2. NCSLI 2002 August 4-8, 2002 1 Improving Temperature Accuracy for Rapid Thermal Processing at NIST August 4-8, 2002 NCSL International Annual Workshop and Symposium San Diego, California B.K. Tsai and D.P. DeWitt Optical Technology Division National Institute of Standards and Technology

3. NCSLI 2002 August 4-8, 2002 2 Objectives Goal: Improve LP calibration accuracy and understand LP performance. Review NIST LP calibration facility and procedures Outline methods of LP characterization Evaluate optical inspection techniques for LPs Make recommendations for accurate LP calibrations

4. NCSLI 2002 August 4-8, 2002 3 RTP Technology Moore’s Law

5. NCSLI 2002 August 4-8, 2002 4 RTP Technology Importance 1995 total semiconductor equipment sales was about 15 billion dollars 1995 RTP equipment sales was less than 1% of total sales but is steadily increasing

6. NCSLI 2002 August 4-8, 2002 5 RTP Technology Types of Processing Batch Multiple wafer processing RTP (Rapid Thermal Processing) Single wafer processing

7. NCSLI 2002 August 4-8, 2002 6 RTP Technology Comparison of batch vs. RTP processing

8. NCSLI 2002 August 4-8, 2002 7 RTP Technology Temperature Measurement Challenges Stray light Temperature variations with time Emissivity and reflectivity changes Nonuniform wafer temperature distributions

9. NCSLI 2002 August 4-8, 2002 8 RTP Test Bed and Lightpipes

10. NCSLI 2002 August 4-8, 2002 9 ITRS Requirements (International Technology Roadmap for Semiconductors) Goal: To measure RTP temperatures and temperature differences of ±2 °C and ±0.25 °C at 1000 °C. Don Lindholm, SEMATECH, RTP ‘97 Conference SIA Roadmap 1999 goal for 0.18 µm line widths requires that temperature accuracy and repeatability in the RTP environment is better than ±2 °C and ±0.25 °C at 1000 °C

11. NCSLI 2002 August 4-8, 2002 10 NIST RTP Project Tasks Radiation thermometer in situ calibration using thin-film thermocouples Characterization of new generation radiation thermometers Characterization of wafer radiation environment Collaboration with industry

12. NCSLI 2002 August 4-8, 2002 11 Temperature Measurement Equation  eff = effective emissivity T = corrected temperature T = spectral radiance temperature = spectral radiance c 2 = second radiation constant

13. NCSLI 2002 August 4-8, 2002 12 Sodium Heat Pipe Blackbody

14. NCSLI 2002 August 4-8, 2002 13 Na-HPBB Calibration Uncertainty Factor Uncertainty, k=2 [°C] Na-HPBB radial uniformity0.57 Na-HPBB length uniformity0.10 LPRT noise0.02 LPRT short-term drift0.05 Total0.60

15. NCSLI 2002 August 4-8, 2002 14 NIST LP Calibration Procedures Inspection visually Clean with ethyl alcohol Set Na-HPBB to temperature Surround LP with water-cooled sleeve Take three cold measurements

16. NCSLI 2002 August 4-8, 2002 15 NIST LP Calibrations (4 LPs over 1 y)

17. NCSLI 2002 August 4-8, 2002 16 Other Calibration Procedures Reset sensor factor using Na-HPBB Calibrate before and after use Clean with flame if necessary Keep LP attached to LPRT

18. NCSLI 2002 August 4-8, 2002 17 LP Spatial Response

19. NCSLI 2002 August 4-8, 2002 18 LP Spectral Response

20. NCSLI 2002 August 4-8, 2002 19 LP Temporal Response

21. NCSLI 2002 August 4-8, 2002 20 Visualization Techniques Sapphire light pipe He/Ne laser (0.95 mW) Quartz-fiber cable Camera Microscope

22. NCSLI 2002 August 4-8, 2002 21 Photograph of LPRT2-LP2 under microscope using HeNe laser

23. NCSLI 2002 August 4-8, 2002 22 Photograph of LPRT2-LP2 under microscope without HeNe laser

24. NCSLI 2002 August 4-8, 2002 23 Laser Illumination LPRT2-LP2 LPRT1-LP2

25. NCSLI 2002 August 4-8, 2002 24 Integrating Sphere Technique He/Ne laser (0.95 mW) Integrating sphere Current amplifier Digital voltmeter Computer Quartz-fiber cable Silicon detector Sapphire LP

26. NCSLI 2002 August 4-8, 2002 25 Integrating Sphere Setup HeNe laser (0.95 mW) Integrating sphere A B LP

27. NCSLI 2002 August 4-8, 2002 26 Integrating Sphere Results (1: LPRT1-LP2, 2: LPRT2-LP2) Before or After Cleaning LP Make LocationDifference ApertureInside[%] Before11.04356 V1.04803 V0.43 Before21.08129 V1.09079 V0.88 After11.06788 V1.06901 V0.11 After21.06654 V1.06947 V0.27

28. NCSLI 2002 August 4-8, 2002 27 Vendor Calibrations Large variability within single vendor Large variability among vendors Differences are a slight function of temperature Need to understand vendor calibrations

29. NCSLI 2002 August 4-8, 2002 28 Hot versus Cold Calibrations General trend is initial constant period, slight decrease, and increase to final stable period Other patterns observed Correlation of patterns with visualization results

30. NCSLI 2002 August 4-8, 2002 29 Issues from Hot Calibrations Particle contamination Disturbance of radiation environment Importance of uncertainty analysis Frequency of recalibration Stray radiation

31. NCSLI 2002 August 4-8, 2002 30 Recommendations 1.Visually inspect the LP first 2.Understand the factory calibration 3.Characterize the LPRT 4.Minimize lateral scattering 5.Calibrate the LPRT as it will be used 6.Calibrate the LPRT using blackbodies that are traceable to a National Measurement Institute, such as NIST 7.Calibrate before and after use