Formation of nanoporous structure in silicon substrate using two-stage annealing process

Abstract

The experimental results relating to exciting the defect–impurity subsystem of a (001)-oriented Si substrate containing ion-synthesized buried Si:P:O layer and transformation of the material into a porous medium are represented. After coimplantation with P + and O 2 + ions, the substrates are subjected to the annealing in non-isothermal reactor at two average temperatures (900 and 1100°C, 5 min) and two opposite directions of an axial temperature gradient grad T. The temperature difference between reversed sides of the substrate is estimated of the order of ~ 1.5 and ~ 3 °C, respectively. After further thermal evolution in conventional furnace (1150 °C, 4 hours) and cleaving, the formation of two types of a porous structure in the specimens is exposed. The first type of this structure is the developed porous structure, where initially spheroid-like empty voids have grown up in size and changed their shape to form octahedron construction. The second type of this structure is a regular array of hollow tubes oriented along screw components of misfit dislocations. In the both cases, the porous structures always are initiated on the substrates, whose implanted sides have been faced to the cold pedestal during annealing in non-isothermal reactor.