Development of an Edge Bead Remover (EBR) for thick films

摘要

During the development of AZ~(~R) EXP PLP~(TM) 100XT thick film resist, the need for an effective Edge Bead Remover (EBR) was demonstrated for coatings of 50 microns. Because of the use of high solids content resist, a large amount of resist solvent was retained in the thick film coating as it was cast. Residual solvent can also come from diffusion of the EBR solvent into the spreading resist. The residual solvent can significantly affect the EBR process and cause secondary flow problems such as rough edges stringers and reflow. Current EBRs such as AZ~(~R) EBR 70/30, which is excellent for removing thin film residues, were not effective for use with resist coatings of 50 microns because of secondary flow issues. A number of solvents either alone or in pairs were evaluated. From the sole solvent studies no strong correlation was seen between physical properties and EBR performance. However a weak correlation was seen between EBR performance and volatility. The EBR performance was further optimized by increasing its volatility. The optimized solvent system consists of a mixture of dimethyl carbonate (DMC) and cyclopentanone (CP). The dimethyl carbonate/cyclopentanone solvent system is significantly more volatile than the conventional EBRs such as AZ~(~R) EBR 70/30. The cyclopentanone insures good edge cleaning. This system demonstrated good performance characteristics such as no secondary flow, sharp resist edge and a clean wafer edge. The safety issues of toxicity and flash point will also be discussed.