Effect of composition of post etch residues (PER) on their removal in choline chloride–malonic acid deep eutectic solvent (DES) system

In back end of line (BEOL) processing of copper/dielectric stacks, the composition of the post etch residues (PER) affects their removal by wet chemical formulations. For the removal of PER composed mainly of copper oxides and fluorides, deep eutectic solvent (DES) systems composed of choline chloride (CC) and urea (U) or choline chloride (CC) and malonic acid (MA) have been shown to be very effective. This paper will discuss the applicability of CC/MA system with and without the addition of glacial acetic acid (HAc) for the removal of residues that exhibit both inorganic and organic character. Different types of residues were created by CF4/O2 plasma etching of deep UV (DUV) photoresist (PR) films on Cu. By varying the time of etching, post-etch residues of varying inorganic and organic composition were generated and characterized using XPS. The effectiveness of CC/MA and HAc/CC/MA systems in removing the prepared post etch residues was characterized by SEM, XPS and single frequency impedance measurements. The results indicate that HAc/CC/MA system is very effective in removing different types of residues.

Figure optionsDownload as PowerPoint slideHighlights
► Formation of post etch residue models by varying the dry etching time of DUV photoresist spin coated on Cu wafers.
► Chemical and morphological characterization of post etch residues (PER).
► Test novel wet cleaning formulation based on choline chloride–malonic acid deep eutectic solvent (CC/MA DES) to remove PER.
► Addition of HAc to the wet cleaning formulation based on CC/MA DES to enhance removal of organic PER.
► Report PER removal rates and propose possible PER removal mechanisms in CC/MA and HAc/CC/MA formulations.