Advanced CVD Barrier Technology for Copper Interconnect
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4]. The dual inlaid integration places an additional requirement on the barrier process capability to provide uniform film coverage along the side walls of high aspect ratio via and interconnect structures to prevent out diffusion of Cu. All this has led to advancements in barrier deposition by sputtering [6] as well as an industry initiative to develop CVD barrier technology. The primary diffusion barrier materials are transition metals (Group IVB through VIB), metal-nitrides and metal-silicon-nitrides [5]. Among them tantalum (Ta), tungsten (W), and titanium (Ti) based compounds and their alloys are likely candidates because these elements are being used in one form or another in either memory (e.g. tantalum pentoxide Ta2O5 ) or microprocessor (e.g. tungsten W, titanium nitride TiN) products. The semiconductor industry has long term process reliability data on these transition metals and therefore is unlikely to soon consider other exotic new materials for barrier applications. This is also reflected in the literature survey which has predominantly focused on the above mentioned materials (e.g. Ta, TaN, W2N, TiN, Ta-Si-N, Ti-Si-N, etc) [5].
Ternary phase Ta-Si-N [7] and Ti-Si-N [8] have been reported as the most robust diffusion barriers. This is because these ternary films are amorphous and the absence of grain boundaries minimizes potential paths for Cu diffusion. Among the binary films, TaN offers better Cu diffusion barrier properties compared to TiN and WxN [5]. However, most reports test barrier at elevated thermal budgets and above -500 'C [5]. This temperature higher than that used for current back-end of line fabrication, and the trend is to lower maximum allowable temperature and thermal budget for incorporation of thermally sensitive low-k materials [9]. These barriers can be deposited by CVD as well as by sputter processes. For CVD processes availability of high purity precursors at low cost is a factor for selecting a barrier system. The precursor must be gaseous or a liquid at room temperature to enable vapor phase transport to the substrate. The deposition temperature should be below _>. ,E,IoS881
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organic precursors such as TDMAT and TDEAT are readily available in high purity. On the other hand, metal organic precursors for CVD of TaN and W5N are available at limited R&D usage levels. The precursor must also be either gaseous or a low viscosity liquid with high vapor pressure to enable controlled vapor phase transport of the precursor to the substrate by either a mass flow controller (MFC) or a direct liquid injection (DLI) system. Based on this criteria, WF 6 (g), TiCl 4 (liq), TDMAT(liq), and TDEAT (liq) are desirable candidates for CVD barrier processes. Another consideration is the deposition temperature of the process, which must be kept as low as possible to allow future incorporation of thermally sensitive low-k materials [9]. In ad
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