05_Ion Implantation=) - Ion Implantation Introduction...

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(Gan 2010/11) Ion Implantation Introduction Implant Profiles Masking Implants Stopping Powers Lattice Damage Annealing Readings: Plummer sections 8.1 - 8.6
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(Gan 2010/11) Introduction Dominant doping technique for Si IC Accurate control of number of dopant atoms (dose) into Si Large range of doses: 1 x 10 12 to 1 x 10 16 cm -2 atoms can be introduced MOS threshold voltage (V T ) control Dopant ions accelerated at high energy into Si will create large lattice damage Low temperature process – allows wider choice of mask materials
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(Gan 2010/11) Introduction Source of ions come from a solid source that is vaporized or gas source (e.g. arsine, phosphine, BF 2 ) Gas is ionized by energetic electrons from a hot filament or by a plasma discharge Ions are extracted by a voltage bias on a grid and mass analysed to select only one ion species Ions are accelerated towards wafer and buried in wafer Depth of implantation depends on acceleration voltage Typical implanters range from 30 to 200 keV High energy implants (in MeV) for deep wells in CMOS Ultra-low energy implants for shallow junctions (less than 100 nm)
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(Gan 2010/11) Implant Profiles Ion implantation is a random process High energy ions (1 to 1000 keV) bombard the Si substrate and lose energy through nuclear collisions with lattice and electronic drag forces Each ion follows a random trajectory with a range R On average, distribution of a large group of ions will peak at a projected depth R P below the wafer surface R P depends on energy of implant, higher energies give deeper range
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(Gan 2010/11) Gaussian Distribution Profiles described by a Gaussian distribution, with a projected range ( R P ) and standard deviation ( ' R P ) Heavier ions stop at shallower depth, e.g. Sb vs B Heavier ions with smaller range have a more narrow distribution 200 keV implants in crystalline Si
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(Gan 2010/11) R p - location of peak concentration of ions in the direction of implantation ' R p - distribution around R p is called the straggle R A - straggle normal to direction of implantation is called the transverse straggle Range & Straggle
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(Gan 2010/11) Concentration & Dose Number of ions implanted: where R P = average projected range normal to surface ' R P = standard deviation or straggle about that range C P = peak concentration where Gaussian is centred Total number of ions implanted, i.e. dose (in cm -2 ) ³ f dx x C Q )( ² ´ ¸ ¸ ¹ · ¨ ¨ © § ' ± ± 2 2 2 exp ) ( p p p R Rx Cx C pp CR Q ' µ S 2
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(Gan 2010/11) Range & Straggle
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(Gan 2010/11) Implant Profiles Monte Carlo simulations of random trajectories of a group of ions implanted at a spot (0,0,0) on the wafer shows 3-D spatial distribution of ions Side view shows R P and ' R P ¸ ¸ ¹ · ¨ ¨ © § ' ± A 2 2 2 exp ) ( ) , ( R y xCy x C vert Beam direction shows lateral straggle Two-dimensional distribution is assumed to be composed of the product of the vertical and lateral distributions 35 keV P implants
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(Gan 2010/11) Real Implant Profiles Blanket implants occur on whole wafer
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This note was uploaded on 02/21/2012 for the course MSE MS3002 taught by Professor Gancheelip during the Spring '12 term at Nanyang Technological University.

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05_Ion Implantation=) - Ion Implantation Introduction...

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