Green and high-efficiency CMP Slurry for Cu planarization

Chemical mechanical planarization/polishing (CMP) is an important process for Through-silicon-via (TSV) technology in 2.5D and 3D integration and is the only technology that can balance the global and local surface planarization. In recent years, there is an urgent need to develop new CMP slurry with environmental friendly and non-toxic components because traditional CMP slurry contains strong acids, alkalis, or harmful and toxic chemicals, which are detrimental to the environment, and harmful to the public health. The low or none toxic amino acids and other substances may be the promising candidates to replace the harmful chemicals normally used in the CMP slurries.In this paper, we proposed a CMP slurry with high material removal rate and non-toxic chemicals for Cu planarization. In this green slurry, silica sol was used as the abrasive, and the amino acids and hydrogen peroxide (H2O2) were used as the coordination and the oxidization regents, respectively. Adenine (AD) and chitosan (CTS) are used as corrosion inhibitors. The experimental results of CMP showed that the material removal rate of copper could be stabilized at about 1100 nm/min with the synergistic effect of glycine (Gly) and sarcosine (Sar), and Sar could also promote the post-CMP cleaning by modifying the copper surface. The material removal rate of copper decreased rapidly (from ~1000 to ~ 400 nm/min) after the introduction of a single corrosion inhibitor AD, and the material removal rate was effectively stabilized by using a mixture of AD and CTS, and the combination of 0.20 wt% AD and 0.20 wt% CTS corrosion inhibitors resulted in a material removal rate of 621.27 nm/min. The surface morphology of the copper was determined by atomic force microscopy, and the surface roughness could be significantly reduced via BTA utilization (from ~ 4.75 to ~ 1.4 nm), and then was further reduced to less than 1 nm by using the combined inhibitor, i.e., AD and CTS. The results of static etch experiments showed that the introduction of Sar in the slurry can effectively inhibit the over-corrosion of the copper surface and homogenize the corrosion pits on the etched copper surface. Electrochemical analysis showed that both AD and CTS can effectively coordinate with copper cations and form passivation films to protect the surface. The qualitative composition XPS analysis for the high-resolution Cu 2p3/2 spectra revealed that the coordinated Cu-Gly, Cu-Sar, Cu-AD, Cu-CTS and Cu-BTA were present in the corresponding solutions. Therefore, high material removal rate (~ 600 nm/min) and low surface roughness (<1 nm) after Cu CMP could be achieved by applying the developed green and high-efficiency slurry composed of promising complexing and inhibition agents.