Chemical Mechanical Polishing Using Mixed Abrasive Slurries

Abstract

Chemical mechanical polishing ͑CMP͒ of metal and dielectric films was performed using mixed abrasive slurries ͑MAS͒. MAS containing alumina and silica particles dispersed in deionized water were evaluated as second step slurries for Cu damascene polishing. It was demonstrated that MAS with proper selection of constituents and composition of abrasive particles can yield desired slurry/CMP characteristics. Based on the results of transmission electron microscope and particle size analysis of the abrasives in these MAS, possible reasons for the improved CMP performance are discussed.Chemical mechanical polishing ͑CMP͒ has emerged as a viable technique for planarizing metal and dielectric films for the fabrication of microelectronic devices. CMP is used to remove the overburden Cu from damascene structures and to achieve global planarization. Polishing of materials like Ta and tantalum nitride ͑TaN͒, used as a liner layer for Cu to serve as both an adhesion promoter and as a diffusion barrier in damascene patterning, has also gained importance in the recent years. Due to the vastly different mechanical and chemical properties of Cu and the barrier layer ͑Ta or TaN͒, these layers are polished sequentially in two separate steps. The main concerns in this patterning process are dishing of Cu lines and erosion of nearby areas. 1 Minimization of these phenomena in a damascene CMP process requires that the polishing be highly selective to Ta or TaN during the second step polishing. In addition, the film surface after CMP must be free of defects such as pits, microscratches, and particles.Typical slurries contain two phases, namely, liquid and solid phases even though some abrasive free slurries have been recently proposed. 2 Liquid phase consists of deionized ͑DI͒ water with additives like oxidizers, complexing agents, inhibiting agents, and surfactants. 3 Solid phase consists of abrasives, which are typically metal oxides, e.g., alumina, silica, ceria, etc. In single abrasive slurries ͑SAS͒, the solid phase consists of only one type of abrasive particle. Despite widespread use of SAS at all levels of metallization, polish rate selectivity, surface finish, and slurry stability still remain as major challenges. 4 Mixed abrasive slurries ͑MAS͒ consist of a mixture of at least two types of abrasive particles, which can be chosen from inorganic ͑alumina, silica, ceria, etc.͒ or organic ͑poly-meric resins͒ groups. 5 It has been observed that some of the problems associated with the use of SAS can be easily controlled by using MAS with proper composition and choice of constituents of the solid phase. In this paper, slurries containing alumina and silica particles dispersed in DI water at pH 4 have been studied for the second step Cu damascene polishing process. The modified abrasives in MAS are evaluated with respect to their particle size, surface morphology, and surface potential/charge. Arguments are presented to account for the improved CMP characteristics of these particles. ExperimentalChemical mechanical polishing.-Polish...

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Scratch formation and its mechanism in chemical mechanical planarization (CMP)

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Key Chemical Components in Metal CMP Slurries

“…The hardness of the alumina would still contribute toward the removal rate, and the surface coating with softer silica abrasives would prevent the surface defects. Hegde and coworkers [102,103] demonstrated this concept using the electrostatic interaction between the individual abrasives at a given operating pH.…”