Voids in Silicon by He Implantation: From Basic to Applications

Abstract

The mechanism of bubble formation when He is implanted into silicon is described. Many experiments are reviewed and several techniques are considered. During implantation and subsequent annealing, complex Hen–Vm clusters are formed, trapping vacancies, while Si self-interstitials recombine directly at the surface. By increasing temperature He atoms out-diffuse, and the entire process produces a supersaturation of vacancies (void formation). Their evolution is studied during isothermal and isochronal annealing, describing the mechanisms involved; that is, direct coalescence or Ostwald ripening. The internal surface is an efficient trap for self-interstitials and for metals. The gettering mechanism is governed by a surface adsorption at low impurity concentration while at high value a silicide phase is observed. The high getter capability is ensured by the large number of traps introduced (1017–1019 cm−3). Finally, voids introduce mid gap energy levels that act as minority carrier recombination centers, providing a powerful method to control lifetime locally in silicon devices. The reviewed results demonstrate that the trap levels are due to the dangling bonds present on the void surface. This property can be used in many applications.

Gettering of copper in silicon at half of the projected ion range induced by helium implantation

“…8-the existence of a He induced cavity layer located at R p . This result is at variance with previous published reports 23,24 where no cavities were found after furnace thermal annealing between 700 and 1000°C. The authors of Refs.…”

“…He atoms are known to be trapped by divacancies stabilizing them and favoring their evolution into more complex He-V clusters during annealing. 24,28 This results in accumulation and stabilization of vacancies in the R p region contrary to what happens in the case of the Si implant. The silicon atoms displaced during the implantation diffuse during the annealing.…”

Long-Range Electron Interferences at a Metal Surface Induced by Buried Nanocavities

“…The shape of the subsurface reflector can also determine particular angles of backscattering and contribute to the formation of the long-range beams especially if it contains flat planes. Several experimental reports [7,8,19] prove the presence of flat facets forming nanocavities in single-crystalline solids. In our model, the interface with the nanocavity is built by three types of differently oriented facets f001g, f110g and f111g similarly to a Wulff construction [20].…”

Enhanced densification under shock compression in porous silicon

“…Moreover, the transition barriers to these high-pressure phases are lowered under shear, according to DFT calculations [9][10][11]. Porous crystalline silicon has been produced through high-energy helium implantation and annealing [12,13]. To our knowledge, no shock loading experiments have been conducted on porous silicon.…”