Year of Publication
Doctor of Philosophy (PhD)
Dr. J. Todd Hastings
Scanning-electron-beam lithography (SEBL) is the primary technology to generate arbitrary features at the nano-scale. However, pattern placement accuracy still remains poor compared to its resolution due to the open-loop nature of SEBL systems. Vibration, stray electromagnetic fields, deflection distortion and hysteresis, substrate charging, and other factors prevent the electron-beam from reaching its target position and one has no way to determine the actual beam position during patterning with conventional systems. To improve the pattern placement accuracy, spatial-phase-locked electron-beam lithography (SPLEBL) provides feedback control of electron-beam position by monitoring the secondary electron signal from electron-transparent fiducial grids on the substrate. While scanning the electron beam over the fiducial grids, the phase of the grid signal is analyzed to estimate the electron-beam position error; then the estimates are sent back to beam deflection system to correct the position error. In this way, closed-loop control is provided to ensure pattern placement accuracy. The implementation of spatial-phase-locking on high speed field-programmable gate array (FPGA) provides a low-cost method to create a nano-manufacturing platform with 1 nm precision and significantly improved throughput.
Shot-to-shot, or pixel-to-pixel, dose variation during EBL is a significant practical and fundamental problem. Dose variations associated with charging, electron source instability, optical system drift, and ultimately shot noise in the beam itself conspire to increase critical dimension variability and line width roughness and to limit the throughput. It would be an important improvement to e-beam patterning technology if real-time feedback control of electron-dose were provided to improve pattern quality and throughput even beyond the shot noise limit. A novel approach is proposed in this document to achieve the real-time dose control based on the measurement of electron arrival at the sample to be patterned, rather than from the source or another point in the electron-optical system. A dose control algorithm, implementation on FPGA, and initial experiment results for the real-time feedback dose control on the e-beam patterning tool is also presented.
Yang, Yugu, "Feedback Control for Electron Beam Lithography" (2012). Theses and Dissertations--Electrical and Computer Engineering. 9.