Barbara Horváth

Through silicon via filling methods with metal/polymer composite for three-dimensional LSI

The novel use of metal/polymer composite can be a new candidate for filling through silicon vias (TSV) for three-dimensional (3D) LSI, as it provides a much faster and inexpensive fabrication process compared to copper electroplating. In this study, different process methods have been tested in order to optimize TSV filling with Ag/polypyrrole composite. All together nine method set-ups have been examined to analyse their average filling ratios. The statistical analysis of the techniques showed that the masking and scratching in vacuum environment proved to be the most effective, in average up to 98% filling ratio could be reached within 5 min. The technological differences of the two techniques to remove the additional deposited composite material on the surface caused by the wet dipping in aspect of the resulting via fillings are also detailed in this paper. The use of these techniques can contribute to improve through-put for production of 3D-LSI with metal/polymer composites.

Diffusion Barrier and Adhesion Properties of SiOxNy and SiOx Layers between Ag/Polypyrrole Composites and Si Substrates

This paper describes the interface reactions and diffusion between silver/polypyrrole (Ag/PPy) composite and silicon substrate. This composite material can be used as a novel technique for 3D-LSI (large-scale integration) by the fast infilling of through-silicon vias (TSV). By immersion of the silicon wafer with via holes into the dispersed solution of Ag/PPy composite, the holes are filled with the composite. It is important to develop a layer between the composite and the Si substrate with good diffusion barrier and adhesion characteristics. In this paper, SiOx and two types of SiOxNy barrier layers with various thicknesses were investigated. The interface structure between the Si substrate, the barrier, and the Ag/PPy composite was characterized by transmission electron microscopy. The adhesion and diffusion properties of the layers were established for Ag/PPy composite. Increasing thickness of SiOx proved to permit less Ag to transport into the Si substrate. SiOxNy barrier layers showed very good diffusion barrier characteristics; however, their adhesion depended strongly on their composition. A barrier layer composition with good adhesion and Ag barrier properties has been identified in this paper. These results are useful for filling conductive metal/polymer composites into TSV.

Tin whisker growth from tin thin film

In this paper, the tin whisker growth from vacuum evaporated Sn thin film is studied. The aim was to characterize the whiskering behavior of submicron thick tin layers which have large grain size. For this purpose, 99.99% pure tin was vacuum evaporated onto 1.5 mm thick copper and ceramic substrates. The average thickness of the tin films was ~400nm with ~1-1.5μm grain size. The samples were stored at room environment for 150 days. Whisker growth was monitored every 15 days by Scanning Electron Microscope (SEM) and at the end of the investigation by a HIROX KH-7700 3D optical microscope. Cross-sections of the layers were prepared by Focused Ion Beam (FIB) to study the change of the layer structure during the test by FIB - Scanning Ion Microscope (SIM). It was found that the submicron thick tin layers with larger grain size on copper substrate can develop large amount and long tin whiskers, as compared to the samples with ceramic substrate which surface remained whisker free. The results indicated that the whiskering was caused by copper-tin intermetallic layer growth between the copper substrate and Sn thin film which resulted in large compressive stress in the Sn thin film.

Fast filling of through-silicon via (TSV) with conductive polymer/metal composites

Toward fast formation of TSV for 3D-IC or 3D-LSI, a composite with polypyrrole as a conducting polymer and metal silver prepared through the solution photo chemistry was studied with respect to filling status of vertical holes in silicon chip, electrical characteristics and interfacial structures between the filling composite and silicon substrate. Based on the experimental results, the composite was capable of filling within 10 minutes, evaluation procedures of electrical resistance was established and excellent barrier layer was found.