Quality of Silica Capping Layer and its Influence on Quantum-Well Intermixing

Abstract

The quality of spin-on silica films prebaked at different temperatures has been studied using Fourier transform infrared spectroscopy, spectroscopic ellipsometry, and P-etch [HF(40%):HNO3(70%): H2O=3:2:60] measurements. Low-temperature photoluminescence (PL) was performed on GaAs/AlGaAs quantum-well (QW) structures encapsulated by the same films. For all the prebaked films, not only the Si-O-Si peaks, but also OH-related peaks were detected in the IR spectra. After annealing at 950°C for 60 s, almost all OH-related peaks disappeared. Spectroscopic ellipsometry modeling and P-etch measurements showed that the porosity of high-temperature (>300°C) baked samples was similar, and was significantly higher than the low-temperature (210°C) baked sample. The same trend was observed in the PL energy shifts from the GaAs/AlGaAs QWs, indicating a direct correlation between the film quality and quantum-well intermixing.