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SEMI E45-1101 © SEMI 1995 , 2001 1 SEMI E45-1101 TEST METHOD FOR THE DETERMINA TION OF INORGANIC CONTAMINATION FROM MINIENVI RONMENTS USING VA POR PHASE DECOMPOSITION-TOTA L REFLECTION X-RAY SPECTROSCOPY (VPD/TXRF), VPD-…

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.

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 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

copyrights asserted in connection with any items

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.

International), 3081 Zanker Road, San Jose, CA 95134. Reproduction o

the contents in whole or in part is forbidden without express written

consent of SEMI.

SEMI E45-1101 © SEMI 1995, 20011

SEMI E45-1101

TEST METHOD FOR THE DETERMINATION OF INORGANIC

CONTAMINATION FROM MINIENVIRONMENTS USING VAPOR PHASE

DECOMPOSITION-TOTAL REFLECTION X-RAY SPECTROSCOPY

(VPD/TXRF), VPD-ATOMIC ABSORPTION SPECTROSCOPY

(VPD/AAS), OR VPD/INDUCTIVELY COUPLED PLASMA-MASS

SPECTROMETRY (VPD/ICP-MS)

This test method was technically approved by the Global Metrics Committee and is the direct responsibility

of the European Equipment Automation Committee. Current edition approved by the North American

Regional Standards Committee on August 27, 2001. Initially available at www.semi.org September 2001; to

be published November 2001. Originally published in 1995; previously published March 2001.

1 Purpose

1.1 This test method provides the analytical procedures

to determine the level of inorganic contamination from

a minienvironment.

2 Scope

2.1 This document relates to inorganic impurities,

which includes metallic contaminants, whether they

occur as atoms, molecules, or particles. The number of

metals to be analyzed is restricted to the four elements

sodium (Na), calcium (Ca), iron (Fe), and copper (Cu)

in order to rapidly characterize minienvironments from

a practicable point of view. While Na, Ca, and Fe

represent one ensemble of highly detrimental impurities

with respect to contamination from human sources

(Na), the environment (Ca), or from equipment and

corrosive effects (Fe), Cu is analyzed due to its

increasing importance in semiconductor manufacturing.

Additionally, they are easily analyzed with sufficiently

low detection limits. It is up to the user of this test

method to quantify additional elements. A list of

suggested polished wafer surface metal contamination

inappropriate to circuits and devices is shown in Table

1 (based on SEMI M1). The inorganic contamination

on silicon wafer surfaces is collected by VPD.

2.2 To quantify Ca and Fe, VPD/TXRF is used due to

its sufficiently low detection limits. Na and Cu are

quantified by VPD/GFAAS or VPD/ICP-MS. All

analytical methods are widely used for the

characterization of surface cleanliness.

2.3 This measurement technique can also be used to

check the influence of certain process steps on

minienvironments.

2.4 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 limitations prior to use.

Table 1 Suggested Polished Wafer Surface Metal

Contamination Inappropriate to Circuits and

Devices

Element Test Method

Na VPD/(AAS or ICP-MS)

Al VPD/(AAS or ICP-MS)

K VPD/(AAS or ICP-MS or TXRF)

Cr VPD/(AAS or ICP-MS or TXRF)

Fe VPD/(AAS or ICP-MS or TXRF)

Ni VPD/(AAS or ICP-MS or TXRF)

Cu VPD/(AAS or ICP-MS or TXRF)

Zn VPD/(AAS or ICP-MS or TXRF)

Ca VPD/(AAS or ICP-MS or TXRF)

3 Referenced Standards

3.1 SEMI Standards

SEMI C28 — Specifications and Guidelines for

Hydrofluoric Acid

SEMI C35 — Specifications and Guidelines for Nitric

Acid

SEMI E19 — Standard Mechanical Interface (SMIF)

SEMI M1 — Specification for Polished

Monocrystalline Silicon Wafers

3.2 ISO Standards

ISO 9001 — Quality Systems—Model for Quality

Assurance in Design, Development, Production,

Installation, and Servicing

ISO 14644-1 — Cleanrooms and associated

environments – Classification of air cleanliness

1 International Organization for Standardization, ISO Central

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

Switzerland. Website: http://www.iso.ch

SEMI E45-1101 © SEMI 1995, 2001 2

3.3 DIN Standards

DIN 12650 Part 6 — Mechanical, physical and

electrical laboratory apparatus; Piston operated

volumetric apparatus; Gravimetric assessment of

metrological reliability

NOTE 1: Unless otherwise indicated, all documents cited

shall be the latest published versions.

4 Terminology

4.1 Abbreviations and Acronyms

4.1.1 GFAAS — Graphite Furnace Atomic Absorption

Spectroscopy

4.1.2 ICP-MS — Inductively Coupled Plasma – Mass

Spectroscopy

4.1.3 PFA — Perfluoroalkoxy

4.1.4 PTFE — Polytetrafluoroethylene

4.1.5 PVDF — Polyvinylidene fluoride

4.1.6 TXRF — Total Reflection X-Ray Fluorescence

Spectroscopy

4.1.7 ULSI — Ultra Large Scale Integration

4.1.8 VPD — Vapor Phase Decomposition

4.2 Definitions

4.2.1 box — a protective portable container for a

cassette and/or substrates.

4.2.2 cassette — an open structure that holds one or

more substrates (e.g., wafer, masks).

4.2.3 DI water — deionized water (specified with

specific resistivity ≥ 18 MΩcm, cations: Na, Cu, Fe, Ca

≤ 0.2 µg/L).

4.2.4 minienvironment — a localized environment

created by an enclosure to isolate the product from

contamination and people.

4.2.5 pod — a box having a Standard Mechanical

Interface (SMIF) (See SEMI E19).

4.2.6 reference wafer — a cleaned wafer (see Section

8.2).

4.2.7 sampling wafer — a cleaned wafer (see Section

8.2), which will be or was exposed to the

minienvironment for a certain time.

4.2.8 standard mechanical interface (SMIF) — the

interface plane between a pod and another

minienvironment (see SEMI E19).

2 Available from Deutches Institut für Normung e.V., Beuth Verlag

GmbH, Burggrafenstrasse 4-10, D-10787 Berlin, Germany. Website:

http://www.din.de

4.2.9 vapor phase decomposition — a method in which

impurities on the surface are collected by the so-called

VPD procedure, i.e., the non-volatile products formed

by acid decomposition of the oxide at the wafer surface

are collected by a droplet of collecting agent, usually

ultra-pure hydrofluoric acid or other reagent or

combination of reagents, and the droplet subsequently

being analyzed by AAS or ICP-MS, or dried in a

manner which gives the least environmental

contamination, the residue from the droplet

subsequently being analyzed by TXRF.

5 Interferences

5.1 For worst cases, preconditioning of wafers can

result in different surface properties indicated by

different sensitivities for contamination absorption.

5.2 Non-linearity effects of the TXRF detector are

significant at higher concentration levels (> 10

atoms/cm

under the detector area).

5.3 The collection efficiency of VPD depends on:

• the chemistry of the collecting solution

• the bonding of the metal impurities to the silicon

surface

• the speed of the droplet, which is rolled over the

wafer surface

5.3.1 Careful control of contamination and all other

factors affecting the results such as solution

concentrations, scanning methods and other procedures

are necessary to obtain reproducible analytical results.

5.4 The measured TXRF intensity depends on the

accuracy of the procedure to localize and to adjust to

the sampled residue. It also depends on the distribution

of different elements in and around the residue.

5.5 The detection of Fe or Ca using ICP-MS can be

interfered with by background ions originated from the

plasma unless some controlled measures are taken to

minimize these interferences to acceptable levels.

6 Safety Precautions

6.1 Handling hydrofluoric acid is dangerous and shall

be performed according to local regulations for

laboratories. Operators shall be trained to deal with

dangerous chemicals and vapors, especially

hydrofluoric acid and HF vapor. Protective clothes and

glasses must be worn when handling hydrofluoric acid.

7 Apparatus

7.1 The VPD treatment and contamination collection

particularly, but also the handling and measurement of

the specimen wafer is to be carried out in a specified