1. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 1 DI Water Reduction in Rinse Processes Contributions by: Thomas W. Peterson, University of Arizona Andy Hebda, University of Arizona Thomas Roche, Motorola Corp. Eric Hansen, Santa Clara Plastics  1999 Arizona Board of Regents for The University of Arizona

2. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 2 Overview DI water use during rinsing: –~ 10 3 gallons/wafer ==> ~10 7 - 10 8 gallons/year (SEMATECH) Minimal recycle and reuse across the industry Primary objective: CLEAN WAFERS

3. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 3 Indicators of “Clean Wafers” ON-LINE –Resistivity in the Rinse Tank OFF-LINE –Particle Counts on Wafer Surface –Elemental Analysis of Wafer Surface –Device Characteristics Testing

4. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 4 Terminology Resistivity –Primary measurement of ionic concentration of rinse water. The higher the ion concentration, the lower the resistivity. –[=] MW - cm Conductivity –The inverse of resistivity. For dilute solutions, conductivity is proportional to ionic concentration –[=] 1/ (MW - cm)

5. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 5 Terminology (cont’d) Integrated Conductivity –The conductivity in the rinse water integrated over the time period required to “recover” from the chemical burden introduced to the system by the wafers Carryover –Amount (moles or grams) of chemical “carried over” with the wafers and the boat from »chemistry tank to first rinse tank »first rinse tank to second rinse tank

6. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 6 “Typical” DI Water Resistivity (M  - cm) Clean water, high flow conditions (greater than 11 gpm): 17 - 18+ Clean water, low flow conditions: 8-17 or lower Rinse bath containing wafers, immediately following chemistry: <<0.01 (mdl for monitor)

7. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 7 Resistivity, Conductivity and Ionic Concentration

8. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 8 Integrated Conductivity and “Carryover”

9. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 9 Resistivity is the Primary Measurement

10. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 10 K(t) = 1/ R(t)

11. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 11 Resistivity and Conductivity

12. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 12 Integrated Conductivity

13. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 13 Continuous Stirred Tank Model

14. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 14 CSTR Characteristics

15. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 15 Evidence of CSTR

16. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 16 Evidence of CSTR (cont’d)

17. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 17 CSTR vs. PFR Model For a theoretically pulsed input, the response of a PFR reactor is significantly smaller than that of a CSTR reactor. Input Response 0 PFR CSTR

18. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 18 Hypothesis: Wafers can be adequately “cleaned and rinsed” with less water Select the methods of reduction Establish “base-line” water requirements for current processes Alter water usage in rinse bath by various means Examine “Indicators” of wafer cleanliness

19. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 19 Methods for DI Reduction Pulsed rinse baths –HF chemistry –Piranha (H 2 SO 4 /H 2 O 2 ) chemistry Decrease in bath volume

20. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 20 Example Rinse Sequence: SCP 9400 tool Motorola MOS 12 Piranha Super Q Rinse HF SC1 IPA DRYER

21. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 21 Pulsing Experiments HF Chemistry 2 minutes in 10:1 HF 6 minute overflow “first rinse” @ 15 gpm 2 minute overflow “second rinse” @ 15gpm ** ** Other chemistry steps with “first rinse” baths could precede this step.

22. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 22 Experimental Variations HF Chemistry “First Rinse” time: 4, 5, 6 minutes “First Rinse” flow rate: 8 - 15 gpm “Pulsed” flow conditions –Period:10 seconds to 2 minutes –High Flow Time:1 second to 60 seconds Wafer loading: 1 to 50 wafers

23. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 23 Chemical Carryover Results HF Chemistry Pulsed flow exhibits an improvement over conventional flow in terms of the volume of water employed to obtain the same level of wafer cleanliness.

24. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 24 Pulsing Experiments Piranha Chemistry 10 minutes in 7.5:1 H 2 SO 4 / H 2 O 2 at 120 °C 5 “quick-dump rinses (“first rinse”) -3 hot water, 2 cold water -High flow for ~1 minute, ~5 second drain, ~30 second refill -Flow rate ~ 15 gpm 2 minute overflow “second rinse” @ 15 gpm ** ** Other chemistry steps with “first rinse” baths could precede this step.

25. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 25 Experimental Variations Piranha Chemistry ~ 50 experiments conducted “First Rinse” utilized both quick dump and overflow modes “First Rinse” time 3 - 9 minutes “First Rinse” flow rate 8 - 15 gpm “Pulsed” Flow conditions –period:10 seconds to 4 minutes –high flow time:2 seconds to 2 minutes Hot and Cold Rinses “Agitation” (using robot arm)

26. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 26 Effect of Pulsing and Quick-Dump Rinsing

27. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 27 Effect of Pulse “Sequence” “’On’ first” provides a marginally more effective rinse due to the occurrence of convection before diffusion.

28. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 28 Effect of Temperature and Agitation Hot rinses and cold rinses with agitation reduce the amount of carryover associated with a standard cold rinse. This is possibly due to an increased rate at which chemical contaminants are swept from the wafer surface.

29. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 29 Comparison: Carryover to Surface Loading Piranha Chemistry “ Clean” Carryover: 0.01 mg H 2 SO 4 ==> 10 -7 moles Surface Measurements by XRF: 10 13 molecules S/cm 2 For 50 200mm wafers ==> 10 -7 moles

30. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 30 Rinse Bath Volume Experiments Bath Comparison

31. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 31 Comparison of Rinse Tank Performance HF Chemistry, Bare Wafers The lower volume tank exhibits an improvement over the standard tank in rinsing bare Si wafers.

32. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 32 Comparison of Rinse Tank Performance HF Chemistry, Oxide Wafers For oxide wafers, no significant difference is seen between the standard and Dynaflow tanks.

33. NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Peterson, et al. 33 Summary Under certain conditions, pulsing has a pronounced effect on rinse efficiency. Combining pulsing sparingly with quick-dumps (in those processes which allow for quick-dumps) can further increase rinse efficiency. A substantial portion of the time during rinsing is spent “cleaning up the water” rather than cleaning up the wafer surface. Moving the characteristic operating conditions of the rinse tank closer to Plug flow conditions can potentially reduce water usage over that required for CSTR conditions. A new rinse bath shape using less water volume can decrease water usage while achieving an effective rinse for bare silicon wafers.