How low can deposition go?

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  • September 20026

    LADI keeps Moore going


    A new low temperature, non-vacuum technique fordepositing crystalline oxidefilms could reduce costs inmany electronic and opticalapplications [Science (2002)297, 65].Developed by researchers atOregon State University (OSU)in collaboration with Hewlett-Packard and ReyTech Corp.,the technique uses a simplewater-based chemistry todeposit crystalline films ofZn2SiO4, ZrO2, and MnO2. Itcombines a precipitation andhydrothermal dehydration

    process with successive-ionic-layer-absorption-and-reaction(SILAR). "We found that youcan take certain materials thatcontain water and let themdehydrate slowly and at lowtemperatures, and still observecrystallinity," says DouglasKeszler of OSU. "Processing isdone in a bath, rather thanrequiring expensive technology,vacuums, and very hightemperatures. There has neverbeen a way before to bothdeposit and crystallizeelectronic or photonic films atsuch low temperatures."

    Lanthanum aluminate (LAO) isbeing hailed as a potentialreplacement for silicon dioxidein the next generation ofMOSFET (metal oxidesemiconductor field effecttransistor) devices. Motorola,Nanjing University, and theChinese Institute of Physics(CAS) have just completedcharacterization of LAO andthe related material lanthanumaluminum oxynitride (LAON) todetermine their potential as agate dielectric. With adielectric constant of morethan 20, LAO has one of the

    best thermal stabilities ofcurrent candidates. Accordingto Motorola, it should also bepossible to integrate withexisting CMOS processes."Traditional materials will lastone or two more generations,"explains Karen Guo, thedirector of Motorola ChinaR&D Institute and DigitalDNALaboratories China. "We arevery excited about the potentialof this material. While moreresearch is required, LAO isthe most promising materialwe have seen."FFuurrtthheerr ddeettaaiillss::

    How low can deposition go? Next generation insulator

    Stephen Chou and co-workersat Princeton University havedeveloped a new techniquethat allows patterns to beimprinted into silicon at recordspeeds [Nature (2002) 417,835-837].Laser-Assisted Direct Imprint or LADI could replacelithography and etching for

    micro- and nano-fabrication ofsilicon, which are costly, time-consuming, and resolutionlimited, say the researchers.The technique uses a quartztemplate to pattern silicon, orother materials such aspolysilicon. The template ispressed against the silicon anda single excimer laser pulse

    melts the material in itsvicinity. The melted siliconconforms to the shape of themold and resolidifies (seeschematic diagram). Thequartz template is removedand can be reused. "You justimprint the pattern directly intothe silicon," explains Chou."You not only reduce thenumber of steps, you can do itin nanoseconds." The resultingsilicon structures, as shown,reveal resolution better than10 nm and can be applied tolarge areas. Questions still remain onwhether the template could

    cause and propagate defects and if its features can be madesmall enough. Nevertheless, in anaccompanying News and Viewsarticle [Nature (2002) 417,802-803], R. Fabian Peasesays that the new imprintingtechnology could keep Moore'slaw on track for another twodecades. One implication ofMoore's Law is that as thenumber of transistorscrammed onto a chipincreases, so does the cost ofmanufacture. But a techniquelike Chou's LADI could providevital financial savings.

    Schematic of the LADI process for nano-patterning of silicon. (Courtesy of Stephen Chou,Princeton University, and Nature.)

    Scanning electron micrograph of a cross-section of a LADI-patterned silicon sample.(Courtesy of Stephen Chou, Princeton University, and Nature.)


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