Controlled doping by self-assembled dendrimer-like macromolecules

Abstract

Doping via self-assembled macromolecules might offer a solution for developing single atom electronics by precisely placing individual dopants at arbitrary location to meet the requirement for circuit design. Here we synthesize dendrimer-like polyglycerol macromolecules with each carrying one phosphorus atom in the core. The macromolecules are immobilized by the coupling reagent onto silicon surfaces that are pre-modified with a monolayer of undecylenic acid. Nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) are employed to characterize the synthesized macromolecules and the modified silicon surfaces, respectively. After rapid thermal annealing, the phosphorus atoms carried by the macromolecules diffuse into the silicon substrate, forming dopants at a concentration of 1017 cm−3. Low-temperature Hall effect measurements reveal that the ionization process is rather complicated. Unlike the widely reported simple ionization of phosphorus dopants, nitrogen and carbon are also involved in the electronic activities in the monolayer doped silicon.

Advances in ultrashallow doping of silicon

“…The diversity of organic molecules and the flexibility of self-assembly process make MLD an attractive and controllable doping technique. Dopants including phosphorus [20][21][22][23][24][25][26][27][28][29][30], boron [8,20,[31][32][33][34], nitrogen [35], arsenic [27,36] and antimony [37] have been introduced to silicon by MLD using commercial or synthetic reagents.…”

“…The areal dose can be modulated by tuning molecule size, monolayer constitutes, reaction time, reaction temperature, and molecular structure. Several strategies on dose modulation have been investigated [20,21,23,24,28,31,37,38]. In the first MLD report, Ho et al [20].…”

“…As presented in Figure 3, polymers with narrow molecular weight distribution can be used to tune the footprint of precursors, and hence the areal density of dopant distribution. Wu et al designed hyperbranched polyglycerols with each one carrying only one phosphorus dopant in the core [23,24]. Characterized by nuclear magnetic resonance and dynamic light scattering, the number average molecular weight of the synthesized molecules was found to be approximately 84,000 g/mol with an average diameter around 11 nm.…”

Full Activation of Dopants by Carbon-free Self-Assembled Molecular Monolayer Doping

“…In contrast, the SAMM doping is a mild doping technique that causes no lattice damages. The self-assembly nature of the SAMM doping will form a uniform and conformal coverage of semiconductor surfaces and therefore is compatible with 3D or complex structure doping. − …”

Full Activation of Boron in Silicon Doped by Self-Assembled Molecular Monolayers

“…12,13 In addition, single dopants may be potentially controlled at large scale by combining "top-down" large-scale nanofabrication and "bottom-up" self-assembly. 14 One of the main concerns for solution-based SAMM doping is organic contamination and dopant deactivation. 15−17 Shimizu et al 16 have demonstrated that carbon and oxygen diffused unintentionally into silicon during the thermal annealing process, and they suggested to sacrifice a top layer of 2−3 nm for industrial application.…”