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To obtain clear EM images, plasma cleaners can be used for TEM and SEM sample cleaning. This method allows fine-probe microanalysis for extended period without carbonaceous accumulation under the irradiation of electron beams in TEM and STEM. To have correct cleaning to prevent the contamination occurrence, we need to optimize some parameters:
i) Proper reactive gas plasmas. The efficiency of plasma cleaning significantly depends on the gas used in the process. For instance, a Fischione plasma cleaner model 1400 was used to clean FIB prepared specimens with a mixture of 75% Ar to 25% O [1]. Furthermore, it has been demonstrated that some multi-step processes are actually more efficient in eliminating contamination than a single step process.
ii) Ion energy. A minimum ion energy is practically required for effective cleaning of TEM specimens.
iii) Plasma density.
iv) Electron temperature.
For instance, Figure 4497 indicates the correlation of ion energy at the specimen surface with respect to plasma chamber pressure with a typical specimen position of 10 cm from the center (0 cm) of the antenna coil. The typical gas pressure in the plasma
process is 5 - 50 mTorr during plasma cleaning.
| Figure 4497. Ion energy as a function of chamber pressure for a specimen
position of 10 cm from the center (0 cm) of the HF antenna coil. [2] |
Except for the application of plasma cleaning of removing contamination on specimens, plasma cleaning can also be used to clean apertures and EM columns or/and chambers.
Examples of plasma cleaners for TEM and SEM samples are:
i) Gatan Solarus Plasma Cleaner: Can be used for treatments of oxygen and a 25% O2, 75% Ar mixture.
ii) E.A. Fischione Instruments Model 1400 Plasma Cleaner.
[1] Eduardo Montoya, Sara Bals, Marta D. Rossell, Dominique Schryvers, and Gustaaf Van Tendeloo, Evaluation of Top, Angle, and Side Cleaned FIB Samples for TEM Analysis, Microscopy Research and Technique 70:1060–1071 (2007).
[2] Thomas C. Isabell, Paul E. Fischione, Catherine O’Keefe, Murat U. Guruz, and Vinayak P. Dravid, Microsc. Microanal. 5, 126-135, 1999.
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