Lec_12 - Professor N Cheung, U.C. Berkeley Lecture 12 EE143...

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Professor N Cheung, U.C. Berkeley Lecture 12 EE143 F2010 1 Vacuum Basics 1. Units 1 atmosphere = 760 torr = 1.013x10 5 Pa 1 bar = 10 5 Pa = 750 torr 1 torr = 1 mm Hg 1 mtorr = 1 micron Hg 1Pa = 7.5 mtorr = 1 newton/m 2 1 torr = 133.3 Pa 2. Ideal Gas Law: PV = NkT k = 1.38E-23 Joules/molecule –K = 1.37E-22 atm cm 3 /K N = # of molecules T = absolute temperature in K [Note] At T = 300 K ; kT = 3.1E-20 torr-liter 1
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Professor N Cheung, U.C. Berkeley Lecture 12 EE143 F2010 2 For mixture of non-reactive gases in a common vessel, each gas exerts its pressure independent of others. P total = P 1 + P 2 + … + P N (Total P = Sum of partial pressure) N total = N 1 + N 2 + … + N N P 1 V = N 1 kT P 2 V = N 2 kT ................... P N V = N N kT 3. Dalton’s Law of Partial Pressure
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Professor N Cheung, U.C. Berkeley Lecture 12 EE143 F2010 3 4. Average Molecular Velocity v = (8kT/ m) 1/2 where m = molecular weight of gas molecule 5. Mean Free Path of molecular collision = 1 2 d 2 o n where n = molecular density = N/V, d o = molecular diameter [Note] For air at 300 ーK, = 6.6 P(in Pa) = 0.05 P(in torr) with in mm Assumes Maxwell-Boltzman Velocity Distribution
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Professor N Cheung, U.C. Berkeley Lecture 12 EE143 F2010 4 6. Impingement Rate, = n v 4 = # of molecules striking unit surface /unit time. = 3.5 10 22 P mT in #/cm 2 -sec with P in torr, m in amu [Note] For air at 300 ーK ; (in #/cm 2 -sec) =3.8 10 20 P Example Calculation : Contamination from Residual Vacuum For a residual vacuum of 10 -6 torr, = 4 10 14 /cm 2 -sec If each striking molecule sticks to the surface, the equivalent deposition rate of the residual gas is ~ 1/3 of a monolayer of solid per second.
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Professor N Cheung, U.C. Berkeley Lecture 12 EE143 F2010 5 Pressure (Torr) Time to form a monolayer (sec) Impingment Rate (Molecules/cm 2 s) Mean free Path (mm) At 25 o C M I P 1 meter! m/min Vacuum Basics (Cont.) Residual Vacuum Plasma Processing CVD
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Professor N Cheung, U.C. Berkeley Lecture 12 EE143 F2010 6 Thin Film Deposition substrate film Applications: Metalization (e.g. Al, TiN, W, silicide) Poly-Si dielectric layers; surface passivation. Evaporation Sputtering Reactive Sputtering Chemical Vapor Deposition Low Pressure CVD Plasma Enhanced CVD Physical Methods Chemical Methods
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Professor N Cheung, U.C. Berkeley Lecture 12 EE143 F2010 7 (1) Evaporation Deposition Al film wafer Al vapor Al hot
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Lec_12 - Professor N Cheung, U.C. Berkeley Lecture 12 EE143...

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