Approaching Angstrom-Scale\nResolution in Lithography\nUsing Low-Molecular-Mass Resists (<500 Da)

Resists that enable high-throughput and high-resolution\npatterning\nare essential in driving the semiconductor technology forward. The\nultimate patterning performance of a resist in lithography is limited\nbecause of the trade-off between resolution, line-width roughness,\nand sensitivity; improving one or two of these parameters typically\nleads to a loss in the third. As the patterned feature sizes approach\nangstrom scale, the trade-off between these three metrics becomes\nincreasingly hard to resolve and calls for a fundamental rethinking\nof the resist chemistry. Low-molecular-mass monodispersed metal-containing\nresists of high atom economy can provide not only very high resolution\nbut also very low line-width roughness without sacrificing sensitivity.\nHere we describe a modular metal-containing resist platform (molecular\nmass <500 Da) where a molecular resist consists of just two components:\na metal and a radical initiator bonded to it. This simple system not\nonly is amenable to high-resolution electron beam lithography (EBL)\nand extreme ultraviolet lithography (EUVL) but also unites them mechanistically,\ngiving a consolidated perspective of molecular and chemical processes\nhappening during exposure. Irradiation of the resist leads to the\nproduction of secondary electrons that generate radicals in the initiator\nbonded to metal. This brings about an intramolecular rearrangement\nand causes solubility switch in the exposed resist. We demonstrate\nrecord 1.9–2.0 nm isolated patterns and 7 nm half-pitch dense\nline-space features over a large area using EBL. With EUVL, 12 nm\nhalf-pitch line-space features are shown at a dose of 68 mJ/cm<sup>2</sup>. In both of these patterning techniques, the line-width roughness\nwas found to be ≤2 nm, a record low value for any resist platform,\nalso leading to a low-performance trade-off metric, <i>Z</i> factor, of 0.6 × 10<sup>–8</sup> mJ·nm<sup>3</sup>. With the ultimate resolution limited by instrumental factors, potential\npatterning at the level of a unit cell can be envisaged, making low-molecular-mass\nresists best poised for angstrom-scale lithography.