Lecture 07 CVD and Oxidation

Lecture 07 CVD and Oxidation - 1 Dept of ECE Univ of Texas...

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CVD, Oxidation, and Diffusion Fundamentals of Micromachining Dr. Bruce K. Gale BIOEN 6421 EL EN 5221 and 6221 ME EN 5960 and 6960 Thin-Film Deposition Spin-on Films – Polyimide (PI), photoresist (PR) Spin-on glass (SOG) Physical Vapor Deposition (PVD) – Evaporation – Sputtering Chemical Vapor Deposition (CVD) – Oxidation – LPCVD – PECVD Dean P. Neikirk © 2001, last update February 2, 2001 1 Dept. of ECE, Univ. of Texas at Austin Thin film processes “grown” films typically “converted” from original substrate material example: SiO2 formed by oxidation of Si substrate “deposited” films crystalline, poly crystalline, amorphous electro-deposition not standard IC process liquid phase deposition not standard IC process vapor phase deposition PVD: physical vapor deposition CVD: chemical vapor deposition R. B. Darling / EE-527 Physical Vapor Deposition Gas Phase Gas Phase Condensed Phase (solid or liquid) Condensed Phase (usually solid) Evaporation Transport Condensation
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R. B. Darling / EE-527 Stages of Thin Film Growth Island Stage Coalescence Stage Channel Stage Continuous Film Stage R. B. Darling / EE-527 Modes of Thin Film Growth (1) Volmer-Weber: (island growth): (2) Frank-Van der Merwe: (layer growth; ideal epitaxy): (3) Stranski-Krastanov: (layers + islands): M. Volmer and A. Weber, Z. Phys. Chem. 119 , p. 277 (1926). F. C. Frank and J. H. Van der Merwe, Proc. R. Soc. London , Ser. A 198 , p. 205 (1949). J. N. Stranski and L. Krastanov, Ber. Akad. Wiss. Wien 146 , p. 797 (1938). Dean P. Neikirk © 2001, last update February 2, 2001 2 Dept. of ECE, Univ. of Texas at Austin Silicon Oxides: SiO 2 Uses: diffusion masks surface passivation gate insulator (MOSFET) isolation, insulation Formation: grown / “native” thermal: “highest” quality anodization deposited: C V D, evaporate, sputter vitreous silica: material is a GLASS under “normal” circumstances can also find “crystal quartz” in nature m.p. 1732 Û±&²±JODVV±LV±³XQVWDEOH´±EHORZ± 1710 Û±& BUT devitrification rate (i.e. crystallization) below 1000 Û±&±QHJOLJLEOH network former hydroxyl group network modifier silicon bridging oxygen non-bridging oxygen Thermal Oxidation of Silicon Formation of the oxide of silicon on the silicon surface is known as oxidation . Thermal Oxidation is characterized by high temperatures (900 - 1200 C) . Two main processes : Dry Oxidation Si(s) + O 2 --> SiO 2 1 atm , 1000 C Wet Oxidation Si (s) + 2H 2 O --->SiO 2 + 2H 2 Dry oxidation produces a better (more dense) oxide as compared to wet oxidation.
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Dean P. Neikirk © 2001, last update February 2, 2001 3 Dept. of ECE, Univ. of Texas at Austin in dry (<< 20 ppm H2O) oxygen Si + O 2 SiO 2 once an oxide is formed, how does this chemical reaction continue?
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