Reliability Study of Reference Semiconductor Encapsulation Materials for Biocompatible Packaging

摘要

Material selection is the key issue when developing a biocompatible packaging process for implantable electronic systems. To secure a reliable performance of the chip in such a package, its encapsulation has to be considered upfront in the wafer-level integration scheme. A differentiation of two main material types can be made: 1) Insulating or passive materials functioning as a bi-directional diffusion barrier preventing body fluids leaking into the package causing systems malfunction due to possible materials corrosion and also avoiding a leakage of built-in materials to the in-vivo environment and 2) Conductive or active materials as diffusion barriers, e.g. against copper diffusion or as direct external contacts responsible for electrical performance of the system. This study investigates the properties of two widely used insulating materials in the semiconductor industry, the nitride and the oxide. Both material types are deposited in a PECVD system using different temperatures; 400°C for CMOS compatibility and 200°C for wafer back side process integration when a temporary carrier system is used. The biocompatibility investigations of these materials (evaluated using cell lines and primary cells) show promising results. However, for the long term application, the stability results for the oxide layers show hydration effects resulting in material degradation where the nitride layers clearly show corrosion and are even etched when elevated temperatures are applied. This fact is surprising since nitride layers are widely used as a humidity barrier for various chip types but obviously not suitable for a direct contact with liquids. Various analysis methods using e.g. Fourier Transformed IR Spectroscopy or mass measurements substantiate this thesis.