2) a) A phosphorous doped n-type silicon wafer of 1 92-cm resistivity is subjected to a boron diffusion at a temperature of 1150 °C. A constant surface concentration of 2 x

10¹⁹ cm³ is maintained throughout the diffusion. i) Calculate the background concentration in the wafer. ii) How long should the diffusion be carried out for to obtain a junction depth of 4 microns. iii) Calculate the charge, Q. [15 1/3 marks] b) Describe with the aid of a diagram, a liquid source diffusion system. [5 marks] c) State Henry's Law. Explain why predeposition is performed at the solid solubility limit in industrial practice. [5 marks] excitation: primary ion beam: ot, Art, O, Cst ooooooooooooo Figure 2. SIMS Schematic Diagram analytical signal secondary ions: X*, X, X-Y*, X-Y- not used: neutrals, excited atom d) Figure 2, above, shows a schematic diagram illustrating Secondary Ion Mass Spectroscopy (SIMS) Briefly describe the technique. Why would SIMS be a poor method to use to profile dopant concentrations in a multi-quantum-well laser consisting of several ultra-thin layers of different materials? How is this measurement attempted in practice? [5 marks] e) Rapid Thermal Processors use several methods to compensate for higher radiant heat losses at the periphery of the wafer. Briefly discuss one of these methods. [3 marks]