Ion Implantation and Synthesis of Materials - Studium

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234 15 Ion Implantation in CMOS Technology: Machine Challenges15.5.2 Impact of Endstation Design and Beam Scan MechanismThe choice of endstation design and the mechanism of beam scan can alsocompromise angle control. We consider several examples below.Wafer Rotation Effect on Multiwafer EndstationAll multiwafer implanters with adjustable disk tilt angle induce a systematic errorin ion beam angle due to geometric effects. When the disk is tilted to achieve thedesired tilt and/or twist, the resulting misalignment between the ion beam and theaxis of disk rotation results (under most circumstances) in a rotation of the waferas it is passed under the stationary ion beam. Additionally, the wafers are mountedon pedestals angled up a few degrees from the disk face in the direction of theincoming ion beam (to ensure adequate thermal contact for wafer cooling). Thenet result is that the wafer tilt and twist become functions of positions on the wafersurface. It is the disk rotation about an axis not parallel to the ion beam that causesthe tilt and twist angles to vary; the slow scan motion has no effect because it islinear. Since the tilt and twist angles are functions of positions only in the fast scandirection, the set of points on any disk radius will all have the same tilt and twistangles.Travel Path Length Effect for a Ribbon Beam on a Single-WaferEndstationIf a beamline utilizes symmetrical scanning, the distance traveled by the ion beamfrom the source to the wafer will be nearly independent of scan position.However, some modern implanters have highly asymmetric parallelizing magnets(see Fig. 15.15). As suggested by the figure, this architecture makes the distancetraveled by the beam vary considerably across the wafer. Were it not for the beamdivergence (see Sect. 15.3.1), this might not matter. We have seen that divergencecauses not only the beam diameter but also the angle of the ions at the edge of thebeam envelope to be functions of beam travel distance. Consequently, this type ofarchitecture causes beam density and potentially beam angle to vary horizontallyacross the wafer. This may result in across-wafer variations in deviceperformance, especially for implants near the amorphization threshold. The effectwill be most severe for the most divergent (i.e., lowest energy) ion beams.Implanters utilizing a fast-scanned beam with a one-dimensional mechanicalscan can be further divided into a vertical scan and a plane-of-wafer scan, seeFig. 15.16. In the former, the mechanical scan direction is always perpendicular tothe ion beam vector. In the latter, the mechanical scan direction is adjusted withthe wafer tilt, so that it is always in the plane of the wafer. It is clear that, for thecase of a zero-degree implant, the two methods are identical. However, for tiltedimplants, the vertical scan method results in the beam travel distance (and hencethe beam size in the case of highly divergent beams) becoming a function ofvertical position on the wafer. The degree of across-wafer variation increases with the
15.5 Angle Control 235Fig. 15.15. Illustration of how unequal travel paths through the scan magnet andparallelizing lens can lead to a large variation in beam size and beam divergenceFig. 15.16. A comparison of two different types of endstation motion. (a) A vertical scan(perpendicular to the beam) can result in different beam spot sizes on opposite edges of thewafer (the numbers here are for a 300 mm wafer) and (b) a plane-of-wafer (constant focallength) scan which exposes all points to the same size beamsine of the tilt angle. This type of variation does not occur for the plane-of-wafermethod; hence this method is referred to as the constant focal length method ofscanning. It improves the across-wafer reproducibility of the implant at theexpense of additional endstation complexity. The complexity occurs because thescan mechanism must be designed so that the scan direction can change withwafer tilt angle.
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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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128 10 Crystallization and Regrowth
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144 11 Si Slicing and Layer Transfe
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160 12 Surface Erosion During Impla
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180 13 Ion-Induced Atomic Intermixi
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182 13 Ion-Induced Atomic Intermixi
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Page 247 and 248: References 237No. of implants504540
Page 249 and 250: Appendix ATable of the Elementselem
Page 251 and 252: Appendix A 241elementatomicnumber(Z
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Page 265 and 266: Appendix BPhysical constants, conve
Page 267 and 268: IndexAlpha particle 8amorphization
Page 269 and 270: Index 259differential cross-section
Page 271 and 272: Index 261layer transfer 143Lennard-
Page 273: Index 263thermodynamiceffect ion be
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