Efficient TSV Resist and Residue Removal in 3DIC

The continuing challenge to meet the need for lighter, smaller, faster and smarter electronic systems has pushed the advancement of 2.5D and 3D technology. The ability to create and integrate through-silicon vias (TSV) into device designs in 2.5- and 3-D platforms allows a decrease in interconnection path length, which results in improved device performance and reliability in a small form factor. Mainly due to its high silicon etch rate and selectivity to mask materials, the Bosch process is often used in the TSV fabrication. In this process, the silicon via is created by the deep reactive ion etching (DRIE). DRIE is comprised of repeating a combination of steps: an etch step and a passivation step. The passivation created in the DRIE process results in a fluoropolymer residue remaining on the wafer at the end of the process. The residue must be removed to enable deposition of a defect-free barrier, which enables a defect-free seed layer and void-free plating into the via. There are numerous technical papers and presentations on the etching and filling of these vias but the process for cleaning remains under addressed. Initially, standard processes used after RIE and consisting of an ashing process to remove any remaining photoresist, followed by immersion in a solution-based post etch residue remover were adopted for post-TSV cleans. However, the fluoropolymer does not have the same chemical characteristics as typical post-RIE etch residues and the major challenge has been the difficulty to completely remove it, especially on the via sidewall, using traditional post etches residue removers. Therefore, new formulated cleaning solutions and processes are actively sought for the removal of post etch residue for TSVs. This paper will describe a robust cleaning process for one step removal of both the photoresist and sidewall polymer residues from TSVs. A combination soak and high pressure spray process using a proprietary environmentally friendly chemistry, coupled with a megasonic final rinse provides a unique solution for both polymer residue and photoresist removals on high aspect ratio vias. SEM, EDX and Auger analysis will illustrate the cleanliness levels achieved.