Formation Of Interfacial Oxide Research Articles

Characterization of Interfacial Oxide Layers in Heterostructures of Hafnium Oxides Formed on NH3-Nitrided Si(100)

In the stack structures fabricated by NH3 nitridation of Si(100) at 650–700°C and subsequent electron-beam evaporation of HfO2, the blocking properties of ultrathin SiNx (x=∼1.3) upon oxidation in dry O2 ambient in the temperature range of 300–600°C have been studied by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared attenuated total reflection (FT-IR-ATR). Although the oxidation of Si(100) during O2 anneal is retarded using a ∼1-nm-thick SiNx layer grown by 700°C nitridation in NH3 ambient prior to the HfO2 evaporation, the surface oxidation of the ultrathin SiNx layer proceeds, accompanied by the movement of nitrogen atoms from the oxidized SiNx surface to the Si surface. As a result, the interfacial layer thickness is increased with no significant changes in nitrogen bonding features at the interface. From the temperature dependence of the interfacial oxide formation in the stack structure of HfO2 on thermally nitrided Si(100), we suggest that the control of O2 partial pressure is practically inevitable in suppressing completely the interfacial oxide growth at a thermal budget higher than 350°C.

Interfacial oxide determination and chemical/electrical structures of HfO 2/SiO x/Si gate dielectrics

An expression that can be used to determine the thickness of an interfacial oxide layer between a high-K dielectric and Si substrate has been derived using the photoelectron intensity ratio of high resolution X-ray photoelectron spectroscopy (HRXPS). Experimental results show the interfacial silicon oxide thickness obtained with the expression fits very well with Ellipsometer measurements. We also studied the formation of an interfacial layer between a high-k HfO 2 film and a Si substrate as well as its thermal stability. The results have revealed that: (i) the interfacial oxide formation requires the existence of thermally energized oxygen in an environment to break the H–Si bonds first for hydrogen terminated Si surface and (ii) the thermodynamic stability of the oxide interfacial layer depends on its initial formation process. The valence band structures of Si, SiO 2, and HfO 2 have been analyzed using HRXPS and an energy band diagram of HfO 2/SiO 2/Si has been constructed.

Electrical breakdown in a two-layer dielectric in the MOS structure

AbstractThe formation of interfacial oxide between high-k and Si creates a two-layer dielectric in the MOS structure. In this paper, we present a model to describe electrical breakdown in the two-layer dielectric. Depending on the thickness ratio of the two dielectric layers, electrical breakdown can occur either in one dielectric after the other or simultaneously. In the case of one-by-one breakdown, the current through the two-layer dielectric shows three regimes with applied voltage: tunneling through two layers, tunneling through one layer, and breakdown for both layers. Our model has been compared with experimental data obtained from the HfOx/SiO2 MOS structure, and a good agreement is achieved. This model can be used to estimate either the thickness, breakdown field, or dielectric constant of each of the two dielectric layers. It can also predict the overall breakdown voltage for different combinations of dielectric layers. When combined with C-V measurements, more information about the two-layer dielectric is obtained.

Interfacial oxide formation and oxygen diffusion in rare earth oxide–silicon epitaxial heterostructures

We report on controlled interfacial oxide formation within epitaxial (LaxY1−x)2O3/Si(111) heterostructures under UHV environments. Results indicate that exposure of these epitaxial films to molecular oxygen right after deposition results in the formation of an amorphous interfacial layer thicker than that expected when a bare silicon surface is exposed to molecular oxygen under the same conditions. The results imply significant oxygen diffusion through the epitaxial dielectric and reaction at the silicon–oxide interface. Arguments have been developed to explain these observations.

Improvement of RCA transistor using RTA annealing after the formation of interfacial oxide

A polysilicon emitter RCA transistor (an ultra-thin interfacial oxide layer exists between polysilicon and silicon emitter) is presented which can operate at 77 K for the first time. An ultra-thin (1.5 nm) interfacial oxide layer is grown deliberately between polysilicon and silicon emitter using RCA oxidation and excellent device stability is obtained after rapid thermal annealing (RTA) treatment in nitrogen atmosphere. The RCA transistor exhibits good electrical performance at very low temperature for an emitter area of 3 /spl times/ 8 /spl mu/m/sup 2/. The maximum toggle frequency of a 1:2 static divider is 1.2 GHz and 732 MHz at 300 K and 77 K, respectively.

Characterisation of ALCVD Al2O3–ZrO2 nanolaminates, link between electrical and structural properties

Al2O3 and ZrO2 mixtures for gate dielectrics have been investigated as replacements for silicon dioxide aiming to reduce the gate leakage current and reliability in future CMOS devices. Al2O3 and ZrO2 films were deposited by atomic layer chemical vapor deposition (ALCVD) on HF dipped silicon wafers. The growth behavior has been characterized structurally and electrically. ALCVD growth of ZrO2 on a hydrogen terminated silicon surface yields films with deteriorated electrical properties due to the uncontrolled formation of interfacial oxide while decent interfaces are obtained in the case of Al2O3. Another concern with respect to reliability aspects is the relatively low crystallization temperature of amorphous high-k materials deposited by ALCVD. In order to maintain the amorphous structure at high temperatures needed for dopant activation in the source drain regions of CMOS devices, binary Al/Zr compounds and laminated stacks of thin Al2O3 and ZrO2 films were deposited. X-ray diffraction and transmission electron microscope analysis show that the crystallization temperature can be increased dramatically by using a mixed oxide approach. Electrical characterization shows orders of leakage current reduction at 1.1–1.7 nm of equivalent oxide thickness. The permittivity of the deposited films is determined by combining quantum mechanically corrected capacitance voltage measurements with structural analysis by transmission electron microscope, X-ray reflectivity, Rutherford backscattering, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectroscopy. The k-values are discussed with respect to formation of interfacial oxide and possible silicate formation.

Fabrication of n-metal–oxide semiconductor field effect transistor with Ta2O5 gate oxide prepared by plasma enhanced metalorganic chemical vapor deposition

n-metal–oxide semiconductor field effect transistors (MOSFETs) were fabricated with plasma enhanced metalorganic chemical vapor deposited Ta2O5 gate oxide on Czochralski grown Si wafers using localized oxidation of silicon isolation technology by the conventional Si-based process. The Ta2O5 gate oxide n-MOSFETs showed excellent electrical characteristics such as subthreshold swing of 68–74 mV/dec, transconductance of 4 μS/μm for 4 μm gate length, and carrier mobility of 400 cm2/V s at the saturation region. The large Cox of the gate oxide with the high dielectric constant, εr=20–25, allowed the higher drain current of the device. During the whole process of n-MOSFET fabrication, the cross sectional transmission electron microscopy analysis of the Ta2O5/Si interface showed SiO2 interfacial oxide formation of about 35 Å thick. The Ta2O5 gate oxide n-MOSFET showed good performance compared to the high-temperature silicon oxide gate devices and thus has great potential for applications in the electronic devices.

Formation of ohmic contacts to n-GaAs using (NH4)2S surface passivation

Ohmic contacts between Au and sulfur-passivated n-GaAs have been formed without annealing after deposition of the metal. The GaAs samples doped with either 2×1016 or 3×1018 cm−3 Si were passivated with (NH4)2S in an aqueous solution, then the passivating sulfur was thermally desorbed in a vacuum. Desorption was followed immediately by in situ thermal evaporation of Au with the substrate at room temperature. Ohmic I-V behavior was measured ex situ. C-V measurements on a sample with a native oxide surface barrier layer showed the surface carrier concentration on the higher doped sample increased from 3×1018 to 7×1018 cm−3 after S desorption. Secondary ion mass spectroscopy data showed that S had diffused into the GaAs surface region. Thus S passivation prevented interfacial oxide formation during the exposure to air after the sample was passivated and before the vacuum chamber was pumped to a low pressure. Sulfur apparently diffused into the surface region during flash desorption in vacuum and increased the surface n-doping concentration which led to ohmic contacts without post-annealing of the Au films.

Comparison of the diffusion barrier properties of tungsten films prepared by hydrogen and silicon reduction of tungsten hexafluoride

We have made a comparative study of the thermal stability with respect to aluminum and silicon of tungsten films prepared by two different chemical vapor deposition processes. The first set of films were prepared via the direct reduction of WF 6 by the silicon substrate whereas the second set were deposited by hydrogen reduction of WF 6. The latter layers have a metallurgical behavior comparable with that of tungsten films deposited by other techniques while the former exhibit a very high thermal stability with no reactions between tungsten and aluminum or silicon detected up to temperatures as high as 625°C. This results from the high oxygen content of these films which allows the formation of interfacial oxides and thereby inhibits further interreactions. In the absence of oxygen, the barrier begins to fail at 550°C, leading eventually to the formation of a hexagonal silicide structure of the form W(Si,Al) 2. The role of aluminum in enhancing the formation of the silicide and the nature of the hexagonal aluminum-containing silicide are discussed in some detail.