Reliability Aspects and Study of Copper Seed Deposition on Polyimide via Sputtering

Flexible substrates are being sought after as an alternative to meet the demand of the integrated circuit industry. Polyimide (PI) is a promising option due to its excellent mechanical and electrical properties. This study uses PI as a substrate to test different copper (Cu) seed deposition processes via sputtering. Results showed that deposition time, pressure, and power have the greatest impact on film thickness and sheet resistance. Reliability was evaluated through peel tape tests after deposition, temperature cycling, and highly-accelerated stress testing (HAST). Most failures occurred in non-plasma treated samples, and there was a 17% increase in failure after temperature cycling. Film detachments were observed in all experiments after HAST, which may be attributed to moisture between PI and Ti/Cu caused by their different thermal expansion coefficients.