ECMP planarization efficiency

FIGURE 10.12 Influence of electrolyte on ECMP planarization efficiency. 

FIGURE 11.17 ECMP planarization efficiency at removal rate of 6000A/min on 100 X 100 pm lines (from Ref 25 ). 

The formation of an anodic film (ion-concentrated diffusion layer or salt film) depends on electrolyte and processing conditions. The characteristics of the film are critical to the planarization efficiency of ECP and ECMP. Hence, the analysis, especially in situ analysis of anodic films, is highly valuable. A few techniques can be used for the purpose. 

To achieve better planarization efficiency than ECP, different modified ECP approaches have been explored. These approaches, including ECP-DI water technique [27], sectorial cathode ECP [28], membrane-mediated ECP [29], and contact ECP (i.e., ECMP) [30,31], work by different mechanisms and exhibit different performances. 

These conditions mainly depend on the electrolyte. However, the thickness and surface profile of the anodic film, which strongly affect planarization efficiency, also depend on the ECMP pad. 

Conventional CMP typically requires an overburden of copper of at least 4000 A due to low planarization efficiency. An overburden of 1000 A is sufficient for ECMP to achieve planarization without compromising performance in terms of dishing, erosion, and defectivity. A stress migration test was carried out at 250 °C for 333 h on a structure with metal level 1 and level 2 lines with thickness in the range of 0.14-0.16 pm. An increase in resistance by more than 10% is considered a fail. The reduction in electroplated copper thickness can reduce the number of fails in stress migration test as shown in Table 11.1. 

Unlike in the ECMP process described earlier, the initial conductivity of the liquid between the wafer and the pad is not required. As a matter of fact, a conductive solution actually lowers the planarization efficiency as shown in Fig. 11.24. Similar to ECMP, high planarization efficiency can be obtained at... 

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