Fabrication of the semiconductor devicesUnit cell of siliconcrystal is cubicEach Si atom has 4nearestneighbours5.43A
Fabrication of the semiconductor devices • Unit cell of silicon crystal is cubic. • Each Si atom has 4 nearest neighbours
EcTop ofconduction bandEg=9eVemptyEcE.=1.1 eVfilledEvEvEcConductorSio, (Insulator)Si (Semiconductor)
Conduction bandEBand gapEEValence band Energy band diagram shows the bottom edge of conduction bandEc, and top edge of valence band, E, : E。 and E, are separated by the band gap energy, Eg
Dopants in SiliconSi: Si:SiSiSiSiB: Si:Si: As: Si:SiSi: Si: Si:Si: Si: Si: As, a Group V element, introduces conduction electrons and createsN-type silicon, and is called a donor.? B, a Group III element, introduces holes and creates P-type silicon.and is called an acceptor
Measuring the Band Gap Energy by Light AbsorptionelectronEcphotonsEgphoton energy: hv> EgEvOhole: E. can be determined from the minimum energy (hv) ofphotons that are absorbed by the semiconductor.Bandgap energies of selected semiconductorsSemi-DiamonsiGeGaPdInSbGaAsZnSeconductor62.70.180.671.121.422.25Eg (eV)
SiO2OxidationSiSiO,selectivelyetched1SiO2Lithography and EtchingSiDopant atomsintroduced into exposed siliconSiOlon ImplantationsiSiO2Annealing and DiffusionDopantatomsdiffuseinto SiSi
Oxidation Lithography and Etching Ion Implantation Annealing and Diffusion
Quartz tubeSiWafersFlowcontrollerH,O or TCE(trichloroethylene)Resistance-heatedfurnaceN
Si + O2 → SiO2Dry Oxidation :Si +2H,0 → SiO2 + 2H,Wet Oxidation :101200°CdryPREdry1100°℃1.01000°CdryUswetA900°Cdry0010000.111900°Cwet(100)LE0.01101001.00.1Oxidation time (hr)
EXAMPLE : Two-step Oxidation(a) How long does it take to grow 0.1um of dry oxide at 1000 oC ?(b) After step (a), how long will it take to grow an additional0.2um of oxide at 900 oC in a wet ambient ?
Lithography(c) Development(a) Resist CoatingPositive resistNegative resistPhotoresistOxide(b) ExposureSSi(d) Etching and Resist StripDeep Ultraviolet LightOpticalPhotomask withLens systemopaque andclear patterns
Lithography