Defforge et al. Nanoscale Research Letters 2012, 7:375 http://www.nanoscalereslett.com/content/7/1/375 N A N O E X P R E S S Copper-selective electrochemical filling of macropore arrays for through-silicon via applications Thomas Defforge1*, Jérôme Billoué1, Marianne Diatta1, François Tran-Van2 and Gaël Gautier1 Open Access Abstract In this article, the physico-chemical and electrochemical conditions of through-silicon via formation were studied. First, macropore arrays were etched through a low doped n-type silicon wafer by anodization under illumination into a hydrofluoric acid-based electrolyte. After electrochemical etching, ‘almost’ through-silicon macropores were locally opened by a backside photolithographic process followed by anisotropic etching. The 450 × 450-μm² opened areas were then selectively filled with copper by a potentiostatic electrochemical deposition. Using this process, high density conductive via (4.5 × 105 cm − ²) was carried out. The conductive paths were then electrically characterized, and a resistance equal to 32 mΩ/copper-filled macropore was determined. Keywords: Silicon electrochemical etching, Macropore arrays, Copper electrochemical deposition, Through-silicon via Background Nowadays, the scaling down (known as ‘More Moore’) of devices is coming to an end. To maintain a constant evolution of the device performances in the future, alter- native ways must be explored. The main one is the de- vice functional diversification and the three-dimensional (3D) integration (‘More than Moore’). The 3D integra- tion is based on the use of the semiconductor volume to connect both sides of a silicon wafer [1,2]. This tech- nique enables the stacking of the dies and leads to an important surface gain. The through-silicon via (TSV) technology is the key parameter for 3D integration allowing through-silicon connections. This technique is based on the etching of TSV and then the filling of these through holes by a conductive metallic material such as copper or tungsten [1]. The TSV are usually etched into the silicon using deep reactive ion etching (DRIE) [3,4]. This technique requires both chemical and physical silicon attacks [5] to achieve anisotropic etching of silicon. The Bosch process [6] is often employed to reach high aspect ratio (HAR) struc- tures. It consists of the alternative insertion into the * Correspondence: thomas.defforge@univ-tours.fr 1Université François Rabelais de Tours, GREMAN UMR CNRS 7347, 16 Rue Pierre et Marie Curie, BP 7155, Tours Cedex 2 37071, France Full list of author information is available at the end of the article etching chamber of two gaseous species: an etching one (e.g., SF6) and a polymerizing one that immunizes the sidewalls from the SF6 attack. This enables the formation of versatile structures into the silicon wafer. Despite its high versatility, DRIE technique suffers of several limita- tions. The first limitation is the value of the via aspect ratio that can be attained. Indeed, this value is limited to around 30 or 40 because of homogeneity defects [7]. Fur- thermore, the main issue of DRIE is the corrugation (or scalloping) development on the silicon sidewalls. This corrugation is directly imputed to the alternative steps of the Bosch etching process. The scalloping is known to be responsible for deposition conformity defaults. The electrochemical etching of silicon leading to porous silicon formation is an alternative to DRIE for low-cost TSV fabrication. Indeed, macropore formation (pore diam- eter > 50 nm and most of the time > 1 μm) presents sev- eral advantages as compared with dry etching technique. In this case, the wafers are immersed into a HF-based solu- tion (often mixed with solvents and/or surfactants) and an anodic current (or potential) is applied to the sample. The morphology of porous silicon is influenced by the substrate nature (its orientation, doping type, and concentration), the electrolyte composition (HF and additive concentra- tions), and the anodization parameters (applied current or potential, illumination, etc.) [8]. To obtain HAR, high- © 2012 Defforge et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.