Photofluid dispense systems within coater/developer tools have been designed with the intent to minimize cost of ownership to the end user. Waste and defect minimization, dispense quality and repeatability, and ease of use are all desired characteristics. One notable change within commercially available systems is the sequence in which process fluid encounters dispense pump and filtration elements. Traditionally, systems adopted a pump-first sequence, where fluid is “pushed through” a point-of-use filter just prior to dispensing on the wafer. Recently, systems configured in a pump-last scheme have become available, where fluid is “pulled through” the filter, into the pump, and then is subsequently dispensed. The present work constitutes a comparative evaluation of the two equipment sequences with regard to the aforementioned characteristics that impact cost of ownership. Additionally, removal rating and surface chemistry (i.e., hydrophilicity) of the point-of-use filter are varied in order to evaluate their influence on system start-up and defects.
An effective filter start-up method has been required by device manufacturers, mainly in order to reduce waste volume of
lithography process chemicals, which become more expensive as lithography technology advances. Remaining air was
monitored during static-pressure-driven filter start-up. As a result, 3500 ml of the resist was needed to eliminate
remaining air. For improvement, cyclohexanone pre-wetting was applied prior to the resist introduction. As a result, the
resist volume needed for the solvent displacement was 1900 ml, approximately half the volume required for staticpressure-
driven start-up. Other solvents were evaluated for the pre-wetting start-up method. Results, in descending
order of performance were PGME (best) < PGMEA = IPA < cyclohexanone (worst). Moreover, air displacement
performance strongly correlated with Hansen solubility parameter distance between each solvent and nylon 6,6 material.
Reduced tolerance for defectivity is a well-documented consequence of the semiconductor industry's constant
progress toward smaller IC device dimensions. Among all manufacturing functional areas, photolithography is arguably
the most sensitive to process defects, and thus, strongly influences manufacturing process yield. Microbridging is a
well-known type of "killer" defect that can become prevalent in KrF and ArF photoresist systems. When present in
BEOL lithography layers, bridge defects can manifest as catastrophic, single-line open circuit faults ("opens") in the
metal lines of the finished device. Previous work in BARC + resist systems has demonstrated the effectiveness of
improved filtration in reducing bridge defects. The present work evaluates the impact of improved filtration on both
litho defectivity and device yield. Application of asymmetric nylon 6,6 filters to a bi-layer resist yielded a significant
reduction in microbridge defects via removal of gel-like particle defect precursors. Ultimately, these changes are
responsible for two-thirds of baseline defectivity reduction in single-line opens. The same benefits are realized-though
via a different mechanism-when all-fluoropolymer filters are introduced for a post-develop rinse, which uses ultrapure
water (UPW) that is ozonated to 50ppb. Filtration is applied both to the water point-of-supply and at point-of-use. Over
time, a significant reduction in microbridge defects-caused by residual developed resist-was realized for several
BEOL KrF litho layers. As with the bi-layer resist process, enhanced filtration contributes significantly (36%) to
reduction in the single-line opens defect baseline.