Patent Publication Number: US-2021166965-A1

Title: Electrostatically clamped edge ring

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a Continuation of U.S. application Ser. No. 15/894,670 filed on Feb. 12, 2018, entitled “ELECTROSTATICALLY CLAMPED EDGE RING”, which is a Divisional of U.S. application Ser. No. 15/343,010 filed on Nov. 3, 2016, entitled “ELECTROSTATICALLY CLAMPED EDGE RING” (U.S. Pat. No. 9,922,857 patented on Mar. 20, 2018) the entire contents of which are incorporated herein by reference thereto. 
    
    
     BACKGROUND 
     The disclosure relates to a method and apparatus for plasma processing a substrate. More specifically, the disclosure relates to a method and apparatus for clamping an edge ring in a plasma processing chamber. 
     In plasma processing, a plasma processing chamber with an edge ring may be used to provide improved process control. 
     SUMMARY 
     To achieve the foregoing and in accordance with the purpose of the present disclosure, a method for electrostatically clamping an edge ring in a plasma processing chamber with an electrostatic ring clamp with at least one ring backside temperature channel for providing a flow of gas to the edge ring to regulate the temperature is provided. A vacuum is provided to the at least one ring backside temperature channel. Pressure in the at least one ring backside temperature channel is measured. An electrostatic ring clamping voltage is provided when the pressure in the at least one ring backside temperature channel reaches a threshold maximum pressure. The vacuum to the at least one ring backside temperature channel is discontinued. Pressure in the at least one ring backside temperature channel is measured. If pressure in the at least one ring backside temperature channel rises faster than a threshold rate, then sealing failure is indicated. If pressure in the at least one ring backside temperature channel does not rise faster than the threshold rate, a plasma process is continued, using the at least one ring backside temperature channel to regulate a temperature of the edge ring. 
     In another manifestation, an edge ring for use in a plasma processing chamber with a chuck is provided. An edge ring body has a first surface to be placed over and facing the chuck, wherein the first surface forms a ring around an aperture. A first elastomer ring is integrated to the first surface and extending around the aperture. 
     These and other features of the present invention will be described in more details below in the detailed description of the invention and in conjunction with the following figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG. 1  is a schematic cross-sectional view of a plasma processing chamber with an embodiment. 
         FIG. 2  is a schematic view of a computer system that may be used in practicing an embodiment. 
         FIG. 3  is an enlarged view of the etch ring and electrostatic ring chuck, shown in  FIG. 1 . 
         FIG. 4  is a bottom view of an edge ring of an embodiment. 
         FIG. 5  is a flow chart of an embodiment. 
         FIG. 6  is an enlarged view of part of the ESC system in another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention. 
       FIG. 1  is a schematic view of a plasma processing chamber that may be used in an embodiment. In one or more embodiments, the plasma processing system  100  comprises a gas distribution plate  106  providing a gas inlet and an electrostatic chuck system (ESC system)  108  comprising a ceramic plate  112  and a base plate  114 , within a processing chamber  149 , enclosed by a chamber wall  150 . Within the processing chamber  149 , a substrate  104  is positioned on top of the ESC system  108 . The ESC system  108  may provide a bias from the ESC source  148 . A gas source  110  is connected to the plasma processing chamber  149  through the distribution plate  106 . An ESC temperature controller  151  is connected to the ESC system  108 , and provides temperature control of the ESC system  108 . A vacuum source  160  is connected to the ESC system  108 . An RF source  130  provides RF power to ESC system  108  and an upper electrode, which in this embodiment is the gas distribution plate  106 . In a preferred embodiment, 2 MHz, 60 MHz, and optionally, 27 MHz power sources make up the RF source  130 . In this embodiment, one generator is provided for each frequency. In other embodiments, the generators may be in separate RF sources, or separate RF generators may be connected to different electrodes. For example, the upper electrode may have inner and outer electrodes connected to different RF sources. Other arrangements of RF sources and electrodes may be used in other embodiments, such as in another embodiment the upper electrodes may be grounded A controller  135  is controllably connected to the RF source  130 , the ESC source  148 , an exhaust pump  120 , and the etch gas source  110 . An edge ring  116  is supported by the ESC system  108  at the outer edge of the substrate  104 . An example of such a plasma processing chamber is the Exelan Flex™ etch system manufactured by Lam Research Corporation of Fremont, Calif. The process chamber can be a CCP (capacitive coupled plasma) reactor or an ICP (inductive coupled plasma) reactor or may be another type of powered plasma in various embodiments. 
       FIG. 2  is a high level block diagram showing a computer system  200 , which is suitable for implementing a controller  135  used in embodiments of the present invention. The computer system may have many physical forms ranging from an integrated circuit, a printed circuit board, and a small handheld device, up to a huge super computer. The computer system  200  includes one or more processors  202 , and further can include an electronic display device  204  (for displaying graphics, text, and other data), a main memory  206  (e.g., random access memory (RAM)), storage device  208  (e.g., hard disk drive), removable storage device  210  (e.g., optical disk drive), user interface devices  212  (e.g., keyboards, touch screens, keypads, mice or other pointing devices, etc.), and a communication interface  214  (e.g., wireless network interface). The communication interface  214  allows software and data to be transferred between the computer system  200  and external devices via a link. The system may also include a communications infrastructure  216  (e.g., a communications bus, cross-over bar, or network) to which the aforementioned devices/modules are connected. 
     Information transferred via communications interface  214  may be in the form of signals such as electronic, electromagnetic, optical, or other signals capable of being received by communications interface  214 , via a communication link that carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, a radio frequency link, and/or other communication channels. With such a communications interface, it is contemplated that the one or more processors  202  might receive information from a network, or might output information to the network in the course of performing the above-described method steps. Furthermore, method embodiments of the present invention may execute solely upon the processors or may execute over a network such as the Internet, in conjunction with remote processors that share a portion of the processing. 
     The term “non-transient computer readable medium” is used generally to refer to media such as main memory, secondary memory, removable storage, and storage devices, such as hard disks, flash memory, disk drive memory, CD-ROM, and other forms of persistent memory, and shall not be construed to cover transitory subject matter, such as carrier waves or signals. Examples of computer code include machine code, such as one produced by a compiler, and files containing higher level code that are executed by a computer using an interpreter. Computer readable media may also be computer code transmitted by a computer data signal embodied in a carrier wave and representing a sequence of instructions that are executable by a processor. 
       FIG. 3  is an enlarged view of part of the ESC system  108  and substrate  104 . The ESC system  108  comprises a ceramic plate  112  and a base plate  114 . An elastomer bond  304  holds the ceramic plate  112  to the base plate  114 . In a raised central portion  306  of the ceramic plate  112  are substrate clamping electrodes  308 , which are used to apply a voltage to electrostatically chuck the substrate  104 . At least one substrate chucking clamping electrode lead  309  is connected between the substrate clamping electrodes  308  and the ESC source  148 , shown in  FIG. 1 . In a lower peripheral portion  310  of the ceramic plate are edge ring clamping electrodes  312 , which are used to apply a voltage to electrostatically chuck the edge ring  116 . At least one edge ring clamping electrode lead  314  is connected between the edge ring clamping electrodes  312  and the ESC source  148 , shown in  FIG. 1 . In one embodiment, the ESC source  148  may be a plurality of voltage sources. In another embodiment, the ESC source  148  may be a single voltage source with a plurality of switches to independently apply different voltages to the substrate clamping electrodes  308  and the edge ring clamping electrodes  312 . A portion of the lower peripheral portion  310  may be recessed to form a gap formed by a cooling groove  350  between the lower peripheral portion  310  and the edge ring  116 . The cooling groove  350  provides a region, which allows the coolant to flow near the backside of the edge ring  116 , and facilitate creating a seal for the coolant. 
     In the raised central portion  306  is a plurality of substrate backside temperature channels  320 , which are connected through a fluid connection  324  to the ESC temperature controller  151 , shown in  FIG. 1 . In the lower peripheral portion  310  are a plurality of ring backside temperature channels  328 , which are connected through a fluid connection  332  to the ESC temperature controller  151 , shown in  FIG. 1 . A first sealing groove  336  in the upper surface of the lower peripheral portion  310  makes a ring around the raised central portion  306 . A second sealing groove  340  in the upper surface of the lower peripheral portion  310  makes a ring around and is concentric with the first sealing groove  336 . 
     The edge ring  116  comprises an edge ring body  394  and a first elastomer ring  344  integrated to the edge ring body  394  and a second elastomer ring  348  integrated to the edge ring body  394 .  FIG. 4  is a bottom view of the edge ring  116 . The bottom of the edge ring  116  forms a first surface  404 , which is also shown in  FIG. 3 . The edge ring  116  has an outer diameter  408  and an inner diameter  412 . In this example, the outer diameter is  400  mm and the inner diameter is  290  mm. Within the inner diameter is a central aperture of the edge ring  116 . In this example, the edge ring  116  is formed from silicon, so that the edge ring  116 , including the first surface  404 , is conductive. In this example, the first elastomer ring  344 , and the second elastomer ring  348 , and the edge ring  116  are all concentric, as shown. The hole in the center of the edge ring  116  forms a central aperture, as shown. 
     The edge ring clamping electrodes  312  form an electrostatic ring chuck. The substrate clamping electrodes  308  form an electrostatic wafer chuck. If the entire edge ring  116  or first surface  404  is not conductive, then the edge ring  116  would need to have conductive portions. As shown in  FIG. 3 , when the edge ring  116  is mounted on the electrostatic ring chuck, so that conductive portions of the edge ring  116  are over the edge ring clamping electrodes  312  and the raised central portion  306  passes through the central aperture, the first elastomer ring  344  is placed in the first sealing groove  336  and the second elastomer ring  348  is placed in the second sealing groove  340 . 
     In this example, the first sealing groove  336  and the second sealing groove  340  have a depth of 0.5 mm. The first elastomer ring  344  and the second elastomer ring  348  have a height of 0.5 mm after clamping. 
       FIG. 5  is a high level flow chart of a process for chucking the edge ring  116 . The edge ring  116  is placed on the electrostatic ring chuck (step  504 ). The edge ring  116  may be placed on the electrostatic ring chuck, as shown in  FIG. 1  and  FIG. 3 . The electrostatic ring chuck is formed by the edge ring clamping electrodes  312 . The lower peripheral portion  310  of the ceramic plate  112 , the first sealing groove  336  in the upper surface of the lower peripheral portion  310 , the second sealing groove  340  in the upper surface of the lower peripheral portion  310 , the cooling groove  350 , and the plurality of ring backside temperature channels  328  may further make up the electrostatic ring chuck. A vacuum is provided to the plurality of ring backside temperature channels  328  by connecting the fluid connection  332  to vacuum source  160  (step  508 ). The vacuum source  160  provides a vacuum, which causes the edge ring  116  to move towards the upper surface of the lower peripheral portion  310 , which causes the first elastomer ring  344  and the second elastomer ring  348  to be compressed within the first sealing groove  336  and the second sealing groove  340 , respectively. Preferably, the chamber pressure is atmospheric pressure, so that the pressure on top of the edge ring  116  is atmospheric pressure. The applied vacuum causes mechanical movement of the edge ring  116  to facilitate electrostatic clamping of the edge ring  116  and allows for testing of the seal. The pressure in the backside temperature channels is measured. When the pressure is lowered to a threshold pressure, a ring clamping voltage is applied (step  512 ). The pressure threshold indicates that the edge ring  116  has been forced to a threshold distance, which will allow the edge ring clamping electrodes  312  to clamp the edge ring  116 . 
     The application of the vacuum is then discontinued (step  516 ). Pressure in the backside temperature channels  328  is measured (step  520 ). If the measured pressure increase is larger than a threshold rate, it indicates that the seal has failed (step  524 ). Then the seal must be re-created (step  528 ). This may be done by re-seating the edge ring. This may require replacing the edge ring  116  so that the first elastomer ring  344  and the second elastomer ring  348  are replaced. If the measured pressure increase is smaller than the threshold rate, it indicates that the seal is sufficient. The backside temperature channels  328  are then used for temperature control of the edge ring  116  (step  532 ). The edge ring clamping electrodes continuously clamp the edge ring during the placement of a substrate over the substrate clamping electrodes of the ESC system, and during the clamping of the substrate, the processing of the substrate, the declamping of the substrate, and the removal of the substrate. Therefore, the ring clamping electrodes and the substrate clamping electrodes are operated independently, allowing the ring clamping electrodes to continuously clamp, while the substrate clamping electrodes are used to clamp and subsequently declamp the substrate. 
     This embodiment provides an edge ring seal, which allows for temperature control of the edge ring. Allowing temperature control of the edge ring provides greater control during plasma processing, which improves the plasma processing. 
     This embodiment provides various advantages over a configuration that uses O-rings. In order to use an O-ring for the similar purposes, the O-ring would need to be thin with a large diameter and be made of a soft material. The placement of such an O-ring to create the desired seal will require a highly skilled technician, due to the fragileness of the O-ring and the various requirements to create the seal, such as preventing pinching or bunching of the O-ring. This embodiment allows a less skilled technician to simply and easily place the edge ring on the electrostatic ring chuck. 
     In other embodiments, the ceramic plate may be in two parts, with the raised central portion  306  being separate from the lower peripheral portion  310 . The entire edge ring may be made of a conductive material, such as silicon. In other embodiments, the edge ring is a dielectric material with conductive parts, which would be placed over the ring clamping electrodes when the edge ring is placed on the electrostatic ring chuck. The conductive parts facilitate electrostatic clamping. Preferably, the edge ring is at least one of silicon, silicon carbide, or quartz. 
     In various embodiments, the height of each elastomer ring is greater than the depth of the groove in which the elastomer ring is placed. This causes the elastomer ring to be compressed when creating the seal, which helps to establish the seal. In various embodiments, the elastomer may have different cross-sections. Preferably, the cross-section of the elastomer ring is at least one of rectangular, square, triangular, trapezoidal, or semicircular. More preferably, the bottom of the cross-section of the elastomer ring is narrower than the top of the elastomer ring, which is integrated with the rest of the edge ring. Most preferably, the elastomer ring is trapezoidal, as shown in  FIG. 3 . Preferably, the elastomer ring has a height between 0.25 mm to 2 mm. Preferably, the height of the elastomer ring is between 10 to 50 microns greater than the depth of the groove. Preferably, the tolerance of the height of the elastomer ring is 50 microns or better. More preferably, the tolerance of the height elastomer ring is 12-13 microns. Preferably, the outer diameter of the edge ring is between 200 mm to 450 mm. More preferably, the outer diameter of the edge ring is between 300 mm to 400 mm. Preferably, the edge ring, the first elastomer ring, and the second elastomer ring are concentric. Preferably, the first elastomer ring is within 10 mm of the inner edge of the edge ring and the second elastomer ring is within 30 mm of the outer edge of the edge ring. 
     In chucking a wafer, an elastomer ring is not needed, since a wafer will bend to help create a seal. Since edge rings are much thicker than a wafer, the edge ring does not sufficiently bend to create a seal without elastomer rings. In some embodiments, the elastomer ring may be formed by applying a wet or liquid elastomer on the edge ring, and then drying or solidifying and curing the elastomer on the edge ring. In various embodiments, the elastomer ring is made of a soft elastomer that will not outgas beyond a specific limit, such as silicone. Preferably, an elastomer ring comprises silicone with a ring diameter of at least 200 mm and a height between 0.25 mm to 2 mm. Preferably, the thickness of a cross-section of the elastomer is less than 3 mm. Preferably, an elastomer ring comprises silicone with a diameter of at least 200 mm and a height between 0.25 mm to 1.5 mm. The grooves in the surface of the ceramic plate allow the surface of the edge ring to be placed close to the electrostatic ring clamps to allow clamping. The height of the elastomer ring and depth of the groove with some compression of the elastomer ring provides a gas seal around the circumferences of the elastomer rings and while compensating for 20 microns of nonflatness of the edge ring, which requires an additional 20 microns of elastomer compression (elastomer compression is height of elastomer seal minus the groove depth). An optional feature in the surface of the ceramic plate provides a 10 micron gap between the surface of the ceramic plate and the edge ring. The gap  350  can range from 0 microns to 20 microns. 
     In an embodiment, the height of the elastomer is equal to the depth of the groove plus the tolerance of the groove depth plus the tolerance of the elastomer seal height (all assuming symmetric tolerances) plus the flatness of the edge ring. So if the groove depth is 0.5 mm±25 um, the elastomer seal can be controlled to within ±15 um of target height, and the flatness of the ring is 20 um, then the elastomer seal target height should be 0.5 mm+25 um+15 um+20 um=0.56 mm. This ensures that when the elastomer is at its smallest height, and groove is at its largest depth, and flatness at its worst, the seal will still make contact with the ring surface at the bottom of the groove. Since having all items at worst case simultaneously is unlikely, we sometime use RSS addition, in which case elastomer seal target height should be 0.5 mm+square root (25 um 2 +15 um 2 +20 um 2 )=0.535 mm 
     In an embodiment, the edge ring has a thickness of at least 1 mm in order to tolerate wear during plasma processing and to provide flexibility in height. In some embodiments, the edge ring has an upper surface that is above the upper surface of the wafer to provide sheath control. 
     Preferably, the backside temperature control channels are helium channels that carry helium gas coolant. The coolant is used to cool both the substrate and the edge rings. Such an embodiment allows for temperature control of both the substrate and edge ring. In addition, the embodiment allows for separate temperature control of the substrate and edge ring. In other embodiments, other gases or liquids may be used as a coolant, such as argon, air, nitrogen, or a liquid with a very low vapor pressure. 
       FIG. 6  is an enlarged view of part of the ESC system  108  and substrate  104  in another embodiment. The ESC system  108  comprises a ceramic plate  112  and a base plate  114 . An elastomer bond  604  holds the ceramic plate  112  to the base plate  114 . In this embodiment, the ceramic plate  112  comprises a central substrate support section  606  and a peripheral ring shape edge ring support section  610 . In the edge ring support section  610  of the ceramic plate  112  is a circular cooling groove  650 , which surrounds the substrate support section  606  and central aperture of the edge ring support section  610 . Under the bottom of the cooling groove  650  are edge ring clamping electrodes  612 , which are used to apply a voltage to electrostatically chuck the edge ring  116 . At least one edge ring clamping electrode lead  614  is connected between the edge ring clamping electrodes  612  and the ESC source  148 , shown in  FIG. 1 . The cooling groove  650  causes a gap to be between the edge ring support section  610  and the edge ring  116 , when the edge ring  116  is placed on the edge ring support section  610 . 
     In the edge ring support section  610  are a plurality of ring backside temperature channels  628 , which are connected through a fluid connection  632  to the ESC temperature controller  151 , shown in  FIG. 1  and to the cooling groove  650 . The edge ring  116  has an elastomer ring  644  integrated to the edge ring  116 . In this example, the elastomer ring  644  is in the shape of a sheet forming a ring. Preferably, the sheet is no more than 25 microns thick and a width that is greater than the width of the cooling groove  650 . 
     The edge ring clamping electrodes  612 , the cooling groove  650 , and the edge ring support section  610  form an electrostatic ring chuck. As shown in  FIG. 6 , when the edge ring  116  is mounted on the electrostatic ring chuck, so that conductive portions of the edge ring  116  are over the edge ring clamping electrodes  612  and the central substrate support section  606  passes through the central aperture, the elastomer ring  644  and the elastomer ring  644  extends across the cooling groove  650 , as shown. 
     While this invention has been described in terms of several preferred embodiments, there are alterations, modifications, permutations, and various substitute equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, modifications, permutations, and various substitute equivalents as fall within the true spirit and scope of the present invention.