What is Nanolithography and Its Applications?

The art of creating structures on the nanometer scale is known as nanolithography.

It has applications in the creation of integrated circuits and parts for semiconductor technology, in which the ability to construct the most compact transistors and circuits enables the building of smaller devices, as well as improving the components’ power efficiency and performance.¹

Furthermore, developments in lithography techniques have enabled the construction of complex structures that can be utilized for microelectromechanical or nanoelectromechanical systems (MEMS or NEMS) devices.

While these compact devices have already been employed as pH sensors and transistors, there are myriad possibilities for the future development of this technology, including the use of these devices for the delivery of drugs.²

How Does Nanolithography Work?

There are numerous distinct methods for carrying out nanolithography machining, depending on the kinds of materials in use and the specifications of the final structure. In general, the majority of nanolithography methods engage the properties of light or electrons to produce patterns in a substrate.

This patterning can be targeted by adding masks onto the photoresist so as to shield particular regions from the incoming light. The pattern is subsequently etched onto the exposed regions and, if required, the previously masked areas can be removed.

To produce the smallest features (as small as 5 nm), a technique known as electron beam lithography (EBL or e-beam lithography) can be employed ³. In this process, a closely focused beam of electrons is scanned across the surface, as opposed to using light to illuminate the surface.

The pattern is exposed by the electron beam, after which the resist can be developed. Following this, the pattern transfer can be concluded either by etching and resist removal or by evaporating a metal onto the resist and dissolving the residual unwanted metal and resist.

The Technical Challenges

Although nanolithography allows for the shaping of remarkably small and complex devices, the more compact the scale of the manufacturing, the more vital the issue of exactitude becomes in the pattern transfer. Problems with precision can result in manufacturing errors, with squandered materials and related expenditure wastage.

In order to enable ultra high precision pattern transfer, there are several technical difficulties that must be addressed.

To allow the electron beam or light source to effectively trace a pattern over a resist, feedback on its relative position is needed, both in terms of the source’s relative height and its position in the horizontal plane of the resist.¹

The ‘stitching error’ refers to another related difficulty in electron beam lithography. As larger patterns are transferred, the complete pattern is divided down into smaller writing areas that are joined by movements of a translation stage.

Here, it is vital that the movements of the translation stages be entirely accurate so as to preserve the whole pattern over its constituent areas.⁴

Raith’s Solutions

Fortunately, a number of options are available to increase the stability and accuracy of nanolithography fabrication. Raith is a market-leader in developing technologies for nanofabrication that find solutions to various technical challenges linked to nanolithography fabrication.⁵

Raith has developed a wide variety of electron and ion beam technologies, from 20 eV to 100 kV for e-beam lithography. In the 100 kV range, Raith offers the EBPG5200⁶, which has an overlay accuracy of ≤ 5 nm for extreme direct write precision.

In instances which require 50 kV, and where users require a machine with a small footprint, the VOYAGER⁷ includes the Raith’s patented eWRITE system to enable quick processing (up to 1 cm²/h) for samples of up to 8 inches.

Raith has attained this outstanding precision over even large write areas with the use of a pair of complementary lasers, one for working distance and a second for staging distance. Working distance is controlled by employing a laser source and measuring the reflected signal from the resist.

Measuring interference pattern with a mirror mounted on the stage offers relative high-precision positioning of the electron beam to the surface. This technology enables errors in the field of view to be mapped to an accuracy of 1 nm.⁸

However, the increased precision is not the only advantage of XY Staging. What is even more advantageous is that this precision can be upheld even over complex surface shapes, including those with inclined surfaces and those with significant curvature.

Since extra errors and inaccuracies often stem from stitching areas in nanolithography, Raith has created the traxx and periodixx technologies, which enable stitch-free lithography.⁹

When translating the sample with Raith’s exclusive Fixed-Beam-Moving Stage (FBMS) technology, users can draw patterns up to centimeters in length in a continuous writing mode.

This eliminates any of the stitching errors related to writing region by region, and is especially advantageous in high-precision manufacturing applications, such as the manufacture of waveguides and X-ray optics.

Alongside traxx, peridoixx employs a comparable principle; the Modulated-Beam-Moving-Mode (MBMS) to pool the advances of FBMS with some beam movement as needed for drawing repetitive patterns.

Either of these write modes can be joined with the Laser Interferometric Stage and both are available on a number of the Raith lithography instruments, including VOYAGER, RAITH150 Two, eLINE Plus and VELION.

The extreme precision and abilities of minute scale machining make the broad range of instruments developed by Raith perfect for almost any nanolithography application.

References

1. A. Pimpin and W. Srituravanich, Eng. J., 2012, 16, 37–55
2. H. Fujita and Y. Mita, Nanofabrication Handb., 2012, 353–378.
3. Y. Chen, Microelectron. Eng., 2015, 135, 57–72.
4. R. K. Dey and B. Cui, J. Vac. Sci. Technol. B, Nanotechnol. Microelectron. Mater. Process. Meas. Phenom., 2013, 31, 06F409
5. Raith Company Profile, https://www.raith.com/company/corporate-profile.html, (accessed January 2019)
6. EBPG5200, https://www.raith.com/products/ebpg5200.html, (accessed January 2019)
7. VOYAGER, https://www.raith.com/products/voyager.html., (accessed January 2019)
8. Laser Interferometric Stage, https://www.raith.com/technology/true-large-area-sem-with-various-detectors.html, (accessed January 2019)
9. Stitch-Free Lithography, https://www.raith.com/technology/stitch-free-lithography.html#sflt, (accessed January 2019)

This information has been sourced, reviewed and adapted from materials provided by Raith.

For more information on this source, please visit Raith.