how low can deposition go?

September 2002 6 LADI keeps Moore going RESEARCH NEWS A new low temperature, non- vacuum technique for depositing crystalline oxide films could reduce costs in many electronic and optical applications [Science (2002) 297, 65]. Developed by researchers at Oregon State University (OSU) in collaboration with Hewlett- Packard and ReyTech Corp., the technique uses a simple water-based chemistry to deposit crystalline films of Zn 2 SiO 4 , ZrO 2 , and MnO 2 . It combines a precipitation and hydrothermal dehydration process with successive-ionic- layer-absorption-and-reaction (SILAR). "We found that you can take certain materials that contain water and let them dehydrate slowly and at low temperatures, and still observe crystallinity," says Douglas Keszler of OSU. "Processing is done in a bath, rather than requiring expensive technology, vacuums, and very high temperatures. There has never been a way before to both deposit and crystallize electronic or photonic films at such low temperatures." Lanthanum aluminate (LAO) is being hailed as a potential replacement for silicon dioxide in the next generation of MOSFET (metal oxide semiconductor field effect transistor) devices. Motorola, Nanjing University, and the Chinese Institute of Physics (CAS) have just completed characterization of LAO and the related material lanthanum aluminum oxynitride (LAON) to determine their potential as a gate dielectric. With a dielectric constant of more than 20, LAO has one of the best thermal stabilities of current candidates. According to Motorola, it should also be possible to integrate with existing CMOS processes. "Traditional materials will last one or two more generations," explains Karen Guo, the director of Motorola China R&D Institute and DigitalDNA Laboratories China. "We are very excited about the potential of this material. While more research is required, LAO is the most promising material we have seen." Further details: www.motorola.com How low can deposition go? Next generation insulator Stephen Chou and co-workers at Princeton University have developed a new technique that allows patterns to be imprinted into silicon at record speeds [Nature (2002) 417, 835-837]. Laser-Assisted Direct Imprint – or LADI – could replace lithography and etching for micro- and nano-fabrication of silicon, which are costly, time- consuming, and resolution limited, say the researchers. The technique uses a quartz template to pattern silicon, or other materials such as polysilicon. The template is pressed against the silicon and a single excimer laser pulse melts the material in its vicinity. The melted silicon conforms to the shape of the mold and resolidifies (see schematic diagram). The quartz template is removed and can be reused. "You just imprint the pattern directly into the silicon," explains Chou. "You not only reduce the number of steps, you can do it in nanoseconds." The resulting silicon structures, as shown, reveal resolution better than 10 nm and can be applied to large areas. Questions still remain on whether the template could cause and propagate defects – and if its features can be made small enough. Nevertheless, in an accompanying News and Views article [Nature (2002) 417, 802-803], R. Fabian Pease says that the new imprinting technology could keep Moore's law on track for another two decades. One implication of Moore's Law is that as the number of transistors crammed onto a chip increases, so does the cost of manufacture. But a technique like Chou's LADI could provide vital 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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September 20026

LADI keeps Moore going

RESEARCH NEWS

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:: www.motorola.com

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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