Argon cluster cleaning of Ga⁺ FIB‐milled sections of organic and hybrid materials

Abstract

Secondary ion mass spectrometry studies have been made of the removal of the degraded layer formed on polymeric materials when cleaning focused ion beam (FIB)-sectioned samples comprising both organic and inorganic materials with a 30-keV Ga + FIB. The degraded layer requires a higher-than-expected Ar gas cluster ion beam (GCIB) dose for its removal, and it is shown that this arises from a significant reduction in the layer sputtering yield compared with that for the undamaged polymer. Stopping and Range of Ions in Matter calculations for many FIB angles of incidence on flat polymer surfaces show the depth of the damage and of the implantation of the Ga + ions, and these are compared with the measured depth profiles for Ga + -implanted flat polymer surfaces at several angles of incidence using an Ar + GCIB. The Stopping and Range of Ions in Matter depth and the measured dose give the sputtering yield volume for this damaged and Ga +implanted layer. These, and literature yield values for Ga + damaged layers, are combined on a plot showing how the changing sputtering yield is related to the implanted Ga density for several polymer materials. This plot contains data from both the model flat poly(styrene) surfaces and FIB-milled sections showing that these 2 surfaces have the same yield reduction. The results show that the damaged and Ga + -implanted layer's sputtering rate,after FIB sectioning, is 50 to 100 times lower than for undamaged polymers and that it is this reduction in sputtering rate, rather than any development of microtopography, that causes the high Ar + GCIB dose required for cleaning these organic surfaces.

Chemical Imaging of Buried Interfaces in Organic–Inorganic Devices Using Focused Ion Beam-Time-of-Flight-Secondary-Ion Mass Spectrometry

“…In this geometry, the Ar + GCIB is normal to the surface. It is shown elsewhere that the sputtering yield of pure PS at 0° incidence, using 10 keV Ar 2500 + , is 21 nm 3 . However, in sputtering the Ga implanted PS, the yield is reduced to ∼0.6 nm 3 , a reduction of ∼50 times so that the 38 ions/nm 2 is what is required to remove the remaining 23 nm of damaged and implanted PS .…”

“…However, in sputtering the Ga implanted PS, the yield is reduced to ∼0.6 nm 3 , a reduction of ∼50 times so that the 38 ions/nm 2 is what is required to remove the remaining 23 nm of damaged and implanted PS. 32 If we were to overclean by a further 38 ions/nm 2 , we should remove around a further 1 μm of pure PS which would lead to blurring at the edges of included phases by significantly more than this figure because the yield rises strongly at edges. Even if one limited the overclean dose to just 10%, the spatial resolution would begin to be compromised.…”

“…It is shown elsewhere that the sputtering yield of pure PS at 0° incidence, using 10 keV Ar 2500 + , is 21 nm 3 . However, in sputtering the Ga implanted PS, the yield is reduced to ∼0.6 nm 3 , a reduction of ∼50 times so that the 38 ions/nm 2 is what is required to remove the remaining 23 nm of damaged and implanted PS . If we were to overclean by a further 38 ions/nm 2 , we should remove around a further 1 μm of pure PS which would lead to blurring at the edges of included phases by significantly more than this figure because the yield rises strongly at edges.…”

“…In this geometry, the Ar + GCIB is normal to the surface. It is shown elsewhere 32 that the sputtering yield of pure PS at 0° incidence, using 10 keV Ar2500 + , is 21 nm 3 .…”

“…Observation of the columnar structure in each MCP hole using Bi3 + in Figure 6b would indicate that when using Bi3 + sputtering ions, some 2 to 3 μm of organic material may need to be removed to clean up the surface. If this were pure polystyrene, this would need the high dose of 70 ions/nm 2 for 10 keV Ar2500 + , but if the removal of damaged polymer is one to two orders of magnitude slower 27,29,32 , this figure is raised by that factor and would be impossible to remove in a practical time. Clearly, the spatial resolution is very poor and the cleaning of the FIB section cut using Bi3 + may degrade that resolution further.…”