For our research activities the micro- and nanopattering of thin films and single crytsals is essential. Here the same techniques are applied which are used on a large scale in semiconductor industry.
Depending on structure size various methods are applied. For dimensions on the micron scale and above usually optical lithography is used, while submicron and nanostructures require the use of electron beam lithography.
Initially, the desired structure is tranfered from a mask to a resist pattern. Subsequently, the resist pattern is used for patterning of the samples. Here we use either lift-off or various milling/etching techniques.
- Projection technique: Here the image of a mask is scaled down with a microscope to produce an image on a photo resist
- Contact technique: In the clean-room of the "Verfügungsgebäude" (VG) we use exposure of photoresist by a maskaligner MA6/Ba6 (Firma Suess Microtec). Here, the shadow image of a chromium mask allows a 1:1 transfer of the mask structure onto the photo resist.
Fig. 1. Optical lithography room in the cleanroom section (VG) with maskaligner and spinner ("Lackschleuder") for deposition of photo resist.
- The nanolithography unit (Elphy plus system, Raith) offers the possibility of generating nanopatterns with our scanning electron microscope (SEM). In this case, a scanning electron beam transfers arbitrary patterns onto an e-beam-sensitive resist.
Fig. 2: Electron beam lithography for the fabrication of small holes in superconducting thin films.
- Chemical wet etching: Here a thin film is etched using suitable acids.
- Reactive ion etching (RIE): In a plasma of suitable gase/gas mixtures it is possible to selectively etch various materials. Here the material to be removed reacts with the plasma and forms a volatile gas.
- Argon ion beam etching (IBE): Argon ions are accelerated and neutralized and hit the sample. The kinetic energy of the Argon ions allows removal of the thin films.