SEMI PV46 - Test Method for In-Line Measurement of Lateral Dimensional Characteristics of Square and Pseudo-Square PV Silicon Wafers
The geometrical dimensions of PV silicon (Si) wafers are key specification parameters (SEMI PV22).
Parameters such as edge length and diagonal of a wafer appear to be obvious, if the wafers are perfectly square or pseudo-square.
However, SEMI PV22 allows deviations of the side lengths and corner angles of the nominally square wafers within a specified range, potentially resulting in nonsquare wafers.
In addition, the edges of real wafers usually cannot be represented by straight lines. They are curved to some extent.
This creates an ambiguity in measuring the edge lengths and other geometrical dimensions of wafers.
This Test Method defines selected terms and a test method for measuring corresponding parameters.
The test 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.
This Test Method measures lateral geometrical dimensions of crystalline PV Si wafers.
This method employs an in-line, noncontacting and nondestructive method for characterizing clean, dry PV Si wafers supported by a mechanism that move the test specimen through the measurement equipment.
The surface condition of the wafers may be as cut, etched or passivated.
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 recording and evaluating images of the wafer surface obtained by a digital camera under diffuse white light illumination.
The test method does not include the measurement of wafer thickness or thickness variation. For this measurement see SEMI PV41.
Other measurement techniques may also provide similar information, but they are not the subject of this Test Method.
Referenced SEMI Standards
SEMI E89 — Guide for Measurement System Analysis (MSA)
SEMI MF1569 — Guide for Generation of Consensus Reference Materials for Semiconductor Technology
SEMI PV22 — Specification for Silicon Wafers for Use in Photovoltaic Solar Cells
SEMI PV32 — Specification for Marking of PV Silicon Brick Face and PV Wafer Edge
SEMI PV41 — Test Method for In-Line, Noncontact Measurement of Thickness and Thickness Variation of Silicon Wafers for PV Applications Using Capacitive Probes