Depth profiling of ultra-shallow boron implants by high depth resolution ERD

The increase of integration density in modern nano-electronics demands the shrinking of device dimensions in lateral directions as well as in depth. Ultra-shallow p-n junctions in semiconducting materials are vital for this technology [1].
Low-energy ion implantation is a feasible way to incorporate dopant elements such as boron, phosphorous or antimony in the near-surface region of the substrate material. Characterisation of these implants, especially the depth profile of the implant, is important for evaluating the specific process parameters. However, there are not many analysis techniques that can provide depth profiles of nanometre resolution at the very surface of a sample. Secondary Ion Mass Spectrometry (SIMS) is a well established technique for such measurements, but in the near-surface region SIMS encounters problems due to the so-called transient effects, which distort the measured atomic concentrations in that area. [2]. Therefore, complementary techniques capable of providing accurate depth profiles in the upper few nanometres are required.
High depth resolution Elastic Recoil Detection (ERD) is able to provide these depth profiles. ERD in conjunction with a magnetic spectrometer for high depth resolution (setup developed at HZDR, see. Fig. 1) has been performed to evaluate boron implant profiles in silicon for different implantation parameters [3]. Experimental conditions have been optimised to minimise sample damage while measuring. Boron recoil ions are detected using 6.5 MeV chlorine ions. Under those conditions no beam damage could be detected during measurement. Undistorted near-surface depth profiles of the boron implants can be reconstructed.
Acknowledgments: We thank B. Beckhoff (PTB Berlin) for providing the samples and W. Möller for very helpful discussions.

[1] L. Shao, J.R. Liu, Q.Y. Chen, W.K. Chu, Materials Science & Engineering R-Reports 42 (2003) 65-114.
[2] D. Avau,W. Vandervorst, H.E. Maes, Surf. Interf. Anal. 11 (1988) 522–528.
[3] P. Hönicke, B. Beckhoff, M. Kolbe et al., Anal. Bioanal. Chemistry 396 (2010) 2825-2832.