Sputter profile

Yes, over the top 50 A greater depths require sputter profiling... 

Figure 5.37. Average sputter profile from ten grain boundaries in temper brittle rotor steel using 600 eV argon ions. (After Seah 1980, Crown Copyright.)...

Certainly, the inherent lack of depth resolution of the BMP techniques minimizes the utility of sputter profiling combined with BMP analysis. However, gross comparisons of the exterior versus interior composition can be obtained by recording X-ray spectra before and after a minimum of several thousand angstroms of material are sputtered from the particle surface (13,44). Similarly, BSCA is not very suitable when used in conjunction with sputter profiling for reasons that include a) data acquisition rates are very slow, b) potential chemical information is lost since sputtering may alter the chemical forms of the elements present, and c) individual particles cannot be depth profiled (11, 14, 26). 

The results of XPS combined with Ar" -sputtering on a VlNb imp.-sample are shown in Figure 4. In this figure, sputtering profiles are shown for a fresh catalyst and for one which had been used for 300h at 510 °C (at this temperature 100% oxygen conversion was reached, no deactivation was observed). Since XRF showed that no vanadium was lost from the catalyst, it can be concluded that in the fresh catalyst, vanadium is present in a homogeneous layer which is at least 40-80 A thick. Upon use, sub-surface vanadium has diffused into the bulk of the catalyst, while the surface concentration of vanadium remains the same. The vanadium at the surface was found to be mostly V " in both the fresh and the used catalyst. Because of the low concentrations of vanadium at the surface and interference from the Ols peak, the presence of small amounts of reduced vanadium cannot be excluded. 

Figure 4 Ar -sputtering profiles as determined by XPS for a VlNb imp.-catalyst. Sputtering rate 1-2 A/min.

Spectra taken during the Auger sputter profile were transformed into a data matrix and treated by the PHI-MATLAB , version 4.0, software. Each element was treated separately, that is the number of matrices was the same as the number of significant elements, and each matrix was completely independent of the others. The number of factors used for reconstruction was the one predicted by the minimum of the indicator function (IND). Unless specified, no mathematical treatment was performed on the data (differentiation, smoothing). 

The determination of the true principal components was then performed by a sequential target transformation. No pure spectra were added to the data set so that the choice of the single components had to be made in the experimental set of spectra on the base of XRD, RHEED, and the compositions extracted from the sputter profiles. The spectra chosen to be the eigenvectors (i.e. the pure components), were then those with the smallest spoil. 

Figure 26.4(a) presents the usual AES sputter profile of the sample. Two main areas can be distinguished behind the contamination layer. First, the film area which is characterized by constant levels of W and C (40 mol% carbon). Second, the substrate area, where the signal of C decreases and the level of W increases. 

Table 26.1 Number of factors (NF) detected as a function of the number of points used to differentiate the spectra (Ndif) for the treatment of the Auger sputter profile of a J3-WC, film deposited on tungsten. (Ndif = 0 means no differentiation)...

Chemical differences in the Auger peaks are also present in the a-WCl a-W2C sample. Although the usual sputter profile does not give information about the distribution of chemical states in the sample, analysis of the W and C components suggests that besides the surface component, two different carbide components are present. The behaviour of the two bulk components of W and C is the same the first is located near the surface and decreases deeper into the sample the second increases to become the most important in the deeper part of the sample. RHEED analysis indicates a-WC but the depth sensitivity of this method is about 5-10 nm. XRD analysis indicates the presence of a-WC,a-W2C and W with a depth sensitivity of a few pm. Thus, the first bulk component of W and C can be identified as a-WC and the second as a-W2C. The overall sample consists of a contamination layer, followed by a thin layer of a-WC on top of the a-W2C phase. 

The model samples were synthesized and characterized in the Analytical Chemistry Dept of the Universite Libre de Bruxelles under the direction of Prof. C. Buess F.R. is grateful to P. Kons and E. Silberberg for the preparation of the samples. AES sputter profiles and factor analysis was performed at the Vrije Universiteit Brussel, Dept, of Metallurgy, Electrochemistry and Materials Science. Many thanks to Prof. Vereecken, Hubin and Terryn for the discussions concerning the results and to N. Roose and O. Steenhaut for the Auger sputter profiles. The technical collaboration of L. Binst (ULB) is greatly appreciated. 

A new method of interpreting Auger electron spectroscopy (AES) sputter profiles of transition metal carbides and nitrides is proposed. It is shown that the chemical information hidden in the shape of the peaks, and usually neglected in depth profiles, can be successfully extracted by factor analysis (FA). The various carbide and nitride phases of model samples were separated by application of FA to the spectra recorded during AES depth profiles. The different chemical states of carbon, nitrogen and metal were clearly identified. 

Complementary data was obtained by other surface analysis techniques. In one study sputter profiling of Ga, As and 0 by AES and XPS showed a deficiency of As in plasma grown oxides... 

Consideration of Surface Tool Concerns. Reasonably fast data acquisition, small probing beam size (allowing both faster sputter profiling and spatial resolution) and semiquantitative data analysis, give AES a primary role in each of these two experiments. 

Figure 12. Auger sputter profile of insulating film formed during chromating of male PCB connector. Key -A- chromium -A-, copper , oxygen and -O-, carbon. (Reproduced, with permission, from Ref. 50. Copyright 1980, North-Holland Publishing Co.)...

An excellent way to create standards is ion implantation of the elements of interest into the matrix. This works exceptionally well for semiconductors since one can usually start with high-purity single-crystal materials that represent the matrix of interest. Also the use of Eq. (4.8) is well suited for this purpose since ion implanters usually quote doses in atoms per square centimeter. However, Eq. (4.5) serves just as well by converting the matrix concentration to atoms per cubic centimeter. In this procedure, the implant profile is sputtered through, the implant element secondary ions and the matrix element secondary ions are each summed, and the depth of the sputter profile is determined, usually by using a stylus profilome-ter. The sensitivity factor is then calculated from... 

Sputter profiles of the samples OllO and ArH68 (see abbreviation in Table 33.4) are shown in Figure 33.8. Figure 33.8a indicates that (Ar- -H2) plasma treatment applied wasn t enough to remove all oxides, and a significant level of O2 was found... 

Fig. 2 shows the sputter profile of the model catalyst after a 60 minute reduction at 500 K. Before reduction, one does not observe the presence of oxygen and manganese on the nickel surface. After reduction, the segregation of oxygen and manganese is apparent. 

Figure 2. Sputter profile of a 150X Ni/MnO model catalyst after 60 minutes of reduction at 500 K.

Andersen, H.H. The depth resolution of sputter profiling. Appl. Phys. 18, 131 (1979) Cheng, Y.-T. Thermodynamic and fractal geometric aspects of ion-solid interactions. Mater. Sci. Rep. 5, 45 (1990)... 

Fig. 11. Auger sputter profiles (Auger amplitude vs. ion-bombardment time) for unreduced (open points, dashed curves) and reduced (solid points and curves) Rh/(single crystal) Ti02 model catalysts. Curves for Ti and O have been shifted up for clarity. (After Ref. 27.)...

---