Metal Contamination Removal on Silicon Wafers using Dilute Acidic Solutions

Abstract

Several acids as very dilute (1:100‐1:106) water solutions were tested to remove metallic contaminants on silicon wafers. Total reflection x‐ray fluorescence (TXRF), deep‐level transient spectroscopy (DLTS), and minority carrier recombination lifetime measurements were used to evaluate the removal efficiencies. The resulting surface concentrations for iron were well below the 1010 at/cm2 level for most solutions. The particle levels were low, comparable to an SC‐1 clean. The solutions behaved in a different way compared to the other tested acids, , , and , leaving a higher concentration of iron on the wafers, but a considerably lower surface recombination rate of the minority carriers in oxidized wafers. The minority carrier bulk lifetimes were in excess of 100 μs for the oxidized acid cleaned wafers, except to the cleans. Iron was found to be the dominant lifetime shortening contamination for concentrations larger than 1011 at/cm3.