Sinton lifetime

Device location: F&E4-SOLAR LAB

Lab location: Building 310 Room no. 203

Phone number:

Lab leader: Ulrich Paetzold

Principal users: Ulrich Paetzold, Wensheng Yan

Access: Only trained and authorized users may use the instrument.

Short Description

WCT-120 instruments showcase our unique measurement and analysis techniques, including the highly regarded Quasi-Steady-State Photoconductance (QSSPC) lifetime measurement method developed by Sinton Instruments in 1994. The QSSPC technique is ideal for monitoring multicrystalline wafers, dopant diffusions, and low-lifetime samples. This method complements the use of the transient photoconductance technique that is also standard on this instrument.The QSSPC lifetime measurement also yields the implied open-circuit voltage (versus illumination) curve, which is comparable to an I-V curve at each stage of a solar cell process.

WCT System Capabilities:

Primary application:

Step-by-step monitoring and optimization of a fabrication process.

Other applications:

• Monitoring initial material quality;
• Detecting heavy metals contamination during wafer processing;
• Evaluating surface passivation and emitter dopant diffusion;
• Evaluating process-induced shunting using the implied I-V measurement.

Some key features refer to the official webpage[[1]].

Start-up Procedure

Standard Operating Procedure:

Precautions:

1. Do NOT touch the filters or the filter tray which has glass diffuser glued into it, with bare hands. Use gloves or tissue paper for the same.

2. Make sure that the filter tray/flash mount assembly does NOT fall down while sliding it over the flash tower for adjusting height of the flash.

3. Ensure that the BNC cable and flash trigger connections are in place based on the measurement to be done i.e. to lifetime tester stage or Suns VOC stage.

4. Note down the height of the flash from the stage, the setting on the flash (1/1 or 1/64) and the filter being used during measurement. Different users tend to change this according to their requirements.

5. Make sure that the reference cell is NOT covered during the measurement.

6. Do NOT start the measurement on Lifetime tester until it is thermally stabilized i.e. Red LED is OFF.

7. During chemical passivation, ensure that solution does NOT spill on the stage.

8. For Suns VOC measurement, ensure that sample consists of P-N junction and both P N sides can be probed properly.

9. Ensure that proper action is taken for addressing error messages in the measurement:i.Saturated reference cell: Height of the flash is adjusted to change the intensity of light to avoid saturation of reference cell.ii.Min MCD < Specified MCD < Max MCD: Change the specified minority carrier density to fit in the measured range of minority carrier density.iii.Remove the sample on lifetime tester stage during zeroing of the instrument: No sample in the vicinity of stage during zeroing of the instrument.

10. Ensure that SUMMARY file is NOT cut pasted during the data transfer. A.Sinton WCT 120 Photo-conductance Lifetime tester

Introduction to the system:

The system is used for carrier lifetime measurement of samples after different processing steps during solar cell fabrication, as a step by step monitoring tool. The photo-conductance based contactless measurement technique makes use of RF sensor to measure sheet conductivity of the sample and light sensor to measure intensity of the flash to which sample is exposed. These measurements are then used to calculate the effective carrier lifetime of the samples.

Assembly of the Equipments:

1. The flash consisting of the bulb and reflector has already been installed in the filter tray /flash mount assembly.

2. The flash lamp controller trigger and the outputs of the instrument are connected to the computer through connector box.

Connections to the Equipments:

1. Insert the appropriate filter in the filter tray assembly, if required. IR pass filter is used for general usage and is already placed in the tray.

2. Connect the trigger cable to the side of the flash and other side of it into the connector box.

Measurement

Preliminary measurements

1. Open lifetime analysis spreadsheet in excel.

2. Enter correct values for wafer parameters (sample name, width, resistivity, type, optical constant). For test sample (50ohmc,, 0.7optical constant)

3. Analysis parameters – Specified MCD, 5E14 Fit range, 30% light bias, 0 Area frac, 1:analysis type.

Calibrating the coil

1. Remove any silicon; ensure the sensor areas are open.

2. Click on “Calibrate Coil”.

3. Wait for the trace to be zero. And then click “done”.

Measuring the test sample (QSSP)

1. Place the wafer on the test sate making sure it fully covers EF region but not the hole for light sensor. LIFETIME MEASUREMNT ONLY FOR THE SECTION ABOVE THE RF COIL IS DONE.

2. Click on ‘Measure Wafer’ button.

3. Click on zoom to fill the graph and peak of each trace.

4. Excel automatically calculates the lifetime.

Shutdown Procedure

1. Make sure you have saved all the data.

2. Switch OFF the instrument.

3. Turn OFF the software.

4. Turn OFF the computer.