Laser-Enhanced Gas Phase Surface Modifications of Teflon AF1600 for Increased Copper Adhesion

Abstract

Multilevel interconnect devices, made of alternating layers of a low permittivity polymer (e.g., Teflon AF1600^TM) and a low resistivity metal (e.g., copper), are increasingly being used in microelectronics in order to decrease the RC signal transmission time delay. The mechanical stability of the multilevel interconnects is related to the adhesion developed at the metal-dielectric interface. Since Cu/Teflon AF1600 adhesion is moderate and may not satisfy the requirements of the microelectronics industry, new treatments of the fluoropolymer surface are needed to improve it. In this note, we present several surface modifications, such as the formation of reactive sites during intense X-ray exposure, and S- or N-grafting, activated by UV radiation in the presence of H₂S and NH₃; copper is well known to react with both thiols (R—SH) and amines (R—NH₂) to form strong bonds. Both X-ray exposure and N-grafting lead to enhanced adhesion.

Key Words:

• Adhesion
• copper
• fluoropolymer
• excimer laser
• X-ray damage