Prediction and experimental determination of the layer thickness in SIMS depth profiling of Ge/Si multilayers: Effect of preferential sputtering and atomic mixing

The analysis of polymers by secondary ion mass spectrometry (SIMS) has been a topic of interest for many years. In recent years, the primary ion species evolved from heavy monatomic ions to cluster and massive cluster primary ions in order to preserve a maximum of organic information. The progress in less-damaging sputtering goes along with a loss in lateral resolution for 2D and 3D imaging. By contrast the development of a mass spectrometer as an add-on tool for the helium ion microscope (HIM), which uses finely focussed He+ or Ne+ beams, allows for the analysis of secondary ions and small secondary cluster ions with unprecedented lateral resolution. Irradiation induced damage and depth profiling capabilities obtained with these light rare gas species have been far less investigated than ion species used classically in SIMS. In this paper we simulated the sputtering of multi-layered polymer samples using the BCA (binary collision approximation) code SD_TRIM_SP to study preferential sputtering and atomic mixing in such samples up to a fluence of 1018 ions/cm2. Results show that helium primary ions are completely inappropriate for depth profiling applications with this kind of sample materials while results for neon are similar to argon. The latter is commonly used as primary ion species in SIMS. For the two heavier species, layers separated by 10 nm can be distinguished for impact energies of a few keV. These results are encouraging for 3D imaging applications where lateral and depth information are of importance.

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A new method for the determination of the diffusion-induced concentration profile and the interdiffusion coefficient for thin film systems by Auger electron spectroscopical sputter depth profiling

Journal of Materials Research ◽

10.1557/jmr.2004.0430 ◽

2004 ◽

Vol 19 (11) ◽

pp. 3389-3397 ◽

Cited By ~ 29

Author(s):

J.Y. Wang ◽

E.J. Mittemeijer

Keyword(s):

Concentration Profile ◽

Interdiffusion Coefficient ◽

Auger Electron ◽

Depth Profiling ◽

Interface Roughness ◽

Diffusion Annealing ◽

Multilayered Structures ◽

Preferential Sputtering ◽

Atomic Mixing ◽

Fitting In

A new Auger electron spectroscopical sputter depth profiling method was developed to determine the interdiffusion coefficient for the initial stage of diffusion annealing of thin films. The method is based on (i) adoption of an interdiffusion model appropriate for the specimen investigated and (ii) convolution of an accordingly calculated diffusion-induced concentration profile with the smearing effects due to atomic mixing, surface/interface roughness, escape depth of the Auger electrons, and preferential sputtering. The diffusion-induced concentration profile and the interdiffusion coefficient are determined by fitting in an iterative least-squares procedure of the calculated Auger electron spectroscopical depth profile to the measured one. The method was applied to bilayered and multilayered structures, exhibiting dominant grain-boundary diffusion and dominant volume diffusion, respectively. A very small extent of interdiffusion, characterized by diffusion distances as small as 1 nm, could be quantified.

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