Scanning exposures with a MAPPER multibeam system

Currently, three MAPPER multi-electron beam lithography tools are operational. Two are located at customers, TSMC and LETI, and one is located at MAPPER. The tools at TSMC and LETI are used for process development. These tools each have 110 parallel electron beams and have demonstrated sub-30 nm half pitch resolution in chemically amplified resists. One important step towards the high volume tool is the capability to stitch the exposure of one electron beam to the next. The pre-alpha tool at MAPPER has been upgraded with an interferometer to enable exposures with a scanning stage and demonstrate first beam-to-beam stitching. A scan of 200 micrometers has been used to create a stitch area of 50 x 3 microns. The stitch error over all stitches was found to be below 25 nm. The electron beam position stability during the 10 seconds required for beam-to-beam stitching showed a contribution to the stitch error of 2.3 nm. The beam separation measurement, used to correct the static error, adds about 2.2 nm and the stage stability and linearity adds another 5 nm in the scan (interferometer) direction. In the perpendicular direction the stage instability gives the largest contribution to the stitch error (15 nm) due to the use of capacitive sensors. Overall, the electron beam stability and the beam position correction method work correctly and with sufficient accuracy for the high volume tool, 'Matrix'. The wafer stage for the Matrix system will incorporate full interferometer control to attain the needed positioning accuracy and stability.