In front of or additionally to traditional photolithography, where the use of a photomask and a mask aligner tool or a reticle and a stepper are needed to transfer the designed layouts onto the substrates via a photosensitive resist coating, Direct Writing Lithography constitutes another photolithography technique which provides a fast and versatile technology especially suited for its use in R+D or in the prototyping stages.
In this technology, Direct laser writers are used in nsubstitution of traditional mask aligners or even steppers to directly expose the photoresist that is covering the surface of the substrates, being controlled by a software which reads the patterns in the designed layout (for instance GDS files) and guides a deflector to reproduce the patterns onto the resist.
Some tools can combine two approaches of photoresist exposition: the rasterized approach, for larger patterns, and the vectorial direct writing approach, where the radiation is focused to a narrow beam that is scanned in vector form across the resist, which allows the best resolution at the cost of lowering the exposition speed.
Noticeably, a key advantage of maskless lithography is the ability to change lithography patterns from one run to the next, avoiding incurring in most of the costs of generating a new photomask, both in economical and time terms
E-Beam evaporation is a physical vapor deposition (PVD) technique whereby an intense electron beam is generated from a filament and steered via electric and magnetic fields to strike the source material (e.g. pellets of Au) and vaporize it within a vacuum environment.
RIE is used to etch various materials under vacuum in the presence of reactive ions. The sample to be etched is placed in a vacuum chamber and gas is injected into the process chamber via a gas inlet in the top electrode. The lower electrode is negatively biased and a single RF plasma source determines both the ion density and their energy.
In SEM a beam is scanned over a sample surface while a signal from secondary or back-scattered electrons is recorded. SEM is used to image an area of the sample with nanometric resolution, and also to measure its composition, crystallographic phase distribution and local texture.
XRD provides non-destructive information on the structural order of a material. At large scattering angles XRD permits to identify different crystal phases and to quantify lattice distances and crystalline volume fractions. At low angles of incidence the surface roughness of a single crystal and the thickness of a deposition layer can be obtained.
AFM is a surface sensitive technique permitting to obtain a microscopic image of the topography of a material surface and certain properties (like friction force, magnetization properties…). Typical lateral image sizes are within a range of only a few Nanometers to several Micrometers, and height changes of less than a Nanometer.