Phosphorus δ-layers in SiO 2 have been prepared by means of poly(methyl methacrylate) (PMMA), terminated with a phosphoruscontaining moiety acting as an anchoring group. In particular, grafting of two P-terminated PMMA samples with M n = 7.5 kg/mol (D̵ = 1.14) and M n = 17.8 kg/mol (D̵ = 1.23) onto 10 nm thick SiO 2 films deposited on Si substrates has been investigated, focusing on the thickness evolution of the brush layer as a function of the processing parameters, that is, annealing temperature and time. Upon removal of the polymer chains and subsequent encapsulation into a SiO 2 matrix, the concentration of phosphorus atoms into the P δ-layers has been monitored by time-of-flight secondary ion mass spectrometry. The effective P dose in the P δ-layer is mainly dictated by the molecular weight of the P-terminated PMMA, and the doping process results are highly reproducible, provided that tight control over the experimental protocol is granted. However, although the grafting density is expected to progressively increase as a function of annealing time with a linear correlation between grafting density and thickness, the measured P dose in the δ-layers is observed to follow the opposite trend. This effect has been accounted for by considering a distortion of the molecular weight distribution of the grafted species with respect to the initial molecular weight distribution of the polymer. The overall picture reveals important information about the mechanism and dynamics governing the "grafting to" process of P-terminated PMMA polymers onto nondeglazed Si substrates.

Monodisperse polypeptoids with 5, 10, 14, and 19 monomer units and a phosphorus containing moiety at one end were prepared through the submonomer solid-phase synthetic approach. The insertion of defects at specific positions along the polymer chain enables the suppression of their crystallinity thus leading to amorphous samples with improved solubility. Polypeptoid brushes were prepared by performing the “grafting to” process at high temperature for a short time thus decoupling the grafting process from thermal degradation. Precise control of the brush thickness is achieved by selection of the polypeptoid chain length. Ashing the polypeptoid brushes by O2 plasma leads to complete removal of the chains while preserving the dopant atoms covalently bound to the silicon surface. In this way, phosphorus δ-layers with precisely predetermined amounts of dopant atoms are obtained. These results highlight the possibility to integrate precision polymers prepared by perfectly reproducible procedures in the sophisticated processes of the microelectronics industry.

In this work, block copolymer lithography and ultralow energy ion implantation are combined to obtain nanovolumes with high concentrations of phosphorus atoms periodically disposed over a macroscopic area in a p-type silicon substrate. The high dose of implanted dopants grants a local amorphization of the silicon substrate. In this condition, phosphorus is activated by solid phase epitaxial regrowth (SPER) of the implanted region with a relatively low temperature thermal treatment preventing diffusion of phosphorus atoms and preserving their spatial localization. Surface morphology of the sample (AFM, SEM), crystallinity of the silicon substrate (UV Raman), and position of the phosphorus atoms (STEM-EDX, ToF-SIMS) are monitored during the process. Electrostatic potential (KPFM) and the conductivity (C-AFM) maps of the sample surface upon dopant activation are compatible with simulated I−V characteristics, suggesting the presence of an array of not ideal but working p− n nanojunctions. The proposed approach paves the way for further investigations on the possibility to modulate the dopant distribution within a silicon substrate at the nanoscale by changing the characteristic dimension of the self-assembled BCP film.