SEMI PV51 - Test Method for In-Line Characterization of Photovoltaic Silicon Wafers by Using Photoluminescence
Multicrystalline silicon (mc-Si) wafers produced by casting and controlled solidification usually contain regions containing high grown-in defect density in addition to the grain boundaries.
These defects may consist of impurity elements as well as structural defects within grains such as dislocations and dislocation networks, which may impact the solar cell efficiency negatively.
The defective areas are frequently close to the sidewalls and bottom of the ingot from which the wafers are cut.
Wafers containing highly defective areas impact the yield of a manufacturing line and should be excluded from solar cell manufacturing.
Therefore methods are required that allow a fast in-line characterization and sorting of wafers.
This method uses photoluminescence for detecting defective areas in wafers.
This Test Method identifies defective areas in crystalline silicon (Si) wafers.
It employs an in-line, noncontacting and nondestructive method for characterizing clean, dry, as-cut Si wafers supported by a mechanism that moves the test specimen through the measurement equipment.
The method covers square and pseudo-square Si wafers for photovoltaic (PV) applications, with a nominal edge length ≥125 mm and a nominal thickness ≥100 µm. It applies to both single-crystalline as well as multicrystalline Si wafers.
The method is intended for in-line high throughput measurements. Therefore it is mandatory to operate the measurement system under statistical process control (SPC) [e.g., ISO 11462] in order to obtain reliable, repeatable and reproducible measurement data.
The method is based on recording and evaluating near-infrared photoluminescence (PL) radiation emitted from the wafer after excitation with monochromatic light.
Other measurement techniques may also provide similar information about the defective areas of a wafer as compared to this Test Method, but they are not the subject of this Test Method.
The test may also be used for off-line, stationary characterization of Si wafers provided the requirements of the test method are met.
Referenced SEMI Standards
SEMI E89 — Guide for Measurement System Analysis (MSA)
SEMI M59 — Terminology for Silicon Technology
SEMI MF1569 — Guide for Generation of Consensus Reference Materials for Semiconductor Technology