> Does anyone know how hot the substrate gets inside an RIE chamber when
> you are etching  at a power of say 150 W?

The temperature varies greatly,
depending on the thermal contact to the back side of the wafer,
the thermal conductivity of the wafer,
how exothermic the reaction is, exposed area, and other parameters.
It may vary from wafer to wafer for your process.

It can be measured by placing temperature dots (available from Omega)
on the wafer. These turn dark when a threshold temperature is reached
and are available in a range of temperatures. Your temperature is probably
in the range of 50 C to 150 C.

After placing a temperature dot, cover it with a little piece of Kapton
tape.
Poke a hole through the tape to allow air to escape in the vacuum chamber.

        --Kirt Williams Agilent Technologies