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The continued reduction in device linewidths and film thicknesses has led to the need for tighter control of the photochemical dispense process. Accurate and repeatable application of thin films of photoresist is complicated by the need for point-of-use filtration as close to the dispense nozzle as possible. This paper describes the design, validation, and reliability testing of a new photochemical pump whose primary requirements were cleanliness and repeatability. Both the dispense rate and the dispense volume were to be unaffected by changes in temperature, fluid viscosity, filter loading, or air in the filter. The Wafergard GEN-2TM photochemical dispense system is a stepper-motor driven, diaphragm-dispense pump which provides point-of-use filtration to reduce contamination (gels, microbubbles, and particles) and provide precise and repeatable dispense of photochemicals. The pump is a two-stage system in which a 0.1 micrometers stacked disk TeflonTM filter is isolated from the dispense chamber, thus allowing the filtration rate to be uncoupled from the dispense rate. The chemical flowpath is all-Teflon. The dispense diaphragm is hydraulically coupled through a metal bellows to a zero-backlash stepper linear actuator. These design features make the dispense rate, profile, and volume independent of the filter loading. Performance validation testing has been done. Long term (greater than 100,000 cycles) testing using 30 cps positive photoresist with typical operating conditions (2 mL dispense volume at a 2 mL/sec dispense rate through a ten foot 5/32' I.D. section of tubing) showed total volume repeatability to be within +/- 0.02 grams (3 Std Dev). A new method for quantifying the dispense flowrate profile has been developed and used to record the effect of system compliancy on flow dynamics. Wafer coating performance studies using an SVG 90 Series Resist Processing System addressed uniformity and resist consumption. Extensive reliability testing of GEN-2 has been performed. The pump contains a Teflon diaphragm which drives the photochemical out through the dispense nozzle. Possible permeation through this critical component was thoroughly investigated. Several common photochemical solvents, such as xylene, NMP, ethyl lactate, and PGMEA were tested for compatibility and permeability through the diaphragm. Examination using Graphite Furnace AA identified no cross contamination of ions in the pump at the ppb level. Diaphragm and drive train reliability testing of five pumps is underway. Two pumps have been operated for more than 1,000,000 cycles and one for over 500,000 at normal case volume and pressure conditions, and two have past 275,000 cycles at worst case volume and pressure. Analysis was done of the long-term volume precision, ion contamination of the fluids, and mean-time-before-failure.
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