Sains Malaysiana 48(6)(2019): 1163–1169

http://dx.doi.org/10.17576/jsm-2019-4806-02

Reflectance Characteristics of Silicon Surface Fabricated with the Arrays of Uniform Inverted Pyramid Microstructures in UV-Visible Range

(Ciri Pantulan Permukaan dalam Julat UV-Nampak Bagi Silikon yang Difabrikasi dengan Jajaran Seragam Mikrostruktur Piramid Sonsang)

MOHD FAIZOL ABDULLAH & ABDUL MANAF HASHIM*

Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, Jalan Sultan Yahya Petra, 54100 Kuala Lumpur, Federal Territory, Malaysia

Received: 16 July 2018/Accepted: 15 November 2018

ABSTRACT

In this paper, inverted pyramidal microstructures are designed and fabricated on silicon (Si) surface. The characteristics of surface reflectance are simulated using two-dimensional (2D) finite-difference time-domain (FDTD) method by varying the spacing (S) and width (W) of the pyramidal microstructures. The results showed that the effect of S is more significant compared to W where the reflectance of the irradiated light has been increased gradually with the increase of S from 0 to 3 μm, and the difference is around 9.6%. Due to the etching constraint, S= 3 μm is chosen for the fabrication. Textured structure is fabricated by the anisotropic etching of tetramethyl-ammonium hydroxide (TMAH) with additional of isopropyl alcohol (IPA). Long etching time of 120 min is required to form uniform arrays of pyramidal microstructures with smooth and well-terminated four sidewalls at (111) plane. Due to the undercut etching under SiO2 mask, it results to the formation of slightly larger W and smaller S in the fabricated structures. The measured average reflectance in UV-visible range for the Si with inverted pyramidal microstructures is very low down to 10.4%. The discrepancy between the measured and simulated values is speculated to be due to the use of 2D FDTD instead of three-dimensional (3D) FDTD.

Keywords: Anisotropic etching; FDTD; reflectance; Si inverted pyramid; TMAH/IPA; UV-visible

ABSTRAK

Dalam kertas ini, mikrostruktur piramid songsang Si bersaiz mikro telah direka bentuk dan difabrikasi di atas permukaan silikon (Si). Ciri pantulan permukaan telah disimulasi menggunakan kaedah domain-masa perbezaan-terhingga (FDTD) dua-dimensi (2D) dengan membezakan jarak dan lebar mikrostruktur piramid. Data menunjukkan kesan jarak (S) adalah lebih ketara jika dibandingkan dengan kesan lebar (W) terhadap pantulan permukaan. Pantulan cahaya yang disinarkan telah meningkat secara beransur-ansur dengan peningkatan S daripada 0 kepada 3 μm dan perbezaan adalah sekitar 9.6%. Disebabkan kekangan punaran, S= 3 μm telah dipilih untuk difabrikasi. Tekstur telah difabrikasi dengan cara punaran anisotropik oleh tetra metil ammonium hidroksida (TMAH) berserta campuran alkohol isopropil (IPA). Punaran pada tempoh yang lama iaitu 120 min diperlukan untuk membentuk jajaran mikrostruktur piramid yang seragam dengan empat sisi tepi pada satah (111) yang licin berserta penamatan yang baik. Disebabkan potongan bawah punaran di bawah topeng SiO2, ia membentuk W yang sedikit lebih besar dan S yang lebih kecil bagi struktur yang telah difabrikasi. Purata pantulan dalam julat UV-nampak yang telah diukur bagi Si dengan mikrostruktur piramid songsang adalah sangat rendah iaitu 10.4%. Percanggahan antara nilai yang diukur dengan nilai yang disimulasi telah dispekulasi disebabkan penggunaan FDTD 2D dan bukannya FDTD tiga-dimensi (3D).

Kata kunci: FDTD; pantulan; piramid songsang Si; punaran anisotropik; TMAH/IPA; UV-nampak

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*Corresponding author; email: abdmanaf@utm.my