SEMI PV42 - Test Method for In-Line Measurement of Waviness of PV Silicon Wafers by a Light Sectioning Technique Using Multiple Line Segments -

Abstract

Si wafers for PV applications cut from a Si ingot or Si brick by multiple wire sawing contain surface undulations/ripples characteristic for this cutting process, so called waviness.

　

This waviness is a surface feature where the peaks and valleys of the waves are parallel to the wires of the saw and the direction of the wave is perpendicular to those wires. Waviness may significantly impact the quality of solar wafers. Waviness is frequently specified for Si wafers for solar cells as a maximum peak-to valley range.

　

Therefore process and quality control during manufacturing of wafers requires continuous monitoring of saw marks and waviness with a method that provides reproducible values.

　

Process and quality control during manufacturing of wafers requires continuous monitoring of waviness with a noncontact method that supports high throughput.

　

This Test Method determines the maximum peak-to-valley of waviness of multi or single crystal Si wafers that typically runs across the entire wafer surface and along the wire direction.

　

This Test Method employs an in-line, noncontacting and nondestructive method for measuring the waviness of clean, dry as-cut silicon wafers supported by two belts that move the test specimen through the measurement equipment.

　

This Test Method covers square and pseudo-square PV Si wafers, with a nominal edge length ≥125　mm and a nominal thickness ≥100　µm. It applies to both single-crystalline and multi-crystalline Si wafers.

　

The Test 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 Test Method is based on a light sectioning technique (see Related Information 1) where patterns of line segments or spots of light are projected onto a wafer surface and saw marks as well as the waviness peaks and valleys are oriented perpendicular to the direction of wafer transport.

　

Other measurement techniques may also provide similar information about the waviness of a wafer as compared to this Test Method, but they are not the subject of this Test Method.

　

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

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