Sample Preparation

The research programs at NaMLab typically require very specific preparation of samples. This preparation can include deposition of thin films and layers, thermal treatment of samples, patterning by lithography and etching, as well as sample cutting, grinding, polishing and engravings. For this purpose, the 330 m² cleanroom facility includes various types of deposition tools: physical vapor deposition (PVD), atomic layer deposition (ALD), chemical vapor deposition (CVD), and molecular beam epitaxy (MBE). Post deposition anneals can be performed in various hot and cold wall ovens, which cover a temperature range for room temperature up to 1200°C. There are fast ramping Rapid Thermal Processing machines available as well as furnaces for long-term treatment. Structures in the range of micro- and nanometers can be manufactured by employing shadow masking and lithographic methods like electron beam and laser lithography. The removal of the material includes wet chemical and reactive ion etching (RIE).

Additional requirements of the scientific processing is adapting wafer geometries, chip dicing and creation of process compatible gadgets e.g. for sample handling. Therefore, NaMLab provides several tools to meet these requirements.

A Synova LSC 300 W Laser cutter (Fig. 1) is located in NaMLabs clean room. A  Laser (λ = 532 nm) beam is guided by a water jet of 50 µm in diameter, which additionally cools the sample during the cutting process. It offers the possibility to process wafers with diameters up to 300 mm and substrate thicknesses up to 1 mm. Via a CNC based vacuum chuck any shape can be produced as well as wafer recess and surface roughening is possible. This technique is used for dicing silicon wafers or cutting small pieces without destroying processed and reusable wafers.

Fig. 1:  Laser cutter tool for wafer cutting and engraving: Synova LSC 300W.

In order to prepare the produced layer stacks and device structures for the analysis by scanning electron microscopy or atomic force microscopy, NaMLab uses a Bühler MetaServ250 chemical-mechanical polishing tool for smoothening previously cut or broken sample edges. In addition, high-precise cross sections and the removal of individual layers is possible with the aid of special polishing rags and suspensions. For cleaning and wet chemical treatment (Fig. 2) of samples, NaMLab owns four wet benches equipped with overflow basins. They are located in a DIN ISO 5 cleanroom. Ultra and mega sonic tools for mechanical supported surface cleaning in deionized water are in operation. Also cleaning steps like RCA clean and selective material etching can be performed.

Fig. 2: Various possibilities to perform controlled wet chemical and reactive ion etching.

For sample preparation and combined surface analysis in the micro and nanometer range, NaMLab uses a FEI Expida 1285 Focused Ion Beam (FIB) system. The gallium ion beam current can be set be-tween 1 pA and 30 nA. Cross section formation and milling of TEM lamellas are scopes of application as well as localized removal and deposition of material. Samples can be in-situ covered with protecting or decorating layers via several gas inlets.

Fig. 3: a) FEI Expida 1285 Focused Ion Beam (FIB) system and
b) SEM image of a FIB milled transistor cross section.


Dr. Matthias Grube
Senior Scientist
Phone: +49.351.21.24.990-00