| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
W6, In Situ Stress Measurements during GaN Growth on Ion Implanted AlN/Si Substrates |
| Author(s) |
Jarod C. Gagnon, Mihir Tungare, Xiaojun Weng, Fatemeh (Shadi) Shahedipour-Sandvik, Joan M. Redwing |
| On-Site Speaker (Planned) |
Jarod C. Gagnon |
| Abstract Scope |
Ion implantation of AlN/Si substrates has been shown as a viable pathway to reduce the crack density of GaN thin films grown on Si. These substrates consist of a thin AlN buffer layer grown by metalorganic chemical vapor deposition (MOCVD) on (111) Si followed by N<sup>+</sup> implantation to form a defective layer at the AlN/Si interface. While the use of this approach reduces residual stress and dislocation density in the GaN films, the mechanism of stress relaxation is not clear. In this study, <i>in situ</i> wafer curvature measurements were used to investigate the effect of thermal annealing and GaN growth on substrate curvature and film stress. Post-growth transmission electron microscopy (TEM) was used to study the structural properties of the layers. The starting substrates used for this study consisted of 34nm AlN/Si(111). One substrate was implanted with N<sup>+</sup> ions at a dose of 2 × 10<sup>16</sup> cm<sup>-2</sup> and a range of 105 nm below the AlN/Si interface while the other served as a control and was not implanted. The substrates were annealed for 10 minutes at 1100°C in N<sub>2</sub> at 50 Torr followed by growth of a 1µm thick GaN film using trimethylgallium, NH<sub>3</sub> (V/III=13,000) and H<sub>2</sub> as the carrier gas. <i>In situ</i> stress measurements revealed that for the unimplanted sample, the GaN initiated growth under a compressive stress of 1.35 GPa which arises due to lattice mismatch with the AlN buffer layer. In contrast, GaN growth on the ion implanted sample begins at a lower compressive stress of 0.7 GPa which suggests a reduction in epitaxial stress. In both cases, the compressive growth stress is fully relaxed after ~0.7 µm of growth. During post-growth cooling, tensile stress is introduced in the GaN layer of both samples due to thermal expansion mismatch. Post-growth optical microscopy characterization, however, demonstrated that the ion implanted sample had a lower density of channeling cracks compared to the unimplanted sample. Cross-sectional TEM images revealed the formation of horizontal cracks in the ion implanted region beneath the AlN buffer layer which may provide an additional mechanism of stress relief. The effects of annealing conditions, AlN buffer layer thickness and ion implantation dose on the film stress and structural properties of the GaN layers will also be discussed. |
| Proceedings Inclusion? |
Undecided |