Ionized physical vapor deposition of Cu on 300 mm wafers: A modeling study

A two-dimensional model has been used to understand the physics and process engineering issues associated with a conceptual 300 mm Cu internal-coil io nized physical vapor deposition reactor. It has been found that inductive c oupling from the coil is the primary source of plasma production. Since the coil is in direct contact with the plasma, a significant fraction of the c oil power is deposited in the gas capacitively as well. This results in spu ttering of the Cu coil, which tends to improve Cu flux uniformity at the ou ter edges of the wafer. Since the Cu ionization threshold is much lower tha n Ar, Cu+ density is comparable to Ar+ density even though ground state Cu density is much smaller than Ar. Significant fraction of the neutral Cu flu x to the wafer is in the metastable or athermal state. The effects of sever al actuators, reactor dimensions, and buffer gas on important plasma and pr ocess quantities have also been investigated. Electron density in the react or and Cu ionization fraction increases with increasing total coil power be cause of enhanced ionization. Total coil power however does not affect the Cu density appreciably, except near the coil where enhanced coil sputtering increases the Cu density. Decrease in dc target voltage with increasing co il power decreases Cu+ loss to the target and results in an increase in tot al Cu flux to the wafer. Electron and Cu density in the reactor increase wi th increasing dc target power. This is due to enhancement in target sputter ing and consequent ionization of the sputtered Cu. While this increases the total Cu flux to the wafer, ionization fraction is not affected much. It i s demonstrated that uniformity of Cu flux to the wafer and ionization fract ion can be controlled by means of the terminating capacitor at the coil. De creasing the terminating capacitance increases the coil voltage, enhances c oil sputtering and enhances Cu flux toward the outer edges of the wafer. Th is, however, decreases the amount of power that is transferred to the plasm a inductively, reducing the ionization efficiency. Increasing the coil-wafe r distance results in fewer sputtered Cu atoms being ionized as the target- coil distance becomes smaller than the mean free path for thermalization of hot sputtered Cu atoms. Also, one can control the ionization fraction of C u flux to the wafer by replacing Ar by Ne or Xe, without significantly impa cting the total Cu flux. (C) 2001 American Institute of Physics.