To increase processing speed and reduce power consumption of electronic devices, the microelectronics industry continues to push for smaller feature sizes. Transistors in today's cellphones are typically 10 nanometers (nm) across — about 50 silicon atoms wide — or smaller. Scaling transistors down below these dimensions with higher accuracy requires advanced materials for lithography — the primary technique for printing electrical circuit elements on silicon wafers to manufacture electronic chips. One challenge is developing robust resists, or materials used as templates for transferring circuit patterns into device-useful substrates such as silicon.
Infiltration synthesis was used to create resists that combine the organic polymer poly(methyl methacrylate, PMMA) with inorganic aluminum oxide. Owing to its low cost and high resolution, PMMA is the most widely used resist in electron-beam lithography (EBL) in which electrons are used to create the pattern template; however, at the resist thicknesses that are necessary to generate the ultra-small feature sizes, the patterns typically start to degrade when they are etched into silicon, failing to produce the required high aspect ratio (height to width).
These hybrid organic-inorganic resists exhibit a high lithographic contrast and enable the patterning of high-resolution silicon nanostructures with a high aspect ratio. By changing the amount of aluminum oxide (or a different inorganic element) infiltrated into PMMA, the parameters can be tuned for particular applications.
Though other hybrid resists have been proposed, most of them require high electron doses (intensities), involve complex chemical synthesis methods, or have expensive proprietary compositions. Thus, these resists are not optimal for the high-rate, high-volume manufacture of next-generation electronics. Conventionally, the microelectronics industry has relied upon optical lithography, whose resolution is limited by the wavelength of light that the resist gets exposed to; however, EBL and other nanolithography techniques, such as extreme ultraviolet lithography (EUVL), can push this limit because of the very small wavelength of electrons and high-energy ultraviolet light.
Going forward, the team will study how the hybrid resists respond to EUV exposure. The energy absorption by the organic layer of EUVL resists is very weak. Adding inorganic elements, such as tin or zirconium, can make them more sensitive to EUV light.