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We analyzed defective bonding pad in various ways and determined the causes of defects that boosts oxidation of aluminium by fluoride residue on surface of pad with moisture. Additionally, we compared and evaluated methods to minimize pad defects in aspects such as etching and wafer storage environment. In case of wafers after pad open etching process using common CF 4 stored in FOUP, the concentration of fluoride ions in FOUP was 230 ng L -1 and it decreased down to 170 ng L -1 when Ar sputtering step was added after using CF 4 . Also under the same condition, fluoride ion concentration in FOUP decreased down to 20 ng L -1 when nitrogen purge was introduced for 10 minutes to the FOUP where wafers were stored and the moisture also decreased from 40% before purge to 10% after purge. As a result of observation on pad surface after storing wafers in FOUP for 120 hours under each condition, negligible amount of defects were found when nitrogen was purged. Therefore, we conclude that defects on pad were generated by existing fluoride ions after etching process and moisture in the air.

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Through Silicon Via (TSV) Package (PKG) technology that forms a 3D stack with chip to chip or wafer to wafer contact, uses a variety of wet chemicals unlike conventional package technology. Therefore, new kinds of defects related to the wet chemical occur. In this a new failure mode of disappeared Al pad will be presented, a problem came up to disappear Al pad, which served as the fiducial key during the metal residue removal process after forming the TSV PKG front bump, the mechanism of disappearance of Al pad was investigated. Through chemical analysis of process and equipment, we found that Cu etchant (including H3PO4) can damage for Al pad. The process simulation demonstrated that Al pad actually disappeared. Therefore, it confirmed that it needs to be removed through sufficient rinsing time after applying the wet chemical applied to the TSV PKG process. As a result we solved problem through modified equipment and increased rinsing time.

No abstract