Free-standing line patterns of nanocrystalline electrodeposits
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Free-standing line patterns of nanocrystalline electrodeposits Karen Pantleon1, Henrik Myhre Jensen2*, Marcel A.J. Somers1 The Technical University of Denmark, DK – 2800 Kgs. Lyngby, Denmark 1 Department of Manufacturing Engineering and Management (IPL) 2 Department of Mechanical Engineering (MEK) (*now: Aalborg University, Department of Building Technology and Structural Engineering) ABSTRACT Free-standing Cu- and Ni-line patterns with varying line dimensions in the range of a few micrometers were manufactured by means of electrodeposition through a lithographically prepared mask. XRD studies revealed for Cu-lines a pronounced influence of the pattern geometry on crystallographic texture and peak broadening. Information on the strain distribution within individual Cu-lines was obtained from FEM. INTRODUCTION Electrochemical deposition has been successfully implemented in various microfabrication technologies [1-3]. For instance, plating through a mask results in free-standing patterns, which can either directly be used as metallic patterns in micro-systems or act as mould for the specially developed injection moulding process. The two most important materials in this field are Cu, which has become the dominating material for interconnects in integrated circuits in microelectronics, and Ni, a promising material to realize movable structures for micro-electromechanical applications. Successful miniaturization of the feature sizes in microelectronics, sensor and actuator technologies requires a thorough understanding of the correlation between manufacturing process and resulting properties of patterned electrodeposits. The present paper reports about free-standing line patterns of electrodeposited Cu- and Ni-films. X-ray diffraction (XRD) studies were carried out in dependence on the geometry of the line patterns, in order to quantify crystallographic texture and to investigate the shape of diffraction peaks as a measure of lattice imperfections. Supplementary to XRD, finite element modeling (FEM) of the strain distribution within individual Cu-lines was performed. EXPERIMENT AND SIMULATION Electrochemical deposition In order to ensure electrical conductivity during the deposition, a polycrystalline Au-layer (thickness 200 nm) was deposited on a glass wafer. UV-lithography (photo-resist thickness 6.5 µm) was carried out in clean room atmosphere in order to obtain a three-dimensional template, which was subsequently filled with Cu and Ni, respectively, by electrochemical deposition. Deposition parameters are summarized in Table 1. During deposition, a current thief was placed around the wafer in order to improve the current density distribution over the surface area.
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Table 1: Parameters used for electrochemical deposition of Cu- and Ni-deposits (a PEG polyethylene glycol, molar mass: 3400 g/mol, b MPSA - 3-mercapto-1-propanesulfonate). Cu-electrodeposits Ni-electrodeposits Ni-sulphamate bath: electrolyte acidic Cu-bath: 1.9 mol/L Ni(NH2SO3)2 · 4H2O (air agitation) 0.56 mol/L CuSO4 · 5H2O + 1.4 mol/L
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