Photon Factory Activity Report 2004 #22 Part B (2005)
Surface and Interface

2C/2002S2-002

Crystallization with annealing in ZrO2 gate insulatorsstudied by photoemission and x-ray absorption spectroscopy

Jun Okabayashi,* Satoshi Toyoda, Hiroshi Kumigashira, Masaharu Oshima, Koji Usuda,
Masaaki Niwa, and Guo Lin LIU
Department of Applied Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
Semiconductor Technology Academic Research Center, Kohoku-ku, Kanagawa 222-0033, Japan78

Users' ReportValence bandhν = 800 eVO K-edge XAS(a)x3

800 ¼Cx3

700 ¼C

as-grown(b)

800 ¼C

Absorption Intensity (arb. units)

2. Experimental
ZrO2 films were grown by a pulsed laser deposition(PLD) method using an ArF laser on hydrogen-terminatedp-type Si(100) substrates. The thickness of the gate
dielectric film was determined with ellipsometry to be 3nm including the interface layer of 1 nm at the as-grownstage [3]. Photoemission spectroscopy using synchrotron
radiation was performed at the undulator beam line BL2C of the Photon Factory in High-Energy Accelerator
Research Organization (KEK). The total energy
resolution was about 0.35 eV at photon energy of 800 eV.
Annealing was performed in ultra-high vacuum by thedirect current flowing method through the samples. X-ray
absorption spectroscopy was performed by a totalelectron-yield made.
3. Results and discussion
Annealing-temperature dependence in valence-band
spectra are shown in Fig. 1(a). The line shapes from EF toabout -4 eV are identical to those of Si, meaning that thisenergy region is completely derived from the Si-substratecomponent. After annealing above 800°C, double-peakstructures appeared with the splitting of 3.0 eV in thebinding energy region of 5-9 eV. It may be related to thecrystallization of the ZrO2 layer by annealing. Thus, the O

2p non-bonding state may be clearly observed due to thechanges in the chemical states since the crystallizationfrom the amorphous structure promotes the changes to a
sharp peak structure.
O K-edge absorption spectra can be deconvoluted into
two absorption edges for the ZrO2 layer and the SiO2
interfacial layer. The absorption edge around 532 eV isderived from ZrO2, while that around 537 eV comes fromthe SiO2 interfacial layer. The absorption edge at 532 eV
became a sharp structure and additional peaks (solidtriangles) appeared by annealing at 800 °C in the higher
photon energy region than 540 eV. The fact that sharp
features and additional peaks in XAS spectra are clearlyobserved by annealing is well correlated with the splittingin the valence-band spectra.

Photoelectron Intensity (arb. units)

1.Introduction
Due to the decrease in the size of complementary
metal-oxide-semiconductor field effect transistors, aconventional SiO2 gate oxide layer with less than 2 nm is
not applicable because of excess direct tunneling leakage
current. Consequently, alternative gate dielectrics withhigher electrical dielectric constant (high-k) than SiO2 arewidely investigated. ZrO2 is one of the promising
candidates as high-k dielectric materials for gate
dielectrics. Although characteristics of ZrO2 on Si havebeen extensively investigated [1], there remain serious
problems to be solved such as the crystallization in ZrO2
layers which promotes the leakage current through thecrystallized grains after the annealing for activation.
Although high-resolution core-level photoemission
spectra are useful to reveal the precise chemical states dueto the silicidation by the annealing above 860°C [2], theinformation about crystallization cannot be affected incore-level photoemission spectra. Therefore, we focus on
the valence-band spectra and XAS to deduce theinformation about crystallization in the lower temperature
range than that of the silicidation.

700 ¼Cx3

as-grown

H-terminated Si(001)

14 12 108642Binding Energy (eV)

0520

530

540550560

Photon Energy (eV)FIG. 1: (a) Valence-band spectra and (b) x-ray
absorption spectra of ZrO2/SiO2/Si with the annealingtemperature dependence.
References[1] K.Muraoka, Appl. Phys. Lett. 80, 4516 (2002).
[2] J. Okabayashi et al., Appl. Phys. Lett. 85, 5959 (2004).
*jun@sr.t.u-tokyo.ac.jp