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SEMI M33-0998 © SE MI 1998 8 the recovery rate of t he VPD treat m ent and t he scanning soluti o n as descri bed in Section 15.19 of this document. The relative error is to be calculated by: dc i , VPD c i , VPD = dR i …

SEMI M33-0998 © SEMI 19987

• measurement time,

• analysis results on the blank microdroplet,

• compositions and amount of the scanning droplet,

• running time since last calibration or frequency of

SPC measurement,

• lab environment classification by U.S. Federal

Standard 209,

• edge exclusion, if any (c.f., Sections 4.2 and 11.6).

13.3 Quantification of areal density is in units of 10

atoms/cm

13.4 Detection spot area is the surfa ce area where

above the fluorescence counts are integrated.

13.5 Scanned surface area is the sur face area where

the impurities are collected from, according to Section

9.1.

13.6 Calculate the areal density of i mpurity i

according to the following algorithm:

VPD

⋅

(atoms/cm

)

⋅

(atoms/cm

)

where;

VPD

density of impurity (

) at scanned

area of wafer surface in [atoms/cm

]

measured concentration of impurity

at measured spot [atoms/cm

]

VPD - scanned wafer area in [cm

]

measuring spot area in [cm

]

recovery rate of the collected impurity

1) c.f., Section 4.13

measured number of atoms of analyte

The measured concentration c

of impurity (i) can be

related to the reference standard by means of the

following expression.

NOTE: The reference standard element is assumed to be Ni in

this section.

⋅

[atoms/cm

]

where;

= number of impurity atoms (Ni)

in the standard reference specimen

= measured fluorescence intensity

of impurity (

) in counts per second [cps]

= measured fluorescence intensity

of the standard reference specimen (Ni)

in counts per second [cps]

instrumental sensitivity factor

of the analyte

relative to the standard

element (Ni)

This formula provides the areal density for the impurity

of interest with LOD as given in Section 13.7.

13.7

Calculation of LOD

, the lowe st detectable

number of impurity atoms i from a scanned surface, is:

LOD

(t) ≡ 3 ⋅c

i ,VPD

⋅

(t)

netto,i

(t)

where;

(t) denotes the background fluorescence

cps, integrated over time (t)

(t) = I

⋅t,

with

= intensity of the background in cps, and

where;

netto,i

(t) denotes the netto number of the

impurity fluorescence [cps], integrated

over the time,

netto,i

(t) = I

⋅t

The equation for the LOD

(t) can be rewritten as :

LODi(t ) = 3⋅

i,VPD

⋅

14 Bias and Precision

14.1 Relative error of the described VPD-TXRF

method must be assessed according to Section 15.11 of

this document. Under the given measurement

conditions the accuracy of the results is limited by the

error summarized in Section 14.2.

14.2

Under given solute amounts an d measurement

conditions the accuracy of the results is limited only by

SEMI M33-0998 © SEMI 1998 8

the recovery rate of the VPD treatment and the

scanning solution as described in Section 15.19 of this

document. The relative error is to be calculated by:

i ,VPD

ℜ

ℜ

ℜ

ℜ

dRSF

RSF

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

ℜ

14.3 Relative error of the reference droplet standard is

determined by the error of the micropipette aliquot (V)

and of the stock solution (c

ℜ

ℜ

ℜ

ℜ



ℜ

ℜ

ℜ

ℜ

ℜ



ℜ

ℜ

14.4 The relative error of areal concentrations below

the concentration of the calibration standard reference

are strongly dependent upon the relative error of the

micropipette aliquots. In the given range bias due to

crystallization and/or mass absorption can be

anticipated to be less than 1% as described in Sections

15.6 and 15.11 of this document.

14.5

Reproducibility of the measure ment system must

be tested with calibration standard reference in five

complete analysis cycles (load-analyze-unload). The

standard deviation of the 5 results shall not exceed

more than 10% of the theoretical value of the standard

deviation of the respective Poisson statistics

Nx. For

long term reproducibility, please refer to Section 2.6.

14.6 The minimum sample size for controlling the

wafer-to-wafer reproducibility of the complete

procedure must consist of a group of 3 wafers of the

very same polishing and/or cleaning batch as described

in Section 15.20 of this document. Tolerated standard

deviation of 3 groups should be defined by the

interested parties.

14.7

In interlaboratory tests (round robin), the

reproducibility of the method can preferably be

evaluated in accordance with DIN ISO 5725 or ASTM

E 691.

NOTE: Report reproducibility in accordance with this

document. Calibration accuracy was found to be within 10%

relative standard deviation for K, Ca, Ti, Cr, Fe, and Cu

among five TXRF stations as stated in Section 15.21 of this

document. W and other compounds forming volatile fluorides

shall not be analyzed after VPD because of low recovery

rates.

15 References

Analytical Determination of Fe in Thin SiO(2) Layers

on Si Wafers by Atomic Absorption Spectroscopy — M.

Briska, in Technical Disclosure Bulletine (IBM), 06–

1977, p. 227

Application of Total Reflection X-Ray Fluorescence

Analysis for Metallic Trace Impurities on Silicon Wafer

Surfaces

— P. Eichinger, H. J. Rath, and H. Schwenke,

ASTM STP 990, ASTM 1989, pp. 305–13

Automated TXRF Analysis in Silicium Manufacturing

— S. Pahlke, L. Kotz, E. Heindl, and P. Eichinger, PV

98–1, The Electrochemical Society, 1998

Basic Features of Total Reflection X-Ray Fluorescence

Analysis on Silicon Wafers — W. Berneike,

Spectrochimica Acta 48B (2), 269–75, 1993

Calibration Accuracy of Different ATOMIKA TXRF

8010 Instruments — P. W. Mertens, S. De Gendt, and

K. Kenis, IIAP-UCP Meeting, IMEC, September 26,

1996, Leuven, Belgium

Calibration of TXRF Equipment — J. Knoth, H.

Schwenke, and P. Eichinger, Proceedings 2nd

International Symposium Ultra-clean Processing of Si

Surface, IMEC-Acco 1994, pp. 107–10

Chemical Analysis of Metallic Impurity on the Surface

of Silicon Wafers — T. Shiraiwa, N. Fujino, S. Sumita,

and Y. Tanizoe, AST STP No. 850 NBS/IEEE, 1987, p.

314

Determination of the Critical Thickness and the

Sensitivity for Thin-Film Analysis by Total Reflection

X-Ray Fluorescence Spectrometry

— R.

Klockenkämper and A. von Bohlen, Spectrochimica

Acta 48B (5), 461–9, 1989

Introduction to Control Charts in the Analytical

Laboratory — SPC, E. Mullins, Analyst, 119, 369–75,

1994

Is My Calibration Linear? — Analytical Methods

Commission — Analyst 119, 2363-6, 1994

A Modification of the Linear Least-Squares Fitting

Method which Provides Continuum Suppression — F.

H. Schamber, X-ray Fluorescence Analysis, Editor, T.

Doubay Ann Arbor Science Publication Ann Arbor MI,

1977, pp. 241–257

Origins of Spurious Peaks of Total Reflection X-Ray

Fluorescence Analysis of Si Wafers Excited by

Monochromatic X-Ray Beam W-Lß

— K. Yakushiji, S.

Ohkawa, A. Yoshinaga, and J. Harada, Japan Journal

Applied Physics, 33 (2), Part 1, 1130–5, 1994

Standardization of TXRF Using Microdroplet Samples

— L. Fabry, S. Pahlke, L. Kotz, Y. Adachi, S.

Furukawa, Advanced in X-ray Analytic Japan, 26s, 19–

24, 1995

Statistical Process Control in Microelectronics

Manufacturing — W. A. Levinson, Semiconductor

International, 1994 November, pp. 95–102

Sub-ppm Monitoring of Transition Metal

Contamination on Silicon Wafer Surfaces by VPD-

TXRF

— A. Huber, H. J. Rath, P. Eichinger, T. Bauer,

L. Kotz, and R. Staudigl, PV 88–20, The

Electrochemical Society, 1988, p. 109

Theory of Analytical Chemistry — K.S. Booksh and B.

R. Kowalski, Journal Analytical Chemistry 66A (15),

782–91, 1994

Trace-Analytical Methods for Monitoring

Contamination in Semiconductor-Grade Si

Manufacturing — L. Fabry, S. Pahlke, L. Kotz, and G.

Tölg Fresenius Journal Analytical Chemistry, 349, 260–

71, 1994

TXRF in the Daily Routine — L. Fabry, S. Pahlke, L.

Kotz, E. Schemmel, and W. Berneike, PV 93–15, The

Electrochemical Society, 1993, pp. 232–9

Ultra-Trace Analysis of Metallic Contamination on

Silicon Wafer Surfaces by Vapor Phase

Decomposition/Total Reflection X-Ray Fluorescence

(VPD/TXRF)

— C. Neumann and P. Eichinger,

Spectrochimica, Acta 46B (19), 1360–77, 1991

Verfahren Zum Schutz Von Polierten Oberflächen — I.

Lampert, Europe Patent 0 222 400 (11/13/86)

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