Mechanism Of Dissolution And Planarization Of Copper Tantalum Films During Chemical Mechanical Polishing PDF Download

Chemical mechanical planarization (CMP) is becoming a promising mainstream semiconductor processing method because of its demonstrated capability to achieve better local and global planarization for various materials. However, the CMP process is influenced by a set of factors, which lead to a poor understanding of the material removal mechanisms (MRMs) and inhibits the migratability of the lab-scale experiments to industrial practice. This work focuses on the synergistic effects between chemical dissolution and mechanical abrasion to understand the MRMs during CMP. Initial in-situ wear test in chemically active slurry showed an increased material removal rate (MRR) relative to dry wear tests. To understand the synergistic effects, two plausible MRMs; (i) chemical dissolution enhanced mechanical abrasion and (ii) mechanical abrasion accelerated chemical dissolution, were investigated. In addition, a phenomenological MRR model based on scratch-intersections was formulated to understand the role of consumables and the process parameters. For mechanism I, a combined experimental and modeling technique was devised to understand the mechanical properties of the soft layer formed on the surface due to chemical exposure in CMP. The developed approaches utilized nano-scratch tests, nano-dynamic mechanical analysis (DMA) tests, the limit analysis solution of surface plowing under a spherical traveling indenter, and finite element simulation to deconvolute the soft layer thickness, hardness and elastic modulus. For mechanism II, it is found that the residual stress caused by the mechanical wear enhances the chemical etching rate, as manifested by an increase in wear depth. It is also found that the roughness with wavelength above a critical value grows while roughness of lower wavelength decays during etching, in which an established fact for stress-enhanced chemical dissolution is used. The developed understanding would enable understanding the root causes of defect generation mechanism and render remedies for yield improvements. The proposed models, through their mechanistic description, will facilitate an exploration of the design space and identification of realistic CMP process domains, including: (i) particle shape, size and concentration; (ii) adapting slurry chemistry for required rates of chemical dissolution and mechanical abrasion; and (iii) selecting pads with the proper surface morphology and stiffness.