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Rochester Institute of Technology
Microelectronic Engineering Dept.
Mlcrolithography II Laboratory
Dry development of photoresist through silylation processing
The surface imaging of photresist materials, followed by a silylation operation allows for dry
development processing. Such a process is attractive for imaging into planarizing resist films and
for application at short wavelengths where single layer wet developed resists may not exist. This
laboratory will explore these processes. Coat, exposure, silylation, and etch-development
processes will be explored.
SILYLATION
A description of the silviation oven
To silylate wafers a vacuum oven is used, all silylation processes are performed under %acuum. A
vacuum pump is connected to the oven through a valve, this valve is located towards the back and
to the left of the oven and it’s labeled “1”. To measure the pressure in the chamber a gauge is
located on top of the oven, the pressure indicator of this gauge moves clockwise consequently a
higher number on the dial means lower pressure (a reading of 28 inches of Hg means pressure of 2
inches of Hg, approximately 50 Torr). Just above the vacuum gauge, there is an “inverted L”
shaped tube, at one end of this tube there is a septum (a thin rubber membrane labeled “septum”,
through which the silylating agent is injected into the chamber) the other end of the tube goes into
the oven. Also on top of the oven there is a valve (labeled “2”) which controls the venting nitrogen.
A thermometer is placed inside the oven to measure the temperature. This thermometer is attached
to the metal plate on which the wafer is placed for silylation. The dial of the thermometer is
visible through the glass window on the door. Just below the door there are two regulators and two
switches The regulator labeled “control thermostat” is used to control the power input to the
heating elements of the oven. The other regulator is for limiting the power supply to the heating
elements for safety reasons and it should not be touched. The switch on the left side is the power
switch and the one on the right is for controlling how many heating elements are to be used, this
switch is labeled “3”, this switch should always point up so that only one heating element is used.
A description of the silylaton process
1.
Make sure that the oven is under vacuum (vacuum gauge should read 28 inches of Hg) if not
open the vacuum valve and close it once the vacuum gauge reaches 28.
2.
Turn on the oven and wait until the temperature reaches 120 C and stabilizes, this takes
approximately 1.5 hours.
3.
a. Before passivation make sure that the oven is under vacuum (28 inches of Hg on the
vacuum gauge) the vacuum valve is closed and the temperature is stable at 120C.
b.
Passivate the chamber by injecting 2 cc of DMSDMA through the septum using the
hypodermic needle which is usually kept on top of the oven. There would be a momentary
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increase in the pressure reading immediately following the injection.
c. Passivation should be performed at least two minutes before the first silylation run,
passivation is performed only once before every batch. Now the oven is ready for silylation.
4.
Before opening the chamber door several purge and evacuation cycles should be performed.
This is done by purging the chamber with nitrogen (opening valve labeled “2”) for four to
five seconds, closing it and then evacuating the chamber again so that the gauge reads 28.
This process should be repeated twice before venting the chamber with nitrogen.
Note: Do not leave the oven door open for a long time while loading the wafer because
this leads to fluctuations in the oven temperature.
5.
Load the wafer by placing it on the metal plate. Close the door and pump the chamber down
so that the vacuum gauge reads 28 inches of Fig Close the vacuum valve once the dial reads
28. Leave the wafer in the chamber for one minute, this is the post exposure bake for P7
material. The temperature should be stable at 120C.
6.
Inject 1 cc of DMSDMA with vacuum off to begin silylation. Silylation time is two minutes.
Before opening the chamber door follow the procedure described in step 4.
Note: Leave the oven under vacuum when not in use.
7.
Measure the thickness in unexposed areas using the Nanospec. The increase in thickness
should be around 200A.
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