Pad Properties

Some work has been done to correlate oxide CMP performance with pad properties [46]. This work indicated that the specific gravity of the pads and the cross-linking densities affect polish performance. Other work has been done to correlate CMP performance with slurry composition [47]. This work suggests that the friction during polish is proportional to the removal rate when the abrasive content is greater than 10%, and inversely proportional to the removal rate when it is less than 10%. 

It is now possible to model the wafer-level performance for most CMP processes. These models cover only some of the important tool or process design issues, such as relative velocities and pressure dependencies additional work is needed to predict the results for other parameters such as slurry composition or particle size, temperature dependencies, pad properties, and other effects. Die-level modeling has been used effectively to identify... 

It is also apparent that the composite pad properties of interest are affected by a large number of process and structural variables. Interaction effects make analysis of property variability particularly difficult. As a consequence,... 

Manufacturing Process Variables and Their Effects on Pad Properties... 

During actual CMP process, on a macroscale, these effects may cancel out each other. However, the transient, microscale effects on CMP pad properties and hence material removal are not yet clear and need to be further studied. 

Another important factor that is often not taken into consideration is the process temperature during polishing. Recent researches [12,13] have elucidated the effect of temperature on the coefficient of friction during both copper and ILD CMP by conducting polishing experiments at different pad and slurry temperatures. Sorooshian et al. [12] have attributed the changes in coefficient of friction to the changes in pad properties, which result in an increase in shear force. Conversely, removal rate, surface chemical analysis. 

Urethane stoichiometry also plays a key role in influencing the polyurethane pad properties. Stoichiometry refers to the ratio of reactive groups (usually diol or diamine moieties) to isocyanate groups. The presence of excess isocyanates... 

TABLE 5.3 Relationships between Pad Properties and Polishing Performance [1]. 

The choice of polyol, especially its size (moleeular weight), flexibility of its molecular structure, and functionality, has significant effect on the properties of the resultant polyurethanes. Varying isoeyanates also have major influenee on the properties of polyurethanes, sinee the reaetion of di- or polyfunctional isocyanates with polyols forms the polyurethanes. When there is excessive isocyanate with respect to diol, many secondary reactions may occur to create chemical cross-links between chains and network strueture in the polyurethanes. Thus pad properties can be eontrolled and fine-tuned through the control of the stoichiometric ratio of isocyanate to diol. 

What are the main components of polyurethane pads and how the pad properties can be controlled through polyurethane components Suggest some additional variations. 

Figure 4.10 An SEM micrograph of a new pad (Rodel s Suba IV) material. Table 4Jl Pad Properties ...

In addition to between wafer conditioning, pad break-in techniques are often performed before the pad is first used. Pad break-in often involves the same techniques employed for conditioning, along with running dummy wafers to stabilize the pad performance before running product wafers. In addition to setting the surface roughness, pad break-in is also likely to stabilize other pad properties such as water absorption. 

Polishing pad structure and material pad properties are important determinants in the polish rate and planarization in a CMP process. The impact of pad properties on rate, uniformity, and planarization is still not well understood. However, pad properties that are... 

Zhang, X.H., Pei, Z.J., and Fisher, G.R., 2007, Measurement methods of pad properties for chemical mechanical polishing. Proceedings of the 2007 ASME International Mechanical Engineering Congress and Exposition (IMECE 2007), Seattle, WA, November 11 — 15, vol. 3, pp. 517-522. 

---