kSA BandiT: Band-edge Thermometry

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kSA BandiT Band-edge Thermometry
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Band-edge Thermometry Principles

• Semiconductors transparent for h? lt Eg, opaque
  for h? gt Eg
• Semiconductors as substrate temperature
  increases, Eg ? and ?g ?
• Look at diffusely scattered light component not
  the specular component. Specularly reflected
  (front surface) light does not interact with the
  wafer.

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Band-edge Thermometry vs. Pyrometers

• Pyrometers
• Typically inaccurate or no measurement below
  400-450oC
• Potential interference from stray IR (esp. at low
  Ts), internal reflections (heterojunctions),
  coated view ports
• Absolute temperature calibration from machine to
  machine is difficult
• Eg thermometers
• Need good light collection detection system
• Need good normalization fitting software
• Absorbing over layers limit thickness for
  temperature measurement

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kSA BandiT vs. Competitor Instruments

• State-of-the-art solid state spectrometer - 1000x
  more sensitivity and no moving parts (longer
  lifetime, no need for constant recalibration)
• Excellent S/N without a chopper
• Efficient collection optics
• Powerful software and full software development
  team
• Operates in either transmission or reflection
  mode
• Single USB connection to laptop computer
• Full technical service and support

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kSA BandiT Product Specifications

• BandiT System Schematic

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BandiT Light Source
kSA BandiT Product Specs. Contd

• 150W halogen lamp with gold coated parabolic
  reflector.
• Light source collimating optics.
• Real-time output power control via BandiT
  software.
• Internal feedback control for stable intensity
  and spectral output.
• NOTE above 300 oC can use heater as light
  source

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BandiT Detector
kSA BandiT Product Specs. Contd

• 2-inch collection optics focusing to 400 um
  fiber.
• Single-axis gimble mount for radial scanning
  between inner/outer platen rings
• Dual fiber with visible laser for easy
  alignment.

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kSA BandiT Product Specs. Contd

• Spectrometer
• Visible Model (B-VIS)
• 512x64 element Peltier-cooled CCD array detector
• Wavelength Range 380 nm 1100 nm or custom
• SiC, ZnTe, ZnSe substrates
• NIR Model (B-NIR)
• 128 element InGaAs temperature stabilized
  photodiode array with on-board interpolation
  yields 1024 elements
• Wavelength Range 875 nm 1400 nm
• GaAs, Si, InP substrates

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kSA BandiT Software

• Full hardware control and real-time feedback of
  lamp and spectrometer
• Powerful, flexible fitting algorithms
• Ability to store full, partial, or no spectra and
  temperature data
• Full analog and digital I/O capability
• USB interface, runs from a laptop

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kSA BandiT Performance Specifications

1 B-VIS model
2 B-NIR model
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BandiT Stability Data GaAs _at_ 300C
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kSA BandiT Performance Specs (contd)

• Noise from rotation 1-2oC for all size wafers
• Pyrometer noise typically much worse for ¼ X 3
  pieces
• No interference from
• hot sources
• highly doped epi (2um of GaAsC, p 6.5e19/cm3)
• high-on-low Eg growth (AlGaAs/GaAs)
• Low-on-high Eg growth InGaAs/InP
• InGaAs strong IR absorber
• Clean measurement thru 1.2 um of epi (using
  heater only)

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kSA BandiT Calibration File Generation

• material
• thickness
• dopant level

Calibration depends on
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BandiT, TC, and Pyro Measurement
GaAs Oxide Desorption
Pyro reads high at low temps because substrate is
transparent
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Interference Oscillations
Oscillations in temperature
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Low Temp GaAs Growth
TC does not see temp rise due to As Absorption
Temp increase due to As absorption
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BandiT Measurement During Substrate
RotationSpatially Resolved Wafer Temperature

• Speed of solid state spectrometer provides
  spatially resolved temperature across all wafers
• Wafer temperature can vary widely depending on
  thermal contact with holder
• Temperature uniformity across each wafer
  depends on holder mechanism