Why is coordination chemistry stretching the limits of micro-electronics technology?

Abstract

As a result of its low resistivity and ability to reliably carry high-current densities, copper is a reasonable alternative to more commonly used contact materials, such as tungsten and aluminum in integrated circuits (ICs). Copper films can be deposited by different techniques: sputtering, electroless or electrolytic plating and CVD (chemical vapor deposition). We report here that CVD is the only conformal film growth method, and surface chemistry controls conformality which is critical for the next generation of integrated circuits (ICs) with interconnect dimensions of 0.18 μm. In the case of Cu CVD, the precursors used are volatile coordination compounds. In this paper, we develop mainly our own contribution to the study of volatile β-diketonate copper complexes that have been designed and synthesized to be used as precursors for Cu CVD. These complexes are volatile liquids under ambient conditions and decompose at temperatures between 130 and 240 °C to a clean copper film and volatile stable species through a disproportionation reaction. Besides the Cupra-select [(VTMS)Cu(hfac) from Schumacher where VTMS is vinyltrimethylsilane and hfac is hexafluoroacethylacetonate], which is by far the most widely used precursor for the deposition of blanket and selectively deposited copper films, several compounds such as (MHY)Cu(hfac) (where MHY is 2-methyl-1-hexen-3-yne) appear well suited for Cu CVD. We give here our latest results on the performances of these new stable precursors. For interconnection dimension less than 0.1 μm, selective metallization by Cu CVD is an alternative to the Damascene process which is the envisaged process for the metallization of ICs by Cu CVD. In contrast to the Damascene process, selective metallization by CVD is a very simple process that can be performed on flat surfaces. The problem is to obtain on a surface growing and non-growing areas for Cu CVD. We report in this paper our results obtained on new processes using CVD precursors and self-assembled molecules (SAMs). We achieved selective metallization of surfaces using (VTMS)Cu(hfac) or (MHY)Cu(hfac) in a completely dry two-step process. Silica surfaces, Si 3N 4 and TiN were derivatized with mono- or trifunctional silanes by gas phase silylation. UV-exposure of the halogen terminated molecules employing a mask resulted in a controlled pattern of the surface affinity towards the copper complex and hence selective Cu CVD was achieved. Such ultrathin monolayers are potentially useful for very high resolution resists because the lateral resolution which is accessible, is on the order of molecular dimensions. Metallization of substrates at a nanometric scale using Cu CVD and hence copper coordination complexes is discussed.