Lecture_6_oxidation

Lecture_6_oxidation - Thermal Oxidation of Silicon Lecture...

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Unformatted text preview: Thermal Oxidation of Silicon Lecture 6 IH2655 SPRING 2009 Mikael stling KTH Thermal oxidation of silicon Applications Properties and fabrication Linear parabolic model Extensions of model Masking properties Defects in SiO 2 Characterization IH2655 SPRING 2009 Mikael stling KTH (Plummer Fig 6-1 p. 288) Equivalent oxide thickness t ox : Thickness of arbitrarily oxide re-calculated to corresponding SiO 2 thickness Applications of thermally grown oxides Field oxide for isolation (e.g. LOCOS) Pad, screen and masking oxides during implant, diffusion, etc Tunneling oxides in EEPROM (flash memories) Gate oxides in MOS: Today's production around 30 in 180 nm CMOS For passive devices: Capacitor dielectric in DRAMs IH2655 SPRING 2009 Mikael stling KTH Basic Properties of SiO 2 Usually thermally-grown SiO 2 is amorphous Melting point: 1700 C Mass density: 2.27 g/cm 3 Molecular density: 2.2 10 22 /cm 3 Refractive index n=1.46 Dielectric constant 3.9 High K EOT IH2655 SPRING 2009 Mikael stling KTH Easily selectively etched using lithography Mask most common impurities (B, P, As, Sb) Excellent Insulator ( > 10 16 cm, E g > 9 eV) High breakdown field (>10 7 V/cm) Stable bulk electric properties(>900 C, > 10-9 Torr) Stable and reproducible interface with Si Basic Properties of SiO 2 IH2655 SPRING 2009 Mikael stling KTH 0.8 nm Gate Oxide Ion Implantation Mask Isolation Back-end Insulators Low k IH2655 SPRING 2009 Mikael stling KTH SiO 2 Structure Classification Crystalline: Quartz, etc. Amorphous Quartz Made up of Si O tetrahedron Silicon atom lies in the tetrahedral center and oxygen atoms at the four vertices Tetrahedrons are connected by Si-O-Si Oxygen atoms connected two silicon atoms are called bridging oxygen or oxygen bridge IH2655 SPRING 2009 Mikael stling KTH Tetrahedron Bridging Oxygen Non-bridging Bridging Structure 0.262nm 0.262nm 0.162nm IH2655 SPRING 2009 Mikael stling KTH Doped SiO 2 IH2655 SPRING 2009 Mikael stling KTH SiO 2 Application in IC STI IH2655 SPRING 2009 Mikael stling KTH Properties of SiO 2 from different fabrication methods IH2655 SPRING 2009 Mikael stling KTH Overall Oxidation Reaction 9 Both reactions happen at 700 ~1200 C 9 Steam Oxidation is about 10 times faster than Dry Oxidation Si(s) + O 2 (g) SiO 2 (s) Si(s) + 2H 2 O(g) SiO 2 (s) + 2H 2 (g) z Dry Oxidation z Wet/Steam Oxidation IH2655 SPRING 2009 Mikael stling KTH Oxide Growth Consuming Si Volume Expansion (~ 2.2 times) 1- m-thick SiO 2 consumes 0.45 m Si SiO 2 suffers from stress IH2655 SPRING 2009 Mikael stling KTH Basic reactions: Dry oxidation: Si(s) + O 2 (g) SiO 2 (s) Wet oxidation: Si(s) + 2H 2 O SiO 2 (s) + 2H 2 (g) Oxidation by inward diffusion of oxidant through the growing oxide to the interface (Wolf Fig 3 p 202) Very good adhesion to Si leads to volume expansion upwards compressive stress in SiO 2 IH2655 SPRING 2009 Mikael stling KTH In LOCOS, SiO 2 volume is 2.2 times larger than that of oxidized Si IH2655 SPRING 2009...
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Lecture_6_oxidation - Thermal Oxidation of Silicon Lecture...

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