Photoresist characterization and wet strip after low-k dry etch

Abstract

In new semiconductor technology generations, with BEOL feature sizes shrinking to 65nm and below, the amount of damage induced by plama etch and ash processes to porous low-k materials is becoming an issue. The k-value degradation from densification and chemical modification of the low-k is generally unacceptable, while the removal of the damaged layer may affect critical dimension(CD)control to be severely taken into account in the design. Consequently, all-wet processes are gaining renewed interest for the removal of post-etch photoresist(PR). However, specifications on material loss and k-value integrity considerably reduce the operating space for a purely wet-chemical clean. The composition of post-etch PR is strongly dependent on integration scheme, etch plasma chemistry and materials used. PR composition in turn determines its cleanability. Hence, the identification of a chemical solution that is capable of removing modified PR layers greatly benefits from a thorough chemical characterization of these layers. In the present work, PR layers are characterized by spectroscopic techniques commonly used for semiconductor/wafer analysis, as well as by polymer science characterization techiques less frequently employed in silicon technology development. Cleans based on dissolution by solvents and physical forces(megasonic) are evaluated that comply with requirements on materials loss.