Alexeij Y. Kovalgin

Systematic TLM Measurements of NiSi and PtSi Specific Contact Resistance to n- and p-Type Si in a Broad Doping Range

We present the data on specific silicide-to-silicon contact resistance (rhoc) obtained using optimized transmission-line model structures, processed for a broad range of various n- and p-type Si doping levels, with NiSi and PtSi as the silicides. These structures, despite being attractive candidates for embedding in the CMOS processes, have not been used for NiSi, which is the material of choice in modern technologies. In addition, no database for NiSi-silicon contact resistance exists, particularly for a broad range of doping levels. This letter provides such a database, using PtSi extensively studied earlier as a reference.

Growth Kinetics and Oxidation Mechanism of ALD TiN Thin Films Monitored by In Situ Spectroscopic Ellipsometry

Spectroscopic ellipsometry (SE) was employed to investigate the growth of atomic layer deposited (ALD) TiN thin films from titanium chloride (TiCl4) and ammonia (NH3) and the followed oxidation in dry oxygen. Two regimes were found in the growth including a transient stage prior to a linear regime. The complementary ex situ characterization techniques showed a good agreement with the results obtained from SE measurements. A columnar structure of the as-deposited TiN film, which was composed of grains surrounded by amorphous material in between, was obtained. The X-ray photoelectron spectroscopy (XPS) analyses indicated low chlorine impurity content and slightly N-rich TiN films. The existence of an intermixed layer between the nitride and oxide during the oxidation was verified by the XPS depth profile analysis for a partially oxidized TiN film. A three-layer optical model was constructed for SE in situ monitoring the oxidation. A four-regime oxidation was found for 15-nm TiN films whereas only two regimes were seen in the case of 5-nm films. A new oxidation mechanism was proposed to explain the oxidation behavior of thin TiN films.

Cross-Bridge Kelvin Resistor Structures for Reliable Measurement of Low Contact Resistances and Contact Interface Characterization

The parasitic factors that strongly influence the measurement accuracy of Cross-Bridge Kelvin Resistor (CBKR) structures for low specific contact resistances (¿c) have been extensively discussed during last few decades and the minimum of the ¿c value, which could be accurately extracted, was estimated. We fabricated a set of various metal-to-metal CBKR structures with different geometries, i.e., shapes and dimensions, to confirm this limit experimentally and to create a method for contact metal-to-metal interface characterization. As a result, a model was developed to account for the actual current flow and a method for reliable ¿c extraction was created. This method allowed to characterize metal-to-metal contact interface. It was found that in the case of ideal metal-to-metal contacts, the measured CBKR contact resistance was determined by the dimensions of the two-metal stack in the area of contact and sheet resistances of the metals used.

Evaluation of Transmission Line Model Structures for Silicide-to-Silicon Specific Contact Resistance Extraction

In order to measure silicide-to-silicon specific contact resistance rhoc, transmission line model (TLM) structures were proposed as attractive candidates for embedding in CMOS processes. We optimized TLM structures for nickel silicide and platinum silicide and evaluated them for various doping levels of n- and p-type Si. The measurement limitations and accuracy of the specific contact resistance extraction from the optimized TLM structures are discussed in this paper.

Initial growth, refractive index, and crystallinity of thermal and plasma-enhanced atomic layer deposition AlN films

The authors have studied and compared the initial growth and properties of AlN films deposited on Si(111) by thermal and plasma-enhanced atomic layer deposition (ALD) using trimethylaluminum and either ammonia or a N2-H2 mixture as precursors. In-situ spectroscopic ellipsometry was employed to monitor the growth and measure the refractive index of the films during the deposition. The authors found that an incubation stage only occurred for thermal ALD. The linear growth for plasma-enhanced ALD (PEALD) started instantly from the beginning due to the higher nuclei density provided by the presence of plasma. The authors observed the evolution of the refractive index of AlN during the growth, which showed a rapid increase up to a thickness of about 30 nm followed by a saturation. Below this thickness, higher refractive index values were obtained for AlN films grown by PEALD, whereas above that the refractive index was slightly higher for thermal ALD films. X-ray diffraction characterization showed a wurtzite crystalline structure with a (1010) preferential orientation obtained for all the layers with a slightly better crystallinity for films grown by PEALD.

Integration of Solar Cells on Top of CMOS Chips—Part II: CIGS Solar Cells

We present the monolithic integration of deep-submicrometer complementary metal-oxide-semiconductor (CMOS) microchips with copper indium gallium (di)selenide (CIGS) solar cells. Solar cells are manufactured directly on unpackaged CMOS chips. The microchips maintain comparable electronic performance, and the solar cells on top show an efficiency of 8.4 ± 0.8% and a yield of 84%, both values being close to the glass reference. The main integration issues, i.e., adhesion, surface topography, metal ion contamination, process temperature, and mechanical stress, can be resolved while maintaining standard photovoltaic processing. A tight process window is found for the manufacturing of CIGS solar cells on the CMOS side of the microchip. More process margin exists for backside integration.

Low-Temperature Fabricated TFTs on Polysilicon Stripes

This paper presents a novel approach to make high-performance CMOS at low temperatures. Fully functional devices are manufactured using back-end compatible substrate temperatures after the deposition of the amorphous-silicon starting material. The amorphous silicon is pretextured to control the location of grain boundaries. Green-laser annealing is employed for crystallization and dopant activation. A high activation level of As and B impurities is obtained. The main grain boundaries are found at predictable positions, allowing transistor definition away from these boundaries. The realized thin-film transistors (TFTs) exhibit high field-effect carrier mobilities of 405 cm2/Vmiddots (NMOS) and 128 cm2/Vmiddots (PMOS). CMOS inverters and fully functional 51-stage ring oscillators were fabricated in this process and characterized. The process can be employed for large-area TFT electronics as well as a functional stack layer in 3-D integration.

Interaction of epitaxial silicene with overlayers formed by exposure to Al atoms and O2 molecules

As silicene is not chemically inert, the study and exploitation of its electronic properties outside of ultrahigh vacuum environments require the use of insulating capping layers. In order to understand if aluminum oxide might be a suitable encapsulation material, we used high-resolution synchrotron photoelectron spectroscopy to study the interactions of Al atoms and O2 molecules, as well as the combination of both, with epitaxial silicene on thin ZrB2(0001) films grown on Si(111). The deposition of Al atoms onto silicene, up to the coverage of about 0.4 Al per Si atoms, has little effect on the chemical state of the Si atoms. The silicene-terminated surface is also hardly affected by exposure to O2 gas, up to a dose of 4500 L. In contrast, when Al-covered silicene is exposed to the same dose, a large fraction of the Si atoms becomes oxidized. This is attributed to dissociative chemisorption of O2 molecules by Al atoms at the surface, producing reactive atomic oxygen species that cause the oxidation. It is concluded that aluminum oxide overlayers prepared in this fashion are not suitable for encapsulation since they do not prevent but actually enhance the degradation of silicene.

Low-temperature deposition of high-quality siliconoxynitride films for CMOS-integrated optics

The growth of silicon oxynitride thin films applying remote inductively coupled, plasma-enhanced chemical vapor deposition is optimized toward high optical quality at a deposition temperature as low as 150°C. Propagation losses of 0.5±0.05 dB/cm, 1.6±0.2 dB/cm, and 0.6±0.06 dB/cm are measured on as-deposited waveguides for wavelengths of 1300, 1550, and 1600 nm, respectively. Films were deposited onto a 0.25 μm technology mixed-signal CMOS chip to show the application perspective for three-dimensional integrated optoelectronic chips.

Above-CMOS a-Si and CIGS solar cells for powering autonomous microsystems

Two types of solar cells are successfully grown on chips from two CMOS generations. The efficiency of amorphous-silicon (a-Si) solar cells reaches 5.2%, copper-indium-gallium-selenide (CIGS) cells 7.1%. CMOS functionality is unaffected. The main integration issues: adhesion, surface topography, metal ion contamination, process temperature, and mechanical stress can be resolved while maintaining standard photovoltaic processing.