Apparatus and methods for focusing plasma

Abstract

Apparatus and methods for plasma etching are disclosed. In one embodiment, a method for etching a plurality of features on a wafer includes positioning the wafer within a chamber of a plasma etcher, generating plasma ions using a radio frequency power source and a plasma source gas, directing the plasma ions toward the wafer using an electric field, and focusing the plasma ions using a plasma focusing ring. The plasma focusing ring is configured to increase a flux of plasma ions arriving at a surface of the wafer to control the formation of the plurality of features and structures associated therewith.

1 . A method of etching a plurality of features on a wafer, the method comprising:
 positioning the wafer within a chamber of a plasma etcher;   generating plasma ions using a radio frequency power source and a plasma source gas;   directing the plasma ions toward the wafer using an electric field; and   focusing the plasma ions using a plasma focusing ring, the plasma focusing ring configured to increase a flux of plasma ions arriving at a surface of the wafer to control the formation of the plurality of features and structures associated therewith.   
     
     
         2 . The method of  claim 1 , wherein the structures are pillars. 
     
     
         3 . The method of  claim 2 , wherein the plurality of features comprises a plurality of vias. 
     
     
         4 . The method of  claim 3 , wherein the plurality of features comprises a plurality of through-wafer vias. 
     
     
         5 . The method of  claim 4 , further comprising removing effluent gases from the chamber at a rate sufficient to prevent etch byproducts from forming pillars in the plurality of the through-wafer vias. 
     
     
         6 . The method of  claim 4 , wherein each through-wafer via has a volume greater than about 100,000 μm 3 . 
     
     
         7 . The method of  claim 4 , wherein each through-wafer via has a depth greater than about 90 μm. 
     
     
         8 . The method of  claim 1 , wherein the wafer is a GaAs wafer. 
     
     
         9 . The method of  claim 8 , wherein the wafer has a diameter greater than or equal to about 150 mm. 
     
     
         10 . The method of  claim 9 , wherein the wafer has a thickness less than about 200 μm. 
     
     
         11 . The method of  claim 10 , wherein the wafer is bonded to a carrier substrate. 
     
     
         12 . The method of  claim 11 , wherein the carrier substrate is a sapphire substrate. 
     
     
         13 . The method of  claim 9 , wherein the plasma source gas comprises chlorine. 
     
     
         14 . The method of  claim 1 , wherein the plasma focusing ring has an inner diameter in the range of about 5 inches to about 12 inches. 
     
     
         15 . The method of  claim 14 , further comprising positioning the focusing ring at a distance ranging between about 1 inches to about 4 inches from the wafer. 
     
     
         16 . The method of  claim 14 , wherein the plasma focusing ring comprises a ceramic. 
     
     
         17 . An apparatus for etching a plurality of features on a wafer, the apparatus comprising:
 a chamber;   a holder disposed in the chamber configured to hold the wafer;   a gas channel configured to receive a plasma source gas;   a radio frequency power source configured to generate plasma ions from the plasma source gas;   a pump configured to remove gases and etch particulates from the chamber; and   a focusing ring configured to focus plasma ions toward the holder, thereby increasing the density of plasma ions delivered to the wafer to control the formation of the plurality of features and structures associated therewith.   
     
     
         18 . The apparatus of  claim 17 , wherein the structures are pillars. 
     
     
         19 . The apparatus of  claim 18 , wherein the plurality of features comprises a plurality of vias. 
     
     
         20 . The apparatus of  claim 19 , wherein the plurality of features comprises a plurality of through-wafer vias. 
     
     
         21 . The apparatus of  claim 17 , wherein the holder is configured to hold a wafer bonded to a carrier substrate, the carrier substrate having a diameter greater than a diameter of the wafer. 
     
     
         22 . The apparatus of  claim 21 , wherein the holder is configured to hold a wafer having a diameter greater than or equal to about 150 mm. 
     
     
         23 . The apparatus of  claim 17 , wherein the plasma focusing ring has an inner diameter in the range of about 5 inches to about 12 inches. 
     
     
         24 . The apparatus of  claim 23 , wherein the plasma focusing ring is positioned from holder by a distance ranging between about 1 inches to about 4 inches. 
     
     
         25 . The apparatus of  claim 17 , wherein the plasma focusing ring comprises a ceramic. 
     
     
         26 . The apparatus of  claim 17 , further comprising a clamp for holding the wafer against the holder. 
     
     
         27 . The apparatus of  claim 26 , further comprising a spring clamp assembly and a rod, the spring clamp assembly having a first end connected to the clamp and a second end connected to a first end of the rod. 
     
     
         28 . The apparatus of  claim 27 , further comprising an anode positioned above the holder and a cathode positioned beneath the holder, the anode and the cathode electrically connected to the radio frequency power source. 
     
     
         29 . The apparatus of  claim 28 , further comprising an electrode shield surrounding the cathode. 
     
     
         30 . The apparatus of  claim 29 , wherein the electrode shield includes a rod hole configured to receive a second end of the rod. 
     
     
         31 . The apparatus of  claim 27 , wherein the spring clamp assembly comprises an upper body and a lower body, the upper body includes an assembly hole for receiving both a spring and a screw for attaching the upper body to the lower body. 
     
     
         32 . The apparatus of  claim 31 , wherein the upper body further includes a mounting hole for receiving a screw for attaching the upper body to the clamp. 
     
     
         33 . The apparatus of  claim 31 , wherein the lower body includes a hole for receiving a screw for attaching the lower body to the first end of the rod.