Scanning probe lithography (SPL) describes a set of nanolithographic methods to pattern material on the

nanoscale The nanoscopic scale (or nanoscale) usually refers to structures with a length scale applicable to nanotechnology, usually cited as 1–100 nanometers (nm). A nanometer is a billionth of a meter. The nanoscopic scale is (roughly speaking) a lo ...

using scanning probes. It is a direct-write, mask-less approach which bypasses the

diffraction limit The resolution of an optical imaging system a microscope, telescope, or camera can be limited by factors such as imperfections in the lenses or misalignment. However, there is a principal limit to the resolution of any optical system, due to t ...

and can reach resolutions below 10 nm. It is considered an alternative lithographic technology often used in academic and research environments. The term ''scanning probe lithography'' was coined after the first patterning experiments with

scanning probe microscope Scan may refer to: Acronyms * Schedules for Clinical Assessment in Neuropsychiatry (SCAN), a psychiatric diagnostic tool developed by WHO * Shared Check Authorization Network (SCAN), a database of bad check writers and collection agency for bad ...

s (SPM) in the late 1980s.

Classification

The different approaches towards SPL can be classified by their goal to either add or remove material, by the general nature of the process either chemical or physical, or according to the driving mechanisms of the probe-surface interaction used in the patterning process: mechanical,

thermal A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

, diffusive and

electrical Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...

Overview

Mechanical/thermo-mechanical

Mechanical scanning probe lithography (m-SPL) is a nanomachining or ''nano-scratching'' top-down approach without the application of heat. Thermo-mechanical SPL applies heat together with a mechanical force, e.g. indenting of polymers in the

Millipede memory Millipede memory is a form of non-volatile computer memory. It promised a data density of more than 1 terabit per square inch (1 gigabit per square millimeter), which is about the limit of the perpendicular recording hard drives. Millipede stor ...

Thermal

Thermal scanning probe lithography (t-SPL) uses a heatable scanning probe in order to efficiently remove material from a surface without the application of significant mechanical forces. The patterning depth can be controlled to create high-resolution 3D structures.

Thermo-chemical

Thermochemical scanning probe lithography (tc-SPL) or ''thermochemical nanolithography'' (TCNL) employs the scanning probe tips to induce thermally activated chemical reactions to change the chemical

functionality Function or functionality may refer to: Computing * Function key, a type of key on computer keyboards * Function model, a structured representation of processes in a system * Function object or functor or functionoid, a concept of object-oriente ...

or the phase of surfaces. Such thermally activated reactions have been shown in

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

organic semiconductor Organic semiconductors are solids whose building blocks are pi-bonded molecules or polymers made up by carbon and hydrogen atoms and – at times – heteroatoms such as nitrogen, sulfur and oxygen. They exist in the form of molecular crystals or ...

electroluminescent Electroluminescence (EL) is an optical and electrical phenomenon, in which a material emits light in response to the passage of an electric current or to a strong electric field. This is distinct from black body light emission resulting from ...

conjugated polymers, and nanoribbon resistors. Furthermore,

deprotection A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic synthesis. In man ...

functional group In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the re ...

s (sometimes involving a temperature gradients), reduction of oxides, and the crystallization of piezoelectric/ferroelectric

ceramics A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...

has been demonstrated.

Dip-pen/thermal dip-pen

Dip-pen scanning probe lithography (dp-SPL) or ''dip-pen nanolithography'' (DPN) is a scanning probe lithography technique based on

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemica ...

, where the tip is employed to create patterns on a range of substances by deposition of a variety of liquid inks. Thermal dip-pen scanning probe lithography or ''thermal dip-pen nanolithography'' (TDPN) extends the usable inks to solids, which can be deposited in their liquid form when the probes are pre-heated.

Oxidation

Oxidation scanning probe lithography (o-SPL), also called ''local oxidation nanolithography'' (LON), ''scanning probe oxidation, nano-oxidation, local anodic oxidation,'' ''AFM oxidation lithography'' is based on the spatial confinement of an

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

reaction.

Bias induced

Bias-induced scanning probe lithography (b-SPL) uses the high electrical fields created at the apex of a probe tip when voltages are applied between tip and sample to facilitate and confining a variety of chemical reactions to

decompose Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is ...

gases or liquids in order to locally deposit and grow materials on surfaces.

Current induced

In current induced scanning probe lithography (c-SPL) in addition to the high electrical fields of b-SPL, also a focused electron current which emanates from the SPM tip is used to create nanopatterns, e.g. in polymers and molecular glasses.

Magnetic

Various scanning probe techniques have been developed to write magnetization patterns into ferromagnetic structures which are often described as magnetic SPL techniques. Thermally-assisted magnetic scanning probe lithography (tam-SPL) operates by employing a heatable scanning probe to locally heat and cool regions of an exchange-biased ferromagnetic layer in the presence of an external magnetic field. This causes a shift in the

hysteresis loop Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of ...

of exposed regions, pinning the magnetization in a different orientation compared to unexposed regions. The pinned regions become stable even in the presence of external fields after cooling, allowing arbitrary nanopatterns to be written into the magnetization of the ferromagnetic layer. In arrays of interacting ferromagnetic nano-islands such as artificial spin ice, scanning probe techniques have been used to write arbitrary magnetic patterns by locally reversing the magnetization of individual islands. Topological defect-driven magnetic writing (TMW) uses the dipolar field of a magnetized scanning probe to induce

topological defects In mathematics, topology (from the Greek words , and ) is concerned with the properties of a geometric object that are preserved under continuous deformations, such as stretching, twisting, crumpling, and bending; that is, without closing ho ...

in the magnetization field of individual ferromagnetic islands. These topological defects interact with the island edges and annihilate, leaving the magnetization reversed. Another way of writing such magnetic patterns is field-assisted magnetic force microscopy patterning, where an external magnetic field a little below the switching field of the nano-islands is applied and a magnetized scanning probe is used to locally raise the field strength above that required to reverse the magnetization of selected islands. In magnetic systems where interfacial Dzyaloshinskii–Moriya interactions stabilize magnetic textures known as

magnetic skyrmion In physics, magnetic skyrmions (occasionally described as 'vortices,' or 'vortex-like' configurations) are statically stable solitons which have been predicted theoretically and observed experimentally in condensed matter systems. Skyrmions can be ...

s, scanning-probe magnetic nanolithography has been employed for the direct writing of skyrmions and skyrmion lattices.

Comparison to other lithographic techniques

Being a serial technology, SPL is inherently slower than e.g. photolithography or nanoimprint lithography, while parallelization as required for mass-fabrication is considered a large systems engineering effort (''see also

''). As for resolution, SPL methods bypass the optical

due to their use of scanning probes compared with

photolithographic In integrated circuit manufacturing, photolithography or optical lithography is a general term used for techniques that use light to produce minutely patterned thin films of suitable materials over a substrate, such as a silicon wafer, to protect ...

methods. Some probes have integrated in-situ metrology capabilities, allowing for feedback control during the write process.
Scanning probe nanolithography system and method (EP2848997 A1) SPL works under Standard conditions for temperature and pressure, ambient atmospheric conditions, without the need for ultra high vacuum ( UHV), unlike e-beam or EUV lithography.

References

* {{Nanolith Lithography (microfabrication) Nanotechnology Scanning probe microscopy