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SEMI F72-1102 © SEMI 2002 4 spectral resolution and si gnal/noise, and that has at least ten data points in each sp ectral window. The depth profile sho uld be continue d into the depth of the sam ple until the Fe, Cr an…

SEMI F72-1102 © SEMI 2002 3

11 Test Specimens

11.1 Specimens are to be sectioned to appropriate size

for the particular AES instrument using a clean, dry

hacksaw or dry low speed bandsaw. Any sample

preparation shall avoid introducing contamination onto

the surface to be measured. Clean noncontaminating

gloves and tweezers should be used to handle samples,

avoiding contact with the area of interest. In addition,

preparation must avoid excessive heating of the sample;

i.e., the surface temperature shall not exceed 50

C, to

avoid oxide growth or change in surface composition.

11.2 Sample preparation should preferably be done by

the component manufacturer. Following sectioning the

sample(s) are to be cleaned and packaged per the

manufacturer’s standard final cleaning and packaging

procedures.

11.3 If sample preparation is done by other than the

manufacturer, the sample(s) may be cleaned in DI water

and dried promptly. If the sample(s) are not to be

analyzed immediately they should be packaged by

wrapping in clean metal foil or sealing in cleanroom

quality nylon bags.

11.4 If sample preparation is done by other than the

manufacturer this shall be stated in the report narrative

and the analytical results are not to be interpreted as

indicative of the manufacturer’s quality of cleaning and

packaging procedures. A note to this effect shall be

included in all tables of reported results of the

composition of the surface.

11.5 After preparation, samples should be analyzed

promptly, with allowance for shipping times and

queuing time at the analyst.

12 Preparation of Apparatus

12.1 Instruments shall be routinely tested in

accordance with manufacturer recommendations to

assure proper performance. The instrument vacuum

shall be 1.0 × 10

-7

Torr or better during the analysis.

13 Calibration and Standardization

13.1 Instrument calibration for etch rates and

sensitivity factors shall be performed in accordance

with instrument manufacturer recommendations or

other established method.

14 Procedure

14.1 The sample is to be mounted in accordance with

manufacturer's recommendations and in a manner

consistent with ultra-high vacuum surface analytical

procedures. Some of these practices are detailed in

ASTM E 1078. The area to be analyzed should be

mounted parallel to the sample holder surface so that

the TOA is known.

14.2 Place the sample in the AES introduction chamber

for pumpdown. Transfer to the analytical chamber at

the manufacturer's recommended base pressure.

14.3 Align the sample with respect to the electron

beam and analyzer so that optimum count rate from the

desired analytical location is obtained. The surface area

to be analyzed should be free of sample preparation

debris, visible particles and large defect features, if

possible.

14.4 A large beam size or scan area should be used to

attempt measurement of a representative surface.

Elemental survey data (approximately 0-2000 eV) are

to be measured from the sample surface to determine

the elements present and their approximate surface

abundances. A signal-to-noise ratio of 2 is usually

adequate to ensure detection of elements present at one

atomic percent or greater levels. A typical survey

spectrum is shown in Figure 1.

Figure 1

Auger Spectrum of Stainless Steel Surface

14.5 Acquire a depth composition profile to determine

the relative abundances of Cr, Fe, Ni, O, and C. The

profile may be acquired in a simultaneous or an

alternating etch/data acquisition mode. Measurement

of each element shall be made at a frequency of at least

one data point every 5 Å within the first 50 Å and one

data point every 10 Å from 50 Å to the profile end. An

appropriate scan acquisition time is one that optimizes

SEMI F72-1102 © SEMI 2002 4

spectral resolution and signal/noise, and that has at least

ten data points in each spectral window. The depth

profile should be continued into the depth of the sample

until the Fe, Cr and Ni levels are approximately

constant.

14.6 Depth profile data are presented as signal intensity

of each element with etch time (i.e., depth), and as

atomic concentration with etch time. Depths may be

estimated from etch times by determination of the etch

rate on a known thickness of standard material. A

typical AES profile is shown in Figure 2.

Figure 2

Auger Depth Profile of Stainless Steel

15 Calculations and Interpretation of Results

15.1 Most manufacturers supply software for

calculation of the approximate elemental composition

from the survey spectrum and the depth profile data.

The elemental composition should be estimated using

sensitivity factors appropriate to the instrument, each

element, and resolution settings for each measurement.

AES spectra are considered only semiquantitative, due

to instrument geometry and the chemical form

dependency of each element's sensitivity factor.

Evaluations of elemental composition should therefore

be limited to similar samples analyzed on the same

instrument.

15.2 The signal intensity with etch time graph may be

used to calculate oxide thickness, defined as the point at

which the oxygen signal decreases to half its maximum

value. The thickness of surface carbon contamination

is calculated in the same way from the carbon signal.

15.3 Relative abundances of profiled elements are

recorded on the atomic concentration with etch time

graph.

16 Reporting Results

16.1 A tabular summary of estimated surface elemental

composition is to be supplied with its associated

elemental survey spectrum.

16.2 Tabular summaries of oxide thickness, thickness

of the region in which Cr concentration exceeds Fe

concentration, thickness of a surface Fe enrichment (if

present), and carbon thickness are to be supplied with

associated depth profile graphs.

16.3 Optionally, parameters such as maximum Cr/Fe

ratio may be reported. However, the value of the

maximum Cr/Fe ratio is subject to instrument geometry

and sensitivity factor variations, and should not be used

for primary evaluation purposes. Comparative

evaluations should only be made from data collected by

the same instrument with an identical protocol.

16.4 Data acquisition parameters, including instrument

geometry, electron beam size or scan area, and other

pertinent settings are to be supplied. The manufacturer

and model number of instrument used is to be reported.

Analyst identity and analysis date are also required

information. Each table and graph must be clearly

labeled with sample identification.

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 or equipment mentioned

herein. These standards are subject to change without

notice.

By publication 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.

SEMI F72-1102 © SEMI 2002 5

APPENDIX 1

DISCUSSION OF EFFECTS OF DEPTH OF ANALYSIS ON DEPTH

PROFILE ANALYSIS BY AUGER ELECTRON SPECTROSCOPY FOR

SURFACE CHEMISTRY ANALYSIS OF PASSIVATED STAINLESS

STEEL

NOTE: The material in this appendix is an official part of SEMI F72 and was approved by full letter ballot procedures. This

appendix was derived from presentations made to the Stainless Steel and Surface Analysis Workshop

2 Stainless Steel and Surface Analysis Workshop, March, 1999; Interpratation of Depth Profile Analysis Data, Dave Harris, Charles Evans and

Associates.

A1-1

A1-1.1 The purpose of this appendix is to describe the

Auger Electron Spectroscopy (AES) technique and

explain the interpretation of the depth profile analysis

with respect to the structure and composition of the

passive oxide layer on stainless steel. The effect of the

depth of analysis on the measured chromium to iron

ratio, the oxide thickness, and the depth of enrichment

is discussed. The discussion also applies to depth

profile analyses performed by ESCA (Electron

Spectroscopy for Chemical Analysis, sometimes

referred to as X-Ray Photoelectron Spectroscopy, or

XPS).

A1-1.2 Auger — The mechanism of Auger electron

generation is illustrated in Figure A1-1. The energy of

the Auger electron is determined by the energies of the

electron energy levels participating in the generation

process and are unique for each chemical element.

Thus the elements present in the analyzed region may

be determined by analysis of the energies of emitted

Auger electrons.

K or 1s

Auger Electron

or 2p

or 2s

Electron

Energy

Levels

Electron Hole

Electron from higher energy

level drops into electron hole

created by incident electron or

photon

2. Energy released by 1

“kicks out” Auger Electron

from hi

her ener

level

Figure A1-1

Schematic Representation of Auger Electron

Generation Process

A1-1.3 The Auger technique makes use of an electron

beam for primary excitation, typically of energy in the

range 2 to 5 keV. The electron beam may by defocused

to analyze a relatively large area of the surface, of the

order of micrometers, or focussed and rastered to

“map” the distribution of elements on the surface. An

electron energy analyzer is focused at the same point as

the incident electron beam, and the Auger electrons that

escape the surface are detected and analyzed. The

analysis is commonly presented as the derivative of the

electron signal intensity N as a function of energy E,

dN(E)/dE, of the spectrum to enhance the visibility of

the small Auger electron peaks relative to the

background. An example of an Auger electron

spectroscopy spectrum of a stainless steel surface is

shown in Figure 1 of this test method.

A1-2 Illuminated Volume and Surface

Sensitivity

A1-2.1 The incident electron beam penetrates well

below the surface. Auger electrons are generated all

through this illuminated volume. The Inelastic Mean

Free Path (IMFP) of an electron in a solid is the mean

distance through the solid that an electron can travel

before losing some of its energy (suffering an inelastic

interaction). The IMFP is a function of the electron’s

energy and the matrix through which it is traveling.

Electrons with an energy typical of Auger and ESCA

electrons, approximately 1 keV, have an IMFP of about

10 angstroms. That means that a 1 keV electron will

travel, on average, 10 angstroms before interacting with

the matrix and giving up some of its energy. In other

words it will be scattered to lower energy and will not

be part of the photoelectron or Auger electron line for

its element. The IMFP is a statistical parameter and an

electron may travel several IMFPs before having a

collision. The “several IMFPs” is called the escape

depth of the electron, or the depth of analysis, as shown