Feature filling

Subsequent work by Kruglikov and coworkers [217, 316] explored the action of levelers under well defined hydrodynamic conditions. The analogy between the diffusive flux distribution and the primary current distribution (i.e. Laplace equation) was used for calculating the leveling power. The expression for the attenuation of the amplitude of a sinusoidal profile was shown to be  

10 imAcm-2 and 400 rpm, from an the field, represent simulations of leveling for 

A significant difference between leveling models is the manner by which the inhibiting adsorbates are deactivated. In general, leveler coverage evolution is obtained from mass balance allowing for adsorption, desorption and deactivation  

Levelers have traditionally been used to fill features with characteristic dimensions, typically tens of micrometers, which are a substantial fraction of the thickness of the 100 pm hydrodynamic boundary layer [1-5]. However, the role of leveling in 

Equation 2.37) the leveling power (LP) is defined as the ratio of (r vaiiey - (peak)/ valley The results correspond to deposition of 3 pm of nickel on the planar field, or 0.1 of the original groove depth (source Ref. [58]). 

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A quantitative description of feature filling requires a shape change algorithm to convert the quantitative description of the effed of adsorbates on metal deposition... 

The distinction between the two forms has been examined in some detail as submicrometer feature filling and relaxation of the diffusive boundary layer occur on the same time scale [64, 302]. Boundary conditions are required at the top, bottom and sides of the domain as shown in Figure 2.25 a statement of the initial conditions is also required for the time-dependent form. Where temporal evolution is considered, the relaxation of the boundary layer is usually arrested at the same value, 8, corresponding to the experimentally relevant hydrodynamic conditions used in... 

Figure 2.34 (a) Experimental demonstration of the dependence of feature filling on catalyst concentration in the electrolyte. 

In the following discussion, specimens are identified by the catalyst precursor concentrations used in the derivatization step. The feature filling images shown in Figure 2.35 [343] reveal several distinct shape transitions and related phenomena. The acceleration of the deposition rate provided by the disulfide (or thiolate) catalysts is evident from the decrease in the feature filling time from ri200 s for a specimen derivatized in 0.5 pmol L 1 SPS to 40 s for derivatization in 500 pmol L-1 SPS. For the specimens derivatized in 0.5 pmol L 1 S P S, deposition proceeds conformally and... 

Figure 2.35 Sequential feature filling images for trenches that were pre-treated with SPS/M PS catalyst prior to copper plating for indicated times in a PEG-CI electrolyte at — 0.25 V. The conditions used for electrode derivatization are indicated (source Ref. [343]).

Figure 2.36 Simulations of feature filling of correspond to those anticipated for the catalyst pre-treated electrodes. Interface motion derivatization treatments specified in is displayed using colorized contour lines to Figure 2.35. The feature filling times reflect the local catalyst coverage. Each corresponding to the last growth contour are ...

Increasing the initial catalyst coverage to 0.05 3 is predicted to result in near optimal superfilling behavior, as shown in Figure 2.36c. Enrichment at the bottom comers leads to rapid formation of first the V-notch and then the nearly flat bottom. As in the other simulations, the advancing bottom surface accelerates further as it collects catalyst from the eliminated sidewall areas. It also exhibits subtle oscillations in shape associated with the continual translation of catalyst from the sidewalls to the bottom surface. The oscillations are also detailed in the analytical solution of feature filling. The catalyst coverage approaches unity as the bottom surface reaches the top of the trench. 

Figure 2.39 Tracking the interface mid-height position during via filling provides a comparison between simulation and experiment (Figure 2.38). The inset shows the simulated bottom-up feature filling, with contours colorized to reflect the local 0Sps coverage (source Ref. [12]).

The possibility of using electroless deposition to superfill sub-micrometer features has also been explored[347-349] successful filling was recently reported for an alkaline EDTA-complexed electrolyte containing SPS and PEG as additives [349]. However, the tilted sidewalls in the lower half of the features, combined with the absence of kinetic data, make a mechanistic assessment of feature filling difficult. 

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