Surface modification of polytetrafluoroethylene (PTFE) with Vacuum UV radiation from helium microwave plasma to enhance the adhesion of sputtered copper

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Liao, Xiaolu
thesis / dissertation description
Teflon® materials are well known for excellent thermal and chemical resistance properties. Their low dielectric constant makes them good materials for substrates in electronic packaging of microsystems where copper is often used as the conductor. Good adhesion between Cu and the hydrophobic PTFE is required in the microelectronics industry. A low-pressure helium MW plasma was used to modify the surface of PTFE located downstream from the plasma. Sometimes, oxygen was flowed over the surface of PTFE. Negligible photo-etching (≤ 1nm/min) was observed. The contact angle of treated PTFE film was found to decrease from an average value of 104° for untreated material to an average of about 86° and showed improved wettability with treatment time. Without modification, the adhesion of copper to PTFE was very weak. Significant improvement in adhesion occurs when PTFE is modified with VUV radiation downstream from a helium MW plasma with O2 flowing over the surface. SEM results show the modified PTFE has a rougher surface than untreated samples which provide more anchor sites to copper. XPS analysis shows defluorination and formation of oxygen-containing structures on the surface of the modified PTFE that contributes to the improved hydrophilic nature of the surface and stronger chemical bonding between copper and the modified PTFE. ® Trademark of E.I. Dupont De Nemours & Co., Wilmington, DE.