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RIJO V JOHN

S7 EE-41

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Extreme ultraviolet lithography is an advanced technology formaking microprocessors a hundred times more powerful thanthose made today.optical projection lithography has been the lithographic technique

used in the high-volume manufacture of integrated circuits.The key to creating more powerful microprocessors is the size ofthe light's wavelength. The shorter the wavelength, the moretransistors can be etched onto the silicon wafer.Deep-ultraviolet lithography uses a wavelength of 240

nanometers.The current technology will reach its limit by 2010

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Two fundamental characteristics of an imaging system areResolution (RES) and Depth of focus (DOF).RES = k1 / NAandDOF = k 2 / (NA) 2

UV radiation has shorter , high energy.If we further reduce wavelength , it become EUV radiation-13nmEUVL is required for the continuity of Moores law

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Silicon is the traditional substrate used in chip making.To create IC light is directed to mask(stencil of circuit pattern).Light shines through mask,then through a series of optical lensesthat shrinks the image down.Projected to wafer covered with photoresistLight hardens the photoresist.Region not exposed remain gooey and is chemically washed awayand the remaining is hardened photoresist and exposed siliconwafer.

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EUVL imaging systems are entirely reflective.EUV reflectivity of individual materials at near-normal incidenceis very low. In order to achieve reasonable reflectivities nearnormal incidence, surfaces must be coated with multilayer, thin-

film coatings known as distributed Bragg reflectors.Because EUVL utilizes short wavelength radiation for imaging,the mirrors that comprise the camera will be required to exhibit anunprecedented degree of perfection in surface figure and surfacefinish in order to achieve diffraction-limited imaging.

EUVL is carried out in vaccum.

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Laser is directed at a get of xenon gas. When laser hits xenon gas itheats the gas and creates plasma.Electrons began to come out of plasma and it radiates light at13nm.

Light travels in to a condenser , which gathers the light so that it isdirected on to a mask.The pattern on the mask is reflected on to a series of curvedmirrors which shrinks the image and focus the image to siliconwafer.

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EUV multilayer are made of alternatinglayers of Mo and Si, and they function

best for wavelengths of about 13 nm.peak reflectivites of 6 8% can now be

routinely attained for Mo:Si ML

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Top: EUV multilayer and absorber constituting mask pattern forimaging a line.

B ottom: EUV radiation reflected from the mask pattern is absorbedin the resist and substrate, producing photoelectrons and secondaryelectrons.

These electrons increase the extent of chemical reactions in theresist.

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EUVL leverages much of the learning and supplier infrastructureestablished for conventional lithography.Decrease in size of chip but the speed and storage capacityincrease.

EUVL technology achieves good depth of focus and linearity forboth dense and isolated lines with low NA.The robust4X masks are patterned using standard mask writingand repair tools and similar inspection methods can be used as forconventional optical masks.

The low thermal expansion substrates provide good imageplacement.Experiments have shown that existing DUV can be extended foruse with EUV.

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Positive charging, due to ejectionof photoelectrons freed from thetop resist surface by the EUVradiation.

Contamination deposition on theresist from ambient or outgassedhydrocarbons, which results fromEUV- or electron-driven reactions.

No known method for repairing defects in a ML coating.

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EUVL will opens a new chapter in semiconductor technology.Successful implementation of euvl would enable projectionlithography to remain semiconductor indusrys patterntechnology of choice for years to come.

Much work is to be done in order to determine whether euvl isready for large scale production.

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Sang Hun Lee, Yashesh Shroff, Manish Chandhok. Flare and LensAberration Requirements for EUV Lithographic Tools.Proceedings of SPIE, Volume 5751, Emerging LithographicTechnologies IX, May 2005. Pages 707714.

Euv lithography- vivek bakshiA complete course of lithography by Alois.www.howstuffwork.comwww.sandia.comwww.euvl.comwww.lasers.llnl.gov/lasers/IST/euvl.html

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