Local planarization

Working with different microporous materials, Korb and coworkers built a different model for the dynamics of the liquid. As in other approaches (46), the effective dimensionality for the diffusive process that drives relaxation is lower than three, and the model is based on locally planar constraints. 

Before local planarity is achieved (i.e., while local step height still exists), the final film thickness is inversely proportional to the effective local density. The film is assumed to polish linearly at the blanket rate afterward. The key... 

SOD + EB), and CMP. Among all these techniques, CMP is the only one that can offer excellent local and global planarities at the same time. More specifically, CMP can yield local planarization of features in the order of tens of microns and near-global planarization as far as tens of millimeters [5,20]. 

Here and t] are, respectively, the relative permittivity and the viscosity of the electrolyte solution. This formula, however, is the correct limiting mobility equation for very large particles and is valid irrespective of the shape of the particle provided that the dimension of the particle is much larger than the Debye length 1/k (where k is the Debye-Htickel parameter, defined by Eq. (1.8)) and thus the particle surface can be considered to be locally planar. For a sphere with radius a, this condition is expressed by Ka l. In the opposite limiting case of very small spheres (Ka 3> 1), the mobility-zeta potential relationship is given by Hiickel s equation [2],... 

Figure 2.2 Degrees of surface planarity (a) unplanarized, fl)) surface smoothing, (c) local planarization, and (d) global planarization.

A second method of local planarization involves spinning photoresist onto the SiOj ILD to obtain local planarity. The resist is then hard baked and etched with an RIE etch tailored to remove SiOz (or ILD) at the same rate as the photoresist. Because the etch rate of the two materials is equal, the planarity of the resist film transfers into the SiOz film. However, a precise match in SiOj and photoresist etch rates is difficult to maintain because the relative ratio of SiOj to photoresist exposed increases as the etch back proceeds. Loading effects then result in a decrease in the Si02 etch rate and increase in the photoresist etch rate. Furthermore, polymer deposits build up on the etch reactor chamber walls over time etching of this polymer depletes the chemicals used to etch the photoresist, which slows the photoresist etch rate. If the etch rates are not matched, the planarity of the photoresist layer will not transfer well to the SiOz. 

Lastly, if the SiOj deposition is highly conformal, the regions between closely spaced metal lines may be filled without the production of gaps. If the film thickness is equal to half the space width, the space will fill completely and the comers of the film will join at the top of the space, thereby leaving a nearly planar film. Examples of CVD SiOj processes capable of the required high degree of conformality are ECR deposition and tetraethyl orthosilicate (TEOS) plasma CVD-enhanced. While this approach yields local planarization above closely spaced lines, the wide spaces between metal lines are not filled, and thus a sharp step is experienced at the edge of such spaces. Therefore, this approach is often coupled with SOG or resist etch-back processes or CMP.< >... 

TEM scans of typical air crazes in PS samples of low and high molecular weight are shown in Fig. 12. It is evident from these TEM micrographs, as well as from the SEM scan of the fracture surface of PSAN shown in Fig. 10, that the craze is a highly deformed, localized planar region with sharp boundaries separating it from the bulk... 

For instance, in solutions substituted cyclopropanes with locally planar groups, such as the acetyl (MeC=0) or vinyl (H2C=CH) groups, may exist as equilibria of several conformers. One can find bisected (VI) perpendicular (VII) or intermediate (gauche) conformationsIn these conformations, furthermore, s-trans and s-cis arrangements... 

Local planarization is achieved far more easily than global planarization, but both contribute to resolution loss. 

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