According to my research, these machines can etch around 150 wafers per hour and each wafer can fit around 50 top-of-the-line GPUs. This means we can produce around 7500 AI chips per hour. Sell them for $1k a piece. That's $7.5 million per hour in revenue. Run the thing for 3 days and we recover costs.
I'm sure there's more involved but that sounds like a pretty good ROI to me.
This will get you started: https://youtu.be/B2482h_TNwg
Keep in mind that every wafer makes multiple trips around the fab, and on each trip it visits multiple machines. Broadly, one trip lays down one layer, and you may need 80-100 layers (although I guess DRAM will be fewer). Each layer must be aligned to nanometer precision with previous layers, otherwise the wafer is junk.
Then as others have said, once you finish the wafer, you still need to slice it, test the dies, and then package them.
Plus all the other stuff....
You'll need billions in investment, not millions - good luck!
I drive by a large fab most days of the week. A few breweries I like are down the street from a few small boutique fabs. I got to play with some experimental fab equipment in college. These aren't just some quickly thrown together spaces in any random warehouse.
And it's also ignoring the water manufacturing process, and having the right supply chain to receive and handle these ultra clean discs without introducing lots of gunk into your space.