Alongside with our high-accuracy high-temperature nk database for Arsenides and Phosphides, which enables in-situ process control of layer thickness and composition at the same level of accuracy as XRD or PL, LayTec has developed an improved nk database for the III-Nitrides as part of the latest version of our EpiNet software. These high accuracy nk data in conjunction with Pyro 400 wafer temperature control opens a pathway to a more comprehensive and direct SPC of III-Nitride based manufacturing on Patterned Sapphire Substrates (PSS), silicon and, most importantly, on GaN wafers.
As an example, you can find some measurement results in the talk of Mr. Christoph Berger "In-situ metrology during growth of novel nitride-based semiconductor Bragg mirrors": Download the PDF of the talk.
RF power transistors like HEMTs based on AlGaN/GaN or InAlN/GaN combine high electron mobility and high critical electric field strength. Their nearly three orders of magnitude lower specific on-resistance (theoretical value) compared to silicon based devices could enable an at least 10-fold reduction of power losses, device size and cost. Typically, the best performance is reached on semi-insulating silicon carbide (SiC). However, the MOCVD growth of the related AlGaN and AlInGaN structures on large SiC-4H wafers needs complex growth recipes for strain management and tight statistical process control (SPC) for high process yields. For this technology, LayTec has expanded its high-temperature nk database and implemented additional real-time analysis routines to feed SPC systems with highly accurate in-situ data. Fig. 1 gives an example:
Fig. 1: AlN buffer growth on SiC-4H in a three-step high-temperature process. The 405 nm reflectance data is highly accurate due to auto-calibration to the true SiC-4H substrate temperature measured in-situ by Pyro 400 (blue - measured, red - fitted reflectance). The fit gives the thickness dAlN=73.2±0.5 nm. Data provided by confidential customer.
The initial AlN growth on SiC-6H is performed at very high wafer temperature (measured by Pyro 400 at ±0.5 K accuracy) and with a sophisticated three-temperature process. This ensures significant defect reduction for the subsequent HEMT growth. Despite the varying wafer temperature in this AlN buffer growth process, the latest real-time analysis function library of LayTec's EpiNet software allows our tools to reach ±0.5 nm accuracy in real-time AlN film thickness measurement. This has been achieved by tightly correlating the absolute SiC-4H wafer temperature with high accuracy SiC-4H and AlN nk optical data and implementing new analysis algorithms that separate reflectance changes caused by temperature ramping from the AlN growth effects.
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