In Situ vs. Ex Situ Indentation for Adhesion Evaluation of Nitride/Polymer Interfaces: A Comparative Study Under Controlled Ambient Conditions

Polybenzoxazole (PBO) and silicon nitride (SiN) are widely used in the semiconductor industry as protective layers in a vast group of products, acting respectively as a polymeric physical barrier for humidity and a mechanical passivation layer. This work investigates the reciprocal adhesion of these two materials with a focus on the combined effects of surface chemistry and environmental conditions, i.e. temperature and relative humidity. A set of six samples, including standard and silicon-rich SiN substrates treated with oxygen (O2) or carbon tetrafluoride (CF4) plasma, was fabricated and characterized by AFM, XPS, and TEM/EDX to quantify surface roughness and interfacial chemical modifications. Adhesion with PBO was then assessed through nanoindentation both in-situ, during ambient control, and ex-situ, after aging in a climatic chamber. O2 plasma treatment was shown to significantly improve adhesion by forming a surface oxide layer that enhances chemical affinity, whereas CF4 plasma effects were limited. Notably, the adhesion loss with increasing severity of the ambient in terms of temperature and relative humidity was observed across all samples regardless of surface treatment, reinforcing the critical role of absorbed moisture on polymeric film adhesion. However, this trend was mainly visible for in-situ testing, while ex-situ tests showed a marked recovery of adhesion properties, leading to measurements no longer reflecting the actual state of the samples inside the altered environment. The results presented in this paper highlight a substantial difference in environmental control methods and may provide an alternative approach to classical aging treatments and subsequent characterization for qualifying polymer/inorganic interfaces exposed to stressful operational conditions.