In-situ metrology system maker LayTec AG of Berlin, Germany recently shipped a comprehensive EpiCurve TT/Pyro 400 in-situ metrology hybrid system to an industrial customer in North America. The metrology station combines automated in-situ wafer bow and film thickness measurements with two pyrometry wavelengths: near-infrared (NIR) at 950nm and near-ultraviolet (near-UV).
In gallium nitride on silicon carbide (GaN-on-SiC) and gallium nitride on silicon (GaN-on-Si) metal-organic chemical vapor deposition (MOCVD) technology, the growth of sophisticated nucleation and strain management layers is essential for the quality of the material and the performance of the final devices, says LayTec.
At the same time, these layers are a challenge for highly accurate wafer temperature control: IR light from other hot parts of the reactor is scattered into the NIR pyrometer and causes Fabry-Perot artifacts, affecting its precision. However, the GaN buffer specifically emits thermal radiation in the near UV and the temperature measured with Pyro 400 is not affected by the NIR thermal radiation scattered by the buried functional layers. Therefore the combination of NIR pyrometry with Pyro 400 allows precise control of the wafer temperature during the whole deposition process, says LayTec.