How a microfabrication researcher uses SEM to verify nanoscale structures

By Jake Wilkinson - May 12, 2017

Microfabrication, the creation of microscale structures and features, is an essential tool for the creation of next-generation semiconductors, processors and the ‘lab-on-a-chip’ microfluidic systems found in chemical analysis systems that can fit in the palm of your hand. 

Until now, microfabrication has relied on masking techniques such as lithography, which limits the variety of structures that can be produced. However, new research into microscale 3D printing systems is allowing complex 3D shapes to be assembled at scales smaller than ever achieved before.

The future beckons

Tommaso Baldacchini is a microfabrication researcher for the Technology and Applications Center (TAC) at Newport Corporation. In his research into laser-assisted nanofabrication, a Phenom Pro scanning electron microscope is an essential tool.

Newport Corporation’s TAC labs are very similar to those that you would see at a University, and they closely cooperate with academic customers. TAC conducts experiments for academic partners and fabricates micro-devices and components for use in other academic research areas.

The current microfabrication landscape

Up to the current time, much microfabrication has been dominated by traditional machining and photolithographic processes, which are planar techniques. According to Tommaso Baldacchini, photolithography can produce an extremely fine structure with high throughput, but the process is limited by two-dimensionality. Baldacchini said “this means that fabricators are missing out on one entire dimension.” Other limitations include:

  • The expense of the instrumentation for producing these structures
  • A clean room environment is often required
  • The number of substrates and materials is limited to silicon and semiconductors

Baldacchini mentiones: “There is definitely a need to break the barriers of these limitations to produce new micro and nano devices.

Breaking down barriers to nanofabrication

A number of challenges are presented when fabricating nanostructures. These depend mostly on the specific technique used to fabricate the structure and the features of the structure itself — such as its size, shape and surface area.

Laser assisted nanofabrication (Journal of Laser Applications 24, 042007 (2012)) provides a whole raft of unique abilities for building nano- and microstructures. Laser irradiation projected on material surfaces can cause several effects, including localised heating, melting, ablation, decomposition and photochemical reaction — and leads to the realisation of various complex nanostructures with materials such as graphene, carbon nanotubes and even polymers and ceramics.

Characterisation

When characterising structures, it is crucial to have a tool that allows precise measurements to examine fabricated structures at nanoscale precision. There is a need to look at the structures topology and uniformity to make sure the ‘build’ quality is up to scratch. It is also important to be able to characterise the new material by determining its surface composition, and even its internal composition.

SEM image of ablated sample from Newport mag 2150x.png                  CT Phenom at Newport Corp4.jpg

Phenom desktop SEM images at 2,150x (left) and 8,300x (right) magnification of ablated samples

A scanning electron microscope (SEM) is the ideal tool for this type of work, providing the ability to focus in to tens of thousands of nanometers and view small scale and nanoscale sample features. Baldacchini said “A scanning electron microscope is an invaluable tool to characterise products. We can view changes in the samples surface when it is ablated, or we can use SEM to study the topology of a sample we have produced using additive manufacturing.”

Innovative techniques

TAC have developed a high-resolution, nanoscale 3D printing technique called two-photon polymerization. Using two-photon polymerisation allows the creation of extremely 3D polymeric structures which are often tens of microns large with nanoscale features. SEM is frequently used for structure characterisation, as a means of verifying the nanoscale structure that has been built. In addition to this, Baldacchini’s research has involved applying nonlinear optical microscopy, such as CARS microscopy, to investigate the chemical and mechanical properties of the microstructure created by two-photon polymerization.

One of the tools that we developed in the TAC for aiding laser microfabrication is called the Laser µFAB. It is a complete system that enables customers to connect their own laser to the machine and perform different types of laser micromachining.

The system is provided with software that enables customers to import a two-dimensional drawing and reproduce the drawing using the motion of the stages with respect to the stationary laser. This allows users to create any three-dimensional objects they want to produce.

Characterisation with a SEM

So, according to Baldacchini at Newport Corporation, a scanning electron microscope proves to be an invaluable tool to characterise products and verify nanoscale structures. If you would like to learn even more about how TAC utilizes SEM to verify nanoscale structures, you can download the detailed Case Study here:

Download the Newport case study


About the author

Jake Wilkinson is an editor for AZoNetwork, a collection of online science publishing platforms. Jake spends his time writing and interviewing experts on a broad range of topics covering materials science, nanoscience, optics, and clean technology.

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