The diameter of semiconductor wafers is an important parameter in microelectronic fabrication. Wafer diameters must conform to the limits specified in SEMI M1; or other agreed upon limits, or product that is otherwise suitable may not fit correctly in process equipment.

Cam-follower edge rounding usually results in wafers that are circular. However, wafers ground with edge-follower edge rounding equipment may be elliptically shaped. Measurements made at the three positions specified in this Guide do not provide complete information about the roundness of the wafer.

This Guide defines standardized positions for measuring diameter of circular wafers of silicon and other semiconducting materials especially those processed with edge-follower edge-rounding equipment that contain flats or notches (fiducials) on the periphery. It was developed for use with silicon wafers of 150 mm diameter or less with standard diameter and fiducial positions as given in SEMI M1.

It may be applied to other types of semiconductor wafers if the flat locations are properly taken into account or if the fiducial is a notch.

No recommendations are given regarding the test instrumentation to be used, but either contacting (taking suitable precautions to avoid edge chipping) or noncontacting gauges have been found to be satisfactory. Wafers of any size can be measured provided that suitable test jigs and instruments are available.

Roundness of wafers cannot be determined from measurements made solely at the positions defined in this Guide. No information is provided concerning the diameter of the wafer at points other than those measured.

Referenced SEMI Standards (purchase separately)
SEMI M1 — Specification for Polished Single Crystal Silicon Wafers
SEMI M20 — Practice for Establishing a Wafer Coordinate System

Revision History
SEMI MF2074-0912 (Reapproved 1023)
SEMI MF2074-0912 (Reapproved 0718)
SEMI MF2074-0912 (technical revision)
SEMI MF2074-0707 (technical revision)
SEMI MF2074-1103 (first SEMI publication)