Factors controlling the etching rate and etching profile in the O ₂ reactive ion etching pattern transfer step in multilevel lithography

Physical bombardment plays a dominant role in the O 2 reactive ion etching (RIE) pattern transfer step in multilevel lithography. Etching rates are determined by the flux and energy distribution of the bombarding ions and energetic neutrals (charge transfer products), while anisotropy is determined by their directionality. Measurements of the sheath thickness and voltage drop may be used to estimate flux, energy distribution, average energy, and angular distribution of ions and the energetic neutral products of charge transfer collisions. The estimated flux of bombarding particles allows measured etching rates to be converted into yields. The trends for the etching rate as a function of pressure, bias voltage, and other system variables reflect a single fundamental trend for the yield as a function of bombardment energy. Etching rates of an organic novolac polymer are proportional to the energy flux from bombarding particles while the yield per bombarding particle is proportional to its energy. These kinetics are combined with angular distribution and interface evolution models to predict etching profiles in multilevel lithography.