Curing of polyimide and the effect of the TEOS SiO2 barrier layer on the electromigration of sputtered Cu with polyimide passivation

Journal of Electronic Materials, Jan 2002 by Hung, HAnyi, Chiou, Bi-Shiou

The curing process of polyimide and the electromigration of copper films with polyimide (PI) passivation are studied. Thermal analysis of polyimide suggests that imidization completes at -200degC with an endothermic reaction associated with the breaking of the C-OH and N-H bonds as revealed by Fourier transformation infrared spectroscopy (FTIR). Although there is 89.8% weight loss when PI is heated from 20degC to 200degC, outgassing of PI passivation is still observed at higher temperatures. Carbon, nitrogen, and oxygen atoms diffuse into Cu during thermal processing of PI/Cu films. The tetraethyl orthosilicate (TEOS) SiO2 films are used as the barrier layer between PI and Cu to retard the poisoning of Cu. The effect of TEOS SiO2 film on electromigration of Cu is investigated. Keywords: Polyimide, electromigration, curing process, imidization

INTRODUCTION

Copper has been considered as a substitute for Alalloy metallization for future generations of on-chip interconnections, due to its high electromigration endurance and low resistivity. Electromigration (EM) of metal interconnects is a primary mechanism that causes interconnects to fail.1,2 As devices scale down, given present-day device layouts and ground rules, the majority of resistance-capacitance (RC) delay is due to capacitive loading. Therefore, the use of low dielectric constant polymers in conjunction with a high conductivity interconnect metal offers significant performance gains.3

Polyimide (PI) is one type of long-chain macromolecule with a repeating monomer and a feature of cross-link between monomer chains, which provides high rigidity. Polyimide films are one of the most attractive interlayer dielectrics because of their good surface planarization characteristics, low residual stress, and low dielectric constant.' However, interdiffusion was observed between the copper and polyimide interface after annealing of the Cu film.5 The diffused copper formed clusters inside the polyimide, which raised both the dielectric constant and the dissipation factor of the polyimide and, consequently, degraded the properties of the polyimide. The impurities C and N diffused from the polyimide into the Cu films cause resistance changes in the Cu metallization.7

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HA.NYI HUNG and BI-SHIOU CHIOU

Department of Electronics Engineering and Institute of Electronics, National Chiao Tung University, Hain&14 Taiwan/ aI

(Received December 20, 2000; accepted August 28, 2001)