NEEP 541

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NEEP 541 Sputtering

• Fall 2002
• Jake Blanchard

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Outline

• Sputtering
• Definitions
• Models
• Sample Data
• Angle of Incidence
• Correlations

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Definitions

• Sputteringejection of atoms from solid surface
  under bombardment by energetic ions
• Measured as recession rate of surface (m/s)

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Schematic of Process
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Modeling

• Determine scattering cross section
• Determine amount of energy deposited near surface
• Convert energy to density of recoils near surface
• Determine number of recoils which reach surface
• Compare energy to binding energy

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Modeling

• Use inverse power law potentials

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Modeling
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Sigmund Theory

• Assume sputtering is proportional to energy
  deposited (FD) near surface
• Hence, sputtering is proportional to stopping
  power near surface

Angle of incidence
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Stopping and Sputtering Distributions Kr on Cu
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Modeling

• Let Gd3vdx be the average number of atoms
  moving at time t with velocity v in the layer
  between x and xdx

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Modeling

• Expand in Legendre polynomials
• Take moments
• Separate elastic and inelastic collisions
• Neglect Ed
• Use only leading terms

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Result

• ? depends on m, incidence angle, and on mass ratio

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Copper Target
E (keV)
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Z1 Dependence
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He on ??
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Tungsten Self-Sputtering
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Mass Ratio Dependence
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Angle of Incidence

• Empirically, the dependence of sputtering on the
  angle of incidence is

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Ar on Copper
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Copper Target
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Empirical Correlation
threshold
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Empirical Correlation
C. Garcia-Rosales, Revised Formulae for
Sputtering Data, J. Nuc. Mat., 218, 1994, p. 8.
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Some Data
Incident Target Eth U0
He Pb 40 2
Ar Pb 45
He Ag 45 3
Ne Ag 45
Ar Ag 23
Kr Ag 85
Ar Cu 34 3.5
Kr Cu 56