Ion Implantation and Synthesis of Materials - Studium

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166 12 Surface Erosion During Implantation: SputteringY A (0), to values of N sA ( ∞)and Y sA ( ∞ ) , which occurs at times sufficient toachieve steady state.At the start of sputtering, t = 0, (12.13) takes the formbbA(0) A(0)A= r = rsbB(0) B(0)BY N NY N N(12.14)When steady state conditions have been achieved, conservation of mass requiresthat the ratio of partial yields equals the bulk concentration ratioYA( ∞ ) =Y ( ∞)BNNbAbB(12.15)For example, if there is preferential sputtering where r > 1, the sputtering yield ofA is greater than that of B, and the surface will be enriched in B. This enrichmentproduces an increase in the sputtering yield of B (more B atoms) and a decreasein the sputtering yield of A (fewer A atoms). As the process continues withmacroscopic amounts (greater than 10 nm) of material removed, the increasedconcentration of B balances out the preferential sputtering of A. Therefore, atsteady state the surface concentration ratio will differ from that of the bulk ratiowhen r ≠ 1.sAsBbAbBN ( ∞ ) 1 N =N ( ∞)r N(12.16)That is, the surface composition will be rearranged so that the total sputteringyield gives the bulk composition despite differences in yields of the individualatom species.12.4.2 Composition ChangesAn example of the change in composition of a silicide layer is shown in Fig. 12.5for PtSi that was sputtered with 20 keV argon ions and then analyzed with2 MeV 4 He ions. The Rutherford backscattering spectrum shows an enrichment ofthe Pt concentration in the surface region. The ratio of Pt/Si increased from thevalue of unity associated with that of the bulk to a value near two in the surfaceregion. The increased concentration of Pt at the surface occurs because the partial
12.4 Sputtering of Alloys and Compounds 167Fig. 12.5. RBS spectrum of a PtSi film after sputtering with 20 keV Ar ions. The shadedportion in this Pt signal indicates an increase in the concentration of Pt in the near surfaceregion as a result of the enhanced Si sputtering (from Liau and Mayer 1978)Fig. 12.6. Dose dependence of the partial sputtering yields of Si and Pt emitted from PtSifor 40 keV AR bombardment (from Liau and Mayer 1980)sputtering yield of Si is greater than that of Pt, Y Si > Y Pt . Figure 12.6 shows thepartial yields as a function of argon ion dose. At low bombardment doses thesputtering yield of Si is significantly greater than that of Pt and at the onset ofsputtering the yield ratio is Y Si (0)/Y Pt (0) = 2.4. As the bombardment proceeds, the
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M. Nastasi J.W. MayerIon Implantati
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To our loved ones
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xContents4 Cross-Section ..........
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Contentsxiii14.3.2 Punch-Through St
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2 1 General Features and Fundamenta
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10 1 General Features and Fundament
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12 2 Particle InteractionsThe restr
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142 Particle Interactions(a)V(r)r 0
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162 Particle InteractionsHowever, a
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182 Particle Interactionswhere the
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202 Particle Interactionsa0.8853a0L
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3 Dynamics of Binary Elastic Collis
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3.3 Kinematics of Elastic Collision
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3.4 Center-of-Mass Coordinates 27Fi
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3.4 Center-of-Mass Coordinates 29an
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3.5 Motion under a Central Force 31
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3.5 Motion under a Central Force 33
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Problems 35The reduced energy for 1
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4 Cross-Section4.1 IntroductionIn C
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4.2 Scattering Cross-Section 39unit
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4.2 Scattering Cross-Section 41Rdθ
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4.3 Energy-Transfer Cross-Section 4
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4.4 Approximation to the Energy-Tra
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Problems 47ReferencesNastasi, M., M
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5 Ion Stopping5.1 IntroductionWhen
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5.3 Nuclear Stopping 51MeV mg −1
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5.3 Nuclear Stopping 531−m1−2mC
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5.4 ZBL Nuclear Stopping Cross-Sect
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5.5 Electronic Stopping 575.5.1 Hig
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5.5 Electronic Stopping 59Table 5.1
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Problems 61Problems5.1 Calculate th
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64 6 Ion Range and Range Distributi
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78 7 Displacements and Radiation Da
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94 8 Channeling1.00.8Non-aligned Im
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96 8 ChannelingMeV ION BEAMSUBSTITU
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98 8 ChannelingThe channeling effec
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100 8 Channeling4.0Silicon2.0P (mic
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102 8 ChannelingdσσD( ψc) = ∫
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104 8 ChannelingDechanneled fractio
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106 8 ChannelingProblems8.1 Calcula
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108 9 Doping, Diffusion and Defects
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Page 126 and 127: 116 9 Doping, Diffusion and Defects
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15.2 Implanters Used in CMOS Proces
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15.3 Low Energy Productivity: Beam
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15.5 Angle Control 233Fig. 15.13. O
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15.5 Angle Control 235Fig. 15.15. I
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References 237No. of implants504540
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Appendix ATable of the Elementselem
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Appendix A 241elementatomicnumber(Z
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Appendix A 243element atomicnumber(
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Appendix BPhysical constants, conve
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IndexAlpha particle 8amorphization
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Index 259differential cross-section
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Index 261layer transfer 143Lennard-
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Index 263thermodynamiceffect ion be
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