More vertical etch profile using a Faraday cage in plasma etching

Scanning electron microscope images of sidewalls obtained by plasma etching of an SiO2 film with and without a Faraday cage have been compared. When t he substrate film is etched in the Faraday cage, faceting is effectively su ppressed and the etch profile becomes more vertical regardless of the proce ss conditions. This is because the electric potential in the cage is nearly uniform and therefore distortion of the electric field at the convex corne r of a microfeature is prevented. The most vertical etch profile is obtaine d when the cage is used in fluorocarbon plasmas, where faceting is further suppressed due to the decrease in the chemical sputtering yield and the inc rease in the radical/ion flux on the substrate. (C) 1999 American Institute of Physics. [S0034-6748(99)00205-1].