Discrete, Shallow Doping of Semiconductors via Cylinder-Forming Block Copolymer Self-Assembly

Block copolymer (BCP) self-assembly-assisted doping for semiconductors is used to achieve discrete doping with nanometer-scale junction depth, high throughput, and large area coverage. As devices become smaller and more sophisticated, spatial control of dopants becomes more critical. A variety of doping methods, such as monolayer doping and delta-doping, have been developed to replace the conventional doping method, ion-implantation; however, lateral patterning of dopants relies on photo- or e-beam lithography. To address these challenges, a self-assembling dopant (boron)-containing BCP is designed to directly pattern dopants on the nanometer scale. This method skips the lithography step and is compatible with directed self-assembly approaches. The effect of the boron concentration in the BCP on the doping performance is systematically studied by changing the volume fraction of the boron-containing block while keeping the domain spacing and the mesoscale morphology constant. Successful self-assembly of the BCP into a hexagonally packed cylindrical morphology is confirmed by small-angle X-ray scattering and resonant soft X-ray scattering with a 26 nm cylinder-to-cylinder distance. Doping silicon using these BCPs enables discrete doped areas with shallow (7-13 nm) junction depth as demonstrated by the depth profile of boron, and supported by a sheet resistance study.