MECH466-Lecture-4 - 1 MECH 466 Microelectromechanical...

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Unformatted text preview: 1 MECH 466 Microelectromechanical Systems University of Victoria Dept. of Mechanical Engineering Lecture 4: Semiconductor Sheet Resistivity Basic Concepts of Stress and Strain May 17th, 2007 Mech 466, N. Dechev, UVic 2 Selective Doping of Silicon Sheet Resistivity Compliant Mechanisms Mechanics of Materials Stress and Strain Overview Mech 466, N. Dechev, UVic 3 Doping of Silicon Doped silicon can be created in one of two methods: Using the crystal growth process, the doping element is introduced and will be distributed uniformly throughout the bulk of the solid. Using a photolithographic method, selected areas can be doped using a diffusion process or ion implantation. Mech 466, N. Dechev, UVic 4 Diffusion Doping Diffusion doping is done using a deposition and baking process. (a) A temporary mask is patterned onto the silicon. (b) A layer containing a high concentration of the desired dopant element is deposited onto the material (for example, PSG). (c) The chip is then baked at an elevated temperature, which promotes the diffusion of the dopant atoms into the exposed silicon surfaces. (d) The dopant layer is removed by chemical etching. (e) Finally, the mask layer is removed by chemical etching. Mech 466, N. Dechev, UVic 5 Ion Implantation Ion implantation involves the insertion of ions of one material, into another. (a) The implant material is energized to create charged ions (single atoms). (b) The ions are accelerated using an electric field toward a target. (c) (Optional) a separation magnetic field can be applied to remove impurities. (d) (Optional) a deceleration electric field may be used to control the implant energy. (e) This mechanical implantation creates damage to the crystal structure, therefore, a thermal annealing process follows implantation to heal some of these defects. Mech 466, N. Dechev, UVic Ion Implantation Process [image from Wikipedia] 6 Sheet Resistivity A concept used to determine the resistance of the doped paths in the silicon. The resistance of the tracks can be determined based on the track geometry and the resistivity....
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MECH466-Lecture-4 - 1 MECH 466 Microelectromechanical...

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