Assessing atomically thin delta-doping of silicon using mid-infrared ellipsometry
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Sandia National Laboratories, Albuquerque, New Mexico, 87123, USA Department of Electrical Engineering, The State University of New York at Buffalo, Buffalo, New York 14260, USA a) Address all correspondence to this author. e-mail: [email protected] 2
Received: 16 March 2020; accepted: 21 May 2020
Hydrogen lithography has been used to template phosphine-based surface chemistry to fabricate atomic-scale devices, a process we abbreviate as atomic precision advanced manufacturing (APAM). Here, we use mid-infrared variable angle spectroscopic ellipsometry (IR-VASE) to characterize single-nanometer thickness phosphorus dopant layers (δ-layers) in silicon made using APAM compatible processes. A large Drude response is directly attributable to the δ-layer and can be used for nondestructive monitoring of the condition of the APAM layer when integrating additional processing steps. The carrier density and mobility extracted from our room temperature IR-VASE measurements are consistent with cryogenic magneto-transport measurements, showing that APAM δ-layers function at room temperature. Finally, the permittivity extracted from these measurements shows that the doping in the APAM δ-layers is so large that their low-frequency in-plane response is reminiscent of a silicide. However, there is no indication of a plasma resonance, likely due to reduced dimensionality and/or low scattering lifetime.
Introduction Both the push of the microelectronics industry to shrink transistor feature sizes below 10 nm (approximately 30 silicon atoms) and the recent rise of solid-state devices for quantum information science has created a demand to understand and manipulate materials and interfaces with atomic precision [1, 2]. Incorporation of atomic-scale fabrication can provide insights into future directions for transistor technologies, e.g., the use of 2D materials for transistor channels, and in achieving applicability for quantum systems, e.g., the deterministic creation of color centers in diamond for quantum sensing [3]. However, in general, atomic-scale fabrication techniques require appreciable additional processing, with unconventional requirements, to produce a useful device [4]. While there are an ever-increasing number of atomic-scale characterization techniques being discovered, simple characterization techniques that probe structures at the atomic scale by proxy are needed to determine the integrity of every chip at every step of increasingly complex fabrication workflows.
© Materials Research Society 2020
Here, we examine a way to quickly characterize devices fabricated using atomic precision advanced manufacturing (APAM), which can place phosphorus donors with single-lattice-site uncertainty at the surface of silicon and has been used to make boutique ultra-scaled electronic devices and rudimentary quantum demonstrations [2]. Both atomically precise placement of dopants and a dopant density that exceeds the solid solubility limit for phosphorus in silicon can only be preserved by limiting the thermal budget of any process
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