Wet Oxidation
Parameters
The thickness and uniformity of the oxide will be very dependent on temperature and time. The recommended flow of N2 and temperature can be found in the table below to allow a uniform oxide layer to form. To achieve the thickness desired it is recommended to calculate the time needed while keeping the other parameters static.
Wet Oxidation Parameters
Parameter |
Temperature (C) |
Time (Hrs) |
N2 flow (cc/min) |
Flask Temp (C) |
Value |
1050 |
Calculate for desired Thickness |
50 |
95 |
Procedure: Furnace Preparation
- Ensure that there is enough N2 in the nitrogen tank for the duration of the oxidation run.
- Stabilize the center furnace at the appropriate temperature with dry N2 flowing constantly at 50 cc/min. Refer to the Furnace Section for instructions on how to set the furnace. Note that the furnace needs about 1 hour to stabilize.
- Add DI to the flask and heat to 95 °C. This is accomplished by setting the flask heaters knob to the highest point near boiling point (Nitrogen will cool down water so temperature needs to be increased. Allow nitrogen to bubble constantly through the H2O at a flow rate of approximately 50 cc/min. After the H2O has reached a temperature of 95 °C, allow the steam to enter the furnace. Be sure bubbler is not bubbling to the point where too much water is coming out of the flask. Close the dry N2 valve (not the bubbler valve). Periodically check the H2O level and add as needed. Appendix A shows the procedures to set up the furnace and the valves.
Procedure: Wet Thermal Oxidation
- Don the high temperature protective gloves.
- Place the boat of wafers in the open end of the center furnace with the polished side facing forward (towards the flow of gases) for 5 minutes.
- Slowly push the boat into the flat zone of the furnace tube. This “push” should take about 10 minutes. After removing the push-rod from the furnace, hold vertically while cooling.
- Start marking time and oxidize the wafers for the appropriate length of time.
- After length of time has elapsed, turn off H20 and turn on O2. Proceed to next step.
- After the appropriate length of time has elapsed, slowly remove the boat. This removal should take about 10 minutes. Leave the boat at the open end of the furnace tube and allow the wafers to stabilize for about 5 minutes.
- Remove the boat from the open end of the furnace tube and allow to cool for at least 10 minutes.
- Turn off all gases, and reduce temperature set point to 0 C. Leave the furnace controls on until temperature is below 300 C.
Figure 2 shows the silicon wafer after growth of the field oxide layer.
Figure 2: Growth of the field oxide
Procedure: Oxide Thickness Check
- Note: Use wafers from previous lab.
- After turning on the Filmetrics F20 Interferometer wait for 5 minutes for the lamp to heat up.
- Start the Filmetrics software from the computer.
- Follow the instruction to setup the background.
- After setup is complete do the measurements.
- Take at least 5 measurements (at different section of the wafer).
- Take the average to determine the thickness of the SiO2.