Research On Nanostructure Processing By Using RIE And AFM-based Mechanical Scratching Method

As an effective method for processing nanostructures, AFM-based nanoscratchinghas been applied to two or even three dimensional structure fabrication on materials likepolymers and metals. Due to the restriction of AFM tip’s hardness, the interactionbetween the tip and silicon surface results in large normal force, which causes excess tipwear, and the depth of the nanostructure on silicon can not be guaranteed. In the presentstudy, nanostructure is machined on polymer resist by AFM tip, which is thentransferred to silicon by Reactive Ion Etching. Eventually we obtain exquisitenanostructure on the silicon wafer. There are three parts of the thesis as following:By studying the influence of spin-coating speed and concentration of the PMMAsolution on the thickness of the PMMA films, PMMA films with dimensions of thethickness spanning from dozens to hundreds nanometers are obtained. Elastic moduli ofthe PMMA films spin coated with different parameters are evaluated using thePeakForce Quantitative NanoMechanics (QNM) module of the AFM system. Therelationship between elastic moduli and machinability of the PMMA films is obtainedby contrasting the depth of the grooves, thus conforming the preparing condition of thePMMA films which are suitable for AFM mechanical machining.So as to obtain good nanostructures on resist, multiple passes of scratching andultrasonic force regulated nanomachining experiments are conducted. Multiple passes ofthe tip’s scratching maintain the structural consistency and enhance the depth of thegrooves. However, the low machining efficiency confines its practical application.While ultrasonic force regulated nanomachining enhances the structural depth andreduces the bond and wear of the tip as well.Reactive Ion etching experiment is conducted for transferring the nanostructuresfrom PMMA film to silicon substrate. By comparing the etching results from PMMAfilms of different thicknesses, the film thickness is confirmed for perfect pattern transfer.By optimizing the etching parameters and introducing experimental program of doubleresist, exquisite nanostructure is obtained on silicon substrate.