SELECTIVE ELECTROLESS COPPER PLATING ON SILICON SEEDED BY COPPER-ION IMPLANTATION

We report on the successful use of copper (self) ion implantation into silicon to seed the electroless plating of copper on silicon (100) surfaces. Copper ions were implanted into silicon to doses of 5 x 10(14)-6.4 x 10(16) ions cm(-2) using a metal vapour vacuum are ion implanter at extraction voltages of 10 kV and 20 kV. A copper film was then deposited onto implanted silicon using a commercial electroless plating solution. The ion energy was kept low enough to facilitate a low critical 'seed' threshold dose which was measured to be 2 x 10(15) Cu ions cm(-2). Test patterns were made using polyimide to study the adaptability of this technique to forming thick structures. Plated films were studied with Rutherford backscattering spectrometry, scanning electron microscopy (SEM), profilometry, energy-dispersive X-rays and Auger electron spectroscopy. The adhesion of films was estimated by a 'Scotch tape test'. The adhesion was found to improve with increasing dose. However, thicker films exhibited rather poor adhesion and high internal stress. Detailed examinations of the top and bottom of the film establish that delamination takes place at the amorphous-crystalline interface of the implanted silicon. SEM results show that the films grow first as isolated islands which become Iarger and eventually coalesce into a continuous film as the plating time is increased.