1/18 Steam-Injected SPM Process for All-Wet Stripping of Implanted Photoresist Jeffery W. Butterbaugh 7 FSI International, 3455 Lyman Blvd., Chaska, MN 55318 USA jeff.butterbaugh@fsi-intl.com
Outline 2/18 Motivation Implanted PR All-Wet Stripping Challenge SPM (Sulfuric acid hydrogen Peroxide Mixture) Making it More Reactive Results Summary
Low Material Loss An All-Wet Driver 3/18 low material loss ultra-shallow jct Lower material loss requirements during cleaning driven by ultra-shallow junction (USJ) source-drain extension (SDE) or lightly-doped drain (LDD)
Stripping Implanted Photoresist 4/18 dehydrogenated, amorphous carbon layer Ion implantation process affects stripping - Species: B, P, As, Si, Ge, BF 2 - Energy: < 1keV to > 1keV - Dosage: 1x1 11 to >1x1 16 ions/cm 2 - Normal incidence or angled gate gate photo source: P. Gillespie et al, Semiconductor International, October, 1999 Most challenging where carbonized PR fused to wafer surface especially at wafer edge, near EBR region
High Activation Energy to Remove Crust 5/18 Robert Doering and Yoshio Nishi, Handbook of Semiconductor Manufacturing Technology (CRC Press, 27).
SPM Making it More Reactive 6/18 H 2 SO 4 + H 2 O 2 H 2 SO 5 + H 2 O H 2 O added with 31% H 2 O 2 will force this equilibrium back to the left 2HO HSO 4 + HO Higher temperature Half Cell Oxidation Reactions HSO - 5 + 2H + + 2e - HSO - 4 + H 2 O 1.44V H 2 O 2 + 2H + + 2e - H 2 O 1.78V HSO 4 + H + + e - H 2 SO 4 2.6V HO + H + + e - H 2 O 2.8V More oxidizing power
SPM Mixing is Exothermic 7/18 4:3 ratio gives highest temperature rise, but higher concentration is desired (H 2 O 2 includes 69% water, which dilutes and lowers reactivity) Final Temperature (Deg. C) 14 12 1 8 6 4 2 4:1 68 1:1 38 rise 2:1 91 4:3 98 1:1 86 higher concentration (9%H 2 SO4; 2%H 2 O 2 ; 8% H 2 O) 4:5 82 highest POU mixing temperature (66%H 2 SO 4 ; 1%H 2 O 2 ; 24% H 2 O) 3 6 9 12 15 H2O2 Added (cc) Resulting temperature when 2 C 31% H 2 O 2 is mixed with 1 cc of 2 C 96% H 2 SO 4.
How to Achieve High Temperature Without Dilution? 8/18 Pre-heating SPM above 15 C causes rapid degradation of H 2 O 2 before contacting the wafer POU 4:3 SPM mixing gives temperature boost, but causes dilution Preheating H 2 SO 4 above 15 C requires specialized fluid handling SOLUTION = STEAM INJECTION (ViPR+) First, lets review a useful tool for illustrating the advantage of steam injection....
Sulfuric Acid Enthalpy-Concentration Diagram 9/18 Mixing sulfuric acid and water produces interesting energetics Enthalpy-Concentration diagram allows easy analysis of mixing temperature effects gas-liquid equilibrium isotherms minor differences between 1% H 2 O (B.P.=1 C) and 69%H 2 O/31%H 2 O 2 (B.P.=17 C) enthalpy of mixture including vapor (J/g) 372 186 21 C C 14 C 11 C 38 C 66 C 121 C gas liquid 93 C 121 C 2 4 6 8 1 288 C 26 C
Mixing Room Temperature 96% Sulfuric Acid with Water 1/18 enthalpy of mixture including vapor (J/g) Connecting two points produces an adiabatic mixing curve 372 186 21 C C 14 C 11 C 121 C 38 C 66 C 93 C 121 C 2 4 6 8 1 288 C 26 C 16 12 8 4 adiabatic mixing temperature ( C) 2 4 6 8 1 maximum temperature at about 13 C and 4:3 mixing ratio (66%H 2 SO 4 ; 1%H 2 O 2 ; 24%H 2 O)
Mixing 95 C 96% Sulfuric Acid with Water 11/18 Starting with 95 C H 2 SO 4 causes intersection with gas-liquid curve enthalpy of mixture including vapor (J/g) 372 186 21 C C 14 C 11 C 121 C 38 C 66 C 93 C 121 C 2 4 6 8 1 288 C 26 C 2 16 12 8 4 adiabatic mixing temperature ( C) 2 4 6 8 1 boiling point at about 19 C and 2.5:1 mixing ratio (77%H 2 SO 4 ; 6%H 2 O 2 ;17%H 2 O)
Mixing 15 C 96% Sulfuric Acid with Water 12/18 Starting with 15 C H 2 SO 4 allows 4:1 mixing ratio before boiling enthalpy of mixture including vapor (J/g) 372 186 21 C C 14 C 11 C 121 C 38 C 66 C 93 C 121 C 2 4 6 8 1 288 C 26 C 24 2 16 12 8 4 adiabatic mixing temperature ( C) 2 4 6 8 1 boiling point at about 21 C and a 4:1 mixing ratio (83%H 2 SO 4 ; 4%H 2 O 2 ;13%H 2 O)
Mixing 15 C 96% Sulfuric Acid with Water and Steam 13/18 Heat of Vaporization = The Steam Advantage enthalpy of mixture including vapor (J/g) 372 186 14 C 11 C 121 C 288 C 26 C converting water from liquid to gas at 1 C = 227 J/g 21 C C 38 C 66 C 93 C 121 C 2 4 6 8 1 heating water from 21 C to 1 C = 331 J/g
Mixing 15 C 96% Sulfuric Acid with Water and Steam 14/18 Using steam provides temperature boost with minimal dilution enthalpy of mixture including vapor (J/g) 372 186 21 C C 14 C 11 C 121 C 38 C 66 C 93 C 121 C 2 4 6 8 1 288 C 26 C 26 22 18 14 add 31% H 2 O 2 to reach 1:1 mixing ratio then add steam adiabatic mixing temperature ( C) 8 1 boiling point at about and an equivalent 5.5:1 mixing ratio (86%H 2 SO 4 ; 3%H 2 O 2 ;11%H 2 O)
Results on Implanted Photoresist 15/18 2.5x1 14 ions/cm 2, 4 kev As Implant batch spray system 2 min Standard POU SPM Resist Still Present 5.5 min Steam-Injected SPM Resist Stripped Time to clear blanket 2.5x1 14 ions/cm 2, 4keV As implanted photoresist dropped from 5 min SPM to 5.5 min SPM
All-Wet PR Strip with Low Material Loss 16/18 FSI ZETA System (Batch Spray) with ViPR Technology for Steam-Injected SPM Stripping Implanted Photoresist Dose (ion/cm 2 ) Energy & species SPM time (min) oxide loss (Å) 5x1 14 4keV As 4 <.2 1x1 15 2keV As 4 <.2 LDD implant ITRS indicates <.3 Å 3x1 16 7keV BF 3 (PLAD) 4 <.2
Very Fast Single-Wafer Photoresist Stripping 17/18 8% Reduction in Time and Cost for Single Wafer Stripping of Arsenic-implanted Photoresist time to strip (s) 1 75 5 25 standard POU SPM 5E14 / 4keV 1E15 / 2keV steam-injected POU SPM $1.67 $1.25 $.84 $.42 [standard SPM = POU mixing with 15 C sulfuric acid] SPM chemical cost ($/wafer)
Summary 18/18 Sulfuric acid hydrogen peroxide mixture continues to be a common approach to all-wet implanted PR strip Trade-off between POU heat of mixing temperature gain and dilution effect Patent-pending Steam-Injected SPM process provides increased temperature at the wafer surface with minimal dilution Steam-Injected SPM process meets ITRS material loss requirements for LDD implants