Improvement of Plated Copper Adhesion in Glass Interposer Applications

Abstract

Glass interposers offer a compelling alternative to silicon interposers with highest I/Os and excellent electrical performance, with potential for low cost from large panel processing. For sub-32nm IC nodes and 3D-IC packages at fine I/O pitch, organic substrates are reaching their limits in terms of I/Os, design rules and CTE mismatch. Glass offers the best combination of electrical insulation, dimensional stability, CTE match to Si ICs, and flat, smooth surfaces for ultra-fine line lithography. The biggest challenge in glass interposers is the formation and metallization of ultra-fine pitch through vias. The formation of small via diameters in thin glass substrate have been demonstrated. The focus of this paper will be on wet metallization of glass interposer with through via, and addressing the challenge of providing reliable adhesion on the copper-to-glass interface. Two main approaches are currently pursued in the wet-chemical metallization of glass interposers: the electroless and electrolytic copper deposition on a) bare glass with photo-structured or laser-ablated through vias and b) the deposition on an intermediate polymer surface layer, requiring glass metallization only on the via sidewalls. Therefore, in addition to the analysis and optimization of adhesion-improving techniques on different glass types, their performance on different polymer liners is also assessed. The techniques include surface conditioning with cationic polyectrolytes and deposition of silica. The effect of the above surface pretreatments on plated copper adhesion is analyzed and the results provide guidelines for reliable glass interposer TPV metallization.

Copper-filled anodic aluminum oxide: A potential substrate material for a high density interconnection

“…To avoid these issues of TSV inherited from Si, some types of glass interposer have been proposed as alternative materials to Si interposer [10][11][12][13]. Since glass itself is a proper insulator, no additional formation of an insulation layer is needed, and issues related to the capacitive coupling can be remarkably mitigated [10].…”

“…Some electrical characteristics of the vias made through to a glass substrate (TGV) have been reported to vary depending on type and correlated process conditions of the laser drilling used. Whereas the typical manner to form vias is sequential laser drilling, several methods of simultaneous via forming, such as sand blasting, ultrasonic drilling, glass melting over metal (tungsten)-plugs [11] and photo-structuring [13], have been developed. Although these methods are advantageous in cutting down the manufacturing cost, it seems difficult to produce high density vias with less than 50 μm of pitch with an acceptable cost.…”