Atomic-Scale Patterning of Arsenic in Silicon by Scanning Tunneling Microscopy

Abstract

Over the last two decades, prototype devices for future classical and quantum computing technologies have been fabricated, by using scanning tunneling microscopy and hydrogen resist lithography to position phosphorus atoms in silicon with atomic-scale precision. Despite these successes, phosphine remains the only donor precursor molecule to have been demonstrated as compatible with the hydrogen resist lithography technique. The potential benefits of atomic-scale placement of alternative dopant species have, until now, remained unexplored. In this work, we demonstrate the successful fabrication of atomic-scale structures of arsenic-in-silicon. Using a scanning tunneling microscope tip, we pattern a monolayer hydrogen mask to selectively place arsenic atoms on the Si(001) surface using arsine as the precursor molecule. We fully elucidate the surface chemistry and reaction pathways of arsine on Si(001), revealing significant differences to phosphine. We explain how these differences result in enhanced surface immobilization and inplane confinement of arsenic compared to phosphorus, and a dose-rate independent arsenic saturation density of 0.24±0.04 monolayers. We demonstrate the successful encapsulation of arsenic delta-layers using silicon molecular beam epitaxy, and find electrical characteristics that are competitive with equivalent structures fabricated with phosphorus. Arsenic delta-layers are also found to offer improvement in out-of-plane confinement compared to similarly prepared phosphorus layers, while still retaining >80% carrier activation and sheet resistances of <2 kΩ/□. These excellent characteristics of arsenic represent opportunities to enhance existing capabilities of atomic-scale fabrication of dopant structures in silicon, and are particularly important for threedimensional devices, where vertical control of the position of device components is critical. TOC GRAPHICS

Single Ion Implantation of Bismuth

“…In order to confirm this and to obtain measurements for the errors in both the pulse duration and ion current, we positioned a CEM (same detector as used for the SE measurements) at the sample position and obtained the measured number of events per pulse ν from the proportion of empty pulses as described in the previous section. We varied the nominal pulse duration T and performed a linear regression for ν ¼ LðT À T 0 Þ, taking into account the systematic variation in the error bars sðνÞ given by Equation (3). In this case, L ¼ a=b AE p ðSð1Þ=bÞ and…”

“…Single impurity atoms in semiconductors and insulators are receiving significant interest for quantum technology and other applications. Large arrays of impurity atoms are needed, requiring a repeatable and scaleable method of positioning single atoms with nanometer precision, often referred to as “deterministic doping.” Single atom lithographic techniques based on scanning probes have managed to achieve the positioning of single dopant [ 1–4 ] atoms with precision of less than a nanometer and high success rates, but the technique is (at present) limited to a small number of species in a small number of substrates, and it is relatively slow. Ion implantation, on the other hand, is much less precise in terms of positioning, but is much more flexible in terms of species and host, and is potentially much faster and easier to scale up for such purposes.…”

Nanoscale imaging of mobile carriers and trapped charges in delta doped silicon p–n junctions

“…Using scanning tunnelling microscopy (STM) hydrogen resist lithography, both acceptors [7] and donors [8] can be patterned with atomic resolution into dopant nanostructures [6] such as sheets [9], wires [10] and dots [11]. This atomicresolution doping has also been implemented in three-dimensional (3D) structures [12] and can be integrated into a CMOS platform [13].…”

Error Rates in Deterministic Ion Implantation for Qubit Arrays

“…[3] Scanning probe-based lithography techniques can be used for atomically precise placement of impurities, but although highly precise, this technique is slow and in use for only a few species (P and As with a silicon host and P with a germanium host). [4][5][6] Ion implantation is attractive for speed and flexibility, even though it offers much less positioning precision (and some schemes do not require it [2] ). Techniques for flexible implantation of single atoms are under development, and may be separated into pre-implant and post-implant determinism systems.…”