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SEMI E43-0301 © SEMI 1995 , 2001 12 RELATED INFORM A TI ON 2 NOTES ON TEST METHODS NOT E: T his relate d information is not an of ficial part of this standa rd. How ever, it contai ns relevant inf ormation f or using t h…

SEMI E43-0301 © SEMI 1995, 200111

RELATED INFORMATION 1

NOTES ON 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.

R1-1 A charged conductive plate establishes a uniform

electrostatic field as long as measurements are not made

close to the edges and the measurement distance is

small relative to the dimensions of the plate. This

specification requires meters capable of making field

measurements at a distance of 2.54 cm (1 inch) or less

from a 15 cm (6 inch) square plate as a practical means

to ensure performance verification to a known field.

R1-2 Charged plate monitors using 15 cm square plates

with a 20 picofarad capacitance are commonly used to

determine the performance of air ionization systems.

Isolators are used to assure minimal leakage to ground.

A 15 cm square plate of any metal approximately 1 mm

thick and isolated from adjacent surfaces using

insulative standoffs is a perfectly acceptable substitute.

R1-3 The verification procedure is intended to ensure

that the meter used does not drift excessively (less than

5% in 5 minutes) and can repeatedly measure a known

field to within 5%. When actually using the meter to do

a field survey, maintaining the correct distance from the

sensor head to the surface or object being measured

becomes the greatest source of error. If the ability of the

meter operator to maintain the correct distance is within

10%, then the total error of the measurement would be

within about 12% using this calibration procedure

(RMS of the 5% drift, 5% repeatability, and 10%

distance errors).

R1-4 If two operators using two different meters

follow the verification procedure, and they both are

able to maintain the correct distance to within 10% as

above, then they both would be within 12% of the true

field strength when measuring the same surface or

object. Taking the RMS of these errors, the two

operators using two meters should be within 17% of

each other.

R1-5 Many meters read out in volts/inch. 100

volts/inch is about 4,000 volts/m.

SEMI E43-0301 © SEMI 1995, 2001 12

RELATED INFORMATION 2

NOTES ON TEST METHODS

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.

R2-1 Prior handling and environmental conditions will

significantly impact the field strength to be measured.

Below are a number of these considerations:

• The presence of nearby grounded surface or object

will tend to reduce the measured field strength.

This phenomena is known as field suppression and

is illustrated in Figure R2-1.

• Ionization of the surrounding air will tend to

reduce the measured field strength by neutralizing

the static charge on the surface of the object.

• Rubbing or contacting the surface being measured

with another object or surface will tend to increase

the measured field strength depending upon the

tendency of the two materials in question to

tribocharge.

• Increasing humidity will tend to reduce the field

strength to be measured because it in turn will

reduce the magnitude of the charge generated on

objects and, over time, assist in the neutralization

of charge on objects.

• Projections and sharp protrusions on the object

being measured, or nearby objects, will increase

the field strength.

• Insulating objects may have very irregular charge

distributions.

• As a result of these considerations, a static

measurement or survey made using this standard is

only useful if these factors are taken into account in

a realistic manner. For example:

• If a surface is only used in a humidity or

temperature controlled environment, field

strength measurements made under these

conditions are the main ones of interest.

Measurements made at different humidities

may be irrelevant.

• An object may present close to zero field in an

ionized environment, yet when contacted by

another object may become highly charged.

This charge may persist for a period of seconds

or minutes while it is neutralized by the ionized

environment. The time required to return the

object to its original state may be a parameter

of interest.

• An object resting on a grounded metal surface

may have very low external field strength. If

the object is picked up and measured the field

may be much higher.

• Objects of irregular shape and size will give

highly variable readings, depending on the

position of the sensor relative to the object.

• Dielectric objects may give highly variable

readings, depending upon the position of the

sensor relative to the charge distribution on the

object.

• The simple act of handling an object while

performing a static survey can change the

charge on the object. The best results will

derive from making sure that objects and

surfaces are treated and handled within the

bounds of their actual use.

• During equipment verification, maintaining

constant/steady voltage is important. If the plate is

initially charged and allowed to float, its voltage

will change as the meter is moved close to it.

+ + + + + + + + + + + + +

Grounded Surface

Field Lines Terminate on Ground

and Do Not Accurately

Represent Charge on the Surface

Charged Surface

Field Lines Due to Static Charge

+ + + + + + + + + + + + + + + + +

Figure R2-1

Field Suppression