Using Plasma Etching on the Nanoscale

Started in January 2013, the European Framework 7 project 'SNM' has generated some remarkable results. At the Micro Nano Engineering conference (MNE 2013) held at Imperial College London in September, a full session was dedicated to the results of this project, beginning with an invited talk from the project coordinator, Prof Ivo Rangelow.

Nanoscale Plasma Etching

Partners at Bayreuth University have created new vacuum-deposited molecular glass materials with glass transition temperatures higher than 100oC. These have been utilized to write patterns with the help of a modified atomic force microscope at TU llmenau, and were etched at Oxford Instruments.

Etch depth in nanometres for different materials

Figure 1. Etch depth in nanometres for different materials

At Oxford Instruments, the plasma etch resistance of the molecular glasses was examined in SF6, chlorine, oxygen, and HBr plasma. Figure 1 shows the etch depth in nanometres for the same etch process in these gases for different materials.

Evaporation and spin casting were compared for some materials with only slight variations in etch resistance. A low etch depth denotes a better material. Here, these are proposed as resist mask materials. Since the tip-writing techniques being developed can only create patterns in thin layers, selectivity is very important.

Layout of tip-written patterns transferred into silicon wafer

Figure 2. Layout of tip-written patterns transferred into silicon wafer

Prof Rangelow reported initial results of plasma etching, utilizing a 60MHz/13.56MHz etch process in HBr. Etch depths of more than 50nm were determined with a Si: mask selectivity of no less than 5:1. The tip-written patterns were effectively transferred into silicon (Figure 2).

Limitations in Existing Pattern Transfer Methods

These early results were aimed to establish the limitations to existing pattern transfer techniques. Until now, plasma etching had the ability to reproduce some degree of pattern that can be made on silicon, even at 10nm.

Proving reproducible profile control lower than 10nm is possible in the future, only partly restricted by the available metrology methods. For this reason, VSL in the Netherlands brings know-how in metrology atomic force microscope to the project.

Conclusion

Producing 10nm-wide patterns at cost-effective throughputs continues to pose a major challenge. Nonetheless, plasma etching is still able to replicate some degree of pattern even when the size is small.

This information has been sourced, reviewed and adapted from materials provided by Oxford Instruments Plasma Technology.

For more information on this source, please visit Oxford Instruments Plasma Technology.

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