The orientation of flats on silicon wafers is an important materials acceptance requirement. The flats are used in semiconductor device processing to provide consistent alignment of device geometries with respect to crystallographic planes and directions.

 

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

 

This Standard covers two test methods for determining flat orientation. Either one of these test methods is appropriate for process development and quality assurance applications. Until the interlaboratory precision of these test methods has been determined, it is not recommended that they be used between supplier and customer unless correlation studies are completed satisfactorily.

This Test Method covers the determination of α, the angular deviation between the crystallographic orientation of the direction perpendicular to the plane of a fiducial flat on a circular silicon wafer, and the specified orientation of the flat in the plane of the wafer surface.

 

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

 

The orientation accuracy achieved by this Test Method depends directly on the accuracy with which the flat surface can be aligned with a reference fence and the accuracy of the orientation of the reference fence 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 Test Method A of SEMI MF26, except that it uses special wafer holding fixtures to orient the wafer uniquely with respect to the X-ray goniometer. The technique is capable of measuring the crystallographic direction of flats to a greater precision than the Laue back reflection method.

 

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

 

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

 

Referenced SEMI Standards (purchase separately)

SEMI M1 — Specification for Polished Single Crystal Silicon Wafers

SEMI M59 — Terminology for Silicon Technology

SEMI MF26 — Test Method for Determining the Orientation of a 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)