Qui2Review - P-N Junctions: contact between p-type and...

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P-N Junctions: contact between p-type and n-type material used in voltage rectifiers, capacitors Fabrication of Junctions Doping: When it is made: Ingot stage During epitaxial growth: added layer is a doped crystal Diffusion: random motion of dopants, requires high temperature Can use: funace – low temp, slow; rapid thermal processing- high temp, fast Activation energy: potential energy barrier to dopant migration Thermal budget: distance dopants diffuse over time characterized by time and temperature dependant diffusivities Total thermal budget: includes continuos varying temps over time The greater the activation energy, the greater the temp. sensitivity most important element of diffusion doping Ion Implantation: high energy ions fired into semiconductor more control than diffusion Projection range: average penetration depth ions come to rest at after firing increases with increased implantation energy Straggle: characteristic width of region ions come to rest increased with increased implantation energy annealing: high temperature process that removes damages to the crystal caused by ion implantation increase width of dopant distribution (alters straggle) Electrical Insulation: Thermal Oxidation: Si to SiO2 high temperature
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consumes about a ¼ nm of Si for every nm SiO2 grown Easy and cheap, high quality, most popular Chemical Vapor Deposition (CVD): Si to SiO2 low temperature --> little increase in thermal budget, low pressure doesn't use of Si crytal vs. thermal oxidation can grow high-k dialectrics (thicker, less tunneling) Metallization: formation of metal layers and vias vias: vertical connections between layers sputtering: application of layers via vapor deposition (i.e. Evaporation) Lithograpthy: control of position, area, and shape of junction/insulation (layout) Lithography: writing and developing of patterns Etching: removal of amterial below the openings reticle: iron oxide coated quartz plate with circuit patterns creation o resist: thin layer of e-beam sensitive material, exposed to e-beam containing pattern (lithography) slow, done once two types developed (etching) positive: removal of exposed portion negative: removal of unexposed portion Transfer of reticle o UV photoresist: b/c of high spatial resolution (short optical wavelength) fast, for mass production Additionally: back end processing: addition of metallization layers
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front end processing: creation of device itself mask: single wafer die: single chip, multiple on wafer stepper: step and repeat application of die-reticles Junction Equilibrium: Fermi levels must be aligned Contact Potential: electrostatic potential drop from the n to p-side in equilibrium (positive) larger doping --> larger contact potential larger the band gap --> larger the doping, larger the band bending
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Qui2Review - P-N Junctions: contact between p-type and...

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