Depth profile range, SIMS

In another review, Magee and Honig [24] discuss three important aspects of depth profiling by SIMS depth resolution, dynamic range and sensitivity. First, the depth resolution is a measure of the profile quality. They point out that the depth resolution is limited by atomic mixing effects and the flatness of the sputtered crater within the analyzed area. Second, the dynamic range of depth profiles is limited by crater edge... 

The most common application of dynamic SIMS is depth profiling elemental dopants and contaminants in materials at trace levels in areas as small as 10 pm in diameter. SIMS provides little or no chemical or molecular information because of the violent sputtering process. SIMS provides a measurement of the elemental impurity as a function of depth with detection limits in the ppm—ppt range. Quantification requires the use of standards and is complicated by changes in the chemistry of the sample in surface and interface regions (matrix efiects). Therefore, SIMS is almost never used to quantitadvely analyze materials for which standards have not been carefiilly prepared. The depth resoludon of SIMS is typically between 20 A and 300 A, and depends upon the analytical conditions and the sample type. SIMS is also used to measure bulk impurities (no depth resoludon) in a variety of materials with detection limits in the ppb-ppt range. 

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. 

Initial results prove the high potential of LA-based hyphenated techniques for depth profiling of coatings and multilayer samples. These techniques can be used as complementary methods to other surface-analysis techniques. Probably the most reasonable application of laser ablation for depth profiling would be the range from a few tens of nanometers to a few tens of microns, a range which is difficult to analyze by other techniques, e. g. SIMS, SNMS,TXRE, GD-OES-MS, etc. The lateral and depth resolution of LA can both be improved by use of femtosecond lasers. 

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. 

SIMS and SNMS are versatile analytical techniques for the compositional characterization of solid surfaces and interfaces in materials research.92-94 As one of the most important applications, both surface analytical techniques allow depth profile analysis (concentration profile as a function of the depth analyzed) to be performed in materials science and the semiconductor industry with excellent depth resolution in the low nm range. For depth profiling in materials science, dynamic SIMS and SNMS using high primary ion beam doses are applied. Both techniques permit the analysis of light elements such as H, , C and N, which are difficult to measure with other analytical techniques. 

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. 

The development of surface analytical techniques such as LA-ICP-MS, GDMS and SIMS focuses on improvements to sensitivity and detection limits in order to obtain precise and accurate analytical data. With respect to surface analytical investigations, an improvement of spatial and depth resolution is required, e.g., by the establishment of a near field effect or the apphcation of fs lasers in LA-ICP-MS. There is a need for the improvement of analytical techniques in the (j,m and nm range, in depth profiling analysis and especially in imaging mass spectrometry techniques to perform surface analyses faster and provide more accurate data on different materials to produce quantitative 3D elemental, isotopic and molecular distribution patterns of increased areas of interest with high spatial and depth resolution over an acceptable analysis time. 

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. 

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