lecture_6_chex42

lecture_6_chex42 - Si Oxidation Si ! A method of forming...

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Si Si Oxidation Oxidation ! A method of forming SiO 2 which is used as Mask (e.g., for ion implantation) Oxide in MOSFETs Surface passivation ! Forms perfect Si-SiO 2 interface SiO 2 Si O Reaction takes place @ the Si-SiO 2 interface Oxidant diffuses through the SiO 2 film ) g ( ) s ( ) g ( ) s ( ) s ( ) g ( ) s ( H SiO O H Si SiO O Si 2 2 2 2 2 2 2 + → + → +
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Deal Deal - - Grove Model of Oxidation Grove Model of Oxidation Journal of Applied Physics Journal of Applied Physics 36 36 , 3770 (1965) , 3770 (1965) ! A model that treats oxidation process as a series of mass transfer resistances for the oxidant from the gas phase to the Si-SiO 2 interface. ! Valid for 700-1300 o C and oxide thickness > 300 Å. SiO 2 Si · · · P g , C g P s , C s C o C i δ d o
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Deal Deal - - Grove Model of Oxidation Grove Model of Oxidation Journal of Applied Physics Journal of Applied Physics 36 36 , 3770 (1965) , 3770 (1965) SiO 2 Si · · · P g , C g P s , C s C o C i δ d o ! At the gas-SiO 2 interface we invoke Henry’s law. Henry’s law is valid in absence of dissociation effects at the interface which implies that species moving through the interface is molecular s o HP C = Partial pressure of the oxidant source just above the SiO 2 surface; related to C s through ideal gas law kT P C g g = kT P C s s =
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Gas Phase Mass Transport Gas Phase Mass Transport ! In the gas phase b ax C dx C d D + = = 0 2 2 ! Boundary conditions δ ) C C ( a C C x @ C b C C x @ s g g s s = = = = = = 0 SiO 2 Si · · · P g , C g P s , C s C o C i δ d o ! If there was no mass transfer resistance in the gas phase P s =P g and the concentration at the surface would be g * HP C = x x=0 ! Solution s s g C x ) C C ( C + =
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lecture_6_chex42 - Si Oxidation Si ! A method of forming...

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