VLSI_Class_Notes_6_2010

VLSI_Class_Notes_6_2010 - EEL 5322 W.R. Eisenstadt -1- VLSI...

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EEL 5322 W.R. Eisenstadt - 1 - VLSI Class Notes Fall 2010, Class 6 Homework #5 Problem Due Sept 13, 2010, Problem 4.8 Jaeger Read Jaeger 3.1, 3.1 and 3.3 Lecture discussion : Successive Diffusion, Sheet Resistance Two-Step Diffusion, A short constant-source diffusion followed by a long thermal cycle is considered a two-step diffusion process. Constant source step is call the pre-deposition, the long thermal cycle is called the drive-in. Typically, Dt of the drive-in is >> than Dt of the pre-deposition, Then, the final diffusion profile is roughly Gaussian. Successive Diffusions: May thermal cycles occur during wafer processing. By multiplying the diffusion coefficient by the temperature we have the Dt which we can sum for the IC process steps. ( ) i i total i Dt Dt = (1.1) Solid-Solubility Limits: As temperature increases there is an upper amount of a dopant or impurity that the Silicon crystal will accept. This is the solid-solubility limit. This is shown in Jaeger Fig 4.6. At high concentrations only a fraction of the dopants are
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VLSI_Class_Notes_6_2010 - EEL 5322 W.R. Eisenstadt -1- VLSI...

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