It is difficult to use standard bulk-CMOS-technology at temperatures higher than 175°C due to high pn-leakage currents. Silicon-on-insulator-technologies (SOI), on the other hand, are usable up to ...250°C and even higher, because leakage currents can be reduced by two to three orders of magnitude. Nevertheless, performance and reliability of SOI devices are strongly affected at these high temperatures. One of the main critical factors is the gate oxide quality and its reliability. In this paper, we present a study of gate oxide capacitor time-dependent dielectric breakdown (TDDB) measurements at temperatures up to 350°C. The experiments were carried out on gate oxide capacitor structures realized in the Fraunhofer 1.0 μm SOI-CMOS process. The gate oxide thickness is 40 nm. Using the data of the TDDB measurements, the behavior of field and temperature acceleration parameters at temperatures up to 350°C was evaluated. For a more detailed investigation, the evolution of the current in time was also studied. An analysis of the oxide breakdown conditions, in particular the field and temperature dependence of the charge to breakdown and the current just before breakdown, completes the study. The presented data provide important information about accelerated oxide reliability testing beyond 250°C, and make it possible to quickly evaluate the reliability of high temperature CMOS technologies at operation temperature.
This article presents reliability studies of single polysilicon electrically erasable programmable read-only memory (EEPROM) cells at temperatures from 50°C to 450°C. The technically challenging ...measurements at elevated temperatures >250°C have been carried out for accelerated reliability studies. Furthermore, a SPICE macro model has been extended to the wide temperature range to describe the retention and endurance performance of the memory cell and to enable a better insight into the physics involved.
Local environments of Si suboxides at the interface between a thermally grown SiO2 film and Si(111) were studied by angle-scanned photoelectron diffraction. Si 2p core-level spectra containing ...chemically shifted components were recorded. The components were deconvoluted by least squares fitting and assigned to different Si oxidation states. The obtained diffraction patterns of the various suboxides exhibit different features. Comparison of these patterns with multiple scattering calculations including a multipole R-factor analysis shows that a simple chemical abrupt interface model describes well the environment of the suboxides and indicates ordered SiO2 close to the interface.
Standard bulk CMOS technology targets operating temperatures of not more than 175°C. Silicon-on-insulator technologies are commonly used up to 250°C. In this work, we evaluate the limit for ...electronic circuit function realized in thin film SOI technologies for even higher temperatures. At Fraunhofer IMS, a versatile 1.0 μm SOI-CMOS process based on 200 mm wafers is available. It features three layers of tungsten metallization with excellent reliability concerning electromigration, as well as voltage-independent capacitors, various resistors, and single-poly-EEPROMs. We present a study of the temperature dependence of MOSFETs and basic circuits produced in this process. The electrical characteristics of an NMOSFET transistor and a PMOSFET transistor are studied up to 450°C. In a second step, we investigate the functionality of a ring oscillator (representing a digital circuit) and a band gap reference as an example of a simple analog component. The frequency and the current consumption of the ring oscillator, as well as the output voltage and the current of the band gap reference, are characterized up to 450°C. We find that the ring oscillator still oscillates at this high temperature with a frequency of about one third of the value at room temperature. The output voltage of the band gap reference is in the specified range (change < 3%) up to 250°C. The deviations above this temperature are analyzed and measures to improve the circuit are discussed. The acquired data provide an important foundation to extend the application of CMOS technology to its real maximum temperature limits.
In recent years CMOS image sensors have gained a major market share for general imaging applications. However, when standard CMOS image sensors are employed in applications that require the detection ...of light with a very small spectral width, like 3D-time-of-flight imaging or other applications with laser light illumination, problems arise, that are negligible in standard imaging applications with broadband illumination. For a given wavelength a strong variation of the sensitivity upon small process related variations of the dielectric stack on top of the photodiodes leads to large die to die variations. In this paper a method is presented that decreases these sensitivity variations by introducing multiple optical path lengths of the dielectric stack within each photodiode. Using this method the maximum quantum efficiency variation for process induced thickness variations could be reduced significantly for a broad range of wavelengths without any additional processing steps.
The clean and hydrogen terminated 2×1-reconstructed Si(1
0
0) surfaces were investigated by surface-core level shift photoelectron diffraction at low kinetic energies. The photoelectron spectra ...contain shifted components due to the different environment of the atoms at the surface. Photoelectron diffraction patterns were recorded for the full solid angle above the sample. The diffraction patterns show different intensity distributions for the different shifted spectral components indicating their local environment. A comparison of experimental and calculated patterns for model structures clearly allows to assign the shifted components to distinct dimer atoms at the Si-surface.
Photoelectron diffraction patterns of the different silicon sub-oxides have been recorded and compared with simulated patterns for various model structures. Each silicon sub-oxide is embedded in an ...ordered environment since individual diffraction patterns and differences among them were exhibited. In particular, the intensity maxima are located at different angles. In the simulation the silicon-oxide/silicon interface was assumed to be abrupt and within one atomic layer. Excellent agreement between experimental and calculated patterns was achieved. At the interface, horizontally compressed SiO
2 was found. Furthermore, the highest oxidation state of silicon, Si
4+, displays a diffraction pattern indicating an ordered structure for this chemical state.
The clean and hydrogen terminated 2x1-reconstructed Si(100) surfaces were investigated by surface-core level shift photoelectron diffraction at low kinetic energies. The photoelectron spectra contain ...shifted components due to the different environment of the atoms at the surface. Photoelectron diffraction patterns were recorded for the full solid angle above the sample. The diffraction patterns show different intensity distributions for the different shifted spectral components indicating their local environment. A comparison of experimental and calculated patterns for model structures clearly allows to assign the shifted components to distinct dimer atoms at the Si-surface.
Angle- and energy-resolved photoelectron diffraction patterns of Si(111) were measured for electron kinetic energies between 196
eV to 784
eV. The diffraction patterns were holographically ...reconstructed in order to obtain real-space atom images of the near-neighbor environment of the emitter. The reconstruction yields real atom positions in a plane parallel to the surface when the spherical electron-wave approximation is used. Also, maxima corresponding to no atom coordinates were found in the reconstruction. Less intense maxima as in the spherical electron-wave approximation were obtained if a complex scattering factor was included in the reconstruction algorithm. The atom images were calculated for different scattering factors used in the reconstruction. These results are compared with the images obtained for a phase-locked summation of the multiple-energy data. This directly demonstrates the sensitivity of the atom images on the phase in a holographic reconstruction from photoelectron diffraction data.
