Abstract
The purpose of this project has been twofold: firstly, to develop further FTIR reflectance spectroscopy as a technique for the quantitative characterisation of SOI multilayer structures and secondly, to use it in combination with other techniques, such as RBS/Channelling, XTEM, SIMS, AES and SRP, to investigate the evolution and structure of novel SOI materials. In order to evaluate the FTIR results, many SIMOX samples were fabricated with a wide range of Si and buried SiO2 layer thicknesses with one or two buried oxide layers. The FTIR results are compared to those obtained with the other experimental techniques and with theoretical calculations. We show that, given an "a priori" knowledge of the structure which is used to define the initial structural model, FTIR can be used as a non-destructive, fast, and inexpensive control method for characterising SOI structures. FTIR offers +/-2 nm accuracy in layer thicknesses and +/-5 nm in interfacial region thicknesses, over a wide (0.5 to >10mum) depth range, while for shallower depths an error of 15% on average is likely. FTIR gives Si thickness values which are within 5%, and buried layer or interfacial region thickness values which are within 10% to 20%, from the values obtained by other techniques. The sensitivity to oxygen content variations is down to 5 x 1020 O cm-3 for the top of a Gaussian profile, and 1 X 1022 O cm-3 over a 20 nm thick layer. FTIR gives a value for the retained dose within 5% of the nominal dose for both unannealed and annealed samples. Novel SOI materials, such as deep buried oxide layers and double SIMOX structures were fabricated and characterised, and the processing parameters optimised. We show that, for 2 MeV oxygen implantation into Si at 700°C to a dose of 2 x 1018 O+ cm-2 and after annealing at 1300°C for 6 hours, a buried layer is formed which is continuous but contains Si islands. It is found that by increasing the annealing time to 12 hours, the homogeneity of the buried layer is improved. We propose that an increase of both the oxygen dose and the annealing temperature would result in a higher quality buried oxide layer. The adverse effect of high beam current densities to the sample structure after annealing is demonstrated for the high energy SIMOX samples. We show that double SIMOX structures can be fabricated by a three step process, with one only annealing step at the end. Such structures can be used for Si waveguiding applications and we present preliminary results of waveguiding loss measurements, where a value of 18 dB/cm was obtained.