S-Space College of Natural Sciences (자연과학대학) Dept. of Physics and Astronomy (물리·천문학부) Physics (물리학전공) Theses (Ph.D. / Sc.D._물리학전공)
A study of the atomic force microscopy lithography and its applications
원자힘 현미경을 이용한 식각 및 그 응용에 대한 연구
- 자연과학대학 물리·천문학부(물리학전공)
- Issue Date
- 서울대학교 대학원
- 학위논문 (박사)-- 서울대학교 대학원 : 물리·천문학부(물리학전공), 2014. 2. 제원호.
- We fabricated reproducible quantum dots and nanowires while minimizing atomic force microscopy (AFM) tip damage. Uniform patterns of quantum dots and nanowires were reproducibly fabricated by creating holes in a double-layer structure using AFM indentation, dry-etching of polymer resists, and metal deposition through the indentation holes. The double-layer was fabricated by depositing a thin gold layer onto a polymethyl methacrylate (PMMA) layer on a silicon dioxide substrate. The indentation force exerted on the double-layer was set so that the AFM tip penetrated the thin gold layer without the tip touching the silicon dioxide substrate in order to minimize of AFM tip. This double-layer indentation was used to create a pattern of holes in the thin gold layer which acts as a metal mask in the dry-etching process. The PMMA was exposed to an isotropic O2 plasma etchant through the holes in the indentation pattern to form an undercut between the substrate and the gold layer. The undercut enables the deposition of metal on the substrate without having polymer residues. Quantum dots were subsequently created through the deposition of gold on the exposed silicon dioxide substrate through the indentation holes.
Gold nanowires were also fabricated by consecutive-hole-indentation method by adjusting the distance between the holes using the same double-layer indentation method. The topographic and electrical measurements of the fabricated gold nanowires suggest that our method is capable of making uniform and reproducible nanowires. The scanning electron microscopy images of the tips confirmed that the consecutive-hole-indentation method is less invasive than the conventional ploughing method, where constant tip contact occurs with the substrate during the formation of nanowires. We also investigated removal of the bulge containing the metal by sonification.
We investigated the dependence of indented structures on the speed at which a tilted AFM tip penetrated a double-layer consisting of metal and an organic material for the potential development of a reproducible AFM-based nanolithography technique. Distorted half-circles were formed by the AFM tip when the indentation speed was slower than 5 ㎛/s for gold and PMMA thin film, whereas triangular structures were formed when the speed was faster than 5 ㎛/s. As the indentation speed increased, the depth of the indented structure also increased while its length decreased. We found that such structural changes from the tetrahedral shape of AFM tip originated from the rotational motion of the tilted AFM tip in the double-layer.