Design of structures and preparation of data for exposure
The basic steps of design and preparation of data include:
Design
Structure design begins with the creation of a new (or loading an existing)
Graphics Database file. NanoMaker allows one to design a structure of
almost any size and any complexity, using a few simple geometric figures
(points, lines and polygons), just like it happens in any system of computer-aided
design (CAD). In contrast to CAD, these geometric shapes - elements are
inherent additional attributes specific to lithographic structures - dose
of exposure, 3D attribute, layer, etc.
Correction
Unlike CAD NanoMaker also includes the special subsystem for processing
designed structures, which allows to achieve maximum resolution at electron
beam exposure. For example, this subsystem performs the proximity effect
correction, in which the original structure is cut into smaller elements
and each element is assigned its own time of exposure (dose).
Import / Export
The results of the design are stored in a special Graphics Database
format (file name extension is GDB). To ensure compatibility with other
CAD and / or with other lithography systems NanoMaker provides import
/ export structures in formats GDS, CSF, DXF, DC2 and ELM.
Special transformations in postprocessing
For best results in preparing the data for other lithographic systems
NanoMaker includes additional operations for the whole structure or its
selected part, such as leveling of the exposure doses (Union), search
and removal of overlapped parts of elements (Overlaps Out), inversion
of exposure field at transition from negative to positive resists (Negative),
etc.
The system of choosing parameters for exposure, proximity correction
and simulation of resist development
NanoMaker includes the reference table of recommended parameters, which
essentially help to choose regimes of proximity effect correction, exposure
and resist development simulation. Data obtained from a large number
of experiments for several types of resists and substrates allow to
approximate the parameters of the proximity function for a wide range
of accelerating voltages, resist thicknesses and primary e-beam diameters.
One can add the table with own data. Furthermore, data for selecting
the parameters of exposure, correction and development simulation can
be calculated using the Monte Carlo sub, which is integrated into NanoMaker.
Exposure, including exposure with stage displacements
Exposure, exposure modeling, estimation of time
One of the main NanoMaker functions is exposure at which the electron
beam is deflected by pattern generator to certain point and is held a
given time. With all this going on NanoMaker automatically performs the
movement of the stage, if the structure exceeds the scanning field.
Special procedure allows to assess in advance an exposure time, as well
as to show on the PC screen the trajectory of the beam.
Alignment for successive lithographies, including fields stitching
by means of automatic markers detection
Typically, lithography involves several sequential exposures, and therefore
NanoMaker provides (automatic) search for and correct orientation of
the exposed structure with respect to already existing structures on
the substrate due to the search and recognition of markers.
Special interrupts to compensate for drift
In the case of long exposures (half an hour and longer), when accurate
stage displacements are used, the special interrupts are provided (with
storage of the position where termination of exposure happened), during
which the NanoMaker moves one of markers to the scan field, measures
shift of its position, introduces the necessary amendments to the beam
deflection system to compensate for drift and returns to the place of
exposure.
Resist development simulation
NanoMaker allows to predict the shape of resist after exposure and development.
In addition resist contrast parameter or dose curve as a whole are used
for the simulation of positive and negative resists development. Simulation
of resist development is useful for lithography training and for choosing
of optimal technological conditions, because very quickly, without executing
the real exposure and development allows to predict the results of the
lithography.
Controlling of SEM, stage, beam blanker et al
NanoMaker allows to control the stage movement in most scanning systems
with focused beam equipped with a motorized or laser controlled stages.
If microscope is equipped with beam blanker, NanoMaker can control the
blanking of the electron beam in the column. For some modern models
of SEMs NanoMaker makes it possible to control the microscope, which
includes, for example, controlling of working distance, magnification,
accelerating voltage, beam current, etc.
Image acquisitions for measurements and multi-layer exposure alignments
Image acquiring from a list of windows with graphics processing
When connecting to analogue SEMs the NanoMaker can be used for high-resolution
image recording, which can be saved in TIFF format files. Graphics processing
is available (filtering, contrast optimization, adding of scalier and
comments, etc.). There is a possibility of image acquisition with signal
accumulation and averaging.
Automatic and manual search and recognition of the markers
NanoMaker has a procedure where one can specify a system of windows
(with a variation of the size and resolution), which corresponds to
position of markers on a substrate, and also provides a flexible controlling
procedure for image acquisitions in these windows and recognition of
the marker's images. This feature is widely used in NanoMaker for calibration
of a scan field, for alignment of coordinate systems, for matching layers
in multi layer lithography, for drift compensation, etc.
Measurement of static and dynamic distortions. Software compensation
for errors in beam positioning
NanoMaker contains special subsystem for fast and convenient measurement
of static and dynamic distortions of deflection system of a SEM. The
measured data then is used for software "on the fly" compensation
of errors in positioning of the beam. These are an extremely important
functions. They can significantly reduce the exposure time (6-10 times)
by avoiding blanking and waiting of the beam settling after jumps through
the active compensation
of dynamic distortions, as well as to increase the writing field
due to its linearization.
Alignment of coordinate systems
During exposure it is often necessary to align multiple coordinate systems,
for example, coordinates of projected structure, coordinates of substrate,
coordinates of the beam deflection system, stage coordinates and others.
NanoMaker makes it possible to choose the one as master and to lead
all the rest to it. For example, in presence of an accurate laser stage
all the coordinate systems can be aligned to an exact stage movement.
Unique Features
The following unique features distinguish NanoMaker among of similar systems on a market:
Proximity effect correction for 2D-and 3D-structures.
Simulation of the proximity effect and resist development.
Measurement and active compensation of dynamic distortions of a beam
deflecting system, which significantly reduces the total time of exposure.
The possibility of exposure without blanking the beam because of
active compensation of dynamic distortions.
The compensation of static errors (distortion) deflecting system for exposure in
a large field.
Special options for the design of hologram and kinoform applications.
Calculation of data for exposure on multilayered substrates with an
integrated Monte Carlo module.
None of the companies on the market involved in the development of similar
systems offers such feature set.
