23 Feb 2005
Raghav Sreenivasan
Stanford University
476 Lomita Mall
McCullough Bldg, room 203
Stanford, CA 94305, USA
Subject:
TXRF (Total Reflection X-Ray Fluorescence) Report
EAG Number: C05J9583
Purchase Order Number: 14124460
Dear Dr. Sreenivasan:
Please find enclosed the final report for the TXRF analysis of your 75 mm wafer
containing a thin hafnium oxide film, as detailed in the following table.
Date received:
22 Feb 2005
Results faxed/emailed:
28 Feb 2005
Results emailed to:
raghavs@stanford.edu
Number of samples:
one
Analysis cost (@ $375 per wafer): $375
Priority Surcharge: (none)
$0
Total analysis cost:
$375
Sample Disposition:
Transferred to SIMS for further analysis
Please note that your samples will be retained for 8 weeks after their receipt. After this
time they will be disposed of unless you have specifically requested otherwise. Current
disposition instructions are shown in the table above. We will maintain copies of the
data and report for three years.
Thank you for using the analytical services of Charles Evans & Associates, a division of
the Evans Analytical Group. We appreciate your business and welcome any
suggestions you may have for improving the quality and efficiency of our service.
Please do not hesitate to call me if you have any questions regarding this work.
Sincerely,
Cynthia Gonsalves
Scientist, TXRF Services
(Tel. 408-530-3632; Email: cgonsalves@eaglabs.com)
Charles Evans & Associates
810 Kifer Rd  Sunnyvale, CA 94086 USA  408-530-3500  Fax 408-530-3501  www.eaglabs.com
TOTAL REFLECTION X-RAY FLUORESCENCE (TXRF)
SURFACE ANALYSIS REPORT
23 Feb 2005
EAG NUMBER C05J9583
PO NUMBER 14124460
for
Raghav Sreenivasan
Stanford University
476 Lomita Mall
McCullough Bldg, room 203
Stanford, CA 94305, USA
Prepared by:
____________________________
Cynthia Gonsalves
Scientist, TXRF Services
(Tel. 408-530-3632; cgonsalves@eaglabs.com)
Reviewed by:
____________________________
Lori Bisaha
Scientist, TXRF, XRF, and SEM Services
(Tel. 408-530-3614; lbisaha@cea.com)
Charles Evans & Associates
810 Kifer Rd
Sunnyvale, CA 94086 USA
TEL 408-530-3500
FAX 408-530-3501
Charles Evans & Associates
810 Kifer Rd  Sunnyvale, CA 94086 USA  408-530-3500  Fax 408-530-3501  www.eaglabs.com
TOTAL REFLECTION X-RAY FLUORESCENCE (TXRF) SURFACE ANALYSIS REPORT
Requester:
EAG Number:
Analysis Date:
Raghav Sreenivasan
C05J9583
23 Feb 2005
Purpose:
The purpose of this analysis was to measure metal contamination on the surface of one 75
mm diameter wafer. This wafer has a 50Å hafnium oxide film on top of 20Å SiO2 on top of Si.
The sample is identified by the description on the individual sample container.
Summary:
All results are shown in Table 1. Ca, Ti, and Fe are observed at all three locations; Cr is
present at two out of three locations. Results will include contamination in the HfOx film and
may also include some contamination at the SiO2 interface.
Experimental:
TXRF measurements were made using a TREX 610-T TXRF instrument. The following
measurement conditions were used:
Source:
W rotating anode
Beam Energy:
30 kV
Beam Current:
50 mA
Incident angle:
0.037
Integration time: 1000 seconds
Measurements were made on the polished side of each wafer, at locations shown graphically
on the data printouts and in the diagram below.
Flat or Notch
The analysis area is 10 mm in diameter, and analysis depth is ~50Å for polished silicon
surfaces (using W primary beam). Analysis depth for this HfOx/SiO2/Si sample is not known.
Analyses were performed with the sample in a nitrogen ambient at ~1 Torr.
Charles Evans & Associates
810 Kifer Rd  Sunnyvale, CA 94086 USA  408-530-3500  Fax 408-530-3501  www.eaglabs.com
TXRF Analysis Report
CEA Number C05J9583
Raghav Sreenivasan
Stanford University
Page 2
23 Feb 2005
Results and Discussion:
Results are summarized in Table 1.
Ca, Ti, and Fe are observed at all three locations; Cr is present at two out of three locations.
At these levels in the spectra, identification and quantification of Ti is more uncertain due to
possible diffraction artifacts that can occur at similar intensities in this region of the spectra.
Identification and quantification of Cr and Mn are complicated by the high background/rising
slope in this region and software subtraction of a Hf L escape peak near the Mn peak.
Signal from the Hf in the film also interferes with measurement of several other species that
are measured by TXRF on Si surfaces, as discussed below.
The intense Hf peaks from Hf L-lines interfere with detection of Co, Ni and Cu due to overlap
between the Hf L-peaks and the K-peaks for these elements. It is possible that Co may be
present in these spectra. The software fitting of the Hf Ll line is improved if Co is included.
However, unambiguous identification of Co is impossible due to the interference from the
overlap of the Hf Ll peak with the Co K peak and the overlap of the Hf L peak with the Co
K peak.
Overlap of the Fe K and Hf Ll peak makes the quantification accuracy of Fe uncertain. The
intense Hf M-lines interfere with measurement of S.
The detection limits for other elements on this film are also higher than typically observed for a
polished Si surface due to the higher background observed from the HfOx film and the reduced
power of TXRF analysis necessary due to the intensity of the Hf fluorescence. The presence
of the Hf M sum peak also increases the detection limits for K.
The film thickness was given as 50 Å. The analysis depth for a polished Si surface using a W
primary beam is ~50Å under normal power and angle conditions. The analysis depth for a
Hafnium Oxide film under these reduced power and angle conditions is not known, but should
be similar to or less than this (50Å). The analysis results here include the HfO x film, but may
include contamination on the SiO2 interface below. It is not possible to sort out Si intensity in
this data (in Si K-peaks) due to overlap of the Si K and the Hf M-peaks and the instrument
software difficulties in fitting M-peaks.
Quantification of TXRF data depends on the index of refraction at the surface of the sample. If
the results include significant amount of the SiO2 interface, the quantification factors will be in
error and the results overestimated.
Other techniques might be useful in evaluation of thin hafnium oxide films. A wet chemical or
vapor method may be useful for dissolving the film or leaching contamination from the surface.
Jim Norberg (operations coordinator) would be the contact person to discuss analysis of this
type. TOF-SIMS may also be used to look at this surface. The contact person to discuss this
technique is Dr. Thomas Fister (manager, TOF-SIMS Analytical Services).
Charles Evans & Associates
810 Kifer Rd  Sunnyvale, CA 94086 USA  408-530-3500  Fax 408-530-3501  www.eaglabs.com
Page 3
23 Feb 2005
TXRF Analysis Report
EAG Number C05J9583
Raghav Sreenivasan
Stanford University
Table 1. TXRF Results for W source measurements (units of 1010 atoms/cm2).
C05J9583
2/21/05 Hf 134 60 cyl
Center
14,-14
-14,14
S
Cl
K
Ca
Ti
Cr
Mn
Fe
Ni
Co
Cu
Zn
Ar
<2600
<1940
<6500
<380*
<300*
<860*
<30
<30
<100*
140
76
160
30
33
63
34
18
<44
<21*
<18*
<43*
120
86
180
Int
Int
Int
Int
Int
Int
Int
Int
Int
<7
<6
<11
<50
<40
<80
*may be present near detection limit
Uncertainty values (±) reported are 1 standard deviations calculated from instrumental reproducibility and background signal-to-noise
ratios. These numbers do not include uncertainties from interferences, if any. Practical detection limits (indicated by ‘<’) are calculated for
each spectrum and may vary between analyses.
Elements in the ranges S-Zn and Mo-Hf can be detected by W-source TXRF. If an element in this range is not reported in the table, it was
not detected. X-ray lines for elements in the range Mo-Hf overlap X-ray lines for elements in the range S-Zn, making identification and/or
quantification difficult if they are present at high levels. For example, it is not possible to distinguish S and Mo; what is reported as sulfur
may be in part molybdenum.
Correction factors: Corrections have been applied to Fe and Cu to compensate for detector background.
Measurement locations: Locations are given in mm from the center of the wafer, assuming that the wafer is oriented with the notch at the
bottom. Positive values are to the right and up, and negative values are left and/or down from the wafer center.
‘Int’ indicates interference.
Charles Evans & Associates
810 Kifer Rd  Sunnyvale, CA 94086 USA  408-530-3500  Fax 408-530-3501  www.eaglabs.com
Page 4
23 Feb 2005
TXRF Analysis Report
EAG Number C05J9583
Raghav Sreenivasan
Stanford University
Appendix A
Brief Explanation of the Total Reflection X-Ray Fluorescence (TXRF) Technique
Total Reflection X-Ray Fluorescence (TXRF) is a nondestructive method of analyzing flat, smooth
samples. It is a survey technique, measuring a range of elements in a single analysis.
primary
beam
detector
wafer
X-rays from a primary beam impinging on the surface of a flat, smooth sample at a low angle (less than
the angle of total external reflection) excite impurity atoms on or near the surface of the sample. The
excited atoms emit X-ray photons of characteristic energies which are detected and recorded by a
large-area Si(Li) detector and the associated electronics. The photon energies are used to identify the
elements present. The intensity of the X-ray fluorescence for each element is used to quantify the areal
density of that atomic species.
Reflection of the primary x-ray beam from the sample surface is maximized by use of mirror polished
samples. Less penetration of the primary beam into the sample results in fewer excited matrix atoms
and a proportionally larger number of photons from surface impurity atoms, leading in turn to enhanced
detection capability.
Analysis of rough surfaces such as wafer backsides, unpolished wafers, and patterned wafers, is
possible however. Degradation of detection limits, accuracy, and precision of the analysis depend on
the roughness of the sample.
TXRF analysis is performed on unbroken full wafers from 100 to 300 mm in diameter. Smaller samples
and partial wafers can be analyzed by mounting on carrier wafers. At Evans Analytical Group (EAG)
laboratories, TXRF samples are handled and analyzed in a Class 10 environment to minimize chances
of accidental contamination.
The range of elements that can be analyzed in a single analysis depends on energy of the primary
beam. TXRF instruments within the Evans Analytical Group use either a rotating W anode or a fine
focus Mo X-ray tube, each with a monochromator, to produce and refine the primary X-ray beam. The
two primary beams excite different ranges of elements:
Tungsten source (W L) - sulfur through zinc, molybdenum through the lanthanide series
Molybdenum source (Mo K) - gallium through bromine; tantalum through lead.
Charles Evans & Associates
810 Kifer Rd  Sunnyvale, CA 94086 USA  408-530-3500  Fax 408-530-3501  www.eaglabs.com
Page 5
23 Feb 2005
TXRF Analysis Report
EAG Number C05J9583
Raghav Sreenivasan
Stanford University
Appendix B
Quantification, Detection Limits, Precision, and Accuracy
QUANTIFICATION
Quantification is based on the measurement of a reference sample with known areal density of impurity
atoms on the surface. However, no universally accepted standards for TXRF quantification exist. Each
laboratory must develop and provide its own reference wafers, which may lead to inter-laboratory
discrepancies.
Quantification for TXRF is based on measurement of one element (or several elements) present at a
known areal density. Levels of all elements on the unknown sample are calculated using measured
photon counts for each element on the unknown, photon counts for the standard element, and relative
fluorescence yield factors for the different elements.
Results can be quantified by extrapolation from measurement of a reference sample of known areal
density, as long as the reference and the unknown are measured using the same instrument
conditions. A separate reference sample for each element is not required because relative
fluorescence yields are known.
Signal response for a given element in TXRF analysis is sensitive to the way in which the element is
distributed, as shown in Figure 1. As the glancing angle is changed, signal intensity varies by a factor
of ~5 if the element is thinly plated on the surface, but remains constant within the range of angles
normally used for analysis if the contamination is particulate or residue. If contamination is buried (e.g.
an implanted layer), signal intensity will rise with increasing angle in a manner similar to the curve for
plated contamination, but will not drop as sharply at higher angles. The matrix curve refers to signal
response for the element(s) of the bulk material.
Arbitrary Intensity
Plated
Residue
Matrix
0
0.05
0.1
0.15
0.2
Glancing Angle (degrees)
0.25
0.3
0.35
Figure B-1. Schematic representation of signal intensity variation with glancing angle.
Charles Evans & Associates
810 Kifer Rd  Sunnyvale, CA 94086 USA  408-530-3500  Fax 408-530-3501  www.eaglabs.com
Page 6
23 Feb 2005
TXRF Analysis Report
EAG Number C05J9583
Raghav Sreenivasan
Stanford University
The EAG procedure is to assume that all contamination is present as a thin uniformly distributed plating
on the sample surface unless otherwise stated in the Discussion section of the report. If contamination
is present as particles greater than 0.1m diameter, as a thick residue, or as a buried layer, reported
values will be high by an unspecified factor.
DETECTION LIMITS
Detection limits are variable, depending on element, sample surface, analysis conditions, and
interferences. Interference free detection limits for first row transition metals (Fe, Ni, Cu) may be as low
as 3E9 atoms/cm2. Sample roughness and interferences from other elements adversely affect
detection limits.
PRECISION AND ACCURACY
Precision of TXRF measurement varies with the source, level of the element measured, and
measurement conditions. Using EAG standard conditions, the precision on tungsten source TXRF
measurements ranges from 1% at the 1X1015 atoms/cm2 level to ~100% at the levels near detection
limit.
Precision of repeat measurements on our SPC sample, which is vanadium at a level of 2x1013
atoms/cm2, is 16% over a period of more than six months. EAG TXRF instruments are calibrated to
nickel contaminated wafers which have been verified by a Cr standard analyzed with HIBS.
Uncertainty on the HIBS measurement is approximately 10%.
Precision of molybdenum source repeat measurements on the SPC sample, vanadium at a level of
2X1013 atoms/cm2, is 17% over a period of more than six months.
The molybdenum source is calibrated to a wafer with plated nickel contamination. The nickel level is
taken from tungsten source TXRF measurement, and verified by measurement of a commercially
available spin-coated reference wafer.
Charles Evans & Associates
810 Kifer Rd  Sunnyvale, CA 94086 USA  408-530-3500  Fax 408-530-3501  www.eaglabs.com
Page 7
23 Feb 2005
TXRF Analysis Report
EAG Number C05J9583
Raghav Sreenivasan
Stanford University
Appendix C
The EAG TXRF Data Printout
You will receive a data printout for each measurement made on your samples. Each printout consists
of a listing of analysis identification and instrument conditions used for the measurement, graphical
presentation of the data, and a data table.
Analysis identification:
file - name of data file stored on disk
sample - sample name
sub - substrate. Si Wafer or GaAs wafer
memo 1 - company and name of client, EAG job identification number
Analysis conditions:
Slot - position in the special cassette into which samples are loaded for analysis
M - measurement type (manual, programmed, angle scan, etc.)
Size - wafer size in inches
X: and Y: - analysis position measured in mm from wafer center
Time - integration time for the analysis
X-ray Voltage - anode operating voltage in kV
X-ray Current - anode operating current in mA
X-ray Target - anode material
D.T.: - Dead time: percent of real time that detector does not accept new data
Angle: - glancing angle at which measurement is made
DP Cond: - Name of reference file used for data acquisition and processing
Element Cond: - Name of reference file used for quantification
Quant: - Name of reference file used for quantification
Spectrum:
The spectrum is a graph of fluorescence X-ray energy (from 1 to 10 keV for W primary beam or
1 to 18 keV for Mo primary beam) versus photon counts per second. For analysis of silicon
wafers, the large peak at the low energy end of the spectrum is the silicon signal from the wafer
substrate. High counts at the high energy end of the spectrum are due to scattered primary Xrays (W L or Mo K). Characteristic X-ray peaks of elements S through Zn (K) and Rb
through Re (L) (W anode) or elements S through Br (K)and Rb through Bi (L) (Mo source)
have energies between the silicon peak and the high-energy scatter.
Quantitative Results:
Spectrum: - symbol for the element and the name of the X-ray line used in calculation of areal
density
Energy keV - energy at which the line for that element appears on the spectrum
Peak Int. cps - integrated counts per second for the identified peak
Conc *E10 - uncorrected calculated areal density for the element, in units of 1010 atoms/cm2
Stand.Dev cps - standard deviation of counts per second in peak signal
BG Int cps - background counts per second in peak region
Charles Evans & Associates
810 Kifer Rd  Sunnyvale, CA 94086 USA  408-530-3500  Fax 408-530-3501  www.eaglabs.com