Effect of aminoguanidine hydrochloride on chemical mechanical polishing of Ta-based barrier layers on TSV wafers

Abstract

As the feature size of planar semiconductor processes gradually decreases, the development of chips to increase integration in the 2D direction gradually stagnates. Consequently, to keep pushing the boundaries of chip integration, the Through Silicon Via (TSV) technology as a representative of the 2.5D and 3D integrated circuits (IC) technology, has become the new type of solution. Chemical Mechanical Polishing (CMP) of TSV is a key process to ensure the surface flatness of silicon through-holes, to remove excess material, to improve interconnect quality and reliability, and to meet the demands of advanced processes, which is of great significance to enhance the performance and production efficiency of semiconductor devices. The removal rate of Ta barrier layer and the surface quality of TSV wafer after CMP is a contradiction that needs to be balanced. Aminoguanidine Hydrochloride (AGHCl) as a complexing agent in the slurry can effectively solve the above problems. Aminoguanidine is coordinated by the N2 atom of the terminal hydrazine group and the N3 atom of the imine to form a complex with the metal ions in a planar five-membered ring structure, thus realizing the removal of the material. Electrochemistry, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and density functional theory calculations (DFT) were used to analyze the complexation mechanism of AGHCl on Ta and Cu; Atomic force microscope (AFM) was used to compare the surface quality before and after the polishing; step profiler was used to reveal the correction ability to dishing pits; and a laser nano-particle sizer was used to characterize the stability of the slurry. When the concentration of AGHCl was 0.75 wt%, the removal rate of Cu was 979 Å/min and that of Ta was 1305 Å/min, and the rate-selective ratio of Ta and Cu was 1.33:1. The surface roughness of Cu and Ta decreased from 1.98 nm to 0.287 nm and 2.39 nm–0.111 nm respectively, and the surface quality was effectively improved. The depth of the dishing pit of copper block on the TSV wafer was reduced from 2442 Å to 1160 Å after polishing, which meets the requirement of industrial application.