Research On Fabrication And Magnetic Properties Of Magnetic Microstructures

Recently,magnetic microstructures and nanostructures have attracted much attentionfor a variety of applications such as high density magnetic recording, magnetoresistive sensing,and magnetic random access memories. Researches on magnetic microstructures and nanostructures include fabrication of magnetic elements and characterization of them.These very small elements have totally different magnetic properties from the bulk materials and continuous thin films.Wherein,the anisotropy,the interaction between the nearby elements and the domain of different magnetization states are the most important properties because they give influences on their hysteresis loop,coercivity,remanence,saturation field which are important in the applications of magnetic micro- and nano- structures.Although there are variety of researches focused on them,they need to be studied penetratingly, because of the complexity of the magnetic properties of magnetic elements. In plentiful magnetic materials,CoFe alloy is regarded as one of ferromagnetic materials with varieties applied in the field of spintronics.In this thesis,The Ta\Co_0.9Fe_0.1\Ta film substrates deposited on oxidated Si wafers by using magnetron sputtering method are patterned into micrometer,sub-micrometer and deep sub-micrometer elements by holographic lithography combined with ion beam etching,and the magnetic properties of these Co_0.9Fe_0.1elements are studied.The most significant advance of the work described in this thesis is as the follows.â… .Fabrication of Ta\Co_0.9Fe_0.1\Ta arrays by using holographic lithography combined with ion beam lithography1)Researches on two dimensional patterns fabricated by holographic lithography.In this thesis,positive photoresist,RZJ-390 produced by Su Zhou Ruihong company,is exposed twice with Lloyd's Mirror interferometer.The process of the evolvement of the patterns form holes to dots is studied systemically.And the best exposure dose and developing time to form resist holes and dots are given.The process conditions of holographic lithography and optimized process parameters are discussed.2)Studies on vertical standing wave pattern.Holographic lithography suffers from vertical standing wave pattern caused by interference of the coming light with light reflecting from the film surface.Ta\Co_0.9Fe_0.1\Ta film possesses high reflectivity to the laser with wavelength 441.6nm,which induces severe vertical standing wave pattern in the lithographic pattern.To restrain vertical standing wave pattern,procedure which apply antireflection coatings(ARC) under the photoresist is idiomatic,and increasing exposure dose is applied too.But the procedure of antireflection coatings is complex,and the repetition and controlling of lithographic process are decreased with increasing exposure dose.We develop photoresist ashing process to restrain vertical standing wave pattern well,which make the controlling of holographic lithography improved.3)Pattern under critical dimension 100nm fabricated by holographic lithography.Photoresist stripe pattern with critical dimension 200nm is fabricated by increasing exposure dose.By increasing incident angle and increasing exposure dose,100nm diameter dots array are achieved.Utilizing the isotropy of photoresist ashing,we develop photoresist ashing technology to realize the fabrication of resist nanostructure,which make the fabrication process rigor and controllable.Elements with size under 150nm are obtained.4)Preventing the magnetic pattern from oxidation.Cobalt and iron are prone to be oxidized in the air.The oxidation of the etched Co_0.9Fe_0.1pattern is characterized by XPS.The result shows that most Fe is oxidized into Fe³⁺.To prevent the magnetic pattern from oxidation,we apply in-situ Au film deposition after ion beam etching,which solve the problem of oxidation.â…¡.Magnetic properties of Co_0.9Fe_0.1patternsWe applied soft.X-ray magnetic circular dichroism(XMCD)to characterize the magnetic properties of Co_0.9Fe_0.1patterns.On the base of U18 beam line of NSRL,the condition to apply XMCD to characterize the magnetic properties of magnetic nanostructures.The infection of the decrease of available absorb area to the XMCD spectra is investigated.We obtained hysteresis loops of the samples by SQUID magnetometer and SMOKE technology,and got the approximate saturation magnetization field and coercivity field.The magnetic state of the samples was observed by magnetic force microscopy(MFM).Our research production enriches the research of magnetic sub-micrometer elements.