Lec8p.SurfaceMicromachiningI

Lec8p.SurfaceMicromachiningI - EE 245: Introduction to MEMS...

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EE 245: Introduction to MEMS Lecture 8: Surface Micromachining I CTN 9/22/09 Copyright © 2009 Regents of the University of California EE C245 : Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 66 Diffusion Modeling EE C245 : Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 67 Diffusion Modeling (cont.) EE C245 : Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 68 Diffusion Modeling (Predeposition) EE C245 : Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 69 Diffusion Modeling (Limited Source)
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EE 245: Introduction to MEMS Lecture 8: Surface Micromachining I CTN 9/22/09 Copyright © 2009 Regents of the University of California EE C245 : Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 70 Diffusion Modeling (Limited Source) EE C245 : Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 71 Two-Step Diffusion Two step diffusion procedure: ª Step 1 : predeposition (i.e., constant source diffusion) ª Step 2 : drive-in diffusion (i.e., limited source diffusion) For processes where there is both a predeposition and a drive-in diffusion, the final profile type (i.e., complementary error function or Gaussian) is determined by which has the much greater Dt product: (Dt) predep »(Dt ) drive-in Ö impurity profile is complementary error function (Dt) drive-in »(Dt ) predep Ö impurity profile is Gaussian (which is usually the case) EE C245 : Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 72 Successive Diffusions For actual processes, the junction/diffusion formation is only one of many high temperature steps, each of which contributes to the final junction profile Typical overall process: 1. Selective doping ( Implant effective (Dt) 1 = ( Δ R p ) 2 /2 (Gaussian) ( Drive-in/activation D 2 t 2 2. Other high temperature steps ( (eg., oxidation, reflow, deposition) D 3 t 3 , D 4 t 4 , … ( Each has their own Dt product 3. Then, to find the final profile, use in the Gaussian distribution expression. () i i i tot t D Dt = EE C245 : Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 73 The Diffusion Coefficient (as usual, an Arrhenius relationship) = kT E D D A
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EE 245: Introduction to MEMS Lecture 8: Surface Micromachining I CTN 9/22/09 Copyright © 2009 Regents of the University of California EE C245 : Introduction to MEMS Design LecM 4 C. Nguyen 8/20/09 74 Diffusion Coefficient Graphs Substitutional & Interstitialcy Diffusers Interstitial Diffusers ª Note the much higher diffusion coeffs. than for substitutional
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This note was uploaded on 10/30/2010 for the course C 218 taught by Professor Clarknguyen during the Fall '09 term at Berkeley.

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Lec8p.SurfaceMicromachiningI - EE 245: Introduction to MEMS...

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