By the time the Arizona fab begins production in 2024, 5nm will seem a somewhat mature process compared with 3nm and potentially some form of Forksheet transistor silicon at 2nm. Of course, fabs get upgraded and migrated during the course of their lifetime but the 5nm label sends a signal. It is also notable that the cost is in the semiconductor manufacturing equipment so TSMC's commitment is not a major one until some time after it has built the fab shell. Fab shells lying idle for years before being equipped or repurposed are a fact of life in the semiconductor industry that has always been a commercial rollercoaster ride of boom and bust.
To be fair TSMC has been one of the most sure-footed of semiconductor manufacturers and rarely has to pull back from a commitment. Again, it makes sense that the really big spending on Gigafab production fabs remains in Taiwan but it feels like TSMC is doing the minimum required to remain in US and Apple's good graces.
The final indicator is the use of a conditional verb in the last sentence of TSMC's press release. "The Arizona facility would be TSMC’s second manufacturing site in the United States." It suggests the condition, "if it goes ahead." The verb will is used elsewhere in the press release.
The bottom line is that successful semiconductor policy is mapped out over several years while US administrations are around for just four years at a time. So, there is no harm in TSMC planning for a $12 billion spend in the US for now, secure in the knowledge that such plans can be changed, delayed or cancelled if they no longer make sense under different circumstances.
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