Auto

Run

Introduction AutoRun is a RAITH proprietary technology that, as its name suggests, enables EBL exposure jobs to be performed “at the push of a button,” fully automated from sample holder loading to […]

Introduction

AutoRun is a RAITH proprietary technology that, as its name suggests, enables EBL exposure jobs to be performed “at the push of a button,” fully automated from sample holder loading to unloading, including all calibration, leveling, alignment, and focussing routines, even where many different samples are attached. No need for advance alignment procedures, other sample preparation requirements, or manual user intervention throughout the entire exposure job.

Key features

Benefits for applications

Fully automated exposure jobs with highest precision – literally at the push of a button

Minimum stitching errors and highest pattern placement accuracy

By relying on a specific calibration standard in the periphery of each available sample holder, all write fields are thoroughly and repeatedly calibrated for each individual sample in such a way that write-field borders are perfectly matched and optimum pattern placement accuracy within the individual write field is achieved, regardless of the sample holder utilized.

Highest resolution and pattern fidelity

Autofocus algorithms in combination with an automatic height detection system are integral to AutoRun technology. They serve to continuously maintain optimum focussing conditions and write with optimum beam for highest-quality results, which are crucial for e.g. highest resolution and pattern fidelity.

Sample pre-alignment free workflow

Autorun technology provides a unique in situ sample leveling mechanism for sample height and tilt correction. Manual sample pre-adjustments are thus redundant, saving valuable process time.

Exposure dose control ensuring highest process stability

In order to stay within the EBL process window, the exposure dose can be permanently measured and corrected for in the event of potential beam current drift during exposures lasting days and nights.

Focus control on samples with strong bowing

Even strongly bowed samples can be exposed while maintaining perfect focus. 2D height map (WD) values obtained by automated height mapping can be extrapolated and used for focus readjustment across the full sample during exposure. This results in faster exposure with better focus settings.

How it works

AutoRun relies on fully automatic calibration, alignment, leveling, and focussing

AutoRun technology stands for a combination of several sequentially applied automatic routines during the EBL exposure process, and represents corresponding hardware and software technology bricks required for the purpose.

Prior to any exposure and automatic write- field calibration procedure, the laser interferometer stage drives precisely to the Farady cup mounted on the sample holder periphery. The beam current is measured with high precision in order to assign the correct exposure dose automatically in accordance with the parameters defined in the exposure job. Should the exposure take days and nights, AutoRun technology includes the opportunity to automatically interrupt the exposure, measure the beam current, and accordingly correct for the exposure dose if necessary before continuing with the exposure.

AutoRun features technology bricks that can identify and correctly level the calibration sample. To do this, the system comprises an automatic height measurement system with a laser line that is reflected from the surface and then focused onto a detector yielding the current focus or working distance (WD) value. Once the system is focused, staying in focus requires maintenance of a constant WD. Should the WD change, the resulting focus changes can be corrected for by adjusting focus settings or alternatively correcting the Z position of the stage.

In order to minimize focus corrections across the entire sample during exposure, the sample is initially leveled to keep WD changes as small as possible. For small samples or masks, the surface is typically almost “ideally flat,” meaning that after careful leveling of the focal plane, the focus can be easily maintained within the focus depth range across the sample. This leveling procedure is globally unique to RAITH systems with AutoRun technology. Automatic sample leveling takes place in situ and is realized by three leveling piezos mounted below the sample holder. There is no need to apply any manual leveling adjustments before loading the sample (holder) .

After the calibration sample is leveled, the write field including focus, astigmatism, and distortion correction settings is automatically calibrated using AutoRun´s algorithms for autofocusing onto the design elements of the RAITH proprietary calibration sample. Careful write-field calibration ensures good stitching at the borders of adjacent write fields. Taking into account multiple reference points on the calibration standard for write-field calibration, higher order distortions can be corrected for. Write-field calibrations are repeatedly performed for any individual sample on the sample holder prior to exposure, no matter what sample holder is used.

Upon successful write-field calibration, the laser interferometer stage drives from the calibration standard to the relevant sample on the sample holder and repeats the leveling procedure. WD value is compared with that of the calibration standard and adjusted by accordingly moving the stage in Z, thus achieving top reference conditions for the sample surface. The sample is then in focus, the calibrated write field is aligned, and the exposure is launched.

Any further sample is processed following the same method: driving to the calibration standard, repeating all leveling, autofocussing, and calibration routines, then driving to a specific clamp/sample, autodetecting height, sample leveling, and making final focus adjustments to calibration standard in Z by moving the stage. This method ensures that the stigmation, focus, and distortion correction values obtained from the calibration standard also apply for the exposure on the specific sample.

The workflow may differ slightly if the sample exhibits pronounced topographies such as strong wafer bowing. In this case, AutoRun technology offers the option of acquiring a sample height map with many definable reference points, typically on a full wafer. Relying on this sample height map, which is represented by a 2D matrix containing a huge number of WD values, the sample is leveled in such a way that the sample surface is adjusted according to the height map characteristics, taking into account an average/medium value for topography/bow from the wafer height map. During exposure, the focus is adjusted continuously and automatically according to/by extrapolation of previously and automatically acquired height map data.

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.

Area grating with a pitch of 1 µm, fabricated by “stitching” 50 µm wide strips patterned using MBMS.

Honeycomb structure

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