Deterioration Of Depth Resolution Research Articles

Wavelength scanning interferometry using multiple light sources

A novel sensing method is proposed for wavelength scanning interferometry using multiple tunable light sources. As it is well known, a deterioration of depth resolution usually occurs when multiple phase intervals, corresponding to the multiple tunable light sources, are used for distance measurement purposes. It is shown here, that it is possible to regain depth resolution characteristics of a complete scan by means of a temporal phase unwrapping extrapolation method. With the proposed method, the resulting phase differences among multiple phase intervals can be successfully unwrapped to find out the intermediate phase. This effectively allows the application of whole-scan phase sensing for distance measurement using reduced scanning intervals, increased speed, and improved depth detection.

Ion-induced electron emission ERDA with a nuclear microprobe

With intention to be used for the 3D analysis of hydrogen, a new ion-induced electron emission (IEE) ERDA system has been installed on the nuclear microprobe. A better depth resolution has been obtained with IEE particle identification system when compared to conventional ERDA systems that use stopping foil. Spectra of the forward scattered ions as well as the recoiled atoms are collected using the same particle detector. This simplifies normalization needed for quantitative analysis without the use of an additional detector. However, well defined but rather small solid angle of the IEE detector requires higher ion beam currents if sufficient sensitivity for H detection needs to be achieved. High beam currents focused to several micrometer spot size lead to rather high current densities and increased probability of H loss from the sample, which may limit the achievable sensitivity. By positioning IEE ERDA system at 45° instead of 30°, as well as by using heavier ions (O ions instead of He), two orders of magnitude better sensitivity can be obtained without a significant deterioration of depth resolution due to the increased recoil cross-section. In this work, several different sample types containing H have been studied. The capabilities of system for 3D imaging of H in samples have been demonstrated.

Correction for the loss of depth resolution with accurate depth calibration when profiling with Cs + at angles of incidence above 50° to normal

The deterioration of depth resolution with depth was investigated by profiling a B delta-layer resolution standard, with Cs + at glancing impact angles. The deterioration was eliminated for 1 keV Cs + at 60° using a trapezoidal scan correction, available on the ATOMIKA 4500. The SIMS responses were partially deconvolved by fitting a sum of analytical response functions. A depth scale was assigned using a two point fit to XTEM data. The post-calibration peak positions agree with the XTEM to within 0.34 nm.

Factors causing deterioration of depth resolution in Auger electron spectroscopy depth profiling of multilayered systems

We have investigated the effects of the sputter-induced roughness on the depth resolution Δz and on the interface position zc obtained by Auger electron spectroscopy (AES) depth profiling of a Ni/Cr multilayer and of an AlAs/GaAs superlattice. We also correlated the escape depth λ with Δz and zc. First, the sputter-induced roughness was evaluated by atomic force microscopy (AFM). Second, both Δz and zc were evaluated quantitatively using an error function fitting method of AES, depth profiles. The AFM observation shows that the height distribution of sputter-induced roughness is approximated to first order by a Gaussian distribution and is correlated with the resolution function which depends strongly on the sputter-induced roughness. The precise measured height distribution is, however, somewhat different from the Gaussian distribution. The computational simulation using the error function approximation fitting is in good agreement with experimental results. We also estimated the escape depth λ using the same computational simulation results. The results indicate that the error function approximation fitting is useful to evaluate Δz and zc as a practical method, but anomalies of Δz and zc are discernable at the specific interface. These anomalies are assumed to come from preferential sputtering.

Depth profiling with sample rotation: Capabilities and limitations

AbstractDepth profiling with sample rotation has become a frequently applied method to obtain the in‐depth distribution of composition in thin films with high resolution. Sample rotation strongly diminishes the effect of local variations of the ion beam intensity and of the sputtering yield, which are the main cause of increasing surface roughness during sputtering and therefore of profile broadening. Capabilities and limitations of rotational profiling are considered with respect to its dependence on various parameters, such as inhomogeneity of the ion beam instensity, ion incidence angle and rotation speed. In particular, it is shown that non‐linear components and excentric movement of the sample lead to periodic features in the profile and to non‐vanishing degradation of depth resolution with depth. For smooth sample surfaces, depth resolution improves with increasing ion incidence angle but is much less pronounced, as for profiling with stationary samples. For originally rough surfaces, the deterioration of depth resolution with increasing ion incidence angle is considerably reduced. The key parameter for optimized conditions in rotational profiling is the ratio of sputtering rate and rotation speed. The minimum necessary, useful rotation speed depends on this ratio and on the magnitude of other contributions to the depth resolution that are not affected by sample rotation.

Depth resolution for sputter sectioning of Ni

The depth resolution function for sputter sectioning of nickel was quantitatively investigated with respect to its dependence on primary ion energy, current density, and on temperature. The depth resolution is independent of current density and of temperature below 500 K and worsens with increasing sputter energy. At elevated temperatures a further deterioration of depth resolution was observed which could be quantitatively attributed to radiation-enhanced diffusion. The results will be discussed within a diffusion model of depth resolution and the contributions of atomic mixing and surface roughening will be separated.

The depth resolution of sputter profiling

It is shown that the bulk radiation damage accompanying sputtering events sets ultimate limits to the depth resolution attainable in sputter profiling. These limits have been reached in a few cases but most published experimental resolutions are dominated either by instrumental effects or deterioration of depth resolution caused by surface-topography changes. The radiation-damage induced mixing is called “cascade mixing”. Guidelines for selection of projectile species and energies to minimize such mixing are given and numerical estimates for attainable depth resolutions are presented. Finally, the influence of cascade mixing is assessed relative to that of recoil implantation.