EFFECT OF THIOUREA ON ELECTRODEPOSITION OF COPPER FROM ACID SULFATE SOLUTION

摘要

Copper was electrodeposited from sulfate bath onto copper substrate over silicon wafer with titanium adhesive film and the resistivity was measured using four point probe method. The measured resistivities increased with an increase in thiourea concentration from 10~(-6)M to 10~(-3)M as well as with an increase in the current density from 1 mA/cm~2 to 50 mA/cm~2. The deposition potentials shifted to more negative values with an increase in thiourea concentration and cathodic overpolarization was observed in presence of thiourea, indicating chemisorption of thiourea on cathodic sites. Scanning electron micrographs (SEM) 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 occurrence of the reaction H_2NCSNH_2 + 2H~+ + 2e→ NH_4CN + H_2S at electrolyte-electrode interface. This reaction can further lead to ultimate incorporation of sulfur based species in the deposit and resulting increase in resistivity of electrodeposited copper.