By LayTec GmbH
Best practice for AbsoluT temperature calibration to reduce system-to-system variations. LayTec is continuously improving its products in order to reduce system-to-system variations and improve performance. To improve specifically the temperature measurement and calibration, both a new generation of the AbsoluT calibration tool and a new generation of detection units within EpiTT and EpiCurve® TT was released. Since the new generation AbsoluT* and detection units are ideally matched, they provide the best possible precision, reproducibility and accuracy. To further increase precision, reproducibility, and accuracy of the calibration, LayTec has developed a procedure to match individual EpiTT/EpiCurve® TT systems with an individual AbsoluT used for calibration. Each pair of EpiTT/EpiCurve® TT and AbsoluT can be assigned an individual reference temperature (so called paired reference temperature) that is then used in the calibration process. This procedure works best with a combination of new EpiTT/ EpiCurve® TT and new AbsoluT. However, it can also be used with older EpiTT/EpiCurve® TT and older AbsoluT – in any combination. The increase in precision, reproducibility, and accuracy might not be as big as with the new generation, though. Option 1: Best possible accuracy (system-to-system reproducibility/precision). The best overall accuracy can be achieved by strictly using the new “paired reference temperatures” for each used EpiTT/EpiCurve® TT paired with each used AbsoluT. To do that, the spectral properties of the systems must be known. For EpiCurve TTs and AbsoluTs of the new hardware generation this data is known and available at LayTec. In case of the usage of an AbsoluT of generation 1, the AbsoluT needs to be characterized at LayTec (please contact support@laytec.de for further information). To achieve the best accuracy, the paired reference temperatures will be provided by LayTec customer support on request: 1. Send EpiTT/EpiCurve® TT system serial numbers to LayTec customer support 2. Send AbsoluT system serial number to LayTec 3. LayTec will inform you if your AbsoluT needs to be sent back for recalibration and characterization 4. LayTec will send calibration certificate for paired reference temperatures 5. Calibrate the EpiTT/EpiCurve® TT in the fab by entering the new paired reference temperatures into the EpiNet AbsoluT calibration device This option can lead to a temperature offset when comparing to the old calibration on each system. The offset depends on the hardware generation of both AbsoluT and EpiTT and laboratory tests at LayTec application engineering have shown values up to 6K. Even in this case, usage of a new generation AbsoluT will increase long-term stability of the calibration. In order to avoid a change in absolute values, the “house calibration” of the old AbsoluT needs to be transferred to the new AbsoluT. The best consistency between old and new AbsoluT can be achieved by transferring the calibration with the old AbsoluT over to the new one: 1. Calibrate the EpiTT/EpiCurve® TT with the old AbsoluT that was formerly used for calibration 2. Measure the temperature of the new AbsoluT on that EpiTT/EpiCurve® TT system for a specific corrected reference temperature 3. Generate your own paired reference temperature table 4. Using the new AbsoluT for calibration: to keep the consistent calibration value, use the corrected temperature generated in step 3 Option 2: Consistency in calibration history. Consistency in calibration history may be more important than absolute accuracy (e.g. due to a qualified process or a desired long-term stability of calibration values). Recommendation: Generally, it is recommended to use a new generation AbsoluT due to its higher stability and accuracy. It is recommended to use the paired reference temperature for calibration, especially for new fabs/systems. In case of qualified processes, quality control specifications or other reasons, the method for keeping a consistent calibration is possible. In any case it is necessary to decide for one of the options and not mix them.
