Gases at high drive pressure can initially dissolve into the fluids used in lithography and other critical processes during
the fabrication of integrated circuits. In the low pressure portion of the dispense train, the dissolved gases can revert to
bubbles. These bubbles can:
1. Affect the compressibility of the working fluid and change the flow characteristics of the dispense heads
which require frequent re-tuning of the coating tools.
2. Contribute to defect formation if the bubbles are trapped on the surface of the wafer.
Photosensitive Polyimides (PI) have high viscosities (1000 to 20,000 cP). Because of the high viscosity, high-powered,
expensive pumps are needed to effectively remove the fluid from its container. Suction from the pump filling cycle
easily causes cavitation, which can create flow rate variability, and micro-bubble formation. It is a common practice to
apply pressure to the PI resists to minimize cavitation in the pump. The trade-off to this practice is the entrainment
(dissolution) of the drive gas into the resist and the risk of micro-bubbles forming later in the dispense train.
In the current study, ATMI measured the effects of two methods of pressure dispense from the container on the amount
of gas entrained in a viscous fluid: (1) indirect pressure dispense and (2) direct pressure dispense. The main analytical
method employed to measure the amount of dissolved gases is a gas chromatograph (GC), which can measure the
concentration of gases dissolved in a volatile fluid. It is not suitable to measure gases in low volatility fluids. The new
test method developed, however, is capable of measuring dissolved gases in low volatility fluids.