A Comparative Study of Ti/Low-k HSQ (Hydrogen Silsesquioxane) and Ti/TEOS (Tetraethylorthosilicate) Structures at Elevat
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A Comparative Study of Ti/Low-k HSQ (Hydrogen Silsesquioxane) and Ti/TEOS (Tetraethylorthosilicate) Structures at Elevated Temperatures Yuxiao Zeng1, Linghui Chen, and T. L. Alford Department of Chemical, Bio and Materials Engineering, NSF Center for Low Power Electronics, Arizona State University, Tempe, Arizona 85287-6006, USA 1 Current address: Epitronics Corporation, an ATMI company, Mesa, AZ, USA ABSTRACT For the benefit of reducing capacitance in multilevel interconnect technology, low-k dielectric HSQ (hydrogen silsesquioxane) has been used as a gapfill material in Al-metallizationbased non-etchback embedded scheme. The vias are consequently fabricated through the HSQ layer followed by W plug deposition. In order to reduce the extent of via poisoning and achieve good W/Al contact, thin Ti/TiN stack films are typically deposited before via plug deposition. In this case, HSQ makes direct contact with the Ti layer. The reliability of the Ti/HSQ structures at elevated temperatures has been systematically studied in this work by using a variety of techniques. These results are also compared with those from Ti/TEOS (Tetraethylorthosilicate) structure, where TEOS is a conventional intra-metal dielectric. When the temperature is below 550 °C, a significant number of oxygen atoms are observed to diffuse into the titanium layer. The primary source of oxygen is believed to come from the HSQ film. When the temperature is above 550 °C, HSQ starts to react with Ti. At 700 °C, a TiO/Ti5Si3/HSQ stack structure forms. The Ti/HSQ system exhibits a higher reactivity than that of the Ti/TEOS system. INTRODUCTION A number of low-k dielectric materials are being actively studied [1-3] to replace conventional interlayer dielectric SiO2 due to the following benefits: to increase device speed by lowering interconnect RC delay, to diminish crosstalk by reducing the capacitance between parallel running lines, and to reduce power dissipation because the heat given off is directly proportional to the capacitance. Hydrogen silsesquioxane (HSQ) is one of the promising candidates because of its low dielectric constant ( 300 °C), the Ti (002) peak shifts towards lower θ angle. The peak shift is almost completed at 600 °C for Ti on HSQ, and at 650 °C for Ti on PETEOS. The shift of the Ti (002) peak is also reported by Russell et al. [10] in their studies on the Ti/SiO2 system. Their studies show that for the Ti/SiO2 system reacting at high temperatures, liberated oxygen atoms interstitially diffuse into the Ti lattice to form initially a solid solution of Ti and thus lead to the expansion of the Ti lattice and corresponding shift of Ti diffraction peaks. This suggests that the Ti (002) peak shift in the present study may arise from the O incorporation as well. Figure 1(b) is a plot of the O concentration in 50 nm Ti films (O/Ti ratio) as a function of annealing temperature (60 min annealing time), which shows an increasing O content in the Ti films as the anneal proceeds (T > 300 °C). The correlation between the lattice constant C0 of Ti, as
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