6.152J/3.155J What does Materials Science have to do with Microelectronic Processing? Need to understand DIfferences: metals, oxides and semiconductors Atomic bonding Oxidation rates, compound formation(GaAs) chemical reactions Solubility of Impurities In SI ChemIcal reactlons for CVD precursors, byproducts Need to understand Gas concentration(critical to CVD reaction rates) Gas diffusivity. Surface mobilIty (key to quallty film growth) Solid-state What controls Interfaces(e.g. SIO/Al diffusion crystal growth, and Impurities How manage grain growth, film mlcrostructure Electrical, mechanical properties depend on all of the above Wed, Sept. 10, 2003 Vacuum Technology and fllm growth (poly-Gate p-MOSFET) P++ Poly Diffusion Poly Si Resistor All layers above n-type SI made by CVD except gate oxide and Al 6.152J3.155 Wed, Sept 10, 2003
6.152J/3.155J 6.152J/3.155J 1 What does have to do with Microelectronic Processing? • Need to understand Di l i i i i i l ili i iti i i i l i s • Need to understand i iti l i ili li il ls i iO2 l) l i iti i il i Electrical, mechanical properties depend on all of the above chemical reactions Gas diffusivity, Solid-state diffusion Wed., Sept. 10, 2003 Materials Science fferences: meta s, ox des and sem conductors Ox dat on rates, compound format on (GaAs) So ub ty of mpur es n S Chem ca react ons for CVD precursors, byproduct Gas concentrat on (cr ca to CVD react on rates) Surface mob ty (key to qua ty f m growth) What contro nterfaces (e.g. S /A crysta growth, and mpur es How manage gra n growth, f m m crostructure Atomic bonding, Vacuum Technology and film growth ( FET) Al n Diffusion Resistor Poly Si Resistor Al Al P ly P ly p- Implant poly-Gate p-MOS -Si ++ Po ++ Po All layers above n-type Si made by CVD except gate oxide and Al 6.152J/3.155J Wed., Sept. 10, 2003 2 1
6.152J/3.155J What will we cover in next few lectures? Chemical vapor deposition(CVD) Mon. Sept 15 Most widely used method for growth of mlcro-electronlc grade semIconductor fiim also widely used for metals and oxides Oxidatio Wed. Sept 17 Key advantage of SE: stable uniform oxide How control Its growth, thickness, quallty Diffusion and ion implantation Mon. Sept 29 How semIconductor surfaces are doped Wed. Oct. 1 Physical vapor deposition(PVD) Nov 5.12 Growth of quallity films by sputter deposltlon or evaporation These processes take place in vacuum or controlled environment Therefore, need to understand vacuum technology,. gas kinetics. 6.152J3.155J Wed, Sept 10, 2003 Gas Kinetics and Vacuum Technology How far does a molecule travel between collisions? m 5x 10-26 k velocity molecule mpact parameter, scattering cross section T d2 Mean free path=x Volume swept out by 1 molecule between collisions=λxd 6.152J3.155 Wed, Sept 10, 2003
6.152J/3.155J 6.152J/3.155J 3 What will we cover in next few lectures? • Chemical vapor deposition (CVD) i l mi l i i il al i l l i • Oxidation Wed. Sept 17 i l i i l i i li vacuum technology,… gas kinetics. • Diffusion and ion implantation i Wed. Oct. 1 • Nov 5,12 li il iti i Wed., Sept. 10, 2003 Mon. Sept 15 Most w de y used method for growth of cro-e ectron c grade sem conductor f ms, so w de y used for meta s and ox des Key advantage of S : stab e un form ox de How contro ts growth, th ckness, qua ty These processes take place in vacuum or controlled environment. Therefore, need to understand Mon. Sept 29 How sem conductor surfaces are doped Physical vapor deposition (PVD) Growth of qua ty f ms by sputter depos on or evaporat on 6.152J/3.155J 4 i i l l l l llisi “Movie” d d l le i i i p d2 => l p d 2 Volume swept out by 1 molecule lpd2 i l V 2) L velocity “Snap shot” n = N V = N L3 m 5 x 10-26 kg Wed., Sept. 10, 2003 Gas K net cs and Vacuum Techno ogy How far does a mo ecu e trave between co ons? Mean free path ≡ l mo ecu mpact parameter, scatter ng cross sect on = between collisions = Cons der a vo ume of gas (e.g. N number N, 2
6.152J/3.155J Gas Kinetics Volume swept out by 1 molecule ⊥3=VNrd2 More accuratelyλ deal gas: pV=NkB T, k T 6.152J3.155J Wed, Sept. 10, 2003 What is flux of atoms hitting surface per unit time? ea J(#/ area time)=s Analogous to current density related to pressure(elec field We need v. v Calculating gas velocitie Maxwell speed distribution Po)-adl2m- vexpl-2T v=vP()d 6.152J3.155 Wed, Sept. 10, 2003
6.152J/3.155J 6.152J/3.155J 5 Total volume of sample L3 = V N lpd 2 \l = V Npd2 = 1 npd2 (n = N V ) More accurately l = 1 2 npd 2 Ideal gas: pV = NkBT, n=p / kBT => \l = kB T 2pd2 p l p d 2 Volume swept out by 1 molecule between collisions = lpd 2 i i p l (cm) 1 atm 10-5 10-2 1 mT 10 Wed., Sept. 10, 2003 Gas K net cs 1 Torr 6.152J/3.155J 6 What is flux of atoms hitting surface per unit time? area # / vol. vx J / nvx 2 related to pressure (elec. field) vx , v speed P(v) vvms v v = Ú vP(v)dv Maxwell speed distribution: P(v) = 4p m 2pkT È Î Í ˘ ˚ ˙ v 2 exp - mv 2 2kT È Î Í ˘ ˚ ˙ vrms = 3kT m v = 8kT pm v , x = 2kT pm vrms ≈ 500 m/s v x = v /2 Wed., Sept. 10, 2003 ( # area time) = Analogous to current density, Calculating gas velocities We need 3/ 2 3
6.152J/3.155J So flux of atoms hitting surface per unit time k T DImensional analysts: (force/area- en/vol ) p- vol =n——=Jmv Numerically,-35×l02 Tom)(atos/ sec) This gives a flux 1 monolayer (ML) arriving per sec at 10-6 Torr 6.152J3.155J Wed, Sept. 10, 2003 Diffusivity ooO Recall for solids: Debye 101351 For gas, no energy barrier, just collisions. recall 2=- kT much weaker T-dep than In solld 6.152J3.155J Wed, Sept. 10, 2003
6.152J/3.155J 6.152J/3.155J 7 So flux of atoms hitting surface per unit time area # / vol. vx Jx = nvx 2 = n 2 2kT pm ideal gas p 2pmkT = Jx Di i l l i l p = Ekin Vol = n mv 2 2 = Jmv Numerically, Jx = 3.5 ¥1022 p(Torr) MT(g / mole ⋅K) (atoms /cm 2 sec) This gives a flux 1 monolayer (ML) arriving per sec at 10-6 Torr l = kB T 2pd 2 p Compare: Wed., Sept. 10, 2003 mens ona ana ys s: (force/area = en/vo .): Diffusivity DG D0 exp - È DG˘ Recall for solids: D = Í˙ Î kT ˚ Debye n 1013 s-1 For gas, no energy barrier, just collisions. dC n Jgas gas = D @ D dx l lvx Dgas ª nv 2 x (cm2 2 /s) kT recall l = 2pd 2 p v \D x µ T much weaker T-dep. than in so gas µT lid 3/ 2 6.152J/3.155J Wed., Sept. 10, 2003 8 4
6.152J/3.155J Knudson number L= dimension of chamber or reactor k t 1 atm 10-5 102 Flow is viscous: p>1 mT Knudsen No L Pump power >viscosity must transport lg. of molecules λ Molecular ballistic flow: p< 1 mT Pump efficiency critical must attract and hold molecules What does this imply for pumping? Wed, Sept. 10, 2003 Gas flow and pump speed Gases are compressible unlike liquids. so express flow as number of molecules/t, not volume/t [Units of Q(std-p)=> liters/min Conductance of vacuum component: Obm's law →Q=C(P-P [Units of conductance Pp pump 6.152J3.155 Wed, Sept 10, 2003
6.152J/3.155J 6.152J/3.155J 9 L Flow is viscous; p > 1 mT Molecular, p What does this imply for pumping? Pump power > viscosity; must transport lg. # of molecules must attract and hold molecules. Knudsen N0 ≡ l L l L <1 l L >1 L L l = kB T 2pd 2 p Recall: p l (cm) 1 atm 10-5 10-2 1 mT 10 Wed., Sept. 10, 2003 = dimension of chamber or reactor ballistic flow; < 1 mT Knudson number Pump efficiency critical; 1 Torr 6.152J/3.155J 10 Gas flow and pump speed Gases are compressible unlike liquids… so express flow as number of molecules/t, /t. N µ pV Define throughput, Q: Q = dN dt µ p dV dt ≡ pS Q (std-p I = 1 R Ê Ë Á ˆ ¯ ˜V q t l p pp fi Q = Cp - p ( ) p [Units of conductance µ area/length] Wed., Sept. 10, 2003 not volume [Units of ) => liters/min or sccm] Ohm’s aw: pump chamber Conductance of vacuum component: 5