Effects of the biasing frequency on RIE of Cu in a Cl2-based discharge

The reactive ion etching of copper films is examined in several Cl2 containing gas mixtures at different discharge frequencies. Low (< 1 MHz) and high (13.56 MHz) frequency biasing was used to study the influence of the ion bombardment on the etch profile. Using the low excitation frequency anisotropic profiles have been obtained even without the formation of a thick sidewall protecting film in contrast to the high frequency discharge. Despite the enhanced ion bombardment using the low frequency discharge, the etch selectivity with respect to masking and bottom materials, respectively, is high enough for its application in multilevel metallization systems. To reduce any residues in the etch ground the addition of CF4 to the Cl2Ar mixture was found to be advantageous for low Cl2 partial pressures. Both PVD-Cu and CVD-Cu layers have been patterned with dimensions of about 1 μm.