SIMS depth profiling

ToF SIMS separated ion beams are used for etching and analysis purposes. A depth profile is obtained by periodically switching between etching and analysis. In addition, the pulse mode operation in ToF SIMS further slows down the process. ToF SIMS, however, can be used to obtain more accurate depth profiles if time is not a concern. The next section introduces depth profiling based on the dynamic SIMS technique, which is very popular in analyzing electronic materials. 

The mass spectra often contain peaks of adventitious ions such as Na. K. AP, C-, 0-. OH-, Cl- [126, 127], 

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Figure 7 SIMS depth profile of Si implanted into a 1- im layer of Al on a silicon substrate for 6-keV O2 bombardment The substrate is B doped.

Figure 8 SIMS depth profile of (100) Si for 6-keV O2 bombardment at approximately...

Figure 10 SIMS depth profiles with end without sample rotation during bombardment by 3-keV O2 at 40° from normal incidence. ...

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. 

Fig. 3. SIMS depth profiles of hafnium silicate films deposited at 200 C (a) using HfCl2[N(SiMej)2]2 and H2O, (b) using HfCl2[N(SiMe3)2]2 and H2O2, and (c) HfCl2[N(SiMe3)2]2, TBOS and H2O...

Figure 3. Ti" " SIMS depth profile of 30 X Pt on oxidized Ti(OOOl)...

Sputter-Ion Depth Profiling. Although it is essentially a destructive technique, SIMS depth profiling is rapid, and possesses parts per million or even parts per billion sensitivity to all elements and isotopes, coupled with a depth resolution of a few nanometres. Concentration-depth plots can be accurate to 5%. 

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. 

FIGURE 6.4 SIMS depth profiles of (a) an ITO film prepared with pure argon gas and (b) an ITO film prepared at hydrogen partial pressure of 7.9 x 1(T6 torr. 

FIGURE 6.10 Comparison of SIMS depth profiles of relative oxygen concentration on the nontreated and oxygen plasma-treated ITO surfaces. 

Depth scale calibration of an SIMS depth profile requires the determination of the sputter rate used for the analysis from the crater depth measurement. An analytical technique for depth scale calibration of SIMS depth profiles via an online crater depth measurement was developed by De Chambost and co-workers.103 The authors proposed an in situ crater depth measurement system based on a heterodyne laser interferometer mounted onto the CAMECA IMS Wf instrument. It was demonstrated that crater depths can be measured from the nm to p,m range with accuracy better than 5 % in different matrices whereas the reproducibility was determined as 1 %.103 SIMS depth profiling of CdTe based solar cells (with the CdTe/CdS/TCO structure) is utilized for growing studies of several matrix elements and impurities (Br, F, Na, Si, Sn, In, O, Cl, S and ) on sapphire substrates.104 The Sn02 layer was found to play an important role in preventing the diffusion of indium from the indium containing TCO layer. 

Barrier layers for Cu metallization in surface acoustic wave (SAW) devices, which are increasingly used in the information technique and telecommunications industry, have been investigated by SIMS depth profiling in comparison to AES (Auger Electron Spectrometry).125 Development trends in SAW devices focus on smaller structures, higher input power or higher frequency. Two Cu metallization systems (of 150 nm thickness) on a LiNb03 substrate with different barrier layers ... 

Figure 2. SIMS depth profile of 9ge+ ions in GaAs and AlGaAs matrices.

Figure 2. SIMS depth profiles of the isotopic oxygen distribution for GaAs. Key to (A) A, anodically oxidized in H,leO , anodically oxidized in H,IS0. Key to (B) , anodically oxidized in H,lsO and A, anodically oxidized in H,laO. (Reproduced, with permission, from Ref. 29. Copyright 1979, Electrochemical Society.)...

Figure 1. SIMS depth profiles in a simulated nuclear waste glass. Major and minor elemental profiles are shown for fractured surfaces exposed to 25° C aqueous leaching for 2 d (a) and 50 d (b). (Reproduced, with permission, from Ref. 4. Copyright 1980, North-Holland Publishing Co.)...

Figure 2. SIMS depth profiles for a sodium borosilicate glass blank sample, air-exposed only (a), and sample exposed to aqueous leaching at 25°C for 30 min (b).

Figure 3. Comparison of SIMS depth profiles of aqueous leaching of a sodium borosilicate glass, for 30 min (a). Key ----------, 0°C and--------, 25°C. Error func-...

Figure 4. SIMS depth profiles for a borosilicate glass exposed to 0°C aqueous leaching for periods of 5 (-----------------------) and 30 (------) min.

In the semiconductor industry, SIMS has been particularly useful for the depth profiling of dopants that are present in silicon in very low concentrations. As an example, a SIMS depth profile for boron implanted into silicon is shown in Figure 27. One of the significant features is that we can detect about 101S boron atoms/cm3 in a silicon matrix of 5 x 1022 atoms/cm3. This illustrates an ability to detect 20 ppb. Also, the method spans 5 orders of magnitude in boron concentration. No other technique can span such a large range accurately. 

Figure 5. SIMS depth profiles of Ti/thin Cu films on polyimide as deposited, showing O18 from polyimide and ambient humidity exposure exposed to H2018 and annealed in nitrogen at 350 C...

Figure 6. SIMS depth profiles of Ti/thick Cu peel strip surfaces originally deposited on polyimide, exposed to h2ol8 and peeled (a) as-deposited and (b) after 350"C forming gas anneal (200W,30min RF)...

Figure 8. SIMS depth profiles of Cr/thin Cu films on polyimide (a) as deposited, showing O 8 from ambient humidity exposure (normalized for isotopic abundance) (b) exposed to H2018 and (c) exposed to H,018 and annealed in forming gas at 350 C (200 W, 30 min RF) and (d) exposed to H20 8 and annealed in forming gas at 350 (50 W, 10 min RF).

Figure 2. SIMS depth profiles of A. NO2, B. NO, and C. OH ions in the non adsorbed BHAC and BHAC after NOx adsorption and desorption.

Nesbitt H. W. and Muir I. J. (1988) SIMS depth profiles of weathered plagioclase and processes affecting dissolved A1 and Si in some acidic soils. Nature 334(6180), 336-338. 

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