3.155J6.152J Physical Vapor Deposition(PVD) SPUTTER DEPOSITION ◆. PECVD lasma enhanced surface diffusion without need for ◆… Dry etching Momentum transfer from plasma to remove surface species e We will see evaporation: Evaporate source material, Peg, vap P. s 10- Torr (another PVD) Poor step coverage, alloy fractionation: A P vapor Now sputter deposition. Noble or reactive gas P=10 mTorr What is a plasma? 6.1523.155 Nov.5.2003 What is a plasma? A gas of ionized particles, conducting at low freq Initiate ionization(breakdown) with spark Voc>>Vbkdn ions(e.g. Ar*+e) ions <s 1%o of atoms elf sustaining plasma in V> vnkdn P≈10-100 m Torr Ionizatio cathode What goes on inside a plasma?
3.155J/6.152J 6.152J/3.155J Nov. 5, 2003 1 Physical Vapor Deposition (PVD): SPUTTER DEPOSITION We will see evaporation: (another PVD) Evaporate source material, Peq.vap.Pg £10-6 Torr Poor step coverage, alloy fractionation: D Pvapor u u Now sputter deposition. Noble or reactive gas P § 10 mTorr We saw CVD Gas phase reactants: Pg § 1 mTorr to 1 atm. Good step coverage, T > > RT u …PECVD Plasma enhanced surface diffusion without need for elevated T u u …Dry etching Momentum transfer from plasma to remove surface species What is a plasma? 6.152J/3.155J Nov. 5, 2003 2 Initiate ionization (breakdown) with spark VDC > > Vbkdnfi ions (e.g. Ar+ + e- ) ions < < 1% of atoms. Self sustaining plasma in V > Vbkdn What goes on inside a plasma? P § 10-100 m Torr cathode anode V § 1 kV - Ex ve - vAr+ Ionization event What is a plasma? A gas of ionized particles, conducting at low freq
3.155J6.152J What is molecular density at 10 mT? Ideal gas: n=P/(hBT) 2.5x1025m3 LogIn(#/m)I I Atm= 0.1 MPa n=3.2x1030m I Torr :0 mi Spacing between molecules =l/5=0.15 microns. Is this=2? 6.1523.155 Nov.5.2003 Spacing between molecules rl/=0.15 microns. (Ar’ much less 0.1% to 1% of A, are ions: E field accelerates Ar e between collisions Eq WoLEy 2×10° 6.152J.155J Nov.5.2003
3.155J/6.152J 6.152J/3.155J Nov. 5, 2003 3 012345 Log[P (N/m2 )] 25 24 Log[n (#/m3)] 23 22 21 20 1 Atm= 0.1 MPa §14 lb/in2 2.5 x 1025 m-3 1 Torr 10 mT n = 3.2 x 1020 m-3 Ideal gas: n = P/(kBT) Spacing between molecules § n-1/3 = 0.15 microns. Is this = l ? What is molecular density at 10 mT? 6.152J/3.155J Nov. 5, 2003 4 l l l l l l l l l l l 0.1% to 1% of nAr are ions: E field accelerates Ar+, e- between collisions. v f 2 = v0 2 + 2ax ª 2 Eq m l lAr ª 3 cm ( l[Ar + ] much less) l = kBT 2pd2 P Spacing between molecules § n-1/3 = 0.15 microns. Is this = l ? No! ve- ª 2 ¥109 cms v , Ar ª107 cms J = nqvx cathode anode V § 1 kV - Ex ve - vAr+ Ionization event And ne- >> nAr+
3.155J6.152J Which species, e-or Ar+ is more likely to dislodge an atom at electrode P≈10-100 m Torr cathode Cathod source material Ar--- V≈lkv (1/2)MxVA2=916m2V A=/43 =(1/2)mv2=(1/2)mv2 PA=MV=1832mv/43 Momentum transfer? No surprise From ion implantation, most energy transfer when: AE=E, 4M, A i.e. incoming particle has mass close to that of target. 6.1523.155 Nov.5.2003 Sputtering process Ar* impact, momentum transfer at cathode e avalanche and released target atoms, ions Atomic billiards Elastic energy transfe 4M.M st for m E,4 For e- hitting anode, substrate, M,<<M But e" can give up all its Er in inelastic collision mv→△U Excitation of atom or ion 6.152J.155J
3.155J/6.152J 6.152J/3.155J Nov. 5, 2003 5 Which species, e- or Ar+ , is more likely to dislodge an atom at electrode ? P § 10-100 m Torr cathode anode V § 1 kV - Ex ve - vAr+ Ekin § 1 keV = = (1/2) MArVAr2 = 916 meVAr2 = (1/2) merve 2 = (1/2) meve 2 \ VAr = ve/43 Momentum transfer? PAr = MV = 1832mv/43 pe = mv No surprise. From ion implantation, most energy transfer when: i.e. incoming particle has mass close to that of target. DE = E1 4M1M2 ( ) M1 + M2 2 P § 10-100 m Torr cathode anode V § 1 kV - Ex ve - vAr+ Cathode is “target”, source material 6.152J/3.155J Nov. 5, 2003 6 Sputtering process Ar+ impact, momentum transfer at cathode fi e- avalanche and released target atoms, ions. For e- hitting anode, substrate, M1 < < M2 E2 E1 ª 4M1 M2 (small) But e- can give up all its EK in inelastic collision: 1 2 me ve 2 fi DU Excitation of atom or ion Elastic energy transfer E2 E1 µ 4M1M2 ( ) M1 + M2 2 cos2 q E2 greatest for M1 q @ M2 E1 E2 Atomic billiards
3.155J6.152J Sputtering process P≈10-100 m Torr cathode Cathode is" target” V≈1kV cathode e Momentum transfer of Ar+ on cathode erodes cathode atoms source atoms Target material(cathode s flux to anode substrate must be conductive or use RF sputtering (later) 6.1523.155 Nov.5.2003 Inside a plasma Cathode e Art impact on cathode electrons ② 1.5eV Faraday dark space ①Ek ②1.5≤Eks3eV③ e. induced no action optical excitation ofAr→ visible glow 6.152J.155J Nov.5.2003
3.155J/6.152J 6.152J/3.155J Nov. 5, 2003 7 P § 10-100 m Torr cathode anode V § 1 kV - Ex ve- vAr+ Cathode is “target”, source material cathode anode V § 1 kV - Mostly-neutral source atoms Target material (cathode) must be conductive …or use RF sputtering (later) Momentum transfer of Ar+ on cathode erodes cathode atoms fi flux to anode, substrate. Sputtering process Ar+ 6.152J/3.155J Nov. 5, 2003 8 ve - vAr+ Ex Cathode Anode x Ar+ impact on cathode fimostly electrons ¿ ¡ ¬ x 1.5eV EK ~ ve - 2 3 eV Ionization glow v f 2 = 2ax ¿ EK e - <~ 1.5eV Cathode dark space, no action ¡ 1.5 < EK e - ~ ~< 3eV e- - induced optical excitation of Ar fi visible glow cathode anode - Inside a plasma ¬ EK > 3eV fi ionization, High conductivity plasma Faraday dark space
3.155J6.152J Inside a plasma 3ev (D.C. or cathode sputtering 1. 5eV ionization Cathode relative to anode Film species Cathode sheath Substrate ow ion density High conductivity How plasma results in deposition 5)Deposited at anode 1)Ar+ accelerated to cathode cathode ano 2)Neutral kicked off Ar =Ar++e 3) some neutral⊙ V≈1kV (e.g.O→0) 6)Some physical of al by Ar
3.155J/6.152J 6.152J/3.155J Nov. 5, 2003 9 ¿ ¡ ¬ x 1.5eV EK ~ ve - 2 3 eV Ionization glow Je- ,ve- >> JAr+ ,vAr + fi \ plasma § 10 V positive relative to anode cathode anode - Inside a plasma (D.C. or cathode sputtering) Cathode sheath: low ion density Plasma High conductivity Cathode Anode e- Ar+ + VD.C. Film species Target Substrate 6.152J/3.155J Nov. 5, 2003 10 cathode anode V § 1 kV - Al Ar Al + Ar+ + Ar+ 1) Ar+ accelerated to cathode Al Ar =Ar+ + ee- 2) Neutral target species (Al) kicked off; 3) some neutral Ar and e- also. 4) e- may ionize impurities (e.g. O => O- ) O- 5) Deposited at anode: Al, some Ar, some impurities 6) Some physical resputtering of Al by Ar Al How plasma results in deposition