Ion dose, energy, and species dependencies of strain relaxation of SiGe buffer layers fabricated by ion implantation technique

Abstract

We systematically studied on ion dose, energy, and species dependencies of strain relaxation ratios for SiGe buffer layers fabricated by ion implantation technique where the epitaxial growth of SiGe layers was carried out on Si or Ar ion preimplanted Si substrates. For Si+ implantation, we found that there was an optimal ion-implantation condition to effectively enhance strain relaxation of the SiGe layers, that is, relaxation ratios increased with the ion dose but reduced remarkably when it exceeded a certain critical dose (∼1×1015 cm−2). The drop of relaxation also occurred as the implantation energy increased. Based on simulations and transmission electron microscopy (TEM) observations, it was concluded that end-of-range (EOR) defects generated by Si+ implantation crucially caused formation of high-density misfit dislocations at the heterointerface, and the observed complicated results were well understood in terms of the position of EOR defects from the heterointerface. We confirmed this conclusion by observing that relaxation ratios monotonically increased as the EOR defects position from the heterointerface was decreased by means of surface etching. On the other hand, for Ar+ implantation, relaxation ratios were seen to increase monotonically with the increase in ion dose without any drop even in the high dose region. Void-related defects formed around projected range of ion implantation were thought to dominate strain relaxation of the SiGe layers differently from Si+ implantation case. This difference in the relaxation mechanism between Si+ and Ar+ implantation was also found in and confirmed by TEM and atomic force microscopy observations.

Unexpected Dominance of Vertical Dislocations in High‐Misfit Ge/Si(001) Films and Their Elimination by Deep Substrate Patterning

“…In particular, threading dislocations (TDs) emerging on the surface can drastically decrease the top layer quality, for example, by affecting the carrier mobility and lifetime in devices 6. Several techniques have been proposed for reducing the TD density, such as annealing steps,7 aspect‐ratio‐trapping (ART)8 and selective area depositions (SAD),9 or growth of buffer layers localizing plastic relaxation, such as virtual graded layers,10 low temperature silicon buffers,11 compliant substrates,12 two‐temperature epilayers13 and ion implanted substrates 14. TD densities as low as few 10 6 cm −2 for micrometer thick Ge layers have been obtained 15.…”

Line Width Dependence of Anisotropic Strain State in SiGe Films Induced by Selective Ion Implantation

“…Ion implantation is known to be one of the useful tools for the fabrication of relaxed SiGe layers. [10][11][12][13][14][15] When a SiGe layer is grown on an ion-implanted Si substrate, the strain relaxation of the overgrown SiGe layer is largely enhanced because ion-implantation-induced defects in the Si substrate act as effective misfit dislocation nucleation sources. Recently, we have shown that the degree of strain relaxation of SiGe layers can be locally controlled by means of selective ion implantation.…”

Compressively strained Si/Si1− xCx heterostructures formed on Ar ion implanted Si(100) substrates

“…In this method, the thin-film relaxed SiGe layers can be fabricated at low temperature owing to defects generated by annealing after ion implantation, which act as dislocation nucleation sources and enhance strain relaxation of the overgrown SiGe layers. [20][21][22][23][24][25] The relaxation ratio in the SiGe layers monotonically increases by increasing the Ar ion dose, and the SiGe layers are largely relaxed on the Ar ion implanted Si substrates with a dose of 1 × 10 15 cm −2 . 22,24) In addition, void-related defects, which are formed around the projected range of the ion implantation, are found to contribute to the strain relaxation of the SiGe layer significantly.…”

“…[20][21][22][23][24][25] The relaxation ratio in the SiGe layers monotonically increases by increasing the Ar ion dose, and the SiGe layers are largely relaxed on the Ar ion implanted Si substrates with a dose of 1 × 10 15 cm −2 . 22,24) In addition, void-related defects, which are formed around the projected range of the ion implantation, are found to contribute to the strain relaxation of the SiGe layer significantly. It is therefore thought that the relaxed Si 1−x C x layers with thin thickness can be fabricated on Si substrates at low temperature by utilizing the Ar ion implantation technique.…”