STS etcher question

Jim McVittie mcvittie at snf.stanford.edu
Wed May 11 12:03:52 PDT 2005


Jim,

During plasma etching there is significant heat flow into the top surface of
your wafer from the ion bombardment. The wafer temperature will rise until there
is a balance between the heat flow into the top and out the bottom. If the wafer
temperature goes too high ( about 110C range) the resist can flow and/or burn.
To improve heat flow out the bottom of the wafer, the space between the wafer
and cooled chuck is fill with He gas at a pressure around 10 torr. The STS
etcher is designed to have about a 50C temperature difference between the cooled
chuck and the wafer. When you mount a wafer on a carrier wafer, you are
increasing the thermal resistance between the top wafer and the chuck. If the
resist is thin and there are no gas bubbles, the increase in thermal resistance
is not too high and the resist does not burn. However, if mounting of the
carrier wafer is not great and you have bubbles, you are going to have heating
problems during a long etch. One approach to minimizing this problem is to use
the IR camera and to make sure there are no gas bubbles between the wafers.
Also have an experienced user show you the best procedure for the mounting.

    Jim

Steve Zhuang wrote:

> Hi all,
>
> I have a question concerning overheating and resist burning in the STS
> etcher. I STS etched from the back side of a silicon wafer that was bonded
> to a quartz wafer using photoresist. The photoresist adhesive was uniform
> and baked property. However, during the 1 hour etching time, the photoresist
> mask on the silicon wafer was partially burned, and the adhesive photoresist
> between the silicon and quartz wafers became very non-uniform. I think this
> problem might have been caused by overheating during etching. Does anyone
> have similar experiences? Your input is highly appreciated!
>
> Thanks
>
> Steve Zhuang
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