Plasma is created in a similar way to PECVD (apply potential, accelerate electrons, gas is ionised by collisions with electrons, etc.), the only difference is the gas introduced (the gas reacts with the surface and the reaction product is volatile, thus it is removed instead of deposited)
in the first picture it can be seen the system that controls the gas flows, pressure, the bias applied to ignite the plasma
In the second picture the reactor in which plasma is ignited can be seen,
In the third picture the chuck with 4 wafers can be observed, the chuck is introduced in the plasma reactor from the second picture
Objectives of plasma etch
Etch depth - plasma should be able to etch deep trenches
Selectivity - for example etch only polysilicon but not the photoresist or SiO2 (in the lower picture)
Anisotropy - vertical walls
Spatial uniformity - the etched trench should have the same depth everywhere on the wafer
Substrate preparation
