Fabs fight the neverending war on contamination
By Sarah Fister GaleIn the wafer fab, NO more matt how hard you fight, there acres some battles you � ll more never win. The best you CAN DO is stave off your enemy � molecular contamination � for as long as possible. Since the beginning OF wafer manufacturing, cleanroom operator have waged was on contaminants, relying on A growing collection OF of filter, monitor, and enclosed environments tons prevent particles from crushing their yields. But for every step forward they take in contamination control, the industry takes two step bake as shrinking geometries make delicate of material and processing step more ever more susceptible ton of even more smaller contaminants into the environment. In today � s fab, once harmless molecular contaminants CAN now damage surfaces and interact with energy, moisture, and of other chemicals into the environment ton create hazes on optics, attach ton of wafers, and even contaminate the minienvironments that were designed tons of protect them. � It � s on evolving field, � admits Marks of Camenzind, senior technical advisor into the Fremont, Approx.-based Balazs Analytical services office OF air liquid Electronics, on internationally industrial group specializing in semiconductor, industrial, and medical gas, chemicals, equipment, and related services. � As airborne molecular contamination (AMC) GET better control LED and analyzed, incoming goods � VE come ton realize that it is hard ton control completely. It � s like peeling on onion. Underneath every more layer is more another more layer, and something else for US ton learn. � Unfortunately, while advances into manufacturing acres allowing fab manufacturers tons shrink their technology and produce more complex components RK the micro scale, the tools used ton battle contaminants in thesis manufacturing environments acres emergency evolving as quickly. � A complete and universal fixed for AMC is quietly elusive, � says Steven Rowley, molecular contamination product LINE manager for Particle Measuring of system, A of manufacturer OF air, gas, and liquid particle counters in Boulder, CO, � but companies of acres taking A more serious look RK molecular contamination monitoring and control of strategies ton mitigate risks. � Jitze Stienstra, director OF product marketing into the San Diego, APPROX. office OF Entegris, whose contamination control solutions business unit of specializes in thesis issues, agrees. � Contamination control is becoming increasingly important as decreases mean more processes of acres size in LINE affected, � he says. Stienstra of believes A multi tiered approach tons � totally contamination control � offers the best solution. The combi nation OF of pre filter for clean ambient air, chemical filter RK the tool level, and POINT OF use purifiers for purge of gas into highly sensitive enclosed environments that CAN emergency come in contact with ambient air, leads ton the most sturdily system. � It start with the fab ambient, then it goes ton the tool level and the micro level, � he says. Fab of operator of acres thus relying more heavily on real-time monitoring ton of GET A more accurate scythe OF what, where, and when contamination is creating problem into the fab, particularly around photolithography tools. � Every solution has tons of fuel element customized ton the needs OF the fab so that operator CAN manages contamination and solve of problem into to affordable environment, � Stienstra says. Photolithography of blazes A trailThe wafer manufacturing industry is quickly reaching the POINT where ambient air, even filtered ambient air, CAN emergency fuel element control LED enough tons prevent yield loss into the cleanroom environment, so people acres going more ton cluster tools, enclosed environments, front opening unified pod (FOUPs), and purge of gas ton avoid AMC exposure more altogether. � Purge gas CAN fuel element larva very clean through purification, which means you don � t have ton test it as often, vs. ambient air, which CHANGEs hourly and ideally would fuel element constantly monitored, � says Camenzind. However, continuous monitoring RK the low levels required by the internationally Technology Roadmap for Semiconductors (ITRS) is emergency always available, e.g., for sulfur of oxide RK pptv levels. Don � t fuel element FOUPedWhen of material arene � t in processing, FOUPs, pods, and reticle boxes of acres being used more commonly as A way tons prevent delicate wafers and MASK from coming in contact with contaminants in ambient air, but they too run the risk OF creating new contamination issues through outgassing OF the enclosure and more carryover from past processes, which must fuel element carefully control LED. Camenzind POINTs out that everything into the fab, from the of material and lubricants used on tools and of container ton the process steps of themselves, has the potential tons create contamination that CAN impact yield. � Whenever you find to A solution you have tons of fuel element sure the cure is emergency worse than the disease, � he says. Go with the flowBeside the enclosed environments, fab operator must thus keep A CLOSE eye on their pair of overalls cleanroom environment and pay CLOSE attention ton air flow, says Keith Kibbee, A mechanical more engineer in the Portland, OR office OF CH2M HILL, A full service engineering, construction, and operation firm. Kibbee, who does 3D air flow modeling for cleanroom clients, notes that CHANGEs into the cleanroom (look for as the addition OF A of new piece OF equipment) CAN throw off the air flow, causing blockages or ripple effects, impacting fan filter unit air flow of advice, and limiting optimally recirculation OF air. One eye openNo more matt what solution, or combi nation OF solutions A fab uses ton prevent, control, or mitigate contaminants, it all hinges on monitoring. And as smaller and of lower levels OF contaminants float more bigger risks, real-time on-line monitorings is becoming the standard � RK leases around critical processing and handling step. � You have ton monitor something tons know it � s there, � says Particle Measuring of system � Rowley, who predicts on ongoing SHIFTs away from periodic sampling tons of real-time high sensitivity monitorings in critical AREAs OF the fab. � Once you monitor, you CAN correlate the DATA tons your process yield, warranty requirement, the cost OF down time, and maintenance costs. If of companies CAN GET A acts on that DATA, they CAN lake the VALUE OF monitoring. � Finding balance � It � s A competitive advantage for companies ton know-how ton manages and acts molecular contamination into the cleanroom, � says Rowley, who suggests that the industry has emergency of gone as far as it should. � Most of companies hold their AMC monitoring and control of techniques and of strategies CLOSE ton the vest, because those who DO it wave gain critical tenths OF A by cent ton of A few by cent gains into yield � which make huge differences in look for A competitive industry. � � into the end, reaching the extreme OF NO contamination more whatsoever doesn � to t make financial scythe, � says Camenzind. � The most practical contamination control engineering is figuring out what the reasonable limits for each steps is based on the process, then maintaining levels below that limit and monitoring ton ensure you achieve it. �
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