Lithography

For electron beam lithography, the substrate is first coated with an electron-beam-sensitive resist. An electron beam then scans previously defined structures on the coated substrate. The structures can either be located in a single writing field (typically < 1 mm²) or created by placing several writing fields next to each other. In the exposed areas, the resist is chemically altered in such a way that, depending on the type of resist used, the exposed or unexposed areas can be dissolved in a developer. After the development step the patterned resist remains. By means of a dry or wet-chemical etching step, the structures can then be transferred into the layers below. Alternatively, an additional metal layer can be deposited after development. The remaining resist is then removed and the excess areas of the metallization process are also rinsed off. Electron beam lithography allows structure sizes up to 10 nm, but is a very time-consuming and therefore expensive process.

JEOL JSM-6500F

Our scanning electron microscope is also equipped with a PG2 from XENOS Semiconductor Technologies GmbH. The SEM offers typical beam currents of 20 - 400 pA and has a maximum resolution of 2 nm. Thus, structures of up to 10 nm can be realized in electron beam resists. The substrate sizes are limited to a maximum of 20 x 20 mm². The desktop software can be installed by LISA⁺ members on any PC. The software makes it possible to create structures and arrays from the common basic shapes (points, rectangles, triangles, polygons, circles, rings and segments of each) in a very simple way. It is extremely flexible and offers an integrated editor for calculating complex structures.

Nanoimprint lithography (NIL) enables cost-effective and time-efficient reproduction of nanostructures using a nanostructured stamp. For the UV-NIL process, the substrate is coated with a UV-sensitive polymer. In the next step, the stamp is pressed into the polymer in order to displace it at the structured areas down to a just a few nm thin residual layer. With the UV exposure, the polymer is completely cross-linked and the substrate can then be removed from the stamp. Finally, a short O₂ plasma step is required to remove the residual layer and open the structures completely. The structures can now be transferred with appropriate etching steps into layers below.

Karl Süss UV-NIL Tool

Our Mask Aligner MA/BA6 is equipped with the upgrade UV-NIL tool by Karl Süss. The UV-NIL tool allows the imprinting of up to 25 x 25 mm² areas on substrates from < 5 x 5 mm² to 4". The stamps required for the NIL are typically produced by us in accordance with the final structures as masters (e. g. in Si or SiO2) by means of electron beam lithography and reactive ion etching. With special polymers, such as OrmoStamp (micro resist technology, Berlin), these can be transferred into daughter stamps which are then used in the actual imprint process. A possibly contaminated or damaged stamp in the process can thus be replaced quickly and cost-effectively by a new moulding of the master.

The µMLA is a Maskless Aligner. Patterns are transfered via a DMD (Digital Micromirror Device) and an optical objective onto the resist-coated substrate without any mechanical contact. Since there is no need for an optical mask, the system is extremly flexible and and thus bridges the gap to the electron beam writer in terms of its functionality.

The resolution can be varied in three modes - 0.6 µm, 1.0 µm and 3.0 µm - to suit the specific application, increasing the writing speed from 10 mm²/min to 40 mm²/min or 130 mm²/min, respectively.

The permitted substrate sizes are min. 5 x 5 mm² to max. 150 x 150 mm² at 0.1 mm to 12 mm thickness.

The Mask and Backside Aligner MA/BA6 is a contact lithography system, i. e. for exposure the coated substrate is pressed onto the chrome mask with slight pressure to ensure direct contact. A prerequisite for contact exposure is a UV-permeable photomask with the required structure in the form of a chromium layer, which blocks the UV light. During exposure, the structure of the chrome layer is then transferred 1:1 into the resist. At a wavelength of 365 nm (i-line of a Hg high-pressure lamp) a resolution of < 800 nm can be achieved if a perfect contact between mask and resist is ensured, but in practice a resolution of 1-2 µm is much more realistic.

In order to realize several consecutive process steps on a substrate, markers are typically first of all structured on the substrate, by which the substrate can later be aligned to the subsequent optical masks under the reflected light microscope. A positioning accuracy of a few µm can be achieved. The backside alignment option allows you to align to the mask from the bottom side. For this purpose, two microscopes are available below the substrate and the mask, which can be aligned separately to the relevant marker positions.