Bahman Raeissi

Interface Defects in HfO2, LaSiOx, and Gd2O3 High-k/Metal-Gate Structures on Silicon

In this work, we present experimental results examining the energy distribution of the relatively high (> 1 X 10(11) cm(-2)) electrically active interface defects which are commonly observed in high-dielectric-constant (high-k) metal-insulator-silicon systems during high-k process development. This paper extends previous studies on the Si(100)/SiOx/HfO2 system to include a comparative analysis of the density and energy distribution of interface defects for HfO2, lanthanum silicate (LaSiOx), and Gd2O3 thin films on (100) orientation silicon formed by a range of deposition techniques. The analysis of the interface defect density across the energy gap, for samples which experience no H-2/N-2 annealing following the gate stack formation, reveals a peak density (similar to 2 X 10(12) cm(-2) eV(-1) to similar to 1 X 10(13) cm(-2) eV(-1)) at 0.83-0.92 eV above the silicon valence bandedge for the HfO2, LaSiOx, and Gd2O3 thin films on Si (100). The characteristic peak in the interface state density (0.83-0.92 eV) is obtained for samples where no interface silicon oxide layer is observed from transmission electron microscopy. Analysis suggests silicon dangling bond (P-bo) centers as the common origin for the dominant interface defects for the various Si(100)/SiOx/high-k/metal gate systems. The results of forming gas (H-2/N-2) annealing over the temperature range 350-555 degrees C are presented and indicate interface state density reduction, as expected for silicon dangling bond centers. The technological relevance of the results is discussed. (c) 2007 The Electrochemical Society.

Leakage current effects on C-V plots of high-k metal-oxide-semiconductor capacitors

With the employment of ultrathin, high dielectric constant gate materials in advanced semiconductor technology, the conventional capacitance-voltage measurement technique exhibits a series of anomalies. In particular, a nonsaturating increase in the accumulation capacitance with reducing measurement frequency is frequently observed, which has not been adequately explained to our knowledge. In this article, the authors provide an explanation for this anomaly and hence set a criterion for the lower bound on measurement frequency. We then present a model which allows the easy extraction of the required parameters and apply it to an experimental set of data.

Vibronic nature of hafnium oxide/silicon interface states investigated by capacitance frequency spectroscopy

Using a method based on the frequency dependence of capacitance, cross sections for electron capture into energy states at the interlayer/silicon interface have been investigated for HfO2 that is deposited on silicon by reactive sputtering. We find that the capture cross sections are thermally activated and steeply increase with increasing energy depth. Both features can be attributed to the same physical origin, indicating vibronic trap properties, where the capture mechanism is governed by multiphonon processes.

Multiparameter admittance spectroscopy for metal-oxide-semiconductor systems

Admittance spectroscopy is extended for measuring capacitance and conductance on metal-oxide-semiconductor (MOS) structures as a function of gate voltage, frequency, and temperature. An automatic setup has been designed for collecting data along these dimensions in one measurement cycle. The theory for admittance spectroscopy has been developed by starting from basic charge carrier statistics. Using numerical integration of energy dependent parameters instead of the commonly used analytical solution, conductance dispersion curves are obtained which do not need to be adjusted by assuming lateral surface potential variations at the oxide-semiconductor interface. Also, we find that interface state densities extracted by using traditional methods are four times lower than those obtained by using our theory. Experimental data presented in three-dimensional plots are compared with theoretical calculations, revealing the possibilities and limitations of the conductance method.

The conductance method in a bottom-up approach applied on hafnium oxide/silicon interfaces

Starting from basic statistical properties of interface states, we demonstrate the influence of energy dependent interface state distributions and thermal emission rates including their capture cross sections on measured differential conductance data for Al/HfO2/SiOx/Si structures. Theoretical plots calculated this way reproduce experimental conductance data without correction for lateral surface potential variations. Close to the silicon conduction band edge, we find an energy dependence of the capture cross sections revealing the existence of electron states with capture processes deviating from the multiphonon mechanisms found for the deeper lying states at interfaces between high-k dielectrics and silicon.

High-k-oxide/silicon interfaces characterized by capacitance frequency spectroscopy

Electron capture into insulator/silicon interface states is investigated for high-k dielectrics of Gd2O3 prepared by MBE and ALD, and for HfO2 prepared by reactive sputtering, by measuring the frequency dependence of MOS capacitance. The capture cross sections are found to be thermally activated and to increase steeply with the energy depth of the interface electron states. The methodology adopted is considered useful for increasing the understanding of high-k-oxide/silicon interfaces.

Characterization of Traps in the Transition Region at the HfO2 ∕ SiOx Interface by Thermally Stimulated Currents

Thermally stimulated currents (TSCs) have been measured to investigate electron traps in HfO2 prepared by reactive sputtering on silicon. Broken planes of the silicon crystal, which may contribute to the occurrence of interface states, were identified between the silicon and SiOx interlayer by transmission electron microscopy (TEM). A second domain was found between SiOx and HfO2 constituting a gradual transition region between the two oxides. This interface region was found to be a source of unstable charge traps where captured electrons interact with the silicon energy states through a combined tunneling and thermal process.

Extracting the relative dielectric constant for "high-k layers" from CV measurements : Errors and error propagation

The paper pursues an investigation of the errors associated with the extraction of the dielectric constant (i.e., kappa value) from capacitance-voltage measurements on metal oxide semiconductor cap ...

The Role of Mobile Charge in Oxygen Plasma-Enhanced Silicon-to-Silicon Wafer Bonding

Mechanical bonding energies of oxygen plasma treated and room-temperature wafer bonded silicon surfaces have been measured as a function of storage time in parallel with measurements of electrical interface properties. The surface energy increases with time dependence similar to that of decreasing interface state concentration. The current vs voltage behavior reveals the existence of mobile ions. We suggest that these mobile charges, after the reaction with the interface states, give rise to the increased surface energy responsible for bonding.

Multiparameter Admittance Spectroscopy as a Diagnostic Tool for Interface States at Oxide/Semiconductor Interfaces

Multiparameter admittance spectroscopy (MPAS) measurements have been performed on Al/HfO_2/SiO_x/Si structures before and after postmetallization annealing. Contour plots of conductance data as a function of the logarithm of inverted signal frequency and applied voltage as obtained by MPAS are compared with standard capacitance versus voltage ( C-V) data demonstrating the advantage of MPAS as a diagnostic tool. MPAS reveals more detailed properties of oxide/semiconductor interface states and renders measured data for better perceptiveness.