Abstract
ABSTRACTWe 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 CF4 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 CF4. 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.
Highlights
According to miniaturization, speed acceleration and mass storage in semiconductor, manufacturing process to form chip on wafer and packaging process to install the completed chip on circuit is continuously being developed (Mönch et al, 2011; Nakamura et al, 2013; Joyce et al, 2015)
We investigated the cause of defects on aluminium pad which often occurs in packaging process
After pad open etching using common CF4, wafers are stored in Front opening unified pod (FOUP) and fluoride ions which is one of chemicals used in etching adsorbed onto wafer diffused into FOUP at 230 ng L–1
Summary
According to miniaturization, speed acceleration and mass storage in semiconductor, manufacturing process to form chip on wafer and packaging process to install the completed chip on circuit is continuously being developed (Mönch et al, 2011; Nakamura et al, 2013; Joyce et al, 2015). There is not a single part unimportant in packaging process, but interconnecting technology connecting chip and package which enables to interact electrically and structurally is considered as most the important Among these techniques, the wire bonding technology is a technique which connects aluminium pad of chip with lead frame of package by gold wire and is already a very commonly used technology. The aluminium pad of chip for wire bonding is a part that is exposed to the outside after wafer process, which can be continuously affected by the surrounding atmosphere until it is insulated from packaging. It can be contaminated by molecular contamination due to silicon
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