Many coating failures are described as deposition problems even when the decisive event happened before the substrate entered the chamber. Fingerprints, oxide condition, residual detergent, particles and time in ambient air all influence the first interface.
Clean means process-specific
A surface that looks clean may still carry an organic film or native oxide. The correct preparation depends on the substrate and the intended layer. A cleaning sequence should state chemistry, rinse quality, drying method, allowable delay and handling controls.
Storage can undo preparation
Freshly cleaned surfaces begin interacting with the environment immediately. Packaging materials, humidity and airborne hydrocarbons matter. When the delay between cleaning and deposition varies, adhesion and nucleation may vary with it.
In-vacuum treatment is not a universal reset
Plasma cleaning, ion bombardment and heating can remove some contamination or activate a surface, but they can also alter roughness, chemistry or temperature-sensitive materials. The treatment should be qualified as part of the process rather than added casually when adhesion becomes inconsistent.
Make the interface measurable
Record the incoming surface condition and choose tests that relate to the application. Contact angle, microscopy, surface analysis and witness samples can provide different evidence. A useful specification connects preparation controls to a verified film property instead of relying on the word clean.
