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

As a result of its low resistivity and ability to reliably carry high-curre nt densities, copper is a reasonable alternative to more commonly used cont act materials, such as tungsten and aluminum in integrated circuits (ICs). Copper films can be deposited by different techniques: sputtering, electrol ess or electrolytic plating and CVD (chemical vapor deposition). We report here that CVD is the only conformal film growth method, and surface chemist ry controls conformality which is critical for the next generation of integ rated circuits (ICs) with interconnect dimensions of 0.18 mu m. In the case of Cu CVD, the precursors used are volatile coordination compounds. In thi s paper, we develop mainly our own contribution to the study of volatile be ta-diketonate copper complexes that have been designed and synthesized to b e used as precursors for Cu CVD. These complexes are volatile Liquids under ambient conditions and decompose at temperatures between 130 and 240 degre es C to a clean copper film and volatile stable species through a dispropor tionation reaction. Besides the Cupra-select [(VTMS)Cu(hfac) from Schumache r where VTMS is vinyltrimethylsilane and hfac is hexafluoroacethylacetonate ], which is by far the most widely used precursor for the deposition of bla nket 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 C VD. We give here our latest results on the performances of these new stable precursors. For interconnection dimension less than 0.1 mu m, selective metallization b y 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 Damascen e 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 growi ng and non-growing areas for Cu CVD. We report in this paper our results ob tained on new processes using CVD precursors and self-assembled molecules ( SAMs). We achieved selective metallization of surfaces using (VTMS)Cu(hfac) or (MNY)Cu(hfac) in a completely dry two-step process. Silica surfaces, Si 3N4 and TiN were derivatized with monoor trifunctional silanes by gas phase silylation. UV-exposure of the halogen terminated molecules employing a ma sk resulted in a controlled pattern of the surface affinity towards the cop per complex and hence selective Cu CVD was achieved. Such ultrathin monolay ers are potentially useful for very high resolution resists because the lat eral resolution which is accessible, is on the order of molecular dimension s. Metallization of substrates at a nanometric scale using Cu CVD and hence copper coordination complexes is discussed. (C) 1998 Elsevier Science S.A. All rights reserved.