semi合集-English.pdf - 第5352页

SEMI M53-1103 © SEMI 2003 3 4.3 ISO Standar ds 3 ISO 14644-1 Cleanroo ms and associated controlled environm ents — Part 1: Classi fication of airbo rne particulates ISO Guide 30 : 1992 Terms and defi nitions used i n con…

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.)

SEMI M53-1103 © SEMI 2003 3

4.3 ISO Standards

ISO 14644-1 Cleanrooms and associated controlled

environments — Part 1: Classification of airborne

particulates

ISO Guide 30: 1992 Terms and definitions used in

connection with reference materials

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

5 Terminology

5.1 Definitions for general terms for silicon technology

are found in SEMI MF1241.

5.2 Additional terminology is defined in SEMI M1.

5.3 Definitions

5.3.1 capture rate (CR) — the probability that a

scanning surface inspection system (SSIS) detects a

localized light scatterer (LLS) of latex sphere

equivalent (LSE) signal value at some specified SSIS

operational setting.

5.3.2 certified reference material (CRM) — a material

accompanied by a certificate, one or more of whose

property values are certified by a procedure that

establishes its traceability to an accurate realization of

the unit in which the property values are expressed, and

for which each certified value is accompanied by an

uncertainty at a stated level of confidence [ISO Guide

30].

5.3.2.1 Discussion — In the context of this practice, a

CRM is a certified PSL sphere deposition on an

unpatterned wafer with the same surface films and

finish as the wafers to be examined by the calibrated

SSIS. The deposition property values that must be

certified are the peak sphere diameter and the diameter

distribution on the wafer and are determined by both

the PSL sphere source and the deposition process. The

wafer may contain more than one CRM. See Related

Information 1.

5.3.3 coefficient of variation (CV) — one standard

deviation, σ, expressed as a percentage of the mean of a

Gaussian distribution.

5.3.4 deposition — an approximately known number of

PSL spheres of known size distribution placed in a

known location on the surface of a reference wafer.

3 International Organization for Standardization, ISO Central

Secretariat, 1, rue de Varembé, Case postale 56, CH-1211 Geneva 20,

Switzerland. Telephone: 41.22.749.01.11; Fax: 41.22.733.34.30

Website: www.iso.ch; also available in the US from American

National Standards Institute, New York Office: 11 West 42nd Street,

New York, NY 10036, USA. Telephone: 212.642.4900; Fax:

212.398.0023 Website: www.ansi.org, and in other countries from

ISO member organizations.

5.3.5 deposition process — the procedure used to place

the PSL spheres on the reference wafer.

5.3.6 dynamic range — of a scanning surface

inspection system, the signal range covered by an

instrument with one set of measurement conditions.

5.3.6.1 Discussion — The useful dynamic range is

limited on the small signal side by the background

noise or the inherent resolution of the instrument and on

the large signal side by saturation of the detector and/or

the related electronics. The small signal limit is usually

defined as the smallest PSL diameter than can be

measured with a capture rate of at least 95%.

5.3.7 false count — a laser-light scattering event that

arises from instrumental causes rather than from any

feature on or near (in) the wafer surface; also called

false positive; compare nuisance count.

5.3.7.1 Discussion — False counts would not be

expected to occur at the same point on the wafer surface

during multiple inspection scans, and hence they could

be considered as random “noise” that could be

identified by examining the results of repeated scans.

5.3.8 histogram — a representation of a partitioned

(binned) data set as a bar graph in which the widths of

the bars are proportional to the sizes of the bins of the

data set variable, and the height of each bar is

proportional to the frequency of occurrence of values of

the variable within the bin.

5.3.8.1 Discussion — In presenting data for the size

distribution of LLSs, the data set variable is usually the

derived LLS size; in presenting haze data, the data set

variable is usually the haze in ppm. The data set is

usually partitioned into bins of equal size on either a

linear or logarithmic scale, as appropriate. The bins at

the low and high ends of the data set variable range are

customarily plotted with the same width as the

remainder of the histogram even though they may

represent a larger or smaller range of the independent

variable than the rest of the bins.

5.3.9 laser-light scattering event — a signal pulse that

exceeds a preset amplitude threshold, generated by the

interaction of a laser beam with an LLS at a wafer

surface as sensed by a detector.

5.3.9.1 Discussion — The amplitude of the signal into

a single detector, as measured for any combination of

incident beam direction and collection optics, does not

by itself convey topographic information, for example,

whether the LLS is a pit or a particle. It does not allow

the observer to deduce the size or origin of the scatterer

without other detailed knowledge, such as its index of

refraction and shape. In a scanning surface inspection

system, laser-light scattering events and the background

SEMI M53-1103 © SEMI 2003 4

signal due to haze together comprise the signal due to

light scattering from a wafer surface.

5.3.10 latex sphere equivalent (LSE) — the diameter of

a monodisperse polystyrene latex sphere that, under

identical test conditions, produces the same detected

scattering intensity as the LLS under investigation.

5.3.10.1 Discussion — If the LLS is assumed to be due

to a particle (or pit), the LSE size (diameter) of the

particle (or pit) is given in units of length followed by

LSE; for example, 0.12 µm, LSE. This unit varies in

different ways for different materials from instrument

to instrument because of differences in the optical

systems and signal processing procedures of different

instruments. Therefore a particular LLS generally does

not have the same LSE size when measured on different

model instruments or on different channels of the same

instrument. If elements of the optical system, such as

incidence angle, collection solid angle, or polarization,

of an SSIS can be varied, the LSE size of a particular

LLS will not necessarily be the same for each

configuration of the optical system.

5.3.11 localized light scatterer (LLS) — an isolated

feature, such as a particle or a pit, on or in a wafer

surface, resulting in increased light scattering intensity

relative to that of the surrounding wafer surface;

historically called light point defect because under high

intensity optical illumination features of sufficient size

appear as an isolated point of light.

5.3.11.1 Discussion — Localized light scatterers are

observed by automated inspection techniques as laser-

light scattering events. Automated inspection

techniques are quantitative in the sense that scatterers

with different scattering intensities can be segregated.

However, the amplitude of the scattered light intensity,

or “laser-light scattering event”, as measured by any

combination of incident beam direction and collection

optics, does not by itself convey topographical

information about the LLS; particles and pits cannot be

distinguished solely on the basis of single-channel

amplitude data. Also, the observer cannot deduce the

size, shape, or composition of the LLS from single-

channel amplitude alone. The presence of LLSs does

not necessarily decrease the utility of the wafer.

5.3.12 missing count — the case in which an LLS fails

to produce a laser-light scattering event; also called

false negative.

5.3.13 multipoint calibration — a procedure for

calibrating the size response of an SSIS using a set of

accurately sized polystyrene latex spheres, deposited on

a wafer surface of the type to be inspected by the SSIS.

5.3.13.1 Discussion — The purpose of a calibration is

to relate the amount of light captured by an SSIS to the

physical size of the light scatterer. The amount of light

scattered from a localized light scatterer (LLS) that is

captured by the SSIS is a function of both the scattering

characteristics of the LLS (including the directional

dependence of the scattering) and the geometry of the

collection optics of the SSIS. For a given wavelength

of incident radiation, regular objects of certain sizes

exhibit non-linearities, usually in the form of a dip, so

that the curve of scattering amplitude as a function of

physical size of the scatterer may not be monotonic.

Thus, similar objects with modest variations in physical

size can scatter the same amount of light. Different

materials may exhibit non-linearities at different sizes.

Because these effects tend to be less pronounced for

irregular particles such as may be found on polished

wafer surfaces, instrument calibration is usually carried

out by avoiding the sizes of spheres that correspond to a

dip. Sometimes, however, it is desired to fully

characterize the response of the SSIS to a particular

type of scatterer; in this case, the calibration can be

carried out with a set of particles with sizes that cover

the desired range with adequate density to ensure that

any non-linearities in the scattering amplitude-size

curve are detected.

5.3.14 nominal sphere size distribution — the stated

diameter distribution of a suspension of PSL spheres of

a certified diameter used in the calibration of SSISs.

5.3.14.1 Discussion — The nominal sphere size

distribution is usually expressed as the standard

deviation or the coefficient of variation of the

distribution about the certified diameter. Depending on

how the deposition is made, the size distribution of the

deposited spheres may be equal to the distribution in

the original suspension or it may be significantly

narrowed by the deposition process.

5.3.15 nuisance count — a signal pulse that arises from

discrete or area surface or near-surface features other

than the localized light scatterers being investigated;

compare false count.

5.3.15.1 Discussion — The presence of nuisance

counts is dependent on the threshold and gain settings

and may be a function of the optical configuration of

the SSIS, the orientation of the wafer surface, or both.

5.3.16 reference wafer — for calibrating an SSIS in

accordance with this practice, an unpatterned wafer

with the same surface films and finish as the wafers to

be examined by the calibrated SSIS and upon which

one or more PSL sphere depositions have been certified

to specified uncertainties for peak diameter and

diameter distribution.

5.3.17 response curve (RC) — the modeled relation

between measured scattered light intensity (or SSIS

signal response) and PSL sphere peak diameters. The