A scanning-electron micrograph of a test sample used to demonstrate a
superlens's resolving power of better than 50 nanometers.
A method that boosts the contrast of high-resolution optical images has
the potential to enable lithography at the nanoscale
When looking to produce the tiny
semiconductor components used in electronic devices, photolithography is the
process of choice. It not only provides high-resolution images, but also allows
high-throughput production. However, as miniaturization of electronic circuits
advances unceasingly, traditional photolithography hits both fundamental and
cost limits. Now, a new photolithographic technique that will produce features
smaller than those possible today is on the horizon1. This development is
thanks to an international research team led by Jing Hua Teng and Hong Liu from
the A*STAR Institute of Materials Research and Engineering, Singapore, which
included co-workers from the A*STAR Data Storage Institute, Singapore.
In traditional photolithography,
light is used to write, for example, the layout of an electronic circuit onto a
substrate coated with a light-sensitive material. The assembly is then
chemically processed in a way that makes the desired pattern appear on the
final component. The minimum size of the features that can be produced with
this method is given by the optical diffraction limit: the resolution that can
be obtained in optical images cannot be higher than about half of the
wavelength of the light used. This limit is typically on the order of several
hundreds of nanometers. And, with a view to further miniaturization of
electronic components, it constitutes a genuine roadblock, explains Teng.
Physicists have proposed several
methods to beat the diffraction limit, including the use of so-called
superlenses. The resolution of superlens images exceeds the diffraction limit;
however, these images tend to suffer from poor contrast, and this has limited
their usefulness for lithography.
Teng and his co-workers
demonstrated that they could produce superlens images with a resolution below
50 nanometers and a contrast sufficient for photolithographic purposes. The
trick was to carefully control the surface of the lens, which consists of a
thin silver film. “A smooth surface ensures that very little light is lost due
to scattering,” explains Teng. Through careful optimization of the fabrication
process, he and his team succeeded in producing silver superlenses with
imperfections that were less than 2 nanometers in height.
The team’s next goal is to
optimize the lithography process and the materials involved to meet the high-throughput
requirements for industry-scale applications. The result should be a versatile
tool for optical lithography in the nano-regime. “Superlens lithography is a
promising technology for next-generation optical nanolithography for the
semiconductor industry, but also for bioengineering and data storage,” says
Liu.
The A*STAR-affiliated researchers
contributing to this research are from the Institute of Materials Research and
Engineering and the Data
Storage Institute
References
- Liu, H., Wang, B., Ke, L., Deng, J., Choy, C. C. et
al. High contrast superlens lithography engineered by loss reduction. Advanced
Functional Materials 22, 3777–3783 (2012). | article
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