Digital Hydrogen Depassivation Lithography for Improving Precison of Donor Placement in Si

Hydrogen depassivation lithography (HDL) has been used to place dopants on the Si surface for Si donor qubits, single electron transistors¹, and shows promise for analog quantum simulation devices². We use image analysis to identify lithography pixels which are defined as two dimers along a dimer row³. During lithography, the tip moves over the pixels to be exposed, following vectors defined from the device pattern. There is a tip position tolerance of +/- 1.3Å. However, thermal drift, tip changes, creep, and hysteresis all make keeping this tolerance during lithography difficult.
We describe a new digital exposure strategy that moves the tip in imaging mode to a position above a pixel then holds still while transitioning to lithography conditions and exposes all four H atoms in that pixel. Once the pixel is exposed, the tip is returned to imaging conditions and moved to the next pixel to be exposed. Exposure conditions can be optimized to increase the tip position tolerance to +/- 1.9Å. We also include functions for exposure completion, more stable current control, and tip position correction.

1 Hill, C. D. Sci. Adv. 1 (2015)
2 Wyrick, J. Adv. Funct. Mater. 29 (2019)
3 Randall, J. J. Vac. Sci. Technol. B 37 (2019)