This little experiment was performed to determine how quickly native oxide forms on a silicon wafer:

1. Measure a new bare silicon wafer, "fresh" from the box, on the Rudolph ellipsometer. Oxide Thickness = 15 A

2. Run a new bare silicon wafer through a "diffusion" clean (H2SO4/H2O2, rinse, 50:1 HF dip, rinse, HCl:H2O2:H2O, rinse, spin dry)
Oxide thickness measures 16 A

3. Take the cleaned wafer from step 2, dip in 50:1 HF, rinse, blow dry. Measure immediately.
Oxide thickness = 5A.

4. Keep the wafer from step 3 in the fab enviroment and measure over time on the same ellipsometer. Data is available in <linear> or <logarithmic> form.

Results courtesy of Duncan Stewart, Patricia Beck, and Uli Thumser.