PSI researchers use extreme UV light to produce tiny structures for information technology.

Researchers at PSI have refined a process known as photolithography, which can further advance miniaturisation in information technology.

In many areas of information technology, the trend towards ever more compact microchips continues unabated. This is mainly because production processes make it possible to achieve ever smaller structures, so that the same number of information-processing components takes up less and less space. Fitting more components into less space increases the performance and lowers the price of the microchips used in smartphones, smartwatches, game consoles, televisions, Internet servers and industrial applications.

A research group led by Dimitrios Kazazis and Yasin Ekinci at the Laboratory for X-ray Nanoscience and Technologies at the Paul Scherrer Institute PSI, in collaboration with researchers from University College London (UCL) in the UK, has now succeeded in making important progress towards further miniaturisation in the IT industry. The scientists have demonstrated that photolithography – the method of patterning widely used in the mass production of microchips – works even when no photosensitive layer has been applied to the silicon.

Photolithography, which literally means “drawing on stone with light”, is the most important process in the industrial manufacture of electronic components. In principle, it works like exposing a photographic film to light, except that the carrier material is silicon rather than celluloid. A light-sensitive material, technically known as a photoresist, is applied to a silicon wafer. This is exposed to light in the pattern of the blueprint for the chip, which alters the chemical properties of the photoresist. This either becomes firmer or less firm. Subsequent treatment removes the exposed (positive process) or the unexposed (negative process) areas, leaving behind the desired circuit pattern, including the conductive traces. At present, this process is mainly carried out using lasers with a wavelength of around 240 to 193 nanometres.

However, the PSI researchers took a different approach. They opted against a photoresist, which degrades the image and is therefore an obstacle to miniaturisation.

Read more on the PSI website

Image: The PSI researchers involved at the XIL-II beamline of the SLS. From left to right: Yasin Ekinci, Gabriel Aeppli, Matthias Muntwiler, Procopios Christou Constantinou, Dimitrios Kazazis, Prajith Karadan

Credit: Paul Scherrer Institute/Mahir Dzambegovic

Direct X-ray and electron-beam lithography of halogenated zeolitic imidazolate framework

Metal-organic frameworks (MOFs) offer disruptive potential in micro- and optoelectronics because of their chemical versatility and high porosity. For instance, the low dielectric constant (low-k) resulting from their porosity makes MOFs competitive candidates for high-performance insulators in future microchips. Both the MOF and microelectronics communities have been striving towards integrating MOFs in microchips, which requires two key engineering steps: thin film deposition and lithographic patterning. However, conventional lithography techniques use a sacrificial layer, so-called photoresist, to transfer a pattern into the desired material. The use of photoresist complicates the process, and might induce contamination of the highly porous MOF films. 

A group of researchers from KU Leuven (Belgium) coordinated by Rob Ameloot has used the deep X-ray lithography (DXRL) beamline at Elettra to demonstrate that MOFs can be patterned by X-ray lithography without the use of resist layer. The method is based on selective X-ray exposure of the MOF film, which induces chemical changes that enable its removal by a common solvent. This process completely avoids the resist layer, thus significantly simplifying patterning while maintaining the physicochemical properties of patterned MOFs intact. 

Read more on the Elettra website