A study of capping layers for sulfur monolayer doping on III-V junctions

Abstract

Recently, high dosage doping on Si multi-gate field effect transistors and III–V planar structures using a self-limiting monolayer doping technique was reported to overcome challenges in scaling nano-sized transistors. The stoichiometry or composition of the capping layer was found to affect the diffusion efficiency of this process. In this work, we study the effect of a capping layer in sulfur monolayer doping on III–V junctions. Various capping temperatures and growth methods were compared. Based on the theoretical and experimental results, we suggest an optimized scheme consisting of a bi-layer capping structure. From Hall measurements and secondary ion mass spectrometry, a SiNx/BeO bi-layer capping, compared to single layer cap, exhibited the best results with a surface sheet resistance of 232 Ω/sq, junction depth of 11 nm, dopant profile abruptness of 3.5 nm/dec, electrically active S concentration of 4.9 × 1019/cm3 (=1.34 × 1013/cm2), and 3 times higher activation efficiency without significant transient-enhanced dopant diffusion.

Chemical approaches for doping nanodevice architectures

“…MLD is well suited for this purpose due it to its highly conformal nature, ability to provide ultra-shallow junctions and lack of damage to the III-V zinc blende lattice structure as shown by Yum et al in the first report of solution-based MLD on InGaAs. [52] Here, ammonium sulphide (NH4)2S was used to clean the InGaAs substrates which also resulted in the S-termination of the surface. While this study focused more on the effect of differing capping layers on the surface, mean concentrations of S ranged from 5 × 10 20 atoms/cm 3 to 1 × 10 21 atoms/cm 3 with average junction depths of 11 nm, depending on the particular capping layer used, were reported.…”

P₂S₅/(NH₄)₂S_{<italic>x</italic>}-Based Sulfur Monolayer Doping for Source/Drain Extensions in n-Channel InGaAs FETs

“…It has been shown that this technique is capable of achieving abrupt, ultrashallow, and damage-free junctions with high doping concentrations. Sulfur MLD (SMLD) using (NH 4 ) 2 S x solution has been demonstrated on gallium arsenide (GaAs) Manuscript [17], [18], indium arsenide (InAs) [19], and InGaAs [20], [21]. MLD of InGaAs using Si as a dopant was also demonstrated recently [22].…”

Review—Dopant Selection Considerations and Equilibrium Thermal Processing Limits for n+-In0.53Ga0.47As

“…In monolayer doping the dopant species is introduced to the surface of the substrate material and encapsulated before a subsequent thermal anneal step used to drive in the dopant from the surface into the bulk. [32][33][34] Monolayer doping of III-V materials will present the similar challenges and disadvantages to activation and diffusion associated with ion implantation due to annealing. Monolayer doping may be advantageous over ion implant, however, since it could be applied to 3-D structures which are hard to dope conformally via ion implantation and does not result in radiation damage.…”