Electron Source For Electron-beam-induced Metal Structure Direct-writing

In recent years,science and processing methods experienced continuous breakthroughs,new materials,new structures and new properties at the nanoscale have become very popular research directions.However,for the functional and practical application of nano-materials and nano-devices,a mature and stable interconnection method is crucial to the application of nano-technology.Traditional device-interconnection method often needs to prepare the connection in advance by circuit exposure or other technical means,and there are some problems to be solved,such as high impedance,low degree of operational freedom,and cannot be in-situ processed,so we urgently need a high-performance,high operational degree nano-device interconnection method.Electron-beam-induced direct-write is a new method based on physical field.Its basic principle is to realize direct-writing and operation of micro-nano structure through the operation of electric field,and finally achieve the interconnection of device and direct-writing of metal structure.However,the processing mechanism and the electron source mechanism are still not clear enough.In order to promote the development of new interconnection method,this paper mainly conducts research from the following aspects:1.The effect of electron beam on metal nanomaterials was studied.The melting and movement of metal nanoparticles under electron beam irradiation were analysised from the perspective of electron beam thermal power density and gradient electric field.Electron beam spot with power density of 1.9×106W/cm2 was successfully used in transmission electron microscopy to irradiate Cu particles and its melting behavior was observed.In the scanning electron microscope(SEM),two electron beams with thermal power density of 1.53×105W/cm2 and 4.9×105W/cm2 were used for direct-writing experiments on Cu particles.Experimental results suggested that the electron source used for direct-writing should have the following characters:thermal power density 4.9×105W/cm2 or above,working distance of micron size,tip diameter less than 100nm,working voltage less than 1kV,etc.2.According to the theoretical requirements of direct-writing electron source and the analysis of field emission theory for direct write electron source,several key parameters applicable to electron source for near-field electron-beam-induced direct-writing were summarized.Through comparative experiments,it was found that the carbon nanotube with 3-5?m length,less than 25nm diameter,clear surface and straight shape have obviously advantages in several characters.In our experiment,a 3.53?m carbon nanotube emitter with 25nm diameter emitted 500nA current at the voltage of 130V.the maximum effective thermal power density of the electron source is up to 7.96×107W/cm2 when the working distance is 1?m.Carbon nanotube electron source has obvious advantages over other common electron source materials in spot size,threshold voltage and electron beam parameters,which can meet the requirements of direct-writing experiment.3.The vacuum level of the electron-beam-induced process is very low,the stability of isolated carbon nanotube electron source under low vacuum need to be considered.A field emission selective deposition technique was proposed to coat the tips of carbon nanotubes with Pt shells.After a 10 minute growth operation under 500nA,we successfully grew a Pt nanowire at the tip of the carbon nanotubes for 374 nm and prepared a Pt-coated carbon nanotube electron source.After experiment,we found that the prepared electron source can work for nearly 50 hours under the vacuum degree of 3.5×10-3Pa,which greatly improves the stability of isolated carbon nanotube electron source under the low vacuum.We prepared an electron source with low working voltage and high current density,which can work under low vacuum for a long time under control,this electron source can be used for electron-beam-induced metal structure direct-writing.