Direct Dopant Patterning by a Remote Monolayer Doping Enabled by a Monolayer Fragmentation Study

The development of new doping methods extending beyond the traditional and well-established techniques is desired to match the rapid advances made in semiconductor (SC)-processing methods and nanostructure synthesis in numerous emerging applications, including the doping of 3D architectures. To address this, monolayer doping (MLD) and monolayer contact doping methods have been introduced recently. The MLD methods enable separation of the doping process of nanostructures from the synthesis step; hence, it is termed ex situ doping. Here, we present a new ex situ MLD method termed remote MLD (R-MLD). The noncontact doping method is based on the thermal fragmentation of dopant-containing monolayers and evaporation processes taking place during annealing of the uncapped monolayer dopant source positioned in proximity, however, without making physical contact with the target SC surface. We present a two-step annealing procedure that allows the study of the dopant monolayer fragmentation and evaporation stages and quantification of the doping levels obtained during each step. We demonstrate the application of R-MLD for achieving a large-scale direct patterning of silicon substrates with sharp doping profiles. The direct dopant patterning is obtained without applying lithographic processing steps to the target substrate. The noncontact doping process, monolayer decomposition, and fragment evaporation were studied using thermogravimetric analysis coupled with mass spectrometry and sheet resistance measurements. The doped patterns were characterized using scanning electron microscopy, scanning capacitance microscopy, and time-of-flight secondary ion mass spectroscopy.