Theoretical assessments of major physical processes involved in the depth resolution in sputter profiling

Carter, G.; Gras‐Martí, A.; Nobes, M. J.

doi:10.1080/00337578208222785

Cited by 50 publications

(6 citation statements)

References 54 publications

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“…Seen in a historical context, however, many of the earlier studies on surface evolution were driven by the effort to minimize surface roughening by energetic ions. Thus roughness induced by the stepwise or continuous removal of thin surface layers by ion beam sputtering is very critical for surface cleaning processes and many depth profiling analytical techniques like secondary-ion mass spectrometry (SIMS) and Auger electron spectroscopy (AES) [7][8][9][10][11][12][13][14][15]. In microtechnology and nanotechnology using ion beam and plasma etching fabrication techniques the roughness evolution of the etched surfaces is very crucial for the operation and quality of optical components and electronic devices, which becomes more and more important with shrinking device dimension [16].…”

Section: Introductionmentioning

confidence: 99%

Large area smoothing of surfaces by ion bombardment: fundamentals and applications

Frost¹,

Fechner²,

Ziberi³

et al. 2009

J. Phys.: Condens. Matter

119

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Ion beam erosion can be used as a process for achieving surface smoothing at microscopic length scales and for the preparation of ultrasmooth surfaces, as an alternative to nanostructuring of various surfaces via self-organization. This requires that in the evolution of the surface topography different relaxation mechanisms dominate over the roughening, and smoothing of initially rough surfaces can occur. This contribution focuses on the basic mechanisms as well as potential applications of surface smoothing using low energy ion beams. In the first part, the fundamentals for the smoothing of III/V semiconductors, Si and quartz glass surfaces using low energy ion beams (ion energy: ≤2000 eV) are reviewed using examples. The topography evolution of these surfaces with respect to different process parameters (ion energy, ion incidence angle, erosion time, sample rotation) has been investigated. On the basis of the time evolution of different roughness parameters, the relevant surface relaxation mechanisms responsible for surface smoothing are discussed. In this context, physical constraints as regards the effectiveness of surface smoothing by direct ion bombardment will also be addressed and furthermore ion beam assisted smoothing techniques are introduced. In the second application-orientated part, recent technological developments related to ion beam assisted smoothing of optically relevant surfaces are summarized. It will be demonstrated that smoothing by direct ion bombardment in combination with the use of sacrificial smoothing layers and the utilization of appropriate broad beam ion sources enables the polishing of various technologically important surfaces down to 0.1 nm root mean square roughness level, showing great promise for large area surface processing. Specific examples are given for ion beam smoothing of different optical surfaces, especially for substrates used for advanced optical applications (e.g., in x-ray optics and components for extreme ultraviolet lithography).

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Section: Introductionmentioning

confidence: 99%

Large area smoothing of surfaces by ion bombardment: fundamentals and applications

Frost¹,

Fechner²,

Ziberi³

et al. 2009

J. Phys.: Condens. Matter

119

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“…1981;Sanz & Hofmann 1986) that took into account the statistical roughening of the surface during sputtering. Further roughening during sputter profiling was considered by Carter et al . (1982).…”

Section: Introductionmentioning

confidence: 99%

Sputter-depth profiling for thin-film analysis

Hofmann¹

2003

Philosophical Transactions of the Royal Society of London. Seri

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Following a brief historical background, the concepts and the present state of sputter-depth profiling for thin-film analysis are outlined. There are two main branches: either the removed matter (as in mass- or optical-spectroscopy-based secondary-ion mass spectrometry or glow-discharge optical emission spectroscopy), or the remaining surface (as in Auger electron spectroscopy and X-ray photoelectron spectroscopy) is characterized. These complementary methods show the same result if there is no preferential sputtering of a component. The common root of both is the fundamental ion-solid interaction. Understanding of how the latter influences the depth resolution has led to important improvements in experimental profiling conditions such as sample rotation and the use of low-energy ions at glancing incidence. Modern surface-analysis instruments can provide high-resolution depth profiles on the nanometre scale. Mathematical models of different sophistication were developed to allow deconvolution of the measured profile or quantification by reconstruction of the in-depth distribution of composition. For the latter purpose, the usefulness of the so-called mixing-roughness-information (MRI) depth model is outlined on several thin-film structures (e.g. AlAs/GaAs and Si/Ge), including its extension to quantification of sputter-depth profiles in layer structures with preferential sputtering of one component (Ta/Si). Using the MRI model, diffusion coefficients at interfaces as low as 10(-22) m(2) s(-1) can be determined. Fundamental limitations of sputter-depth profiling are mainly traced back to the stochastic nature of primary-particle energy transfer to the sputtered particle, promoting atomic mixing and the development of surface roughness. Owing to more sophisticated experimental methods, such as low-energy cluster ion bombardment, glancing ion incidence or 'backside' sputtering, these ultimate limitations can be reduced to the atomic monolayer scale.

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“…This mutation process continues as ion fluence increases, continuously exposing deeper atomic layers; clearly, also, the number of atcms in each layer exposed to a1. 39 direct ion impact varies with increasing ion fluence. This process can be modelled by a set of hierarchal mutation equations which, when solved, indicate that the surface roughens with increasing fluence and the number of exposed atoms in each layer changes from a Poisson distribution with layer depth to a Gaussian distribution.…”

Section: Surface Perturbationsmentioning

confidence: 98%

Ion‐beam‐induced topography and compositional changes in depth profiling

Carter

Nobes

1992

Surface & Interface Analysis

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When energetic ions penetrate and stop in solids they not only add a new atomic constituent to the matrix but they also create atomic recoils and defects. The fluxes of these entities can give rise to spatial redistribution of atomic components, which may be partly or completely balanced by reordering and relaxation processes. These latter, in turn, may be influenced by fields and gradients induced by the primary relocation processes and by the energy deposited. These will include quasi-thermal, concentration (or chemical potential) and electrostatic gradients and may act to enhance or suppress atomic redistribution. Some, or all, of these processes will operate, depending upon the system under study, when energetic ions are employed to sputter erode a substrate for depth sectioning and, quite generally, can perturb the atomic depth profile that it is intended to evaluate. Theoretical and computational approaches to modelling such processes will be outlined and experimental examples shown which illustrate specific phenomena.In particular the accumulation of implant species and defect generation or redistribution can modify, with increasing ion fluence, the local sputtering mechanism and create further problems in depth profile analysis as a changing surface topography penetrates the solid. Examples of such topographic evolution and its influence on depth protiling analysis will be given and models to explain general and specific behaviour will be outlined. The commonality of models which examine both depth-dependent composition modification and surface topography evolution will be stressed.

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Theoretical assessments of major physical processes involved in the depth resolution in sputter profiling

Cited by 50 publications

References 54 publications

Large area smoothing of surfaces by ion bombardment: fundamentals and applications

Large area smoothing of surfaces by ion bombardment: fundamentals and applications

Sputter-depth profiling for thin-film analysis

Ion‐beam‐induced topography and compositional changes in depth profiling

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