Extraction of stress and dislocation density using in-situ curvature measurements for AlGaN and GaN on silicon growth

Abstract

We have analyzed the in-situ measurements of bow and reflectance during growth of GaN on silicon layers for HEMT based devices, varying the quality of the layers by changing the AlN nucleation layer. By fitting the curves and applying the Stoney equation, we were able to extract stress profiles in the layers, and convert these into out of plane strain profiles. This allowed us to simulate X-Ray Diffraction profiles which matched well with measured data, confirming the validity of our data extraction. Finally, we see that we incorporate less stress with a higher dislocation density in the GaN layers, and so for a given set of growth conditions, we can infer the dislocation by looking at the relaxation rate.

The Surface Morphology Evolution of GaN Nucleation Layer during Annealing and Its Influence on the Crystal Quality of GaN Films

“…The surface roughness drops rapidly which results in the reflectivity intensity dropping abruptly, close to zero. With the annealing time increases, the GaN NL not covered with NIs is completely etched away, and the flat sapphire surface increases the reflectivity intensity [11][12][13]. The stage 3 corresponding to the early stage of un-doped GaN growth at 1080 • C is the three-dimensional (3D) NI growth.…”

X‐Ray Diffraction Microstrain Analysis for Extraction of Threading Dislocation Density of GaN Films Grown on Silicon, Sapphire, and SiC Substrates

“…Note that this broadening can be asymmetrical, depending on the gradient shape, whereas the broadening from microstrain is always symmetrical. The stress gradient is especially strong in GaN‐on‐Si samples and has therefore a large influence on the diffraction peak shape compared with GaN grown on SiC. As shown in Figure , the diffraction measurements show a quasisymmetrical broadening of the peaks in the case of the GaN sample grown on an SiC substrate, likely indicating a broadening mainly induced by the microstrain effect.…”

“…In addition to the TD, GaN layers are generally strained by a biaxial in‐plane stress introduced during the heteroepitaxy process and the following cooldown to room temperature, due to the mismatch between the coefficients of thermal expansion of GaN and its substrate. Depending on the deposition condition, this may lead to a macrostress gradient throughout the layer, in the direction normal to the surface, with a correlated macrostrain gradient. This varying strain introduces a second source of broadening to the radial XRD peaks, which adds to the microstrain broadening.…”

“…In this study, we performed microstrain measurements on GaN layers grown on a wide range of substrates, including GaN‐on‐Si, and compared them with CL and XRD misorientations measurements. For GaN‐on‐Si samples in particular, the layers have high macrostress gradients that complicate the analysis. This work aims at showing how to bypass this additional effect and allow accurate TD densities measurements using XRD.…”

Capacitance Temperature Dependence Analysis of GaN-on-Si Power Transistors

“…Concerning the device physics, the piezoelectric polarization strain model with Vurgaftman values [17] was used for the calculation of spontaneous and piezoelectric polarization effect. This model was activated only at the AlGaN/Si 3 N 4 interface and at the GaN/AlN/AlGaN interfaces because the strain in the buffer layers evolves strongly during growth [18] and is quite challenging to model accurately. In addition, the activation of this model was tuned to fit the electron density in the 2DEG.…”