Neutron transmutation doping conceptual design

When silicon is irradiated the objective is to produce number of phosphorus atoms in the target sample in order to obtain a given resistivity after the treatment. The resistivity of the sample is decreased by the transmutation of the silicon, by neutrons, to phosphorus. Irradiation is carried out by thermal neutrons. The silicon doping facility at ETRR-2 had commission for production of 5- inches silicon ingot. The trend in the semiconductors industry is to increase the wafer diameter to increase the number of integrated circuits produced from each wafer which leads to reduce the cost of the product. Hence, it is necessary to upgrade the silicon doping facility to 6-inches diameter. A new neutron transmutation doping conceptual design (NTDCD) has followed to upgrade the silicon doping facility. The new design has main three branches. First, is the mechanical design of the irradiation rig and silicon ingot handling tools. In the new design two graphite blocks are dispensed with to increase the ingot height and reduce the weight for ease the handling the silicon ingot container, safe handling, and to enhance the cooling of the silicon ingot during irradiation. The second branch in the new design is the neutronic analysis and design. The neutronic design, includes the neutron flux measuring in the two positions are available in the thermal column. From the neutronic design the axial resistivity variation can be predicted. Two irradiation methods are proposed. They are based on irradiating two ingots simultaneously in one position. These two methods are explained in the thesis. The axial resistivity variation obtained is (6.21%-8.2%) for 500 mm ingot length irradiated in position (1) using irradiation method (2), and axial resistivity variation (5.56%-12.52%) for position (2) using irradiation method (2). The axial resistivity variation for 400 mm ingot length is (3.82%-4.28%) for position (1) using method (2) and a value between (3.65%-6.2%) has been obtained for position (2) using the same method. The silicon ingots are mounted on hollow aluminum cylinder (spacer) to adjust it in the high symmetric thermal neutron flux Instead of the graphite block. The third branch in the new design is the thermal analysis of the silicon ingot during irradiation. The temperature of the silicon ingot during irradiation should be less than 180 degree C to minimize the diffusion of the defects such as swirl defects. The finite element heat transfer code (FEHT) has used for ingot thermal analysis. The maximum temperature detected in 6-inches, 500 mm silicon ingot is 70.4 degree C in case of all the silicon ingots considered convective boundaries cold case (k= 84 W/m2.degree C, h= 128 W/ W/m2.degree C). The maximum temperature (78.6 degree C) detected in 5-inches 400 mm ingot in case of all the silicon ingots considered convective boundaries cold case. These calculations show that the maximum temperature can be detected under virtual cases under the safe limit (180 degree C).The new silicon container has tested using 5-inches silicon ingot with length 280 mm. the average initial resistivity of that ingot is 4952 ohm.cm and the target final resistivity is 200 ohm.cm. The silicon ingot irradiated with total flounce is 2.08 x 1017 n/cm2. The measured final average resistivity is 209.39 ohm.cm. The resistivity value obtained with tolerance 4.69 % is accepted, since the standard resistivity tolerance is 5-10 %. Whoever as the doping ratio increases the radial resistivity variation decreases. The maximum axial resistivity measured in that sample is 1.242 %. With the new design the sample is isothermally annealed at 850 degree C for 1 hour instead of 3.5 hours in old design case. By this work ETRR-2 has the ability to produce 6-inches and 5-inches silicon ingot with high electronic quality.