Direct Au and Cu wire bonding on Cu/low-k BEOL

The purpose of this work is to develop a technique which allows for direct Cu and Au wire bonding on Cu/low-k BEOL Si chips. In order to accomplish bond pad cleanliness and minimum oxidation, a thin organic self assembled monolayer (SAM) has been used, which protects the metal surface. A number of organic compounds have been evaluated and the process of application onto Si wafers optimized. The processing of the organic layers is performed at wafer level, before dicing the individual chips, providing protection up to the wire bonding process. Patterned Cu features on oxide have been tested, achieving a close to 100% bond stick rate. Further work is being performed on optimization of the SAM coating process on 8" Si wafers and reliability of the bonds and the coating itself. Direct bonding of Cu and Au wire onto Cu bond pads has been achieved. Preliminary results on various organic coatings for Cu pad protection show promising application of this technology. Moreover, the further broadening of these results to full Cu/low-k BEOL Si devices has been demonstrated. Ease of manufacturability of the process and reliability of the results, could lead to a trouble-free scaling of this technology into industrial dimension.