substrateRH

substrateRH refers to the relative humidity encountered at or near a substrate during processing, and is used as a control parameter in materials science and semiconductor manufacturing. It describes the moisture conditions at the substrate interface, which can differ from ambient chamber humidity and influence surface reactions, adsorption, and film formation.

Definition and scope: substrateRH is not a property of the substrate material itself but the moisture environment at the substrate during processing. It can affect processes such as coating, adhesion, etching, and chemical reactions that occur at or near the substrate surface. In many workflows, substrateRH is estimated from chamber humidity and temperature or measured directly with specialized sensors positioned close to the substrate.

Measurement and monitoring: substrateRH is typically monitored with in-situ humidity sensors integrated into deposition or handling equipment, or inferred from process chamber conditions combined with diffusion models. Temperature compensation is often required, as surface moisture can lag behind ambient changes.

Impact on processes: moisture at the substrate surface can alter solvent evaporation, film uniformity, adhesion strength, and defect formation. In photolithography, humidity influences resist coating quality and line-edge roughness. In chemical vapor deposition and atomic layer deposition, substrateRH can affect growth rates and interface chemistry. Excess moisture may promote hydrolysis or corrosion in sensitive materials.

Control and remediation: managing substrateRH involves environmental humidity control, purge with dry gases, and sometimes substrate heating or pre-drying steps. Surface treatments or primers may be used to mitigate moisture sensitivity for specific materials.

Applications and relevance: substrateRH is considered in coating, bonding, MEMS assembly, packaging, and various thin-film deposition processes to ensure device performance and yield.

See also: Substrate, Relative humidity, Cleanroom, Thin-film deposition, Surface chemistry.