Once rust starts, it is porous & flaky and allows more oxygen to infiltrate and hit the next layer of iron. The reason it is porous & flaky is due to creating a mix of FeO and Fe2O3 which have different crystal structures so it doesn't create a nice protective barrier.
I’m not sure that’s accurate: ASML don’t make masks (i.e. the patterns), they make the EUV photolithography machines that are used in conjunction with the masks.
The physical masks themselves are usually made by Hoya, and the technology to actually etch the masks is made by Veevo.
It'd be a smaller amount that gets injected into the stratosphere, as opposed to what we normally release into the troposphere. A quick skim of the wikipedia link seems to suggest 5M tons in total, not sure what the annualized basis would be.