Lecture 03 Vacuum Systems

Lecture 03 Vacuum Systems - Fundamentals of Micromachining...

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Unformatted text preview: Fundamentals of Micromachining Vacuum Systems Outline Vacuum principles Vacuum pumps Vacuum materials and components Vacuum instrumentation Vacuum systems Uses of Vacuum in Microfabrication Rough Vacuum High Vacuum Ultra-High Vacuum wafer chucks evaporation surface analysis load locks ion implantation molecular beam epitaxy (MBE) sputtering reactive ion etching (RIE) low pressure chemical vapor deposition (LPCVD) Units of Pressure Measurement 1 atmosphere = 760 mm Hg = 760 torr 760,000 millitorr or microns 29.9213 in. Hg 14.6959 psi 1.01325 bar 1013.25 millibar 101,325 pascals (Pa) 407.189 in. H 2 O 33.9324 ft. H 2 O 1 Pascal = 1 N/m 2 1 Torr = 1 mm Hg 1 micron = 1 m Hg 760 mm Hg 33.93 ft H 2 O Vacuum Ranges Low or Rough Vacuum (LV) 760 to 10-3 torr High Vacuum (HV) 10-3 to 10-8 torr Ultra-High Vacuum (UHV) 10-8 to 10-12 torr Partial Pressures of Gases in Air at STP Gas Symbol Volume Percent Partial Pressure, Torr Nitrogen N 2 78 593 Oxygen O 2 21 159 Argon Ar 0.93 7.1 Carbon Dioxide CO 2 0.03 0.25 Neon Ne 0.0018 1.4 x 10-2 Helium He 0.0005 4.0 x 10-3 Krypton Kr 0.0001 8.7 x 10-4 Hydrogen H 2 0.00005 4.0 x 10-4 Xenon Xe 0.0000087 6.6 x 10-5 Water H 2 O Variable 5 to 50, typ. Ideal Gas Law - 1 V = volume of enclosure N = number of molecules N m = number of moles = N/N A n = particle density = N/V P = pressure T = absolute temperature k B = Boltzmanns constant = 1.381 x 10-23 J/K N A = Avogadros number = 6.022 x 10 23 particles/mole R = Gas constant = N A k B = 8.315 J/mole-K T nk P T Nk PV RT N PV B B m = = = Ideal Gas Law - 2 Historical Laws: Boyles Law: P 1 V 1 = P 2 V 2 at constant T Charles Law: V 1 /T 1 = V 2 /T 2 at constant P Gay-Lussacs Law: V = V (1 + T/ 273) Kinetic Gas Theory Velocity of a molecule is Mean square velocity is Pressure exerted on a wall in the x-direction is If velocities for all directions are distributed uniformly, Thus, Each molecular DOF has an average excitation of k B T/2. z v y v x v v z y x + + = r 2 2 2 2 z y x v v v v + + = 2 x x v nm P = 2 2 3 x v v = T nk v nm P B = = 2 3 1 T k v m B 2 3 2 2 1 = Distribution Functions - 1 Boltzmanns postulates for an ideal gas: The number of molecules with x-components of velocity in the range of v x to v x + dv x is proportional to some function of v x 2 only: The distribution function for speed v must be the product of the individual and identical distribution functions for each velocity component: z z vz y y vy x x vx dv v N dN dv v N dN dv v N dN ) ( ) ( ) ( 2 2 2 = = = z y x z y x z y x vz vy vx dv dv dv v v v dv dv dv v N dN ) ( ) ( ) ( ) ( 2 2 2 2 , , = = Distribution Functions - 2 A mathematical solution to the above equations has the form of ( A and v m are constants): Normalization of the distribution functions: 2 2 / 2 ) ( m x v v x Ae v = N v NA dv NAe dN m x v v vx...
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This note was uploaded on 11/16/2011 for the course MSE 5960 taught by Professor Douglas during the Fall '04 term at University of Florida.

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Lecture 03 Vacuum Systems - Fundamentals of Micromachining...

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