Stitch-free lithography with continous writing modes

Stitching errors are a common and very important issue in nanolithography. A pattern written by nanolithography is often bigger than the size of the write field (WF) that can be exposed by the electron or ion beam without moving the stage.

This is typically in the order of (100 µm)² or a few hundreds thereof. If the pattern design exceeds the max. applicable WF size for the specific application, the design is thus fractured into multiple subpatterns corresponding to the desired WF size, which are subsequently exposed in sequence.

After the writing process is completed for one area, the beam is therefore blanked and the stage of the nanolithography system moves on in order to continue the writing process on the next writefield. This movement needs to be absolutely precise in order to prevent stitching error at the boundaries of the write field.

All Raith systems are equipped with a highest-precision laser interferometer stage which already minimizes stitching error down to a few single-digit nanometers, and this is sufficient for many applications. However, in some applications (e.g. waveguides) even the tiniest kink at a stitch field border can cause significant degradation in device performance.

Raith now presents a solution to completely circumvent stitching error, which takes the form of two stitch-free exposure technologies: traxx and periodixx.

Questions?

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traxx - Continuous writing without stitching errors using FBMS technology 

traxx is a unique feature based on fixed beam moving stage (FBMS) exposure technology with “zero stitching error” approach. traxx is exclusively available for Raith electron beam lithography and FIB systems and is not provided by any other vector scan EBL system. Unlike conventional stitching exposures, traxx capitalizes on sophisticated FBMS using a unique continuous writing mode. The beam remains stationary while the stage underneath follows arbitrary shaped paths of the desired patterns.

Patterns can be several millimeters to centimeters long, while maintaining lateral dimensions from below 20 nm to some micrometers with minimum line edge roughness. This unique continuous writing mode avoids stitching error altogether and can therefore improve the quality and transmission of photonic devices such as (tapered) waveguide and X-ray optics.

traxx is fully integrated into the Raith Nanosuite software and fully compatible with the built-in GDSII data handling function. traxx is available for VOYAGER, RAITH150 Two, eLINE Plus, and VELION. Please consult with Raith if you are interested in upgrading your existing instrument.

Contact

To learn more about traxx and the FBMS technology, download the Application Note “Continous electron beam lithography writing modes for optical waveguides” here.

Microring resonator structure. G. Piaszenski, Raith GmbH.
picture of an arrayed waveguide grating
SEM picture of a several mm long arrayed waveguide

An arrayed waveguide grating (AWG) over a length of several mm. Courtesy R. Schmits et al., TNO Delft, Netherlands.

periodixx - Periodic patterning without stitching errors using MBMS technology

periodixx is another unique exposure technology with “zero stitching error” approach that is exclusively available for Raith EBL and FIB systems.

Large-area periodic structures with high pattern fidelity are particularly important in photonics and plasmonics. periodixx was developed to meet the need for a fabrication technique enabling the production of superior devices with periodic structures.

The exposure mode is based on Raith’s modulated beam moving stage (MBMS) technology and complements the traxx exposure mode, which uses Raith’s well-established fixed beam moving stage (FBMS) technology. FBMS allows continuous writing of elongated paths such as optical waveguides without stitching; the width of the path is defined by dynamic beam expansion.

However, in MBMS exposure mode the (repetitive periodic) beam movement is defined such that the combination of patterning and synchronized continuous movement of the laser interferometer stage results in stitch-free, strip-shaped periodic structures.

periodixx is fully integrated into the Raith Nanosuite software and fully compatible with the built-in GDSII data handling function. periodixx is available for VOYAGER, RAITH150 Two, eLINE Plus, and VELION. Please consult Raith if you are interested in upgrading your existing instrument.

Contact

To learn more about periodixx and the FBMS technology, download the Application Note “Sub-nm path control of stitch-error-free, millimeter-long periodic structures” here.

SEM picture of a 450nm wide waveguide
450nm wide waveguide structures in silicon master stamp; R. Schmits, TNO Delft, Netherlands
Stitch-free photonic crystal waveguides 1 mm in length fabricated by MBMS. Figure a) shows an overview with 5 waveguides (optical microscope, 10×). Figure b) was made out of 10 SEM images with a size of 10 × 10 µm.
Honeycomb structure
Area grating with a pitch of 1 µm, fabricated by “stitching” 50 µm wide strips patterned using MBMS.