06_Oxidation=) - Oxidation Introduction Silicon Oxide...

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(Gan 2010/11) Oxidation Introduction Silicon Oxide Structure Oxidation Reaction and Kinetics Deal Grove Model Growth Rate Oxidation Parameters Oxide Charges Effects of Oxidation Readings: Plummer sections 6.1 - 6.6
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(Gan 2010/11) 10 nm 0.1 μm 1 μm 1 nm Masking Oxides Gate Oxides Tunneling Oxides Field Oxides Pad Oxides Chemical Oxides from Cleaning Native Oxides Thermally Grown Oxides Oxide Thickness Deposited Oxides Backend Insulators Between Metal Layers Masking Oxides Uses of Silicon Oxide Film passivation of surface states to physically protect devices insulating layers gate oxides interlayer dielectric (ILD) (insulator between layers of metallization) CMOS Non-volatile memory For implantation & doping Lateral isolation
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(Gan 2010/11) Si 3 N 4 tensile SiO 2 compressive to compensate for stress Si 3 N 4 acts as diffusion mask to prevent oxidation Thick (field) oxide grown for lateral isolation Active devices made here Lateral oxidation Selective oxidation Local Oxidation of Silicon (LOCOS)
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(Gan 2010/11) Thermally oxidized SiO 2 films on Si are amorphous Silicon atoms in center of tetrahedral surrounded by 4 oxygen atoms Basic unit of SiO 2 Structure of Silicon Oxide
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(Gan 2010/11) Amorphous SiO 2 always contains non-bridging O atoms, i.e. SiO 4 tetrahedra are only locally coordinated and do not have long range order If all the oxygen atoms are bridging, this would be crystalline quartz Structure of Silicon Oxide
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(Gan 2010/11) Silicon Silicon oxide Oxide layers grown on Si are in compressive stress (5x10 9 dyne cm -2 ) Large CTE mismatch between Si and SiO 2 generates additional stress during cool down These stresses place Si in tension, manifested as a measurable wafer bow Si/SiO 2 interface consists of a transition region (~ one atomic distance) Other than that, the interface is abrupt and quite flat Silicon Oxide / Silicon Interface
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(Gan 2010/11) Even though the interface looks structurally perfect, different electronic defects are present Defect density ~ 10 9 -10 11 cm -2 Related to incompletely oxidized Si, broken Si-O bonds or mobile ions (largely eliminated) Some are repairable through thermal anneal Silicon Oxide / Silicon Interface Silicon Silicon oxide
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(Gan 2010/11) Experimentally confirmed that oxidant (O 2 , H 2 O) diffuses through oxide to the reacting Si/SiO 2 interface, where: Si + O 2 -> SiO 2 or Si + 2H 2 O -> SiO 2 +2H 2 (rather than Si diffusing upwards and reacting with O at the surface) Oxidation Reaction Si atoms bonds in substrate are broken Oxygen atoms inserted between Si atoms Si-O bonds form Results in volume expansion due to inserted oxygen atoms
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(Gan 2010/11) 30% volume expansion during oxidation Constrained by substrate, volume expansion occurs as a larger thickness of SiO 2 compared to thickness of Si consumed 1 μm-thick of consumed Si will produce 2.2 μm-thick of SiO 2 Interface grows “into” the Si, although the surface is also being displaced from its original position because of the need to accommodate the volume expansion Volume Expansion 1 1 1.3 1 1 1 1.2 1 1 1 1.3 1.3 Si substrate Si substrate
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This note was uploaded on 02/21/2012 for the course MSE MS3002 taught by Professor Gancheelip during the Spring '12 term at Nanyang Technological University.

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06_Oxidation=) - Oxidation Introduction Silicon Oxide...

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