The monitored thermocouple temperature gauge is located behind, and not in direct thermal contact with, the substrate (Fig. 4.7a). The recorded thermocouple temperature is calibrated with measurements using a one-wavelength infrared pyrometer that measures the average temperature across the surface of the wafer. Thus, pyrometer values are considered more accurate.
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Figure 4.8. Pyrometer/Thermocouple Temperature Calibration. Due to the location of the thermocouple (Fig. 4.7a) behind the substrate, the measured thermocouple values are anticipated to differ from pyrometric values taken across the wafer surface. The pyrometer value is roughly $55^\circ\textrm{C}$ below the measured thermocouple values. The pryometric calibration data are found to be consistent with the well-known transition temperature of $1\times 1$ to $7\times 7$ surface reconstructions of Si(111) wafers ($830^\circ \textrm{C}$). |
The pyrometric calibration data are found to be consistent with the well-known $1\times 1 \to 7\times 7$ phase transition temperature, cooling through $830^\circ\textrm{C}$, at a thermocouple temperature of $883^\circ\textrm{C}$ (Fig. 4.8).
Temperature values reported are either directly measured, or equivalent, pyrometer values of thermocouple measurements given by the empirical expression $T_{\textrm{pyr}}\approx T_{\textrm{TC}}-55^\circ \textrm{C}$ (Fig. 4.8).