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SEMI M53-1103 © SEMI 2003 1 SEMI M53-1103 PRACTICE FOR CALIBRATING S CANNING SURFACE INSPECTION SYSTEMS USING DEPOSI TIONS OF MONODISPERSE POLYSTYRENE LATEX SPHERE ON UNPATTER NED SEMICONDUCTOR WAFER SURFACES This practi…

SEMI M52-0703 © SEMI 2002, 2003 13

Item Recommended Specification Comments References

3.3 Calibration

automated,

In order to reduce PSL

sphere sizing

uncertainty in the

65 nm to 200 nm range,

the diameter

distribution should have

a full width at half

maximum (FWHM)

≤5%. In addition, it is

desirable that the peak

PSL diameter as

deposited on the wafer

have a relative

expanded uncertainty at

about 95% confidence

level as small as

possible but not greater

than 3%. See NOTE 2.

SEMI M53

NOTE 1: At the calibration points, if it is assumed that the SSIS sizing of PSL spheres is exactly correct, then the sizing error is caused by

differences between the response predicted by the calibration curve and the exact response of the SSIS away from calibration points. Details for

calculating this error are being developed for another standard.

NOTE 2: This specification limits the width of the diameter distribution of PSL spheres as they appear on the wafer in the calibration deposition.

The deposition system transfer function (often nominally triangular in shape) times the actual PSL diameter distribution shape presented to the

system defines the deposition width. Thus the width of the deposition on the wafer is no larger than the width of the transfer function. A narrow

width decreases calibration uncertainty in three ways. First, in the presence of background noise, it makes the distribution peak signal easier to

locate. Second, a narrow transfer function makes the deposition distribution peak easier to determine. Third, a narrow transfer function reduces

the deposition distribution asymmetry if the input PSL distribution is not symmetrical about the peak value.

NOTICE: 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.

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SEMI M53-1103 © SEMI 2003 1

SEMI M53-1103

PRACTICE FOR CALIBRATING SCANNING SURFACE INSPECTION

SYSTEMS USING DEPOSITIONS OF MONODISPERSE POLYSTYRENE

LATEX SPHERE ON UNPATTERNED SEMICONDUCTOR WAFER

SURFACES

This practice was technically approved by the Global Silicon Wafer Committee and is the direct

responsibility of the North American Silicon Wafer Committee. Current edition approved by the North

American Regional Standards Committee on July 25, 2003. Initially available at www.semi.org October

2003; to be published November 2003. Originally published March 2003.

1 Purpose

1.1 Calibration of a scanning surface inspection system

(SSIS) using a deposition of polystyrene latex (PSL)

spheres as a known source of scatter signal is a

necessary step in matching the responses of SSISs.

However, the measured amplitude of the light scatter

signal depends on both the characteristics of the SSIS

and the characteristics of the scatter source. The use of

a deposition of polystyrene latex (PSL) spheres (see

Section 5.3.4) as a known source of scatter signal

allows meaningful comparisons to be made between

scatter signals from PSL spheres as measured by dark

field detection systems of different designs. On the

other hand, calibration with PSL spheres alone does not

guarantee meaningful performance comparisons to be

made between dark field detection SSISs of the same or

different designs when detecting either real particles of

materials different from PSL spheres or other surface

defects.

1.2 This practice describes calibration of SSIS dark

field channels so that the SSIS accurately sizes PSL

spheres deposited on unpatterned polished, epitaxial, or

filmed semiconductor wafer surfaces (see Related

Information 1).

1.3 This practice defines the use of latex sphere

equivalent (LSE) signals as a means of reporting real

surface defects whose identity and true size are

unknown.

1.4 This practice provides a basis for quantifying SSIS

performance as used in related standards concerned

with parameters such as sensitivity, repeatability and

capture rate.

2 Scope

2.1 This practice covers

• Requirements for the surface and other

characteristics of the semiconductor substrates on

which the PSL spheres are deposited to form

reference wafers (see Section 8.1),

• Selection of appropriate certified depositions of

PSL spheres for SSIS calibration (see Section 8.2),

• Size distribution requirements to be met by the

PSL sphere depositions (but not the deposition

method), and

• Multipoint calibration procedures for dark field

channels.

2.2 Appendix 1 covers a single-point calibration

procedure that may be used in limited production

applications.

2.3 PSL spheres from 10 µm to the smallest size that

can be detected by the SSIS being calibrated can be

used in this practice.

NOTE 1: At the time of development of this edition of the

practice, the smallest practical deposited PSL spheres have

diameters approaching 30 nm, but as IC technology evolves to

smaller and smaller critical dimensions it is expected that

depositions of smaller diameter PSL spheres will become

available.

2.4 Background information to enable an

understanding of the need for the various requirements

imposed on the PSL sphere depositions is provided in

Related Information 1.

2.5 Both the deposition process and calibration

procedures must be carried out in a Class 4 or better

environment as defined in ISO 14644-1.

NOTE 2: ISO class 4 is approximately the same as Class

M2.5 (Class 10) as defined in Federal Standard 209E.

2.6 Although it was developed primarily for use in

evaluation of SSISs to be used for detection of localized

light scatterers (LLSs) on polished silicon wafers with

geometrical characteristics as specified in SEMI M1,

this practice can be applied to SSISs to be used for

detection of LLSs on other unpatterned semiconductor

surfaces provided that suitable reference wafers are

employed.

2.7 This practice does not in any way attempt to define

the manner in which LSE values are used to define the

SEMI M53-1103 © SEMI 2003 2

true size of LLSs other than PSL spheres (see Section

3.1).

2.8 This practice supports requirements listed in SEMI

M52.

NOTICE: 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 and health practices and determine

the applicability of regulatory or other limitations prior

to use.

3 Limitations

3.1 LLSs are normally assigned only LSE sizes, not

physical diameters, because the response of an SSIS to

an LLS depends on the SSIS optical system

characteristics as well as the size, shape, and

composition of the LLS. The LSE size assigned to a

particular LLS by an SSIS calibrated against PSL

spheres may be different from that assigned to the same

LLS by another similarly calibrated SSIS, because

different SSISs have different optical system

characteristics.

3.2 PSL spheres may have specified characteristics

(mean diameter uncertainty, diameter distribution,

spread between mean and modal diameter) that differ

significantly from the characteristics of the resulting

deposition due to the transfer function of the deposition

system. For this reason the practice is limited to the use

of PSL sphere depositions that are appropriately

characterized. See Related Information 1.

3.3 If calibration points occur at, or near, dips in the

response curve (see Section 5.3.17), the calibration

curve will not be single valued; therefore dips must be

avoided as calibration points if a monotonic calibration

curve is to be obtained. However, if a complete

calibration is desired, the locations and magnitudes of

the dips must be determined. In this case there may not

be a one-to-one correlation between SSIS response and

LSE size; i.e., a particular instrument response may

correspond to more than one LSE size.

(See Section

5.3.13.1.)

3.4 Background Contamination

3.4.1 The presence of localized light scatterers with

LSE sizes near that of the nominal PSL diameter on the

reference wafer may skew the results. This condition

1 See, for example, Locke, B. R., and Donovan, R. P., “Particle

Sizing Uncertainties in Laser Scanning of Silicon Wafers,” Journal of

The Electrochemical Society, Vol 134, No. 7, 1987, pp. 1763–1771;

or Liu, B. Y. H., Chae, S.-K., and Bae, G.-N., “Sizing Accuracy,

Counting Efficiency, Lower Detection Limit and Repeatability of a

Wafer Surface Scanner for Ideal and Real-World Particles,” ibid., Vol

140, No. 5, 1993, pp. 1403–1409.

may result in a large error or poor equivalent sizing

accuracy.

3.4.2 High levels of localized light scatterers on the

reference wafer or wafers may overload the SSIS or

obscure the peak of the deposited PSL sphere

distribution. This condition may also result in a large

error or poor equivalent sizing accuracy.

3.4.3 For these reasons, both the deposition process

and calibration procedures must be carried out in a

clean environment, and the reference wafers must be

handled in such a way as to avoid contamination

between deposition process and calibration.

3.5 If the surface roughness of the reference wafer or

wafers is excessive, the peak of the PSL sphere

distribution may be obscured or distorted.

3.6 If the SSIS being calibrated is not operating in a

stable condition, the calibration may not be appropriate

for subsequent use of the system. System stability can

be evaluated by making repeated calibrations, in

accordance with this practice, over suitable time

periods.

4 Referenced Standards

4.1 SEMI Standards

SEMI M1 — Specification for Polished Monocrystal-

line Silicon Wafers

SEMI M20 — Specification for Establishing a Wafer

Coordinate System

SEMI M50 — Test Method for Determining Capture

Rate and False Count Rate for Surface Scanning

Inspection Systems by the Overlay Method

SEMI M52 — Guide for Specifying Surface Scanning

Inspection Systems for Silicon Wafers for the 130-nm

Technology Generation

SEMI MF1241 — Standard Terminology of Silicon

Technology

4.2 Federal Standard

Fed Std 209E — Airborne Particulate Cleanliness

Classes in Cleanrooms and Clean Zones

2 Standardization Documents Order Desk, Bldg. 4 Section D, 700

Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS (This

standard has been superseded by ISO 14644-1 and may no longer be

available.)