Vs. Donepudi et al., Electrodeposition of copper from sulfate electrolytes - Effects of thiourea on resistivity and electrodeposition mechanism of copper, EL SOLID ST, 4(2), 2001, pp. C13-C16
Copper was electrodeposited from sulfate bath onto copper substrate over si
licon wafer with titanium adhesive film and the resistivity was measured us
ing a four-point probe method. The measured resistivities increased as thio
urea concentration increased from 10(-6) to 10(-3) M and as the current den
sity was increased from 1 to 50 mA/cm(2). The deposition potentials shifted
to more negative values with an increase in thiourea concentration and cat
hodic overpolarization was observed in presence of thiourea, thereby sugges
ting chemisorption of thiourea on cathodic sites. Scanning electron microgr
aphs show the presence of sulfur in the deposit when thiourea is present in
the solution. The presence of thiourea in the deposit is suggestive of the
reaction H2NCSNH2 + 2H(+) + 2e(-) --> NH4CN + H2S at electrolyte-electrode
interfaces. This reaction can further lead to deleterious formation of cop
per sulfide in the deposit and a consequent increase in resistivity of elec
trodeposited copper. (C) 2001 The Electrochemical Society.