In situ XPS investigation about the growth of the first atomic layer of Ta(N) films deposited by thermal TBTDET ALD
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1146-NN09-08
In situ XPS investigation about the growth of the first atomic layer of Ta(N) films deposited by thermal TBTDET ALD S. Strehle, D. Schmidt, S. Gutsch, M. Knaut, M. Albert, J.W. Bartha Technische Universität Dresden, Institute of Semiconductor and Microsystems Technology (IHM), 01062 Dresden, Germany
ABSTRACT Ta based films are important building blocks for modern microelectronic applications. To meet the requirements of miniaturization, atomic layer deposition appears to be an alternative technology in comparison to PVD and CVD. In the present paper investigations of a thermal TBTDET ALD process will be presented with emphasis to the first ALD reaction cycles on native silicon oxide and HF etched silicon surfaces. The investigations show that the substrate chemistry is a crucial parameter for the film growth and appears to be a key to control the ALD deposition. The investigations were done by XPS without any vacuum break between the deposition and the surface analysis.
INTRODUCTION Ta(N) films are used in microelectronics as effective copper diffusion barriers and they are considered for electrodes of memory devices, capacitors and CMOS transistors. To fulfill present requirements of step coverage and conformity with respect to miniaturization and high aspect ratios of trench or stack structures, conventional deposition technologies like chemical and physical vapor deposition can be hardly applied. However, atomic layer deposition (ALD) permits the fabrication of ultra-thin films with excellent step coverage and precisely determined film thickness of a few nanometers by sequential self-limiting chemical reactions between substrate or film surface and a gas phase, respectively [1]. For this reason substrate surface chemistry (e.g. functional groups at the surface) is important for the solid-gas reaction leading to the ALD film growth. From the cyclical nature of ALD, the chemical state of the previous layer can change or influence the subsequent ALD reaction. Therefore, the growth mechanisms and the chemistry of the first layers are highly relevant for the interface quality, the composition and the microstructure of the film. In the present paper an example of Ta based ALD film growth will be presented beginning from the first precursor pulse. The investigations were done exemplarily on substrates with two different pretreatments and consequently, demonstrate the effect of substrate surface chemistry.
EXPERIMENT For the deposition of Ta based films by ALD various precursor molecules exist [1]. In our investigations TBTDET (tert-butylimidotris(diethylamido)tantalum) was used in combination with ammonia as reactive gas. The standard ALD was done thermally at 270°C in four steps: (i) monolayer chemisorption of the precursor, (ii) Ar purging to remove excessive molecules, (iii) NH3 reaction step, (iv) Ar purging to remove all reaction byproducts from the chamber. The whole TBTDET process as well as the deposition/metrology system is described in [2]. Pieces of single crystalline silicon wafers were used
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