ASTM F2358-04

The measurements described in this guide can significantly affect the function of the sapphire substrate.

Substrates with excessive form errors in the free state may cause processing errors in production.

The restrained state of the substrate is intended to simulate as closely as possible the form that the substrate will take in one of its intended uses. During processing, one surface of the substrate is sometimes forcibly restrained to a flat state through either vacuum or adhesion to a flat surface. The measurements in the clamped state are intended to model the form of the front surface of the substrate when the back surface is constrained to the reference plane. The form in the clamped state may have a direct impact on the performance of the substrate in use.

The user should determine whether the unrestrained or restrained measurements are most pertinent to the application and specify the appropriate parameters accordingly.

Knowledge of these characteristics can help the producer and consumer determine if the dimensional characteristics of a specimen substrate satisfy given geometrical requirements.

This guide is suitable for sapphire substrates in the as-sliced, lapped, polished, or other condition. Refer to SEMI M3 for substrate specifications.

Until the results of a planned interlaboratory evaluation of this guide are established, use of this guide for commercial transactions is not recommended unless the parties to the test establish the degree of correlation that can be obtained.

1.1 This guide covers a nondestructive procedure to determine the form of clean, dry sapphire substrates.

1.2 This guide is applicable to substrates 25 mm or larger in diameter, with a minimum thickness of 100 μm. This guide is independent of surface finish.

1.3 The measurements described in this guide may be applied to the entire global surface of the substrate, or to smaller localized areas.

1.4 The value of the measurements described in this guide will be affected by the amount of edge exclusion (that is, the area around the perimeter of the part which is ignored). The amount excluded should be agreed upon by the producer and consumer using this standard.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory requirements prior to use.