| AVS 59th Annual International Symposium and Exhibition | |
| Helium Ion Microscopy Focus Topic | Wednesday Sessions |
| Session HI+AS+NS-WeA |
| Session: | Basics of Helium Ion Microscopy |
| Presenter: | N. Vanhove, Centre de Recherche Public – Gabriel Lippmann, Luxembourg |
| Authors: | T. Wirtz, Centre de Recherche Public – Gabriel Lippmann, Luxembourg N. Vanhove, Centre de Recherche Public – Gabriel Lippmann, Luxembourg L. Pillatsch, Centre de Recherche Public – Gabriel Lippmann, Luxembourg D. Dowsett, Centre de Recherche Public – Gabriel Lippmann, Luxembourg S. Sijbrandij, Carl Zeiss J. Notte, Carl Zeiss |
| Correspondent: | Click to Email |
The ORION Helium Ion Microscope (HIM) has become a well-established tool for high-resolution microscopy [1]. The high brightness ALIS gas field ion source can operate with helium and, after special prototype modifications, with neon [2]. However, the detection of backscattered atoms can provide only limited specimen composition information. By contrast, Secondary Ion Mass Spectrometry (SIMS) is an extremely powerful technique for analyzing surfaces due to its excellent sensitivity, high dynamic range, very high mass resolution and ability to differentiate between isotopes. In order to get chemical information with a higher sensitivity and a high lateral resolution, we have investigated the feasibility of performing SIMS on the HIM.
Therefore, the secondary ion formation process under He+ and Ne+ bombardment has to be investigated and optimized. To investigate secondary ion formation an experimental study was performed; to investigate sputtering effects on resolution and practical implementation aspects a simulation approach was taken.
First, secondary ion yields for different elements sputtered from different materials exposed to helium and neon ion beams were experimentally determined on a test set-up. The basic yields could be increased by several orders of magnitude by using reactive gas flooding (i.e. O2 and Cs0 [3,4]). Afterwards, detection limits have been calculated taking into account the experimentally obtained useful yields. Depending on the dwell time, ppm sensitivity can be obtained for Ne+ bombardment on silicon with oxygen flooding. Second, a detailed study of the sputtering phenomena using TRIM simulations was carried out in order to determine the effect of the collision cascade on the lateral resolution. The diameter (FW50) of the area from which sputtered atoms originate has been determined for 10 keV He+ and Ne+ bombardment on different materials. While the obtained results are very encouraging, the practical instrumentation aspects have to be investigated as well in order to obtain a high secondary ion transmission and maintain the excellent primary beam characteristics. Therefore, the practical limitations imposed by adding an extraction system to the HIM have been studied in detail with respect to the extraction geometry.
In general, the combination of high-resolution microscopy and high-sensitivity chemical mapping on a single instrument will lead to a new level of correlative microscopy.
[1] L. Scipioni et al., J. Vac. Sci. Technol. B 27, 3250 (2009)
[2] F. Rahman et al., Scanning 33, 1 (2011)
[3] K. Franzreb et al., Surf. Sci. 573, 291 (2004)
[4] P. Philipp et al., Int. J. Mass Spectrom. 253, 71 (2006)