Aluminum oxynitride interfacial passivation layer for high-permittivity gate dielectricstack on gallium arsenideMing Zhu, Chih-Hang Tung, and Yee-Chia Yeo

Citation: Applied Physics Letters 89, 202903 (2006); doi: 10.1063/1.2388246 View online: http://dx.doi.org/10.1063/1.2388246 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/89/20?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Improved interfacial and electrical properties of GaAs metal-oxide-semiconductor capacitors with HfTiON as gatedielectric and TaON as passivation interlayer Appl. Phys. Lett. 103, 092901 (2013); 10.1063/1.4818000 HfO 2 – GaAs metal-oxide-semiconductor capacitor using dimethylaluminumhydride-derived aluminum oxynitrideinterfacial passivation layer Appl. Phys. Lett. 97, 062908 (2010); 10.1063/1.3475015 Atomic-layer-deposited Hf O 2 on In 0.53 Ga 0.47 As : Passivation and energy-band parameters Appl. Phys. Lett. 92, 072901 (2008); 10.1063/1.2883967 Impact of surface chemical treatment on capacitance-voltage characteristics of GaAs metal-oxide-semiconductorcapacitors with Al 2 O 3 gate dielectric Appl. Phys. Lett. 91, 063501 (2007); 10.1063/1.2764438 Ultrathin Hf O 2 (equivalent oxide thickness = 1.1 nm ) metal-oxide-semiconductor capacitors on n - Ga Assubstrate with germanium passivation Appl. Phys. Lett. 88, 252906 (2006); 10.1063/1.2216023

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Aluminum oxynitride interfacial passivation layer for high-permittivity gatedielectric stack on gallium arsenide

Ming ZhuSilicon Nano Device Laboratory, Department of Electrical and Computer Engineering,National University of Singapore, Singapore 117576, Singapore

Chih-Hang TungAgency for Science, Technology and Research, Institute of Microelectronics, 11 Science Park Road,Singapore 117685, Singapore

Yee-Chia Yeoa�

Silicon Nano Device Laboratory, Department of Electrical and Computer Engineering,National University of Singapore, Singapore 117576, Singapore

�Received 10 July 2006; accepted 7 October 2006; published online 13 November 2006�

The authors demonstrate a passivation technique for GaAs substrate by employing an aluminumoxynitride �AlON� interfacial passivation layer. X-ray photoelectron spectroscopy and transmissionelectron microscopy results show that the AlON interfacial passivation layer effectively suppressesthe formation of Ga or As oxide during the gate dielectric deposition process. This enabled thefabrication of high quality GaAs n-channel metal-oxide-semiconductor capacitors with HfO2 gatedielectric and TaN metal gate electrode. The metal gate/high-k gate dielectric stack on GaAsdemonstrated an equivalent SiO2 thickness of 2.2 nm and low leakage current density of 4.27�10−4 A/cm2 at a gate bias equal to Vfb−1 V. Excellent capacitance-voltage characteristics withlow frequency dispersion ��4% � were also obtained. © 2006 American Institute of Physics.�DOI: 10.1063/1.2388246�

III-V compound semiconductors are attractive channelmaterial candidates for extending the performance limits ofmetal-oxide-semiconductor field effect transistors �MOS-FETs� due to their significantly higher carrier mobility com-pared to that of Si or strained Si. However, a major obstacleis the lack of high quality and thermodynamically stable in-sulators on III-V semiconductors with a low interface statedensity comparable to that of the SiO2/Si interface.1,2 In situdeposition of Ga2O3,3 Ga2O3 �Gd2O3�,4,5 and single crystalGd2O3 dielectric films6 on GaAs surface using molecularbeam epitaxy, and atomic layer deposition �ALD� of Al2O3

on III-V semiconductors have been reported.7–9 In comple-mentary MOS technology, hafnium-based gate dielectricshave been extensively explored for gate leakage reduction.HfO2 formed on a Si surface passivation layer on GaAsshowed good capacitance-voltage �C-V� characteristics andlow gate leakage current.10,11 Since Si is a n-type dopant inGaAs, its use as a passivation layer could be limited, particu-larly in n-channel device applications and in processes whichincur significant thermal budget. The development of an al-ternative passivation process for GaAs MOSFET is thereforeimportant. In this letter, we report the demonstration of analuminum oxynitride �AlON� interfacial passivation layer onp-type GaAs, and its application in n-MOS capacitors withHfO2 high-k gate dielectric and TaN metal gate electrode.Excellent electrical characteristics with an equivalent oxidethickness �EOT� of 2.2 nm and low frequency dispersion��4% � were achieved.

MOS capacitors were fabricated on p-type �Zn-doped�GaAs �100� wafers with a doping concentration of �1–3�

�1018 cm−3. The wafers were degreased using acetone andisopropanol, cleaned in HCl for native oxide removal, anddipped in NH4OH for elemental As removal.12 �NH4�2S so-lution was then used to passivate the GaAs surface.13 AlONinterfacial passivation layer with a thickness of 1.5 nm wasdeposited by reactive sputtering of Al in N2/Ar ambient.ALD of 4, 7, and 10 nm thick HfO2 gate dielectrics wasperformed at 300 °C using H2O and HfCl4 precursors. Forcomparison, HfO2 was also directly deposited on GaAs with-out the AlON interlayer. Postdeposition anneal was then per-formed in a rapid thermal processor at 500 °C for 60 s in N2.TaN was sputtered and patterned as gate electrode. Finally,forming gas �H2+N2� annealing was performed.

To study the effects of AlON interface passivation layeron GaAs substrates, three samples, as-cleaned GaAs,HfO2/AlON/GaAs, and HfO2/GaAs, were analyzed byx-ray photoelectron spectroscopy �XPS�. The thickness ofHfO2 was thinned down to �0.5 nm after deposition toavoid problems associated with the photoelectron spectrumof Hf 4f overlapping with that of Ga 3d. Figure 1�a� showsthe core-level spectra of all the three samples. It is clear thatthe contribution from Ga 3d is larger than that of Hf 4f ,although there is still another peak from the Hf 4f doubletwhich overlaps with the Ga 3d peak. The main peak at 19 eVis mainly attributed to Ga–As bond from the substrate. Nopeak corresponding to the Ga–O bond was observed aftercleaning, indicating that native Ga oxide was completely re-moved. For the sample without AlON passivation, a shoulderappeared in the 20–21 eV energy range �Fig. 1�a��, indicat-ing the formation of Ga oxide at the gate dielectric interfaceduring the ALD process. With the insertion of an AlON in-terfacial passivation layer, this Ga–O peak is clearly absent.The presence of AlON was confirmed by the Al 2p spectrum,as shown in the inset of Fig. 1�a�. The binding energy of

a�Author to whom correspondence should be addressed; electronic mail:yeo@ieee.org

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74.6 eV is contributed by two types of Al bonds: Al–O�75.1 eV� and Al–N �73.8 eV�. The As 3d core-level spectraof the three samples are shown in Fig. 1�b�. AlON passiva-tion gives a weaker As–O peak. Ga or As oxide formation

during the HfO2 deposition was effectively suppressed usingthe AlON interfacial passivation layer. AlON could act as anoxygen reaction barrier14 and minimize the formation of alow quality oxide which could cause Fermi level pinning. Asthe surface roughness of the channel can degrade the effec-tive carrier mobility, atomic force microscopy �AFM� wasemployed to examine the surface morphology before andafter AlON deposition �Fig. 2�. The AlON deposition doesnot appear to result in increased surface roughness.

Figure 3�a� shows the C-V characteristics ofTaN/HfO2/AlON/ p-GaAs capacitors measured at a fre-quency of 100 kHz. The physical thickness of AlON was1.5 nm. In our experiments, poor adhesion results whenHfO2 was deposited directly on the GaAs substrate, andthose devices did not yield. On the contrary, capacitors withAlON interfacial passivation layer did not suffer this prob-lem and showed excellent C-V behavior. Figure 3�a� showsthe dependence of capacitance on the HfO2 thickness. Byfitting the data in Fig. 3�a� with a simulated C-V curve thataccounts for quantum mechanical effects, EOTs of 2.2, 2.67,and 3.29 nm were extracted for samples with 4, 7, and 10 nmthick HfO2. The relative permittivity k of the HfO2 dielectric

FIG. 2. AFM images of �a� as-cleaned GaAs �rms roughness of 0.160 nm�and �b� AlON/GaAs sample �rms roughness of 0.178 nm�. The scan areameasured 2�2 �m. The surface remained smooth and uniform after AlONpassivation.

FIG. 3. �a� C-V characteristics of GaAs n-MOS capacitors with AlON in-terfacial passivation layer and HfO2 gate dielectrics with different thick-nesses. C-V curves of the capacitor with 7 nm HfO2 as a function of fre-quency were plotted as inset. �b� JG-VG characteristics of the samples in �a�.Inset shows the dependence of JG at VG=Vfb−1 V on EOT.

FIG. 1. High-resolution XPS analysis was performed using a monochro-matic Al K� source with an energy of 1486.6 eV. �a� Ga 3d and �b� As 3dphotoelectron spectra obtained after wafer cleaning and after HfO2 deposi-tion. The samples with and without AlON interfacial passivation layer werecompared. The inset in �a� shows the Al 2p signal from the sample withAlON passivation.

202903-2 Zhu, Tung, and Yeo Appl. Phys. Lett. 89, 202903 �2006�

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was extrapolated to be 21.9. However, the value of k for theAlON interfacial layer was only 4.2, only slightly higherthan that of SiO2. Further reduction in the thickness of theAlON layer would be required for aggressive scaling of theequivalent oxide thickness of the gate dielectric stack. Thehysteresis values of the samples with EOTs of 2.2, 2.67, and3.29 nm were 0.28, 0.41, and 0.56 V, respectively. The insetin Fig. 3�a� shows the C-V characteristics of the sample with7 nm HfO2 as a function of frequency. Frequency dispersionis small ��4% � in the range of measurement, similar to thecase of p-channel MOS capacitor with Si passivation layer.11

The leakage current density JG as a function of gate bias isshown in Fig. 3�b� and the JG-EOT plot at VG=Vfb−1 V isshown in the inset. Low leakage current of 4.27�10−4 A/cm2 is achieved at Vfb−1 V for the sample with4 nm thick HfO2. JG increases exponentially with decreasingEOT with a slope of 2.5 Å/decade. The dominant leakagemechanism is probably trap-assisted tunneling.15

The high-resolution transmission electron microscope�HRTEM� picture of the GaAs MOS capacitor with AlONinterfacial passivation layer is given in Fig. 4�a�. The thick-nesses of the HfO2 dielectric and the AlON interfacial layerare about 7 and 1.5 nm, respectively. The interface betweenGaAs and AlON was atomically sharp without any evidenceof interfacial reaction after the HfO2 deposition. Figure 4�b�shows the transmission electron microscope image of thegate stack without AlON passivation. A nonuniform interfa-cial layer with a thickness of �7 Å was observed betweenthe HfO2 and GaAs, consistent with a prior report16 and withour XPS results.

In summary, a surface passivation technique using AlONinterfacial layer was demonstrated on GaAs. The AlON layereffectively suppressed the formation of Ga or As oxide onthe GaAs surface. Electrical characteristics of AlON-passivated GaAs n-MOS capacitors with HfO2 gate dielectricdemonstrated low frequency dispersion at an EOT of 2.2 nmand a leakage current density of 4.27�10−4 A/cm2 at VG=Vfb−1 V. Further scaling of EOT can be achieved by de-creasing the thickness and increasing the dielectric quality ofthe AlON layer. The AlON passivation technique is promis-ing for application in GaAs n-MOSFET devices.

The authors acknowledge research funding �Project No.0421140047� from the Agency for Science, Technology andResearch �A*STAR�, Singapore, under the TSRP Nanoelec-tronics Program.

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FIG. 4. HRTEM pictures of the �a� TaN/HfO2/AlON/GaAs and the �b�TaN/HfO2/GaAs structures.

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