High-performance 3D ceramic interposers with aluminum nitride using green chemistry approach for microelectronic applications

Abstract

Thermal management of electronic devices related to heat removal has been a continual challenge since it affects the performance and long term reliability of electronic systems. This heat removal issue is especially crucial for high-performance electronic devices such as 3D Integrated Circuits and all electronic modules where heat dissipating rate is critical under air cooling. A 3D interposer consists of (i) a substrate with (ii) embedded interconnecting metals to form the functional circuitry. (i) Organic substrate is commonly used but its poor heat dissipation has limited its use in high-performance electronics. As such, organic substrates are commonly replaced with higher thermal conductivity aluminum oxide (Al₂O₃) ceramic substrates. However, for advanced applications that require a higher heat dissipation performance, aluminum nitride (AlN) is a possible choice to replace Al₂O₃ due to its higher thermal conductivity by nature. (ii) The common interconnecting metals for 3D interposer are copper but it might not be suitable for ceramic interposer due to its low melting temperature. Molybdenum (Mo) is a refractory metal that can withstand high-temperature and therefore is a good candidate for co-sintering with AlN ceramic to form the 3D ceramic interposer. Besides, the current process of producing 3D ceramic interposers involves multiple steps that require extensive use of solvents, which is costly and not environmental-friendly. Therefore, a simpler and greener processing technology is much needed, and additive manufacturing could be developed to replace the current process technology. The aim of this work is to develop a high-performance 3D ceramic interposer with AlN ceramic substrates and Mo interconnecting metal for microelectronic applications using additive manufacturing, an alternative processing technology based on green chemistry approach. First part of this research work focused on the green chemistry approach using eco-friendly material to form AlN ceramic substrate. A sustainable natural protein, ovalbumin is used to produce high thermal conductivity AlN ceramic substrates. AlN substrate with bimodal particle size distribution (1:1 mixture of 0.5 μm and 1 μm AlN) was found to produce its highest thermal conductivity value of 21 W/mK after sintering for 6 hours at 1600℃, compared to a thermal conductivity of 0.2 W/mK for the organic substrate. In the second part, Mo metal was developed using the same gelcasting process like AlN ceramics with ovalbumin as the gelcasting monomer. The sintering of the Mo gelcast for 6 hours at 1600℃ produces Mo metal with an electrical resistivity of 4.1 x 10⁻⁴ Ωcm, slightly lower than copper plate (3.3 x10⁻⁴ Ωcm) but is sufficient for most of the applications. The XRD result shows only the presence of pure Mo metal phase and the oxide phases are not seen. This result shows that treating Mo powder with stearic acid forms a protective layer that allows gelcasting of Mo using aqueous-based monomer, ovalbumin. The final part of this research adapted an additive manufacturing approach, called direct gelcast 3D printing, to print multi-materials by design that forms the green body of 3D interposer from the CAD system directly. It was confirmed that multi-material that consists of AlN ceramic and Mo metal can be printed concurrently and co-sintered at 1600℃ to produce high-performance functional 3D ceramic interposer. The product can power up a light emitting diode (LED), demonstrating the functionality of 3D ceramic interposer. Overall, this research work has successfully developed an eco-friendly process technology by incorporating 3D printing to produce multi-materials including ceramics, metal or a mixture thereof, directly from the CAD system. The overall result also shows the use of a natural protein with minimum waste as the core processing component. The technology is versatile, allowing combinations of compatible materials to be co-produced, be recycled, and enables in-situ production of multi-materials using a simple process.