Chemical Mechanical Planarization of NiAl

Binary metal alloys with a low resistivity are being studied for advanced interconnects. NiAl is one of the candidate materials in the binary metal alloy group. Chemical Mechanical Planarization (CMP) is a significant process for the metallization and planarization of metals in integrated device manufacturing. This work focuses on the effect of pH on the CMP process of NiAl, concerning material removal rates, surface roughness (Rq), and wettability by contact angle measurements. CMP experiments have been performed at pH 2 and pH 10 to evaluate the role of acid and alkaline conditions. Thus, many of the advanced characterization techniques such as Scanning transmission electron microscopy (STEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectroscopy (ICP-OES), contact angle measurement were used. The results clearly show that pH 10 greatly increased the efficiency of the CMP process. The material removal rate (MRR) was higher in the case of pH 10, and planarization was achieved in a relatively shorter time compared to pH 2. The ICP-OES results show the NiAl was planarized and thinned successfully with 55:45 atomic concentration (Ni:Al) at pH 10. However, the acidic slurry (pH 2) cannot contribute to the thinning of the NiAl layer, achieving a 40:60 atomic concentration (Ni:Al). Surface roughness measurements by Rq value showed faster reduction at pH 10, reaching values below 0.500 nm after 60 seconds, while pH 2 required longer times to achieve similar smoothness. Also, the contact angle analysis was done, which showed a much-improved surface wettability at pH 10, stabilizing at ~35° compared to ~40° at pH 2. These results indicated that alkaline conditions have a good impact in terms of material removal rates, finer surfaces, and good hydrophilicity compared to acidic slurry. Surfactants and complexing agents would be used to understand the entire mechanism CMP of NiAl, and post-CMP cleaning must be studied to evaluate its impact on the CMP of NiAl.