Dopant Electrical Deactivation Induced by FIB Sample Preparation

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Dopant Electrical Deactivation Induced by FIB Sample Preparation

During FIB specimen preparation for TEM, SEM, and SCM analysis, deep-level defects are introduced into the crystalline regions of the specimens. Those defects have the effect of trapping the dopants. [1] This artifact in FIB specimen preparation is one of the main mechanisms of FIB-induced, electrically inactive layer. Table 2553 lists examples of electrically inactive thickness induced by FIB sample preparation process.

Table 2553. Examples of electrically inactive thickness (in nm) induced by FIB sample preparation process. The same inactive thicknesses can be obtained by annealing the FIB-prepared specimens with either 30 or 8 kV Ga ions. [2]

Dopant concentration (cm^-3)	30 kV	8 kV	Annealed for 30 min at 350 °C
1 x 10¹⁹	30	12.5	2.5
2 x 10¹⁸	70	30	5
2 x 10¹⁷	125	6.5	42.5

Therefore, the electrically inactive thickness can be reduced either by reducing the FIB operating voltage or by performing a low temperature anneal on the specimens. Note that the dopant diffusion in Si at 350 °C is not significantly high to cause artifacts.

[1] D. Cooper, A. C. Twitchett, P. K. Somodi, I. Farrer, D. A. Ritchie, P. A. Midgley, and R. E. Dunin-Borkowski, Appl. Phys. Lett. 88, 063510 (2006).
[2] David Cooper, Pierrette Rivallin, Jean-Michel Hartmann, Amal Chabli, and Rafal E. Dunin-Borkowski, Extending the detection limit of dopants for focused ion beam prepared semiconductor specimens examined by off-axis electron holography, Journal of Applied Physics, 106, 064506 (2009).

Practical Electron Microscopy and Database

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Dopant Electrical Deactivation Induced by FIB Sample Preparation