Semi E125

SEMI E125 defines Equipment Self Description (EqSD), the standard that lets equipment publish a complete description of its own available data — not just the GEM-model status variables covered by the Common Equipment Model (SEMI E120), but the full set of parameters an Equipment Data Acquisition (EDA) system can collect, including each one's data type, units, valid range, and how frequently it can be sampled. EqSD exists specifically for the EDA/Interface A ecosystem (the same family as Data Collection Management, SEMI E134, and EDA Common Metadata, SEMI E164), where a host-side data-collection system needs to know, before it ever requests any data, exactly what that equipment is capable of reporting and at what resolution — information that is broader than what CEM's GEM-focused variable model alone describes.

EDA host wants to collect equipment data
But doesn't yet know what's available to collect
SEMI E125 Equipment Self DescriptionPublished before any data request is made
Equipment publishes its full data catalog
Every parameter: type, units, range, max sample rate
Host reads the catalog first
Now knows exactly what it can ask for
Data-collection plan built against real capability
No requesting data the equipment can't actually provide

EqSD and CEM solve a similar-sounding but distinct problem, and conflating them is a common integration mistake: CEM (SEMI E120) describes GEM's own status variables, equipment constants, alarms, and collection events — the vocabulary SECS/GEM messaging already uses — while EqSD (SEMI E125) describes the broader universe of parameters an Equipment Data Acquisition system can stream, which typically includes many more signals than GEM alone exposes, at a level of sampling-rate and metadata detail GEM's status-variable model was never designed to carry. A fab building a high-frequency fault-detection-and-classification (FDC) or virtual-metrology pipeline depends on EqSD specifically because those applications need far more granular, high-rate sensor data than the relatively coarse SVID-based GEM reporting that CEM describes was ever intended to support.

SEMI E125 (EqSD) vs. SEMI E120 (CEM) similar-sounding standards, different scope and data resolution E120 — CEM Describes GEM's own SVIDs, ECIDs, ALIDs, CEIDs Coarser, SECS/GEM-scoped used by host GEM integration E125 — EqSD Describes everything an EDA/Interface A system can collect Finer-grained, high-rate data used by FDC / virtual metrology Published before any data request, in both cases host knows what it can ask for, instead of discovering limits by trial and error conflating the two is the most common integration mistake with these standards

SEMI E125 sits inside the broader EDA/Interface A family — alongside Data Collection Management (SEMI E134) and EDA Common Metadata (SEMI E164) — that exists specifically to support high-rate process-data applications like fault detection and classification and virtual metrology, a different use case from the SECS/GEM equipment-communication family that CEM (SEMI E120) belongs to, even though both standards describe equipment data in XML form.

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