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SEMI E43-0301 © SEMI 1995 , 2001 17 that can be performed w it h the equ ipment operat ing on- line, wi t hout altering or disturbi ng its operation. R4-4 ESD and EMI R4-4.1 W hen ESD occurs, the discharge time is usual …

SEMI E43-0301 © SEMI 1995, 2001 16

RELATED INFORMATION 4

OTHER METHODS FOR DETECTING STATIC CHARGE AND ESD

EVENTS IN EQUIPMENT

NOTE: This related information is not an official part of this standard. However, it contains relevant information for using the

standard in situations commonly encountered with semiconductor manufacturing facilities and equipment. Determination of the

suitability of the material is solely the responsibility of the user.

R4-1 Introduction

R4-1.1 Static charge generation is unavoidable

whenever materials come in contact. Without a static

control program, the problems caused by static charge

are also unavoidable. The most common problem

caused by static charge is electrostatic discharge (ESD).

ESD results in damaged semiconductor ICs, photomask

defects, magneto-resistive (MR) read head defects in

disk drives, and failures of the drive circuits for flat

panel displays (FPD). ESD also creates a significant

amount of electromagnetic interference (EMI). Often

mistaken for software errors, EMI resulting from ESD

interrupts the operation of production equipment. This

is particularly true of equipment depending on high-

speed microprocessors for control. Results include

unscheduled downtime, increased maintenance

requirements, and frequently, product scrap.

Technology trends to smaller device geometries, faster

operating speeds, and increased circuit density make

ESD problems worse.

R4-1.2 For many years static control programs

concentrated on protecting components from the charge

generated on the personnel that handled them. Many

static control methods were devised to control the

charge on people including wrist and heel straps,

dissipative shoes and flooring, and garments.

Increasingly, however, the production of electronic

components is done by automated equipment, and

personnel never come into contact with the static-

sensitive devices. Solving the ESD problem means

assuring that ESD events do not occur in the equipment

used to manufacture and test electronic components.

R4.2 Static Control in Equipment

R4-2.1 An effective static control program in

equipment starts with grounding all materials that might

come close to, or in contact with the static sensitive

components. This prevents the generation of static

charge on machine components and eliminates them as

a source of the charge creating ESD events. Care must

be taken in a grounding program to assure that moving

equipment parts remain grounded when they are in

6 Levit, L. et al, “It’s the Hardware. No, Software. No, It’s ESD! ”,

Solid State Technology, May 1999, Pennwell Publishing Company,

98 Spit Brook Road, Nashua NH 03062.

motion. In some cases, static dissipative materials may

be substituted for conductive materials where

flexibility, thermal insulation, or other properties not

available in conductive materials are needed. If

charging of components is unavoidable, static

dissipative materials may be used to slow the resulting

discharges and prevent component damage.

R4-2.2 Most semiconductors use insulating packaging

materials such as ceramics and epoxy. Handling these

insulating materials inevitably generates static charge,

and this charge cannot be removed by grounding the

materials. If charge generation is unavoidable, the only

effective method of neutralizing the charge on

insulators or isolated conductors is to use air ionization.

Ionizers are typically mounted in the load stations and

process chambers of the automated equipment to

neutralize the static charge.

R4-3 Verifying Equipment Static Control

R4-3.1 A static control program begins when the

automated equipment is designed by the OEM, and then

continues throughout the lifetime of the equipment.

Two basic issues need to be demonstrated. First, are all

components in the product-handling path connected to

ground? Second, as the product passes through the

equipment, is it handled in a way that does not generate

static charge above an acceptable level on the

component? ESD Association Standard Practice,

EOS/ESD SP 10.1-1999

. This document contains test

methods to verify the integrity of the ground path to

equipment parts, as well as to determine if the product

is being charged during its passage through the

equipment. The test methods are applicable during the

original design of the equipment and during acceptance

testing by the end user.

R4-3.2 While the test methods of EOS/ESD SP10.1-

1999 can also be used for periodic verification of the

equipment performance, they have one drawback. The

automated equipment must be taken off-line to do the

testing. This means that there is lost production time,

and often the periodic testing is eliminated to maintain

product throughput. Other test methods are available

7 EOS/ESD SP10.1 - 1999 “Standard Practice for Protection of

Electrostatic Discharge Susceptible Items - Automated Handling

Equipment”, ESD Association, 700 Turin Road, Rome NY 13440.

SEMI E43-0301 © SEMI 1995, 200117

that can be performed with the equipment operating on-

line, without altering or disturbing its operation.

R4-4 ESD and EMI

R4-4.1 When ESD occurs, the discharge time is

usually 10 nanoseconds or less. Discharging energy in

this short time interval results in the generation of

broadband electromagnetic radiation

, as well as the

heat that damages semiconductor components. This

electromagnetic radiation, especially in the 10 MHz to

2 GHz frequency range, is the EMI that can affect the

operation of production equipment. In addition to ESD

damage to semiconductor devices and reticles, ESD-

caused EMI results in a variety of equipment operating

problems including stoppages, software errors, testing

and calibration inaccuracies, and mishandling causing

physical component damage.

R4-4.2 EMI Locators

R4-4.2.1 When component damage or equipment

problems due to ESD are suspected, it may be useful to

detect the electromagnetic interference (EMI) generated

by the ESD event. This type of testing is both a starting

point for determining that static charge has been

generated, and it is a measurement point to ascertain

that any static control methods have been successful.

EMI locators measure dynamic operating conditions, as

it is usually not necessary to interrupt equipment

operations to make measurements.

R4-4.3 Types of EMI Locators

R4-4.3.1 EMI locators are available in a number of

different forms. In its simplest form, it consists of an

AM radio tuned off station. A popping noise will be

heard when an ESD event occurs. At the most complex

it consists of a wideband (greater than 1 GHz) digital

storage oscilloscope with a set of appropriate antennas,

probes, and software. Measurements of radiated

interference can be made using antennas while probes

can be connected to equipment parts or electronics and

power lines.

R4-4.3.2 An oscilloscope attached to a single antenna

can assist in pinpointing the actual location of the ESD

event.

8, 9, 10, 11

A set of antennas can be used to not only

8 Tonoya, Watanabe and Honda, “Impulsive EMI Effects from ESD

on Raised Floor,” 1994 EOS/ESD Symposium, pp. 164-169, ESD

Association.

9 Takai, Kaneko and Honda, “One of the Methods of Observing ESD

Around Electronic Equipments,” 1996 EOS/ESD Symposium, pp.

186-192, ESD Association.

10 Greason, Bulach and Flatley, “Non-Invasive Detection and

Characterization of ESD Induced Phenomena in Electronic Systems,”

1996 EOS/ESD Symposium, pp. 193-202, ESD Association.

11 Smith, “A New Type of Furniture ESD and Its Implications,” 1993

EOS/ESD Symposium, pp. 3-7, ESD Association.

detect the presence of an ESD event, but to determine

the location of the pulse in 3 dimensions.

12, 13

Using the

same concept as a global positioning system (GPS), the

difference in the arrival times of the signal to multiple

antennas is directly related to the difference in the

distance of each antenna from the ESD source. With the

time deltas and the locations of the antennas known, the

location of the spark can be uniquely identified

employing the appropriate analysis program.

R4-4.3.3 Several other types of EMI locating

equipment are currently in use. Most consist of high

frequency receiving circuitry followed by level

detectors to determine the magnitude of the signal. For

the purpose of detecting EMI from ESD events, the

equipment should have some way of differentiating the

short impulse of EMI from the ESD event from the

continuous high frequency radiation of other EMI

sources. Some instruments contain a counter to total

the number of ESD events above the threshold, or

alarms to indicate when the number of ESD events

exceeds a preset number. This type of instrument can be

placed near a piece of equipment that is suspected of

causing ESD events and left in place to monitor.

R4-4.3.4 Several EMI Locators are battery-operated

handheld devices that can be easily carried around a

facility or placed directly in equipment to check for

ESD events. This allows the Locator to detect signals

that might otherwise be shielded by the equipment’s

cover panels. (Note that EMI shielding is usually an

important part of the design of most production

equipment to prevent radiation from the equipment.

This makes the detection of ESD events outside the

equipment more difficult.) It allows pinpointing of the

location of an ESD event, which can then be correlated

to particular machine operations.

8, 14

R4-4.4 Limitation in Using EMI Locators

R4-4.4.1 One caution needs to be observed when using

EMI locators to detect ESD events that cause

component damage. The signal received by these

devices is generated in areas usually surrounded by

grounded metal components. It may have to pass

through equipment panels and travel some distance

through the air before it reaches the detector. There may

12 Bernier, Croft, and Lowther “ESD Sources Pinpointed by Analysis

of Radio Wave Emissions,” Journal of Electrostatics (44) pp. 149-

157, Nov. 1998, Elsevier Science B.V., P.O. Box 211, 1000 AE

Amsterdam Netherlands.

13 Lin, DeChiaro and Jon, “A Robust ESD Event Locator System

with Event Characterization,” 1997 EOS/ESD Symposium, pp. 88-98,

ESD Association.

14 Fujie, A., “Pinpointing Sources of Static Electricity with EMI

Locator”, Parts 1 and 2, Nikkei Electronics Asia, December 1992 and

January 1993, Nikkei Business Publications Asia Ltd., 533 Hennessy

Road, Causeway Bay, Hong Kong.

SEMI E43-0301 © SEMI 1995, 2001 18

be other radio frequency sources and reflecting or

absorbing materials in the area. The actual location of

the ESD event may be a considerable distance from the

EMI locator. It will be difficult to establish any

correlation between the amplitude of the signal received

by the EMI locator and the energy in the ESD event

that produced the signal. The EMI locator primarily

indicates the occurrence of an ESD event and can be

used to illustrate that a particular static control method

has eliminated it. It should not be assumed that every

ESD event detected results in damage to components or

equipment problems. Additional testing will be needed

to establish that connection.

R4-5 Static Event Detectors

R4-5.1 Static event detectors (SED) are devices that

are installed directly on products to detect the presence

of an ESD event. They may be attached in proximity to

an ESD-sensitive component, connected to the external

device leads, or integrated into the device package.

Typically they detect the current pulse of an ESD event

through an antenna or direct connection to the device

circuitry.

R4-5.2 SEDs can be useful in determining the

occurrence of ESD events in operating production

equipment. The SED has the ability to indicate ESD

events of a known level, aiding in the design and

performance verification of automated equipment.

While costly analysis of failed devices can also provide

this information, correlation to machine operations is

usually difficult. An SED that can be monitored

optically as it passes through operating equipment

provides a convenient method to verify that automated

equipment is not generating levels of static charge that

result in ESD damage.

R4-5.3 Types of SED Devices

R4-5.3.1 In some SED devices, the signal is amplified

and processed to produce a reflectance change in the

built-in Liquid Crystal Display (LCD). The SED is

designed to trip at a predetermined threshold voltage,

detecting ESD transients above the selected amplitude.

Some devices can be reset magnetically or optically

making them reusable.

R4-5.3.2 Other devices use the controllable ESD

damage threshold of metal oxide semiconductor field

effect transistors (MOSFET). The test methodology is

to amplify an ESD transient to create sufficient energy

to destroy the gate oxide. The device may be used until

the specified ESD level is achieved, and then the SED

fails. A similar device is based on the metal oxide

semiconductor capacitor (MOSCAP). The current

leakage through the device significantly increases if the

ESD amplitude is sufficient to damage the MOS

structure. Both of these types of SED must be removed

from where they are installed and require additional

instrumentation to determine their status.

R4-5.3.3 Another type of SED employs the magnetic

fields from a current flow to affect a series of magneto-

optic thin films. The magnetic field from the ESD

current alters the film’s magnetic state and affects the

degree of polarization of visible light reflected from the

film. Varying the distance between the film and the

ESD current-carrying conductor indicates different

thresholds. This SED can be read using a microscope

equipped with a polarizing element and does not need

to be removed from the circuitry to be read. It can be

reset with a magnet.

R4-6 Conclusion

R4-6.1 There is little question that static charge

problems continue to result in significant losses in high

technology manufacturing. Increasingly, static control

methods must be applied in the equipment that

produces the product. It will be important to develop

and utilize a range of diagnostic methods and

measurement equipment for ESD in equipment.

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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 manufacture's instructions, product labels,

product data sheets, and other relevant literature,

respecting any materials or equipment mentioned

herein. These standards are subject to change without

notice.

By publications of this standard, Semiconductor

Equipment and Materials International (SEMI) takes no

position respecting the validity of any patent rights or

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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.

15 Jackson, Tan, and Boehm, “Magneto Optical Static Event

Detector,” 1998 EOS/ESD Symposium, pp.233-244, ESD

Association.

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