The use of thermal shields to reduce radiation heat loss in Siemens-type CVD reactors is analyzed, bothudtheoretically and experimentally. The potential savings from the use of the thermal shields is first exploredudusing a radiation heat model that takes emissivity variations with wavelength into account, which is important for materials that do not behave as grey bodies. The theoretical calculations confirm that materials with lower surface emissivity lead to higher radiation savings. Assuming that radiation heat loss is responsible for around 50% of the total power consumption, a reduction of 32.9% and 15.5% is obtained if thermal shields with constant emissivities of 0.3 and 0.7 are considered, respectively. Experiments considering different thermal shields are conducted in a laboratory CVD reactor, confirming that the real materials do not behave as grey bodies, and proving that significant energy savings in the polysilicon deposition process are obtained.udUsing silicon as a thermal shield leads to energy savings of between 26.5-28.5%. For wavelength-dependentudemissivities, the model shows that there are significant differences in radiation heat loss, of around 25%,udwhen compared to that of constant emissivity. The results of the model highlight the importance of havingudreliable data on the emissivities within the relevant range of wavelengths, and at deposition temperatures,udwhich remains a pending issue.
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