why do deposition chambers need clean cycles

KEY GPS TOPIC. A deposition chamber slowly COATS ITSELF — film deposits on the walls and parts, not just the wafer. Over time that buildup changes the deposition rate and uniformity (drift) and flakes off as PARTICLES that kill die. So you periodically run a CLEAN step — an etch gas/plasma that strips the buildup — followed by a PASSIVATION/CONDITIONING step that re-establishes the chamber baseline. Why GPS must know this: chamber condition is the #1 DRIFT SOURCE. 'The film is different this morning' is usually chamber condition, not the recipe. Over-clean wastes time and can damage the chamber; under-clean leaves residue. The key line: 'Deposition is a self-contaminating process — the chamber coats itself, so cleaning and re-conditioning it is as important as the recipe.' Know this cold — it's very field-relevant.