BEoL post CMP cleaning challenges for 22 nm FD-SOI and beyond

In this paper we discuss the different behaviors of four state-of-the-art post CMP cleaning chemistries with respect to cleaning performance, wafer surface properties and electrical performance. The wafer surface properties include roughness and material composition evaluation. In addition to the commonly done investigation of the cleaning performance of the chemistries, analysis like XPS and SEM of post CMP wafer surfaces were performed and a correlation between the properties of the chemistry and the resulting wafer properties is discussed. A significant difference in the kind of carbon bonding on the Cu surface as well as the resulting sulfur residues on the wafers were observed for the different chemistries that were tested. Furthermore, stress tests of the Cu surface revealed different etch damages for the different chemistries. It is also shown that the interaction of cleaning chemistry with wafer surface can cause a decrease in the breakdown voltage inside the BEoL stack. Finally, a comparison of the advantages and disadvantages of the tested chemistries is given and in conclusion, the identified properties of each chemistry are assessed with regard to manufacturability.