Physical and Electrical Characterization of Hafnium Silicate Thin Films
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Physical and Electrical Characterization of Hafnium Silicate Thin Films Patrick S. Lysaght, Brendan Foran, Gennadi Bersuker, Larry Larson, Robert W. Murto and Howard R. Huff International SEMATECH, 2706 Montopolis Drive, Austin, Texas 78741-6499, USA ABSTRACT Evaluation of physically thicker gate insulator materials with significantly higher dielectric constants (k = 10 – 25) as potential replacements for silicon dioxide, SiO2 (k = 3.9), and silicon oxynitride continues to be a focus of the semiconductor industry. The challenge is to provide a film with lower leakage current and with capacitance equivalent to < 1.0 nm SiO2 [1-4]. One such candidate material; metal-organic chemical vapor deposited (MOCVD) hafnium silicate, has been physically characterized by high resolution transmission electron microscopy (HRTEM) in plan view, as a blanket, uncapped film and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) in cross section following integration into capacitors and complementary metal oxide semiconductor (CMOS) transistors. Changes in the material microstructure associated with phase segregation and crystallization as a function of Hf silicate composition and rapid thermal anneal (RTA) temperature have been observed and a discussion of the segregation mechanisms is presented [5-8]. Also, various methods of incorporating nitrogen into bulk hafnium silicate films have been investigated and resultant transistor electrical performance data has been correlated with physical characterization for NH3 post deposition anneal (PDA) treatments at various temperatures.
INTRODUCTION High-k gate dielectric materials evaluation must include the film response to the standard source/drain activation requirement of 1000ºC/10s/N2, which is above the crystallization temperature of binary oxide, HfO2. By alloying the binary metal oxide with SiO2 to form Hf silicate, HfxSi1-xO4, the crystallization onset temperature may be significantly increased, albeit at the expense of permittivity [9]. Blanket Hf silicate films consisting of 20, 40 and 60 mol.% SiO2 have been evaluated by HRTEM in plan view to identify microstructure variations related to phase segregation and crystallization. Cross section HAADF-STEM of Hf silicate as blanket, uncapped films and as the dielectric integrated into metal electrode capacitors utilized quantitative image analysis to identify the dimensions of interfacial / transitional layers (between the sub-oxide and the Hf silicate layer) not easily distinguished by eye from the projected image. While it is difficult to distinguish between interfacial roughness and material intermixing, density gradients provide valuable insight into the material response to RTA processing. Direct correlation between the electrical and physical response of Hf silicate films exposed to NH3 PDA of 700ºC and 900ºC is a result of investigating several process techniques designed to incorporate nitrogen into the high-k layer. Poly-Si electrode transistor current data for Hf silicate gate
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