Critical UPW issues Ultrapure water

1 critical upw issues

1.1 particles control
1.2 point of use (pou) treatment organics
1.3 upw recycling in semiconductor industry

critical upw issues
particles control

particles in upw critical contaminants, result in numerous forms of defects on wafer surfaces. large volume of upw, comes contact each wafer, particle deposition on wafer readily occurs. once deposited, particles not removed wafer surfaces. increased use of dilute chemistries, particles in upw issue not upw rinse of wafers, due introduction of particles during dilute wet cleans , etch, upw major constituent of chemistry used.

particle levels must controlled nm sizes, , current trends approaching 10 nm , smaller particle control in upw. while filters used main loop, components of upw system can contribute additional particle contamination water, , @ point of use, additional filtration recommended.

the filters must constructed of ultraclean , robust materials, not contribute organics or cations/anions upw, , must integrity tested out of factory assure reliability , performance. common materials include nylon, polyethylene, polysulfone, , fluoropolymers. filters commonly constructed of combination of polymers, , upw use thermally welded without using adhesives or other contaminating additives.

the microporous structure of filter critical in providing particle control, , structure can isotropic or asymmetric. in former case pore distribution uniform through filter, while in latter finer surface provides particle removal, coarser structure giving physical support reducing overall differential pressure.

filters can cartridge formats upw flowed through pleated structure contaminants collected directly on filter surface. common in upw systems ultrafilters (uf), composed of hollow fiber membranes. in configuration, upw flowed across hollow fiber, sweeping contaminants waste stream, known retentate stream. retentate stream small percentage of total flow, , sent waste. product water, or permeate stream, upw passing through skin of hollow fiber , exiting through center of hollow fiber. uf highly efficient filtration product upw, , sweeping of particles retentate stream yield extremely long life occasional cleaning needed. use of uf in upw systems provides excellent particle control single digit nanometer particle sizes.

point of use applications (pou) upw filtration include wet etch , clean, rinse prior ipa vapor or liquid dry, lithography dispense upw rinse following develop. these applications pose specific challenges pou upw filtration.

for wet etch , clean, tools single wafer processes, require flow through filter upon tool demand. resultant intermittent flow, range full flow through filter upon initiation of upw flow through spray nozzle, , trickle flow. trickle flow typically maintained prevent dead leg in tool. filter must robust withstand pressure , low cycling, , must continue retain captured particles throughout service life of filter. requires proper pleat design , geometry, media designed optimized particle capture , retention. tools may use fixed filter housing replaceable filters, whereas other tools may use disposable filter capsules pou upw.

for lithography applications, small filter capsules used. similar challenges wet etch , clean pou upw applications, lithography upw rinse, flow through filter intermittent, though @ low flow , pressure, physical robustness not critical. pou upw application lithography immersion water used @ lens/wafer interface 193 nm immersion lithography patterning. upw forms puddle between lens , wafer, improving na, , upw must extremely pure. pou filtration used on upw prior stepper scanner.

for pou upw applications, sub 15 nm filters in use advanced 2x , 1x nodes. filters commonly made of nylon, high-density polyethylene (hdpe), polyarylsulfone (or polysulfone), or polytetrafluoroethylene (ptfe) membranes, hardware typically consisting of hdpe or pfa.

point of use (pou) treatment organics

vanox system point-of-use ultrapure water treatment systems

point of use treatment applied in critical tool applications such immersion lithography , mask preparation in order maintain consistent ultrapure water quality. upw systems located in central utilities building provide fab quality water may not provide adequate water purification consistency these processes.

in case when urea, thm, isopropyl alcohol (ipa) or other difficult remove (low molecular weight neutral compounds) toc species may present, additional treatment required thru advanced oxidation process (aop) using systems. particularly important when tight toc specification below 1 ppb required attained. these difficult control organics have been proven impact yield , device performance @ demanding process steps. 1 of successful examples of pou organics control down 0.5 ppb toc level aop combining ammonium persulfate , uv oxidation (refer persulfate+uv oxidation chemistry in toc measurement section).

available proprietary pou advanced oxidation processes can consistently reduce toc 0.5 parts per billion (ppb) in addition maintaining consistent temperature, oxygen , particles exceeding semi f063 requirements. important because slightest variation can directly affect manufacturing process, influencing product yields.

upw recycling in semiconductor industry

outline typical water system in semiconductor plant

the semiconductor industry uses large amount of ultrapure water rinse contaminants surface of silicon wafers later turned computer chips used in devices use every day. ultrapure water definition extremely low in contamination, once makes contact wafer surface carries residual chemicals or particles surface end in industrial waste treatment system of manufacturing facility. contamination level of rinse water can vary great deal depending on particular process step being rinsed @ time. “first rinse” step may carry large amount of residual contaminants , particles compared last rinse may carry relatively low amounts of contamination. typical semiconductor plants have 2 drain systems of these rinses combined acid waste , therefore rinse water not reused due risk of contamination causing manufacturing process defects.

definitions:

the following definitions used itrs:

upw recycle – water reuse in same application after treatment
water reuse – use in secondary application
water reclaim – extracting water wastewater

water reclaim , recycle:

some semiconductor manufacturing plants have been using reclaimed water non-process applications such chemical aspirators discharge water sent industrial waste. water reclamation typical application spent rinse water manufacturing facility may used in cooling tower supply, exhaust scrubber supply, or point of use abatement systems. upw recycling not typical , involves collecting spent manufacturing rinse water, treating , re-using in wafer rinse process. additional water treatment may required of these cases depending on quality of spent rinse water , application of reclaimed water. these common practices in many semiconductor facilities worldwide, there limitation how water can reclaimed , recycled if not considering reuse in manufacturing process.

upw recycling:

recycling rinse water semiconductor manufacturing process has been discouraged many manufacturing engineers decades because of risk contamination chemical residue , particles may end in upw feed water , result in product defects. modern ultrapure water systems effective @ removing ionic contamination down parts per trillion levels (ppt) whereas organic contamination of ultrapure water systems still in parts per billion levels (ppb). in case recycling process water rinses upw makeup has been great concern , until not common practice. increasing water , wastewater costs in parts of , asia have pushed semiconductor companies investigate recycling of manufacturing process rinse water in upw makeup system. companies have incorporated approach uses complex large scale treatment designed worst case conditions of combined waste water discharge. more new approaches have been developed incorporate detailed water management plan try minimize treatment system cost , complexity.

water management plan:

the key maximizing water reclaim, recycle, , reuse having thought out water management plan. successful water management plan includes full understanding of how rinse waters used in manufacturing process including chemicals used , products. development of critical component, drain collection system can designed segregate concentrated chemicals moderately contaminated rinse waters, , lightly contaminated rinse waters. once segregated separate collection systems once considered chemical process waste streams can repurposed or sold product stream, , rinse waters can reclaimed.

a water management plan require significant amount of sample data , analysis determine proper drain segregation, application of online analytical measurement, diversions control, , final treatment technology. collecting these samples , performing laboratory analysis can characterize various waste streams , determine potential of respective re-use. in case of upw process rinse water lab analysis data can used profile typical , non-typical levels of contamination can used design rinse water treatment system. in general cost effective design system treat typical level of contamination may occur 80-90% of time, incorporate on-line sensors , controls divert rinse water industrial waste or non-critical use such cooling towers when contamination level exceeds capability of treatment system. incorporating these aspects of water management plan in semiconductor manufacturing site level of water use can reduced as 90%.