A temperature control system having a re-circulation loop that uses valves
to selectively circulate a temperature control fluid through a cooling
system, through a heating system, or through a through passage so as to
controlling the temperature of the temperature control fluid, which, in
turn, controls the temperature of a target. A temperature sensor monitors
the target's temperature. A controller controls valve operation in
response to the temperature measured by the temperature sensor to obtain
a predetermined target temperature. Beneficially, the controller controls
the target's temperature according to a predetermined temperature
profile. Continuous etching along a predetermined temperature profile is
possible.