University of Colorado researchers sponsored by Semiconductor Research Corporation (SRC), a university-research consortium for semiconductor technologies, have developed new microscopic imaging techniques to help advance next-generation nanotechnology in applications ranging from data storage to medicine.
The research focuses on leveraging powerful tabletop microscopes equipped with coherent beams of extreme-ultraviolet (EUV) light. Traditional scanning electron and atomic force microscopy techniques can damage a sample. The University of Colorado’s approach promises quantitative full-field imaging with as much as a 20x improvement in spatial resolution, ultimately resulting in smarter, more energy-efficient nanocircuit designs.
“Better imaging techniques are critical for all areas of science and advanced technology, and current imaging techniques have not reached their fundamental limits in terms of spatial and temporal resolutions, dose, speed or chemical sensitivity,” said Margaret Murnane, professor of Physics and Electrical and Computer Engineering at the University of Colorado, Boulder. “Tabletop microscopes are needed for iterative design and optimization across a broad range of nanoscience and nanotechnology applications, as we work as an industry to continue to advance Moore’s Law.”
Until recently, the resolution of X-ray microscopes was severely limited by diffractive optics. Although 10 nanometer (nm) spatial resolution was demonstrated, 25nm is typical – nowhere near the wavelength limit, according to the research team. Electron microscopies cannot simultaneously achieve high spatial and temporal resolution.
Opaque, disordered or scattering samples that are common in chemistry, materials and biology present a formidable challenge using any imaging modality. Notable demonstrations aside, current X-ray, electron and optical microscopies are simply too cumbersome and slow to routinely image functioning systems in real space and time, severely limiting progress.
Murnane explains that new coherent, short wavelength light sources fill the critical need for metrology to bridge this gap. As an example, although the Ruby laser was first demonstrated 55 years ago (which emitted coherent beams in the red region of the spectrum at 694nm), the shortest wavelength laser in widespread use is the excimer laser around 193nm. This means that in 55 years, the wavelength of widely accessible lasers has been reduced by less than a factor of 4.
The University of Colorado’s work employs coherent, or laser-like, beams of EUV light with wavelength at 30nm nearly an order of magnitude shorter that the excimer, achieving very high contrast images with a resolution of 40nm laterally and 5 angstrom (Å) vertically, representing a technology poised to change the industry.
Further leveraging advantages of the tabletop model, the University of Colorado team plans to demonstrate in the next two to five years coherent EUV and X- ray microscopes that produce real-time movies of functioning materials with less than 5nm lateral resolution and 1 Å vertical resolution in 3D.
The team’s deep-ultraviolet and EUV laser-like source technology could be used for defect detection or other nanometrology applications — either as a stand-alone solution or as an inline tool. The EUV microscope could also provide high-contrast, low-damage, full-field, real-time imaging of functioning circuits and nanosystems, among other fabrication application usages.
“Many industries that harness nanotechnologies can benefit from better microscopes for iterative and smart designs,” said Kwok Ng, Senior Science Director of Nanomanufacturing Materials and Processes at SRC. “The resolution will only continue to improve as the illumination wavelengths decrease.”