Low thermal budget high-k/metal surface gate for buried donor-based devices

Abstract

Scaling to smaller transistors is increasingly difficult and expensive, necessitating the investigation of alternative fabrication paths that extend to the atomic scale. Atomically precise donor devices can be created using a scanning tunneling microscope (STM). However, these devices are not currently compatible with industry standard fabrication processes. There exists a tradeoff between low thermal budget (LT) processes to limit dopant diffusion and high thermal budget (HT) processes to grow defect-free layers of epitaxial Si and gate oxide. To this end, we have developed an LT epitaxial Si cap and LT deposited Al2O3 gate oxide integrated with an atomically precise single-electron transistor (SET) that we use as an electrometer to characterize the quality of the gate stack. The surface-gated SET exhibits the expected Coulomb blockade behavior. However, the gate's leverage over the SET is limited by defects in the layers above the SET, including interfaces between the Si and oxide, and structural and chemical defects in the Si cap. We propose a more sophisticated gate stack and process flow that is predicted to improve performance in future atomic precision devices.

AlCl3-Dosed Si(100)-2 × 1: Adsorbates, Chlorinated Al Chains, and Incorporated Al

“…The peak Al concentration was found to be approximately 2.8 × 10 20 cm –3 and was located 35 nm beneath the surface at the buried interface of the Al δ-layer, as expected. We note that the Al content in the deposited film is due to some Al contamination in the Si deposition source (also observed by others using the same model) and not from AlCl 3 dosing, which occurs in a separate chamber. The total estimated areal dose of Al in this sample was 9.0 × 10 13 cm –2 .…”

“…The field of atomic precision advanced manufacturing (APAM) has been steadily advancing such that P-doped, Si-based devices are fabricated, manipulated, and measured in the laboratory with increasing ease. − The surface chemical processes associated with PH 3 adsorption on Si(100) have been thoroughly studied and extensively leveraged to fabricate spin qubit structures with APAM techniques. , Only recently has there been progress in extending capabilities to include acceptor dopants that would enable the realization of hole-based qubits , and complex device structures. , Of particular note, the first demonstration of APAM-fabricated, acceptor-doped devices (an atomic-scale wire, tunnel junction, and an atomically abrupt pn junction) was recently demonstrated utilizing B 2 H 6 as the dopant precursor . However, these devices required activation annealing upward of 850 °C to achieve a sheet resistance of ∼1 kΩ, prompting further investigation to find a more ideal precursor …”

The impact of stochastic incorporation on atomic-precision Si:P arrays

“…A bias spectroscopy measurement would require fabricating such a donor array between two δ-doped nanowire source and drain leads with either another in-plane lead or top gate [44] to adjust the on-site potential across the array. To reduce the likelihood of confounding the measurement with sites consisting of n > 1 donors, we propose making an array comprised exclusively of w = 3 windows.…”

Hole in one: Pathways to deterministic single-acceptor incorporation in Si(100)-2$\times$1

“…Single shallow dopants placed with atomic precision in silicon might be used to realize qubits [1][2][3][4][5][6][7][8][9][10], single-tofew-carrier devices [11][12][13][14][15][16][17], and analog quantum simulators [18][19][20][21][22]. While the placement of phosphorus donors using a phosphine (PH 3 ) precursor has received the most development [23][24][25], recent demonstrations involving arsenic [26], boron [27,28], and aluminum [29,30] indicate that the breadth of viable chemistries is growing.…”