Fabrication of Porous Silicon 3-Dimensional Periodic Structures and Their Structural and Characteristic Evaluation

2003 Fiscal Year Final Research Report Summary

• Project/Area Number: 14550326
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 電子デバイス・機器工学
• Research Institution: University of the Ryukyus
• Principal Investigator: MAEHAMA Takehiro University of the Ryukyus, Faculty of Engineering, Associate Professor, 工学部, 助教授 (60045044)
• Co-Investigator(Kenkyū-buntansha): SONEGAWA Tomihiro University of the Ryukyus, Faculty of Engineering, Assistant, 工学部, 助手 (20295299) ; HIGA Akira University of the Ryukyus, Faculty of Engineering, Associate Professor, 工学部, 助教授 (50228699)
• Project Period (FY): 2002 – 2003
• Keywords: Porous silicon / 3-dimensional photonic crystal / Current density modulation / Selective anodization / Self-cloning / Scanning electron microscope / X-ray diffraction

Research Abstract

When a silicon substrate is anodized in HF solution at a current density lower than the critical current density porous silicon layers(PS) are formed on the silicon substrate. The porosity of the PS relating to the refractive index can be controlled easily by the formation current density. A PS-three dimensional periodic structure(PS3DPS) is fabricated at the surface layer of the silicon substrate by self-cloning a PS-square lattice pattern formed on the silicon substrate by the selective anodization method. The self-cloning is carried out by modulating the formation current density periodically. This PS3DPS is expected to be applied to three-dimensional photonic crystals. This project purpose is to reduce the size of square-lattice of PS3DPS to the wavelength of infrared region or about 1 micron meter and to develop the fabrication technique.
In order to use the examination results for fabricating 1 micron-meter-size PS3DPS, the structures of the PS-one dimensional periodic structures( PS1DPS) were examined by scanning electron microscope and X-ray double-crystal method. PS1DPSs with the almost same periods as designed were fabricated by the current density modulation method in which the currents of 10mA/cm^2 and 50mA/cm^2 were periodically thrown. We fabricated the PS3DPSs by self-cloning method using the photomask of 1〜20μm square lattice and the current density modulation method developed for fabrication of PS1DPS. The structures of the PS3DPS were investigated by scanning electron microscope. The results are as follows : (1)Negative type photoresist was rather suitable as a resist mask for selective anodization than Positive type photoresist. (2)A 5μm-square-lattice PS3DPS of 3.5 periods or 7 layers and the each layer length of 1μm was able to fabricate. In the PS3DPS the structure changed to PS1DPS at deeper region than the seventh layer. The such fabrication trouble of PS3DPS was caused so that the PS grows not only depth direction but also lateral direction.
In future, we need to find the fabrication conditions which reduce the ratio of the growth rate in lateral direction to the rate in depth direction studying the growth mechanism of PS so that we can fabricate 1μm-square-lattice PS3DPS with enough numbers of period to apply to photonic crystal.