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SEMI E43-0301 © SEMI 1995 , 2001 1 SEMI E43-0301 GUIDE FOR MEASURING STA TIC CHARGE ON OBJECTS AND SURFACES This g u ide was technically approved by the Global Metrics Com mittee and is the direct responsibility of the N…

SEMI E35.1-95 © SEMI 1995, 2004 2

compared directly on the basis of particles or other

direct metrics such as uniformity.

5.2.3 The Cost of Equipment Ownership should only

reflect Equipment Yield. The percentage of wafers

which can be passed to the next step can be based on

any criteria, such as broken wafers or wafers

determined to be defective by inspection or test.

5.3 Life — Time over which the fixed and recurring

costs are spread for the annualized basis. Tax Life is

customarily used in COO based upon standard

accounting practice.

COO Lifetimes

1. Tax Lifetime - Depreciation

2. Equipment Production Lifetime

5.4 System Throughput — Wafers per hour capability

for the process system.

5.5 Volume Requirement

5.5.1 The volume requirement is the wafer or IC (unit)

flow to be processed. The volume requirement can be

derived from specification of the product wafers or IC

devices needed corrected for yield and the required

number of other wafers which might be designated as

test, dummy, or monitor wafers. One complication in

accurately dealing with the volume requirement is that

the volume of wafers actually reaching the equipment

will depend on the volume loss from equipment yield

for all the prior steps.

5.5.2 For CEOC, volume should be dealt with

parametrically based upon factory wafer starts. For

multi-chamber equipment, the impact of added

chambers to increase capacity should be included as

well as the impact of adding whole systems.

5.6 Good Wafer Equivalents (GWE) — GWE is

derived from the number of good product die at wafer

probe and is expressed as completely good wafers.

5.7 Systems Required — See SEMI E35.

6 Reporting Results

Conform to SEMI E35.

7 Limitations

7.1 Certain factors are more difficult than others to

accurately determine. Thus, the accuracy of a COO

calculation may be prone to a variety of errors or

omissions. In addition, line balance considerations are

not included in cost of ownership calculation.

7.2 A COO calculation may have more detail than

presented explicitly in this guide. The structure of the

guide however allows for the proper handling of these

situations.

8 Procedures

8.1 The CEOC algorithm requires the specification of

the volume level and the enumeration of appropriate

fixed and recurring costs associated with processing

that volume. The CEOC metric is a function expressed

as the sum of a number of categories which constitute a

classification system as given in SEMI E35. Each item

in the classification system should be defined, a method

for evaluating its expression given, and default values

or handling specified. The cost of equipment ownership

is a sum over the elements in the Category Table as

expressed in Equation 2 and defined in SEMI E35.

8.2 Each item in the classification system is defined, a

method for evaluating its expression given, and default

values or handling specified. All costs must be assigned

through the classification system and calculated per

system for the number of production hours.

CEOC

∑













Volume

Required

# Systems

# Good Units

er year













∑













Volume

Required

# Systems

# Good Units

er yea













(2)

NOTICE: These standards do not purport to address

safety issues, if any, associated with their use. It is the

responsibility of the user of these standards to establish

appropriate safety and health practices and determine

the applicability of regulatory limitations prior to use.

SEMI makes no warranties or representations as to the

suitability of the standards set forth herein for any

particular application. The determination of the

suitability of the standard is solely the responsibility of

the user. Users are cautioned to refer to manufacturer’s

instructions, product labels, product data sheets, and

other relevant literature respecting any materials

mentioned herein. These standards are subject to

change without notice.

The user’s attention is called to the possibility that

compliance with this standard may require use of

copyrighted material or of an invention covered by

patent rights. By publication of this standard, SEMI

takes no position respecting the validity of any patent

rights or copyrights asserted in connection with any

item mentioned in this standard. Users of this standard

are expressly advised that determination of any such

patent rights or copyrights, and the risk of infringement

of such rights, are entirely their own responsibility.

International), 3081 Zanker Road, San Jose, CA 95134. Reproduction o

the contents in whole or in part is forbidden without express written

consent of SEMI.

SEMI E43-0301 © SEMI 1995, 20011

SEMI E43-0301

GUIDE FOR MEASURING STATIC CHARGE ON OBJECTS AND

SURFACES

This guide was technically approved by the Global Metrics Committee and is the direct responsibility of the

North American Metrics Committee. Current edition approved by the North American Regional Standards

Committee on November 22, 2000. Initially available at www.semi.org December 2000; to be published

March 2001. Originally published in 1995.

This document was entirely rewritten in 2001.

1 Purpose

1.1 The purpose is to establish a guide for

reproducible measurement of electrostatic charge(s) on

any surface or object, consistent with the scope and

limitations set forth below.

2 Scope

2.1 The measurement methods described herein can be

applied to characterize the general electrostatic charge

level(s) on objects and surfaces in all environments.

Acceptable instrumentation, calibration, and measure-

ment techniques are described in this document.

Appendices include background information on the

equipment specified and calibration procedure, as well

as information and advice on performing a useful

general static survey.

2.2 This standard does not purport to address safety

issues, if any, associated with its use. It is the

responsibility of the users of this standard to establish

appropriate safety health practices and determine the

applicability or regulatory limitations prior to use.

3 Limitations

3.1 Direct measurement of charge usually requires the

use of a coulombmeter. Charges on an isolated

conductor can be measured by transferring the charge

into the coulombmeter by contacting the isolated

conductor with the coulombmeter input probe. Charges

on isolated conductors and insulators can be measured

by transferring the charged object into a Faraday

enclosure that is connected to the coulombmeter. These

measurements can be relatively precise if care is taken

in the transfer process to avoid changing the charge

level when making the measurements.

3.2 Direct measurement of charge is often impractical.

In these instances, charge is indirectly evaluated by

detecting the electrostatic field from a charged surface

using an electrostatic fieldmeter or an electrostatic

voltmeter.

3.3 This guide does not describe instrumentation and

techniques capable of making highly precise

measurement of electrostatic charge. It is not suitable

for measurement of electrostatic charge on small

objects, such as packaged devices (i.e., reading(s)

obtained are indicative/general area and not precise/

minute). No methods of preconditioning the surface

prior to measurements and no methods of character-

izing the basic electrostatic performance of materials,

such as tribocharging, resistance, and decay rate are a

part of this document. Measurements made using this

guide on the same surface or object may differ due to

differences in the environment or history of the surface

or object between the times any two measurements are

made.

4 Referenced Standards

4.1 None.

5 Terminology

5.1 electrostatic discharge (ESD) — the rapid

spontaneous transfer of electrostatic charge induced by

a high electrostatic field.

5.2 ground — a conducting connection between an

object, electrical equipment, and earth, such as the

portion of an electrical circuit of the same electrical

potential as earth.

5.3 grounded — connected to earth or some other

conducting body that serves in the place of earth.

6 Safety

6.1 Measurements of Very High Static Potentials (>

30,000 Volts) — Measurements of very high static

potentials (> 30,000 V) may need to be done at larger

distances to avoid exceeding the measurement range of

the meter and/or an ESD event to the meter.

6.2 Measurements on Moving Objects or Surfaces —

Care should be taken, when attempting to read

electrostatic charges on moving objects or surfaces, to

maintain correct distance and avoid any contact; this is

to assure “good” readings with no mechanical damage

or personal injury.

6.3 Measurements Using Electrostatic Voltmeters —

Avoid handling electrostatic voltmeter probes during

SEMI E43-0301 © SEMI 1995, 2001 2

operation as their surfaces may be at elevated potentials

that represent a shock hazard to the operator.

7 Equipment and Performan ce Verification

Methods

7.1 Equipment

7.1.1 Electrostatic Locator/Field Sensor/Field Meter

— An electrostatic fieldmeter measures the value of the

electrostatic field at its sensor. Electrostatic fieldmeters

are calibrated and recommended for use at a particular

distance from the charged object. Fieldmeters are best

suited for making general surveys or audits, for making

measurements of surfaces at very high potentials

(charge levels), and for making measurements when

long-term stability is not important. They are not well

suited for measurements of surfaces with very low

potentials or when high spatial resolution of the surface

potential is needed.

7.1.1.1 The electrostatic locator/field sensor/field

meter will henceforth be referred to as “the fieldmeter.”

Note that for measurements to be taken in the presence

of air ionization, a chopper stabilized fieldmeter is

required. The fieldmeter must be capable of making

field measurements at a distance of 2.54 centimeters

(cm) = 1 inch or less, from the field source to the sensor

for this guide, as written. However, see Section 7.2.5

for fieldmeters that are operated at fixed distance(s),

and adjust values in this document where applicable.

7.1.2 Electrostatic Voltmeter — An electrostatic

voltmeter nulls the electrostatic field at its sensor

(probe). An electrostatic voltmeter indicates the

presence and approximate level of the charge(s)

creating the electrostatic field. Under appropriate

conditions, electrostatic voltmeters provide a better

approximation of the charge level as compared to

electrostatic fieldmeters. Electrostatic voltmeters are

relatively free of drift and more environmentally stable

as compared to fieldmeters.

7.1.2.1 Electrostatic voltmeters are well suited for

fixed installation in equipment. Electrostatic voltmeters

exhibit a high degree of accuracy that is independent of

the distance from the charge. Thus, they are considered

better suited for making more accurate and repeatable

measurements as compared to fieldmeters. The probe

can be located very close to a charged surface without

arc-over, and, under appropriate conditions, can resolve

a small spatial area on a surface.

7.1.2.2 Electrostatic voltmeters are best suited for

making measurements of surfaces at potentials below

20kV, or when a calibrated or fixed distance from the

probe to the surface cannot be maintained. They are

also best suited for measuring low surface potentials, or

when it is desired to resolve a small area on the surface.

Electrostatic voltmeters are unsuitable for measuring

surfaces at very high potentials, such as above 20kV.

7.1.2.3 The electrostatic voltmeter will henceforth be

referred to as “the voltmeter.”

7.1.3 Electrometer — An electrometer is a contact

voltmeter with a very high input impedance. Ideally,

this input impedance would be infinite. In practice, it is

limited by intrinsic physical materials properties of

insulators and by stray leakage paths between the input

terminals. Low voltage electrometers (below 200 Volt)

have typical input resistances of 10

ohms, accuracies

better than 0.1%, and can resolve microVolt type

potentials. High voltage electrometers (Kilovolts)

usually rely on resistive voltage dividers and have

typical input resistances in the 10

ohms range with

accuracies in the 1% range. It is important to evaluate

and understand the burden that the input impedance of

an electrometer represents when measuring voltage

potentials on very small charged structures.

7.1.4 Charged Plate Monitor — A charged plate

monitor is an instrument typically used to monitor the

performance of air ionization equipment. Monitoring is

done with an electrically isolated 15 cm × 15 cm (6

inches × 6 inches) metal plate, henceforth referred to as

“the plate.” The instrument typically provides a means

to charge the plate to a known voltage (1000 or 5000

volts of either polarity), a plate sensor to determine the

voltage on the plate, and timing circuitry to determine

the time required to discharge the plate to a percentage

of its initial charge. For the purposes of this guide, the

charged plate monitor, or a separate isolated plate

assembly, can be used for performance verification

purposes as explained in Section 7.2.

7.2 Equipment Performance Verification (Confidence

Test)

7.2.1 Performance Verification of a Coulombmeter —

Refer to Figure 1.

7.2.1.1 Zero the coulombmeter prior to each

measurement.

7.2.1.2 Maintain a reference calibration capacitor. It

should be a polystyrene or polypropylene 10 nF

capacitor (Mallory SX-110 or equivalent). Measure the

value of the capacitor to better than 1%. It is important

to handle the reference calibration capacitor very

carefully. Do not hold the capacitor by its body or

discharge it by touching both leads with the fingers.

Hold the capacitor by one lead only. Use a clip lead

connected between ground and this lead of the capacitor

to maneuver the other lead of the capacitor between the

“hot” side of the charging source and the input terminal

of the coulombmeter.