Abstract
It is known that self-assembled molecular monolayer doping technique has the advantages of forming ultra-shallow junctions and introducing minimal defects in semiconductors. In this paper, we report however the formation of carbon-related defects in the molecular monolayer-doped silicon as detected by deep-level transient spectroscopy and low-temperature Hall measurements. The molecular monolayer doping process is performed by modifying silicon substrate with phosphorus-containing molecules and annealing at high temperature. The subsequent rapid thermal annealing drives phosphorus dopants along with carbon contaminants into the silicon substrate, resulting in a dramatic decrease of sheet resistance for the intrinsic silicon substrate. Low-temperature Hall measurements and secondary ion mass spectrometry indicate that phosphorus is the only electrically active dopant after the molecular monolayer doping. However, during this process, at least 20% of the phosphorus dopants are electrically deactivated. The deep-level transient spectroscopy shows that carbon-related defects are responsible for such deactivation.
Highlights
It is known that self-assembled molecular monolayer doping technique has the advantages of forming ultra-shallow junctions and introducing minimal defects in semiconductors
Shimizu et al.[12] investigated the diffusion behavior of carbon and oxygen contaminants in phosphorus-doped Si substrates by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and atom probe tomography (APT), finding that the contaminants were limited to the first atomic layer and could be removed
The molecular monolayer grafting and doping are characterized by X-ray photoelectron spectroscopy (XPS) and van der Pauw measurements, respectively
Summary
It is known that self-assembled molecular monolayer doping technique has the advantages of forming ultra-shallow junctions and introducing minimal defects in semiconductors. Low-temperature Hall measurements and secondary ion mass spectrometry indicate that phosphorus is the only electrically active dopant after the molecular monolayer doping. Self-assembled molecular monolayer (SAMM) doping is a potential doping technique to tackle the challenges in the formation of sub-10-nm ultra-shallow junction[1] and has the advantage of facilitating mass production and applicability to semiconductors like Si, Ge, InAs, GaAs, etc.[2,3,4,5] In this technique, dopant-carrying molecules are first covalently immobilized on the semiconductor surface via surface reactions. During the thermal annealing process, other atoms in the molecular monolayer such as oxygen, hydrogen, and especially carbon[12] can be driven into silicon together with the desired doping element These impurities are difficult to detect due to their atomic nature and low concentrations. The DLTS study shows that carbonrelated defects are present in the SAMM-doped silicon, resulting in the electrical annihilation of phosphorus dopants due to bonding with interstitial carbon
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