Plasma confinement by use of preferred RF return path

Abstract

A confinement assembly for confining a discharge within an interaction space of a plasma processing apparatus comprising a stack of rings and at least one electrically conductive member. The rings are spaced apart from each other to form slots therebetween and are positioned to surround the interaction space. At least one electrically conductive member electrically couples each ring. The electrically conductive member contacts each ring at least at a point inside of the outer circumference of each ring.

1. A plasma processing apparatus having a top electrode, a bottom electrode, an interaction space confined between the top electrode and the bottom electrode, said plasma processing apparatus comprising:
 a stack of confinement rings, made of electrically insulating material, spaced apart from each other to form slots therebetween and positioned to surround the interaction space, each confinement ring having at least one cavity formed on the surface thereof; 
 a focus ring positioned to surround the bottom electrode; 
 an electrically conductive member passing through each of said cavity of said stack of confinement rings, a top of said conductive member electrically coupled to the top electrode, said electrically conductive member is grounded at a bottom thereof. 
 
     
     
       2. The plasma processing apparatus according to  claim 1  wherein each slot is proportioned such that during operation of the plasma processing apparatus, the distance an exiting charged particle must travel in the slot is substantially longer than its mean free path. 
     
     
       3. The plasma processing apparatus according to  claim 1  wherein said electrically insulating material comprises quartz. 
     
     
       4. The plasma processing apparatus according to  claim 1  wherein said electrically conductive member comprises aluminum. 
     
     
       5. A plasma processing chamber having a top electrode for processing a substrate, the plasma processing chamber comprising:
 a chuck for supporting the substrate during plasma processing; 
 a focus ring assembly substantially encircling said chuck; 
 a stack of confinement rings, made of electrically insulating material, spaced apart from each other to form slots therebetween, said stack of confinement rings surrounding an interaction space defined between the top electrode and said chuck; each confinement ring having at least one cavity formed on the surface thereof, and 
 at least one electrically conductive member passing through each of said cavity of said stack of confinement rings, a top of said at least one conductive member electrically coupled to the top electrode, said electrically conductive member is grounded at a bottom thereof. 
 
     
     
       6. The plasma processing chamber according to  claim 5  wherein said electrically insulating material comprises quartz. 
     
     
       7. The plasma processing chamber according to  claim 5  wherein said electrically conductive member comprises aluminum. 
     
     
       8. A plasma processor for processing a workpiece comprising an RF source arrangement, a processing chamber having (a) an exterior wall, (b) a top electrode assembly, (c) a bottom electrode assembly having a holder for the workpiece, (d) an inlet for gas to be converted to a plasma in a region spaced from the wall and between the top and bottom electrode assemblies, (e) a gas outlet, and (f) a confinement structure between the top and bottom electrode assemblies; the top and bottom electrode assemblies being electrically coupled with the RF source arrangement for exciting the gas in the region to a plasma while the plasma is processing the workpiece; the confinement structure being arranged for substantially preventing the plasma in the region from flowing to a portion of the chamber between the confining structure and the exterior wall while enabling un-ionized gas to flow from the region to said portion of the chamber, thence to the outlet; the confinement structure including: (i) at least one confinement ring between the top and bottom electrode assemblies for providing some confinement of the plasma to the region while the plasma is processing the workpiece, and (ii) an electrically conductive member connected to one terminal of the RF source arrangement and being coupled with the RF source arrangement so RF current from the RF source arrangement flows in the electrically conductive member for further confining the plasma to the region while the plasma is processing the workpiece. 
     
     
       9. The plasma processor of claim 8 wherein the confinement ring is a dielectric. 
     
     
       10. The plasma processor of claim 8 wherein the electrically conductive member is received by the confinement ring. 
     
     
       11. A plasma processor for processing a workpiece comprising an RF source, a processing chamber having: (a) an exterior wall, (b) a region spaced from the wall in which a plasma is adapted to be excited, (c) an outlet for gas exhausted from the chamber; the region including (i) a bottom surface comprising an electrode assembly having a holder for the workpiece, (ii) a top surface, and (iii) a side portion including a structure for substantially confining the plasma to the region while the plasma is excited to process the workpiece; the side portion including (a′) at least one confinement ring between the top and bottom surfaces, (b′) gaps between the confinement ring and the top and bottom surfaces for enabling un-ionized gas to flow from the region to the outlet via a segment of the chamber between the side portion and the exterior wall, and (c′) an electrically conductive member; the confinement ring in combination with the top and bottom surfaces having some confining effect on the plasma in the region while the plasma is excited and is processing the workpiece; the electrically conductive member being coupled to the RF source so RF current from the source flows through the conductive member while the plasma is excited to process the workpiece; the conductive member and coupling of the conductive member to the RF source while the plasma is excited to process the workpiece being such that the RF current flowing in the conductive member while the plasma is excited to process the workpiece produces effects for augmenting the plasma confinement effect of the confinement ring in combination with the top and bottom surfaces. 
     
     
       12. The plasma processor of claim 11 further including a top electrode assembly having a bottom surface including the top surface of the region where the plasma is adapted to be excited. 
     
     
       13. The plasma processor of claim 11 wherein the electrically conductive member is received by the confinement ring. 
     
     
       14. The plasma processor of claim 11 wherein the confinement ring is a dielectric. 
     
     
       15. The plasma processor of claim 11 wherein the electrically conductive member is connected to a terminal of the RF source while the plasma is excited to process the workpiece. 
     
     
       16. A method of processing a workpiece in a plasma processor including an RF source arrangement and a processing chamber having (a) an exterior wall, (b) a top electrode assembly, (c) a bottom electrode assembly having a holder for the workpiece, (d) an inlet for gas to be converted to a plasma in a region spaced from the wall and between the top and bottom electrode assemblies, (e) a gas outlet, and (f) a confinement structure between the top and bottom electrode assemblies; the confinement structure being arranged for substantially preventing the plasma in the region from flowing to a portion of the chamber between the confining structure and the exterior wall while enabling un-ionized gas to flow from the region to said portion of the chamber, thence to the outlet; the confinement structure including: (i) at least one confinement ring between the top and bottom electrode assemblies for providing some confinement of the plasma to the region while the plasma is processing the workpiece, and (ii) an electrically conductive member; the method comprising: supplying gas to the region via the inlet, exciting the gas in the region to a plasma that processes the workpiece by supplying RF energy to electrodes of the top and bottom electrode assemblies, processing the workpiece with charged particles of the plasma excited by the RF energy supplied to the electrodes of the top and bottom electrode assemblies, causing RF current from the RF source arrangement to flow in the electrically conductive member while the charged particles of the plasma are excited by the RF energy and the plasma is processing the workpiece, the RF current flowing in the electrically conductive member while the charged particles of the plasma are excited by the RF energy and the plasma is processing the workpiece producing confinement effects that augment confinement effects of the at least one confinement ring. 
     
     
       17. The method of claim 16 wherein the step of causing RF current from the RF source arrangement to flow in the electrically conductive member includes causing a terminal of the RF source arrangement to be connected to the electrically conductive member while the charged particles of the plasma are excited by the RF energy and the plasma is processing the workpiece. 
     
     
       18. A method of processing a workpiece in a plasma processor including an RF source arrangement and a processing chamber having: (a) an exterior wall, (b) a region spaced from the wall in which a plasma is adapted to be excited, (c) an outlet for gas exhausted from the chamber; the region including (i) a bottom surface comprising an electrode assembly having a holder for the workpiece, (ii) a top surface, and (iii) a side portion including a structure for substantially confining the plasma to the region while the plasma is excited to process the workpiece; the side portion including (a′) at least one confinement ring between the top and bottom surfaces, (b′) gaps between the confinement ring and the top and bottom surfaces for enabling un-ionized gas to flow from the region to the outlet via a segment of the chamber between the side portion and the exterior wall, and (c′) an electrically conductive member; the confinement ring in combination with the top and bottom surfaces having some confining effect on the plasma in the region while the plasma is excited and is processing the workpiece; the method comprising: supplying gas to the region via an inlet to the region, exciting the gas in the region to a plasma that processes the workpiece by supplying RF energy to the region, processing the workpiece with charged particles of the plasma excited by the RF energy supplied to the region, causing RF current from the RF source arrangement to flow in the electrically conductive member while the charged particles of the plasma are excited by the RF energy and the plasma is processing the workpiece, the RF current flowing in the electrically conductive member while the charged particles of the plasma are excited by the RF energy and the plasma is processing the workpiece producing confinement effects that augment confinement effects of the at least one confinement ring. 
     
     
       19. The method of claim 18 wherein the step of causing RF current from the RF source arrangement to flow in the electrically conductive member includes causing a terminal of the RF source arrangement to be connected to the electrically conductive member while the charged particles of the plasma are excited by the RF energy and the plasma is processing the workpiece.