Ion Implantation and Synthesis of Materials - Studium

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144 11 Si Slicing and Layer Transfer: Ion-Cut11.2 Formation of SOI by the Ion-Cut ProcessThe formation of silicon on insulator (SOI) by the Ion-Cut process consists of foursteps (a) hydrogen ion implantation into a Si wafer; (b) cleaning of the bondsurfaces; (c) bonding of the implanted wafer to another substrate, e.g., a SiO 2capped Si wafer; and (c) annealing of the bonded wafers. During the heattreatment, the implanted hydrogen evolves into highly pressurized H 2 gas bubbles,which grow in size and ultimately lead to a crack propagation throughout thewhole hydrogen-implanted silicon wafer. The process is illustrated in Fig. 11.1.Hydrogen is introduced into a single crystal silicon wafer by H-ion implantationto a well-defined depth. After the ion implantation, the surfaces of theimplanted silicon wafer and another silicon wafer capped with a silicon dioxidelayer (the so-called stiffener or handle wafer) undergo a modified RadioCorporation of America (RCA) clean – a surface cleaning process developed by theRCA). The cleaning step is necessary to remove surface contaminants introduced bythe H ion implantation process. The cleaning of the wafer surfaces prior to thebonding must be carried out very carefully to leave both surfaces free of particlesand organic contaminations. The cleaning procedure results in hydrophilic cleanoxide surfaces on both substrates. The substrate surfaces are then bonded together.When the two substrates are pressed together, interactions between water adsorbedFig. 11.1. Schematic illustration of the Ion-Cut process for the production of SOI
11.3 The Silicon–Hydrogen System 145on both surfaces lead to a weak bond the wafers. Next, the joined pair is heated toabout 200°C for a few hours to establish a strong chemical bond between the twowafers.After a strong bond strength between the wafers is achieved, the joined pairundergoes an anneal at elevated temperatures of typically 400°C. During this heattreatment, the implanted hydrogen atoms rearrange within the implantation zone,forming H 2 gas bubbles of high internal pressure. Raman spectroscopy experimentshave measured H 2 gas pressures of up to 50 kbar. The larger andenergetically more favorable gas bubbles grow in size at the expense of smallergas bubbles via Ostwald ripening. Finally, at a critical anneal duration or annealtemperature, the H 2 gas bubbles coalesce and lead to the propagation of a crackthrough the whole silicon crystal. In the final step, the Ion-Cut surface is polishedslightly to remove the damaged layer that resulted from the H ion-irradiationprocess.The development of Ion-Cut provides for the first time a methodology forproducing ultra thin silicon layers that are required for state-of-the-art devices.Over the last two decades, SOI technology has relied on two methods known aswafer-bonding and etch-back SOI, or BESOI, and separation by implantation ofoxygen, or SIMOX. The Ion-Cut process offers many benefits over BESOI andSIMOX. Because in Ion-Cut the electrically insulating oxide layer is thermallyproduced, the buried oxide layer is of high quality and uniform thickness. The SOIstructure is produced in one step without the need for costly grinding or etchback.Furthermore, the hydrogen-induced fracturing of the silicon wafer leaves anextremely uniform, nearly defect-free silicon layer bonded to the handle wafer,requiring only a moderate polish to achieve the 0.1–0.2 nm rms (root meansquare) roughness necessary for further processing. The thickness of the exfoliatedsilicon layer is highly uniform. In addition, the silicon wafer, from which thehydrogen implanted layer is exfoliated, can be reused.11.3 The Silicon–Hydrogen SystemThe physics and chemistry of hydrogen in silicon has been the subject ofconsiderable scientific and technological interest for more than three decades. Thisinterest has been driven by the omnipresent appearance of hydrogen in siliconprocessing, which always leads to either intentional or unintentional hydrogenincorporation into the substrate. Importantly, this hydrogen may strongly alter theelectrical characteristics of the resultant device by diffusion into active regionsand passivation of the dopant. Attention has been focused primarily – although notexclusively – on the diffusion of atomic hydrogen, its molecule formation, and itscomplex formation with and passivation of dopant impurities.The diffusion of H in Si is complex due to the presence of several charge statesand the fact that hydrogen is often present in different forms; it can be atomic,molecular (or larger clusters), or bound to a defect or impurity. The probability ofthe formation of these different forms depends on the defect and impurityconcentration in the material and the hydrogen concentration itself. Thus, 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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Page 104 and 105: 94 8 Channeling1.00.8Non-aligned Im
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Page 118 and 119: 108 9 Doping, Diffusion and Defects
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194 14 Application of Ion Implantat
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15 Ion Implantation in CMOS Technol
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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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Ion Implantation and Synthesis of Materials - Studium

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