Electrochemical techniques are used widely for the fabrication of nanostructured materials, yet a quantitative understanding of nucleation and growth remains elusive. Here we probe electrochemical nucleation and growth of individual nanoclusters in real time by combining current-time measurements with simultaneous video imaging. We show discrepancies between the growth kinetics measured for individual nanoclusters and the predictions of models, and we describe a significant revision to conventional models that can explain the results. This improved understanding of nucleation and growth allows a more quantitative approach to the electrochemical fabrication of nanoscale structures.
Electrochemical deposition of metals onto foreign substrates usually occurs through Volmer–Weber island growth. The mechanism of island nucleation and growth dictates the shape, orientation and number density of islands, and ultimately, the structure and properties of thin films. With increasing emphasis on deposition of ultrathin films and nanostructures, it is critically important to understand the kinetics of nucleation and growth. Here we provide a comprehensive review of island growth in electrodeposition and summarize methods for mechanistic analysis in both the kinetic and diffusion limited regimes.
The growth kinetics for individual islands during electrodeposition of copper have been studied using in situ transmission electron microscopy. We show that for sufficiently large overpotentials, the growth kinetics approach the rate laws expected for diffusion-limited growth of hemispherical islands, characterized by two distinct regimes. At short times, the island growth exponent is 0.5 as expected for diffusion-limited growth of uncoupled hemispherical islands, while at longer times, the growth exponent approaches 1/6 as expected for planar diffusion to the growing islands. These results provide the first direct measurements of the growth of individual islands during electrochemical deposition. However, quantitative comparison with rate laws shows that the island radii are smaller than predicted and the island densities are much larger than predicted, and we suggest that this is related to adatom formation and surface diffusion, processes which are not included in conventional growth models.
A model for copper electroplating of through-silicon vias (TSV) is proposed based on the suppressor adsorption/desorption mechanism, with special emphasis on the bottom-up filling of these structures. The proposed model is applicable for both 2-component (suppressor and accelerator) and 1-component (suppressor only) Cu plating chemistries. Numerical simulation was performed for the filling of 5 μm (diameter) × 40 μm (depth) vias. Simulated Cu profiles and the corresponding dependencies on additive concentration are confronted with existing experimental results.
For systems where deposition occurs through Volmer-Weber island growth, the structure and properties of thin films are critically dependent on the mechanism of nucleation and growth. 1 For example, high nucleus densities are essential for achieving island coalescence at low coverages. For complex structures with small length scales, such as trenches and vias in integrated circuits, 2 a detailed understanding of nucleation and growth during electrodeposition is critical for designing deposition processes for obtaining void-free features.The mechanism of nucleation and growth of copper on TiN from noncomplexing, acidic fluoroborate solution involves instantaneous nucleation of hemispherical clusters followed by diffusion-limited growth, over a wide potential range. 3 The nucleus density is in the range 10 5 -10 9 cm Ϫ2 and is dependent on the applied potential. In this paper we report on the deposition of copper on TiN from pyrophosphate solution and show how deposition from the pyrophosphate complex influences the nucleation and growth process. In particular, we show that the deposition mechanism also follows instantaneous nucleation of hemispherical clusters followed by diffusion-limited growth, however, the nucleus densities are in the range 10 8 -10 11 cm Ϫ2 , about two orders of magnitude larger than for fluoroborate solution.Copper pyrophosphate solutions are used in the electronics industry for through-hole plating. 4,5 For solutions where [P 2 O 7 4Ϫ ]/ [Cu 2ϩ ] > 1, more than 99% of the copper ions are present in the form of the Cu(P 2 O 7 ) 2 4Ϫ complex. Deposition of copper from a complex is kinetically slower than for uncomplexed solutions, generally resulting in better deposition in complex geometries. Common additives include NH 4 ϩ , NO 3 Ϫ (cathode depolarizer), and organic brighteners (e.g., dimercaptothiadiazole). 4,5 Experimental The substrates for deposition were prepared by sputter deposition of 30 nm TiN on n-Si(100), N D ϭ 1 ϫ 10 15 cm Ϫ3 (Wacker Siltronic, AG). The TN layer was rf sputtered at room temperature for about 1 min (V rf ϭ 620 V). In all cases ohmic contacts were made to the back side of the silicon wafer using InGa eutectic. Since the nSi/TiN contact is ohmic, this method avoids limitations associated with the sheet resistance of the TiN layer. The aqueous 50 mM Cu(II) solution was prepared from 25 mM Cu 2 P 2 O 7 и3H 2 O with 0.2 M K 4 P 2 O 7 . The pH of the solution was adjusted to pH 8.5 with pyrophosphoric acid (H 4 P 2 O 7 ). From the equilibrium constants, 6,7 we determine that greater than 99% of the Cu(II) is present in the form of Cu(P 2 O 7 ) 2 6Ϫ . 8 Common additives such as NH 4 ϩ , NO 3Ϫ , and organic brighteners (e.g., dimercaptothiadiazole) were not investigated in this work. NO 3Ϫ , which serves as a cathode depolarizer, is redox active and hence represents an additional contribution to the deposition current. 4 The experiments were performed under ambient conditions using a conventional three-electrode cell with a Ag/AgCl (3 M NaCl) reference electrode connected...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.