TEMPERATURE DISTRIBUTION IN A VERTICAL FURNACE

By: Stefan Poscher, Sabine Wellner, Fraunhofer IIS-B, Erlangen, Germany,

Date: 1998

PHOENICS version: Phoenics-CVD 2.1.3

Description :

The investigated laboratory furnace is used for several high temperature processes used in semiconductor technology. The furnace consists of a quartz tube which is heated from the outside by three heating coils. The heating power of each coil is controlled by an own thermocouple located inside the tube. For the investigated process the upper thermocouple has been set to 755C, the middle to 770C and the lower to 765C in order to compensate for thermal losses. A batch of 71 silicon wafers (150mm diameter, 8mm spacing) is loaded in a quartz boat inside the tube. Three quartz baffles prevent the wafers from loosing radiation to the cold bottom flange. Temperature profiles with constant gradient over the wafer batch are required in the middle (process) zone. The simulation showing a temperature gradient can now be used as a starting point for further optimization of the temperature settings and the geometry of the furnace. As expected, in the lower zone temperature drops to temperature of the base plate. The comparison with wafer temperature measured in-situ shows excellent agreement.

Details :

• Steady 2D-heat conduction in solids and gas phase is considered.
• Surface-to-surface radiation including semitransparent materials and spectral dependence is considered.
• User coded boundary conditons for the 3 heating zones describe the thermo couple controlled heat flux.
• Convection in the gas phase and conduction and radiation of the quartz boat are negelcted.