Atomic concentration depth profile

AES atomic concentration depth profile for an untreated PBTMSS film on Au/Si (1 min. sputtering = 140 A). 

Figure 12. Atomic concentration depth profile in F8G sample the values are related to the calcium concentration...

Figure 11. Carbon, oxygen and nitrogen atomic concentration depth profile for C-PA (open symbols) and PAO (solid ones) membranes...

Sputtered Neutral Mass Spectrometry (SNMS) is the mass spectrometric analysis of sputtered atoms ejected from a solid surface by energetic ion bombardment. The sputtered atoms are ionized for mass spectrometric analysis by a mechanism separate from the sputtering atomization. As such, SNMS is complementary to Secondary Ion Mass Spectrometry (SIMS), which is the mass spectrometric analysis of sputtered ions, as distinct from sputtered atoms. The forte of SNMS analysis, compared to SIMS, is the accurate measurement of concentration depth profiles through chemically complex thin-film structures, including interfaces, with excellent depth resolution and to trace concentration levels. Genetically both SALI and GDMS are specific examples of SNMS. In this article we concentrate on post ionization only by electron impact. 

SIMS is by far the most sensitive surface technique, but also the most difficult one to quantify. SIMS is very popular in materials research for making concentration depth profiles and chemical maps of the surface. The principle of SIMS is conceptually simple A primary ion beam (Ar+, 0.5-5 keV) is used to sputter atoms, ions and molecular fragments from the surface which are consequently analyzed with a mass spectrometer. It is as if one scratches some material from the surface and puts it in a mass spectrometer to see what elements are present. However, the theory behind SIMS is far from simple. In particular the formation of ions upon sputtering in or near the surface is hardly understood. The interested reader will find a wealth of information on SIMS in the books by Benninghoven et al. [2J and Vickerman el al. [4], while many applications have been described by Briggs et al. [5]. 

Fig. 13.3 Concentration depth profiles of boron atoms implanted at 100 keV into polyimid for different boron fluences (in atoms cm ). Rp (TRIM) is a projection of the ion path length on the original ion direction as simulated by TRIM code.

Concentration depth profiles - The ability to perform in situ argon ion etching provides a means for characterizing the elemental composition as a function of depth in the sample. Sensitivity factors are applied to the raw data to yield atomic concentrations. 

The strengths of RBS are in determining the concentration-depth profiles of relatively heavy elements in a polymer matrix largely composed of elements of low atomic number. This is because the sensitivity of the technique is determined by the Rutherford scattering cross sections, which are approximately proportional to the square of the atomic number of the target nuclei. The depth resolution of the technique is generally limited by the energy resolution of the detection system and typically is of the order of 300 A for polymer materials. One of the particularly attractive aspects of the technique is the reliability and... 

Ion implants, particularly for semiconductor materials, are widely used as standards in SIMS. Implants can be made with accurate and controllable dopant concentrations. The implant concentration is known in atom/cm. Depth profiling the implant to obtain the integrated ion signal of the implanted dopant and accurately measuring the depth allows for the conversion of atom/cm to atom/cm. This assumes a constant sputtering rate through the depth profile, SIMS ion intensities linear with concentration, and an accurate depth measurement of the analysis crater [28]. 

SIMS is based on the emission of atomic and molecular particles (.secondary ions) from the surface of a solid under bombardment with primary particles (ions). Under DSIMS conditions, the erosion rate is of the order of mono-layers) per second and concentration depth profiling can be performed with high spectrometric sensitivity, in favorable cases down to the ppb level. The. sensitivity of SIMS is element dependent and varies from I ppb to 100 ppm. and the technique is therefore used for trace and ultratrace analysis. 

Three common uses of RBS analysis exist quantitative depth profiling, areal concentration measurements (atoms/cm ), and crystal quality and impurity lattice site analysis. Its primary application is quantitative depth profiling of semiconductor thin films and multilayered structures. It is also used to measure contaminants and to study crystal structures, also primarily in semiconductor materials. Other applications include depth profilii of polymers, high-T superconductors, optical coatings, and catalyst particles. ... 

Finally, the fundamental unit of concentration obtained by RBS is in atoms/cm or concentration in the sample-versus-bachscattering energy loss. To convert the profile of a backscattering peak into a depth profile it is necessary to assume a density for the material being profiled. For single-element films, such as Si, Ti, and W, an elemental density can be assumed for the film and an accurate thickness is obtained. In the case of multi-elemental films with an unknown density, a density for the film is calculated by summing the density of each element, normalized to its concentration. The accuracy of this assumption is usually within 25%, but for some cases the actual density of the film may vary by as much as 50%— 100% from the assumed density. It is useful to note that ... 

Several features of ISS quantitative analysis should be noted. First of all, the relative sensitivities for the elements increase monotonically with mass. Essentially none of the other surface spectroscopies exhibit this simplicity. Because of this simple relationship, it is possible to mathematically manipulate the entire ISS spectrum such that the signal intensity is a direct quantitative representation of the surface. This is illustrated in Figure 5, which shows a depth profile of clean electrical connector pins. Atomic concentration can be read roughly as atomic percent direcdy from the approximate scale at the left. 

The data chain of the collected atoms can be converted to a one-dimensional composition-depth profile. The depth profile shows an average concentration of solute within the aperture, and there is always a possibility that the chemical information from the selected area is a convolution of more than one phase, as indicated diagrammatically in Figure 1.5, which represents the analysis of a FIM specimen containing second phase particles and also an interface across which there is a change of composition. 

Dynamic SIMS. SIMS depth profiling is normally used to determine the concentrations in the range 1013-102°atoms/cm3 lying at depths of up to 10 pm. 

NRA is a powerful method of obtaining concentration versus depth profiles of labelled polymer chains in films up to several microns thick with a spatial resolution of down to a few nanometres. This involves the detection of gamma rays produced by irradiation by energetic ions to induce a resonant nuclear reaction at various depths in the sample. In order to avoid permanent radioactivity in the specimen, the energy of the projectile is maintained at a relatively low value. Due to the large coulomb barrier around heavy nuclei, only light nuclei may be easily identified (atomic mass < 30). 

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