Patent Publication Number: US-9412555-B2

Title: Lower electrode assembly of plasma processing chamber

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 61/193,151, filed Oct. 31, 2008, the entire content of which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     In the description that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art. 
     In the field of conductor (metal) processing, plasma processing chambers are commonly used to etch one or more layers formed on a substrate. During etching, the substrate is supported on a substrate support surface within the chamber. Substrate supports can include edge rings positioned around the substrate support (i.e., around the substrate) for confining plasma to the volume above the substrate and/or to protect the substrate support, which typically includes a clamping mechanism, from erosion by the plasma. The edge rings, sometimes called focus rings, can be sacrificial (i.e., consumable) parts. Conductive and non-conductive edge rings are described in commonly-owned U.S. Pat. Nos. 5,805,408; 5,998,932; 6,013,984; 6,039,836 and 6,383,931. 
     During plasma etching, plasma is formed above the surface of a substrate by adding large amounts of energy to a gas (or gas mixture) at low pressure. The plasma may contain ions, free radicals, and neutral species with high kinetic energies. By adjusting the electrical potential of the substrate, charged species in the plasma can be directed to impinge upon the surface of the substrate and thereby remove material (e.g., atoms) therefrom. 
     SUMMARY 
     A lower electrode assembly for use in a plasma processing chamber comprises a metal base and upper and lower edge rings. The metal base comprises metal plates brazed together and forming a brazed line on a lower side surface of the base, an edge ring support surface extending horizontally inwardly from the lower side surface and an upper side surface above the edge ring support surface. The upper edge ring comprises a lower surface mounted on the edge ring support surface and the lower edge ring surrounds the lower side surface of the base with a gap between opposed surfaces of the upper and lower edge rings and between the lower edge ring and the outer periphery of the base. The gap has an aspect ratio of total gap length to average gap width sufficient to impede arcing at the location of the braze line. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a conventional plasma processing apparatus. 
         FIG. 2  is an illustration of a comparative lower electrode assembly. 
         FIG. 3  is an illustration of the cross-section of the baseplate shown in  FIG. 2 . 
         FIG. 4  shows details of the upper and lower edge rings of the assembly shown in  FIG. 2 . 
         FIG. 5  shows details of a labyrinth edge ring assembly in accordance with a preferred embodiment. 
         FIGS. 6A-F  show embodiments of labyrinth edge ring assemblies. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Plasma chambers are generally used for etching layers of materials on substrates by supplying an etching gas comprising one or more gases to the chamber and applying energy to the etching gas to energize the gas into a plasma state. Various plasma chamber designs are known wherein radio frequency (RF) energy, microwave energy and/or magnetic fields can be used to produce and sustain medium density or high density plasma. 
     In such plasma processing chambers process gas is supplied through a suitable arrangement such as a showerhead electrode or gas injection system and a semiconductor substrate supported on a lower electrode is plasma etched by plasma generated by supplying RF energy to the process gas. 
     For a metal etch process, the lower electrode assembly can be incorporated in a transformer coupled plasma (TCP™) reactor. Transformer coupled plasma reactors, wherein RF energy is inductively coupled into the reactor, are available from Lam Research Corporation, Fremont, Calif. An example of a high-flow plasma reactor that can provide high density plasma is disclosed in commonly-owned U.S. Pat. No. 5,948,704, the disclosure of which is hereby incorporated by reference. 
     A parallel plate plasma etch reactor is illustrated in  FIG. 1 . The plasma etch reactor  100  comprises a chamber  110 , an inlet load lock  112 , and an optional outlet load lock  114 , further details of which are described in commonly-owned U.S. Pat. No. 6,824,627, which is hereby incorporated by reference in its entirety. 
     The load locks  112  and  114  (if provided) include transfer devices to transfer substrates such as wafers from a wafer supply  162 , through the chamber  110 , and out to a wafer receptacle  164 . A load lock pump  176  can provide a desired vacuum pressure in the load locks  112  and  114 . 
     A vacuum pump  172  such as a turbo pump is adapted to maintain a desired pressure in the chamber. During plasma etching, the chamber pressure is controlled, and preferably maintained at a level sufficient to sustain a plasma. Too high a chamber pressure can disadvantageously contribute to etch stop while too low a chamber pressure can lead to plasma extinguishment. In a medium density plasma reactor, such as a parallel plate reactor, preferably the chamber pressure is maintained at a pressure below about 200 mTorr (e.g., less than 100 mTorr or less than 50 mTorr). 
     The vacuum pump can be connected to an outlet in a wall of the reactor and can be throttled by a valve  173  in order to control the pressure in the chamber. Preferably, the vacuum pump is capable of maintaining a pressure within the chamber of less than 200 mTorr while etching gases are flowed into the chamber. 
     The chamber  110  includes an upper electrode assembly  120  including an upper electrode  125  (e.g., showerhead electrode), and a lower electrode assembly  140  including a baseplate (i.e., lower electrode)  160  and a substrate support surface  150  formed in an upper surface thereof. The upper electrode assembly  120  is mounted in an upper housing  130 . The upper housing  130  can be moved vertically by a mechanism  132  to adjust the gap between the upper electrode  125  and the substrate support surface  150 . 
     A etching gas source  170  can be connected to the housing  130  to deliver etching gas comprising one or more gases to the upper electrode assembly  120 . In a preferred etch reactor, the upper electrode assembly comprises a gas distribution system, which can be used to deliver reactant and/or carrier gases to a region proximate to the surface of a substrate. Gas distribution systems, which can comprise one or more gas rings, injectors and/or showerheads (e.g., showerhead electrodes), are disclosed in commonly-owned U.S. Pat. Nos. 6,333,272; 6,230,651; 6,013,155 and 5,824,605, the disclosures of which are hereby incorporated by reference. 
     The upper electrode  125  preferably comprises a showerhead electrode, which includes apertures (not shown) to distribute etching gas therethrough. The showerhead electrode can comprise one or more vertically spaced-apart baffle plates that can promote the desired distribution of etching gas. The upper and lower electrodes may be formed of any suitable material such as graphite, silicon, silicon carbide, aluminum (e.g., anodized aluminum), or combinations thereof. A heat transfer liquid source  174  can be connected to the upper electrode assembly  120  and another heat transfer liquid source can be connected to the baseplate  160 . 
     While a parallel plate reactor is described above, the edge ring assembly can be used in other plasma processing systems such as inductively coupled plasma chambers. 
       FIG. 2  shows a substrate support  200  which includes a baseplate  202  on which a substrate S is supported, a lower edge ring  204  surrounding the baseplate  202 , and an upper edge ring  206 . The upper edge ring  206  includes a step on its lower surface mating with the upper end of the lower edge ring. 
       FIG. 3  shows a baseplate  300  comprising an upper plate  302 , a middle plate  304  and a lower plate  306 , preferably of an aluminum alloy such as 6061-T6. The middle plate  304  includes coolant passages  308  supplied coolant passing through inlet  310 . Coolant circulated through the baseplate exits through an outlet (not shown). The passages  308  can be machined in a plate of aluminum such as 6061 and the bottom plate  306  is vacuum brazed at braze line  312  to middle plate  304  to enclose the channels. 
     The top plate  302  can include one or more gas channels  314  which are supplied a heat transfer gas such as He. One or more radially extending channels  316  machined into the underside of the top plate  302  can intersect lift pin holes  318  through which lift pins (not shown) move vertically to raise and lower wafers onto and off of the upper surface  320  of the baseplate. Circumferentially spaced apart axially extending gas passages (not shown) direct He of the gas channel  314  against the underside of the wafer. The top plate  302  is vacuum brazed at braze line  322  to the upper surface of the middle plate  304  to enclose the gas channel  314  and gas passage  316 . 
     After brazing the top and bottom plates to the middle plate, an ESC ceramic laminate (not shown) is bonded to the upper surface of the top plate  302 , the baseplate assembly is machined to provide a smooth surface and the assembly is anodized. The anodization results in a raised thickness of about 0.001 inch (25 μm) at the brazed lines  312 ,  322 . 
       FIG. 4  shows an edge ring assembly designed to fit around the periphery of the baseplate  300 . However when used to support a wafer in an inductively coupled plasma chamber during plasma etching of conductive material such as aluminum or other conductive layers arcing spots have been observed at numerous locations around the vacuum brazed joints  312 ,  322  after 45 hours. This edge ring assembly includes upper ring  404  and lower ring  414  having an annular horizontal gap having a gap height (H) ranging from 0.003 to 0.047 inch and gap length (L) of about 0.6 inch. The gap height has a range of 0.003 to 0.047 due to manufacturing machined surfaces with tolerances to allow fitting of the opposed surfaces of the upper and lower edge rings. For example, the rings can be machined quartz rings having inner diameters of about 12 or more inches for use on baseplates suitable for supporting 300 mm wafers. For example, the upper edge ring can have an inner diameter of about 12 inches and the lower edge ring inner diameter can be about 12.6 inches. An annular vertical gap having a gap range of 0.011 to 0.030 inch and length of about 1 inch separates the inner periphery of the lower edge ring from the outer periphery of the baseplate. 
     With reference to the  FIG. 2  edge ring assembly, it has been found that an upper edge ring having a single small step in the lower surface thereof is ineffective at preventing arcing at the braze lines of the baseplate assembly. In contrast, an upper edge ring having a larger step, multiple steps or other modification to increase the aspect ratio of the gap can inhibit arcing at the braze lines. In particular,  FIG. 4  shows a cross section of a one-step edge ring assembly  400  wherein upper edge ring  402  has a height (H) of 0.6 inch, an outer diameter (OD) of 13.820 inch, an inner diameter (ID) of 12.0 inches, a width (W) of 1.820 inches, wherein step  404  provides an offset of about 0.1 inch in lower surface  406 . To accommodate the wafer&#39;s edge overhanging the upper surface of the baseplate, a recess  408  extends 0.108 inch below upper surface  410  inwardly from the inner periphery  412 . Lower edge ring  414  includes upper end  416  which mates with recess  404 . A recess  418  mates with a dielecrtric member beneath baseplate  300 . 
       FIG. 5  shows an edge ring assembly which overcomes the arcing problem. The edge ring assembly includes upper edge ring  508  having a plurality of steps  502 ,  504  on a lower surface thereof which lengthens the gap between the opposed surfaces of the top and bottom edge rings and thus impede penetration of plasma to the location of the vacuum braze lines  312 ,  322 . With this stepped ring, no arcing has been observed even after 2000 RF bias hours. 
     The two stepped edge ring assembly  500  includes inner step  502  and outer step  504 . The inner step has a depth of 0.1 inch and second step  504  provides a recess 0.250 inch at the outer periphery  506  of upper edge ring  508  and extends from the outer periphery to vertical surface  510 . Lower edge ring  512  includes projection  514  which mates with recess  504  and upper inner portion  516  mates with inner step  502 . 
     The labyrinth edge ring assembly can be implemented with various edge ring configurations. In variation A, a single step is provided in the lower surface of the upper edge ring but with an increased vertical offset from the lower surface and the height of the lower edge ring can be increased accordingly. For example, the recess can extend 25 to 50% of the height of the edge ring. In variation B, two steps can be provided in the lower surface of the upper edge ring and the upper surface of the lower edge ring includes one or more projections mating with the lower surface of the upper edge ring. In variation C, a single step extending 25 to 50% of the edge ring height extends into the lower surface of the upper edge ring and the lower edge ring includes a single step mating with the recess in the upper edge ring. In variation D, the step in the lower surface of the upper edge ring extends more than 50% across the lower surface and the lower edge ring includes an inner projection extending over an outer portion of the edge ring mounting surface. The height of the step in variation D extends vertically 30 to 60% of the height of the upper edge ring. In variation E, the comparative edge ring assembly includes a dielectric barrier ring which fits in aligned grooves in the opposed surfaces of the upper and lower edge rings. The barrier ring fits in a groove having a depth of 10 to 40% of the height of the upper edge ring. In variation F, the upper edge ring includes a single annular recess in the lower surface thereof and the lower edge ring includes an annular projection mating with the recess. The recess extends 10 to 40% of the upper edge ring height and has a width of 15 to 60% of the width of the lower edge ring. 
       FIG. 6A  shows an edge ring assembly  600  comprising upper ring  602  and lower ring  604 . The upper ring  602  includes a lower surface  606  which is supported on an annular surface  608  of temperature controlled base  610 , an inner side surface  612  which faces a cylindrical side surface  614  of the base  610 , an outer side surface  616  exposed to the plasma environment, a top surface  618  (surrounding a substrate S supported on the base) exposed to the plasma environment, an upper step  620  which underlies an outer periphery of the substrate, a lower step  622  comprising an outer lower surface  624  and outer lower side wall  626 . Lower edge ring  604  includes outer surface  628 , top surface  630 , inner side surface  632  and lower step  634  at the bottom of inner wall  632 . A gap  640  having a width (W) of 0.003 to 0.055 inch between opposed surfaces of the upper and lower edge rings  602 ,  604  has a length (L) sufficient to prevent arcing at the location of brazed joint  642 . Thus, an aspect ratio of L/W is preferably at least 20 for the average gap width. 
       FIG. 6B  shows an edge ring assembly  600 B comprising upper ring  602 B and lower ring  604 B. The upper ring  602 B includes a lower surface  606 B which is supported on an annular surface  608  of temperature controlled base  610 , an inner side surface  612  which faces a cylindrical side surface  614  of the base  610 , an outer side surface  616 B exposed to the plasma environment, a top surface  618  (surrounding a substrate S supported on the base) exposed to the plasma environment, an upper step  620  which underlies an outer periphery of the substrate, a lower step  622  comprising an outer lower surface  624  and outer lower side wall  626 . Lower edge ring  604  includes outer surface  628 , top surfaces  630 B,  631 B, inner side surface  632  and lower step  634  at the bottom of inner wall  632 . A gap  640  having a width (W) of 0.003 to 0.055 inch between opposed surfaces of the upper and lower edge rings  602 B,  604 B has a length (L) sufficient to prevent arcing at the location of brazed joint  642 . Thus, an aspect ratio of L/W is preferably at least 20 for the average gap width. 
       FIG. 6C  shows an edge ring assembly  600 C comprising upper ring  602 C and lower ring  604 C. The upper ring  602 C includes a lower surface  606 C which has an inner portion supported on an annular surface  608  of temperature controlled base  610  and an outer portion extending beyond the support surface, an inner side surface  612  which faces a cylindrical side surface  614  of the base  610 , an outer side surface  616 C exposed to the plasma environment, a top surface  618  (surrounding a substrate S supported on the base) exposed to the plasma environment, an upper step  620  which underlies an outer periphery of the substrate, a lower step  622 C comprising an outer lower surface  624 C and outer lower side wall  626 C. Lower edge ring  604 C includes outer surface  628 , top surfaces  630 C,  631 C, inner side surface  632  and lower step  634  at the bottom of inner wall  632 . A gap  640 C having a width (W) of 0.003 to 0.055 inch between opposed surfaces of the upper and lower edge rings  602 C,  604 C has a length (L) sufficient to prevent arcing at the location of brazed joint  642 . Thus, an aspect ratio of L/W is preferably at least 20 for the average gap width. 
       FIG. 6D  shows an edge ring assembly  600 D comprising upper ring  602 D and lower ring  604 D. The upper ring  602 D includes a lower surface  606 D which has an inner portion supported on an annular surface  608  of temperature controlled base  610  and an outré portion extending outward of the support surface, an inner side surface  612  which faces a cylindrical side surface  614  of the base  610 , an outer side surface  616 D exposed to the plasma environment, a top surface  618  (surrounding a substrate S supported on the base) exposed to the plasma environment, an upper step  620  which underlies an outer periphery of the substrate, and an annular groove  650  facing an annular groove  652  in lower edge ring  604 D. A dielectric ring  654  is mounted in the grooves  650 ,  652 . Lower edge ring  604 D includes outer surface  628 , top surface  630 D, inner side surface  632  and lower step  634  at the bottom of inner wall  632 . A gap  640 D having a width (W) of 0.003 to 0.055 inch between opposed surfaces of the upper and lower edge rings  602 D,  604 D has a length (L) extended by the dielectric ring  654  sufficient to prevent arcing at the location of brazed joint  642 . Thus, an aspect ratio of L/W is preferably at least 20 for the average gap width. 
       FIG. 6E  shows an edge ring assembly  600 E comprising upper ring  602 E and lower ring  604 E. The upper ring  602 E includes a lower surface  606 E supported on an annular surface  608  of temperature controlled base  610 , an inner side surface  612  which faces a cylindrical side surface  614  of the base  610 , an outer side surface  616 E exposed to the plasma environment, a top surface  618  (surrounding a substrate S supported on the base) exposed to the plasma environment, an upper step  620  which underlies an outer periphery of the substrate, a lower step  622 E comprising an outer lower surface  624 E and outer lower side wall  626 E. Lower edge ring  604 E includes outer surface  628 , top surface  630 E, inner side surface  632  and lower step  634  at the bottom of inner wall  632 . A gap  640 E having a width (W) of 0.003 to 0.055 inch between opposed surfaces of the upper and lower edge rings  602 E,  604 E has a length (L) sufficient to prevent arcing at the location of brazed joint  642 . Thus, an aspect ratio of L/W is preferably at least 20 for the average gap width. 
       FIG. 6F  shows an edge ring assembly  600 F comprising upper ring  602 F and lower ring  604 F. The upper ring  602 F includes a lower surface  606  which is supported on an annular surface  608  of temperature controlled base  610  and an outer portion of surface  606 F includes an annular recess which receives annular projection  658  extending upwardly from lower edge ring  604 F, an inner side surface  612  which faces a cylindrical side surface  614  of the base  610 , an outer side surface  616 F exposed to the plasma environment, a top surface  618  (surrounding a substrate S supported on the base) exposed to the plasma environment, and an upper step  620  which underlies an outer periphery of the substrate. Lower edge ring  604 F includes outer surface  628 , top surface  630 F, inner side surface  632  and lower step  634  at the bottom of inner wall  632 . A gap  640 F having a width (W) of 0.003 to 0.055 inch between opposed surfaces of the upper and lower edge rings  602 F,  604 F has a length (L) sufficient to prevent arcing at the location of brazed joint  642 . Thus, an aspect ratio of L/W is preferably at least 20 for the average gap width. 
     The terms “comprises” and “comprising” as used herein are taken to specify the presence of stated features, steps, or components; but the use of these terms does not preclude the presence or addition of one or more other features, steps, components, or groups thereof. 
     All of the above-mentioned references are herein incorporated by reference in their entirety to the same extent as if each individual reference was specifically and individually indicated to be incorporated herein by reference in its entirety. 
     While the invention has been described with reference to preferred embodiments, it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and scope of the invention as defined by the claims appended hereto.