Hot plate temperature falling down/doesn't rise beyond a point.
I'm running a TMAH etch of silicon in a 2000mL beaker with wafer in a teflon holder. The hotplate is set at 92C with the external probe connected. The temperature doesnt rise beyond 65 or after it reaches 88 falls back to 68.
I have changed hotplates, but the problem exists. Does anyone do any different for a TMAH etch ? I'm interested in getting my etch done at 90C without any problems.