PHYSICAL VAPOR DEPOSITION (PVD PVD II: Evaporation ◆ We saw oⅴD Gas phase reactants: po l mTorr to l atm Good step coverage, T> 350 K ◆ We saw sputtering Noble (+ reactive gas)p 10 mTorr; ionized particles Industrial process high rate reasonable step coverage Extensively used in electrical, optical, magnetic devices Now see evaporation: Source material heated, Peg, vap. 10- Torr, Pg 10- Torr Generally no chemical reaction(except in "reactive depos'n n=10s of meters. Knudsen number n >>1 Poor step coverage, alloy fractionation: 4 pvapor Historical(optical, electrical Campbell, Ch 12 is more extensive than Plummer on evaporation 6.152J3.155J
6.152J/3.155J 1 PHYSICAL VAPOR DEPOSITION (PVD) PVD II: Evaporation We saw CVD Gas phase reactants: pg ≈ 1 mTorr to 1 atm. Good step coverage, T > 350 K We saw sputtering Noble (+ reactive gas) p ≈ 10 mTorr; ionized particles Industrial process, high rate, reasonable step coverage Extensively used in electrical, optical, magnetic devices. Now see evaporation: Source material heated, peq.vap. =~ 10-3 Torr, pg < 10-6 Torr Generally no chemical reaction (except in “reactive depos’n), λ = 10’s of meters, Knudsen number NK >> 1 Poor step coverage, alloy fractionation: ∆ pvapor Historical (optical, electrical) Campbell, Ch. 12 is more extensive than Plummer on evaporation
Standard vacuum chambers 1≈106Tor(1.3×104N Mostly H,O, hydrocarbons, N, He by residual gas analySis(RGa=mass spec 6.152J3.155J
6.152J/3.155J 2 Standard vacuum chambers Σpi ≈ 10-6 Torr (1.3 × 10-4 N / m2) Mostly H2O, hydrocarbons, N2 He by residual gas analysis (RGA = mass spec.)
Ultra-high vacuum chambers p<10-8 Torr demands Stainless steel chamber Bakeable to150°C Turbo, ion, cryo pumps 6.152J3.155J
6.152J/3.155J 3 p < 10-8 Torr demands: Stainless steel chamber Bakeable to 150oC Turbo, ion, cryo pumps Ultra-high vacuum chambers
Knudson number≈1 0.01cm P=10-10 106 10 10-2 100Torr 23 Log[n(#/m5)] 21 I At 0.1MP 760mm 14 lb/in2 Sputtering CVD 15 vaporation Log[P(N/m2) Ballistic. molecular flOw AL>> Generally /L<I High purity films Films less pure Epita Epitaxy is rare 6.152J3.155J
6.152J/3.155J 4 -6 -4 -2 0 2 4 Log[P (N/m2)] 25 23 Log[n (#/m3)] 21 19 17 15 λ = 10 0.01 cm p = 10-10 10-8 10-6 10-4 10-2 100 Torr 1 Atm= 0.1 MPa 760 mm ≈14 lb/in2 Generally λ/L < 1 Films less pure Epitaxy is rare Evaporation Ballistic, molecular flow, λ/L >> 1 High purity films Epitaxy Sputtering CVD Knudson number ≈ 1
Atomic flux on surface due to residual gas atoms nv 2k T area. t 2k V zm, t Given 10-b Torr of water vapor room temp, find flux latm 10'P p=10°Tor 760t atm kgT(R7)=0.025eV=4×102J P=1.3×10-4 18 3×10kg J=4.8x104atoms/molecules cm sec What is atomic density in I monolayer(MD) of Si? N=5x1022cm3=1.3x1015cm So at 10-6 Torr, 1 ML of residual gas hits surface every 3 seconds Epitaxy requires slow deposition, surface mobility So you must keep pressure low to maintain pure film 6.152J3.155J
6.152J/3.155J 5 Atomic flux on surface due to residual gas J atoms area ⋅ t = nv x 2 = p 2kBT 2kBT πm = p 2πmkBT = J Given 10-6 Torr of water vapor @ room temp, find flux p =10−6Torr × 1atm 760 T × 105Pa atm , kBT RT ( )= 0.025eV = 4 ×10−21 J p =1.3×10−4 N m 2 mH2O = 18 NA = 3×10−26 kg What is atomic density in 1 monolayer (ML) of Si? N = 5 x 1022 cm-3 => 1.3 x 1015 cm-2. So at 10-6 Torr, 1 ML of residual gas hits surface every 3 seconds! Epitaxy requires slow deposition, surface mobility, So you must keep pressure low to maintain pure film J = 4.8 ×1014 atoms/molecules cm2sec