Photon Factory Activity Report 2016 #34 (2017)
BL-3B/2016G094

Study on the behavior of the photoelectrons with lower energies
in the ultra thin film of silicon oxide
Motoyasu Imamura ∗11 AIST, 1-1-1 Higashi, Tsukuba 305-8565, JapanIntroduction
X-ray photoelectron spectroscopy (XPS) has beenused for the quantitative and qualitative analysis
methods in the developments of functional materials
because of its high surface sensitivity, and it is useful
to determine the thickness of the thin film. For determination of the the thickness using XPS, the attenuation length (AL) of the photoelectron is an importantparameter. For a long time, the inelastic mean freepath (IMFP) has been used as an alternative of AL
because the values of IMFP can be calculate easily
using the predictive equation TPP-2M [1–3]. However the effect of the elastic scattering is not considered in the evaluation of IMFPs. Recently effective attenuation length (EAL) [1, 4, 5] is proposed and used
for the practical purposes. The author has been experimentally measured the EAL of the photoelectronin the SiO2 thin films with the energy range of 100–
1000 eV [6] at old BL-13C station [7, 8].
For experimental determination of EAL in SiO2 ,the SiO2 thin film and bulk samples of Si and SiO2
are necessary. The thickness of the thin film must be
certified by another method.
As shown Fig. 1, photoelectron intensity from eachsample was measured. From the bulk samples of thesilicon and silicon oxide,1

Ro (hν, θ ) =∞
ISi
∞
ISiO
2(1)

∞ and I ∞is caluculated where ISi
SiO2 are the photoelectron intensities from the Si substrate and oxide filmlayer, respectively.

Rd (hν, θ ) =ISi
ISiO2(2)is calculated where ISi and ISiO2 are the photoelectron
intensities from the Si substrate and SiO2 thin film,respectively.
The EAL is calculated from the equation below:
λSiO2 (hν, θ ) =1d·cos θ ln{[ Ro (hν, θ )/Rd (hν, θ )] + 1}
(3)

For determination of the EAL in the SiO2 thin film, it
is important to measure the Ro precisely.
Experiment
The measurements of XPS spectra were carried at BL-3B using the apparatus built for theangle-resolved x-ray photoemission spectroscopy(ARPES II). In this apparatus, the hemispherical electron analyzers with a 50 mm mean radius (VSWHA54) are fixed on the goniometer, which enable
the analyzer to be rotate in the vacuum chamber asshown in Fig. 2. The energy step was 0.05 eV. The
pass energy was set as 10 eV. The acceptance angle
was ±1◦ . The angle between the incident x-ray andthe surface normal of the sample was fixed as 55◦ .
The emission angle of the photoelectrons from thesurface normal was adjusted to 0◦ , 15◦ , 30◦ , 45◦ , 60◦ ,and 75◦ by rotating the electron analyzer. The energyof the incident x-ray was set as 130 eV, 150 eV, 180 eV,and 200 eV.
As the bulk samples, Si(100) wafer with a thickness of 0.5 mm and SiO2 /Si thin film with a thickness of 100 nm prepared by a thermal process wereused. The thickness 100 nm of the thin film is thickenough to avoid the photoelectron signal from thesubstrate and thin enough to suppress the charging.
Both samples were cut as the size of 5 mm × 3 mm

2AnalyzerSRSample

Fig. 1: Samples for EAL detemination∗ motoyasu@ni.aist.go.jp

Fig. 2: Alignment of sample and analyzer

Photon Factory Activity Report 2016 #34 (2017)using a diamond cutter and fixed on the same stubfor the measurements using carbon tape, because two
samples must be used for measurement by turns inthe same condition to suppress the time dependent
influence.
3 Results and Discussion
Figure 3 and 4 show the Si 2p spectra of SiO2 andSi, respectively, which measured with the emission
angle of surface normal excited by x-ray with theenergy of 150 eV. Si peak and Si oxide peak arerecorded clearly. To estimate the photoelectron intensities in the spectra, curve fitting procedure will
be carried out using Shirley background and Gaussfunction. The Ro is calculated using Eq.(1) for eachenergy and emission angle.

Photoelectron Intensity

SiO2 substrate

36384042444648

50525052

Kinetic Energy (eV)Fig. 3: XPS spectra of SiO2

Photoelectron Intensity

Si substrate

3638

4042444648

Kinetic Energy (eV)Fig. 4: XPS spectra of Si

Acknowledgement
I would like to thank Prof. Ozawa of Tokyo Techand Prof. Mase of PF for their help in my experiments at BL-3B station.

References[1] ISO 18115:2001-surface chemical analysis - vocabulary.
[2] S. Tanuma et al., Surf. Interface Anal., 17 (1991)
927; 20 (1993) 77; 21 (1993) 165.
[3] C. J. Powell and A. Jablonski. NIST Electron
Inelastic-Mean-Free-Path Database: Version 1.1. National Institute of Standards and Technology(2000).
[4] C. J. Powell and A. Jablonski. NIST Electron
Effective-Attenuation-Length Database - Version 1.0.
National Institute of Standards and Technology(2001).
[5] A. Jablonski and C. Powell, Surf. Sci. Rep. 47(2002) 33.
[6] M. Imamura et al., Meas. Sci. Technol. 22 (2011)024007.
[7] N. Matsubayashi et al., Rev. Sci. Instrum. 63 (1992)
1363.
[8] H. Shimada et al., Rev. Sci. Instrum. 66 (1995)
1780.