(Solved): 2. In the fabrication of a p-type semiconductor, elemental boron is diffused a small distance into ...
2. In the fabrication of a p-type semiconductor, elemental boron is diffused a small distance into a solid crystalline silicon wafer. The boron concentration within the solid silicon determines the semiconducting properties of the material. A physical deposition process keeps the concentration of elemental boron at the surface of the water equal to 5.0×1020 atoms boron /cm3 silicon. In the manufacture of a transistor, it is desired to produce a thin film of silicon doped to a boron concentration of at least 1.7×1019 atoms boron/ cm3 silicon at a depth of 0.2μm from the surface of the silicon wafer. It is desired to achieve this target within a 30 -min processing time. The density of solid silicon is 5.0×1022 atoms Si/cm3 solid. At what temperature must the boron doping process be operated? It is known that the temperature dependence of the diffusion coefficient of boron (A) in silicon (B) is given by: DAB=D0e−Q0/RT where D0=0.019cm2/s and Q0=2.74×105J/g mol for elemental boron in solid silicon. The thermodynamic constant R=8.314J/gmol/K.