Control of Doping Level in Semiconductors via Self-Limited Grafting of Phosphorus End-Terminated Polymers

Abstract

An effective bottom-up technology for precisely controlling the amount of dopant atoms tethered on silicon substrates is presented. Polystyrene and poly(methyl methacrylate) polymers with narrow molecular weight distribution and end-terminated with a P-containing moiety were synthesized with different molar mass. The polymers were spin coated and subsequently end-grafted onto nondeglazed silicon substrates. P atoms were bonded to the surface during the grafting reaction, and their surface density was set by the polymer molar mass, according to the self-limiting nature of the "grafting to" reaction. Polymeric material was removed by O plasma hashing without affecting the tethered P-containing moieties on the surface. Repeated cycles of polymer grafting followed by plasma hashing led to a cumulative increase, at constant steps, in the dose of P atoms grafted to the silicon surface. P injection in the silicon substrate was promoted and precisely controlled by high-temperature thermal treatments. Sheet resistance measurements demonstrated effective doping of silicon substrate.

Diffusion Along Dislocations Mitigates Self‐Limiting Na Diffusion in Crystalline Sn

“…Notably, high tensile stresses are observed to develop near Na x Sn particles and tend to increase with the growth in size of these particles. For example, when the particles are several nanometers in size, the magnitude of residual stresses is almost the same (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) as that developed at c-Sn. However, high tensile stresses close to 200 MPa begin to develop near a few tens of nanometer regions in front of Na x Sn particles, as particles grow to sizes greater than 30 nm.…”

“…SLD behavior was first reported in the oxidation of Si nanowires [ 9–14 ] and subsequently observed in various solute atoms such as Li, [ 7,15–17 ] B, [ 18,19 ] P, [ 20 ] and Ge. [ 21,22 ] This peculiar behavior is attributed to the residual stress developed at regions near the advancing reaction layer.…”

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].…”

“…Consequently, the areal dose was significantly reduced to 1.97 × 10 11 cm −2 with a maximum doping concentration about 8 × 10 16 cm −3 . Similarly, Perego et al synthesized polystyrene (PS) and poly-(methyl methacrylate) polymers (PMMA) end-terminated with a P-containing moiety [28]. The functionalized polymers were first spin-coated on the substrate, followed by a rapid thermal annealing process for surface functionalization.…”