Stripping polymers in semiconductor FAB processes: Impact of rheology and substrate-polymer interactions

A typical process to create a simple electronic chip consists of 400-500 steps, with more than 1000 steps being required for the latest chip at IMEC. Here around 10% of the steps involve polymer coating and stripping in various forms. Polymers are used for making lithographic patterns, as protective layers to prevent particle accumulation on active surfaces, as temporary bonding materials during various operations like die transfer from one wafer to another, for wafer grinding etc. Once the polymers have done their job, they need to be removed without leaving even trace residues as this will impede the subsequent processes, thus leading to reduced yield of successful chips, which increases production costs.  The fundamental mechanisms governing the stripping or cleaning of polymers remain poorly understood. Especially the impact of upstream processing undergone by the polymer is largely unknown, hindering progress in this field. With this PhD work we would like to tackle some of the big challenges associated with polymer stripping.

Research Objectives:

• Investigate the relations between polymer network structure and their ease of cleaning, by considering rheological behavior, swelling and dissolution in a solvent environment.
• Investigate how substrate-polymer interactions affect the ease of cleaning, considering both chemical and physical bonding.
• Investigate the impact of upstream processes such as temperature, exposure to chemical etchants and rinsing fluids, on polymer cleaning, both for bulk stripping and for residue removal on a substrate.