2,5D pattern realization for ion nanolithography using focused Ion beam nanomachining technics.
De Felicis D1., Bemporad E1.

1. Science and Technology Group, University of Roma Tre, Rome, Italy

Introduction:
Nowadays various technologies are being used for surface micromachining for microelectronics industry and biological application. Most of the technology to achieve nano-scale features have several limitations due to beam drift, diffraction and costs. The realization of 2.5D pattern needs lithographic techniques. Particularly, ion lithography enables to reduce typical electron and photolithography limitations as small depth, surface sample preparation (photoresist), use of a mask and costs. This work presents a possible solution based on a multiparametrical scripting software developed to obtain complex 2.5D pattern producing a head-print to use as a master in the Indentation lithography (indL) or milling directly over large areas starting “simply” from its CAD. However, this technique have some drawbacks because it is time consuming, the patterned area is limited to few thousands of square microns and, after tens of minutes, the beam drift produces stitching mismatch. These limitations can be reduced, or even eliminated (on some materials), thanks to a proper milling strategy and beam control

Materials and Methods:
Recent FIBs, with Dual Beam system, allow to realize micro and sub-micropattern using script language (not attended modality) and to use stream file to design the milling pattern. The complete control of the ion beam needs to considerate most of the parameters involved in the process: Energy, Ion current, Ion beam diameter, Beam overlap, sample material (sputter rate) and strategy. As the milling process is time consuming (several hours), it is essential to consider a methodology to periodically control and correct the stage and beam drift. A sw interface has been developed to write a stream file (containing hundreds of thousands of rows) considering the above-mentioned parameters and to simulate the FIB operation with the advantage to reduce the instrument testing time). In some case, when large areas to pattern are required, it’s more convenient to realize the negative of the pattern on an indentation diamond tip generally used in the nanoindentation applications. A patented method called Express Test allow to realize very fast indentations with nanometrical accuracy reducing the process time of several hours.

Results:
A new method has been developed to realize 2,5D pattern with ion lithography exceeding the typical limitations. An interface allows in few seconds to prepare a stream file containing the beam coordinates and to simulate the process. For large patterned areas, a diamond tip has been patterned to use as a master in the fast indentation lithography.

Discussion:
It’s known the difficulty to realize 2,5D patter with the lithography. Ion lithography, without masks and sample preparation, can produce very complex geometries but is critical to consider process parameters. For this porpoise a new scan strategy and a dedicated software tool has been developed.