Should be a huge portion of the cost. The material is just silicon. The expertise and know how that goes into this is where most of the money goes. For Taiwan, this expertise is better, faster and cheaper.
Those billions are also mostly R&D. It's also from a country external to Taiwan. ASML, the Ductch.
Yes, Obviously there's a lot that goes on in this process, more then "just" silicon. But if you want a summary, then cost expertise and knowhow, eclipses actual process. In a sense it is just "silicon" when measured relative to the ability and knowledge required to transform that material.
> The material is just silicon.
No, a lot of chemicals are required as well.