ToF SIMS

The use of separation techniques, such as gel permeation and high pressure Hquid chromatography interfaced with sensitive, silicon-specific aas or ICP detectors, has been particularly advantageous for the analysis of siUcones in environmental extracts (469,483—486). Supercritical fluid chromatography coupled with various detection devices is effective for the separation of siUcone oligomers that have molecular weights less than 3000 Da. Time-of-flight secondary ion mass spectrometry (TOF-sims) is appHcable up to 10,000 Da (487). 

Perkin-Elmer Physical Electronics Division, Eden Prairie, MN, model 7000 SALI/TOF-SIMS instrument. 

Dynamic SIMS Static SIMS Q-SIMS Magnetic SIMS Sector SIMS TOF-SIMS PISIMS... 

Useful yield provides an overall measure of the extent to which the sputtered material is used for analysis. It is a quantity employed to estimate the sensitivity of the mass spectrometric method. Values of Y (X (A)) for elements typically range from 10 to 10 in TOF SIMS. The number of sputtered particles A per incident primary ion (sputtering yield) can be measured from elemental and multielemental standards under different operational conditions and can, therefore, by judicious interpolation between standards, be estimated with reasonable accuracy for the material being analyzed. 

Fig. 3.5. High-mass-resolution TOF SIMS spectrum of a contaminated Si wafer.

Fig. 3.10. Positive TOF SIMS spectra from the defective area and from a spot remote from the defect [3.19].

Fig. 3.16. High-resolution TOF SIMS images of silver bromide and silver chloride crystals.

In recent years TOF SIMS has also proved to he a very powerful tool for ultra-shallow depth profiling, having the advantage of simultaneously detecting all elements of interest. The dual beam mode [3.41], in particular, (see Sect. 3.2.2.1) enables optimized depth resolution, because sputtering conditions can be independently optimized. 

Figure 3.17 depicts an ultra-shallow TOF SIMS depth profile of a 100-eV B-implant in Si, capped with 17.3 nm Si. The measurement was performed with 600-eV SF5-sputtering and with 02-flooding. The original wafer surface, into which the B was implanted, is indicated by the maxima of the alkali- and C-signals. Because of these contaminants, a minimum is observed in the °Si-signal. The dynamic range of the B-profile is more than 3.5 decades and the depth resolution is <0.5 nm. 

In TOF-SIMS, the source of primary ions is pulsed at a rate of a few kHz. The pulse width is on the order of 1 ns. Secondary ions ejected from the sample surface are accelerated through a potential V and then drift through a field-free TOF analyzer with different velocities, depending on their masses. The drift velocity of an ion with charge-to-mass ratio zjm can be determined from the expression ... 

Fig. 44. Positive TOF-SIMS spectra of plasma polymerized acetylene film after reaction with a model rubber compound for (A) 0 and (B) 15 min. Positive TOF-SIMS spectra of plasma polymerized acetylene film after reaction with a model rubber compound for (C) 35 and (D) 65 min. Reproduced by permission of Gordon and Breach Science Publishers from Ref. [56].

Fitzpatrick and Watts [57] also applied imaging TOF-SIMS to deteiTnine the failure mechanisms of adhesively bonded, phosphated hot-dipped galvanized steel... 

Fig. 46. Schematic drawing of the failure surface of a lap joint prepared from hot-dipped galvanized steel substrates (top) and TOF-SIMS line scans showing the distribution of several mass numbers as a function of distance from the edge of the overlap (bottom). Reproduced by permission of John Wiley and Sons from Ref. [57].

Fig. 48. TOF-SIMS image showing that ions characteristic of the polymer are also found in some areas within the initiation zone. Image shows (A) total counts, (B) m/z = 88, (C) tn/z = I1 + 9 and (D) in/z = 604-43. Reproduced by permission of John Wiley and Sons from Ref [57].

Fig. 49. TOF-SIMS images showing that the cation-rich areas in the initiation zone do not corre.spond to polymer-rich areas (A) mjz. = 88 on 24 (B) tnjz = 77 + 91 on 24. Reproduced by permission of John Wiley and Sons from Ref. [571.

Brewis et al. used TOF-SIMS to determine the surface composition of hydrocarbon polymers after electrochemical pretreatment with nitric acid alone or in the presence of silver ions [58J. AgNO was generated by electrolysis of a 0.1 M solution of silver nitrate in 3.25 M nitric acid in the anode compartment of a... 

The results obtained by Brewis et al. demonstrate an important feature of TOF-SIMS and that is the ultra-high mass resolution of the teehnique. Without sueh high speetral resolution, it would be impossible to resolve peaks sueh as those shown in Fig. 50 into eomponents and a great deal of information about the oxidation proeess would be unavailable. 

Negative TOF-SIMS speetra of PMDA/ODA polyimide before and after plasma treatment are shown in Fig. 53. The speetra generally show inereas-ing fragmentation as a function of plasma treatment time. This tendency was especially evident for the peak at m/z = 215 (PMDA + H ). 

TOF-SIMS spectra supported the suggestion that eopper interacted with untreated polyimide through the imide earbonyl group as shown in Fig. 27. Numer-... 

After metallization of the plasma-modified polyimide, there were a number of peaks in the TOF-SIMS spectra that confirmed the existence of Cu-N bonds as required by the proposed reaction mechanism (see Fig. 28). The most significant... 

Fig. 53. Negative TOF-SIMS spectra of PMDA/ODA polyimide (a) before plasma treatment and after plasma treatment for (b) 1 s and (c) 60 s. Reproduced by permission of John Wiley and Sons from Ref. 33).

Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS)... 

TOF-SIMS was pioneered by Professor Benninghoven and his group in the early 1980s [109], originally developed in static mode and applied for the chemical analysis (elemental as well as molecular) of the uppermost monolayer of solid surfaces [110]. By the introduction and further development of the dual beam technique, the TOF-SIMS can... 

State-of-the-art TOF-SIMS instruments feature surface sensitivities well below one ppm of a mono layer, mass resolutions well above 10,000, mass accuracies in the ppm range, and lateral and depth resolutions below 100 nm and 1 nm, respectively. They can be applied to a wide variety of materials, all kinds of sample geometries, and to both conductors and insulators without requiring any sample preparation or pretreatment. TOF-SIMS combines high lateral and depth resolution with the extreme sensitivity and variety of information supplied by mass spectrometry (all elements, isotopes, molecules). This combination makes TOF-SIMS a unique technique for surface and thin film analysis, supplying information which is inaccessible by any other surface analytical technique, for example EDX, AES, or XPS. 

TOF-SIMS can be applied to identify a variety of molecular fragments, originating from various molecular surface contaminations. It also can be used to determine metal trace concentrations at the surface. The use of an additional high current sputter ion source allows the fast erosion of the sample. By continuously probing the surface composition at the actual crater bottom by the analytical primary ion beam, multi element depth profiles in well defined surface areas can be determined. TOF-SIMS has become an indispensable analytical technique in modem microelectronics, in particular for elemental and molecular surface mapping and for multielement shallow depth profiling. 

Today the successful application of TOF-SIMS in chemistry and material sciences covers all kinds of organic and inorganic materials—functionalized surfaces as well as mono-molecular or multilayer coatings with lateral structures down to the 50 nm range. TOF-SIMS is here applied in the... 

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