Fabrication And Application Of Metal Nanostructures Based On Nanoimprint And Electroplating

Gold free-standing transmission grating has been proved to be a quite important optical device in X-ray and extreme ultraviolet band.It can be widely used in X-ray laser experiment diagnosis,laser inertial confinement fusion plasma diagnosis and X-ray astrophysics,etc.The fabrication of sub-micron and nano-period grating often uses interference lithography or electron beam lithography.However,the equipment of interference lithography is complex and expensive,the parameters also need a long time to grope.Efficiency of electron beam lithography is too low to prepare structure with large area.Conversely,nanoimprint lithography has the advantages of low cost,high resolution and large area,so it's suitable for the replication of nanograting structure.In this thesis,we designed the fabrication process of gold free-standing transmission grating by combining nanoimprint lithography with gold electroplating,physical vapor deposition,dry etching,wet etching,photolithography,etc.and the problems in the experiment were discussed.We first deposited 5 nm chromium and 10 nm gold as conducting layer on the silicon wafer,then formed grating structure into resist by UV curing nanoimprint,and removed residual layer by inductively coupled plasma etching.We could get the polymer grating on the flat gold film.Afterwards,we deposited gold in polymer grating grooves by sulfite gold electroplating,and then we obtained gold nano-period grating after dissolving the polymer grating by organic solvent.The supporting structure was fabricated by photolithography and secondary electroplating.Finally we etched the silicon substrate with hydrofluoric acid corrosion and obtained the micro-nano hybrid gold free-standing grating.Silicon mold for nanoimprint is quite expensive and vulnerable to damage during hot embossing process,5o it,s not suitable to imprint for many times.This increases the cost of nanoimprint and limits its application in industrial production.Thus,we need enough cheap supply of mold for nanoimprint.The material of mold should have high mechanical strength,good anti.adhesion property,high melting point,good thermal conductivity and low coefficient of thermal expansion.Nickel is a low-cost metal and meets the above requirements.Nickel plating has also been widely developed with mature process and large-scale industrial production.This paper studied the fabrication of nickel template for nanoimprint.We prepared nickel molds with same or reverse structure of silicon molds by three methods.The first was electroplating nickel directly on a silieon mold and then dissolving silicon.Another one was easting and solidifying UV-curable CN975 resist on silicon mold,then deposited nickel seed layer on the UV-cured mold and electroforming,and finally demoulding nickel mold from the UV-cured one.The third was electroforming a flexible nanostructured substrate pattermed by nanoimprint.We also studied the nickel electroplating process and the effects of different plating parameters.Finally,by adjusting the parameters,we obtained nickel templates with nearly non-residual stress through sulfamic acid nickel plating.We performed hot embossing nanoimprint with the obtained nickel mold and transferred the structure into target substrate successfully,and achieved the replication of large-area nanopattems.