Monitoring and control of chemical composition of InGaN layers during MOCVD
Metal-Organic Chemical Vapor Deposition (MOCVD) epitaxial processes are used to deposit the GaN, InGaN, AlGaN and other wide band-gap semiconductor thin films making up the buffer, quantum well, and cap layers of the next generation high-brightness LEDs (HB-LEDs) for Solid State Lighting (SSL). Non-uniformity of the central wavelength over the wafers, run-to-run and reactor-to-reactor non-repeatability are primary contributors to reduced manufacturing yield. On the epitaxial level, non-uniform device performance results from the variations of chemical composition and thickness of the individual InGaN quantum well layers. Being extremely thin, the individual quantum well layers remain beyond the resolution of the standard optical monitoring techniques.
Accustrata is developing a prototype of optical monitoring and control system utilizing its know-how in real-time optical monitoring, intelligent data-mining and process modeling, which has already been commercially demonstrated in the PV industry. AccuStrata will develop, install and validate on a commercial MOCVD reactor a beta-prototype of a spectroscopic optical monitoring and process control system. The system will monitor the LED thin films as they grow in real time on the individual wafers, record the signal in a broad spectral range and process the information to retrieve the most important film parameters and their distribution over a single wafer, all the wafers in a batch and multiple batches. During the epitaxial growth of the thin quantum well films, the recorded spectral signal will be correlated to the process parameters such as substrate temperature and precursor gas composition.
AccuStrata will deploy a novel algorithm for a real-time pattern search in the acquired broadband spectral data and display any abnormalities and differences in the deposition of the individual quantum well layers. This information can be used by the MOCVD engineer to better tune the epitaxial process, and later can be integrated into the MOCVD reactor to ensure better repeatability of the individual quantum well layers in the LED structure and allow tightening of the distribution of the LED central wavelength.