Wet Oxide Instructions

(by ENGS63 lab group, spring 1995 and Simone Ferdinand)

1) Purge furnace with Argon or Nitrogen gas.

a) Turn on the gas into the system from the tanks.
b) Make sure that nitrogen is flowing straight into the furnace (see figure).
c) Turn the gas flowing through the furnace up to about 10 SCFH (turn back down after about 10 minutes--see step 6).

2) Turn on the bubbler.

a) Turn on switch 1 to the actual bubbler and make sure there is adequate water in the bowl.
b) Turn on switch 2 to the entrance tube and make sure that the power does go up to somewhat less than 100.
c) Make sure there is adequate water in the in the bowl. Use only 18M deionized water to fill bowl.

3) Load the wafer.

a) Place the wafer into one of the appropriate slots in the quartz tray.
b) Load the wafers into the furnace right away; no appreciable oxide will grow at 400C, and it's a good idea to continue the purge after the wafers are inside. Gently load the tray into the furnace with the aluminium foil tray holder and slide it into the center third of the furnace with the quartz rod.
c) Place the cap on the end of the furnace.

4) Turn up the furnace.

a) After the furnace has been purged of gases other than nitrogen (about 10 minutes), turn the furnace up to the desired temperature remembering that T(desired) - 200°C = T(dial).
b) Make sure that the output power goes to 5 and +/-50 dials are set at 200 and 500.

5) Turn down the N2 gas flow to about 1 SCFH.

6) Start the wet oxide process.

a) Once the furnace is up to the desired temperature (the output power fluctuates about the center of the dial), make sure that the bubbler has reached the setpoint at 202°F
b) Turn the N2 gas flow rate up to about 4.5 SCFH.
c) Switch the N2 input so that it goes through the bubbler by switching the tube to the northern valve on the back of the clean box.
d) Start the timer as soon as soon as the N2 starts bubbling through the water.

7) Turn down the N2 gas flow.

a) Once the furnace is purged with the steam (about 10 mintues), turn the N2 gas flow rate down to about 1 SCFH. (Unless you are doing a very short run in which case you will do this step as step 9b.)
b) If necessary, check the water level in the bubbler bowl and fill as appropriate.

8) Turn off the bubbler.

a) Once the timer goes off at the approved time switch the nitrogen input from the bubbler back to straight into the furnace.
b) Turn the nitrogen flow back up to about 4.5 SCFH or whatever flow rate it was when it initially first flowed through the bubbler.
c) Turn off switch 1 and 2.

9) Turn down the furnace.

a) After the furnace is again purged with nitrogen, turn down the furnace to the "OFF" temperature of 400\A1\C.
b) Turn down the N2 flow to 1 SCFH.

10) Unload the furnace.

a) Once the furnace is below 500C (about 60-90 minutes), use the gloves to take the cap off of the end of the furnace tube.
b) Taking the quartz rod, slide the tray out to the end of the tube.
c) Wait 5 minutes.
d) Using the gloves AND the aluminum tray holder, slide the tray completely out of the furnace tube and into the glass cooling tube to the right of the furnace.
e) Wait 5 minutes or until the tray is cool.
f) Slide the tray out of the cooling tube and set it down on the aluminum sheets.
g) Using tweezers, remove the wafer from the tray.

11) Turn off the N2 gas.

a) Turn the flow rate into the furnace off
b) Turn the N2 flow into the system off.

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