For some applications, local or global pattern placement accuracy is the most crucial requirement for lithography.
Our direct write lithography systems use differential laser interferometers, optical front- and/or backside alignment or in-situ AFM alignment to measure various parameters for accurate positioning on the samples. Climate control chambers and sample chucks made of Zerodur minimize thermal drifts that cannot be easily measured and compensated actively.
Direct-write lithography has key advantages for pattern placement accuracy as compared to mask aligners, steppers or imprint lithography tools that are bound to masks or stamps. Such tools cannot compensate for local or global imperfections from previous fabrication steps, from thermal effects or from bowing. In case of direct write lithography, the layout data can be individually adapted by local and global position matrix corrections (x-scale-errors, y-scale-errors, rotation, translation, orthogonality errors) to compensate for imperfections from the sample or the tool itself.
Position correction matrix (KOMA)
A position correction matrix (KOMA) is calculated in the software based on measurements with a well-calibrated reference plate (golden plate). This enables corrections for e.g. slightly warped or non-flat interferometer mirrors.
ULTRA system features a pure Zerodur sample chuck. It enables reliable 2nd layer alignment all over the sample with better than 30 nm positioning accuracy.
A SQUID, a magnetic-flow sensor that requires an up to 18-layer-process, fabricated using the fast and accurate alignment process of the MLA150. Alignment is critical for such devices: fabrication with MLA150 increased the yield 3-fold with respect to previous efforts involving mask aligners. Courtesy of the Kirchhoff Institute for Physics, Heidelberg
Markerless Overlay using in-situ AFM
A nanowire contacted without using markers for overlay. (a) The nanowire located under the resist is detected (green), and the layout is drawn on the AFM image (pink). (b) The resulting device after lift-off is shown on the SEM image.