Chemical and mechanical polishing

Zabasajja J, Merchant T, Ng B, Banerjee S, Green D, Lawing S, Kura H. Modeling and characterization of tungsten chemical and mechanical polishing processes. Electrochem Soc 2001 148(2) G73-G77. 

Chemical-mechanical polishing (CMP) (semiconductor processing) A combination of chemical and mechanical polishing that is used to planarize a surface. 

The chemical and mechanical properties have a great influence on the polish quality. Ma et al. [53] have observed that, as shown in Fig. 24, the waviness of polished surface decreases with polish time in the first 15 hours, and then becomes stable. Pad A as shown in Fig. 25(a) can be used stably for more than 65 hours. However, for pad B as shown in Fig. 25(b), it just can be used for only 25 hours and then became unstable. 

Plisson, H. and M. Mauger (2001), Chemical and mechanical alteration of microwear polishes An experimental approach, Chimia 55, 931-937. 

Reexamination of bulk and wafer-level modeling in the context of copper CMP is also underway. Due to the strong interaction between chemical and mechanical processes in copper polishing, consideration of the removal mechanisms as well as proper Preston-equation like modeling is being pursued [37,65]. More work is needed to produce effective and efficient wafer-level, feature-level, and die-level models for copper CMP, particularly as the industry moves to copper interconnect systems. 

As understanding of the CMP process improves, one can expect a great deal of work in all aspects of CMP modeling and simulation. These improvements are likely to extend over many length scales spanning wafer-level polish and uniformity concerns to die-level prediction to microscopic feature, chemical, and mechanical interactions. 

Qin K, Moudgil B, Park CW. A chemical mechanical polishing model incorporating both the chemical and mechanical effects. Thin Solid Films 2004 446 277-286. 

Experimental evidence strongly suggests that material removal in chemical-mechanical polishing (CMP) processes is a result of one or more chemical steps that alter the wafer surface combined with a mechanical step that removes the altered material. Chemical action by itself also removes material by static etching, but generally at a much lower rate than is observed when mechanical action is also present. Similarly, polishing rates observed when a minimally reactive fluid such as water is used instead of slurry are also low. Both chemical and mechanical processes are therefore involved in material removal at commercially practical rates, and the model we describe reflects this dual nature of the process. 

In this chapter, we derive and apply to data a simple two-step model that involves a chemical step followed by a mechanical removal step. The model is abstract in the sense that most of the specifics of the slurry composition or of the chemical reaction involved are not given in any detail. Although this appears to be a disadvantage, it is necessary for the application of the model to the analysis of removal rates from proprietary slurries whose compositions cannot be directly investigated. When applied as a compact formula, the model can provide a highly accurate description of removal rate variations as a function of polishing pressure and sliding speed. This then makes it possible to extract the relative contributions of chemical and mechanical processes to removal and to confidently interpolate or extrapolate rates based on the calibration data. 

In order to be speeilie about the relationship between chemical and mechanical rate constants and polishing variables, we will assume here that the mechanical rate constant is proportional to the frictional power density ... 

The surface quality of the polished Cu substrate is shown in Fig. 7.22. The polished copper surface has an average surface roughness of 6 A without any signs of corrosion or pitting. This is consistent with the fact that the slurry is well balanced between the chemical and mechanical strengths. This is... 

As W CMP is a combination of chemical and mechanical actions, the temperature between the pad and the wafer will rise during polishing because of mechanical friction and chemical reactions. Without a precise control of platen temperature, the removal rate from wafer to wafer will not be consistent. For example, as shown in Fig. 9.12, the removal rates increase significantly and then reach a relative plateau for a typical slurry using a platen that is not temperature controlled. 

Film Microstructure Microstructure provides a surface (to be polished) composed of differently oriented surfaces with different chemical and mechanical behaviors and grain boundaries that are prone to enhanced chemical activity. Thus a relationship between the film microstructure and planarization should be carefully monitored. 

To prevent mechanical damage to the polymer during CMP, either the mechanical component of the polish must be reduced or polymers with high mechanical strength and hardness must be used. In order to decrease the mechanical component and still provide reasonably high polish rates, the chemical component must be increased. However, just as with metals, if the chemical conrq)onent is too aggressive, than the polymer will etch in the slurry and planarization will be difficult. Thus, achieving proper balance between chemical and mechanical components is crucial. 

Discuss the impact of chemical and mechanical damage sto polished surfaces on the reliability of the interconnects. 

All investigators have outlined that surface roughness is a prerequisite for such an enhancement in the Raman scattering intensity. This roughness can be created by various types of processes electrochemical chemical reduction mechanical polishing vapour deposition lithography evaporation and photo-... 

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