Moisture-induced interfacial oxidation of chromium on polyimide

Abstract

Interfacial strength of Cr/polyimide thin film structures and its durability to thermal exposure as a function of process variables was determined by 90° peel testing. Results were correlated with surface and interfacial characterization of thin film structures and peel failure surfaces using Auger, x-ray photoelectron spectroscopy, and secondary ion mass spectroscopy techniques. Initial adhesion in as-deposited Cr/polyimide structures exhibits a mild dependence on radio-frequency Ar plasma surface modifications and deposition process conditions. However, the durability of these structures under thermal process cycles depends strongly on these process parameters, greater doses of energetic ion bombardment were seen to yield greater durability. Characterization of peel failure surfaces revealed that fracture in the as-deposited and peeled samples occurs cohesively in the near surface region within the polyimide. Cohesive fracture was also seen in some samples after thermal process exposures, with peel strengths that were acceptable but somewhat less than the corresponding unannealed samples. Failure at an oxidized Cr to polyimide interface was observed in other thermally annealed samples whose peel strengths were very low. It is proposed that both types of degradation are caused by the water absorbed in the polyimide. The slight adhesion degradation appears to be due to water reaction and hydrothermal weakening of the modified near surface polymer region during thermal processing. The more catastrophic degradation is due to the oxidation of the Cr by the absorbed water during the anneal cycles. Results of critical experiments that verify these hypotheses are presented.

Effects of Mechanical Properties of Metal Films on The Adhesion Strength of Cr/Polyimide Interfaces

“…TEM microscopy showed no evidence of grain growth of the electroplated Cu films during annealing process. Even annealed in N2 atmosphere, it has been reported that interfacial fracture energy of Cr/PI was reduced due to the formation of Cr oxide at the Cr/PI interface and thermal expansion mismatch between polyimide and metal films [16][17][18]. Comparing to specimens which were not annealed, both interfacial fracture energy and mechanical properties of Cu/Cr films were changed with first annealing process.…”

Ductility of copper films on sandblasting polyimide substrates

“…The aforementioned methods, however, have limitations. For example, ion bombardment may thermally degrade the substrate [24], while the Cr interlayer is prone to oxidization [24,25], both leading to reduced interfacial adhesion and ductility of the film/substrate system. It is therefore important to explore new techniques for enhanced interfacial adhesion and ductility of polymer-supported metal films.…”

Adhesion mechanisms in the solid‐state bonding technique using submicrometer aromatic thermosetting copolyester adhesive

“…1 Because polyimides are the most extensively used polymer in microelectronic industries, numerous studies have been conducted to solve polyimides' adhesion problems. Approaches to improve polyimides' adhesion include adding flexible structure into the polyimide backbone, 2 wet chemistry treating the surface of polyimide to reform polyamic acid, 3 partial curing 4 or solvent swelling the polyimide, 5 plasma activating the surface, 6 using Cr as adhesion promoter, 7 and applying adhesive, 8 etc. Most approaches were developed to solve specific interface problems involved with the sequential processing of polyimides.…”