Sample rotation , depth profiling

Ion Implantation Systems. An ion implantation system is used to accelerate ionized atomic or molecular species toward a target sample. The ionized species penetrates the surface of the sample with the resulting depth profile dependent on the implanted species mass, energy, and the sample target s tilt and rotation. An implanter s main components include an ionizer, mass separator, acceleration region, scanning system, and sample holder (168). 

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

Zalar, A. (1985) Improved depth resolution by sample rotation during Auger electron spectroscopy depth profiling. Thin Solid Films, 124, 223-230. 

Bradley, R.M., Cirlin, E. (1996) Theory of improved resolution in depth profiling with sample rotation. Applied Physics Letters, 68,3722-3724. 

Lin, R., Wee, A.T.S. (2004) Sub-keV secondary ion mass spectrometry depth profiling comparison of sample rotation and oxygen flooding. Applied Surface Science, 231-232,653-657. 

Sjovall, P., Rading, D., Ray, S.,Yang, L.,Shard,A.G. (2010) Sample cooling or rotation improves Cm organic depth profiles of multilayered reference samples results from a VAMAS interlaboratory study. /. Phys. Chem. B, 114, 769-774. 

Fig. 4.22 (a) Depth profiles of in poly-TiNATiAriN(OOl) trilayers obtained during 5.5 keV Cs bombardment with 3 rpm sample rotation and without sample rotation at azimuthal angles between the incident beam and the in-plane [010] direction in the TiN(OOl) layer of 0,12, and 40°. (b) Profiles of the same sample with 5.5 keV O2 recording xi (decreased by a factor of 50 for plotting) and Reprinted with permission from Ramanath G, Greene JE, Petrov I, Baker... 

As covered in Section 5.3.2.4.5, sample rotation (also referred to as Zalar rotation) during image depth profiling can minimize the latter. Alternatively, surface topography measurements carried out before and after image depth profiling can account for the latter two. Indeed, the effectiveness of this approach has been demonstrated via ex-situ Atomic Force Microscope (AFM) measurements (van der Heide 1998 Robinson et al. 2012). Based off of the success of this approach, lon-Tof has designed a hybrid APM/TOF-SIMS instrument. 

In spite of the many processes which can induce artefacts into depth profiling, the technique can often provide an excellent picture of the subsurface region. Careful selection of experimental parameters can minimize or eliminate artefacts. Generally, it is desirable to use high ion-sputter rates, low temperatures, and sample rotation. The influence of incident current density is shown in Fig. 38 [110], Unfortunately, some problems such as that of preferential sput-... 

Figure 8. Effect of the rotation of the sample during sputtering on a typical Auger depth profile [81].

Figure 9. SIMS depth profile through a GaAIAs Be-spiked sample (a) with and (b) without sample rotation.

If a sample of polycrystalline material is rotated during the sputtering process, the individual grains will be sputtered from multiple directions and nonuniform removal of material can be prevented. This technique has been successfully used in AES analysis to characterize several materials, including metal films. Figure 9 indicates the improvement in depth resolution obtained in an AES profile of five cycles of nickel and chromium layers on silicon. Each layer is about 50 nm thick, except for a thinner nickel layer at the surface, and the total structure thickness is about 0.5 pm. There can be a problem if the surface is rough and the analysis area is small (less than 0.1-pm diameter), as is typical for AES. In this case the area of interest can rotate on and off of a specific feature and the profile will be jagged. 

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