Study On The Machining Of Micro-nano Optical Array Elements Of Silicon By The CELT

With the rapid development of micro electromechanical systems (MEMS) today，miniaturization，integration and intelligence have become the most important trends inscience and technology. Microsystems will become one of the most challenging fieldsof science and technology in21stcentury. And it will lead to a huge breakthrough onhuman’s ability to understand and reconstruct the world. Recently, as a newlyemerging high-tech，the use of electrochemical machining method for fabricatingmicro/nano structures has become one of the remarkable and great potentialtechnological advances. Electrochemical micro/nano machining methods have greatpotentials in the machining of complex3D micro/nano structures， due to theiradvantages of wide range of materials machined，stress-free，high surface quality，low environmental requirements，high resolution and low cost and so on.The Confined Etchant Layer Technique (CELT)(first proposed by prof.Zhao-Wu Tian in1992) is a new machining method for micro/nano structures. Thismethod has good comprehensive advantages for:(1) Micrometer or nanometer scaleresolution can be reached,(2) Replication of the real3D complex structures can berealized,(3) Mass production of micro/nano structures can be achievedsimultaneously, which is unmatched among the traditional micro/nano fabricationtechnologies. In this paper， CELT was studied to apply to fabricate3Dmicromachining on the surface of the semiconductor Si wafer. Finally，a3D microlensarray has been successfully transferred onto the surface of Si wafer by thePMMA/Ti/Pt microlens array mold with the resolution of submicron level. The mainconclusions of this work is described as follow：1、The etchant and the scavenger which could be effective to etch Si were soughtout and studied by electrochemical measurement and corrosion weightloss method.Through the experiment，HNO3/HF and Br2/HF were selected as the etching systems.The corresponding scavengers were NaOH and L-cystine respectively. The etchingmechanism was investigated. The two etching systems were proved feasible for CELTby the cyclic volt-ampere characteristic curves. In order to improve the etchingresolution， surfactant (CTABr) was added into the etching system to reduce thehydrogen attached. It was shown that a limited increase in temperature of etchingsystem is benefit to Si etching machining. 2、 Pt micro cylindrical electrode was used to investigate the duplicationprocessing experiment for the two etching systems respectively. The etching systemand process parameters were optimized. An optimal concentration ratio for thescavengers to the precursor of electro-generated etching agent was obtained. Throughthe duplication processing research，it was determined that the etching processingresolution of the Br2/HF/L-cystine etching system reached at submicron scale，whichbasically meets the requirements of the CELT processing for selected micro-structures.So this etching system was the optimal etching system for the duplication processingof the micro-optical lens array.3、Micromachining research was done by using CELT to machine micro-opticallens array on p-Si surface. Ultimately，a large area of micro-optical concave lens arrayhad been obtained on the surface of p-Si. The etching precision along the height wasabout0.47μm and its relative error was about4.62%. The etching precision along theradius was about0.98μm and its relative error was about0.90%. The experimentsshowed that submicron resolution could be achieved on the surface of Si by CELTduplicating processing for the micro-optical elements. After further optimization ofthe follow-up work，higher resolution of the etching processing is expected to beachieved，which predicts the broad application prospect of the CELT.