Strain relaxation of pseudomorphic Si1−xGex∕Si(100) heterostructures after Si+ ion implantation

Abstract

The strain relaxation of pseudomorphic Si 1−x Ge x layers ͑x = 0.21, . . . , 0.33͒ was investigated after low-dose Si + ion implantation and annealing. The layers were grown by molecular-beam epitaxy or chemical vapor deposition on Si͑100͒ or silicon-on-insulator. Strain relaxation of up to 75% of the initial strain was observed at temperatures as low as 850°C after implantation of Si ions with doses below 2 ϫ 10 14 cm −2 . We suggest that the Si implantation generates primarily dislocation loops in the SiGe layer and in the underlying Si which convert to strain relaxing misfit segments. Strained Si films grown on strain-relaxed SiGe buffer layers will soon be applied for advanced microelectronic devices since strained Si exhibits significantly enhanced carrier mobilities and therefore, yields to transistors with higher transconductance and drive currents.1,2 However, a key problem is the fabrication of thin strain relaxed SiGe buffer layers, which serve as virtual substrates for the growth of strained silicon. The standard approach is the growth of several micrometer thick, compositionally graded buffer layers. 3Recently, it was shown that He + ion implantation and subsequent thermal annealing can successfully be employed to relax the strain of thin pseudomorphic SiGe layer grown on Si͑100͒.4-6 The required He + implantation doses to achieve substantial strain relaxation during the subsequent annealing are in the range of 5 ϫ 10 15 cm −2 to 2 ϫ 10 16 cm −2 . These relatively high doses lead to long implantation times and limit throughput of wafers in production and form voids in the underlying silicon. Previously it was shown that strain relaxation can also be achieved by H + implantation and annealing.4 However, this method was only successful forSiGe layers with Ge concentrations below 25 at. %. Enhanced strain relaxation due to the introduction of point defects by Ge + ion implantation at 400°C or the implantation of dopants ͑B,As͒ was reported, however, without revealing the resulting microstructure. 7,8 The use of ion implantation for strain relaxation has several advantages: It is easy to use, is highly reproducible, is area-selective by the use of masks, and is fully compatible with existing Si technology. Therefore, there is interest in the development of an ion implantation method, which allows efficient strain relaxation after annealing at moderate temperatures while maintaining a high sample quality. It is important to use ions, which require only a low dose and avoid contamination or unintended doping by the implanted ions.In this work, we have investigated the strain relaxation of pseudomorphic Si 1−x Ge x layers induced by low dose Si + ion implantation at room temperature and subsequent annealing. We also provide a preliminary explanation for the mechanism of strain relaxation. The layers were grown by chemical vapor deposition (CVD) and solid-source molecular-beam-epitaxy (MBE) on Si͑100͒ and on siliconon-insulator (SOI) wafers. The samples were characterized using transmission electron microsco...

Si + ion implantation for strain relaxation of pseudomorphic Si1−xGex/Si(100) heterostructures

“…This would explain why the Si dose required for efficient strain relaxation increases with increasing Si implantation range when the implantation range exceeds the width of the SiGe layer, i.e., when D Ͼ 0. This reasoning is also supported by the observation by Holländer et al 17 that the deposition of a large fraction of the implanted Si in an underlying SiO 2 layer does not reduce the degree of relaxation of the SiGe layer.…”

“…Holländer et al proposed Si + ion implantation into the Si substrate followed by annealing for the purpose of strain relaxation of pseudomorphic SiGe layer grown on SOI material. 17 In the case of He, interstitial type dislocation loops are formed upon pressure relaxation of He filled cavities during annealing, while in the case of Si implantation, dislocation loops form due to the clustering of excess selfinterstitial atoms ͑SIAs͒ corresponding to the implanted Si ions. The reported experiment was primarily aimed at demonstrating the potential of Si + implantation for strained SiGe layer relaxation.…”

Cracking in hydrogen ion-implanted Si∕Si0.8Ge0.2∕Si heterostructures

“…[13][14][15][16] Note that the SiGe layers studied in previous reports were relatively thick. For brittle materials such as Si and SiGe, when the value of J exceeds the energy required to form new surfaces, a crack will propagate.…”

Anisotropy of strain relaxation in (100) and (110) Si/SiGe heterostructures

“…1 Several methods use ion implantation as a mean to generate strain relaxation of SiGe layers. [2][3][4][5][6] As different strain types (tensile, compressive, biaxial, or uniaxial) modify in a specific way the material properties, i.e., carrier mobility, 7,8 dopant diffusion, 9 or dopant solubility, 10,11 the study of dislocation formation and control in Si(Ge) materials regained importance.…”

“…6 During annealing, these loops glide toward the Si/SiGe interface and then further to the surface, accompanied by the extension of the formed threading dislocations (TDs) through the SiGe layer. It results in the formation of a strain relaxing network of misfit dislocations (MDs) at the SiGe/Si interface.…”