Chicane Deceleration – Qualifying a new technique to control energy contamination

1. Chicane Deceleration –Qualifying a new technique to control energy contamination Nick White, John Chen, Chris Mulcahy, Sukanta Biswas, Russ Gwilliam

2. Introduction • Implantation of high-current boron beams at 200eV for SDE with USJ • Goal: Preserve the advantages of conventional implanters while meeting productivity requirements: • Use of established source materials and technologies • Accurate dosimetry • Precise angle control • Robust charging control • Eliminate deep tails caused by energy contamination • Quantify sources of variation

3. 1E+22 0.2 keV B 0.2 keV B 0.5 keV B 1.0 keV B 2.0 keV B 1E+21 1E+20 1E+19 Concentration / Atoms.cm-3 1E+18 1E+17 1E+16 1E+15 0 100 200 300 400 500 600 700 800 900 1000 Depth / Angstroms ULE Boron and Energy Contamination Historical Data • Figure shows 0.2, 0.5, 1.0 & 2.0 keV ion implants • Energy Contamination during implantation canbe observed in most of the implants • 400 eV O2+ was implemented for the lower energy implants whilst 700 eV was applied for the higher energy implants • Lowest implant energies benefit from lower energy O2+ Earlier data compiled by Cascade.

4. Method

5. 200 eV +5,800 V 6,000 eV Chicane deceleration Sending ions up a potential ‘hill’ reduces their energy Tortuous path removes particles with the wrong energy or charge 30:1 shown 4:1 to 30:1 available

6. Chicane

7. Beam currents used in these tests • BF2 current: • 1.0 mA at 200eV • 2.0 mA at 400eV • 3.5 mA at 891eV • Boron current: • 2.5 mA at 200eV • 4.5 mA at 1000eV • Decel ratio from 10:1 to 30:1 (4:1 is available)

8. Direct measurement of angles in the beam Beam burns 150mm beyond plate Aperture plate

9. Beam Divergence and Angle Control Insignificant change in overall angles down to 200eV, but each beamlet spreads more at low energy.

10. Effect of SIMS energy For this study we used 200eV O2+ at 45 degrees, equivalent to ~70 eV O+ at normal incidence.

11. Experimental Details • Prime n-type wafers, 200mm • Most wafers preamorphized • 100keV Ge to 2e15 • because we also investigated higher energies • because if energy contamination was present, we did not want the tails to channel and be distorted • Some coated 50% with photoresist • Energy contamination from neutralization is proportional to pressure • Outgassing from resist at high current must be evaluated • Energy measured directly by voltmeter from ion source to endstation • Only uncertainty is plasma potential in ion source.

12. Implant Matrix and Controls • 891eV BF2 has same velocity as 200eV B • Surface oxide about 1.3 nm

13. Results

14. Boron 200eV 2.5 mA – raw data

15. Profile changes with dose

16. Saturation at 200eV? Retained dose by SIMS

17. Boron 200eV 2.5mA SIMS Profiles

18. Discussion of 200eV data • First 0.5 nm: • Surface is clean. Minimal oxide effects. • Concentration as % of dose falls with dose • 0.5-2.0 nm • Concentration is slightly higher with higher dose • Ion beam mixing during implant • >3 nm • Effect of increased pressure is resolved • Profile becomes ~0.23nm deeper • >4 nm • Channeling is distinct; level is approx 1.23% • Range of channeled ions is ~4nm deeper for 0.1% of dose • >10 nm • No effect of pressure can be resolved • Why does BF2 have a lower background?

19. Discussion Possible Sources of profile shifts and deep tails: • Channeling • We used RBS to look for channeling • Pilot experiments eliminated channeling as source of background variation • Our amorphization was complete • SIMS system background and SIMS knock-on • BF2 has a much lower background • Does the fluorine inhibit SIMS knock-on? • Higher energy beam components • Neutralization close to exit of chicane

20. Zone of possible Energy contamination What contaminants get past the chicane? • Ions can be neutralized within the chicane • This process must occur within the exit zone if the contaminant is to reach the wafer • The electric potentials limit the maximum energy contamination to a fraction of final energy • Proportional to pressure

21. Highly resolved dopant shiftdue to PR outgassing • Obtained by subtracting SIMS from PR wafer from SIMS from bare wafer after re-normalizing • Dose on PR wafer was 5% lower due to beam neutralization and loss

22. USJ Implants using BF2

23. USJ Implants using BF2, smoothed

24. Conclusions: • Chicane technique can deliver ~70 wph at 200eV B 5e14 with Xj (unannealed) of < 7 nm • Magnitude of energy contamination is ~22eV, or < 0.3 nm • Channeling can modify the as-implanted profile by ~ 3nm • Metrology must resolve 3nm! • PAI required • Chicane technique can deliver ~100 wph of 891eV BF2 5e14 • May have tighter profile and less diffusion • PAI required • Chicane technique can deliver ~33 wph for 200eV BF2 5e14 with Xj (unannealed) of < 5 nm • Does not require PAI

25. Acknowledgements: • Implants and beam measurements: • Ed Petersen • Yap Han Chang • SIMS analysis • Neil Montgomery • Paul Ebblewhite • RBS analysis • Chris Jeynes