Dissertation Proposal Defense – Timothy Huang
Prof. Rao Tummala, Advisor, MSE
Dr. Venky Sundaram, ECE
Prof. Dong Qin, MSE
Prof. Preet Singh, MSE
"Studies of Interfacial Adhesion and Copper Plating Chemistry for Metallization of Through-Package-Vias in Glass Interposers"
Driven by increasing demands for higher logic-memory bandwidth in high-performance applications, next-generation 2.5-D and 3-D system packages require fine-pitch copper through-package-vias (TPVs) to support fine-pitch fan-out and fine-pitch bumps. Glass is an excellent substrate material for low electrical loss and high-performance package architectures owing to its superior material properties. Glass has better mechanical properties as compared to organic composites, in addition to superior electrical properties and lower material cost compared to silicon. Current glass interposer metallization technologies lack panel scalability, fine pitch processing, and low cost. Therefore, it is crucial for the glass substrate technology to develop low-cost methodologies that can achieve high-quality Cu metallization in fine pitch vias. State of the art technologies are able to metallize ultra-thin glass (≤ 100 µm) with fine-pitch (≤ 120 µm), small-diameter (≤ 60 µm) TPVs but pose several challenges in terms of throughout, reliability, and cost. The objectives of this research are to investigate three key aspects of Cu metallization on glass interposer substrates, namely 1) understanding adhesion mechanisms of Cu to glass and developing novel seed-layer deposition methods to promote Cu adhesion to glass with TPVs, 2) investigating the role of organic additives in electrolytic Cu plating baths, and 3) the demonstration of Cu-filled glass vias in ultrathin glass interposers.
For the first objective, several methods for depositing a Cu seed layer on glass were tested for adhesive performance, and interfacial failure mechanisms were proposed. Based on these results, a novel process enabling via-first electroless Cu metallization on glass was developed. The second objective utilizes a mixed characterization approach to develop a fundamental understanding of how the molecular structure of organic additives influences the electrochemical plating behavior. Electroanalytical (cyclic voltammetry, potentiometry), in-situ chemical (surface enhanced Raman scattering), and structural (cross sectioning, atomic force microscopy) characterization techniques are employed to investigate the interactions between organic additives and the Cu electrode. Finally, the results of the first two objectives will be utilized to carry out void-free, fully-filled Cu plating in glass TPVs.