Fabrication of 3D-IC interposers

Over the past several years, the semiconductor industry has seen some tremendous developments in using glass as an interposer substrate. Glass has many properties that make it an ideal substrate for interposer substrates such as: ultra-high resistivity, low dielectric constant, ultra-low electrical loss and adjustable coefficient of thermal expansion (CTE) that allows management of 3D-IC stacks. Regardless of technical performance, any glass based solution must also provide significant cost advantages in substrate material, via formation, and subsequent processing. Cost-Effective Solutions In this paper, we will cover how fusion formed glass provides cost-effective solutions for the manufacturing of interposer materials for as-formed 100 μm precision substrate with a pristine surface, without the need for polishing, thus eliminating the manufacturing steps for polishing and thinning. Design Considerations For effective implementation of glass substrates, processing costs for through-glass-vias (TGV) on ultra-thin glass is also a challenge. This paper will reference data from several different designs to demonstrate the impact of design on Corning´s TGV process cost relative to silicon solutions. It will also highlight processing lessons learned in fabricating TGV interposers from bare glass into complete packaged test vehicles and their impact on cost. Via Capabilities Furthermore, glasses via formation capabilities have dramatically improved over the past several months. Fully populated wafers with >100,000 through and blind holes (25 μm diameter) are fabricated today with 20μm diameters. We report on the significant enhancements demonstrated on important quality parameters. We will also report on strength parameters measured on TGV wafers and positive implications with respect to product reliability.