C. L. Hinkle, M. Milojevic, B. Brennan, A. M. Sonnet, F. S. Aguirre-Tostado,

G. J. Hughes, E. M. Vogel, and R. M. Wallace

Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA

Department of Electrical Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA

School of Physical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland

(Received 29 January 2009; accepted 27 March 2009; published online 20 April 2009)

The passivation of interface states remains an important problem for III-V based semiconductor devices. The role of the most stable bound native oxides GaOx (0.5£x£1.5) is of particular interest. Using monochromatic x-ray photoelectron spectroscopy in conjunction with controlled GaAs(100) and InGaAs(100) surfaces, a stable suboxide (Ga2O) bond is detected at the interface but does not appear to be detrimental to device characteristics. In contrast, the removal of the Ga 3+ oxidation state (Ga2O3) is shown to result in the reduction of frequency dispersion in capacitors and greatly improved performance in III-V based devices.

 © 2009 American Institute of Physics. [DOI: 10.1063/1.3120546]

Half-cycle atomic layer deposition reaction studies of Al2O3 on In0.2Ga0.8As (100) surfaces

M. Milojevic, F. S. Aguirre-Tostado, C. L. Hinkle, H. C. Kim, E. M. Vogel, J. Kim, and

R. M. Wallace

(Received 16 June 2008; accepted 29 October 2008; published online 19 November 2008)

The reduction in III–V interfacial oxides by atomic layer deposition of Al2O3 on InGaAs is studied by interrupting the deposition following individual trimethyl aluminum (TMA) and water steps (half cycles) and interrogation of the resultant surface reactions using in situ monochromatic x-ray photoelectron spectroscopy (XPS). TMA is found to reduce the interfacial oxides during the initial exposure. Concentrations of Ga oxide on the surface processed at 300 °C are reduced to a concentration on the order of a monolayer, while AsOx species are below the level of detection of XPS.

© 2008 American Institute of Physics. [DOI: 10.1063/1.3033404]

A. M. Sonnet, C. L. Hinkle, M. N. Jivani, R. A. Chapman, G. P. Pollack,

R. M. Wallace, and E. M. Vogel

Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA

(Received 22 August 2008; accepted 8 September 2008; published online 26 September 2008)

Significant enhancement in metal-oxide-semiconductor field effect transistor (MOSFET) transport characteristics is achieved with InxGa1−xAs (x=0.53, x=0.20) channel material using ex situ plasma enhanced chemical vapor deposited amorphous Si layer. InxGa1−xAs MOSFETs (L=2 mm, Vgs-Vt =2.0 V) with Si interlayer show a maximum drain current of 290 mA/mm (x=0.53) and 2 mA/mm (x=0.20), which are much higher compared to devices without a Si interlayer. However, charge pumping measurements show a lower average interface state density near the intrinsic Fermi level for devices without the silicon interlayer indicating that a reduction in the midgap interface state density is not responsible for the improved transport characteristics.

© 2008 American Institute of Physics. [DOI: 10.1063/1.2991340]

Conformal Al2O3 dielectric layer deposited by atomic layer deposition for graphene-based nanoelectronics

Moon J. Kim, Robert M. Wallace, and Jiyoung Kim

(Received 15 February 2008; accepted 24 April 2008; published online 20 May 2008)

We present a facile route which combines the functionalization of a highly oriented pyrolytic graphite surface with an atomic layer deposition (ALD) process to allow for conformal Al2O3 layers. While the trimethylaluminum
TMA /H2O process caused selective deposition only along step edges, the TMA/O3 process began to provide nucleation sites on the basal planes of the surface. O3 pretreatment, immediately followed by the ALD process with TMA/O3 chemistry, formed Al2O3 layers without any preferential deposition at the step edges. This is attributed to functionalization of graphene by ozone treatment, imparting a hydrophilic character which is desirable for ALD deposition.

 © 2008 American Institute of Physics. [DOI: 10.1063/1.2928228]

F. S. Aguirre-Tostado,M. Milojevic, C. L. Hinkle, E. M. Vogel, and R. M. Wallace

S. McDonnell  and G. J. Hughes

School of Physical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland

(Received 29 February 2008; accepted 8 April 2008; published online 30 April 2008)

Atomic H exposure of a GaAs surface at 390 °C is a relatively simple method for removing the native oxides without altering the surface stoichiometry. In-situ reflection high energy electron diffraction and angle-resolved x-ray photoelectron spectroscopy have been used to show that this procedure applied to In0.2Ga0.8As effectively removes the native oxides resulting in an atomically clean surface. However, the bulk InGaAs stoichiometry is not preserved from this treatment. The In:Ga ratio from the substrate is found to decrease by 33%. The implications for high-mobility channel applications are discussed as the carrier mobility increases nearly linearly with the In content.

 © 2008 American Institute of Physics. [DOI: 10.1063/1.2919047]

C. L. Hinkle, A. M. Sonnet, E. M. Vogel, M. Milojevic, B. Lee, F. S. Aguirre-Tostado, K. J. Choi, H. C. Kim, J. Kim, and R. M. Wallace

S. McDonnell and G. J. Hughes

School of Physical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland

(Received 14 January 2008; accepted 29 January 2008; published online 19 February 2008)

The reduction and removal of surface oxides from GaAs substrates by atomic layer deposition (ALD) of Al2O3 and HfO2 are studied using in situ monochromatic x-ray photoelectron spectroscopy. Using the combination of in situ deposition and analysis techniques, the interfacial "self-cleaning" is shown to be oxidation state dependent as well as metal organic precursor dependent. Thermodynamics, charge balance, and oxygen coordination drive the removal of certain species of surface oxides while allowing others to remain. These factors suggest proper selection of surface treatments and ALD precursors can result in selective interfacial bonding arrangements.

© 2008 American Institute of Physics. [DOI: 10.1063/1.2883956]

APPLIED PHYSICS LETTERS 91, 142122 (2007)

T. Yang, Y. Xuan, D. Zemlyanov, T. Shen, Y. Q. Wu, J. M. Woodall, and P. D. Yea

(Received 1 August 2007; accepted 21 September 2007; published online 5 October 2007)

A systematic capacitance-voltage study has been performed on GaAs metal-oxide-semiconductor (MOS) structures with atomic-layer-deposited HfO2/Al2O3 nanolaminates as gate dielectrics. A HfO2/Al2O3 nanolaminate gate dielectric improves the GaAs MOS characteristics such as dielectric constant, breakdown voltage, and frequency dispersion. A possible origin for the widely observed larger frequency dispersion on n-type GaAs than p-type GaAs is discussed. Further experiments show that the observed hysteresis is mainly from the mobile changes and traps induced by HfO2 in bulk oxide instead of those at oxide/GaAs interface. © 2007 American Institute of Physics.

[DOI: 10.1063/1.2798499]

C. L. Hinkle, A. M. Sonnet, and E. M. Vogel

M. Milojevic, B. Lee, F. S. Aguirre-Tostado, K. J. Choi, J. Kim, and R. M. Wallace

(Received 4 September 2007; accepted 2 October 2007; published online 19 October 2007)

The method of surface preparation on n-type GaAs, even with the presence of an amorphous-Si interfacial passivation layer, is shown to be a critical step in the removal of accumulation capacitance frequency dispersion. In situ deposition and analysis techniques were used to study different surface preparations, including NH4OH, Si-flux, and atomic hydrogen exposures, as well as Si passivation depositions prior to in situ atomic layer deposition of Al2O3. As–O bonding was removed and a bond conversion process with Si deposition is observed. The accumulation capacitance frequency dispersion was removed only when a Si interlayer and a specific surface clean were combined.

© 2007 American Institute of Physics. [DOI: 10.1063/1.2801512]

JOURNAL OF APPLIED PHYSICS 102, 024112 (2007)

C. Driemeier

(Received 30 April 2007; accepted 13 June 2007; published online 25 July 2007)

The chemical bonding of O atoms in HfO2 films on Si was investigated by in situ x-ray photoelectron spectroscopy in the O 1s spectral region. In addition to trivial O forming only O-Hf bonds, O 1s signals corresponding to nontrivial secondary O
Osec were also observed. By ruling out possible roles of impurities as well as by comparing O 1s signals for different thermochemical processing routes, Osec chemical origins were inferred. Moreover, angle-resolved photoelectron analysis was employed to quantitatively separate surface and bulk Osec contributions. Surface Osec was assigned to surface O-H groups generated either by room temperature water vapor exposure or by 600 °C H2 annealing. Bulk Osec was assigned to O-O or O-H bonds and, as indicated by thermodynamic calculations and complementary structural analysis, is located in HfO2 amorphous regions and grain boundaries. This bulk Osec can be partly removed by annealing in reducing atmospheres. For some of the processing routes employed here, we observed additional, water-induced bulk Osec, which was attributed to dissociative water absorption in HfO2 amorphous regions and O-depleted grain boundaries. © 2007 American Institute of Physics.

[DOI: 10.1063/1.2759198]

APPLIED PHYSICS LETTERS 90, 262105 (2007)

Robert M. Wallace, Bruce E. Gnade, Raymond Barnett, Harvey Stiegler, and Hal Edwards

(Received 1 April 2007; accepted 5 June 2007; published online 26 June 2007)

© 2007 American Institute of Physics. [DOI: 10.1063/1.2752533]

APPLIED PHYSICS LETTERS 89, 032904 (2006)

G. Pant, A. Gnade, M. J. Kim, R. M. Wallace, and B. E. Gnade

(Received 30 January 2006; accepted 25 May 2006; published online 19 July 2006)

 © 2006 American Institute of Physics. [DOI: 10.1063/1.222699]

H. N. Alshareef, K. Choi, H. C. Wen, H. Luan, H. Harris, Y. Senzaki, P. Majhi, B. H. Lee, and R. Jammy

(Received 3 October 2005; accepted 23 January 2006; published online 16 February 2006)

It is shown that the work function of Ta1-xAlxNy depends on the electrode and gate dielectric compositions. Specifically, the work function of Ta1-xAlxNy increased with SiO2 content in the gate dielectric, reaching as high as 5.0 eV on SiO2; the work function was nearly 400 mV smaller on HfO2. In addition, the work function decreased with increasing nitrogen content in the Ta1-xAlxNy metal gate. Increasing Al concentration increased the work function up to about 15% Al, but the work function decreased for higher Al concentrations. Chemical analysis shows that Al–O bonding at the interface correlates with the observed work function values.

© 2006 American Institute of Physics. [DOI: 10.1063/1.2174836]

C. Driemeier and L. Miotti
Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre 91501-970, Brazil

I. J. R. Baumvol
CCET, Universidade de Caxias do Sul and Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre 91501-970, Brazil

C. Radtke
Pós-Graduação em Microeletrônica, Universidade Federal do Rio Grande do Sul, Porto Alegre 91501-970, Brazil

E. P. Gusev
IBM Research Division, T. J. Watson Research Center P.O. Box 218, Yorktown Heights, New York 10598

M. J. Kim and R. M. Wallace
Department of Electrical Engineering and Physics, University of Texas at Dallas, Richardson, Texas 75080

(Received 29 August 2005; accepted 7 December 2005; published online 27 January 2006)

HfO2 films (2.5 to 12 nm) deposited on thermal SiO₂ (1.5 nm) on Si were annealed in deuterium gas at 400–600 °C and incorporated D amounts were quantified using the D(³He, p)⁴He nuclear reaction. We found ~10¹³ D cm^-2 in the SiO₂ interlayer region and up to 2.2x10¹⁴ D cm^-2 near the HfO₂ surface, whereas D amounts in the bulk of the HfO₂ films were determined to be below 1013 cm-2. However, analyses employing the ¹H(¹⁵N, ag)¹²C nuclear resonant reaction showed much more spurious H present in the bulk of HfO₂ films. Mechanisms of D incorporation and desorption as well as contribution of the present results to the understanding of HfO₂-based devices are discussed.

 © 2006 American Institute of Physics. [DOI: 10.1063/1.216850]

G. Pant, A. Gnade, M. J. Kim, R. M. Wallace, and B. E. Gnade

(Received 19 September 2005; accepted 25 November 2005; published online 17 January 2006)

The crystallization of ultrathin hafnium silicon oxynitride (HfSiON) gate dielectric is studied as a function of physical thickness. Grazing incidence x-ray diffraction (GI-XRD) was used to detect phase separation and crystallization of 1.5, 2.0, 2.5, and 4.0 nm HfSiON films after 1000 °C 10 s dopant activation anneal. Crystallization peaks corresponding to monoclinic and tetragonal HfO₂ were detected in 2.5 and 4.0 nm HfSiON films. These GI-XRD results were supported by plan-view transmission electron microscopy images of the HfSiON films. Film crystallinity seems to impact voltage instability in thicker HfSiON films.

 © 2006 American Institute of Physics. [DOI: 10.1063/1.2165182]

APPLIED PHYSICS LETTERS 88, 112907 (2006)

L. F. Edge and D. G. Schlom

(Received 28 November 2005; accepted 9 February 2006; published online 16 March 2006)

Amorphous LaAlO3 thin films were deposited at room temperature directly on n-type and p-type Si
001 by molecular beam deposition. The dielectric properties of the stoichiometric amorphous LaAlO3 thin films deposited on silicon were determined through capacitance-voltage and current-voltage measurements. The electrical measurements indicate that the amorphous LaAlO3 thin films have a dielectric constant (K) of K=16±2. This is significantly lower than the K=24 of crystalline LaAlO3. The equivalent oxide thickness values range between 9.8 and 15.5 Å for films deposited on n-type silicon with physical thicknesses of 45–75 Å.

© 2006 American Institute of Physics. [DOI: 10.1063/1.2182019]

APPLIED PHYSICS LETTERS 87, 262902 (2005)

M. A. Quevedo-Lopez

S. A. Krishnan and P. D. Kirsch

(Received 1 August 2005; accepted 27 October 2005; published online 19 December 2005)

A hafnium silicon oxynitride gate dielectric with a universal channel mobility of ~90% at 1 MV/cm, equivalent oxide thickness of approximately 1 nm, and leakage current 200´ less than SiO₂ is reported. X-ray photoelectron spectroscopy results suggest that the small peak mobility loss observed in scaled HfSiON may be attributed to increased Si–N bonding near the silicon interface. In accordance with these mobility results, the Si–N:Hf–N bond ratio decreases with increasing HfSiON physical thickness. Threshold voltage instability at 1 nm equivalent oxide thickness is less than 10 mV after a 1000 s stress at 22 MV/cm. DV_TH monotonically increases with HfSiON physical thickness. This is associated with greater crystallization in thicker HfSiON films.

© 2005 American Institute of Physics. [DOI: 10.1063/1.215058]

APPLIED PHYSICS LETTERS 86, 201901 (2005)

with Si (001)

P. Sivasubramani, M. J. Kim, B. E. Gnade, and R. M. Wallace

(Received 26 January 2005; accepted 19 April 2005; published online 9 May 2005)

We have evaluated the thermal stability of Al2O3/LaAlO3/Si (001) stacks with atomic force microscopy, x-ray diffraction, transmission electron microscopy, and secondary ion mass spectrometry using a back side polishing approach. Crystallization of the amorphous LaAlO3 film was found to occur for rapid thermal anneals (RTA) above 935 °C for 20 s, in flowing N2. Penetration of Al and La into the underlying Si (001) is clearly observed for RTA at or above 950 °C for 20 s in flowing N2.

© 2005 American Institute of Physics. [DOI: 10.1063/1.1928316]

http://dx.doi.org/10.1063/1.1928316

JOURNAL OF APPLIED PHYSICS 97, 043508 (2005)

M. A. Quevedo-Lopez

M. J. Kim, B. E. Gnade, and R. M. Wallace

(Received 4 December 2003; accepted 17 November 2004; published online 21 January 2005)

We present a study of the penetration of B, P, and As through Hf silicate (HfSi_xO_y) and the effect of N incorporation in Hf silicate (HfSi_xO_yN_z) on dopant penetration from doped polycrystalline silicon capping layers. The extent of penetration through Hf silicate was found to be dependent upon the thermal annealing budget for each dopant investigated as follows: B (T³950 °C/60 s),  P (T³1000 °C/20 s), and As (T³1050 °C/60 s). We propose that the enhanced diffusion observed for these dopants in HfSi_xO_y, compared with that of SiO₂ films, is related to grain boundary formation resulting from HfSi_xO_y film crystallization. We also find that, as in the case of SiO₂, N incorporation inhibits dopant (B, P, and As) diffusion through the Hf silicate and thus penetration into the underlying Si substrate. Only B penetration is clearly observed through HfSiON films for anneals at 1050 °C for durations of 10 s or longer. The calculated B diffusivity through the HfSi_xO_yN_z layer is D₀=5.23×10^-15 cm²/s.

© 2005 American Institute of Physics. [DOI: 10.1063/1.1846138]

http://dx.doi.org/10.1063/1.1846138

Appl. Phys. A 80, 1045–1047 (2005)

C. Driemeier, K.P. Bastos, G.V. Soares, L. Miotti, R.P. Pezzi,

P. Punchaipetch, G. Pant, B.E. Gnade, R.M. Wallace

Received: 2 August 2004/Accepted: 19 August 2004

ABSTRACT HfSiO and HfSiON films with thicknesses compatible with the requirements for gate dielectrics alternatives to SiO2 in ultra-large scale integration silicon-based CMOSFET devices were deposited on an ultrathin HfSiO15N interfacial layer on Si(001). These structures were submitted to thermal processing routines typical of post-deposition annealing and dopant activation steps in fabrication technology, namely at 450 or 1000 .C, respectively, and in atmospheres ofN2 and/orO2. N transport and loss were determined by nuclear reaction analysis, including sub-nanometric depth resolution profiling with narrow nuclear reaction resonances. The chemical states of N were accessed by angle-resolved X-ray photoelectron spectroscopy.

After annealing at 450 .C, N is seen to be mobile, whereas the chemical environment of N is not changed at this temperature. Annealing at 1000 .C renders N mobile and its most abundant chemical state in near-surface regions is unstable. Annealing in O2 atmosphere promotes incorporation of O from the gas phase into the films, partly in exchange for N and O atoms and partly by net incorporation of oxygen in the films. The profiles of the newly incorporated O atoms are also determined with sub-nanometric depth resolution by narrow nuclear reaction resonance profiling.

PACS 68.60.-p; 68.55.-a; 73.61.Ng; 73.40.Qv

[DOI: 10.1007/s00339-004-3037-8]

R. P. Pezzi, L. Miotti, K. P. Bastos, G. V. Soares, and C. Driemeier

(Received 24 March 2004; accepted 11 August 2004)

© 2004 American Institute of Physics.

[DOI: 10.1063/1.1801682]

http://dx.doi.org/10.1063/1.1801682

Prakaipetch Punchaipetch, Gaurang Pant, M. J. Kim, Robert M. Wallace, and Bruce E. Gnade

(Received 14 July 2003; accepted 29 December 2003; published 17 February 2004)

Physical and electrical properties of hafnium silicate (HfSi_xO_y) dielectric films prepared by room-temperature UV/ozone (O₃) oxidation of hafnium silicide (HfSi₂) are reported. Angle-resolved x-ray photoelectron spectroscopy was used to determine chemical bonding at the film interface and within the bulk film. These films, with 12 at.% Hf composition, have a dielectric constant  (k) of ~8–9 and exhibit a flat-band voltage shift of 60 mV. The leakage current density at VFB + 1 V is 4.7×10^-5 A/cm² for a 4.7-nm-thick film (capacitance equivalent thickness =2.6 nm) and breakdown strength was >8 MV/cm.

 © 2004 American Vacuum Society.

[DOI: 10.1116/1.1649346]