Alexander Olbrich

Electrical characterization of stressed and broken down SiO2 films at a nanometer scale using a conductive atomic force microscope

A conductive atomic force microscope (C-AFM) has been used to investigate the degradation and breakdown of ultrathin (<6 nm) films of SiO2 at a nanometric scale. Working on bare gate oxides, the conductive tip of the C-AFM allows the electrical characterization of nanometric areas. Due to the extremely small size of the analyzed areas, several features, which are not registered during macroscopic tests, are observed. In particular, before the oxide breakdown, switchings between different conduction states and sudden changes of conductivity have been measured, which have been related to the prebreakdown noise observed in conventional metal–oxide–semiconductor structures. Moreover, similar switchings have been also measured after the oxide breakdown, which have been related to the opening or closure of conduction channels between the electrodes. The C-AFM has also allowed the determination of the areas in which the degradation and breakdown take place. The results have shown that, although degradation takes...

The tunneling field effect transistor (TFET) as an add-on for ultra-low-voltage analog and digital processes

This work presents tunneling field effect transistors (TFET) fabricated with 130nm and 90nm process flows. Good performance of the TFET is achieved. A novel mixed TFET/CMOS (TCMOS) logic family exhibits the advantages with respect to power consumption. For the first time experimental results are presented for a TCMOS ring-oscillator based on a p-channel MOSFET and n-channel TFET. The benefits of the TFET used in analog circuits are outlined.

Nanometer-scale electrical characterization of stressed ultrathin SiO2 films using conducting atomic force microscopy

A conductive atomic force microscope has been used to electrically stress and to investigate the effects of degradation in the conduction properties of ultrathin (<6 nm) SiO2 films on a nanometer scale (areas of ≈100 nm2). Before oxide breakdown, switching between two states of well-defined conductivity and sudden changes of conductivity were observed, which are attributed to the capture/release of single charges in the defects generated during stress.

THE ORIGIN OF THE INTEGRAL BARRIER HEIGHT IN INHOMOGENEOUS AU/CO/GAAS67P33-SCHOTTKY CONTACTS : A BALLISTIC ELECTRON EMISSION MICROSCOPY STUDY

In this work we investigated the relationship between the integral Schottky barrier height (SBH) obtained from conventional current–voltage (I–V) measurement and the distribution of the local SBH measured by ballistic electron emission microscopy (BEEM) on a nanometer scale length. For this purpose, we investigated inhomogeneous Au/Co/GaAs67P33-Schottky contacts. The samples were prepared by the deposition of a discontinuous Co film on the semiconductor followed by the deposition of a continuous Au film. This provided regions with local presence of one or the other metal (Au or Co) at the metal-semiconductor interface, resulting in mesoscopically extended SBH inhomogeneities. The local SBH distribution as well as the integral SBH depended on the preparation parameter of the Co layer, i.e., on the combination of the substrate temperature (300 or 500 K) and the nominal Co thickness (0, 0.25, 0.5, 0.8, 1.0 nm). For the different preparation parameters, statistical distributions of the local SBH were measured by BEEM. Treating these SBH distributions in terms of a parallel conduction model for the electron transport across the MS interface, we calculated for each preparation parameter an integral SBH and compared it with the measured integral SBH obtained from conventional I–V measurement. The calculated and measured integral SBH’s were in very good agreement, demonstrating clearly the strong influence of the low SBH regions on the electron transport across the interface and therefore on the integral SBH. The SBH values for homogeneous Au/GaAs67P33- and Co/GaAs67P33-Schottky contacts, i.e., with only one sort of metal at the interface, were determined to be ΦSBAu=1180±10 meV and ΦSBCo=1030±10 meV. As with regard to the inhomogeneous Schottky contacts the fraction of area of the MS interface covered by Co increased, the local SBH distributions as well as the integral SBH’s decreased gradually from the value of ΦSBAu to ΦSBCo.In this work we investigated the relationship between the integral Schottky barrier height (SBH) obtained from conventional current–voltage (I–V) measurement and the distribution of the local SBH measured by ballistic electron emission microscopy (BEEM) on a nanometer scale length. For this purpose, we investigated inhomogeneous Au/Co/GaAs67P33-Schottky contacts. The samples were prepared by the deposition of a discontinuous Co film on the semiconductor followed by the deposition of a continuous Au film. This provided regions with local presence of one or the other metal (Au or Co) at the metal-semiconductor interface, resulting in mesoscopically extended SBH inhomogeneities. The local SBH distribution as well as the integral SBH depended on the preparation parameter of the Co layer, i.e., on the combination of the substrate temperature (300 or 500 K) and the nominal Co thickness (0, 0.25, 0.5, 0.8, 1.0 nm). For the different preparation parameters, statistical distributions of the local SBH were measured...

POTENTIAL PINCH-OFF EFFECT IN INHOMOGENEOUS AU/CO/GAAS67P33(100)-SCHOTTKY CONTACTS

In this work ballistic electron emission microscopy was used to probe on nanometer scale the local Schottky barrier height in metal-semiconductor (MS) contacts with an intentionally inhomogeneously prepared metallization. Schottky barrier maps of heterogeneous Au/Co/ GaAs67P33(100)-Schottky contacts show areas with different barrier heights which can be correlated to different metallizations (Au or Co) at the interface. The local Schottky barrier height of the Co patches depends on their lateral extension. This result can be explained by the theory of the potential pinch-off effect in inhomogeneous MS contacts.

Oxide thickness mapping of ultrathin Al2O3 at nanometer scale with conducting atomic force microscopy

In this work, we introduce conducting atomic force microscopy (C-AFM) for the quantitative electrical characterization of ultrathin Al2O3 films on a nanometer scale length. By applying a voltage between the AFM tip and the conductive Co substrate direct tunneling currents in the sub pA range are measured simultaneously to the oxide surface topography. From the microscopic I–V characteristics the local oxide thickness can be obtained with an accuracy of 0.03 nm. A conversion scheme was developed, which allows the calculation of three-dimensional maps of the local electrical oxide thickness with sub-angstrom thickness resolution and nanometer lateral resolution from the tunneling current images. Local tunneling current variations of up to three decades are correlated with the topography and local variations of the electrical oxide thickness of only a few angstroms.In this work, we introduce conducting atomic force microscopy (C-AFM) for the quantitative electrical characterization of ultrathin Al2O3 films on a nanometer scale length. By applying a voltage between the AFM tip and the conductive Co substrate direct tunneling currents in the sub pA range are measured simultaneously to the oxide surface topography. From the microscopic I–V characteristics the local oxide thickness can be obtained with an accuracy of 0.03 nm. A conversion scheme was developed, which allows the calculation of three-dimensional maps of the local electrical oxide thickness with sub-angstrom thickness resolution and nanometer lateral resolution from the tunneling current images. Local tunneling current variations of up to three decades are correlated with the topography and local variations of the electrical oxide thickness of only a few angstroms.

Propagation of the SiO2 breakdown event on MOS structures observed with conductive atomic force microscopy

Abstract In this work, for the first time, a conductive atomic force microscope has been used to electrically characterize the degradation and breakdown propagation of stressed ultra-thin ( 2 films at a nanometric scale. The results show that, although a slight lateral propagation of the degradation is observed before breakdown, the affected area (few hundreds of nm 2 ) remains relatively constant. However, breakdown is laterally propagated to neighbor spots, although only in some occasions morphological changes are observed. The breakdown affected area (several thousands of nm 2 ) has been found to be strongly related to the hardness of the breakdown event.

Reliability of ultrathin oxide and nitride films in the 1 nm to 2 nm range

The scaled-down MOSFETs of the 16 Gbit generation and beyond will require a gate dielectric thickness less than 2 nm. Reliability of ultra thin dielectrics were investigated in DC and AC stress at room and elevated temperatures.

A 1 Mbit SRAM test structure to analyze local mismatch beyond 5 sigma variation

We present an area efficient test structure that allows a measurement of the statistical distribution of SRAM cell currents beyond 5 sigma variation. The test structure was fabricated in a 90 nm and a 65 nm CMOS technology. The measured data show that the device variations are Gaussian-distributed for more than 1 million devices, covering more than 5 sigma of variation. Monte Carlo simulations are used to validate the measurements.

A new AFM-based tool for testing dielectric quality and reliability on a nanometer scale

Abstract Conducting AFM (C-AFM) makes it possible to measure local tunneling currents through thin dielectrics with a lateral resolution of a few nanometers. Thereby root causes for oxide fails like thickness inhomogeneity, electrically weak spots or local degradation can be detected. The method yields local currents down to the fA range, thickness determination in the range from 1 run to 80 nm with an absolute accuracy down to 3A, and high resolution thickness maps. We show examples of gate oxide edge thinning, EEPROM data retention fails and low Q BD MOS oxides.