Texture of Thin Films

Texture, or the statistical distribution of grain orientation, is an important characteristic of the microstructure of poly-crystalline films. Texture is known to influence e.g. the mechanical, magnetic and thermoelectrical properties of thin films. Therefore, controlling texture is important for many applications.

In present day Si-based micro-electronics, metal-Si compounds are used to contact the active regions of the transistor. These silicide layers are usually formed by a solid-state reaction between a deposited metal film and the Si substrate. The continued decrease in line width makes it increasingly important to characterize and control the microstructure of the silicide film. Indeed, in some cases silicide lines are in fact bamboo structures of a single row of grains. The orientation or texture of these grains will determine their interface structure and energy, and therefore influence important properties such as work function, barrier height, contact resistance, agglomeration resistance and phase formation sequence. Although a lot of effort was undertaken to optimize the epitaxial growth of certain silicides that have a good lattice match to Si, little is known regarding the texture of 'standard' silicide films (i.e. for silicide phases where no lattice match is expected). Pioneering work on texture analysis for silicide films was performed by Bulle-Lieuwma et al. for CoSi2 [1] and by Ozcan et al. for TiSi2 [2]. In recent years, we have made a detailed study of the texture of various silicide phases. For NiSi layers, they observed complex patterns on the pole figures which could not be explained on the basis of the existing classification of texture in thin films. Further research showed that several silicide phases (NiSi, CoSi2 , alpha-FeSi2) exhibit a new type of texture, which they called 'axiotaxy'. Axiotaxy (1D periodic interface) can be considered as an intermediate case between epitaxy (2D periodicity) and a random interface (no periodicity).


Pole figure for a NiSi film formed on Si(001)

More information on thin film texture can be found in this paper. An overview of the infrastructure that is available for texture measurements is given here. A description of GUSTAV, an in-house developed software package for the analysis and visualization of thin film texture, can be found here. [1] C.W.T. Bulle-Lieuwma, A.H. van Ommen, J. Hornstra, and C.N.A.M. Aussems, J. Appl. Phys. 71, 2211 (1992). [2] A.S. Ozcan, K. F. Ludwig Jr., P. Rebbi, C. Lavoie, C. Cabral Jr. and J.M.E. Harper, J. Appl. Phys. 92, 5011 (2002).

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