Paper AS-ThA2
Towards Ultimate Organic Depth Profiling using Argon Cluster Beams – Recommendations for Dual Beam Profiling and Sample Charge Compensation
Thursday, November 1, 2012, 2:20 pm, Room 20
| Session: |
Applications of Large Cluster Ion Beams - Part 2 (2:00-3:20 pm)/ Surface Analysis using Synchrotron Techniques (3:40-5:40 pm) |
| Presenter: |
R. Havelund, National Physical Laboratory, UK |
| Authors: |
R. Havelund, National Physical Laboratory, UK
A.G. Shard, National Physical Laboratory, UK
M.P. Seah, National Physical Laboratory, UK
I.S. Gilmore, National Physical Laboratory, UK
|
| Correspondent: |
Click to Email |
The recent innovation of large argon cluster ion sources has revolutionised the ability of SIMS to give 3D chemical images of important classes of organic materials, such as organic electronic materials. Furthermore, sputtering with argon clusters gives the best depth resolution currently achievable of 5 nm [1], constant sputtering yields [2] and minimal chemical degradation [3]. It is clear that this important capability will have major impact in the innovation and manufacture of many advanced technologies. Consequently, there is an urgent need to develop the underpinning metrology. An essential first phase has been the VAMAS interlaboratory study [4] which has highlighted two key issues which we now study in detail. Firstly, the improved depth resolution using argon cluster sputtering and reduced chemical damage reveals effects of the primary beam in a dual beam depth profiling experiment become increasingly important. In this study, we use the Irganox organic multilayer reference material [5] and show that the apparent position of a delta-layer depends on which secondary ion signal is used. It is observed that the delta-layer profiles for small fragment ions appear before the molecular ion profile. The position shift increases with primary beam energy and can be more than 4 nm when a 50 keV Bi3 ion beam is used. We understand this in terms of a simple sputtering model and provide recommended analytical conditions to reduce this effect. Secondly, it has been widely reported that an initial increase in intensity is observed when depth profiling some organic materials with argon clusters. This is observed for the Irganox reference material and we show this is due electron beam damage from the charge compensation system. Since, typically, lower sputtering yields are used for argon cluster sputtering (owing to the choice of low energy per atom to reduce the sputtering damage) the emitted flux of positive ions is reduced and more electron beam current is required than typically needed using C60 sputtering. Previously, we have shown that a maximum limit of 6·1018 electrons per m2 should be used to spectroscopy [6]. Here, we show that electron damage extends up to 100 nm into the profile. We conduct a systematic study of the electron beam damage as a function of electron dose and energy and give a recommend dose limit.
[1] A.G. Shard et al., This conference
[2] J.L.S. Lee et al., Anal. Chem. (2010), 82, 105
[3] S. Ninomiya et al., Rapid Commun. Mass Spectrom. (2009), 23, 1601
[4] A.G. Shard et al., Surf. Interface Anal. (2011), 43, 1240v
[5] A.G. Shard et al., J. Phys. Chem. B (2008), 112, 2596
[6] I.S. Gilmore and M.P. Seah, Appl. Surf. Sci. (2002), 187, 89