Silver Metallization on Porosified LTCC Deposited by Pulse Plating Technique

Abstract

Present microelectronic devices especially when including high frequency applications are in need of highly integrated metallization technologies. Silver is considered as a future interconnection material for such devices and systems due to its low bulk resistivity of about 1.6 μΩ·cm at 20°C. Conventional thick film metallization techniques on low temperature co-fired ceramics such as screen printing are only partly capable of meeting the requirements in terms of lateral resolution and precision. Furthermore, on advanced surfaces such as porosified composite LTCC, also thin film metallization techniques (e.g. sputtering) meet their limits due to a poor coverage and hence, a low electrical conductivity. In this study, it is shown, that bipolar pulse plating of silver is capable of bridging the pores of the surface of the porosified substrate without penetrating them. The plated metallizations feature very fine grains with an average diameter of approx. 90 nm and a maximum up to 250 nm. The film resistivity being measured directly during annealing decreases at elevated temperatures above 90°C in air. Compared to the bulk value, the film resistivity of the ‘as deposited’ electroplated silver is increased, but can be improved down to 2 μΩ·cm with a TCR of 4.1·10−3 K−1 at 20°C by a subsequent annealing treatment at 500°C for 5 h in air. Since there is no measureable difference in resistivity between the galvanic silver deposited on non-porosified or porosified LTCC detected, the findings qualify the bipolar pulsed silver plating as an excellent choice for metalizing porosified LTCC substrates.