Semi E148

SEMI E148 defines time synchronization for fab equipment through a standardized TS-Clock object — a shared time reference and synchronization method that lets every piece of equipment, and every event timestamp it generates, agree on exactly when something happened, down to a precision tight enough that cross-tool event correlation is actually meaningful. A fab's EDA/Interface A framework (E147) depends on timestamps throughout — E134's data-collection plans, E142's mapping events, nearly every CEID across the SECS/GEM ecosystem carries a time value — but none of those standards define where that time value actually comes from, and if each tool's internal clock drifts independently, timestamps that look precise down to the millisecond can still be comparing events against two different, silently diverging clocks.

Every tool generates timestamped events (CEIDs, data-collection samples)
Each relies on its own internal clock, with no shared reference by default
SEMI E148 — time synchronization via the TS-Clock objectStandardized shared time reference and synchronization method
Defined TS-Clock object every piece of equipment synchronizes against
A common reference, not each tool's independently-drifting internal clock
Standardized synchronization precision and drift-correction method
Cross-tool event ordering stays meaningful over time, not just at startup
Host can correlate events across multiple tools with real confidence
Two timestamps from different equipment actually mean the same moment

The reason time synchronization needed its own dedicated standard, rather than assuming every tool's clock is close enough, is that cross-tool event correlation — the entire point of collecting timestamped data from multiple pieces of equipment in the first place — silently breaks the moment two clocks drift apart by more than the time resolution the analysis actually needs, and that drift is invisible from inside either tool because each one reports its own clock with full confidence regardless of how far it has wandered from true time. E148 closes that gap by defining the TS-Clock object as the shared reference every piece of equipment synchronizes against, with a standardized precision and drift-correction method, so a host analyzing events from multiple tools can trust that "this happened at 14:32:07.418 on Tool A" and "this happened at 14:32:07.420 on Tool B" really do describe two moments two milliseconds apart, not an artifact of each tool's clock having quietly drifted differently.

Two Clocks, Each Fully Confident, Quietly Diverging drift is invisible from inside either tool reporting its own clock days since last sync clock offset true time Tool A clock (+40ms/week) Tool B clock (-30ms/week) 70ms apart, both "confident" E148 — both resync against one TS-Clock reference, periodically Tool A: resync → true time Tool B: resync → true time Two precise-looking timestamps only mean the same moment if both clocks are the same clock

E148 is what makes cross-tool event correlation trustworthy rather than merely plausible-looking — by defining the TS-Clock object as a shared time reference with standardized synchronization precision and drift correction, it closes a failure mode no individual equipment timestamp can ever reveal on its own: two clocks that have quietly diverged while each one continues reporting its own time with complete, misplaced confidence.

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