MAX IV X-ray beams help seeing inside future nanoscale electronics

Thanks to the innovative concept of the multi-band achromats, MAX IV Laboratory has paved the way for fourth-generation synchrotrons and as of now, it is the most brilliant source of X-ray for research. The high coherence and brilliance delivered at MAX IV are giving scientists the tools for performing research previously unachievable in the X-ray spectrum. This potential is highlighted in a new publication centred on investigating innovative non-destructive characterization of embedded nanostructures.

A team from Lund University composed of researchers from the Department of Electrical and Information Technology, the Department of Physics, and NanoLund, came to the NanoMAX beamline at MAX IV. Here they used the scanning X-ray nanodiffraction to analyze semiconductor nanowires in wrapped, gate-all-around transistor geometry. They proved that X-ray light from fourth-generation synchrotrons is the key for developing non-destructive characterization of nanostructures.

This is a result that the team has been strenuously working towards, as explains Dmitry Dzhigaev, first author of the article. “We performed these experiments at other facilities but weren’t able to successfully gather conclusive data from the samples. Using the fourth-generation X-ray beam here at MAX IV, it took us two days to complete the experiments successfully. We could furthermore access length scales that are very difficult to reach with nanofocus beams from previous generation X-ray sources.”

The true revolutionary potential lies in the array of samples that can be studied using fourth-generation X-rays. Currently, nanoelectronics, such as nanowires, must be isolated to be analyzed, a process that compromises the functionality of the sample. “We were measuring isolated structures, which do not resemble any practical application and are mere proofs of principle” explains Dmitry. In practical applications, nanocomponents are assembled in complex architectures, where the interaction between elements, as well as the assembly process itself, affect the performance of the different parts. “There is a lack of measurement and observations in the X-ray field on the fully processed device following the construction and processing steps. This means that so far we had no way to understand what happens to the functional parts inside, say, a microprocessor.”

Dmitry explains how the performance of nanowires can be severely hampered during the assembly process. Therefore, it is crucial to observe the state of these nanowires once assembled into the final structure. “Microchips are built layer by layer with complex circuits and in the end, you don’t know what happens to the functional parts inside. If you want to create nanostructures using new materials like, for example, processors based on elements other than silicon, you must be able to assess how the components interact and behave once assembled. This is something that before fourth-generation X-ray sources could not be achieved without compromising the sample.”

There’s a clear potential for implementing these new analysis techniques in the industrial manufacturing of nanoelectronics. “We now have the means to adjust the processing step during the construction to optimize the properties of the nanowire and better control how the device behaves.” These X-ray techniques open new possibilities for manufacturers to operate a tighter control on the production process and prevent production flaws. “Companies producing nanoelectronics must be able to verify that the final product corresponds to the design. This is particularly important with regards to security. You don’t want a production flaw to compromise the security of the devices you sell”.

The project at the core of this publication is led by the Electrical and Information Technology department at Lund University, where researchers study how to make processors more power efficient by modifying the amount of voltage needed to switch the transistors. “There are conditions such as space exploration where the amount of energy is limited. By using different elements from the III-V groups of the periodic table in different combinations, we can change the switching behaviour of the processor, making them more energy-efficient.”

The published research focuses on tungsten (W) gates, which are layers of tungsten 10nm thick, wrapped around an InAs-GaSb (Indium Arsenide – Gallium Antimonide) nanowire. The W layer compresses or decompresses the wire, affecting how electrons propagate inside it. The team investigates which combinations give the best performance. X-rays beams from MAX IV are a crucial ally because they enable researchers to observe the performance and behaviour of these nanowires without altering the sample. “We developed a procedure to disassemble the device in lamellae, which are easy to observe in a non-destructive way using fourth-generation X-ray sources.” The next step for the team will be to attempt operando measurements: observe the device in action. “Operando experiments will allow us to see how devices behave while in operation and, in case of any structural change, verify which aspect of its functional activity was compromised during the preparation phase.”

This new publication is yet another proof of the impact that new generation synchrotrons can have on the future of fields such as material science and technology. MAX IV is truly succeeding in making the invisible visible.

Header image: Depiction of the process of nanofocused X-ray beams scattering from a single nanowire transistor. Positively charged particles (+) and negatively charged particles (-) represent charge carriers in a p–n junction (where p–n junction is an interface between p-type and n-type semiconductor materials). Outgoing beams, depicted as white rays, represent scattering from different segments of the device (InAs and GaSb). The bending with arrows represents the strain revealed in the experiment. Illustration by Dmitry Dzhigaev, Lund University.