handout 5 - Impurity Doping Overview Ion Implantation...

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1 Handout 5 EEL 5225, Fall 2009, H. Xie Fabrication Technology, Part I book Senturia, Ch. 3, pp. 38-42, Ch. 4, pp. 79-91 filetalltext3 head2right Agenda boxshadowdwn Impurity Doping boxshadowdwn Heat Treatment boxshadowdwn Example process flows 2 Handout 5 EEL 5225, Fall 2009, H. Xie Impurity Doping square4 Overview square4 Ion Implantation square4 Example Impurity Doping 3 Handout 5 EEL 5225, Fall 2009, H. Xie Impurity Doping – Overview square4 Typical Process square4 square4 Introduction of impurities via ion implantation square4 square4 Redistribution of impurities via heat treatment square4 Applications square4 Doping of p- and n- semiconductors square4 **Ion implant used almost exclusively compared to solid- gas-source diffusion square4 Precise dose/depth control glyph1197-type impurity glyph1197-type impurity glyph1197-type impurity P-type impurity diffusion 4 Handout 5 EEL 5225, Fall 2009, H. Xie Ion Implantation square4 Kinetic bombardment of impurities into semiconductor. +n A Ion current, I +n Projected range, R P Energy, E (keV) = T o dt nqA I Q Ref: S. A. Campbell, Science and Eng. of Micro. Fab. , 2001. Typical Implanter
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5 Handout 5 EEL 5225, Fall 2009, H. Xie square4 The total implant is the superposition of many of these individual stopping events Ion Implantation Distribution Ref: A. Doolittle Notes, Georgia Tech. p R p R Δ Δ R Wafer Surface Projected Range Vertical Straggle Lateral Straggle 6 Handout 5 EEL 5225, Fall 2009, H. Xie Ion Implantation Distribution square4 Key parameters square4 square4 Doping concentration levels square4 square4 , the average distance ion travels into wafer surface square4 the variation in projected range, both normal ( Δ R P ) and transverse ( ) square4 Model for impurity distribution glyph817 p : peak concentration (#/cm 3 ) Gaussian distribution: μ = R p , σ = Δ R p Δ = 2 2 ) ( 2 ) ( exp ) ( p p P R R x glyph817 x glyph817 Δ = 0 2 ) ( p P R glyph817 π dx x glyph817 Q Δ R 7 Handout 5 EEL 5225, Fall 2009, H. Xie Ion Implantation Depth square4 Projected range ( R p ) and straggle (sigma) (∆ R p ) for Si Ref. Campbell, p. 108. Note: 1000 Å = 100 nm = 0.1 μm 8 Handout 5 EEL 5225, Fall 2009, H. Xie Junction Formation square4 Junction depth, x j square4 Defined as depth into silicon surface where impurity concentration ( N A or N D ) equals background concentration ( N B ) For Implant: B p p j P j glyph817 R R x glyph817 x glyph817 = Δ = 2 2 ) ( 2 ) ( exp ) ( Note there may be two “real” junction depths: x glyph817 glyph817 B 0 x j1 x j2 p P R π Q glyph817 Δ = 2
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9 Handout 5 EEL 5225, Fall 2009, H. Xie Ion-Implant Example
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