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SEMI MF1527-1104 © SEMI 2003, 2004 3 which is issue d by a certifying body (ISO Guide 30:1981). 4.1.2 Discussion — ISO 8402 states that in a calibration sense, traceability relates measuring equipment to national or inte…

SEMI MF1527-1104 © SEMI 2003, 2004 2

3 Referenced Standards

3.1 SEMI Standards

SEMI C28 — Specifications and Guidelines for

Hydrofluoric Acid

SEMI C35 — Specifications and Guideline for Nitric

Acid

SEMI C39 — Specification for Potassium Hydroxide

Pellets

SEMI M1 — Specifications for Polished

Monocrystalline Silicon Wafers

SEMI MF43 — Test Methods for Resistivity of

Semiconductor Materials

SEMI MF81 — Test Method for Measuring Radial

Resistivity Variation on Silicon Wafers

SEMI MF84 — Test Method for Measuring Resistivity

of Silicon Wafers with an In-line Four-point Probe

SEMI MF525 — Test Method for Measuring

Resistivity of Silicon Wafers Using a Spreading

Resistance Probe

SEMI MF533 — Test Method for Thickness and

Thickness Variation of Silicon Slices

SEMI MF672 — Test Method for Measuring

Resistivity Profile Perpendicular to the Surface of a

Silicon Wafer Using a Spreading Resistance Probe

SEMI MF673 — Test Method for Measuring

Resistivity of Semiconductor Slices or Sheet Resistance

of Semiconductor Films with a Non-contact Eddy-

current Gage

SEMI MF723 — Practice for Conversion Between

Resistivity and Dopant Density for Boron-doped,

Phosphorus-doped, and Arsenic-doped Silicon

SEMI MF1241 — Terminology of Silicon Technology

SEMI MF1392 — Test Method for Determining Net

Carrier Density Profiles in Silicon Wafers by

Capacitance-voltage Measurements with a Mercury

Probe

SEMI MF1393 — Test Method for Determining Net

Carrier Density in Silicon Wafers by Miller Feedback

Profiler Measurements with a Mercury Probe

SEMI MF1529 — Test Method for Sheet Resistance

Uniformity Evaluation by in-line Four-point Probe with

the Dual-configuration Procedure

SEMI MF1530 — Test Method for Measuring Flatness,

Thickness, and Thickness Variation on Silicon Wafers

by Automated Non-contact Scanning

SEMI MF1618 — Practice for Determining Uniformity

of Thin Films on Silicon Wafers

SEMI MF2074 — Guide for Measuring Diameter of

Silicon and Other Semiconductor Wafers

3.2 ASTM Standard

D 5127 — Guide for Ultra Pure Water Used in the

Electronics and Semiconductor Industry

3.3 DIN Standards

50431 — Measurement of the Electrical Resistivity of

Silicon or Germanium Single Crystals by Means of the

Four-Point-Probe Direct Current Method with Collinear

Four-probe Array

50439 — Determination of the Dopant Concentration

Profile of Single Crystalline Semiconductor Material by

Means of the Capacitance-voltage Method and Mercury

Contact

50445 — Contactless Determination of the Electrical

Resistivity of Semiconductor Wafers with the Eddy

Current Method

50447 — Contactless Measurement of Electrical

Surface Resistivity of Semiconductor Layers by Eddy-

current Method

3.4 ISO Standards

Guide 30:1981 Terms and Definitions Used in

Connection with Reference Materials

ISO 8402 — Quality—Vocabulary

ISO 10012-1 — Quality Assurance Requirements for

Measuring Equipment—Part 1: Management of

Measuring Equipment

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

4 Terminology

4.1 Definitions Terms Related to Reference Materials

4.1.1 certified reference material (CRM) — a reference

material one or more of whose property values are

certified by a technically valid procedure, accompanied

by or traceable to a certificate or other documentation

1 Annual Book of ASTM Standards, Vol 11.01, ASTM International,

100 Barr Harbor Drive, West Conshohocken, PA 19428. Telephone:

610-832-9500, Fax: 610-832-9555, Website:

www.astm.org.

2 Available in both German and English editions from Deutches

Institut für Normung e.V., Beuth Verlag GmbH, Burggrafenstrasse 4-

10, D 10787 Berlin, Germany, website:

www.din.de.

3 ISO Central Secretariat, C. P. 56, CH-1211 Genève 20,

Switzerland, Website:

www.iso.ch, available in the U.S. from

American National Standards Institute, 11 West 42nd Street, 13th

Floor, New York, NY 10036, Website:

www.ansi.org

SEMI MF1527-1104 © SEMI 2003, 2004 3

which is issued by a certifying body (ISO

Guide 30:1981).

4.1.2 Discussion — ISO 8402 states that in a

calibration sense, traceability relates measuring

equipment to national or international standards,

primary standards, or basic physical constants or

properties. In the present guide, as in ISO 10012-1, the

term “measuring equipment” is extended to include

both measuring instruments and measurement standards

(including reference wafers).

4.1.3 reference material (RM) — a material or

substance one or more properties of which are

sufficiently well established to be used for the

calibration of an apparatus, (for) the assessment of a

measurement method, or for assigning values to

materials (ISO Guide 30:1981; ISO 10012-1).

4.1.4 resistivity reference wafer — a CRM or RM in

the form of a silicon wafer or chip used for routine

calibration or control of resistivity measuring

equipment.

4.1.5 Standard Reference Material (SRM

®) — a

certified reference material issued by the U.S. National

Institute of Standards and Technology.

4.1.6 traceability — the ability to trace the history,

application, or location of an item or activity, or similar

items or activities, by means of recorded identification

(ISO 8402).

4.2 Definitions of Terms Related to Four-point Probes

4.2.1 four-point probe — an electrical probe

arrangement for determining the resistivity of a material

in which separate pairs of contacts are used (1) for

passing current through the specimen, and (2)

measuring the potential drop caused by the current.

4.2.2 probe head, of a four-point probe — the

mounting that (1) fixes the positions of the four pins of

the probe in a specific pattern such as an in-line

(collinear) or square array, and (2) contains the pin

bearings and springs or other means for applying a load

to the probe pins.

4.2.3 probe pin, of a four-point probe — one of the

four needles supporting the probe tips; mounted in a

bearing contained in the probe head and loaded by a

spring or dead weight.

4.2.4 probe tip, of a four-point probe — the part of the

pin that contacts the wafer.

4.2.5 probe-tip spacing, of a four-point probe — the

distance between adjacent probe tips.

SRM

is a registered trademark of the U.S. National Institute of

Standards and Technology and the U.S. Government.

4.3 For definitions of other terms used in silicon wafer

technology refer to SEMI M1 and SEMI MF1241.

5 Reagents

5.1 Purity of Reagents — All chemicals for which such

specifications exist shall conform to Grade 1 SEMI

specifications for those specific chemicals. Other

grades may be used, provided it is first determined that

the chemical is of sufficiently high purity to permit its

use without lessening the accuracy of the test.

5.2 Purity of Water — Reference to water shall be

understood to mean water meeting the requirements of

Type E-3 water or better as described in ASTM Guide

D 5127.

5.3 The recommended chemicals shall have the

following nominal assays:

5.3.1 Nitric Acid, HNO

, concentrated, 70 to 71%,

Grade 1 in accordance with SEMI C35,

5.3.2 Hydrofluoric Acid, HF, concentrated, 49.00 ±

0.25%, Grade 1 in accordance with SEMI C28, and

5.3.3 Potassium Hydroxide, KOH, pellets, 85% min,

Grade 1 in accordance with SEMI C39.

5.4 KOH Etching Solution — Dissolve potassium

hydroxide (KOH) in water to make a 50 weight % KOH

solution in sufficient volume to allow complete

immersion of the largest wafers to be prepared for test.

This solution is to be used at a temperature of 65 to

75°C.

5.5 Etching Solution (15 + 1) — Mix 15 parts of nitric

acid (HNO

) with one part of hydrofluoric acid (HF) in

sufficient volume to allow complete immersion of the

largest wafers to be prepared for test.

6 Resistivity CRMs

6.1 Resistivity CRMs are available from several

sources in a variety of configurations, orientations,

conductivity types, and resistivity. Choose the

configuration to match the desired application as

closely as possible. For example, choose whole wafers

for applications involving whole wafer measurements

and chip sets with relatively closely spaced resistivity

values and appropriate orientation and conductivity

type for applications involving spreading resistance.

7 Control of Primary Resistivity Measuring

Instruments

7.1 “Primary” resistivity measuring instruments are

four-point probes used for calibrating resistivity

reference wafers. Such instruments must (1) meet the

requirements of SEMI MF84, (2) be maintained in a

state of control through the use of

and s instrument

SEMI MF1527-1104 © SEMI 2003, 2004 4

control charts (see Section 7.1.1), (3) return measured

resistivity values of appropriate CRMs to within desired

limits through measurement of resistivity CRMs at

regular intervals (see Section 7.1.2), and (4) be operated

within the temperature range specified in SEMI MF84

(see Section R2-4 of this guide).

7.1.1 Instrument Control Charts —

and s control

charts should be maintained to establish the stability of

the instrument over the range of resistivity that the

instrument is expected to measure. A separate control

chart should be maintained for each reference wafer

used. Initially, resistivity CRMs or other wafers with

adequate radial resistivity uniformity (see Section 8.5.1)

should be used for this purpose. As resistivity reference

wafers are prepared, these should be used for

maintaining the control charts. After in-house

resistivity reference wafers become available, it is

recommended that three wafers at each resistivity level

be set aside for control charting. Two of these should

be used for maintaining the

and s charts on a regular

basis. The third is retained as a reference to ensure that

any apparently out-of-control conditions are due to the

instrument and not to changes in sample surface

conditions, as might occur after prolonged use of a

particular sample. Each resistivity determination

should consist of six to ten measurements made in

accordance with SEMI MF84. Established procedures

for generating and maintaining the control charts and

for determining the existence of out-of-control

conditions and the need for corrective action should be

used. A suggested procedure for these determinations

is given in Section R1-2 for use in organizations

without previously established procedures.

7.1.2

Comparison with CRMs — To provide

traceability, measurements of the resistivity of available

CRMs that encompass the range of resistivity expected

to be encountered should be made on a periodic, but

less frequent, basis. In addition to being in control, the

instruments should return measured values of the

resistivity of the CRMs that do not deviate from their

certified value by more than the root mean square of the

two-sigma (95 % confidence level estimate) uncertainty

of the CRM (Note 1) and the two-sigma instrument

variability determined by control charting procedures

(Note 2). A suggested procedure for control charting of

CRMs is given in Section R1-3 for use in organizations

without previously established procedures.

NOTE 1: A laboratory issuing a CRM should provide a

comprehensive statement of its uncertainty associated with

the measurement and reporting of the CRM value. This

should include evaluations, or estimates, of both random and

systematic “errors” following ISO procedures for Type A and

Type B evaluations of components of uncertainty. The result

would be expressed as a Combined Standard Uncertainty

(standard deviation, or square-root of a sum of variances of

uncertainty components), or as an “Expanded Uncertainty” (2

times the Combined Standard Uncertainty). If based on

sufficient statistical degrees of freedom, the Combined

Standard Uncertainty is a one-sigma estimate, and the

Expanded Uncertainty is a two-sigma, or 95% confidence-

level, estimate. If there are insufficient statistical degrees of

freedom, the effective number of degrees of freedom should

be reported by the CRM-issuing laboratory. It is then

necessary to multiply the uncertainty value provided by the

student-t factor appropriate to that number of degrees of

freedom in order to obtain values for the one-sigma or two-

sigma (95% confidence-level) measurement uncertainty.

NOTE 2: A laboratory following this procedure to establish

traceability to resistivity CRMs incorporates a value of its

measurement uncertainty based on its control chart

measurements, which evaluate random components of

uncertainty only. If the laboratory then measures a value for

the CRM within the total uncertainty interval, calculated

following the root-mean-square procedure, above, about the

certified value, its instrument is validated for use. If it

measures a value outside the prescribed interval, this is an

indication that its measurement bias with respect to true value

is statistically significant at the 95% level, and instrument

repair, or “calibration” is necessary before proceeding.

7.1.3 Probe Assembly and Electrical Equipment Tests

— Should an out-of-control or out-of-specification

condition be encountered, the probe assembly and

electrical equipment can be tested in accordance with

the section on Suitability of Test Equipment in SEMI

MF84. These tests may serve to isolate the cause of the

problem encountered. Either or both of these

components should be repaired or replaced if they fail

to meet the requirements specified in this section of

SEMI MF84.

NOTE 3: The stringent requirements on control of probe-tip

spacing as well as the need for off-center diameter correction

factors required for determination of radial resistivity

uniformity (see Section 8.5) are a consequence of the single-

configuration method of using the four-point probe in

accordance with SEMI MF84. Errors resulting from

uncertainty in probe-tip spacing when using the single-

configuration method are considered in Related Information

2. The probe-tip spacing requirements can be relaxed

significantly if the dual-configuration method

of measuring

resistivity with a four-point probe is used. Use of this method

is recommended for determination of the radial resistivity

uniformity (see Section 8.5). However, the dual-

configuration method has not yet been standardized for bulk

resistivity measurements because appropriate thickness

correction factors have not yet been published. Such

corrections are required for thickness to probe spacing ratios

greater than 0.36. Nevertheless, it is noted that the most

5 Perloff, D. S., “Four-point Probe Correction Factors for Use in

Measuring Large Diameter Doped Semiconductor Wafers,” J.

Electrochem. Soc. 123, 1745–1750 (1976).