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Effects of Titanium Layer Oxygen Scavenging on the High-k/InGaAs Interface Roy Winter, Pini Shekhter, Kechao Tang, Luca Floreano, Alberto Verdini, Paul C McIntyre, and Moshe Eizenberg ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b02957 • Publication Date (Web): 10 Jun 2016 Downloaded from http://pubs.acs.org on June 20, 2016
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ACS Applied Materials & Interfaces
Effects of Titanium Layer Oxygen Scavenging on the High-k/InGaAs Interface Roy Winter1*, Pini Shekhter1, Kechao Tang2, Luca Floreano3, Alberto Verdini3, Paul C. McIntyre2 and Moshe Eizenberg1 1
Department of Materials Science and Engineering, Technion-Israel Inst. of Technology, Haifa, Israel
2
Department of Materials Science and Engineering, Stanford University, Stanford, California, USA
3
Laboratorio TASC/IOM-CNR, Area di ricerca, Trieste, Italy
*
[email protected] Keywords: InGaAs, Metal-oxide-semiconductor, Scavenging, High-k, High-mobility, MOS, Synchrotron, XPS.
Abstract One of the main challenges in the path to incorporating InGaAs based metal-oxidesemiconductor structures in nanoelectronics is the passivation of high-k/InGaAs interfaces. Here, the oxygen scavenging effect of thin Ti layers on high-k/InGaAs gate stacks was studied. Electrical measurements and synchrotron X-ray photoelectron spectroscopy measurements, with in-situ metal deposition, were used. Oxygen removal from the InGaAs native oxide surface layer remotely through interposed Al2O3 and HfO2 layers observed. Synchrotron X-ray photoelectron spectroscopy has revealed a decrease in the intensity of InOx features relative to In in InGaAs after Ti deposition. The signal ratio decreases further after annealing. In addition, Ti 2p spectra clearly show oxidation of the thin Ti layer in the ultra-high vacuum XPS environment. Using capacitance-voltage
and
conductance-voltage
measurements,
Pt/Ti/Al2O3/InGaAs
and
Pt/Al2O3/InGaAs capacitors were characterized both before and after annealing. It was found that the remote oxygen scavenging from the oxide/semiconductor interface using a thin Ti layer can influence the density of interface traps in the high-k/InGaAs interface.
1.1. Introduction In0.53Ga0.47As is considered an attractive candidate for high-mobility channel metal oxide semiconductor (MOS) transistors 1,2. However, achieving a good quality high-k/InGaAs interface
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is still a key challenge in the way to obtaining high performance and reliable devices. Native surface oxides of air-exposed arsenide semiconductor substrates are known to be responsible for capacitance reduction, carrier mobility degradation and Fermi level pinning
3,4
. Therefore,
passivation of the high-k/InGaAs interface is necessary to insure permanent removal of these oxides. Many techniques for the passivation of such interfaces have been studied: Si passivation 5
, trimethylaluminum (TMA) treatment 6,7, plasma nitridation 8, AlON or Al2O3 passivation
deposition of high-k dielectrics on an As-decapped InGaAs surface 14
12,13
9–11
,
and InP capping layers
. In the research of high-k based gate stacks for Si MOS, an interfacial SiO2 layer limits
scaling of the effective oxide thickness (EOT). Titanium and TiN have been used as a capping layer for the high-k dielectric in order to inhibit the formation of a thin SiO2-like interfacial layer at the high-k/Si interface, or to reduce the thickness of an existing interface layer by oxygen scavenging oxygen from. The decomposition of interfacial SiO2 leads to an epitaxial regrowth of the silicon 15–17. Recently, the effect of such oxygen scavenging processes was investigated in Ge based MOS capacitors. Fadida et al.
18
observed GeO2 scavenging both on directly adjacent interfaces
and remotely through an Al2O3 intermediate layer. In both cases, partial oxygen scavenging from the interface layer occurred upon deposition of the scavenging metal layer at room temperature under ultra-high vacuum (UHV) conditions, and it was completed by annealing in UHV. In this work, we demonstrate the effect of oxygen scavenging induced by a thin layer of Ti deposited on a high-k/InGaAs stacks. We used electrical measurements and synchrotron x-ray photoelectron spectroscopy (XPS) characterization, with in-situ metal deposition to study this phenomenon in InGaAs MOS stacks.
1.2. Experimental details MOS capacitors were fabricated using an n-type In0.53Ga0.47As (100) substrate with Si doping (~2×1016cm3). The InGaAs was initially covered with an As2-capping layer to avoid surface oxidation. The As2 layer was removed by a thermal desorption process at 370°C in the
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atomic layer deposition (ALD) chamber at a pressure of 10-6 Torr. The substrate was then exposed to air in order to form a thin native oxide layer and was divided into three sets of sample. On sets 1 and 2, layers of 6 nm or 3 nm Al2O3 respectively, were deposited by ALD using TMA and water vapor at a substrate temperature of 270°C. On set 3, a 3nm layer of HfO2 was deposited by ALD using tetrakis diethylamido hafnium and water vapor. Capacitors were defined by deposition of 5nm of Ti and 40 nm of Pt or only 40 nm of Pt by electron beam evaporation at room temperature through a shadow mask on set 1 (6nm of Al2O3). The samples were post metal deposition annealed (PMA) at 400°C for 30min in high vacuum (P
