Control variables for performance optimization include heater
temperatures (powers), baseplate cooling, and reactor pressure.
A typical performance objective is to bring the wafers close to a desired
temperature, while keeping wafer-to-wafer and across-wafer
temperatures within prescribed limits to avoid `cracking' of wafers and
achieve uniformity of wafers.
The above picture is the result of an optimization run with the goal to
compute heater powers to achieve a uniform temperature distribution of
1027 C on the wafers during steady-state operation. The picture on the
left shows the resulting temperatures in the middle of the wafers for the
non-optimal, uniform power distribution (solid line) and the optimized
power distribution (dashed line). The picture on the right shows the
resulting temperature distributions inside the furnace. The percentages
on the right indicate the differences between the optimized power
distributions and the uniform power settings.
(Full size picture)