Electrodeposition of Cu–Al[sub 2]O[sub 3] Thin Films and Microposts in Ammonia-Citrate Electrolytes

Abstract

The electrodeposition of Cu-␥-Al 2 O 3 nanocomposites as thin films and into recessed electrodes prepared with X-ray lithography was examined in ammonia-citrate electrolytes. Partial current density, current efficiency and deposit particle concentration were determined with a rotating disk electrode. At pH 8 the presence of particles resulted in an enhancement of the Cu reaction rate, while at pH 10 the reaction rate appeared inhibited. The amount of particles in the deposit and current efficiency was larger for pH 8 than pH 10, rendering the pH 8 solution a more promising electrolyte to electrodeposit 500 m deep recesses for MEMS composite components.Metal matrix nanocomposites consist of two phases where at least one phase is restricted to the nanoregime. Copper-alumina can be fabricated by chemical routes 1,2 powder metallurgy, 3-8 thermochemical processing 9 and electrodeposition. 10-17 Their interest lies in the enhancement of mechanical properties compared to the parent metal, 8,12 and for their thermal and mechanical stability at elevated temperatures. 18 Applications include its use in electronic packaging, and as materials for electrodes and contact terminals, such as highperformance electrodes for industrial spot welding. 19 The advantage of the electrodeposition fabrication method over others is in depositing material into deep recessed microstructures for microelectromechanical system ͑MEMS͒ components. There are only a few studies of composite deposition into deep recesses. Jakob et al. 20 have codeposited nanometric TiO 2 and Al 2 O 3 along with nickel into microstructures. Yeh et al. 21 demonstrated the electrodeposition of submicron SiC-Ni into lithographic recessed electrodes. Wang 22 and Goods 23 reported conditions for Ni-Al 2 O 3 composites into deep recesses prepared by X-ray lithography. Panda and Podlaha 24 reported NiCu-␥-Al 2 O 3 micropost arrays electrodeposited from a pH 8 ammonia-citrate electrolyte. In this paper, we present the operating conditions to electrodeposit Cu-␥-Al 2 O 3 into deep recessed geometries.It is advantageous to understand how the particles affect the metal deposition rate and current efficiency in order to judiciously select electrodeposition conditions to deposit metal matrix composites into recessed structures. Low current efficiency, with associated gas evolution and local pH changes, can be detrimental to depositing into micro-patterned, recessed substrates due to the blockage of the electrode surface by gas bubbles or unwanted solid products. The decrease of the copper reduction partial current density due to the presence of alumina particles has been observed by Stojak et al. 14 in sulfuric acid electrolytes, and Podlaha and Landolt 15 in an acidic citrate electrolyte. Lozano-Morales and Podlaha 17 identified regions of copper inhibition and enhancement in the kinetic regime, in sulfuric acid electrolytes. Fawzy et al. 11 studied the effect of ␣-Al 2 O 3 and TiO 2 particles on copper electrodeposition from acidic baths. Both, inhibition and enhancement were ...

Electrodeposition of NiCu-matrix nanocomposites using a rotating cylinder Hull cell

“…The depolarizing affect was greater the smaller the particle size. Lozano-Morales et al [9,25] also reported a similar enhancement in the Cu kinetic reduction rate with nanometer size alumina particles. Panda and Podlaha [10] studied the NiCu-c-Al 2 O 3 system for use in fabricating micro-patterned structures.…”

“…Combining them, fabricating metal composites composed of an alloy matrix, can provide additional flexibility in tailoring the deposit properties. Some examples of electrodeposited composites containing an alloy matrix include a-Al 2 O 3 particles with a Cr-Ni alloy [7], a-Al 2 O 3 , and TiO 2 in NiCu [8] and our prior work with c-Al 2 O 3 in NiCu alloys [9,10]. The interest in NiCu alloy materials are well known for their corrosion resistance [2,[11][12][13][14][15], thermoelectrical [16,17], catalytic [18][19][20], and mechanical [8,21,22] properties.…”

Material Microsurgery: Selective Synthesis of Materials via High-Temperature Chemistry for Microrecycling of Electronic Waste

“…However, the superior corrosion resistance of Cu could be beneficial for surface engineering. It is established that the poor mechanical properties of Cu could be tailored and enhanced by reinforcing with nanoceramics, for example, SiC, SiO 2 , Si 3 N 4 , CeO 2 , Y 2 O 3 , CNT, and Al 2 O 3 particles. − A ceramic-reinforced Cu surface coating created through selective synthesis from e-waste could increase the corrosion and wear resistance of the metal substrate. This method could be a suitable alternative to conventional surface coatings and reduce the burden on raw-material feedstocks.…”

Optimization on hardness and internal stress of micro-electroformed NiCo/nano-Al2O3composites with the constraint of low surface roughness

“…The amount of particles in the deposit and current efficiency was larger for pH 8 than pH 10, making the pH 8 solution a more promising electrolyte to electroplate into 500 μm deep recesses for MEMS composite components. Highaspect-ratio microstructures of electrodeposited copper-γ -Al 2 O 3 nanocomposites were successfully performed into deep recesses with uniform concentration of alumina along the length of the microposts [23]. Vidrine et al [24] indicated that particle deposit concentration decreased with applied current density for the chloride baths but increased for the citrate bath.…”

“…2 O 3 content (factor A) and Co content (factor C)[23]. The internal stress in deposit also increases with increasing Al 2 O 3 particle diameter (factor B) and current density (factor E).…”