LayTec’s patented AbsoluT technology currently keeps wafers in about 750 MOCVD systems world-wide at the absolute temperature scale of the National Metrology Institute of Germany (German name: Physikalisch-Technische Bundesanstalt - PTB), assuming that each of the so far shipped 100 AbsoluT calibration tools keeps 5-10 MOCVD systems on track. This makes LayTec’s EpiTTs, which are regularly calibrated by AbsoluT, the tool of choice for emissivity corrected near infra-red pyrometry, wherever it is applicable. For GaN epitaxy on sapphire and SiC, however, EpiTT yields the pocket temperature instead of wafer temperature, and only UV pyrometry can sense the wafer temperature. Therefore, our latest development Pyro 400 comes to the market with a brand-new calibration tool: AbsoluT 400. As its well-established “twin” calibration tool AbsoluT 950, the new AbsoluT 400 emits a PTB calibrated, highly stable and very uniform radiation in the 400-420 nm detection range of our UV pyrometers. Fig. 1 shows the qualification result as recently achieved at a planetary reactor with two optical viewports.
Fig. 1: Two emissivity corrected pyrometers detecting the wafer temperature of a bare silicon wafer in a G3 planetary reactor with two viewports. View-port #1: ECP sensing at 950 nm by EpiTT calibrated by AbsoluT 950 (red line). View-port #2: ECP sensing at 410 nm by Pyro 400 Gen3 calibrated by AbsoluT 400 (blue line).
As you can see, the two independently calibrated emissivity corrected pyrometers Pyro 400 (calibrated by AbsoluT 400 - blue curve in Fig. 1) and EpiTT(calibrated by the established AbsoluT 950 - red curve) give exactly the same wafer temperature. The temperature difference is less than 1 K in the temperature plateaus. During the T-ramps, the temperature difference is about +2 K for up-ramping and -2 K for down-ramping. This is correct, because of the about 3 second time-shift between the two measurements: the Si wafer has to travel 180° of main rotation between the two view-ports and is heated/cooled during this time.
LayTec offers recalibration services for both AbsoluT 950 and AbsoluT 400. Recalibration is recommended every 12 month for keeping the calibration tools within ±0.5 K to the temperature scale of the National Metrology Institute of Germany (PTB). Recalibration on customer site is possible and takes just a few minutes. Alternatively, customers can ship-in their AbsoluT units to LayTec for recalibration. For more information please contact firstname.lastname@example.org.