Thermal scanning probe lithography (t-SPL) is a form of
scanning probe lithography
Scanning probe lithography (SPL) describes a set of nanolithographic methods to pattern material on the nanoscale using scanning probes. It is a direct-write, mask-less approach which bypasses the diffraction limit and can reach resolutions belo ...
(SPL) whereby material is structured 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, primarily through the application of
thermal energy
The term "thermal energy" is used loosely in various contexts in physics and engineering. It can refer to several different well-defined physical concepts. These include the internal energy or enthalpy of a body of matter and radiation; heat, de ...
.
Related fields are ''thermo-mechanical'' ''SPL'' (see also
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 ...
), ''thermochemical'' ''SPL'' (or
thermochemical nanolithography) where the goal is to influence the local chemistry, and ''thermal''
dip-pen lithography as an additive technique.
History
Scientists around Daniel Rugar and
John Mamin at the
IBM research laboratories in Almaden have been the pioneers in using heated
AFM (atomic force microscope) probes for the modification of surfaces. In 1992, they used microsecond
laser pulses to heat AFM tips to write indents as small as 150 nm into the
polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
PMMA PMMA may refer to:
* para-Methoxymethamphetamine, a stimulant drug
* Philippine Merchant Marine Academy
The Philippine Merchant Marine Academy ( fil, Akademiya sa Bapor Pangkalakalan ng Pilipinas) also referred to by its acronym PMMA) is a ma ...
at rates of 100 kHz. In the following years, they developed
cantilevers
A cantilever is a rigid structural element that extends horizontally and is supported at only one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a canti ...
with
resonance frequencies above 4 MHz and integrated
resistive heaters and
piezoresistive sensors for writing and reading of data. This thermo-mechanical
data storage concept formed the basis of the
Millipede project which was initialized by Peter Vettiger and
Gerd Binnig
Gerd Binnig (; born 20 July 1947) is a German physicist. He is most famous for having won the Nobel Prize in Physics jointly with Heinrich Rohrer in 1986 for the invention of the scanning tunneling microscope.
Early life and education
Binnig ...
at the
IBM Research laboratories Zurich in 1995. It was an example of a memory storage device with a large array of parallel probes, which was however never commercialized due to growing competition from
non-volatile memory
Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data.
Non-volatile memory typi ...
such as
flash memory. The storage medium of the Millipede memory consisted of polymers with shape memory functionality, like e.g.
cross-link
In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...
ed
polystyrene, in order to allow to write data indents by
plastic deformation
In engineering, deformation refers to the change in size or shape of an object. ''Displacements'' are the ''absolute'' change in position of a point on the object. Deflection is the relative change in external displacements on an object. Strain ...
and erasing of the data again by heating. However, evaporation instead of plastic deformation was necessary for
nanolithography
Nanolithography (NL) is a growing field of techniques within nanotechnology dealing with the engineering (patterning e.g. etching, depositing, writing, printing etc) of nanometer-scale structures on various materials.
The modern term reflects on ...
applications to be able to create any pattern in the
resist
A resist, used in many areas of manufacturing and art, is something that is added to parts of an object to create a pattern by protecting these parts from being affected by a subsequent stage in the process. Often the resist is then removed.
For ...
. Such local evaporation of resist induced by a heated tip could be achieved for several materials like
pentaerythritol tetranitrate
Pentaerythritol tetranitrate (PETN), also known as PENT, PENTA, (ПЕНТА, primarily in Russian) TEN, corpent, or penthrite (or, rarely and primarily in German, as nitropenta), is an explosive material. It is the nitrate ester of pentaerythr ...
, cross-linked
polycarbonates, and
Diels-Alder polymers. Significant progress in the choice of resist material was made in 2010 at IBM Research in Zurich, leading to high resolution and precise 3D-relief patterning
with the use of the
self-amplified depolymerization Depolymerization (or depolymerisation) is the process of converting a polymer into a monomer or a mixture of monomers. This process is driven by an increase in entropy.
Ceiling temperature
The tendency of polymers to depolymerize is indicated by ...
polymer
polyphthalaldehyde (PPA)
and molecular glasses as resist, where the polymer decomposes into volatile
monomers
In chemistry, a monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization.
Classification
Mo ...
upon heating with the tip without the application of mechanical force and without pile-up or residues of the resist.
Working principle
The thermal cantilevers are fabricated from
silicon wafers using
bulk
Bulk can refer to:
Industry
* Bulk cargo
* Bulk liquids
* Bulk mail
* Bulk material handling
* Bulk pack, packaged bulk materials/products
* Bulk purchasing
*
Baking
* Bulk fermentation, the period after mixing when dough is left alone to f ...
– and
surface
A surface, as the term is most generally used, is the outermost or uppermost layer of a physical object or space. It is the portion or region of the object that can first be perceived by an observer using the senses of sight and touch, and is ...
micro-machining processes. Probes have a radius of curvatures below 5 nm, enabling sub-10 nm resolution in the resist. The
resistive heating
Joule heating, also known as resistive, resistance, or Ohmic heating, is the process by which the passage of an electric current through a conductor produces heat.
Joule's first law (also just Joule's law), also known in countries of former U ...
is carried out by integrated micro-heaters in the
cantilever
A cantilever is a rigid structural element that extends horizontally and is supported at only one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a cant ...
legs which are created by different levels of
doping. The time constant of the heaters lies between 5 μs to 100 μs.
Electromigration limits the longterm sustainable heater temperature to 700–800 °C.
The integrated heaters enable
in-situ metrology of the written patterns, allowing feedback control, field
stitching without the use of alignment markers
and using pre-patterned structures as reference for sub-5 nm
overlay
Overlay may refer to:
Computers
*Overlay network, a computer network which is built on top of another network
*Hardware overlay, one type of video overlay that uses memory dedicated to the application
*Another term for exec, replacing one process ...
. Pattern transfer for semiconductor
device fabrication including
reactive ion etching
Reactive-ion etching (RIE) is an etching technology used in microfabrication. RIE is a type of dry etching which has different characteristics than wet etching. RIE uses chemically reactive plasma to remove material deposited on wafers. The pl ...
and metal
lift-off
Liftoff, lift-off, or lift off may refer to:
Technology
* Lift-off (microtechnology), a fabrication technique
* Flame lift-off, a separation of flame from burner device
* Takeoff, the first moment of flight of an aerospace vehicle
* Reduction ...
has been demonstrated with sub-20 nm resolution.
Comparison to other lithographic techniques
Due to the
ablative
In grammar, the ablative case (pronounced ; sometimes abbreviated ) is a grammatical case for nouns, pronouns, and adjectives in the grammars of various languages; it is sometimes used to express motion away from something, among other uses. ...
nature of the patterning process, no development step (as in: selective removal of either the exposed or non-exposed regions of the resist as for
e-beam and
optical lithography) is needed, neither are
optical proximity correction
Optical proximity correction (OPC) is a photolithography enhancement technique commonly used to compensate for image errors due to diffraction or process effects. The need for OPC is seen mainly in the making of semiconductor devices and is due to ...
s. Maximum linear writing speeds of up to 20 mm/s have been shown with throughputs in the 10
4 – 10
5 μm
2 h
−1 range
which is comparable to single-column, Gaussian-shaped e-beam using
HSQ as resist. The resolution of t-SPL is determined by the probe tip shape and not limited by 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 ...
or by the focal spot size of beam approaches, however, tip-sample interactions during the in-situ metrology process create tip
wear
Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology.
Wear in ...
,
limiting the lifetime of the probes. In order to extend the lifetime of the probe tips, Ultrananocrystalline diamond (UNCD)
and
Silicon-Carbide (SiC)-coated
tips or wear-less floating contact imaging methods
have been demonstrated. No electron damage or charging is caused to the patterned surfaces due to the absence of electron or ion beams.
References
{{reflist
See also
*
Nanolithography
Nanolithography (NL) is a growing field of techniques within nanotechnology dealing with the engineering (patterning e.g. etching, depositing, writing, printing etc) of nanometer-scale structures on various materials.
The modern term reflects on ...
*
Scanning probe lithography
Scanning probe lithography (SPL) describes a set of nanolithographic methods to pattern material on the nanoscale using scanning probes. It is a direct-write, mask-less approach which bypasses the diffraction limit and can reach resolutions belo ...
*
Thermochemical nanolithography
*
Dip-pen nanolithography
Dip pen nanolithography (DPN) is a scanning probe lithography technique where an atomic force microscope, atomic force microscope (AFM) tip is used to create patterns directly on a range of substances with a variety of inks. A common example of th ...
*
Atomic force microscopy
*
Scanning probe microscopy
*
Electron-beam lithography
Electron-beam lithography (often abbreviated as e-beam lithography, EBL) is the practice of scanning a focused beam of electrons to draw custom shapes on a surface covered with an electron-sensitive film called a resist (exposing). The electron b ...
Lithography (microfabrication)
Nanotechnology