Copper CMP for Dual Damascene Technology: Some Considerations on the Mechanism of Cu Removal

Abstract

It was found in a Cu-CMP process using EP-C 5001 slurry and IC 1000 pad that Cu removal rate, being extremely low without H2O2 in the slurry, increases up to a maximum with the addition of H2O2, and then decreases again. Analysis of polarization curves and Eh-pH diagrams shows that without H2O2 Cu has the lowest electric potential, as a result, the highest thermodynamic stability in the Cu/slurry system. Addition of H2O2 shifts the potential up and induces the formation of Cu2O, resulting in a high removal rate. At high H2O2 concentration, a CuO passivation film is formed. In this case, only mechanical removal of the passivating oxide film allows the process to proceed. It is speculated that the moving pad surface adheres the oxidized species via the formation of hydrogen bonds with oxygen atoms of copper oxide molecules, thus detaching them from the wafer surface. Each oxygen atom is capable of pulling out two Cu atoms if Cu2O is formed on the surface and only one Cu atom if CuO is formed. This would explain why the removal rate is high at low H2O2 concentration and low at high H2O2 concentration.

Interaction effects of slurry chemistry on chemical mechanical planarization of electroplated copper

“…Insignificant differences with low levels of H 2 O 2 concentration at both pH levels may also be explained by the formation of Cu 2 O at high pH which is preferred for CMP compared to the CuO. This line of argument is supported by the report of Wei et al [5] who observed and measured the formation of Cu 2 O with the addition of 0.06%H 2 O 2 and the formation of CuO with the addition of 2.5% H 2 O 2 at a slurry pH of 8.…”

“…As mentioned earlier, slurry pH and the concentration levels of H 2 O 2 have been found to result in the formation of a hard passivation layer of CuO or Cu 2 O on the surface of the Cu [4,5]. In general, and in accordance with the Cu Pourbaix diagram [6], a number of studies have shown that surface chemistry in the basic region combined with a given peroxide concentration, can lead to the formation of CuO.…”

“…In Cu CMP, abrasive particles such as alumina or colloidal silica are suspended in the slurry and aid in mechanical removal while slurry pH and hydrogen peroxide (H 2 O 2 ) provide the chemical reactions needed to facilitate the removal of Cu. Although extensive research has been conducted investigating the effects of slurry pH and H 2 O 2 during CMP [3][4][5], limited work has been done exploring the interaction effects between the two variables when dealing with thick Cu layers. The effect of slurry pH and complexing agents such as EDTA, citric acid and glycine on Cu removal rates has been well documented [4].…”

Progress in material removal mechanisms of surface polishing with ultra precision

“…Copper is likely to replace tungsten in ULSI in the near future. There is a great deal of efforts to reveal the removal mechanism for copper polishing [29,33]. Similar to tungsten CMF, the surface passivation can also take place in copper CMF [29].…”

“…Copper atoms are immediately oxidized in the slurry and CU20 remains. Further investigation on the removal mechanism of Cu CMF has been performed by Wei et al [33]. They demonstrated the material removal by pulling out the surface fragments bonded to the interacting oxygen atom.…”