Milling Rate of Materials in FIB
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The milling rate in FIB milling process is defined as the ratio of the volume of the milled material to the product of the beam current and irradiation time, given by,

---------------------------- [2454a]
---------------------------- [2454b]
where,
d - The milled depth,
A - The milled area,
I - The beam current,
t - The beam irradiation time,
q - The electronic charge,
D - The ion dose.

Therefore, the milling rate of materials depends on many factors, including the ion flux, the probability of sputtering per incident ion, the re-deposition of the sputtered material, and the angle of incidence of the ions with the sample surface. Table 2455 lists some examples of milling rates of different materials in FIB.

The correlation between the milling rate and the sputtering yield is given by,

---------------------------- [2454c]
where,
Nt - The atomic density of the target material,
YS(E,Θ) - The sputtering yield,
t - The beam irradiation time.

Table 2455. Examples of milling rates of different materials in FIB. The incident angle is the angle of incidence with respect to target normal. This angle is schematically shown in Figure 2455.

Sputtered material
Milling rate
(µm3nA-1s-1 )
Total Yield (Atoms/Ion)
Beam energy: 70 kV; Ion beam: Ga+; Incident angle*: 30°
GaN 0.577 (10 scans) - 0.592 (50 scans) [2] 8.33 (10 scans) - 8.5 (50 scans) [2]
Beam energy: 70 kV; Ion beam: Ga+; Incident angle: 15°
GaN 0.512 (10 scans) - 0.541 (50 scans) [2] 7.4 (10 scans) - 7.7 (50 scans) [2]
Beam energy: 70 kV; Ion beam: Au++; Incident angle: 0°
Si 0.61 [6]
SiC 0.32 [6]
Beam energy: 70 kV; Ion beam: Co++; Incident angle: 0°
Si 0.305 [6]
SiC 0.07 [6]
Beam energy: 70 kV; Ion beam: Ga+; Incident angle: 0°
Al3O2 0.13
GaN 0.451 (10 scans) - 0.47 (50 scans) [2] 6.5 (10 scans) - 6.75 (50 scans) [2]
Si 0.28
6H SiC 0.15
Beam energy: 70 kV; Ion beam: Ge++; Incident angle: 0°
Si 0.33 [6]
SiC 0.12 [6]
Beam energy: 70 kV; Ion beam: Nd ++; Incident angle: 0°
Si 0.53 [6]
SiC 0.2 [6]
Beam energy: 50 kV; Ion beam: Ga+; Incident angle: 30°
GaN 0.577 (10 scans) - 0.6 (50 scans) [2] 8.3 (10 scans) - 8.7 (50 scans) [2]
Beam energy: 50 kV; Ion beam: Ga+; Incident angle: 15°
GaN 0.51 (10 scans) - 0.54 (50 scans) [2] 7.3 (10 scans) - 7.8 (50 scans) [2]
Beam energy: 50 kV; Ion beam: Ga+; Incident angle: 0°
Al3O2 0.13
GaN 0.45 [2] 6.8 [2]
Si 0.264
6H SiC 0.145
Beam energy: 30 kV; Ion beam: Ga+; Incident angle: 30°
GaN 0.576 (10 scans) - 0.598 (50 scans) [2] 8.3 (10 scans) - 8.6 (50 scans) [2]
Beam energy: 30 kV; Ion beam: Ga+; Incident angle: 15°
GaN 0.51 (10 scans) - 0.536 (50 scans) [2] 7.3 (10 scans) - 7.71 (50 scans) [2]
Beam energy: 30 kV; Ion beam: Ga+; Incident angle: 0°
Al
0.29-0.37

AlAs 0.30 - 0.42 [8]
Al3O2
0.0333 - 0.1
Au
1.5-1.8

C 0.18
Crystalline diamonds 0.02 - 1.8 [4, 5]
Cr
0.1-0.28

Cu 0.25
Fe 0.29
Fe2O3
0.25
GaAs 0.61-0.89
GaN 0.422 (50 scans) - 0.435 (10 scans) [2] 6.1 (50 scans) - 6.26 (10 scans) [2]
Vitreous ice 5
InP 0.96 - 1.2
InAs 1.10 - 1.40 [8]
LiNbO3
0.07 - 0.35
MgO 0.15
Mo 0.12
Nb-Pt1−xNix-Nb-Pt1−xNix multilayers 0.235 - 0.296 [9]
Ni 0.14
PMMA 0.40 - 0.50
Pt 0.23
Si
0.15-0.27

6H SiC 0.15 [2]
SiO2
0.19

SiO2 (thermal) or TEOS 0.24
Si3N4
0.2-0.21

Ta 0.32
Ti 0.37-0.46
TiO 0.15
TiN 0.15
W 0.12
W nanowires ~ 0.60 [3]
Biological Cells 2 [7]
Beam energy: 25 kV; Ion beam: Ga+; Incident angle: 0°
Cu 0.7 [1]
Beam energy: 25 kV; Ion beam: Ga+; Incident angle: 12°
Cu 1.13 [1]
Beam energy: 15 kV; Ion beam: Ga+; Incident angle: 30°
GaN 0.55 [2] 7.9 [2]
Beam energy: 15 kV; Ion beam: Ga+; Incident angle: 15°
GaN 0.43 [2] 6.2 [2]
Beam energy: 15 kV; Ion beam: Ga+; Incident angle: 0°
GaN 0.362 [2] 5.2 [2]
Beam energy: 5 kV; Ion beam: Ga+; Incident angle: 0°
Biological Cells 0.6 [7]
 * The angles are the angles from normal incidence.

The user interfaces on the FIB systems normally have some configured files for sputtering of different materials. In these files, the beam dwell times and overlap have been calibrated for the specific materials in order to obtain the highest sputtering rates.

Figure 2455. The angle (θ) of incidence with respect to the target normal.

[1] Microelectronic Failure Analysis Desk Reference: 2001 Suppplement.
[2] A. J. Steckl and I. Chyr, Focused ion beam micromilling of GaN and related substrate materials (apphire, SiC, and Si…), J. Vac. Sci. Technol. B 17(2), 362 (1999).
[3] Wuxia Li, Ajuan Cui, Changzhi Gu, P. A. Warburton, Atomic resolution top-down nanofabrication with low-current focused-ion-beam thinning, https://doi.org/10.1016/j.mee.2012.07.108.
[4] S. Reyntjens and R. Puers, J. Micromech. Microeng., 11, 287 (2001).
[5] Rustin Golnabi, Won I. Lee, Deok-Yang Kim, and Glen R. Kowach, Mater. Res. Soc. Symp. Proc. Vol. 1282. 111 (2011).
[6] Lothar Bischofl and Jochen Teichert, Focused Ion Beam Sputtering of Silicon and Related Materials, Research Center Rossendorf Inc., Institute of Ion Beam Physics and Materials Research, Germany.
[7] http://www.anff.org.au/case-studies/focused-ion-beam-milling-biological-cells.html.
[8] K. A. Grossklaus and J. M. Millunchick, Mechanisms of nanodot formation under focused ion beam irradiation in compound semiconductors, J. Appl. Phys. 109, 014319 (2011).
[9] Taras Golod, Mesoscopic phenomena in hybrid superconductor/ferromagnet structures, Thesis, Stockholm University, 2011.

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