SiO2 thin film creation in Diffusion furnace - Process Functional Modeling
During the PRE-LOADING - loading wafers into the boat, the furnace remains open, resulting in losing N2 gas and electricity. It would be better to cover the bottom of the furnace.
Turn off the heaters of the furnace and N2 flow during PRE-LOADING - loading the wafers in the boat
Start N2 flow just before the LOADING, before the loading of the boat with wafers into the furnace. Turn on the heaters only when the boat is completely loaded into the furnace
Disconnect the thermocouples control during the LOADING if the furnace is turned on.
Use a mixture of N2 and Ar during LOADING to ensure that all residual air is moved out, even from the bottom zone of the furnace.
Turn off the heaters of the furnace when the boat is removed. The furnace is big enough to keep the temperature for a long time. Besides, the STABILIZATION step is long enough to compensate for the temperature difference.
The quality of the low-zone wafers is different from the mid-zone and top-zone wafers. For instance, the stoichiometry of SiO2 might change. Even small variations of stoichiometry can result in the same change in optical constants that may affect the model of ellipsometric model and result in SiO2 thickness.
During the loading, the lowest thermocouple received the wrong information; therefore, the bottom part of the furnace became overheated.
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