thank you for your response.

It is just normal air in the furnace which I wanted to remove through roughing pump (10^-1-10^-3) but in some experiments, we observed that there is some oxygen diffusion inside the films from outside. That is why I want to know how much concentration of oxygen remained at the pressure of 10^-1-10^-3.

Dear Jeffrey,

Thank you for your response again. In fact, your idea of introducing N2 to avoid oxygen is exactly same which I applied in my experiments. I am doing scientific investigation and trying to give quantitative results of my experiments to show a difference in weak vacuum and N2 environment.

Here is what I did in my experiments:

I tried to anneal my 3 and 6 nm films on a semiconductor substrate in weak vacuum to see the formation of oxide at the interface. We saw some oxide in XPS at the interface. Later we introduced N2 in vacuum and flushed it two to three times to reduce the oxygen content to minimum level (exactly what you suggested) and did same annealing and saw that the oxide is not formed. Now I am looking for an answer to my question that how much oxygen content was present which diffused through the films and formed the buried oxide at the interface.

Dear Jeffrey,

Thank you very much for simple answer. I did not think of this simple calculation. I think this is the answer of my question which I was looking for. Amazingly, I discussed it with many people and could got get right answer.

I do not think that their is much to worry about chemical reactions to deplete the O2 concentration in my case. I was just looking for a general idea about the O2 concentration at certain level of vacuum.