Photoelectric Effect Accelerated Electrochemical Nanoimprint Lithography And Preliminary Study Of Electrochemical Lithography

Materials with three-dimensional micro-nanostructures(3D-MNS)have played a significant role in multiple fields such as integrated circuits,integrated optics,microelectromechanical systems,nanotechnology,and precision machining due to their superiorities of multi-functional high integration,small size,low cost and excellent mechanical,optical and electronic properties.Electrochemical micro-nano fabrication technologies stand out among many micro-nano fabrication technologies on semiconductor due to its high processing efficiency,low cost and wide range of applications.We combine the methods of stamping and imprinting with the principles of metal-assisted chemical etching,and proposes electrochemical nanoimprint lithography that can directly fabricate 3D-MNS on semiconductors.On the other hand,semiconductors under the photoelectric effect generate a large number of photogenerated electron hole pairs which can be used to accelerate electrochemical nanoimprint lithography and direct etching of semiconductors.The work of this paper is mainly divided into two parts:(1)Photoelectric effect accelerates the fabrication of electrochemical nano imprint lithography on n-GaAs wafer.The essence of electrochemical nanoimprint lithography is the electrochemical corrosion and etching of metal/semiconductor/solution three-phase interface induced by the contact potential.The resolution of electrochemical nanoimprint lithography can reach the level of several tens of nanometers.Taking the Pt/n-GaAs/MnO4-system as an example,when Pt is in contact with n-GaAs,the difference in work function causes the electron flow from n-GaAs to Pt to form a contact potential at the contact interface.Due to the high catalytic activity of Pt,the reaction of MnO4-on its surface rapidly reaches the thermodynamic equilibrium,and MnO4-can easily capture electrons from Pt to be reduced(fast step).The electrons will continuously transferr from n-GaAs to Pt and be captured by MnO4-,and the holes accumulated at the Pt/n-GaAs/solution three-phase interface cause anodic dissolution of n-GaAs(decision step),thereby forms 3D-MNS on n-GaAs wafer.If a specific wavelength of light is irradiated on the back side of the n-GaAs wafer during the imprint process,the number of electron-hole pairs will be greatly increased due to the photoelectric effect of the n-GaAs wafer.Since the photogenerated electrons in the conduction band of n-GaAs wafer are rapidly trapped by MnO4-,a large number of holes will be rapidly accumulated at the three-phase interface of the Pt/n-GaAs/solution,thereby increasing the degree of anodic polarization of the n-GaAs and accelerating the anodic dissolution rate of n-GaAs wafer,which accelerates the rate of overall imprint.We measured the interface contact potential,Tafel curves and linear sweep volt-ampere curves under dark and light conditions,and confirmed the feasibility of photoelectric effect to accelerate electrochemical nanoimprint lithography.In the fabrication examples,the maximum etching rate of the dark/illumination state system at the same imprint time is 2.27 ?m3/s,4.56 ?m3/s,and the improvement ratio is 101.3%.The photoelectric effect has a large increase in the rate of electrochemical nanoimprint lithography.(2)Preliminary of Electrochemical Lithography on n-GaAs.The essence of electrochemical nanoimprint is the electrochemical etching of semiconductors.The oxidant in solution needs electron tunneling channels formed by metal/semiconductor contacts to etch the specific regions on semiconductor.In contrast,the essence of electrochemical lithography is the photochemical etching of semiconductors.It is not necessary to use metal as a bridge for electron transport,and the semiconductor is etched directly through electron transfer at the semiconductor/solution interface.Taking the n-GaAs/Fe3+ system as an example,the light of a specific wavelength is irradiated to the region of the micro-nano-scale of the n-GaAs surface,electrons in the valence band absorb photon energy to produce level transitions,and form photogenerated electrons and photogenerated holes in valence bands and conduction bands,respectively.Fe3+ traps photogenerated electrons at the n-GaAs/solution interface to reduce itself to Fe2+,while photogenerated holes cause the anodic dissolution of n-GaAs wafer,and the etching only occurs in the illumination region,thus realizing the fabrication of 3D-MNS on n-GaAs wafer.The etching rate of Fe3+ on n-GaAs is very slowly in dark state,so it can exhibit better anisotropy and fabrication resolution in electrochemical lithography of n-GaAs.We will use xenon lamp and supercontinuum laser as light source and use n-GaAs/FeCl3/HCl system for electrochemical lithography.We will explore the photoetching reaction kinetics of n-GaAs in FeCl3/HCl system and provide theoretical guidance for subsequent electrochemical lithography.In the preliminary experiments,we obtained the complete and uniform micrometer linear,circular and diffraction ring structures,and made a preliminary exploration of the etching process.Photoelectric effect accelerated electrochemical nanoimprint lithography on semiconductors has greatly shorten the machining time at a lower cost,improve the overall efficiency,and promote the development of electrochemical nanoimprint lithography in the field of 3D-MNS fabrication on semiconductors.Electrochemical lithography can directly etch semiconductors in a solution with a mask or a spot with a precise micro-nano structure,which simplifies the cumbersome process and reduces the cost,and has broad development prospects in the field of 3D-MNS fabrication on semiconductors.