Chemically-Enhanced GaAs Maskless Etching Using a Novel Focused Ion Beam Etching System with a Chlorine Molecular and Ra
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CHEMICALLY-ENHANCED GaAs MASKLESS ETCHING USING A NOVEL FOCUSED ION BEAM ETCHING SYSTEM WITH A CHLORINE MOLECULAR AND RADICAL BEAM
N. TAKADO,* K. ASAKAWA,* H. ARIMOTO,** T. MORITA S. SUGATA,*** E. MIYAUCHI,** and H. HASHIMOTO*' Optoelectronics Joint Research Laboratory, 1333 Kamikodanaka, Kawasaki 211, Japan
Nakahara-ku,
ABSTRACT Chlorine-enhanced GaAs maskless etching using a novel focused-ion-beametching (FIBE) system has been examined for establishing high-rate and smooth FIBE. The system is composed of an air-locked ultrahigh-vacuum chamber, a 30 KeV Ga+ FIB column and two kinds of chlorine-irradiation nozzles. A fine nozzle enabled us to irradiate a high-density C12 flux on a desired, small area of the sample while retaining a sufficiently low surrounding-gas pressure for stable Ga' FIB emission. Highly chemically-enhanced sputtering yields (up to 50 GaAs molecules per incident ion) were obtained. At the maximum yield, line-scanned deep-groove (6.5 um) etching with a smooth surface, capable of fabricating a laser-cavity optical mirror, was demonstrated. The chemical-enhancement effect showed high FIB-scanning-time dependence. This effect was also observed by irradiating with a plasma-dissociated Cl radicals using a novel radical beam gun. An analytical model, based on the Ga+-ion bombardment on the chlorine-adsorbed substrate surface, suggested that the maximum chemical enhancement is obtained when the Ga+-FIB scanning time is adjusted to the chlorine-coverage time, given by the C12 -molecule or Cl-radical flux density. INTRODUCTION Focused-ion-beam-etching (FIBE) is a novel micro-fabrication technique capable of maskless, direct etching in which submicron patterns with desired depth distributions are micromachined with an aid of computer control An early stage of the FIBE development was plagued with redeposition of FIB-sputtered substrate materials [1E]-[41, making it difficult to obtain smooth, high-rate and uniform etching due. Recently, FIBE in a reactive gas ambient such as C12 has been proposed to be promising for chemically enhancing the etching rate and reducing redeposition, to smooth, uniform etching. [5] We have developed a novel FIBE system for establishing high-rate, contamination-free and smooth maskless etching for microfabrication of GaAs IC and OEIC (optoelectronic integrated cricuit) as well as Si VLSI. Using this system, chemical-reaction-enhanced GaAs smooth FIBE and its reactive-gas introduction method have been investigated. This paper reports experimental results on chlorine-assisted GaAs smooth etching with Ga+ FIB, including two kinds of chlorine-introduction methods. Smooth surface morphology and etching profile are obtained FIB-scanning-time dependent etching-rate are observed, and are explained by etching mechanism based on Ga+-ion bombardment effects on the chlorine-adsorbed substrate surface.
* Present address: Q3toelectronics Laboratories, NEC Corporation, 1-1, Miyazaki, 4-
chome, Mivamae-ku, Kawasaki, Kanagawa 213. **?resent address: Fujitsu Atsugi Laboratories, Atsugi, Ka
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