Dewetting dynamics of silicon-on-insulator thin films

Microelectronic Engineering, 2018

We address the solid state dewetting of ultra-thin and ultra-large patches of monocrystalline silicon on insulator. We show that the underlying instability of the thin Si film under annealing can be perfectly controlled to form monocrystalline, complex nanoarchitectures extending over several microns. These complex patterns are obtained guiding the dewetting fronts by etching ad-hoc patches prior to annealing. They can be reproduced over hundreds of repetitions extending over hundreds of microns. We discuss the effect of annealing temperature and patch size on the stability of the final result of dewetting showing that for simple patches (e.g. simple squares) the final outcome is stable and well reproducible at 720°C and for~1 μm square size. Finally, we demonstrate that introducing additional features within squared patches (e.g. a hole within a square) stabilises the dewetting dynamic providing perfectly reproducible complex nanoarchitectures of 5 μm size.

Physical Review B, 2012

We report on the anisotropy of solid state dewetting of straight fronts of Si(001)/SiO 2 obtained by electron beam lithography. The 110 front is stable. It recedes with formation of a faceted rim that thickens in a layer-by-layer mode kinetically limited by 2D nucleation on the top facet of the rim. The front position and the height of the rim respectively obey ∼ t 0.37±0.03 and ∼ t 0.38±0.02 power laws. The 100 front is unstable. It breaks down then recedes at constant velocity. The 100 front instability is characterized by the formation of void fingers whose tips retract at constant shape with a kinetics limited by the mass transfer from the void tip to the Si fingers. The conditions of stability of a straight front are discussed in the light of recent theoretical models. New perspectives for controlling solid dewetting are opened.

In this paper, we present a brief survey of stress effects on dewetting. For this purpose, i we develop a simple thermodynamic model to illustrate stress effects ii we study stress effects in strained-Silicon-On-Insulator (s-SOI) thin films by means of Low Energy Electron Microscopy, and Atomic Force Microscopy iii we discuss some available data. In particular, we show that while for s-SOI the strain only provides a relatively small contribution to the total driving force for dewetting, in some other cases stress can really dominate the driving force for the dewetting.

Acta Materialia, 2021

In this paper, the in-situ Scanning Electron Microscopy (in-situ SEM) technique and three-23 dimensional (3-D) phase-field simulation were combined to perform a comprehensive study on 24 the kinetics and mechanisms of dewetting (or agglomeration) of a 30 nm NiSi films on Si(100) 25 substrate at 600 o C. The evolution of texture during agglomeration of the polycrystalline NiSi 26 thin film was also studied by ex-situ Electron BackScattered Diffraction (EBSD). The phase-27 field simulation results showed that abnormal grain growth plays an important role in the 28 dewetting process of polycrystalline films, while the misorientations between NiSi grains and 29 the Si substrate are the main reason for the agglomeration of NiSi polycrystalline thin film on 30 the monocrystal Si substrate. Moreover, 3-D phase-field simulations coupled with experimental 31 information on misorientation distribution and initial grain size were also performed, and the 32 simulated Ni silicide grain morphology is in good agreement with the in-situ SEM results during 33 agglomeration. In order to slow down or to suppress the agglomeration, it is highly 34 recommended to either increase the volume fraction of low angle grains, or decrease the 35 misorientation of the NiSi grain/Si substrate or the NiSi grains. 36

We report that solid state dewetting of Si thin film on SiO2 can be reversibly inhibited by exposing the Si surface to a partial pressure of dioxygen ð107TorrÞ at high temperature ð1100KÞ. Coupling in situ Low-Energy Electron Microscopy and ex situ atomic force microscopy we propose that the pinning of the contact line induced by the presence of small amounts of silicon oxide is the main physical process that inhibits the dewetting.

Spontaneous dewetting of solid thin films proceeds by edge retraction of film edges and/or by heterogeneous void growth. Classical 1D and 2D continuous models of the evolution of a dewetting film, based on surface diffusion mechanisms ,predict that in the long-time limit dewetting obeys universal scaling laws.In this paper,we review 1D and 2D predictions and recent experimental results concerning Si(001)/SiO2 and Ge(001)/SiO2 single-crystalline thin films in different geometries

Physical Review B, 2006

A method has been developed to calculate and use a surface chemical potential which is valid in the large curvature regime for any surface energy function. It is applied to the solid-phase dewetting of a finite film with an initial rectangular profile and considers the surface diffusion mechanism. For an isotropic surface energy, the film aspect ratio and the adhesion energy between the film and the substrate are shown to be the main parameters that quantify the retraction, the breaking time, and the number of agglomerates. Moreover, it is found that mild surface energy anisotropy with an energy minimum in the horizontal plane postpones the mass detachment. Simple models of the ␥-plots for the surface energy illustrate the influence of cusp points on the retraction profiles. Finally, the smooth and facetted experimental surfaces, that are observed in the Si/ SiO 2 system after 900°C annealing under H 2 , are explained by a quite small anisotropy of the ␥-plot.

The dewetting properties of Ge/SiO2 have been studied by low-energy electron microscopy and grazing incidence small-angle x-ray scattering in two temperature ranges characterized by the presence or the absence of {15 3 23} facets on the dewetting fronts. Thanks to a comparison with the Si/SiO2 system, we show that the {15 3 23} facets: (i) play a role in the stabilization properties of Ge dewetting fronts, (ii) lead to a rotation of 45◦ of the Ge fingers with respect to the Si fingers, and (iii) increase the Ge fingers’ stability delaying the formation of a three-dimensional Ge islands with respect to Si for the benefit of the formation of Ge nanowires. Studying the dewetting kinetics enables estimating the activation energy for Ge dewetting to 2.7 ± 0.2 eV. The weak energetics differences between Si and Ge systems are sufficient to change the dewetting morphologies from a squared-void opening for Si/SiO2 to multibranch dendrites for Ge with specific consequences on the relative dewetting velocities of the Si/SiO2 and Ge/SiO2 systems.

Surface Science, 2007

Metal nano clusters are of great importance in physical and chemical science. One simple method for obtaining metal clusters consists in the deposition of a metal film on an inert substrate followed by annealing at high temperature. After this procedure, the metal film reduces in small clusters, whose morphology depends on the annealing temperature and annealing time. In this work we present a grazing incidence small angle X-ray scattering (GISAXS) study carried out in situ to understand the nucleation and formation of Ni metal clusters. For this purpose uniform Ni metal films, of different thicknesses, were deposited onto an oxidized Si(0 0 1) substrate, and annealed at different temperatures in the range 400-800 K. Before annealing the samples were characterized by X-ray reflectivity measurements to exactly determine the values of the thickness and of the starting roughness. The GISAXS patterns show a surface roughness increase starting at about 600 K. By increasing the temperature the diffused intensity breaks in two lines around the reflectivity plane, indication of a characteristic length correlation of the roughness. This correlation length is maintained during the metal clusters formation.

Owing to its ability to produce an assembly of nanoislands with controllable size and locations, the solid state dewetting of patterned films has recently received great attention. A simple Kinetic Monte Carlo model based on two reduced energetic parameters allows one to reproduce experimental observations of the dewetting morphological evolution of patterned films of Si(001) on SiO2 (or SOI for Silicon-on-Insulator) with various pattern designs. Thus, it is now possible to use KMC to drive further experiments and to optimize the pattern shapes to reach a desired dewetted structure. Comparisons between KMC simulations and dewetting experiments, at least for wire-shaped patterns, show that the prevailing dewetting mechanism depends on the wire width.