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Ion Implantation and Synthesis of Materials - Studium

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170 12 Surface Erosion During <strong>Implantation</strong>: SputteringN AJ BJ AJ iDepthSurfaceR pFig. 12.8. A model for the buildup <strong>of</strong> implanted concentration as a function <strong>of</strong> implantationdose. Assuming a very efficient atomic mixing, this model approximates the implantedpr<strong>of</strong>ile with a constant shape, but with an increasing amplitude. The rate <strong>of</strong> increase <strong>of</strong> theimplanted concentration is due to the difference between the flux <strong>of</strong> incident ions <strong>of</strong> speciesA, J i , <strong>and</strong> that <strong>of</strong> the sputtered particles <strong>of</strong> species A, J AJJBAx= Yir + xr= YJir + x(12.18)(12.19)Substituting (12.7) <strong>and</strong> (12.8) into (12.6), yieldsd ⎛ x ⎞xR = −d⎜1 +⎟N J YJt ⎝ x⎠r + xp 0 i i{}.(12.20)Where N 0 ≡ N A + N B . After some rearrangement, (12.20) becomesr + x1d x = (d φ2A ),(1 + x) [ r + (1 − Y) x]NR0P(12.21)where dφ A ≡ J i dt is the incremental ion dose. Equation (12.21) is a differentialequation for x(φ A ), which can be solved by taking the partial fractions for the lefth<strong>and</strong>side <strong>and</strong> integrating. The result is⎡ Ax ⎛ 1 + x ⎞⎤YφAY+ Bln⎜⎟=⎢⎣1 + x ⎝1 − x/ x( ∞)⎠⎥⎦N0RP(12.22)

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