Poly-energy implantation of helium ions into silicon

Abstract

The method of polyenergetic implantation of helium ions into single-crystal silicon was investigated in order to form buried layers of high porosity, promising for creating structures of the "silicon-on-insulator" type. The creation of buried porous layers by implantation of helium ions and subsequent high-temperature annealing is very promising for further obtaining silicon-on-nothing and silicon-on-insulator structures. However, the porosity of the buried layers is limited by the blistering and flecking phenomena, which cause mechanical damage to the surface silicon at high implantation doses. The purpose of this work is to increase the helium ion implantation dose and, accordingly, increase the porosity of the buried layer after high-temperature annealing without deteriorating the quality of the surface silicon layer. We present a method consisting in creating an extended concentration profile with a concentration of 4∙10²¹ He⁺/cm³ with sequential implantation with energies of 70 and 35 keV. High-temperature annealing at 150°C/30 min leads to the formation of huge pores with a diameter of approximately 130 nm near the initial concentration maximum for the energy of 70 keV. It is concluded that the polyenergetic implantation method allows a significant increase in the implanted dose without the occurrence of surface defects, and the regulation of the annealing temperature opens up possibilities for controlling the distribution and size of pores in the buried layer.