Exploring conductivity in ex-situ doped Si thin films as thickness approaches 5 nm

John MacHale, Fintan Meaney, Noel Kennedy, Luke Eaton, Gioele Mirabelli, Mary White, Kevin Thomas, Emanuele Pelucchi, Dirch Hjorth Petersen, Rong Lin, Nikolay Petkov, James Connolly, Chris Hatem, Farzan Gity, Lida Ansari, Brenda Long, Ray Duffy*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Silicon (Si) has been scaled below 10 nm in multigate and silicon-on-insulator (SOI) device technologies, but clearly Si thickness cannot be reduced indefinitely, as we will run out of atoms eventually. As thickness approaches 5 nm, surfaces and interfaces will significantly impact the electrical behavior of Si, and surface physics cannot be discounted. Below that, bulk material properties will be altered considerably in the few-monolayer limit. One of the most basic defining properties of a semiconductor is its conductivity. To improve conductivity, while inducing a channel by appropriate biasing, it is necessary to define an accurate impurity doping strategy to reduce parasitic resistance. In this paper, we investigated the changing electrical conductivity of SOI films as a function of the Si thickness, in the range of 3–66 nm. SOI films were ex situ doped using three different approaches: liquid/vapor phase monolayer doping of phosphorus using allyldiphenylphosphine, gas-phase doping of arsenic using arsine (AsH3), and room-temperature beam-line ion implantation of phosphorus. The circular transfer length method and micro-four-point probe measurements were used to determine the resistivity of the Si films, mitigating the contribution from contact resistance. The resistivity of the Si films was observed to increase with decreasing Si film thickness below 20 nm, with a dramatic increase observed for a Si thickness at 4.5 nm. This may drastically impact the number of parallel conduction paths (i.e., nanowires) required in gate-all-around devices. Density functional theory modeling indicates that the surface of the Si film with a thickness of 4.5 nm is energetically more favorable for the dopant atom compared to the core of the film.
Original languageEnglish
Article number225709
JournalJournal of Applied Physics
Volume125
Issue number22
Number of pages9
ISSN0021-8979
DOIs
Publication statusPublished - 2019

Cite this

MacHale, J., Meaney, F., Kennedy, N., Eaton, L., Mirabelli, G., White, M., ... Duffy, R. (2019). Exploring conductivity in ex-situ doped Si thin films as thickness approaches 5 nm. Journal of Applied Physics, 125(22), [225709]. https://doi.org/10.1063/1.5098307
MacHale, John ; Meaney, Fintan ; Kennedy, Noel ; Eaton, Luke ; Mirabelli, Gioele ; White, Mary ; Thomas, Kevin ; Pelucchi, Emanuele ; Petersen, Dirch Hjorth ; Lin, Rong ; Petkov, Nikolay ; Connolly, James ; Hatem, Chris ; Gity, Farzan ; Ansari, Lida ; Long, Brenda ; Duffy, Ray. / Exploring conductivity in ex-situ doped Si thin films as thickness approaches 5 nm. In: Journal of Applied Physics. 2019 ; Vol. 125, No. 22.
@article{5441f8e7228e4dda9f1670d3bce7c5bf,
title = "Exploring conductivity in ex-situ doped Si thin films as thickness approaches 5 nm",
abstract = "Silicon (Si) has been scaled below 10 nm in multigate and silicon-on-insulator (SOI) device technologies, but clearly Si thickness cannot be reduced indefinitely, as we will run out of atoms eventually. As thickness approaches 5 nm, surfaces and interfaces will significantly impact the electrical behavior of Si, and surface physics cannot be discounted. Below that, bulk material properties will be altered considerably in the few-monolayer limit. One of the most basic defining properties of a semiconductor is its conductivity. To improve conductivity, while inducing a channel by appropriate biasing, it is necessary to define an accurate impurity doping strategy to reduce parasitic resistance. In this paper, we investigated the changing electrical conductivity of SOI films as a function of the Si thickness, in the range of 3–66 nm. SOI films were ex situ doped using three different approaches: liquid/vapor phase monolayer doping of phosphorus using allyldiphenylphosphine, gas-phase doping of arsenic using arsine (AsH3), and room-temperature beam-line ion implantation of phosphorus. The circular transfer length method and micro-four-point probe measurements were used to determine the resistivity of the Si films, mitigating the contribution from contact resistance. The resistivity of the Si films was observed to increase with decreasing Si film thickness below 20 nm, with a dramatic increase observed for a Si thickness at 4.5 nm. This may drastically impact the number of parallel conduction paths (i.e., nanowires) required in gate-all-around devices. Density functional theory modeling indicates that the surface of the Si film with a thickness of 4.5 nm is energetically more favorable for the dopant atom compared to the core of the film.",
author = "John MacHale and Fintan Meaney and Noel Kennedy and Luke Eaton and Gioele Mirabelli and Mary White and Kevin Thomas and Emanuele Pelucchi and Petersen, {Dirch Hjorth} and Rong Lin and Nikolay Petkov and James Connolly and Chris Hatem and Farzan Gity and Lida Ansari and Brenda Long and Ray Duffy",
year = "2019",
doi = "10.1063/1.5098307",
language = "English",
volume = "125",
journal = "Journal of Applied Physics",
issn = "0021-8979",
publisher = "American Institute of Physics",
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MacHale, J, Meaney, F, Kennedy, N, Eaton, L, Mirabelli, G, White, M, Thomas, K, Pelucchi, E, Petersen, DH, Lin, R, Petkov, N, Connolly, J, Hatem, C, Gity, F, Ansari, L, Long, B & Duffy, R 2019, 'Exploring conductivity in ex-situ doped Si thin films as thickness approaches 5 nm', Journal of Applied Physics, vol. 125, no. 22, 225709. https://doi.org/10.1063/1.5098307

Exploring conductivity in ex-situ doped Si thin films as thickness approaches 5 nm. / MacHale, John; Meaney, Fintan; Kennedy, Noel; Eaton, Luke; Mirabelli, Gioele; White, Mary; Thomas, Kevin; Pelucchi, Emanuele; Petersen, Dirch Hjorth; Lin, Rong; Petkov, Nikolay; Connolly, James; Hatem, Chris; Gity, Farzan; Ansari, Lida; Long, Brenda; Duffy, Ray.

In: Journal of Applied Physics, Vol. 125, No. 22, 225709, 2019.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Exploring conductivity in ex-situ doped Si thin films as thickness approaches 5 nm

AU - MacHale, John

AU - Meaney, Fintan

AU - Kennedy, Noel

AU - Eaton, Luke

AU - Mirabelli, Gioele

AU - White, Mary

AU - Thomas, Kevin

AU - Pelucchi, Emanuele

AU - Petersen, Dirch Hjorth

AU - Lin, Rong

AU - Petkov, Nikolay

AU - Connolly, James

AU - Hatem, Chris

AU - Gity, Farzan

AU - Ansari, Lida

AU - Long, Brenda

AU - Duffy, Ray

PY - 2019

Y1 - 2019

N2 - Silicon (Si) has been scaled below 10 nm in multigate and silicon-on-insulator (SOI) device technologies, but clearly Si thickness cannot be reduced indefinitely, as we will run out of atoms eventually. As thickness approaches 5 nm, surfaces and interfaces will significantly impact the electrical behavior of Si, and surface physics cannot be discounted. Below that, bulk material properties will be altered considerably in the few-monolayer limit. One of the most basic defining properties of a semiconductor is its conductivity. To improve conductivity, while inducing a channel by appropriate biasing, it is necessary to define an accurate impurity doping strategy to reduce parasitic resistance. In this paper, we investigated the changing electrical conductivity of SOI films as a function of the Si thickness, in the range of 3–66 nm. SOI films were ex situ doped using three different approaches: liquid/vapor phase monolayer doping of phosphorus using allyldiphenylphosphine, gas-phase doping of arsenic using arsine (AsH3), and room-temperature beam-line ion implantation of phosphorus. The circular transfer length method and micro-four-point probe measurements were used to determine the resistivity of the Si films, mitigating the contribution from contact resistance. The resistivity of the Si films was observed to increase with decreasing Si film thickness below 20 nm, with a dramatic increase observed for a Si thickness at 4.5 nm. This may drastically impact the number of parallel conduction paths (i.e., nanowires) required in gate-all-around devices. Density functional theory modeling indicates that the surface of the Si film with a thickness of 4.5 nm is energetically more favorable for the dopant atom compared to the core of the film.

AB - Silicon (Si) has been scaled below 10 nm in multigate and silicon-on-insulator (SOI) device technologies, but clearly Si thickness cannot be reduced indefinitely, as we will run out of atoms eventually. As thickness approaches 5 nm, surfaces and interfaces will significantly impact the electrical behavior of Si, and surface physics cannot be discounted. Below that, bulk material properties will be altered considerably in the few-monolayer limit. One of the most basic defining properties of a semiconductor is its conductivity. To improve conductivity, while inducing a channel by appropriate biasing, it is necessary to define an accurate impurity doping strategy to reduce parasitic resistance. In this paper, we investigated the changing electrical conductivity of SOI films as a function of the Si thickness, in the range of 3–66 nm. SOI films were ex situ doped using three different approaches: liquid/vapor phase monolayer doping of phosphorus using allyldiphenylphosphine, gas-phase doping of arsenic using arsine (AsH3), and room-temperature beam-line ion implantation of phosphorus. The circular transfer length method and micro-four-point probe measurements were used to determine the resistivity of the Si films, mitigating the contribution from contact resistance. The resistivity of the Si films was observed to increase with decreasing Si film thickness below 20 nm, with a dramatic increase observed for a Si thickness at 4.5 nm. This may drastically impact the number of parallel conduction paths (i.e., nanowires) required in gate-all-around devices. Density functional theory modeling indicates that the surface of the Si film with a thickness of 4.5 nm is energetically more favorable for the dopant atom compared to the core of the film.

U2 - 10.1063/1.5098307

DO - 10.1063/1.5098307

M3 - Journal article

VL - 125

JO - Journal of Applied Physics

JF - Journal of Applied Physics

SN - 0021-8979

IS - 22

M1 - 225709

ER -