Effects of Ion Metal Plasma (IMP) Titanium Deposition on Ti Silicide Formation
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A. Sabbadini, F. Cazzaniga, M. BrambillaC. Bresolin, V. Cusi, T. Marangon, G. Queirolo STMicroelectronics, via Olivetti 2, 1-20041 Agrate Brianza (Mi) Italy ABSTRACT
Titanium disilicide obtained by direct interaction between Si and a deposited Ti layer is a choice for low-resistance gate interconnections and source and drain areas. The properties of the TiSi 2 film can be influenced by many factors; such as substrate nature and doping, the depositing Ti layer, structure dimensions [ 1][2][3114]. This work is addressed to study the properties of TiSi 2 film as obtained from titanium deposited by Ion Metal Plasma (IMP), which has recently been introduced in high aspect ratio contact and via applications. Its suitability for titanium silicide formation is investigated here in comparison to standard IVD deposition. The study was carried out on flat and patterned samples. Titanium silicide formed on mono-Si substrates were characterized as a function of RTP temperature in terms of sheet resistance, tilm morphology, crystallography and phase evolution. It was found that the TiSi2 film obtained from IMP-Ti is very similar to the one obtained from PVD standard deposition. However, for annealing below 700'C, an increase in the sheet resistance of the TiSi 2 C49 phase from IMP-Ti compared to the one from PVD-Ti was found, and is explained by different silicide grain size. Analyses performed on patterned samples with doped silicon and poly-Si lines show similar electrical results for TiSi 2 from IMP and PVD deposition; however, fbr p+ poly-Si lines, the IMP samples displayed correct TiSi 2 formation down to 0.1 8pm line width, while the PVD wafers showed discontinuous results at these minimum feature sizes. INTRODUCTION The Ion Metal Plasma (IMP) sputtering technique has recently been proposed in order to
achieve low cost and eftective Ti deposition in high aspect ratio contact or via applications [51; however, the use of the same IMP technique in a process flow with self aligned Ti silicide has
not been reported so far. Due to the different deposition conditions, IMP films can in principle have some intrinsic properties that could impact on integration into a full siuicide process flow. In fact, as opposed to conventional PVD sputtering, IMP Ti deposition is carried out at a relatively high pressure (20-3(1x10 3 Torr) and utilizes RF power applied to a Ti coil in addition to the given standard DC power to the target (Fig. 1). Under IMP conditions, the ionization efficiency of Ti atoms is very high, up to 70 - 90 9• instead of the 1 % of the PVD case, leading to strong vertical directionality of the ionized metal flux accelerated by the potential difference between wafer and plasma (c.a. 20V). The high directionality promotes a strong columnar structure of the IMP film, and the RF plasma induces some appreciable resputtering during deposition. A rough estimate of the resputtering rate can be inferred by comparing non-IMP to IMP deposition rates, which in our case differ by a factorof 2 for the same DC power.
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