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SEMI E78-1102 © SEMI 1998, 2002 2 discharged at a kn own voltage. This device i s used to establish the ESD dam age threshold for semi conductor products, or t he effect of ESD on equi pment. While the amount of cha rge …
SEMI E78-1102 © SEMI 1998, 2002 1
SEMI E78-1102
ELECTROSTATIC COMPATIBILITY - GUIDE TO ASSESS AND
CONTROL ELECTROSTATIC DISCHARGE (ESD) AND
ELECTROSTATIC ATTRACTION (ESA) FOR EQUIPMENT
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 August 29, 2002. Initially available at www.semi.org September 2002; to be published
November 2002. Originally published September 1998.
1 Purpose
1.1 The purpose of this document is to minimize the
negative impact on productivity caused by static charge
in semiconductor manufacturing environments. It is a
guide for establishing electrostatic compatibility of
equipment used in semiconductor manufacturing.
1.2 Electrostatic surface charge causes a number of
undesirable effects in semiconductor manufacturing
environments. Electrostatic discharge (ESD) damages
both products and reticles. ESD events also cause
electromagnetic interference (EMI), resulting in
equipment malfunctions. Charged wafer and reticle
surfaces attract particles (electrostatic attraction or
ESA) and increase the defect rate. Charge on products
can also result in equipment malfunction or product
breakage. Operating problems and additional product
defects due to static charge can have a negative impact
on the cost of ownership of semiconductor
manufacturing equipment (refer to SEMI E35).
1.3 An increasing amount of semiconductor production
is done in minienvironments or within the production
equipment. The majority of static related problems
occur while the product is in its carriers, or being
transferred from them, by the production equipment.
1.4 Static control methods can be incorporated in the
equipment design to reduce static charge to acceptable
levels. This guide will be used primarily by equipment
manufacturers during the design of their equipment.
There are test methods available (see Sections 6 and 7
of this guide) to demonstrate the effectiveness of the
static control methods. The end user will be able to use
the same test methods to verify compliance with an
equipment purchase specification.
2 Scope
2.1 The scope of this document is limited to methods
of measurement and a guide for the maximum
recommended level of static charge on:
• Product or reticles,
• Carriers, and
• Parts of the input/exit ports of equipment and
minienvironments.
2.2 This document presents a matrix of maximum
recommended levels of static charge on products,
reticles, carriers, and the input and exit ports of
production equipment or minienvironments. The
purpose is to:
• Reduce product, reticle, and equipment damage
due to ESD,
• Reduce equipment lock-up problems due to ESD
events, and
• Reduce the attraction of particles to charged
surfaces.
2.3 This document references SEMI E43 and other
methods of measuring static charge. Related
Information 1 of this document contains a theoretical
investigation of electrostatic particle attraction, as well
as case histories from users and equipment
manufacturers as to the static charge problems
encountered and how they were solved. A bibliography
of related technical papers is also included. Related
Information 2 describes static control methods
commonly used in semiconductor manufacturing.
2.4 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 Static Measurements — Measurements of
electrostatic quantities such as charge, electric field,
and voltage are difficult to make. The nature of the
object (insulator or conductor), its geometry, its
surroundings, and the measuring equipment itself, are
only a few of the factors affecting the accuracy of an
electrostatic measurement.
3.1.1 Similarly, it is difficult to relate the measurement
of an electrostatic quantity to its effect on products or
equipment. For example, an ESD simulator produces a
standardized discharge waveform when a capacitor is
SEMI E78-1102 © SEMI 1998, 2002 2
discharged at a known voltage. This device is used to
establish the ESD damage threshold for semiconductor
products, or the effect of ESD on equipment. While the
amount of charge transferred is known (q = CV), the
maximum current that results is not. There is no
guarantee that the same amount of charge would
produce the same results if different values of
capacitance and voltage were used.
3.2 Location — The test methods and maximum
recommended levels of static charge on product,
reticles, and carriers are meant to be applied at the
input/exit ports of production equipment, and when
possible within the equipment. This document is not
meant to be applied in any way that affects the process
within the equipment.
3.3 Test Methods — The test methods referenced in
this document do not guarantee precise measurements
of static charge levels. The maximum static charge
levels recommended in this document have large
tolerances. (See Section 15.1.)
3.4 Static Charge Control — There are a variety of
static related issues in a semiconductor manufacturing
environment. The issues are complex due to the wide
range of electrostatic problems, and device or
equipment sensitivities to these problems. This guide
contains general recommendations. Users of this
document are cautioned that specific static related
problems may require or allow different levels of static
charge than are recommended in this document.
4 Referenced Standards
4.1 SEMI Standards
SEMI E10 — Standard for Definition and Measurement
of Equipment Reliability, Availability, and
Maintainability (RAM)
SEMI E33 — Specification for Semiconductor
Manufacturing Facility Electromagnetic Compatibility
SEMI E35 — Cost of Ownership for Semiconductor
Manufacturing Equipment Metrics
SEMI E43 — Guide for Measuring Static Charge on
Objects and Surfaces
4.2 ESD Association Standards and Advisories
1
ESD STM5.1 — Sensitivity Testing – Human Body
Model (HBM) - Component Level
ESD ADV1.0 — Glossary of Terms
1 ESD Association, 7900 Turin Road, Rome, NY 13440
ESD ADV 2.0 — Advisory for Protection and
Sensitivity Testing of Electrostatic Discharge
Susceptible Items - Handbook
ANSI/ESD STM5.3.1 — Sensitivity Testing - Charged
Device Model (CDM) - Component Level
ANSI/ESD STM5.2 — Sensitivity Testing -- Machine
Model (MM) - Component Level
4.3 Other Documents
IEC/TS 61000-4-2 — Transient Immunity Standard,
International Electrotechnical Commission (IEC)
2
89/336/EEC — European Union Directive on
Electromagnetic Compatibility
NOTE 1: As listed or revised, all documents cited shall be the
latest publications of adopted standards.
5 Terminology
5.1 Definitions
5.1.1 deposition velocity — Particle flux to a surface
(number of particles deposited per unit area per unit
time) divided by the particle concentration adjacent to
the surface boundary layer.
5.1.2 electromagnetic interference (EMI) — Any
electrical signal in the non-ionizing (sub-optical)
portion of the electromagnetic spectrum with the
potential to cause an undesired response in electronic
equipment.
5.1.3 electrostatic attraction (ESA) — The force
between two or more oppositely charged objects. The
result is increased deposition rate of particles onto
charged surfaces, or movement of charged materials.
5.1.4 electrostatic compatibility — Charge control
adequate for interequipment transfer of products,
reticles, and carriers without electrostatic problems.
5.1.5 electrostatic discharge (ESD) — The rapid
spontaneous transfer of electrostatic charge induced by
a high electrostatic field.
NOTE 2: Usually the charge flows in a spark between two
objects at different electrostatic potentials.
5.1.6 equipment interrupt — Any variance from the
specifications of equipment operation, whether or not
the equipment recovers automatically. Interrupts
include, but are not limited to, equipment stoppage,
equipment data errors, and physical mishandling of
products (reference SEMI E10).
5.1.7 ESD simulator — An instrument providing a
specified electrostatic discharge current waveform
2 IEC, 3, rue de Varembe, CH - 1211 Geneva 20 Switzerland
SEMI E78-1102 © SEMI 1998, 2002 3
when discharged directly to a product or equipment
part.
5.1.8 input and exit ports — The locations where
product and/or product carriers are placed to allow the
equipment to process them, or where they are removed
from the equipment after processing.
5.1.9 minienvironments — A localized environment
created by an enclosure to isolate the product from
contamination and people.
5.1.10 product — Any unit intended to become a
functional semiconductor device.
5.1.11 sensitivity level 1 — Product, reticles, and
equipment are extremely vulnerable to damage and/or
problems from static charge.
5.1.12 sensitivity level 2 — Product, reticles, and
equipment are highly vulnerable to damage and/or
problems from static charge.
5.1.13 sensitivity level 3 — Product, reticles, and
equipment have nominal vulnerability to damage and/or
problems from static charge.
5.1.14 sensitivity level 4 — Product, reticles, and
equipment have negligible vulnerability to damage
and/or problems from static charge.
5.2 Description of Terms Specific to this Standard
5.2.1 carrier — A device for holding wafers, dies,
packaged integrated circuits, or reticles for various
processing steps in semiconductor manufacturing.
6 Requirements
6.1 Measurement Methods and Instrumentation — No
single method of testing for static charge can determine
a “safe” level. The amount of static charge, the
distribution of static charge on an object, and the nature
of the static discharge will all interact to determine if
the charge level is safe. It will be difficult to determine
levels that guarantee static related problems are totally
eliminated. The goal of this guide is to assist the user in
identifying static charge levels likely to cause problems
in process equipment. This guide should provide the
user with enough insight to define a test methodology
for each static problem and understand its limitations.
6.2 ESD Damage
6.2.1 When considering direct ESD damage to an
object (product, reticle, or equipment), the important
parameter is the current accompanying the charge
transfer to or from the object. Under a fixed set of test
parameters, the damaging amount of current due to the
charge transfer to or from the object can be determined.
Established test methods exist for determining the
threshold of damage to a particular object. ESD
simulators of various types are used for this purpose.
Refer to EOS/ESD Association Standards listed in
Section 4 for further information concerning device
testing.
6.2.2 The end user should determine what is damaging
current level due to charge transfer to product or
reticles that will be handled in a particular piece of
production equipment.
6.2.3 In the context of production equipment, it appears
important to know the charge on the product, its
carriers, and any other objects that might directly
contact the product. Charge is measured in coulombs,
or more conveniently in nanocoulombs (10
-9
coulombs)
for this purpose. The measurement is made with
instrumentation known as a Faraday Cup, as shown in
Section 7, Figure 1.
6.2.4 A charged object, like an integrated circuit, is
placed in the Faraday Cup and a reading is taken of the
charge on it. It will be necessary to obtain an instrument
with a large enough “cup” for wafers, cassettes, and
other equipment parts. It will also be necessary to get
the objects into the cup without altering their charge
levels. Further information on making these
measurements should be available from the
manufacturers of the measuring equipment.
6.2.5 The user should determine with an ESD
simulator what levels of ESD cause product, or reticle
damage. The equipment manufacturer will need to
determine with an ESD simulator what levels of static
charge cause equipment damage.
6.2.6 It will be the responsibility of the equipment
manufacturer to demonstrate that equipment operation
does not generate more than the allowable amount of
charge on product, carriers or equipment parts. This is
shown in Section 7, Figure 2.
6.3 Particle Attraction
6.3.1 Electrostatic attraction (ESA) of particles can
occur due to the electrostatic field created by the charge
on the surface of an object. Both the field strength and,
usually to a lesser degree, the divergence of the field
influence the electrostatic contribution to particle
deposition velocity. Electrostatic particle deposition
velocity also depends on particle size and particle
electrical charge. Unfortunately, even under controlled
laboratory conditions, accurate measurements of
electric field strength, particle size distribution, and,
especially, particle charge, are difficult. Of these three
parameters, electric field measurements are the most
likely to be available.
6.3.2 Measurements of electrostatic field can be made
with a commonly available electrostatic fieldmeter. The
units of electrostatic field are volts/cm (volts/inch).