Ionic Sputtering Yield in FIB
- Practical Electron Microscopy and Database -
- An Online Book -

http://www.globalsino.com/EM/  



 

 

=================================================================================

Ionic sputtering yield is the ratio of the number of the target atoms (or molecules) ejected from the target to the number of ions incident on the target surface, i.e., atoms sputtered per incoming ion. The yield depends on many factors, including ion mass, ion energy, atomic mass of the target, and the crystallinity of the sample. For each material there exists a threshold energy below which no sputtering occurs. This energy is normally in the range of 10 to 30 eV.

Table 2455. Examples of sputtering yields on different material surfaces. The incident angle is the angle of incidence with respect to target normal. This angle is schematically shown in Figure 2455a.

Sputtered material
Sputtering yield
Special note
Atomic Weight
Name
i) Beam energy: 30 keV; Ion beam: Ga+; Incident angle: 0°
26.98
Al
3.6 atoms/ion
196.97
Au
15.75-17 atoms/ion
12.01 C 1.69 atoms/ion  
52
Cr
3.7-5.15 atoms/ion
144.6
GaAs
5.6 atoms/ion
28
Si
2.1 atoms/ion
47.87 Ti 2.28 atoms/ion  
183.84 W 7.59 atoms/ion
ii) Beam energy: 30 keV; Ion beam: Ga+; Incident angle: 52°
184
Tungsten (W)
8 atoms/ion
iii) Beam energy: 30 keV; Ion beam: Ga+; Incident angle: 80°
18
Water (H2O) ice
18 molecules/ion

For FIB milling, the ionic sputtering yields of most materials strongly vary with the angle (θ) of incidence with respect to the target normal. Many materials such as Al, Cu, Zn, Si, and SiO2 have the highest sputtering yields at angles in the range of 75° to 85°. Figure 2455b shows the schematic illustration of relative sputtering yield against the angle of incidence with respect to target normal. For instance, the sputtering yields of Si and SiO2 are about 6 to 7 times larger than that at the zero angle.

angle (θ) of incidence with respect to the target normal

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

ionic sputtering yield against the angle of incidence with respect to target normal

Figure 2455b. Schematic illustration of ionic sputtering yield against the angle (θ) of incidence with respect to target normal.

Figure 2455c shows the dependence of ionic sputtering yields on the energies of different ions in the energetic beams. Here, the incident ions (Au, Nd, In, Ga, Co, Si, N, and Li) are normal to the silicon (Si) target surface. In FIB, the ions in the energetic beam are normally Ga+ ions.

The dependence of ionic sputtering yields on ion energies

Figure 2455c. The dependence of ionic sputtering yields on ion energies. The target material is silicon.

Figure 2455d shows the sputtering yield of a FIB as a function of beam-ion mass at 30 keV with a normal incidence on silicon target.

The dependence of ionic sputtering yields on ion energies

Figure 2455d. The sputtering yield of a FIB as a function of beam-ion mass at 30 keV with a normal incidence on Si target.

 

 

=================================================================================