Experiments and Modeling of Si-Ge Interdiffusion with Partial Strain Relaxation in Epitaxial SiGe Heterostructures

Abstract

Si-Ge interdiffusion and strain relaxation were studied in a metastable SiGe epitaxial structure. With Ge concentration profiling and ex-situ strain analysis, it was shown that during thermal anneals, both Si-Ge interdiffusion and strain relaxation occurred. Furthermore, the time evolutions of both strain relaxation and interdiffusion were characterized. It showed that during the ramp-up stage of thermal anneals at higher temperatures (800 • C and 840 • C), the degree of relaxation, R, reached a "plateau", while interdiffusion was negligible. With the approximation that the R value is constant after the ramp-up stage, a quantitative interdiffusivity model was built to account for both the effect of strain relaxation and the impact of the relaxation induced dislocations, which gave good agreement with the experiment data. © 2014 The Electrochemical Society. [DOI: 10.1149/2.0041410jss] All rights reserved.Manuscript submitted May 28, 2014; revised manuscript received July 9, 2014. Published July 26, 2014.As electronic and optoelectronic devices are continuously scaled down for better performance, novel materials and process techniques have been developed and integrated into the state-of-the-art semiconductor device manufacturing. In the last decades, Si 1-x Ge x (0 ≤ x ≤ 1) alloys have become key materials in electronic devices. Examples are channel materials in p-type metal-oxide-semiconductor field-effect transistors (MOSFETs) for higher hole mobilities, 1,2 the tunneling layer in tunneling FETs, 3 and the quantum wells in resonant tunneling diodes. 4 For optoelectronic applications, SiGe alloys and Ge are also employed in modulators, 5 Ge photodiodes 6,7 and Ge/Si lasers. 8,9 Si/Si 1-x Ge x and Si 1-x Ge x /Si 1-y Ge y heterostructures with abrupt changes in Ge concentration have become key structures for many electronic and optoelectronic devices. During the fabrication of those devices, especially the ones requiring high temperature processes, unavoidably, Si and Ge atoms interdiffuse at the interface between two layers in heterostructures. This interdiffusion increases exponentially with Ge concentration and compressive stress, and also increases with ion implantation damage. 10,11 Si-Ge interdiffusion is generally undesirable as it degrades MOSFET performance by reducing strain and carrier confinement and increasing alloy scattering. 12 It also decreases photodetector efficiency, 13 and delays the lasing of Ge/Si lasers.14 Therefore, understanding Si-Ge interdiffusion behavior under different strain conditions is a topic with great technological significance. In Dong et al's previous studies, a unified Si-Ge interdiffusivity model was built for Si-Ge interdiffusion without strain over the full Ge fraction range and was validated with experiments. 15 In addition, the role of compressive strain in Si-Ge interdiffusion was modeled based on experimental data in Dong et al's recent work. 16 However, until now, there have been few studies available on Si-Ge interdiffusion behavior with partial compressive strain ...

Dangling bond defects in silicon-passivated strained-Si1−xGex channel layers

“…i.e., above x=0.2 or similar to this value. This Ge out-diffusion process is well documented in the literature [25][26][27] and under usual processing thermal budgets, Ge in-diffusion depth ranges from several nm to few tens of nm. This mechanism allows us to explain the major experimental observations made in the present study if assuming that the oxide insulator represents a sink of the Ge atoms diffusing in from the Si1-xGex channel region due to the high Ge solubility in the oxide.…”

Interdiffusion in group IV semiconductor material systems: applications, research methods and discoveries

“…Figure 11 shows the schematic as-grown and annealed profiles. 113 Bragg reflection was used to measure the films' average Ge concentration and the strain status. The interdiffusion was modelled with a concentration-dependent diffusivity prefactor D0 and activation energy Ea.…”

“…Not observable for structures with up to 30% Ge with 1% tensile strain [112]. Compressive strain relaxation effect When the strain relaxation history is known, this effect can be modelled as a smaller strain in the compressive strain term [113]. Threading dislocation impact It introduces a dislocation-mediated interdiffusion term, which is significant for low Ge regimes [1,113].…”

“…Not observable for structures with up to 30% Ge with 1% tensile strain [112]. Compressive strain relaxation effect When the strain relaxation history is known, this effect can be modelled as a smaller strain in the compressive strain term [113].…”

“…It introduces a dislocation-mediated interdiffusion term, which is significant for low Ge regimes [1,113]. Doping impact P and As enhances interdiffusion.…”