Douglas J. Tweet

Atomic Layer Deposition of Hafnium Oxide Using Anhydrous Hafnium Nitrate

Atomic layer deposition of uniform thin hafnium oxide films has been demonstrated directly on H-terminated silicon surfaces using anhydrous hafnium nitrate (Hf(NO 3 ) 4 ) precursor and H 2 O vapor. Atomic layer deposition was initiated on hydrogen terminated silicon surfaces and occurred at substrate temperatures as low as 160°C. X-ray diffraction analysis indicated that as-deposited films were smooth, uniform, and amorphous, and that film morphology can be altered by a post-deposition anneal. X-ray photoelectron spectroscopy analysis indicated that films are oxygen rich, contain silicate, and that residual NO 3 and NO 2 from the precursor can be eliminated by a post-deposition anneal. For a ∼57 A HfO 2 film, a dielectric constant of κ ≅ 10.5 and a capacitive equivalent thickness of ∼21 A were obtained.

Atomic layer deposition of thin hafnium oxide films using a carbon free precursor

Thin HfO2 films have been deposited on silicon via atomic layer deposition using anhydrous hafnium nitrate [Hf(NO3)4]. Properties of these films have been investigated using x-ray diffraction, x-ray reflectivity, spectroscopic ellipsometry, atomic force microscopy, x-ray photoelectron spectroscopy, and capacitance versus voltage measurements. Smooth and uniform initiation of film growth has been detected on H-terminated silicon surfaces. As-deposited films were amorphous, oxygen rich, and contained residual NO3 and NO2 moieties from the nitrate precursor. Residual nitrates were desorbed by anneals >400 °C, however, the films remained oxygen rich. Crystallization of thin films (<10 nm) occurred at roughly 700 °C. For films less than ∼10 nm thick, the effective dielectric constant of the film and any interfacial layer (neglecting quantum effects) was found to be in the range of k∼10−11. From a plot of electrical thickness versus optical thickness, the dielectric constant of the HfO2 layer was estimated to b...

DEPOSITION OF HIGHLY CROSSLINKED FLUORINATED AMORPHOUS CARBON FILM AND STRUCTURAL EVOLUTION DURING THERMAL ANNEALING

Highly crosslinked fluorinated amorphous carbon films are obtained by increasing deposition temperature, enhancing ion bombardment, and fine tuning the fluorine-to-carbon ratio. The as-deposited films undergo significant mechanical, chemical, and electrical changes after thermal annealing. Most importantly, these changes occur only at the initial stage of annealing. After the thermal treatment, the films tend to be thermally stable and retain reasonably good electrical properties for use as a low-k dielectric.

Characterization and reduction of twist in Ge on insulator produced by localized liquid phase epitaxy

Conditions for producing high-quality localized Ge-on-insulator film stacks on Si substrates by liquid phase epitaxy are discussed. In particular, we have found that the resulting Ge crystal planes have a tendency to exhibit a twist about the long axis of the crystal. If the wafer is heated much above the Ge melting temperature, this twist can be quite large (∼10°). The twist can be minimized by heating to just above the melting temperature and by using thicker Ge films. In spite of this twist, the Ge regions on top of the insulating Si3N4 are observed to be free of dislocations and stacking faults.

Factors determining the composition of strained GeSi layers grown with disilane and germane

Growth rates and compositions are reported for GeSi alloy films and superlattices epitaxially grown on both Ge(100) and Si(100) substrates using disilane and germane source gases in an ultrahigh vacuum chemical vapor deposition chamber. Although the growth rate changes rapidly with temperature the composition is nearly independent of it. Specifically, we find that the order of the adsorption reaction for disilane and germane is the same, resulting in the composition being determined by the partial pressures and by the ratio of the adsorption reaction rate constants. This ratio depends very weakly on temperature, if at all, and appears to vary slightly with the layer composition.

Effect of interlayer on thermal stability of nickel silicide

The thermal stability of nickel silicide is improved significantly by adding a thin layer of Ir or Co at the Ni/Si interface. The sheet resistance remains low after 850 °C annealing. The thermal stability was evaluated by measuring the junction leakage of an ultra-shallow junction with a 40 nm junction depth. With Ir, the film was stable and the reverse leakage of both N+/P and P+/N junctions remained in the picoampere range at 3 V on 100 μm×100 μm feature after 850 °C annealing. With Co, the leakage from P+/N junctions was low when the temperature was as high as 850 °C; leakage from N+/P junction was in the picoampere range up to 750 °C. These films were characterized by x-ray diffraction. The improved stability and low junction leakage is attributed to a very smooth interface.

Atomic layer deposition of MoS2 thin films

Atomic layer deposition (ALD) was used to grow thin films of MoS2 over 5 × 5 cm areas of silicon oxide coated silicon wafers. Smooth, uniform, and continuous films were produced over a temperature range of 350 °C–450 °C. The as-grown films were analyzed using x-ray photoelectron spectroscopy, Raman spectroscopy, photoluminescence, and x-ray diffraction. Electrical characteristics of the films were evaluated by fabricating a back gated field effect transistor. These analyses indicate that ALD technique can produce large area, high quality MoS2 films.

Atomic layer deposition of two dimensional MoS2 on 150 mm substrates

Low temperature atomic layer deposition (ALD) of monolayer to few layer MoS2 uniformly across 150 mm diameter SiO2/Si and quartz substrates is demonstrated. Purge separated cycles of MoCl5 and H2S precursors are used at reactor temperatures of up to 475 °C. Raman scattering studies show clearly the in-plane (E12g) and out-of-plane (A1g) modes of MoS2. The separation of the E12g and A1g peaks is a function of the number of ALD cycles, shifting closer together with fewer layers. X-ray photoelectron spectroscopy indicates that stoichiometry is improved by postdeposition annealing in a sulfur ambient. High resolution transmission electron microscopy confirms the atomic spacing of monolayer MoS2 thin films.

Strained silicon thin-film transistors fabricated on glass

Strained-Si thin-film transistors were fabricated on glass substrate by direct transfer of a 35nm strained Si film onto glass. The strained Si films were originally grown on a relaxed SiGe layer on Si substrate. The tensile strain for the strained Si on glass (SSOG) was found to be 0.80%±0.02%. The effective electron mobility of the fabricated NMOS TFTs is 820cm2∕Vs. These devices show low interface charge densities at the bonding interface and at the gate oxide interface, as confirmed by the low subthreshold swing of 77mV∕dec for the 0.5μm SSOG device.

Densification and improved electrical properties of pulse-deposited films via in situ modulated temperature annealing

We find that the modulated temperature annealing of pulse-deposited high dielectric constant films, in which brief in situ elevated temperature anneals are performed after every deposition cycle, results in film densification, a reduction in interfacial layer thickness, and a strong improvement in electrical properties. The densification and improvement of electrical properties could not be achieved solely by postdeposition annealing at temperatures up to 850 °C.