Ultrashallow doping is required for both classical field-effect transistors in integrated circuits and revolutionary quantum devices in quantum computing. In this review, we give a brief overview on recent research advances in three technologies to form ultrashallow doping, namely molecular monolayer doping, molecular beam epitaxy, and low energy ion implantation. A research perspective will be provided at the end of this review.

No abstract

Self-assembled molecular monolayer doping may find important applications in doping FinFET and nanowire transistors due to its nature of being conformal, nondestructive, and self-limiting. However, carbon contamination from the dopant carrier molecules is often introduced into silicon, which will affect the device performance. Herein, we use carbon-free phosphorus chloride (PCl3) molecules as dopant carrier molecules to avoid the introduction of carbon contamination. The Hall effect measurements and secondary ion mass spectrometry show that the dopant activation rate is close to full activation even for samples with a low doping concentration.

Self-assembled molecular monolayer doping is an emerging doping technique. In this work, we investigated the activation rate and photoresponses of boron doped silicon by self-assembled molecular monolayer doping. By using low temperature Hall effect measurements and by secondary ion mass spectroscopy, we find that the activation rate of boron in these samples is in the range of 91%–54%, depending on the doping concentration. Interestingly, the photoresponsivity of the boron doped samples is also significantly higher than that of the phosphorus doped samples even though the same doping technique is used. The intriguing photoresponses are closely related to the trapping of photogenerated minority carriers by the defects in the p-type silicon.

Unintentional C-related contamination can be readily introduced into the substrate in self-assembled molecular monolayer doping. These C contaminants can bind with dopants, forming interstitial defects, which will in return electrically deactivate the dopants. This issue will exacerbate when the dopant concentration is low. In this paper, a low temperature oxidation method (550 °C for 30 min) is introduced to remove carbon before the phosphorus dopants are driven into silicon in a rapid thermal annealing process. The samples with and without the pre-oxidation process are characterized by the Van der Pauw, low-temperature Hall effect measurements, and secondary ion mass spectrometry analysis. The results indicate that the surface carbon concentration in silicon is nearly completely removed with the pre-oxidation process, as a result of which the electrical activity of phosphorus is indeed increased.