Thickness of Native Silicon Oxide

First, this varies by how long the wafers have been sitting since they were made or since the oxide was etched back.

I just went into my lab measured some wafers that are quite old (100mm) They varied from 15 ang to 600ang. I suspect the 15 has another coating on it.
I then grabbed a 200mm wafer out of an unopened box that I got directly from the manufacturer two years ago and It measure in at 45ang SiO2.

Silicon oxide will continue to grow very slowly as long as it is exposed to atmosphere.

I have not checked the cal on my elipsometer in a while so these may be off a little.

Have you any idea what coating could give such a small reading on your ellipsometer? (If it was Si₃N₄, the measurement could correspond to a film thickness less than 10 Ang. Would this be thick enough for the coating to have much impact on the oxide growth?)

I noticed that the (other) guest asked about 111 wafers, rather than the 100 wafers in common use today. Someone borrowed my Sze, and I haven't seen it since, but I seem to recollect that growth rates were rather different up to about 1000 Ang.

SilvCrow answered well for oxide that just grows due to sitting around in air. Silicon that has been cleaned and then stored for a short time in a good N₂ atmosphere can be as little as 5-Ang

If you are asking about oxides that grow during diffusions or are grown deliberately, those are much thicker, and will depend on the process