| Periodic micro-nano structures are often used in biomimetic materials,infrared reflection enhancement,surface plasmons,patterned substrates and other fields.Patterned substrate is an important way to solve lattice mismatch,reduce penetration dislocation density,and achieve lowdefect growth in various heterogeneous materials.At present,the methods for preparing patterned substrates include photolithography,inkjet printing technology,and polyacrylamide(PMA)masks.Compared with these preparation methods using precision photolithography,the porous anodic aluminum oxide(AAO)technology for preparing patterned structures has the advantages of simple process,low cost,and adjustable size,which is a new solution with development potential.In this paper,a non-photolithographic AAO is used as a template to prepare a patterned germanium(Ge)substrate by dry etching method.The main research contents and the obtained results are as follows:The optical properties of the patterned Ge substrates with different arrangements(hexagonal and square)and different face types(circular aperture,inverted circular table,inverted cone,inverted pyramid)were investigated by FDTD simulations with finite element difference method,and optimized parameters were obtained for apertures with high transmittance of 0.15 μm or greater and aperture depths of 0.28 μm～1.91 μm.The highest transmittance of 92.11%for the inverted pyramid shape among the five face types.Then the thermal stresses when epitaxial GeSi on planar Ge and epitaxial GeSi on graphical Ge were compared and analyzed by COMSOL finite elements,and the maximum transient temperature of the equivalent surface on graphical Ge was 74℃ lower than the maximum transient temperature of the equivalent surface on planar Ge.AAO template was prepared by two-step anodizing method.The primary oxidation time was maintained for 2 hours to ensure that the oxide layer was uniform,and the AAO template with a cycle of about 450 nm,an average pore depth of about 400 nm,1.1 μm,and an average pore size of about 57.97 nm,151.90 nm,274.59 nm,and 380.08 nm was prepared by changing the secondary oxidation time of 30 min～50 min,50 min and reaming time of 0 min～4 min,the average pore depth was about 400 nm,1.0 μm,1.8 μm,and the average pore size was about 57.97 nm,151.90 nm,274.59 nm,380.08 nm.The obtained template has the advantages of adjustable size,rounded hole shape,and basically no hole blockage.Using AAO templates,a sub-micron multi-morphology patterned Ge substrate was produced by inductively coupled plasma(ICP)etching process.The Ge substrate was etched with C12/B C13/Ar mixture and BCl3/Ar mixture as etching gas,and the influence of the process parameters of the two gas mixtures on the etching morphology of the patterned Ge substrate was explored.The source power of Cl2/BCl3/Ar mixture was optimized,the bias power was 100 W,the flow ratio of Cl2/BCl3/Ar gas was 30 sccm/25 sccm/50 seem,the etching pressure was 2 Pa,and the etching time was 25min,and the Ge morphology of inverted pyramid and square was realized under this parameter,and the average etching depth of inverted pyramid was 1.7 μm.A round hole-shaped Ge morphology with a flat and uniform surface was achieved under BCl3/Ar gas mixture.In this paper,we have realized the preparation process of patterned Ge substrates based on AAO templates and laid the foundation for the subsequent heterogeneous epitaxial SiGe and Ⅲ-Ⅴ materials on patterned Ge substrates. |
