Patterning methods at the nanoscale play a decisive role in our capability to make nanostructures with good control of their interfaces and thus electrical, optical and other properties of the devices. What approaches can be used to achieve highest possible resolution, preferably with atomic-scale accuracy with high throughput? This and other questions are addressed in Novel patterning methods, which include new lithography and etching approaches.
Atomic layer etching
Semiconductor device scaling requires atomic level precision processing and Atomic Layer Etching (ALE) has great potential for this. ALE is a cyclic etching process in which a well-defined atomically thin layer is etched in each cycle, i.e. this etching process is an example of a digital nanofabrication method.
Unlike the conventional reactive ion etching technique, atomic layer etching (ALE) can provide a damage-free pattern transfer with ultimate etch control for features of all length scales, down to the atomic scale, and for all feature geometries. Such feature of ALE is essential for etching structures with different lateral sizes, which is required for e.g. good quality and high-resolution nanoimprint stamps.
Schematic illustration of Atomic Layer Etching (ALE). The ALE process cycle includes several steps: absorption of a reactive gas molecules on the surface, purging of excess molecules, plasma-stimulated etch step, removal of the reaction products followed by purging. One cycle typically removes one monolayer of the etch material, so atomic layer control is possible.
Block Copolymer (BCP) lithography
Block copolymers (BCPs) represent a bottom-up approach of nanofabrication. They consist of covalently bonded dissimilar blocks, and can self-assemble into nanophase separated patterns of typically 10-50 nm periodicity. Most commonly used are hexagonally arranged dots or line patterns. These patterns can be utilized for lithographic purposes, such as pattern transfer into the underlying substrate or creating periodic functionalities. We explore different types of block copolymers for self-assembly, directed self-assembly, and application of BCP in nanofabrication. We apply our knowledge to e.g. create high density, sub-10 nm resolution templates, for selective area vertical nanowire epitaxy, or for nanoimprint applications.
SEM top view of 10 nm pitch alumina (Al2O3) on Si substrate, made using the BCP PS-b-MH, after solvent vapor annealing, sequantial infiltration synthesis and polymer removal.
Displacement Talbot lithography (DTL)
This is a relatively novel lithographic technique, which is based on optical exposure through a mask to create regular patterns with feature smaller than the wavelength of light over large areas (e.g. 6 inch wafers). One of the advantages of the displacement Talbot lithography is its high throughput, since it is a parallel exposure technique and high-resolution, also this technique is a non-contact method, which reduce the risk of surface damage and contamination. Our research includes applications of the displacement Talbot lithography for fabrication of large-area templates for epitaxial growth of III-V nanowires and other applications.
High-Definition Nanoimprint Stamp Fabrication by Atomic Layer Etching, S.A. Khan, D.B. Suyatin, J. Sundqvist, M. Graczyk, M. Junige, C. Kauppinen, A. Kvennefors, M. Huffman, I. Maximov. ACS Applied Nano Materials 1, 2476, 2482 (2018). DOI: 10.1021/acsanm.8b00509
See article nanoimprint stamp fabrication at publisher's site
Atomic Layer Etching of Gallium Nitride (0001), C. Kauppinen, S.A. Khan, J. Sundqvist, D.B. Suyatin, S. Suihkonen, E.I. Kauppinen. Journal of Vacuum Science & Technology, A 35, 060603 (2017). DOI: 10.1116/1.4993996
See article atomic layer etching at publisher's site
Carbohydrate-based block copolymer systems: directed self-assembly for nanolithography applications, I. Otsuka, N. Nilsson, D. B. Suyatin, I. Maximov, R. Borsali. Soft Matter Issue 40 (2017). DOI: 10.1039/C7SM01429E
See article carbohydrate-based block copolymer at publisher's site
Md Sabbir Ahmed Khan, Evaluation of Atomic Layer Etching Possibility at Lund Nano Lab Master thesis, Lund University 2016.
See Sabbir Ahmed Khan's thesis at the Research Portal
Oskar Boström, Inductively-Coupled Plasma Etching for Nanoimprint Si-masters, Master thesis, Lund University 2019.
See Oskar Boström's thesis at the Research Portal