INFRARED OBSERVATION OF EVAPORATIVE COOLING DURING SPIN-COATING PROCESSES

To explore the origin of chuck-related surface nonuniformities in thin films deposited from solutions, real-time observations of evaporative cooling effects during spin-coating of solvents are made using an IR switched-field-effect-transistor (FET) array camera. The evaporative cooling depends strongly on the volatility of the solvent being tested. For acetone (the most volatile solvent tested) the cooling effect can be as large as 10 degrees C when a silicon wafer is used as the substrate. Comparisons are made between wafer type and position on the substrate and sources of the temperature differences are discussed within the framework of the basic spin-coating paradigm. It is likely that these evaporative cooling effects play an important role in the development of chuck-related surface nonuniformities during spin coating; solvent systems may be selected to help optimize film uniformity. These aspects of solution engineering are also discussed.