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 mono crystallinity. 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. In the following, SIMOX technology is overviewed from its origins to its current state of practical use, by classifying its development into three stages.

In this chapter, the low-dose SIMOX process has been reviewed from the viewpoint of thermodynamics. Various innovative tech niques of refinement of the SIMOX process have been introduced and explained based on thermodynamic considerations for generation of nucleation centres, and growth and coalescence of precipitates during the annealing process. The author hopes that readers will have the opportunity to recognise the potential for further developments and refinements of the processes, and this chapter will stimulate further discussions among the scientists.

Silicon-on-insulator (SOI) based devices and circuits increase chip speed, lower voltage operation and enhance resistance to cosmic ray induced “soft error” events. Advanced CMOS logic and memory applications require ultra-thin SOI, with Si layers of less than 1000 Å. The most direct and powerful method to form cost efficient SOI is by separation of implanted oxygen (SIMOX). This method utilises O⁺ implantation into a heated Si substrate (>200°C) at doses >2×10¹⁷ cm^-2 followed by high temperature annealing (above 1300°C), to form a buried SiO₂ layer. Recent advances in improving SIMOX quality by the modified low-dose process (MLD) will be described. It is shown that the quality of the modern MLD SIMOX is comparable to that of bonded SOI. Functional products including microprocessors, SRAM memories and high frequency RF circuits utilising IBM's 0.18 μm and 0.13 μm CMOS technologies show equivalent yield on both bonded SOI and MLD SIMOX.