CMP Optical Endpoint Detector

CMP optical, eddy-current, and motor-current endpoint detection all answer the same question — has this polish step removed exactly the right amount of material — using three physically different signals, because CMP's opaque slurry and moving pad environment rule out some of the clean optical signals that work well for dry-etch endpoint detection.

CMP polish in progress
Slurry and pad motion make the wafer surface hard to observe directly
CMP endpoint signal
Optical endpoint
In-situ optical reflection through a window in the pad
Eddy-current endpoint
Induced-current response detects conductive film thickness directly
Motor-current endpoint
Polish-head motor load shifts as friction changes at material transition
Polish stopped at the correct film transition
Before over-polish causes dishing or erosion

Eddy-current endpoint detection works specifically because it directly senses the conductive film being polished, rather than inferring the transition indirectly the way optical or motor-current methods do. An induced eddy current in a conductive film like copper or tungsten changes measurably as that film thins and finally clears to expose the non-conductive layer beneath, giving a direct electromagnetic readout of remaining conductive film thickness — a signal with no optical window or motor-friction intermediary step, which makes it especially robust for metal CMP steps where the whole goal is clearing exactly to the barrier layer underneath.

CMP Endpoint Detection — Three Signals, One Goal optical, electromagnetic, and mechanical signals each sense the transition differently Optical — pad window reflection changes at film transition Eddy-current — direct film sense induced current senses conductive film thickness Motor-current — friction shift polish head load changes as surface friction shifts most production CMP processes combine two or more of these signals for a more reliable endpoint call

Motor-current endpoint detection catches the transition through a completely mechanical signature, which makes it a useful backup or cross-check even where it's not the primary endpoint method. As CMP polishing transitions from one material to another — say, from copper to the underlying barrier layer — the friction between the pad and the wafer surface can change measurably, which shows up as a detectable shift in the current the polish head's motor draws to maintain its rotation; this signal is coarser than optical or eddy-current detection but requires no additional optical window or electromagnetic sensing hardware, making it a straightforward signal many tools monitor as a sanity check alongside a primary endpoint method.

CMP optical, eddy-current, and motor-current endpoint detection all exist because the same fundamental endpoint problem — stop polishing at exactly the right film transition — needs a different physical signal depending on what's actually detectable through CMP's opaque, in-motion polishing environment, and most production tools lean on more than one of these signals together for reliability.

Take CMP optical endpoint detector further

Ask the copilot about this term, or have our engineers assess it against your process.

Ask CFSGPT about this → Request a technical assessment → Open the CFS app