The effect of ethylenediamine tetramethylphosphonic acid on the chemical mechanical polishing of TSV barrier layer

Abstract

The chemical mechanical polishing (CMP) process of Through Silicon Via (TSV) tantalum (Ta) base barrier layer is essential for 3D packaging and 2.5D packaging of IC chips. However, achieving high tantalum layer removal rates and an adjustable selection ratio of tantalum to copper (Cu) remains a major challenge. The effect of ethylenediamine etramethylenephosphonic acid (EDTMPA) as a complexing agent on the chemical-mechanical polishing of tantalum base barrier layer of TSV was studied in this paper. When the concentration of EDTMPA is 2 wt%, the removal rates of Cu and Ta are 561 Å/min and 1533 Å/min, respectively, and the rate selection ratio of Ta and Cu reaches 2.73:1. Through electrochemical experiments, X-ray photoelectron spectrometer (XPS), Scanning electron microscope (SEM) and Density Functional Theory (DFT) simulation, the mechanism of EDTMPA promoting the removal of Cu and Ta was revealed. It was found that EDTMPA molecules reacted with Cu and Ta and oxides to form mass complexes, which promoted the corrosion of Cu and Ta. By comparing the surface quality before and after polishing with atomic force microscopy, it is found that the surface roughness of Cu decreases from 1.4 nm before polishing to 0.164 nm after polishing, and the surface roughness of Ta decreases from 1.74 nm before polishing to 0.142 nm after polishing. The results show that EDTMPA can effectively improve the surface quality of TSV tantalum barrier layer after polishing.