I think the point that the OP is missing is that Silicon manufacturing is extremely complex, requiring 1000's of steps, tons of water and electricity, and extremely pure materials. That's not something you can fit in a lab, let alone a machine within the lab.
To give you a sense of scale, I ride past Intel's research fab (Ronler Acres) in Oregon and the Hillsboro airport on the way to work. The fab is bigger than the airport, and even that fab does not contain all the equipment necessary to manufacture chips for public consumption. There are separate plants for package and testing.
Considering the investment concentrated in such facilities and the stringent requirements of clean rooms, the 911 attacks would gave done much worse economic damage by targeting those facilities.
You still would have had the TSA and the wars, plus an ongoing economic impact on the cost of chip production. I'm not saying that there wasn't a lot of economic impact. I'm saying there could have been more.
To give you a sense of scale, I ride past Intel's research fab (Ronler Acres) in Oregon and the Hillsboro airport on the way to work. The fab is bigger than the airport, and even that fab does not contain all the equipment necessary to manufacture chips for public consumption. There are separate plants for package and testing.