Abnormal metal oxide formation induced by residual charging in plasma etch process

Electron cyclotron resonance plasma with SF6 and Cl2 gas mixture were used for tungsten plug etch-back processes. The properties of electric contacts between tungsten plugs and Al/Ti/TiN interconnect lines, fabricated by this etching process, have been studied. Particles and abnormal oxide layers at the plug/line interfaces have been found to be the main factor to cause deterioration of the electric contacts. Mechanisms for particle transportation and metal oxide formation have been proposed. The phenomenon was attributed to the residual charging effect, which occurred immediately after the plasma power being turned off. A technique to prevent the residual charging induced tungsten oxide growth has been developed and applied in industrial fabrication lines.