2.1 INTRODUCTION

In 1966, Watanabe and Tooi [1] first reported on the formation of silicon oxide by oxygen-ion implantation into silicon. Their work, however, has not been followed by additional SOI (silicon-on-insulator) studies.

In 1978, Izumi, Doken and Ariyoshi succeeded in fabricating a 19-stage CMOS (complementary metal-oxide semiconductor) ring oscillator using a buried SiO ₂ layer formed by oxygenion ( ¹⁶O ⁺) implantation into silicon. Izumi named the new SOI technology SIMOX, which is short for separation by implanted oxygen [2]. Since then, Izumi and his research group have been constantly committed to the study of SIMOX technology.

SIMOX was originally conceived in order to solve the aluminium auto-doping and crystalline defect problems in SOS (silicon-on-sapphire). There were three key points in SIMOX technology. First, the buried oxide layer must be formed with adequate dielectric isolation characteristics. Second, the top silicon layer above the buried oxide layer must maintain sufficient monocrystallinity. Third, the thermally oxidised silicon layer, which covers the mesa-type island of a MOSFET (metal-oxide semiconductor field-effect transistor), and the buried oxide layer must be combined with sufficient continuation at the bottom edge of the mesa-type island.

Basically, SIMOX technology satisfied these three key points relatively early; however, it still faced other serious difficulties. The synthesis of SiO ₂ by oxygen-ion implantation into silicon requires a huge oxygen dose. Simple calculations indicate that the synthesis of stoichiometrical SiO ₂ requires high-density oxygen atoms of 4.48 10 ²² cm ^?3.