On Chemical Cleaning for Thermocompression Bonding

The removal of a Cr
²
0
³
contaminant oxide film from gold surfaces by a ceric ammonium nitrate (CAN} etch and two different potassium iodide plus iodine (KI + I
2
) etchants was investigated using Auger electron spectroscopy and thermocompression (TC) bonding. It was shown that CAN effectively attacked and removed the Cr
2
0
3
while the KI + I
2
attacked the underlying gold film. The KI + I
2
improved the TC bondability both by undercutting some of the Cr
2
0
3
and by roughening the gold, thereby allowing more deformation to occur,during bonding. The implications of these results on selection of a chemical cleaning agent are discussed. The ability of CAN to dissolve a chromium adhesion layer under the gold metallization has also been investigated. It was shown that a heat treatment of 300°C for two hours in air prevented this undercutting; possible reasons are discussed.