AVS 52nd International Symposium
    Science of Semiconductor White Light Topical Conference Monday Sessions
       Session WL-MoA

Paper WL-MoA4
Temperature Measurement and Control during Group-III Nitride MOCVD

Monday, October 31, 2005, 3:00 pm, Room 310

Session: Science of Semiconductor White Lighting
Presenter: J.R. Creighton, Sandia National Laboratories
Authors: J.R. Creighton, Sandia National Laboratories
D.D. Koleske, Sandia National Laboratories
C.C. Mitchell, Sandia National Laboratories
M.J. Russell, Sandia National Laboratories
Correspondent: Click to Email
Accurate temperature measurement during group-III nitride MOCVD is difficult due to the broad spectral transparency of the substrates and epitaxial layers. In fact, there is no readily available method that measures the true surface temperature during deposition on sapphire substrates. We have developed a pyrometer in our single-wafer research reactor that operates near the high-temperature bandgap of GaN, thus solving the transparency problem once a ~1 micron thick GaN epilayer has been established. The system collects radiation in the near-UV (380-415 nm) and has an effective detection wavelength of ~405 nm. Near 1000°C, the RMS temperature noise of the system is <0.1°C, and at 800°C the RMS temperature noise is <0.5°C. By simultaneously measuring the reflectance, we can also correct for emissivity changes when films of differing optical properties (e.g. AlGaN) are deposited on the GaN template. By employing the virtual interface method, the reflectance measurement can also be used to monitor growth rates and compute optical properties of the thin films. We have recently modified the pyrometer hardware and software to enable measurements in one of our commercial Veeco D-125 multiwafer MOCVD systems. A method of synchronizing and indexing the detection system with the wafer platen was developed so signals only from the desired wafer(s) could be measured, while rejecting thermal emission signals from the platen. The Veeco D-125 also has more limited optical access, in comparison to our research reactor, so the front end collection optics required a redesign and optimization. Despite the losses in optical throughput and duty cycle, we are able to maintain good performance from 750-1100°C. (Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.).