Ion thinning

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The ion milling is a process frequently used physical methods, the most for the structuring of electrical components , and is used for producing dünnster samples. This is a dry etching process . Other names are ion etching , ion beam etching or English milling ion . With a defined bundled ion beam and suitable detectors, the method is used for imaging or material analysis, see Focused Ion Beam .

functionality

The acceleration of ions, mostly argon , in a high vacuum in the direction of the substrate to be processed leads to the fact that when they strike the substrate, impulses are transmitted from the high-energy ions to the substrate and its surface is sputtered and removed. This process is also known as sputtering .

application

Ion thinning makes it possible to produce thin samples with a thickness of less than 100 nm. Samples of this thickness are a necessary prerequisite for transmission electron microscopy . In the case of crystalline samples, the layers near the surface are amorphized (a few nanometers). However, the original crystal structure is retained inside the sample and the amorphous layers do not interfere with the observation. Due to the restricted geometry of these samples, the heat generated by the ion thinning cannot be effectively dissipated and the samples heat up to several hundred degrees Celsius (strongly dependent on the thermal conductivity of the sample and thus on the material used). Temperature-sensitive samples are therefore cooled separately with liquid nitrogen during ion thinning .

Sample thicknesses below 5 nm can also be achieved using ion thinning processes, as is necessary for high-resolution transmission electron microscopy . The amorphous surface layers interfere here, so they also have to be removed. For this purpose, after the actual ion thinning, the samples are thinned again at a very flat angle with very low ion energy. The actual thinning takes place at a larger angle and with more energy, since a higher removal rate is achieved in this way.

Ion thinning is also used as an etching process for structuring microchips . For example, in order to incorporate structures into a layer of less than 200 nm, one cannot use coarse mechanical processes, such as laser processing, etc., one must resort to finer processes. The layer can be coated with photoresist , the structures can be transferred into it using photolithographic structuring processes , and the exposed areas can then be removed using ion radiation.

literature

  • M. Wengbauer, J. Gründmayer, J. Purpose: In-situ temperature measurements on TEM-specimen during ion-milling. In: Martina Luysberg, Karsten Tillmann, Thomas Weirich (eds.): EMC 2008 14th European Microscopy Congress 1-5 September 2008, Aachen, Germany. Springer, Berlin / Heidelberg 2008, ISBN 978-3-540-85154-7 , pp. 833-834, doi : 10.1007 / 978-3-540-85156-1_417 .