SIMOX represents the first effort to compile a broad spectrum of knowledge from various groups of researchers and technologists in the world. It provides the reader with a basic understanding of SIMOX technology and in addition gives a good starting point for further investigation and applications.
Inspec keywords: annealing; ion implantation; SIMOX
Other keywords: high temperature annealing; separation-by-implanted-oxygen technology; SIMOX; silicon-on-insulator structures
Subjects: Annealing processes in semiconductor technology; Metal-insulator-semiconductor structures; Semiconductor doping
SIMOX, separation-by-implanted-oxygen, is a method of fabrication of silicon-on-insulator (SOI) structures and wafers by implanting high doses of oxygen and annealing at high temperature. SIMOX distinguishes itself among the SOI fabrication techniques by excellent uniformity of thin film layers, low defect density, and feasibility of patterned SOI wafers. Suitable for large area wafers and volume production, SIMOX SOI has shown the capability to support present LSI applications.
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.
The physics and chemistry of the SIMOX process are largely understood and volume manufacture of high quality SIMOX/SOI substrates is now becoming a reality with the wafer vendors optimistic that the targets specified in the ITRS for the next generation of CMOS SOI circuits can be adequately met. However, the real challenge for SIMOX is in the commercial arena can production be ramped up quickly to meet market demand with a wafer cost that industry can accept and without compromising substrate quality.
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.
This chapter focuses mainly on the electrical and optical characterisation of SIMOX starting material for CMOS applications. Optical characterisation is used for determining the thicknesses of the Si and BOX layers as well as their thickness uniformities. Electrical characterisation includes determining the I-V behaviour of the BOX (pinhole densities, leakage currents at high fields and breakdown voltages) and the key electrical parameters of the Si film such as mobilities, charge densities and lifetimes. Different characterisation techniques are described, especially those used most often by the author for quality control of SOI material used at IBM.
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.