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Diborane (B2H6) is a promising molecular precursor for atomic precision p-type doping of silicon that has recently been experimentally demonstrated [ Škereň et al. Nat. Electron. 2020 ]. We use density functional theory (DFT) calculations to determine the reaction pathway for diborane dissociating into a species that will incorporate as electrically active substitutional boron after adsorbing onto the Si(100)-2×1 surface. Our calculations indicate that diborane must overcome an energy barrier to adsorb, explaining the experimentally observed low sticking coefficient (<1 × 10-4 at room temperature) and suggesting that heating can be used to increase the adsorption rate. Upon sticking, diborane has an ≈50% chance of splitting into two BH3 fragments versus merely losing hydrogen to form a dimer such as B2H4. As boron dimers are likely electrically inactive, whether this latter reaction occurs is shown to be predictive of the incorporation rate. The dissociation process proceeds with significant energy barriers, necessitating the use of high temperatures for incorporation. Using the barriers calculated from DFT, we parameterize a Kinetic Monte Carlo model that predicts the incorporation statistics of boron as a function of the initial depassivation geometry, dose, and anneal temperature. Our results suggest that the dimer nature of diborane inherently limits its doping density as an acceptor precursor and furthermore that heating the boron dimers to split before exposure to silicon can lead to poor selectivity on hydrogen and halogen resists. This suggests that, while diborane works as an atomic precision acceptor precursor, other non-dimerized acceptor precursors may lead to higher incorporation rates at lower temperatures.

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TYPE Journal Article YEAR 2021

DOI OSTI Scopus

Photothermal alternative to device fabrication using atomic precision advanced manufacturing techniques

Journal of Micro/Nanopatterning, Materials and Metrology

Katzenmeyer, Aaron M.; Dmitrovic, Sanja; Baczewski, Andrew D.; Campbell, Quinn; Bussmann, Ezra; Lu, Tzu M.; Anderson, Evan M.; Schmucker, Scott W.; Ivie, Jeffrey A.; Campbell, Deanna M.; Ward, Daniel R.; Scrymgeour, David; Wang, George T.; Misra, Shashank

The attachment of dopant precursor molecules to depassivated areas of hydrogen-terminated silicon templated with a scanning tunneling microscope (STM) has been used to create electronic devices with subnanometer precision, typically for quantum physics experiments. This process, which we call atomic precision advanced manufacturing (APAM), dopes silicon beyond the solid-solubility limit and produces electrical and optical characteristics that may also be useful for microelectronic and plasmonic applications. However, scanned probe lithography lacks the throughput required to develop more sophisticated applications. Here, we demonstrate and characterize an APAM device workflow where scanned probe lithography of the atomic layer resist has been replaced by photolithography. An ultraviolet laser is shown to locally and controllably heat silicon above the temperature required for hydrogen depassivation on a nanosecond timescale, a process resistant to under- and overexposure. STM images indicate a narrow range of energy density where the surface is both depassivated and undamaged. Modeling that accounts for photothermal heating and the subsequent hydrogen desorption kinetics suggests that the silicon surface temperatures reached in our patterning process exceed those required for hydrogen removal in temperature-programmed desorption experiments. A phosphorus-doped van der Pauw structure made by sequentially photodepassivating a predefined area and then exposing it to phosphine is found to have a similar mobility and higher carrier density compared with devices patterned by STM. Lastly, it is also demonstrated that photodepassivation and precursor exposure steps may be performed concomitantly, a potential route to enabling APAM outside of ultrahigh vacuum.

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TYPE Journal Article YEAR 2021

DOI OSTI Scopus

Path towards a vertical TFET enabled by atomic precision advanced manufacturing

2021 Silicon Nanoelectronics Workshop, SNW 2021

Lu, Tzu M.; Gao, Xujiao; Anderson, Evan M.; Mendez Granado, Juan P.; Campbell, Deanna M.; Ivie, Jeffrey A.; Schmucker, Scott W.; Grine, Albert; Lu, Ping; Tracy, Lisa A.; Arghavani, Reza; Misra, Shashank

We propose a vertical TFET using atomic precision advanced manufacturing (APAM) to create an abrupt buried n++-doped source. We developed a gate stack that preserves the APAM source to accumulate holes above it, with a goal of band-to-band tunneling (BTBT) perpendicular to the gate – critical for the proposed device. A metal-insulator-semiconductor (MIS) capacitor shows hole accumulation above the APAM source, corroborated by simulation, demonstrating the TFET’s feasibility.

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TYPE Conference Presentation YEAR 2021

DOI OSTI Scopus