4.1 INTRODUCTION

Two major breakthroughs in the history of SIMOX (separation by implanted oxygen) technology led to improved crystalline quality of the top silicon layer. One was the high-temperature annealing (at over 1300 C) after oxygen implantation [1], and the other was the invention of low-dose SIMOX [2]. High-temperature annealing reduced the number of dislocations remaining in the SOI layer of standard dose SIMOX from 10 ⁹/cm ² in early material to 10 ⁶/cm ², which could be achieved routinely in volume fabrication. Low-dose SIMOX processes further reduced the dislocation density by 3 4 orders of magnitude, and moreover greatly reduced the wafer fabrication cost. The discovery of the internal thermal oxidation (ITOX) process strengthened the integrity of the buried oxide (BOX) film [3] such that the low-dose SIMOX can support mainstream IC technology.

Although fabrication of SOI structures by implanting O ⁺ ions and annealing at high temperature may appear simple, complex physics aspects need to be taken into account to refine the basic SIMOX process to achieve the desired quality of the layers. In this chapter, detailed analyses of thermodynamic processes in SIMOX are discussed with emphasis on forming high quality SIMOX layers through sophisticated annealing of silicon implanted with oxygen doses lower than the optimum process window. A concept of novel SOI structures emerging from innovative, elaborated annealing schemes is also introduced.

4.2 THERMODYNAMIC PROCESSES IN SIMOX

In traditional standard-dose SIMOX (sometimes called full-dose SIMOX), doses of implanted oxygen exceed peak concentrations...