   d  and the electrode plate  25   e  are arranged with the gas introduction hole  103  interposed between the electrode plate  25   d  and the electrode plate  25   e . The heat transfer gas supplied from the heat transfer gas supply unit  35  via the gas supply pipe  36  and the gas introduction holes  101 ,  102 , and  103  enhances the heat transfer between the wafer W and the electrostatic chuck  25  and the heat transfer between the edge ring ER and the electrostatic chuck  25 . 
     The shower head  24  on the ceiling has an electrode plate  37  having a large number of gas holes  37   a  and an electrode support  38  that supports the electrode plate  37 . In addition, a buffer chamber  39  is provided inside the electrode support  38 , and a gas supply pipe  41  from a processing gas supply unit  40  is connected to a gas introduction hole  38   a  of the buffer chamber  39 . 
     When, for example, a dry etching process is to be performed in the substrate processing apparatus  100 , first, the gate valve  20  is opened, and the wafer W is loaded into the chamber  10  and mounted on the electrostatic chuck  25 . Then, for example, a gas mixture containing C 4 F 8  gas, O 2  gas, and Ar gas with a predetermined flow rate ratio is introduced into the chamber  10  as a processing gas from the processing gas supply unit  40 , and the pressure of the inside of the chamber  10  is set to a predetermined value by the exhaust device  18 . In addition, a DC voltage is applied from the DC power supply  26  to the electrode plate  25   c , and a DC voltage is applied from the DC power supplies  28  and  29  to the electrode plates  25   d  and  25   e , so that the wafer W and the edge ring ER are electrostatically attracted on the electrostatic chuck  25 . Then, a radio frequency power is supplied to the susceptor  11  from the radio frequency power supplies  21 - 1  and  21 - 2 . Accordingly, the processing gas introduced through the shower head  24  is turned into plasma, and the surface of the wafer W is etched by radicals and ions contained in this plasma. 
     &lt;Positional Relationship Between Electrostatic Chuck, Edge Ring, and Wafer&gt; 
     In  FIG. 2 , the edge ring ER has an annular shape, and an inner peripheral portion  51  of the edge ring ER is formed to be thinner than an outer peripheral portion  52  of the edge ring ER. In addition, the outer peripheral portion  25   b  of the electrostatic chuck  25  is formed to be thinner than the central portion  25   a  of the electrostatic chuck  25 . The edge ring ER is mounted on the outer peripheral portion  25   b  of the electrostatic chuck  25 , and the wafer W is mounted on the central portion  25   a  of the electrostatic chuck  25 . In an example, the inner peripheral portion  51  of the edge ring ER is formed so that the upper surface of the inner peripheral portion  51  of the edge ring ER is lower than the upper surface of the central portion  25   a  of the electrostatic chuck  25 . In addition, in an example, the outer peripheral portion  52  of the edge ring ER is formed so that the upper surface of the outer peripheral portion  52  of the edge ring ER has substantially the same height as the upper surface of the wafer W or is higher than the upper surface of the wafer W. In addition, the wafer W has a disc shape, and the diameter of the wafer W is larger than the diameter of the central portion  25   a  of the electrostatic chuck  25 . Therefore, when the wafer W is mounted on the central portion  25   a  of the electrostatic chuck  25 , a peripheral edge portion  61  of the wafer W projects outwards from the central portion  25   a  of the electrostatic chuck  25 , and the lower surface of the peripheral edge portion  61  of the wafer W and the upper surface of the inner peripheral portion  51  of the edge ring ER face each other. 
     In addition, for example, six gas introduction holes  101  and six gas introduction holes  102  are provided in the central portion  25   a  of the electrostatic chuck  25 , and, for example, six gas introduction holes  103  are provided in the outer peripheral portion  25   b  of the electrostatic chuck  25 . The heat transfer gas is introduced into a space between the upper surface of the central portion  25   a  of the electrostatic chuck  25  and the lower surface of the wafer W through the gas introduction holes  101  and  102 , and the heat transfer gas is introduced into a space between the upper surface of the outer peripheral portion  25   b  of the electrostatic chuck  25  and the lower surface of the outer peripheral portion  52  of the edge ring ER through the gas introduction holes  103 . 
     &lt;Configuration of Edge Ring&gt; 
       FIG. 3  is a diagram illustrating a configuration example of the edge ring. An edge ring ER 1  illustrated in  FIG. 3  corresponds to the edge ring ER illustrated in  FIGS. 1 and 2 . 
     In  FIG. 3 , the edge ring ER 1  is formed by joining an annular member M 1  and an annular member M 2  via an adhesive layer B 2 . The member M 1  is made of a first material having plasma resistance, and the member M 2  is made of a second material having a rigidity lower than that of the first material. In other words, the second material constituting the member M 2  is more flexible than the first material constituting the member M 1 . Example of the first material constituting the member M 1  include silicon carbide, tungsten carbide (WC), magnesium oxide (MgO), or yttria (Y 2 O 3 ). In addition, example of the second material constituting the member M 2  can be silicon. 
     The member M 1  has a recess C 1  in a lower surface S 11  of the member M 1 , and the member M 2  is arranged in the recess C 1  of the member M 1 . 
     A thickness T 2  of the member M 2  is, for example, larger than a depth Dl of the recess C 1 . In this case, since a lower surface S 21  of the member M 2  projects towards the electrostatic chuck  25  side further than the lower surface S 11  of the member M 1 , only the member M 2  out of the members M 1  and M 2  is in contact with the upper surface of the outer peripheral portion  25   b  of the electrostatic chuck  25 . As a result, the adhesion of the edge ring ER 1  to the electrostatic chuck  25  is further improved when the edge ring ER 1  is electrostatically attracted to the electrostatic chuck  25 . 
     The adhesive layer B 2  is provided between a bottom surface U 1  of the recess C 1  and an upper surface S 22  of the member M 2 . In addition, a recess C 2  having a depth of, for example, about 40 μm is formed on the upper surface S 22  of the member M 2 , and the adhesive layer B 2  is provided in the recess C 2  formed on the upper surface S 22  of the member M 2 . The adhesive layer B 2  includes, for example, a silicone-based adhesive. 
     The adhesive layer B 2  may further include a conductive filler. The adhesive layer B 2  containing the conductive filler improves the thermal conductivity between the member M 1  and the member M 2 . One example of the conductive filler includes alumina. 
     Seal bands SB 11  and SB 12 , each of which has an annular convex shape and is provided in the central portion  25   a  of the electrostatic chuck  25 , support the wafer W on the central portion  25   a . Thus, a space SP 1  corresponding to the height of the seal bands SB 11  and SB 12  is formed between the upper surface of the central portion  25   a  and the lower surface of the wafer W. The space SP 1  is connected to the gas introduction hole  102 . Then, heat transfer gas supplied from the heat transfer gas supply unit  35  is introduced into the space SP 1  through the gas introduction hole  102 . 
     In addition, seal bands SB 21  and SB 22 , each of which has an annular convex shape, are provided in the outer peripheral portion  25   b  of the electrostatic chuck  25 . Thus, the edge ring ER 1  is supported on the outer peripheral portion  25   b  by the seal bands SB 21  and SB 22 . Then, a space SP 2  corresponding to the height of the seal bands SB 21  and SB 22  is formed between the upper surface of the outer peripheral portion  25   b  and the lower surface S 21  of the member M 2 . The space SP 2  is connected to the gas introduction hole  103 . The heat transfer gas supplied from the heat transfer gas supply unit  35  is introduced into the space SP 2  through the gas introduction hole  103 . 
     In addition, in the above-described embodiment, a case where the member M 1  and the member M 2  are joined via the adhesive layer B 2  is described as an example, but the member M 1  and the member M 2  may be joined by diffusion joining. 
     As described above, the edge ring (edge ring ER 1 ) according to the disclosure has the annular first member (member M 1 ) made of the first material having plasma resistance and the annular second member (member M 2 ) made of the second material having a rigidity lower than that of the first material. The second member is arranged in a recess (recess C 1 ) formed on the lower surface of the first member. 
     In the edge ring according to the disclosure, since the first member exposed to the plasma during the plasma processing is made of the first material having the plasma resistance, the edge ring may have the plasma resistance. In addition, since the second member that is in contact with the electrostatic chuck is made of the second material having a rigidity lower than that of the first material (that is, having a flexibility higher than that of the first material), it is possible to improve the adhesion between the edge ring and the electrostatic chuck. Therefore, the edge ring according to the disclosure makes it possible to reduce the frequency of replacement of the edge ring and suppress the leakage of the heat transfer gas. 
     Heretofore, although the edge ring and the substrate processing apparatus are described by the above-described embodiment, the edge ring and the substrate processing apparatus according to the disclosure are not limited to the above-described embodiment, and various modifications and improvements can be made within the scope of the disclosure. 
     For example, the edge ring according to the disclosure can be applied not only to a capacitively coupled plasma (CCP) apparatus but also to other substrate processing apparatuses. Other substrate processing apparatuses include an inductively coupled plasma (ICP) processing apparatus, a plasma processing apparatus using a radial line slot antenna, a helicon wave excitation type plasma (helicon wave plasma (HWP)) apparatus, an electron cyclotron resonance plasma (ECR) apparatus or the like. 
     In addition, in the substrate processing apparatus  100  according to the present embodiment, two electrode plates for electrostatic attraction are provided in the outer peripheral portion  25   b  of the electrostatic chuck  25 . However, the number of electrode plates provided in the outer peripheral portion  25   b  for electrostatic attraction may be, for example, one or may be three or more. 
     In this specification, the semiconductor substrate is described as the target of the plasma processing, but the target of the plasma processing is not limited to the semiconductor substrate. The target of the plasma processing may be various substrates used for an liquid crystal display (LCD), a flat panel display (FPD), or the like, a photomask, a CD substrate, a printed circuit board, or the like. 
     From the foregoing, it will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting. The scope of the inventive concept is defined by the following claims and their equivalents rather than by the detailed description of the exemplary embodiments. It shall be understood that all modifications and embodiments conceived from the meaning and scope of the claims and their equivalents are included in the scope of the inventive concept.