Skip to main content

Semilab Tool

This page provides details on the Semilab tool in the Stand-Alone Measurements and Characterization bays of the Process Development and Integration Laboratory. This capability is currently operational.

Techniques available with this tool are microwave photoconductive decay (µ-PCD) for measurement of minority-carrier lifetime, light-beam induced current (LBIC) for reflectance and quantum efficiency at four wavelengths, and diffusion length, sheet resistance (by junction photovoltage), eddy-current bulk resistivity, Corona charge passivation for µ-PCD, iodine solution chemical passivation for µ-PCD, and bias lighting for lifetime measurement. Samples can be up to 200 mm x 200 mm.

Photo of apparatus that looks somewhat like a computer printer to left and a computer monitor to right with a colorful image of results.

Semilab technique showing the measurement capability to the left and display of results to the right on the monitor.

Image showing two colorful maps of results from measurements on a solar cell.

Minority-carrier lifetime maps on silicon wafers (left) and finished silicon solar cells (right).



Image showing two colorful maps of results from measurements on a solar cell.

Diffusion length map of finished silicon solar cell. Sheet resistance mapping can be performed (left) after emitter formation and (right) on finished cells.

Applications:

  • Measuring carrier lifetime at any point (any surface: bare, oxidized wafers, patterned finished cell). Lifetime—which is the time constant for carrier recombination—correlates with cell efficiency.
  • Determining diffusion length in finished cells, which is the average distance traveled by a minority carrier before it recombines
  • Measuring resistivity, emitter sheet resistance, quantum efficiencies, and Fe-B dissociation
  • Characterizing heavy metal and crystal defects

Special features:

  • LBIC/reflectance measures diffusion length
    • Measures at four wavelengths (405, 850, 950, and 1015 nm); diffusion length fit can use any combination of those wavelengths
    • Spot size of 100 µm can produce high-resolution maps
    • Direct-current mode
    • Can calculate internal and external quantum efficiencies and diffusion length
    • Step size can vary from as large as 8 mm down to 125 µm
    • Power is up to 1-sun
    • Measurable current range is from microamps to milliamps
  • Bulk lifetime measured by µ-PCD
    • 904-nm wavelength with a penetration depth of 33 µm
    • Pulse width of 200 ns
    • Step size can be as large as 8 mm down to 250 µm
    • Spot size is 1.1 mm
    • Microwave source is 10 GHz
    • Lifetime time constant is determined by decay curve fit, and each measurement is averaged over a programmable number of times
    • Chemical surface passivation for µ-PCD using ethanol-iodine solution
    • Can measure slip lines, oxidation-induced stacking fault (OSF) rings, oxygen striations, boat contamination, and iron mapping
    • Uses Si, Ge materials
    • Microwave source: Field-effect transistor >60 mW
    • Controlled excitation power
    • Measures lifetimes from 0.1 µs to 30 ms
    • Lifetime resolution is 0.1%
    • Resistivity range is 0.1 to 1000 Ω-cm
  • Bias-light option
    • Continuous halogen-lamp illumination acts like sunlight and allows the study of lifetime under working conditions
    • Controlled intensity
  • Junction photovoltage to measure emitter sheet resistance
    • Sample can have n-p or p-n junctions
    • 5-nm minimum junction depth
    • Lateral resolution is 8 mm
    • Accuracy is <3%
    • Repeatability is <1%
    • Measurement range is 10 to 1000 Ω/square with a 2% resolution
  • Automatic Fe-B dissociation unit
    • High-intensity illumination 3000-W flash lamp
  • Corona passivation can be used for bare (native oxide) and oxidized wafers and is non-destructive
    • Can apply a controlled charge deposition to the wafer surface either before or during lifetime mapping

Contact Steve Johnston for more details.