The orientation of flats on silicon wafers is an importantmaterials acceptance requirement. The flats are used in semiconductor deviceprocessing to provide consistent alignment of device geometries with respect tocrystallographic planes and directions.

The orientation of a wafer flat is the orientation of thesurface of the flat (on the edge of the wafer). Flats are usually specifiedwith respect to a low-index plane, such as a (110) plane. In such cases theorientation of the flat may be described in terms of its angular deviation fromthe low-index plane.

This Standard covers two test methods for determining flatorientation. Either one of these test methods is appropriate for processdevelopment and quality assurance applications. Until the interlaboratoryprecision of these test methods has been determined, it is not recommended thatthey be used between supplier and customer unless correlation studies arecompleted satisfactorily.

This Test Method covers the determination of α, the angulardeviation between the crystallographic orientation of the directionperpendicular to the plane of a fiducial flat on a circular silicon wafer, andthe specified orientation of the flat in the plane of the wafer surface.

This Test Method is applicable for wafers with flat length valuesin the range of those specified for silicon wafers in SEMI M1. It is suitablefor use only on wafers with angular deviations in the range from −5° to 5°.

The orientation accuracy achieved by this Test Methoddepends directly on the accuracy with which the flat surface can be alignedwith a reference fence and the accuracy of the orientation of the referencefence with respect to the X-ray beam.

Two test methods are covered as follows:

• Test Method A — X-Ray Edge Diffraction Method
• Test Method B — Laue Back Reflection X-Ray Method

Test Method A is nondestructive and is similar to TestMethod A of SEMI MF26, except that it uses special wafer holding fixtures toorient the wafer uniquely with respect to the X-ray goniometer. The techniqueis capable of measuring the crystallographic direction of flats to a greaterprecision than the Laue back reflection method.

Test Method B is also nondestructive, and is similar toASTM E82, and to DIN 50433-3, except that it uses ‘instant’ film and specialfixturing to orient the flat with respect to the X-ray beam. Although it issimpler and more rapid, it does not have the precision of Test Method A becauseit uses less precise and less expensive fixturing and equipment. It produces apermanent film record of the test.

The values stated in SI units are to be regarded as thestandard. The inch-pound values given in parentheses are for information only.

Referenced SEMI Standards (purchase separately)

SEMI M1 — Specification for Polished Single Crystal SiliconWafers

SEMI M59 — Terminology for Silicon Technology

SEMI MF26 — Test Method for Determining the Orientation ofa Semiconductive Single Crystal

Revision History

SEMI MF847-0316 (Reapproved 0222)

SEMI MF847-0316 (technical revision)

SEMI MF847-0705 (Reapproved 0611)

SEMI MF847-0705 (technical revision)

SEMI MF847-02 (first SEMI publication)