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SEMI MF1390-1104 © SEMI 2004 1 SEMI MF1390-1104 TEST METHOD FOR MEASURING WA RP ON SILICON WAFERS BY AUTOMATED NON-CO NTACT SCANNING This test method was technically approved by th e Global Silicon Wafer Committee and is…

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SEMI MF1390-1104 © SEMI 2004 1

SEMI MF1390-1104

TEST METHOD FOR MEASURING WARP ON SILICON WAFERS BY

AUTOMATED NON-CONTACT SCANNING

This test method was technically approved by the Global Silicon Wafer Committee and is the direct

responsibility of the North American Silicon Wafer Committee. Current edition approved for publication by

the North American Regional Standards Committee on August 16, 2004. Initially available at

www.semi.org

September 2004; to be published November 2004. Original edition published by ASTM International as

ASTM F 1390-92. Last previous edition SEMI MF1390-0704.

1 Purpose

1.1 Warp can significantly affect the yield of

semiconductor device processing.

1.2 Knowledge of this characteristic can help the

producer and consumer determine if the dimensional

characteristics of a specimen wafer satisfy given

geometrical requirements.

1.3 Changes in wafer warp during processing can

adversely affect subsequent handling and processing

steps. These changes can also provide an important

process monitoring function.

1.4 This test method is suitable for measuring the warp

of wafers used in semiconductor device processing in

the as-sliced, lapped, etched, polished, epitaxial or other

layer condition and for monitoring thermal and

mechanical effects on the warp of wafers during device

processing.

2 Scope

2.1 This test method covers a non-contacting,

nondestructive procedure to determine the warp of

clean, dry semiconductor wafers.

2.2 This test method employs a two-probe system that

examines both external surfaces of the wafer

simultaneously.

2.3 The test method is applicable to wafers 50 mm or

larger in diameter, and approximately 100 m and

larger in thickness, independent of thickness variation

and surface finish, and of gravitationally induced wafer

distortion.

2.4 This test method is not intended to measure the

flatness of either exposed silicon surface. Warp is a

measure of the distortion of the median surface of the

wafer.

2.5 This test method measures warp of a wafer

corrected for mechanical forces applied during the test.

Therefore, the procedure described gives the

unconstrained value of warp.

NOTE 1: This warp is indicated by the acronym

“GMLYMER” in Appendix 2, Shape Decision Tree, of SEMI

M1.

NOTE 2: SEMI MF657 measures median surface warp using

a three-point back-surface reference plane. The back-surface

reference results in thickness variation being included in the

recorded warp value. The use (in this test method) of a

median surface reference plane eliminates this effect. The use

(in this test method) of a least-squares fit reference plane

reduces the variability introduced in three-point plane

calculations by choice of reference point location. The use (in

this test method) of special calibration or compensating

techniques minimizes the effects of gravity-induced distortion

of the wafer.

2.6 This test method includes several methods for

canceling gravity-induced deflection which could

otherwise alter the shape of the wafer.

NOTE 3: One of these methods, the Representative Wafer

Inversion Method, is covered by a patent held by ADE

Corporation, 80 Wilson Way, Westwood, MA 02090-1806.

NOTICE: This standard does not purport to address

safety issues, 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 or other limitations prior

to use.

3 Limitations

3.1 Any relative motion along the probe measuring axis

between the probes and the wafer holding device during

scanning will produce error in the measurement data.

Vibration of the test specimen relative to the probe-

measuring axis will introduce error. Such errors are

minimized by system signature analysis and correction

algorithms. Internal system monitoring may also be

used to correct non-repetitive and repetitive system

mechanical translations. Failure to provide such

corrections may cause errors.

3.2 If a measured wafer differs substantially in

diameter, thickness, fiducials, or crystal orientation

from that used for the gravitational compensation

procedure, the results may be incorrect. Estimates of

the errors in gravity induced deflection for differences

1 Poduje, N., “Eliminating Gravitational Effect in Wafer Shape

Measurements,” NIST/ASTM/SEMI/SEMATECH Technology Confe-

rence, Dallas, TX. Technology for Advanced Materials/Process

Characterization, February 1, 1990.

SEMI MF1390-1104 © SEMI 2004 2

in diameter and thickness are shown in Related

Information 1. If the crystal orientation of the sample

to be measured differs from the crystal orientation of

the gravity-compensation wafer, then the measured

warp value may differ from the actual warp value by up

to 15%. Error tables for fiducial variation have not

been generated.

3.3 Different methods for implementing gravitational

compensation may give different results. Varying

levels of completeness of implementing a method may

also give different results.

3.4 Mechanical variations in wafer holding devices

between systems may introduce measurement

differences. This test method allows the use of a

variety of wafer holding devices (see Section 7.1.4.1);

results obtained with different geometrical

configurations of wafer holding device on the same test

samples may differ.

3.5 Most equipment systems capable of this

measurement have a definite range of wafer thickness

combined with warp (dynamic range) that can be

accommodated without readjustment. If the sample

moves outside this dynamic range during either

calibration or measurement, results may be in error. An

over-range signal can be used to alert the operator and

measurement data examiners to this event.

3.6 The quantity of data points and their spacing may

affect the measurement results. This test method does

not specify the data point spacing (see Section 7.1.4.2);

results obtained with different data point spacings on

the same test samples may differ.

4 Referenced Standards

4.1 SEMI Standards

SEMI M1 — Specifications for Polished

Monocrystalline Silicon Wafers

SEMI MF657 — Test Method for Measuring Warp and

Total Thickness Variation on Silicon Wafers by

Noncontact Scanning

SEMI MF1241 — Terminology of Silicon Technology

SEMI MF1530 — Test Method for Measuring Flatness,

Thickness, and Thickness Variation on Silicon Wafers

by Automated Non-contact Scanning

4.2 ASTM Standard

E 691 — Practice for Conducting an Interlaboratory

Study to Determine the Precision of a Test Method

2 Available from ASTM International, 100 Barr Harbor Drive, West

Conshohocken, PA 19428, Tel: 610-832-9500, Fax: 610-832-9555,

Website

http://www.astm.org. Appears in Volume 14.02 of Annual

Book of ASTM Standards.

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

5 Terminology

5.1 Definitions

5.1.1 mechanical signature, of an instrument — that

component of a measurement that is introduced by the

instrument and that is systematic, repeatable, and

quantifiable.

5.1.2 median surface, of a semiconductor wafer — the

locus of points equidistant from the front and back

surfaces of the wafer.

5.1.3 reference plane, of a semiconductor wafer — a

plane from which deviations of a specified surface of

the wafer are measured.

5.1.4 reference plane deviation (RPD) — the distance

from a point on a reference plane to the corresponding

point on a wafer surface.

5.1.4.1 Discussion — A dome-shaped wafer is

considered to have positive RPD at its center; a bowl-

shaped wafer is considered to have negative RPD at its

center.

5.1.5 thickness, of a semiconductor wafer — the

distance through the wafer between corresponding

points on the front and back surfaces.

5.1.6 warp, of a semiconductor wafer — the algebraic

difference between the most positive and the most

negative deviations of the median surface of a wafer

that is not chucked from a reference plane that is a least

squares fit to the median surface.

5.1.6.1 Discussion — Although warp may be caused by

unequal stresses on the two exposed surfaces of the

wafer, it cannot be determined from measurements on

a single exposed surface. The median surface may

contain regions with upward or downward curvature or

both; under some conditions the median surface may be

flat. In all cases, warp is a zero or positive quantity.

Stylized examples of visualization of warp are shown in

SEMI MF657.

5.2 Definitions of other terms related to silicon material

technology can be found in SEMI MF1241.

6 Summary of Test Method

6.1 A calibration procedure is performed to set the

instrument's scale factor and other constants. If the

representative wafer inversion method is used for

gravity correction, the calibration procedure also

determines the mechanical signature of the instrument

and the effect of gravity on the wafer.