Depth Profiling Of Thin Films Research Articles

X-ray diffraction study of concentration depth profiles of binary alloy coatings during thermal diffusion: application to brass coating

Using the Houska method based on X-ray diffraction-line profile analysis, new mathematical treatments are proposed to compute directly the concentration depth profile of thin films obtained by diffusion. As an example, concentration depth profiles of a brass layer have been studied during the thermal diffusion process. This nondestructive method is fast (a few minutes) and allows the sample to be used for complementary analysis if necessary.

Sputter Depth Profiling of Thin Films

An outline of the fundamental principles of compositional depth profiling of thin films by sputtering is given, emphasizing first the importance of optimized experimental conditions in obtaining high resolution depth profiles, in particular sample rotation and low energy primary ions. Based on former and recent developments, the basic approach to profile evaluation and to quantification is briefly reviewed. The fundamental roles of depth resolution and of the depth resolution function are elucidated, including experimental determination and theoretical modeling of the latter by the three fundamental parameters atomic mixing, surface roughness and information depth (MRI-model). Typical application examples for profile reconstruction in depth profiling are presented.

Examples for the improvements in AES depth profiling of multilayer thin film systems by application of factor analysis data evaluation.

Factor analysis has proved to be a powerful tool for the full exploitation of the chemical information included in the peak shapes and peak positions of spectra measured by AES depth profiling. Due to its ability to extract the number of independent chemical components, their spectra and their depth distributions, its information content exceeds the one of the usual peak-to-peak height evaluation of AES depth profile data. Using modern software with a graphically interactive user interface the analyst is put into a position, where he can work with Factor Analysis on a physically intuitive level despite of all the matrix algebra mathematics which it is based upon. The progress brought about by Factor Analysis to AES depth profiles of thin films is demonstrated by the analysis of two thin film systems. The first one is a Pt/Ti metallisation used as bottom electrode for ferroelectric thin films, the second one is a multilayer system where a Ti silicide formation of buried Ti/Si bilayers has been induced. Both examples show that Factor Analysis evaluation of AES depth profile data is capable to give access to stoichiometry information and to reveal interfacial layer phases, information which is hardly obtained from the conventional peak-to-peak height data evaluation.

Nondestructive Optical Depth Profiling in Thin Films through Robust Inversion of the Laser Photopyroelectric Effect Impulse Response

The laser photopyroelectric effect measures an optical absorption depth profile in a thin film through the spatial dependence of a heat flux source established below the film surface by light absorption from a short optical pulse. In this work, inverse depth profile reconstruction was achieved by means of an inverse method based on the expectation-minimum principle (as reported in a companion paper), applied in conjunction with a constrained least-squares minimization, to invert the photopyroelectric theory. This method and zero-order Tikhonov regularization were applied to the inversion of experimental photopyroelectric data obtained from samples with a variety of discrete and continuous depth dependences of optical absorption. While both methods were found to deliver stable and accurate performance under experimental conditions, the method based on the constrained expectation-minimum principle was found to exhibit improved resolution and robustness over zero-order Tikhonov regularization.

Maximum entropy reconstruction of compositional depth profiles from electron probe microanalysis data

SummaryElectron probe microanalysis (EPMA) is a powerful method for the quantitative determination of the elemental composition of micro‐regions of a sample surface. Here, we report on the development of a method of reconstructing compositional depth profiles in thin films from EPMA data measured over a range of electron beam energies, using maximum entropy data processing. The method gives quantitative information on film compositions up to approximately 1 μm in depth, with a lateral spatial resolution of approximately 1 μm. The method is tested using both simulated data and measured experimental data from well‐characterized model sample structures.

Examples for the improvements in AES depth profiling of multilayer thin film systems by application of factor analysis data evaluation

Factor Analysis has proved to be a powerful tool for the full exploitation of the chemical information included in the peak shapes and peak positions of spectra measured by AES depth profiling. Due to its ability to extract the number of independent chemical components, their spectra and their depth distributions, its information content exceeds the one of the usual peak-to-peak height evaluation of AES depth profile data. Using modern software with a graphically interactive user interface the analyst is put into a position, where he can work with Factor Analysis on a physically intuitive level despite of all the matrix algebra mathematics which it is based upon. The progress brought about by Factor Analysis to AES depth profiles of thin films is demonstrated by the analysis of two thin film systems. The first one is a Pt/Ti metallisation used as bottom electrode for ferroelectric thin films, the second one is multilayer system where a Ti silicide formation of burried Ti/Si bilayers has been induced. Both examples show that Factor Analysis evaluation of AES depth profile data is capable to give access to stoichiometry information and to reveal interfacial layer phases, information which is hardly obtained from the conventional peak-to-peak height data evaluation.

In search of the ultimate experiment for quantitative depth profile analysis in glow discharge optical emission spectrometry. Part I: Calibration curves

AbstractThis is the first part of our search for an experiment that will show definitively which is the best method for quantitative glow discharge optical emission spectrometry (GDOES). Three empirical methods for producing quantitative depth profiles from GDOES data are examined: the SIMR method, the IRSID method and the most recent BHP method. All three methods give worthwhile quantitative depth profiles of thin films and coated materials. The first two methods assume that pressure does not have a significant effect on emission yield, while the third method assumes that pressure is the only significant parameter affecting emission yield. The different approaches therefore imply very different physical processes inside the lamp and it is essential for further development of quantitative GDOES that the best approach be determined. Depth profiling in GDOES is, in principle, simply bulk analysis repeated over and over as a function of depth. The three methods are therefore tested here in their ability to do bulk calibration in a range of steels and zinc–aluminium alloy standards, all at constant current. All methods worked well for steel, while the best calibration curves in zinc–aluminium alloys were obtained with pressure‐corrected IRSID and SIMR methods or a voltage‐corrected BHP method. The results suggest that emission yields depend on both voltage and pressure (and presumably current, which was not tested here in Part I).

Optical Depth Profiling of Thin Films by Impulse Mirage Effect Spectroscopy. Part II: Measurements Using Wide-Band Modulated Excitation

Laser mirage effect (photothermal deflection) spectroscopy was used in this work to determine depth profiles of the optical absorptivity of thin polymer films whose thermal properties were approximately invariant with depth. A variety of well-characterized laminates and continuous samples were examined. The key experimental variables affecting optical depth profile resolution were the offset of the probe beam above the surface, the thermal properties of the fluid medium in which optical deflection occurs, and the relative depths of the subsurface features to be resolved. The accuracy of the experimental signal was found to depend on several key factors which included the electrical bandwidth of the electronic detection system and the linearity of the photothermal deflection signal. Experimental procedures for ensuring quantitative signal recovery are described, and a theoretical interpretation of the depth dependence of the mirage signal was made by means of a model presented in a companion paper.

Optical Depth Profiling of Thin Films by Impulse Mirage Effect Spectroscopy. Part I: Theory

Impulse mirage effect/photothermal deflection spectrometry may be used to detect depth-dependent optical absorption in materials, through the time dependence of the probe beam deflection signal occurring in response to sample irradiation with a short excitation pulse. In this work a theoretical expression was derived for the normal and transverse photothermal deflection signals which occur in a sample with homogeneous thermal properties but where optical absorptivity varies with depth from the surface. An analytical solution of moderate simplicity is obtained for several cases of experimental interest, with three-dimensional heat conduction effects included. The depth profile resolution obtained with the mirage effect method is critically dependent on the distance between the sample layer probed and the offset position of the probe beam in the fluid layer above the sample. Saturation conditions and conditions for obtaining optimal depth resolution of continuous and discrete optical profiles are examined in detail.

Application of factor analysis to Auger crater-edge profiling

Factor analysis is applied to the Auger crater-edge profile of a palladium/hydrogenated amorphous silicon layered structure. The results show, apart of a considerable improvement in interface determination, new information not obtainable by the conventional Auger depth profiling technique, which makes this procedure extremely useful for thin film depth profiling.

Depth Profiling in Thin Films by Grazing Incidence Diffraction using Synchrotron Radiation

Depth Profiling in Thin Films by Grazing Incidence Diffraction using Synchrotron Radiation

Significance of sample rotation in auger electronspectroscopy sputter depth profiling of thin films

Sample rotation has always been present in surface analysis techniques when selecting the place to be analysed, ex situ and more recently in situ in the spectrometers' ultrahigh vacuum chambers. However, in this work the advantage of sample rotation during Auger electron spectroscopy sputter depth profiling is shown by a systematic investigation of multilayer Cr/Ni thin films and some other samples from everyday analytical practice. The sample rotation reduced, or—at a favourable sample sputtering geometry, i.e. at a large ion incidence angle—even eliminated some ion beam and sample effects, which optimizes the depth resolution and enables us to keep it constant also in the depth of multicrystalline thin film structures. The more uniform ion sputtering rate is achieved by averaging local incidence angles and by making the ions strike the sample from different sides, as in the case of a multidirectional ion source; all these suppress the sputter-induced roughness, polish the initially rough surfaces and essentially decrease the ion-beam-angle-dependent effects, namely sputtering yield, preferential and selective sputtering as well as the effects caused by the non-homogeneity of the ion beam. The combination of sample rotation and a large ion incidence angle ( > 80°) also reduces other effects on Δ z such as ion mass and energy influence and ion-beam-induced transport processes perpendicular to the sample surface, while a beneficial influence on the reduction in the beam effects on compound samples, such as nitrides and oxides, was also observed; this should be investigated in more detail.

Structural depth profiling of iron oxide thin films using grazing incidence asymmetric Bragg x-ray diffraction

X-ray depth profiling in a grazing incidence asymmetric Bragg geometry is used to obtain the depth-dependent structure of a nominally γ-Fe2O3 thin film, which was oxidized from an Fe3O4 film. As the incidence angle is varied from angles less than the critical angle for total external reflection to angles greater than the critical angle, the x-ray penetration depth increases from about 20 to several thousand angstroms. The observed diffraction originates from this region of variable depth and a structural depth profile of the thin film can be obtained by measuring the diffraction pattern as a function of incidence angle. The iron oxide film is found to have a 45-Å-thick surface layer of α-Fe2O3; beneath this layer the film is predominantly γ-Fe2O3 but also contains about 2.6 at. % α-Fe2O3. These data, together with previous chemical and magnetic data, suggest that during oxidation of the Fe3O4 film the surface layer forms by the outward diffusion of Fe ions and their subsequent oxidization to α-Fe2O3. One possible explanation of the 2.6% α-Fe2O3 in the bulk of the film is that the Fe3O4 film contains small nuclei of material that are structurally similar to α-Fe2O3. During the oxidation to form γ-Fe2O3, these then grow to form small grains of α-Fe2O3 that are observed.

Surface and Ultra-Thin Film Characterization by Grazing-Incidence Asymmetric Bragg Diffraction

AbstractAn effective technique using grazing-incidence X-rays and asymmetric-Bragg diffraction (GIABD) for the characterization of crystalline phases on surfaces and structural depth-profiles in thin films is described. The application of the GIABD using both X-ray and synchrotron radiation sources for the analysis of an iron-oxide magnetic thin film previously reported to have an unexpected magnetically-dead layer is discussed. The X-ray diffraction analysis using the GIABD and the conventional θ-2θ scanning techniques detected an anti-ferromagnetic hexagonal α-Fe2O3 on the surface and a ferromagnetic tetragonal γ-Fe2O3 in the bulk of the film, respectively. The synchrotron diffraction analysis using incident angles below and above the critical angle of total reflection quantitatively determined the structural depth-profiles of α-Fe2O3 and γ-Fe2O3 in the film.

Study of ion beam induced mixing during sputter depth profiling of thin films by LEIS

Ion beam induced mixing during sputter depth profiling was studied for tantalum and lead marker layers in silicon with 5 keV neon by low energy ion scattering spectroscopy (LEIS). The diffusion approximation was used to calculate mixing efficiency values ( D/ JF d ) from decay length measurements. The mixing efficiency values are shown to be sensitive to the preferential sputtering which takes place during ion bombardment. TRIM simulations for Ta/Si are shown to agree with the experimentally determined value for preferential sputtering. Depth profiling at high temperature is shown to separate some of the interrelated mixing mechanisms of radiation enhanced diffusion (RED) and radiation induced segregation (RIS). For the Ta/Si system the mixing efficiency value is observed to remain constant regardless of the 5 keV inert gas ion beam used for depth profiling.

Sputter yields of ammonium chloride and solid glycerol

AbstractWe have measured the sputtering yields of ammonium chloride and of frozen glycerol films under 8 keV Ar+˙ bombardment using a thin film depth profiling technique. The sputtering yield of ammonium chloride was 34±3 molecules (NH4Cl)/ion; for frozen glycerol the sputter yield was 54±9 molecules/ion. The results constrain possible mechanisms of damage suppression in organic secondary ion mass spectrometry.

TiN coatings on M2 steel produced by plasma-assisted chemical vapor deposition

TiN films were deposited onto M2 steel using plasma-assisted chemical vapor deposition. TiCl 4, N 2 and H 2 were the reactant gases used at 1 Torr. A plasma was essential for TiN formation at 500 °C and below. At 500 °C, a highly crystalline stoichiometric TiN coating was formed with a (200) surface orientation and having a columnar zone 2 grain structure. At 400 °C, a zone T structure with an additional amorphous component was observed. Both types of films had good adherence with scratch adhesion critical loads comparable with values for sputtered TiN. The zone 2 films failed by cracking and occasional chipping within the coating. The zone T films failed by cracking in the coating and by chipping, within the coating and by the interface. Auger electron spectroscopy depth profiling of thin films indicates that the interface was sharp and no accumulation of chlorine is observed. Auger electron spectroscopy and scanning electron microscopy suggest that distinct TiN islands or nuclei were present in the early stages of growth. The use of an organometallic source, titanium tetrakis-(dimethylamide), resulted in the formation of carbonitride powders.

Sputter depth profiling of thin films with LEIS and LENRS

Low energy ion scattering spectroscopy (LEIS) and low energy negative recoil spectroscopy (LENRS) have been used to sputter depth profile Fe/Ta thin films on Si. The advantages of the techniques for routine depth profile analysis — good depth resolution and sensitivity to both high and low mass elements through combined LEIS and LENRS are illustrated.

Hydrogen depth profile in sputtered Cu xZr 1-x amorphous alloys studied by nuclear reaction analysis. Evolution as a function of annealing temperature.

Hydrogen depth profiles in thin films of sputtered Cu xZr 1-x amorphous alloys have been measured using the resonant nuclear reaction 1H ( 15N, αγ) 12C. In Cu 0.3Zr 0.7, Cu 0.4Zr 0.6 and Cu 0.5Zr 0.5 alloys the hydrogen bulk concentrations expressed bythe atomic ratio H/Zr are respectively 0.26, 0.45 and 0.80. Hydrogen mobility under beam impact is observed at both interfaces (air-film, film-substrate) and in the molybdenum substrate. Evolution of the hydrogen profiles has been followed as a function of annealing temperature. No departure of hydrogen is observed below 520K; at temperatures close to the crystallisation, the hydrogen content remains high, in the 20–30 at % range. These results are discussed in correlation with physical properties of the alloys.

Depth profiling of thin films using a Grimm-type glow discharge lamp

A Grimm-type glow discharge lamp was used for depth profiling of thin films. The sample surface was etched by cathodic sputtering at a rate of 1–100 nm s −1. Optical emission signals from the discharge were monitored with an optical spectrometer which yielded a depth profile of the chemical composition. The detectability is typically around 0.01 wt.%. For depth calibration purposes, the sputtering rate as a function of the discharge parameters was determined in a number of pure metals, alloys and copper oxide. The possibility of quantitative determinations is discussed. It is suggested that the relative intensities of the emission lines can be empirically described as functions of the discharge parameters and the sputtering rate. This makes it possible to use existing spectroscopic standards and a matrix correction procedure for quantitative analysis.