Dispense systems for semiconductor manufacturing applications are designed to dispense a precise amount of fluid on a wafer. In one-phase systems, fluid is dispensed to a wafer from a dispense pump through a filter. In two-phase systems, fluid is filtered in a filtering phase before entering a dispense pump. The fluid is then dispensed directly to the wafer in a dispense phase.
In either case, the dispense pump typically has a chamber storing a particular volume of fluid and a movable diaphragm to push fluid from the chamber. Prior to dispense, the diaphragm is typically positioned so that the maximum volume of the chamber is utilized regardless of the volume of fluid required for a dispense operation. Thus, for example, in a 10 mL dispense pump, the chamber will store 10.5 mL or 11 mL of fluid even if each dispense only requires 3 mL of fluid (a 10 mL dispense pump will have a slightly larger chamber to ensure there is enough fluid to complete the maximum anticipated dispense of 10 mL). For each dispense cycle, the chamber will be filled to its maximum capacity (e.g., 10.5 mL or 11 mL, depending on the pump). This means that for a 3 mL dispense there is at least 7.5 mL “hold-up” volume (e.g., in a pump having a 10.5 mL chamber) of fluid that is not used for a dispense.
In two-phase dispense systems the hold-up volume increases because the two-phase systems utilize a feed pump that has a hold-up volume. If the feed pump also has a 10.5 mL capacity, but only needs to provide 3 mL of fluid to the dispense pump for each dispense operation, the feed pump will also have a 7.5 mL unused hold-up volume, leading, in this example, to a 15 mL of unused hold-up volume for the dispense system as a whole.
The hold-up volume presents several issues. One issue is that extra chemical waste is generated. When the dispense system is initially primed, excess fluid than what is used for the dispense operations is required to fill the extra volume at the dispense pump and/or feed pump. The hold-up volume also generates waste when flushing out the dispense system. The problem of chemical waste is exacerbated as hold-up volume increases.
A second issue with a hold-up volume is that fluid stagnation takes place. Chemicals have the opportunity to gel, crystallize, degas, separate etc. Again, these problems are made worse with a larger hold-up volume especially in low dispense volume applications. Stagnation of fluid can have deleterious effects on a dispense operation.
Systems with large hold-up volumes present further shortcomings with respect to testing new chemicals in a semiconductor manufacturing process. Because many semiconductor manufacturing process chemicals are expensive (e.g., thousands of dollars a liter), new chemicals are tested on wafers in small batches. Because semiconductor manufacturers do not wish to waste the hold-up volume of fluid and associated cost by running test dispenses using a multi-stage pump, they have resorted to dispensing small amounts of test chemicals using a syringe, for example. This is an inaccurate, time consuming and potentially dangerous process that is not representative of the actual dispense process.