Scanning Probe Lithography (SPL)
Patterning at sub-5nm with FE-SPL
All the lithographic techniques have a cost-dependent resolution. By increasing the resolution, the costs can growth immensely. nano analytik GmbH developed a new cost-effective Scanning Probe Lithography (SPL) System operating at ambient or under vacuum conditions.
This field-emission scanning probe lithography tool is based on the low-energy Fowler-Nordheim (FN) electron field-emission from ultra-sharp scanning probe tips placed in close proximity to a resist-covered specimen. FE-SPL has significant advantages over traditional e-beam lithography including (I) reduced proximity effect; (II) sub-5 nm lateral resolution; (III) low cost of implementation; (IV) ambient operation; (V) no electron column or optics; and (VI) the ability to exposure and image with the same probe in a non-destructive manner.
Therefore, the spatial resolution is defined mainly by the primary beam and the therefrom induced secondary electrons. As a result, backscattering is reduced, the exposure efficiency and sensitivity of the resist are increased, and radiation damage and heating effects are suppressed. Additionally, there is evidence that primary and secondary electrons in EBL, as well as ultraviolet (UV) exposure in optical lithography can considerably damage ultra-thin materials, from graphene to TMDC films ,.
The combination of different approaches and the outstanding capabilities of closed-loop Field-Emission Scanning Probe Lithography (FE-SPL) with other lithography techniques like optical or electron beam lithography (EBL) reveals a promising way to improve the reproducibility, resolution and throughput in combination with excellent overlay and placement accuracy. This approach is called “mix and match” lithography.
In particular, the AFM-imaging and FE-SPL-lithographic resolution capabilities provided by scanning probe microscopy (SPM) methods touches the atomic level, which expresses the theoretical limit of constructing nanoelectronic devices.
The new approach is capable to create routinely sub-5nm features onto non-planar surfaces ,. Reproducible patterning at sub-5nm scale constitutes as the main technological bottleneck in next generation of electronic device manufacturing. Caused by this lithographic limitations prototyping of novel device concepts becomes challenging. In contrast to EBL, we use low energetic electrons of <100 eV. Here, the electron energy is close to lithographically relevant excitation and the electrons penetration volume is minimized. In consequence, a nano-scale confined lithographic interaction is enabled and direct ablation of resist material (so called “positive tone) was technologically established .
FE-SPL has been used for the fabrication of single electron transistors (SETs) operating at room temperature (RT-SETs). Such SETs are a starting point for the realisation of atomic scale devices. Especially, we exploit the confinement of the potential well, created by an embedded dopant atom ( P, As or B) in an insulator, due to high tunnel barriers of SiO2.