Richard B. Gregory

Impact of titanium addition on film characteristics of HfO2 gate dielectrics deposited by atomic layer deposition

The impact of 8-to45-at.% Ti on physical and electrical characteristics of atomic-layer-deposited and annealed hafnium dioxide was studied using vacuum-ultraviolet spectroscopic ellipsometry, secondary ion mass spectroscopy, transmission electron microscopy, atomic force microscopy, x-ray diffraction, Rutherford backscattering spectroscopy, x-ray photoelectron spectroscopy, and x-ray reflectometry. The role of Ti addition on the electrical performance is investigated using molybdenum (Mo)-gated capacitors. The film density decreases with increasing Ti addition. Ti addition stabilizes the amorphous phase of HfO2, resulting in amorphous films as deposited. After a high-temperature annealing, the films transition from an amorphous to a polycrystalline phase. Orthorhombic Hf–Ti–O peaks are detected in polycrystalline films containing 33-at.% or higher Ti content. As Ti content is decreased, monoclinic HfO2 becomes the predominant microstructure. No TiSi is formed at the dielectric/Si interface, indicating fil...

Atomic layer deposited TaCy metal gates: Impact on microstructure, electrical properties, and work function on HfO2 high-k dielectrics

TaCy has been reported to have the appropriate work function for negative metal-oxide semiconductor metal in high-k metal-oxide field-effect transistors. As device size continues to shrink, a conformal deposition for metal gate electrodes is needed. In this work, we report on the development and characterization of a novel TaCy process by atomic layer deposition (ALD). Detailed physical properties of TaCy films are studied using ellipsometry, a four-point probe, Rutherford backscattering spectrometry (RBS), x-ray photoelectron spectroscopy (XPS), and x-ray diffraction (XRD). RBS and XPS analysis indicate that TaCy films are near-stoichiometric, nitrogen free, and have low oxygen impurities. Powder XRD spectra showed that ALD films have a cubic microstructure. XPS carbon bonding studies revealed that little or no glassy carbon is present in the bulk of the film. Excellent electrical properties are obtained using ALD TaCy as a metal gate electrode. Well-behaved capacitance-voltage characteristics with ALD H...

Stress-induced anisotropy of graphitelike amorphous carbon

Ellipsometry spectra of graphitelike amorphous carbon films on Si reveal a strong anisotropy of the optical constants in the 0.7–9.5eV photon-energy range. The films are optically uniaxial, with the optical axis oriented normal to the surface. This birefringence can be explained by ordering of the hexagonal graphene planes perpendicular to the substrate due to tensile stress, which was confirmed by transmission electron microscopy. All films show two peaks in the optical absorption, corresponding to the ordinary and extraordinary absorption peaks in graphite.

Metrology Challenges for 45 nm Strained‐Si Devices

The semiconductor industry has sustained its historical exponential performance gains by aggressively scaling transistor dimensions. However, as devices approach sub‐100 nm dimensions, scaling becomes more challenging and new materials are required to overcome the fundamental physical limits imposed by existing materials. For example, as power supply voltages continue to decrease with successive scaling, enhanced carrier mobility using biaxially tensile‐strained‐Si on SOI or on bulk substrates have become viable options to sustain continual drive current increases without traditional scaling. Although the addition of strained‐Si to conventional MOSFET devices is compatible with existing mainstream CMOS process technology, there are new device and process integration challenges, wafer quality monitoring demands, and stringent requirements for film morphology and strain uniformity, imposing new demands on material characterization. Material requirements for strained‐Si CMOS devices include homogeneous Si or...

Thermal stability, microstructure, and electrical properties of atomic layer deposited Hf 6 Ta 2 O 17 gate dielectrics

The intent of this work is to investigate thermal stability, microstructure, and electrical properties of thin Hf 6 Ta 2 O 17 high-k gate dielectrics. X-ray diffraction and transmission electron microscopy analysis reveal that an as-deposited Hf 6 Ta 2 O 17 film is amorphous with a ∼1-nm interfacial layer. After a 1000 °C anneal, the film is a mixture of orthorhombic-Hf 6 Ta 2 O 17 and monoclinic HfO 2 with a thicker interfacial layer. Uniform Hf and Ta Auger depth profiles are observed for as deposited and annealed films. Secondary ion mass spectrometry (SIMS) analysis shows Hf and Ta profiles are unchanged following the 1000 °C anneal, indicating good thermal stability. There is, however, a clear indication of Si up-diffusion into Hf 6 Ta 2 O 17 , particularly after annealing at 1000 °C. No Hf or Ta is found in the Si substrate. Well-behaved capacitance-voltage curves and low leakage current characteristics were obtained for Mo/ Hf 6 Ta 2 O 17 capacitors for as-deposited and 1000 °C annealed films. A flatband voltage (V fb ) shift towards negative voltage is observed for the annealed film when compared to the as-deposited film, indicating the presence of more positive charge, or less negative charge. Furthermore, capacitance-voltage stress measurements were performed to study charge trapping behaviors. A smaller V fb shift is observed for as deposited ( 6 Ta 2 O 17 , indicating more charge trapping after the high temperature anneal.

Metrology Of Silicide Contacts For Future CMOS

Silicide materials (NiSi, CoSi2, TiSi2, etc) are used to form low‐resistance contacts between the back‐end (W plugs and Cu interconnects) and front‐end portions (silicon source, drain, and gate regions) of integrated CMOS circuits. At the 65 nm node, a transition from CoSi2 to NiSi was necessary because of the unique capability of NiSi to form narrow silicide nanowires on active (monocrystalline) and gate (polycrystalline) lines. Like its predecessors TiSi2 and CoSi2, NiSi is a mid‐gap silicide, i.e., the Fermi level of the NiSi metal is pinned half‐way between the conduction and valence band edges in silicon. This leads to a Schottky barrier between the silicide and silicon source‐drain regions, which creates undesirable parasitic resistances. For future CMOS generations, band‐edge silicides, such as PtSi for contacts to p‐type or rare earth silicides for contacts to n‐type Si will be needed. This paper reviews metrology and characterization techniques for NiSi process control for development and manufac...

Limits of Optical and X‐ray Metrology Applied to Thin Gate Dielectrics

We analyze the limits of optical and x‐ray metrology techniques (spectroscopic ellipsometry, x‐ray reflectivity, and powder x‐ray diffraction) applied to thin films in microelectronics, especially metal oxides used as gate dielectrics. By tilting the substrate from the symmetric scattering geometry, we can enhance the sensitivity of powder diffraction and detect the tetragonal (011) Bragg peak from a 30 A thick HfO2 layer on Si. We have calculated the Bragg peak positions and intensities of tetragonal hafnia. Vacuum‐ultraviolet spectroscopic ellipsometry and grazing‐incidence x‐ray reflectivity spectra for 50 to 200 A thick HfO2 layers on Si (001) can be described by a model, which consists of only a single (metal oxide) layer on the Si substrate. These techniques, within the scope of our work, are unable to determine the thickness of the interfacial oxide layer between the metal oxide and the substrate. A method to determine the optical properties (complex dielectric function) of thin insulating layers o...