Nanoscale Observation of a Grain Boundary Related Growth Mode in Thin Film Reactions

Abstract

We report the atomic scale observation of a thin film growth mode related to grain boundaries in multilayers of polycrystalline gold and amorphous silicon. Using differential scanning calorimetry, in situ x-ray diffraction, and high-resolution electron microscopy, we observe silicide nucleation to take place at grain boundaries in the polycrystalline gold films followed by lateral silicide growth parallel to gold ͞silicon interfaces. This growth mode is related to solid-state reactions at low temperatures where atomic transport is restricted to grain and interphase boundaries. It demonstrates the importance of thin film microstructure for phase selection during thin film reactions at low temperatures.[S0031-9007(97)05118-1] PACS numbers: 81.10. Aj, 61.72.Mm, 81.15.Tv Metal silicides are of still growing interest as low resistivity contact materials for silicon devices. As device dimensions shrink, the controlled and reliable fabrication of silicides increasingly requires the understanding of basic mechanisms of thin film reactions. Thin film diffusion couples represent nonequilibrium systems frequently exhibiting large driving forces (¿k B T , k B : Boltzmann's constant) for phase formation. The final state to which such systems develop is simply determined by the minimum of the Gibbs free energy of the alloy system. The number of intermediate phases accessible by the system increases with increasing driving force. Which of these phases is selected in the early stages of the reaction is determined by the kinetics of the system when it follows the path towards this phase. Frequently, relaxation occurs via metastable intermediate phases, a prominent example being the well-known solid-state amorphization reactions between early and late transition metals [1].For the high-temperature regime where bulk interdiffusion is possible, bulk thermodynamics and kinetics can be used to describe phase selection in terms of nucleation [2] and growth kinetics [2-5] of the competing phases. It is commonly assumed that the product phase nucleates homogeneously at the interface between the parent phases ("a͞b interface") [2] or heterogeneously at triple points with grain boundaries followed by coalescence of the nuclei along the a͞b interface [2,6,7]. In both cases, nucleation evolves into the frequently observed planar growth of the product phase.In the low-temperature regime of negligible bulk diffusion, atomic transport is restricted to defective regions like interfaces, dislocations, and grain boundaries [8][9][10][11]. As a consequence, certain intermediate phases may no longer be accessible from the initial state by thermal fluctuations implying bulk thermodynamics and kinetics to be of lim-ited use for the prediction of the reaction path towards equilibrium. Instead, it seems obvious that microscopic details of the available diffusion paths are of increasing importance. This has been recognized in a recently proposed model which uses irreversible thermodynamics to calculate the effective driving force for product phase nuc...

Fundamentals of Metal‐induced Crystallization of Amorphous Semiconductors

“…a metastable Au 3 Si phase at a very low temperature of $100 8C. [10] In order to understand this observation, thermodynamic calculations on the possible nucleation of Au 3 Si at the Au GBs and at the Au/a-Si interface have also been carried out. Indeed, the calculated critical thickness of a-Si at Au GBs to form Au 3 Si is close to 4 ML at a minimal temperature as low as 80 8C, which is compatible with the observed formation of Au 3 Si at Au GBs at 100 8C in the Au/a-Si system.…”

“…Indeed, the calculated critical thickness of a-Si at Au GBs to form Au 3 Si is close to 4 ML at a minimal temperature as low as 80 8C, which is compatible with the observed formation of Au 3 Si at Au GBs at 100 8C in the Au/a-Si system. [10,15] …”

“…Another fabrication technique is the so-called metal-induced crystallization (MIC), which involves that the temperature for crystallization of a-Si is greatly reduced if it is put into direct contact with a metal, such as Al, Ni, Cu, or Au. [7][8][9][10][11][12][13][14][15][16] As shown in Figure 1, depending on the contacted metal, the crystallization temperature of a-Si can be reduced to temperatures in the range of 500 8C to even only 150 8C. The lower limit for the crystallization temperature (T cryst ) in particular occurs for a-Si in contact with Al.…”

Influence of layer microstructure on the double nucleation process in Cu∕Mg multilayers

“…Different possibilities arise: The product phase can nucleate at the A / B interface, 24 heterogeneously at triple grain boundaries 9,16,25 or inside grain boundaries. 26 As the density and type of grain boundaries depend on the specific microstructure at the interface, it is expected that the growth mode of the layer may be a key point for understanding nucleation. Several authors have previously addressed the influence of microstructure on nucleation.…”

Nanocrystallization of amorphous-Ta40Si14N46 diffusion barrier thin films

“…The microscope's point resolution is 0.188 nm and its information limit is 0.11 nm. 10 Energy-dispersive x-ray ͑EDX͒ analyses of the samples were performed by a Link ISIS system with a Si:Li detector having an energy resolution of 163 eV.…”