Polygonal pits on silicon surfaces that are created by laser-assisted chemical etching

Saori Kimura,Mitsunori Saito

doi:10.1063/1.4973980

Abstract

Laser-assisted chemical etching was conducted for creating periodic textures on silicon surfaces. Silicon plates with the (111) surface orientation were immersed in an aqueous solution of potassium hydroxide, and a pulsed laser beam (532 nm wavelength, 5 ns duration, 10 pulse/s) was irradiated on their surface to promote anisotropic etching. The laser beam was patterned by using a glass capillary plate that contained a hexagonal array of micropores (10μm diameter, 12μm period). The focused beam projected the hexagonal image on the silicon surface, creating bright spots of 4μm period. During the laser irradiation process of 3 min, both laser-induced ablation and chemical etching took place at these bright spots. After stop of laser irradiation, the chemical etching progressed further, and consequently, a periodic array of triangular or hexagonal pits emerged on the silicon surface. The direction of the triangular pits changed by rotation of the silicon plate. When a silicon plate with the (100) surface orientation was used, diamond or rectangular pits were created on its surface. The mechanism of this polygonal texturing was explained by using the normal and intersecting vectors of the (100), (110), and (111) planes that exhibited different etching rates.

Highlights

Laser irradiation on semiconductor surfaces creates micro- or nano-sized textures that exhibit a variety of optical, mechanical, or chemical functions
Researches on the laser ablation process revealed that droplet emission, which was unpreferable for depositing uniform films, was caused by laser-induced roughness or columnar textures on the target surface
When a Si plate was fixed in the perpendicular direction, as shown in Fig. 3(b), the laser irradiation created an array of downward triangles

Summary

Introduction

Laser irradiation on semiconductor surfaces creates micro- or nano-sized textures that exhibit a variety of optical, mechanical, or chemical functions. Afterward the droplet emission from the columnar melt was utilized in a novel deposition technique (laser-induced forward transfer), and a nano-sized Si dot array was fabricated successfully.. Afterward the droplet emission from the columnar melt was utilized in a novel deposition technique (laser-induced forward transfer), and a nano-sized Si dot array was fabricated successfully.10 This finding (self-formation of Si columns or cones) extended the application fields of laser processing, whereas its basic mechanism, i.e., self-formation of periodic ripples (gratings), had been recognized in earlier experiments that used a polarized laser beam.. Applications of these functions include luminescence of porous silicon (Si), reflectance reduction of light emitting diodes (LEDs) and photodiodes, coloration of semiconductor (metal) plates, marking on integrated circuits (ICs), and water repellency of material surfaces. At the early stage of the research, laser ablation was used principally for target evaporation in vapor-phase deposition processes. Researches on the laser ablation process revealed that droplet emission, which was unpreferable for depositing uniform films, was caused by laser-induced roughness or columnar textures on the target surface. Afterward the droplet emission from the columnar melt was utilized in a novel deposition technique (laser-induced forward transfer), and a nano-sized Si dot array was fabricated successfully. In addition, this finding (self-formation of Si columns or cones) extended the application fields of laser processing, whereas its basic mechanism, i.e., self-formation of periodic ripples (gratings), had been recognized in earlier experiments that used a polarized laser beam. It has been clarified that a flow of Si melt (capillary wave) is responsible for formation of columns or cones and that their growth is promoted by reactive gases. A regular arrangement of these columns and cones has been studied extensively; e.g., installation of a photomask or a microlens array (glass spheres) on a Si plate, spatial modulation of a laser beam by use of a liquid-crystal cell, interference-fringe formation by multi-beam irradiation, and successive irradiation of two beams with orthogonal polarization directions.

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