Monitoring Relative Humidity
in Moisture-Sensitive Environments

Reprinted with permission of GE General Eastern Instruments

Many products manufactured and processed in a clean room environment are moisture-sensitive. For this reason, clean room specifications often include relative humidity (RH) control. These control points range from 35-65%RH for year-round operation. These RH levels generally are maintained in a narrow band ±2 percent RH at temperatures below 70°F. The effects of higher humidity levels in close tolerance environments can be detrimental to product quality and production schedules.

In semiconductor manufacturing, when the humidity level fluctuates in a wafer fabrication area, a multitude of problems can occur. Bake-out times typically increase, and the entire process generally becomes harder to control. Humidity levels above 35 percent RH make the components vulnerable to corrosion. Additionally, as developer solvents are sprayed onto the wafer surface, the solvents evaporate rapidly, cooling the wafer enough to condense moisture from the air. This extra water can change the developer characteristics and be adsorbed onto the semiconductor layers. This can cause swelling and further product quality problems, necessitating additional process control.