EFFECTS OF O-2 ADDITION ON BCL3 CL-2 PLASMA CHEMISTRY FOR AL ETCHING/

Effects of low level (0.5-20%) O-2 addition on BCl3/Cl-2 plasma chemis try have been investigated using several diagnostic tools: optical emi ssion spectroscopy, microwave interferometry and mass spectrometry. Ex periments were performed using a magnetically enhanced planar 13.56-MH z rf plasma reactor; where aluminum etching was also performed using s amples masked with a photoresist pattern of lines and spaces. As O-2 w as added into a BCl3/Cl-2 plasma, the Al etch rate first increased and then dropped above approximate to 3% O-2 added; a transition from rea ctive-ion-etching (RIE) lag to inverse RIE lag occurred at an O-2 perc entage of similar to 8%. Optical and mass spectrometric measurements i ndicated that the Cl concentration increases as O-2 is added into a BC l3/Cl-2 plasma, and that above a critical O-2 percentage (similar to 6 % O-2) BxOy species are formed in the plasma through a reaction betwee n boron chlorides and oxygen and then deposit onto the wafer surface d uring etching. Al etching characteristics obtained in BCl3/Cl-2/O-2 pl asmas are interpreted in terms of competitive effects of increased con centrations of Cl and BxOy.