Sains Malaysiana 38(6)(2009): 889–894

Fabrication of Deep Trenches in Silicon Wafer using Deep Reactive Ion Etching with Aluminum Mask

(Fabrikasi Jurang dalam pada Wafer Silikon Menggunakan Punaran Ion Reaktif Dalam dengan Topeng Aluminium)

Bahram Azizollah Ganji* & Burhanuddin Yeop Majlis

Institute of Microengineering and Nanoelectronics (IMEN)

Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor D.E, Malaysia

Bahram Azizollah Ganji

Department of Electrical Engineering, Babol University of Technology, 484 Babol, IRAN

Diserahkan: 13 Januari 2009 / Diterima: 3 Februari 2009

ABSTRACT

In this paper, a deep-reactive ion etching (DRIE) process for fabricating microelectromechanical system (MEMS) silicon trenches with a depth of more than 250 μm is described. The DRIE was produced in oxygen-added sulfur hexafluoride (SF6) plasma, with sample cooling to cryogenic temperature using a Plasmalab System 100 ICP 180 at different RF powers. A series of experiments were performed to determine the etch rate and selectivity of some masking materials such as resists and metal (Al). Experiments showed that different materials have different etch rates, but for the Al mask, an etch rate of 5.44 ¥ 10-3 nm/min was achieved, that exhibited stronger resistance against RIE than photo resists. By controlling the major parameters for plasma etch, an etch rate of 2.85 microns per minute for silicon and a high selectivity of 5.24 ¥ 105 to the Al etch mask have been obtained. A 90 min etching experiments using etching gas SF6 of 60 standard cubic centimeters per minutes (sccm) with oxygen (13 sccm) were performed by supplying RF power of 5 W to an ICP of 600 watts, and silicon etching process with a depth of 257 μm was demonstrated. Our experiments showed that Al is the best mask material for very deep trenches in silicon.

Keywords: Al mask; deep trench; deep trenches ion etching; etch rate; silicon structure

ABSTRAK

Kertas ini menerangkan proses punaran ion reaktif dalam (DRIE) yang dijalankan dalam memfabrikasi jurang-jurang silikon MEMS dengan kedalaman melebihi 250 μm. Proses DRIE dijalankan dalam plasma sulfur heksafluorida (SF6) beroksigen, dengan sampel disejukkan ke suhu kryogenik menggunakan Plasmalab System 100 ICP 180 pada kuasa RF yang berbeza. Satu jujukan uji kaji kemudian dijalankan untuk menentukan kadar punaran dan selektiviti bahan topeng seperti rintang foto dan logam (aluminium). Uji kaji menunjukkan bahan-bahan berbeza mempunyai kadar punaran yang berbeza tetapi bagi topeng aluminium, kadar punaran 5.44 ¥ 10-3 nm/minit telah diperoleh, seterusnya menunjukkan ketahanannya yang kuat terhadap RIE berbanding rintang foto. Dengan mengawal parameter-parameter utama seperti punaran plasma, kadar punaran 2.85 mikron/minit dan selektiviti 5.24 ¥ 105 terhadap topeng aluminium telah diperoleh. Uji kaji punaran selama 90 minit menggunakan gas SF6 pada piawai 60 standard kubik cm per minit (sccm) dengan oksigen (13 sccm) telah dijalankan dengan membekalkan kuasa RF 5W kepada ICP 600 Watt, dan proses pemunaran silikon pada kedalaman 257 μm telah dilaksanakan. Uji kaji kami menunjukkan aluminium adalah bahan yang terbaik untuk dijadikan topeng bagi memfabrikasi jurang dalam pada silikon.

Kata kunci: Jurang dalam; kadar punaran; punaran kering berkedalaman tinggi; struktur silikon; topeng Al

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*Pengarang untuk surat-menyurat; email: baganji@vlsi.eng.ukm.my