5a - CVD, Oxidation, and Diffusion Himanshu J. Sant...

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Fundamentals of Microfabrication CVD, Oxidation, and Diffusion Himanshu J. Sant Fundamentals of Microfabrication Fundamentals of Microfabrication 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
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Fundamentals of Microfabrication Critical Parameters • Thin film quality – Composition and defects • Stresses • Uniformity • Step coverage • Time • Processing conditions – e.g. temperature • Application – e.g. etch mask • Ideal deposition method? Fundamentals of Microfabrication 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. • Why?
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Fundamentals of Microfabrication Dry Oxidation Limitations • The ratio of Si thickness converted (Xs), to resulting oxide thickness (Xox) ~ density diff. – Xs=0.46 Xox – Volume mismatch, thermal expansion difference • Large compressive stress • Limited thickness • Wet oxidation relaxes and has faster growth rate – Bad against alkali diffusion, not for ICs Fundamentals of Microfabrication Growth Rates
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Fundamentals of Microfabrication Chemical Vapor Deposition (CVD) • CVD = formation of non-volatile solid film on substrate by reaction of vapor phase chemicals – Diffusive-convective transport of depositing species to a substrate with many intermolecular collisions-driven by a concentration gradient – Surface reactions Fundamentals of Microfabrication Low Temperature Oxidation of Silicon • (LTO) SiO 2 is formed using three types of CVD Processes. – APCVD ( Most commonly used method ), LPCVD and PECVD SiH 4 + O 2 : ----->SiO 2 + 2H 2 (240 - 550 C) • (200 - 500 nm/min optimal) and (1400 nm/min possible). • Deposition rate increases slowly with increased T (310- 450 C) • Deposition rate can also be increased by increasing the O 2 /SiH 4 ratio • APCVD : 325 C ratio 3:1 , 475 C ratio 23:1 , 550 C ratio 60: 1 • LPCVD : 360 C ratio 1:1 , 450 C ratio 1.45 : 1 • Deposition can occur in the APCVD as low as 130 C • For LPCVD Window (100 - 330 C ) 2-12 torr and 14 nm/min at 300 C
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Fundamentals of Microfabrication PECVD • SiH 4 + 2N 2 O: SiO 2 + 2N 2 + 2H 2 (200- 400 C) , RF, 0.1 - 5 torr . • Low ratio of N
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This note was uploaded on 09/02/2010 for the course MEEN 5050 taught by Professor Himanshuj.sant during the Spring '10 term at University of Utah.

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5a - CVD, Oxidation, and Diffusion Himanshu J. Sant...

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