NCSLI 2002 August 4-8, 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

NCSLI 2002 August 4-8, 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

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

NCSLI 2002 August 4-8, 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

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

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

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

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

NCSLI 2002 August 4-8, 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

NCSLI 2002 August 4-8, 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

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

NCSLI 2002 August 4-8, Sodium Heat Pipe Blackbody

NCSLI 2002 August 4-8, 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

NCSLI 2002 August 4-8, 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

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

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

NCSLI 2002 August 4-8, LP Spatial Response

NCSLI 2002 August 4-8, LP Spectral Response

NCSLI 2002 August 4-8, LP Temporal Response

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

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

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

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

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

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

NCSLI 2002 August 4-8, Integrating Sphere Results (1: LPRT1-LP2, 2: LPRT2-LP2) Before or After Cleaning LP Make LocationDifference ApertureInside[%] Before V V0.43 Before V V0.88 After V V0.11 After V V0.27

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

NCSLI 2002 August 4-8, 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

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

NCSLI 2002 August 4-8, 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