Chemical mechanical planarization material removal mechanism

Luo, J. and Dorfeld, D. A., Material Removal Regions in Chemical Mechanical Planarization for Sub-micron Integrated Circuit Fabrication Coupling Effects of Slurry Chemicals, Abrasive Size Distribution and Wafer-Pad Contact Area, IEEE Trans. Semicond. Manuf, Vol. 16, No. 1, 2003, pp. 45-56. 

CMP processes for oxide planarization (ILD and STI) rely on slurry chemistry to hydrolyze and soften the Si02 surface. Mechanical abrasion then controls the actual material removal. Thus, the key process output control variables (i.e., removal rate and nonuniformity) are strong functions of the mechanical properties of the system, namely, the down force and the relative velocity between the pad and the wafer. Metal CMP processes such as copper CMP rely more on chemical oxidation and dissolution of the metal than mechanical abrasion to remove the metal overburden. Consequently, careful control of the chemistry of the CMP process is more important for these CMP processes than it is for oxide CMP. Thus, CMP tools and processes optimized for ILD may not be optimal for metal CMP and vice versa. 

Chemical-mechanical planarization occurs when the surface of the wafer to be polished is forced against a polishing pad. Aqueous slurry that contains abrasive particles is placed on a polishing pad. The wafer is moved relative to the slurry-covered pad and the rate at which material is removed is often described by the heuristic equation called Preston s law ... 

The chemical-mechanical polishing or planarization (CMP) process is a complex interplay between the wafer and the consumables involved. The consumables include slurry, pad, conditioner, and so on. During polishing, the pad carries the slurry and delivers it to the wafer surface. It also transmits the normal and shear forces from the polisher to the wafer. Therefore, polishing pad plays a critical role in the CMP process and influences the outcomes such as material removal rate (MRR), within-wafer nonuniformity (WIWNU), wafer-to-wafer nonuniformity (WTWNU), step height reduction efficiency (SHRE), and defect counts. 

Wang C, Sherman P, Chandra A. A stochastic model for the effects of pad surface topography evolution on material removal rate decay in chemical mechanical planarization (CMP). IEEE Trans Semicond Manuf 2005 I8(4) 695-708. 

Bastawros A, Chandra A, Guo YJ, Yan B. Pad effects on material-removal rate in chemical-mechanical planarization. J Electron Mater 2002 31(10) 1022-1031. 

Pad plays two important roles (a) provides support against the wafer surface, allowing the wafer siuface to experience the impact of mechanical and chemical forces leading to materials remove and (b) carries sliury (fiom fee feed end to disposal) to affect planarization. In absence of fee... 

Chemical mechanical planarization is the selective planarization of a wafer by mechanical or chemical removal of material. The removal of material is governed by the Preston equation ... 

In the microelectronics community, the acronym CMP has been interpreted as either chemical-mechanical polishing or chemical-mechanical planarization. Polishing means the removal of materials, whereas planarization means flattening. It is the authors preference to interpret CMP as chemical-mechanical planarization. Because technology and integrated circuit (IC) shrinking advance rapidly, planarization has come to be at the heart of the CMP function. 

Chemical-mechanical planarization, CMP , processes are widely used to remove material from the surface of a substrate in the production of a wide variety of microelectronics. In a typical CMP process, the... 

Luo, J., Domfeld, D.A., 2003. Material removal regions in chemical mechanical planarization for submicron integrated circuit fabrication coupling effects of slurry chemicals, abrasive size distribution, and wafer-pad contact area. IEEE Trans. Semicond. Manuf. 16, 45—56. 

Figure 12.6 Material removal rate (MRR) as a function of abrasive concentration. Reproduced from Luo Jianfeng, Integrated Modeling of Chemical Mechanical Planarization/ Polishing for Integrated Circuit Fabrication (PhD Dissertation), 2003, Figure 5.11, page 178, with permission from University of California at Berkeiey.

The CMP material removal mechanism involves a special combination of chemical and mechanical forces [3]. First, chemically active slurry containing fine abrasive particles is released onto the porous pad and attacks the film to be planarized to chemically modify it. This allows the mechanical action involving a three-body contact motion of pad, abrasive, and wafer under an applied pressure to easily facilitate... 

To address this issue, planarization of the wafer surface can be applied. One approach is mechanical polishing, in which the wafer is pressed against a rotating platen and polished by an abrasive slurry. If the slurry includes chemicals that help dissolve the removed material, the process is called chemical mechanical polishing. 

The chemical component of CMP slurry creates porous unstable oxides or soluble surface complexes. The slurries are designed to have additives that initiate the above reactions. The mechanical component of the process removes the above-formed films by abrasion. In most planarization systems the mechanical component is the rate-limiting step. As soon as the formed porous film is removed, a new one is formed and planarization proceeds. Therefore, the removal rate is directly proportional to the applied pressure. To achieve practical copper removal rates, pressures greater than 3 psi are often required. These pressures should not create delamination, material deformation, or cracking on dense or relatively dense dielectrics used in silicon microfabrication on conventional dielectrics. However, the introduction of porous ultra-low-fc (low dielectric constant) materials will require a low downpressure (< 1 psi) polishing to maintain the structural integrity of the device [7-9]. It is expected that dielectrics with k value less than 2.4 will require a planarization process of 1 psi downpressure or less when they are introduced to production. It is expected that this process requirement will become even more important for the 45-nm technology node [10]. 

Goonetilleke PC, Roy D. Electrochemical-mechanical planarization of copper effects of chemical additives on voltage controlled removal of surface layers in electrolytes. Materials Chem Phy 2005 94 388-400. 

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