Energetic photons, ions and electrons can induce carbon growth on surfaces due to residual hydrocarbons present on the sample surface or in the vacuum system. This effect is well known and has been a major obstacle for the successful introduction of EUV Lithography. This has been overcome by introducing a very clean vacuum system in combination with surface cleaning technologies. For EUVL we have developed a plasma cleaning process for the mirrors that has a relatively high efficiency for carbon removal and causes no surface damage[1]. In high resolution imaging applications like SEM, TEM or Helium Ion Microscopy (HIM) this problem is also present and more difficult to counteract due to the delicate nature of samples or that the sample itself is the source of contaminants. We have applied our cleaning process and successfully and non-intrusively cleaned samples for electron microscopes. As a result, and on request of several microscopy users, we have developed a miniature microwave-induced plasma source to be used on various types of imaging systems for sample and chamber cleaning. The miniature source is to be mounted on the load lock of the imaging system or on the microscope chamber by means of a standardized vacuum flange.

We will report on the design, manufacturing and realization of such a miniature source and discuss the results that were obtained on our own HIM as well as other microscopes. This plasma process has already successfully been used to clean samples with graphene, EUV reticle materials or asbestos. Part of the experiments presented include characterization of the plasma with Langmuir probes and Optical Emission Spectroscopy (OES).

[1] N.B. Koster et al, Towards defect free EUVL reticles: carbon and particle removal by single dry cleaning process, and pattern repair by HIM , Proc. of SPIE Vol. 7969 79690X-1, 2011