Thermal Stability of High k Layers
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Thermal Stability of High k Layers C. Zhao1, V. Cosnier2,3, P. J. Chen4,2, O. Richard1, G. Roebben5, J. Maes6, S. Van Elshocht1, H. Bender1, E, Young7,2, O. Van Der Biest5, M. Caymax1, W. Vandervorst1, S. De Gendt1 and M. Heyns1 1 IMEC, Kapeldreef 75, B-3001, Leuven, Belgium; 2 International Sematech; 3 ST Microelectronics assignee in IMEC; 4Texas Instruments Inc. assignee in IMEC; 5 Department of Metallurgy & Material Engineering, K. U. Leuven, Leuven, Belgium; 6 ASM International NV, in IMEC; 7Philips assignee in IMEC ABSTRACT Thermal stability of amorphous phases in various high-k layers (Al2O3, ZrO2, HfO2, ZrAlOx, HfAlOx and HfSiOx) and the phase transformation of crystalline ZrO2 and HfO2 were studied experimentally, as functions of surface preparation, deposition conditions, material composition and post deposition thermal treatment. It is found that pure ZrO2 and HfO2 show relatively low crystallization onset temperatures. The crystalline ZrO2 or HfO2 phases are tetragonal or monoclinic, depending on the layer thickness. The phase transformation of metastable t-phase into stable m-phase has been observed in ZrO2 and HfO2. Crystallization behavior of Al2O3 depends on the surface preparation of the substrate. ALCVD grown Al2O3 layers on an oxide-based surface remain amorphous after 1100°C spike annealing, while those on HF-last surface crystallize at temperatures around 800°C. Alloying Al2O3 into ZrO2 and HfO2 can improve their resistance to crystallization under thermal exposure. The kinetics of the crystallization in the alloys can be described by linear TTT curves. Hf-aluminates show better thermal stability than Zr-aluminates. A defect model relative to the phase transformation is discussed, based on the above observations. INTRODUCTION Morphology stability during the thermal processes in conventional CMOS processing is a basic requirement for high-k dielectrics [1,2]. The thermal processes include postdeposition anneals (PDA) in certain ambient, the high temperature exposure during deposition of poly-silicon, and the source/drain implant activation anneal. The latter sets the thermal budget in temperature. During the annealing, an amorphous layer may crystallize. The phase transition between two crystalline phases is also possible, (e.g. tetragonal ZrO2 to monoclinic ZrO2). For a mixed oxide system, a homogeneous and amorphous layer can separate into two amorphous phases (immiscibility). All these phase transitions might cause degradation of the layer and thus be harmful. In the present work, thermal stability of amorphous phases in various high-k layers (Al2O3, ZrO2, HfO2, ZrAlOx, HfAlOx and HfSiOx), the phase transformation behavior of crystalline ZrO2 and HfO2, and the miscibility of the mixed oxide systems, ZrAlOx, HfAlOx and HfSiOx, were studied. A defect model relative to the phase transformation is discussed, based on the above observations.
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EXPERIMENTAL Al2O3, ZrO2, HfO2, Zr-aluminate, Hf-aluminate and Hf-silicate thin layers with different thicknesses were prepared by ALCVD and M
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