K. De Keyser

Phase formation and thermal stability of ultrathin nickel-silicides on Si(100)

The solid-state reaction and agglomeration of thin nickel-silicide films was investigated from sputter deposited nickel films (1–10 nm) on silicon-on-insulator (100) substrates. For typical anneals at a ramp rate of 3 °C/s, 5–10 nm Ni films react with silicon and form NiSi, which agglomerates at 550–650 °C, whereas films with a thickness of 3.7 nm of less were found to form an epitaxylike nickel-silicide layer. The resulting films show an increased thermal stability with a low electrical resistivity up to 800 °C.

Epitaxial Formation of a Metastable Hexagonal Nickel–Silicide

The growth of epitaxial layers of hexagonal {theta}-nickel-silicide on Si(100) and Si(111) substrates is reported. They form at 370 C on Si(100) and 360 C on Si(111), from codeposited Ni/Si mixtures, containing 37 to 42 atom % Si and the equivalent of a 50 nm Ni layer. These codeposited layers model the Ni/Si mixing layer at the interface in sputter-deposited films. The occurrence and stability at room temperature conflict with the phase diagram for bulk Ni/Si. Congruent crystallization is shown to initiate the growth of this metastable phase.

Single Crystal CaS:Eu and SrS:Eu Luminescent Particles Obtained by Solvothermal Synthesis

Single crystal CaS:Eu and SrS:Eu luminescent particles were synthesized via a solvothermal route at relatively low temperature (200°C). The as-obtained suspensions were strongly photoluminescent (PL), pointing at good Eu incorporation. The phosphors showed a broad PL emission band with an emission peak at 663 and 623 nm for CaS:Eu and SrS:Eu, respectively. The synthesis method meets the growing interest in small monodisperse particles. The composition and morphology of the particles was evaluated with transmission electron microscopy, scanning electron microscopy-energy dispersive X-ray and electron backscatter diffraction, particles were found to be mostly monocrystalline. X-ray diffraction showed a cubic structure with space group Fm3m. To control the growth of the crystallites, thioglycerol was added as capping agent, narrowing the size distribution and facilitating the growth of the single crystals.

Influence of a transient hexagonal phase on the microstructure and morphological stability of NiSi films

The morphological stability of NiSi is investigated when 40% of Si is mixed into an as deposited 10 nm Ni film. When annealing at 3 °C/s, scanning electron microscopy images and in situ sheet-resistance measurements show that NiSi agglomeration is delayed by more than 100 °C. In situ x-ray diffraction reveals that NiSi grows from an unusual transient hexagonal θ-nickel-silicide phase. The significant improvement of the NiSi film’s morphological stability can be related to its microstructure, with large grains and a strong texture. This peculiar microstructure is compared to the microstructure of the θ-nickel-silicide precursor by electron backscattering diffraction and pole figures.

The role of lattice mismatch and kinetics in texture development: Co1-xNixSi2 thin films on Si(100)

Mixed Co1−xNixSi2 films (0≤x≤1) were grown by solid phase reaction of homogeneous Co1−xNix metal films, codeposited on Si(100). The texture of these films was contemplated using complementary experimental techniques: Rutherford backscattering and channeling spectrometry, x-ray pole figure measurements, and orientation imaging with electron backscattering diffraction. Based on the increasing Co1−xNixSi2 lattice parameter with increasing Ni concentration, a gradual, continuous improvement of the epitaxial quality of the film would be expected. The observed trend is significantly different. The epitaxial quality of the disilicide film indeed improves with increasing Ni concentration, but only up to 15% Ni. Moreover, the increasing epitaxial quality is due to a large volume fraction of (110)-oriented grains, instead of the anticipated (100) orientation. The most abundant texture component is not necessarily the one with the best in-plane match with the substrate, i.e., epitaxy, nor the one which assures the c...

Characterization of the texture of silicide films using electron backscattered diffraction

Electron backscattered diffraction (EBSD) was used to characterize the texture of NiSi films. The various texture components (i.e., the types of preferred orientation, e.g., axiotaxy or epitaxy) could be identified, and their volume fraction could be quantified. Moreover, the spatial distribution of texture components could be studied in blanket films. Orientation imaging microscopy using EBSD is a promising technique to study the texture of silicide or germanide films both on blanket and patterned substrates.

Effect of Pt addition on growth stress and thermal stress of NiSi films

We have studied the effect of the addition of Pt on the growth stress and thermal stress of NiSi films. Platinum was added in the form of an interlayer (Ni/Pt/Si), capping layer (Pt/Ni/Si), and as an alloying element within the as-deposited Ni film (Ni–Pt/Si). The evolution of film stress during the solid-state reaction was monitored using in situ curvature measurements. The large transient compressive growth stress observed during the reaction of pure Ni with Si was significantly reduced for samples with a Pt interlayer or alloy. Based on in situ XRD measurements, this reduction in the compressive growth stress could be related to the disappearance of Ni rich phases from the phase sequence and an overall increase in the silicidation temperature during ramp anneals. Pt was also found to affect the buildup of thermal stress while cooling down the sample after Ni1−xPtxSi formation. The presence of Pt as a solute in the monosilicide causes a significant increase in the stress relaxation temperature, and ther...

Texture of Cobalt Germanides on Ge(100) and Ge(111) and Its Influence on the Formation Temperature

The phase formation of cobalt germanides on Ge(100) and Ge(111) substrates was investigated using in situ X-ray diffraction, starting from room-temperature sputter-deposited Co films. The formation temperature of the CoGe{sub 2} phase was dependent on the substrate orientation. X-ray pole figures and electron backscatter diffraction measurements were used to identify the texture and microstructure of the CoGe{sub 2} and the preceding Co{sub 5}Ge{sub 7} films. A significant difference in preferential orientation was found in the Co{sub 5}Ge{sub 7} films, depending on the substrate orientation. This influences the formation temperature of the CoGe{sub 2} and results in the coexistence of Co{sub 5}Ge{sub 7} and CoGe{sub 2} on Ge(111) in a large temperature window.

Nucleation and diffusion during growth of ternary Co1−xNixSi2 thin films studied by complementary techniques in real time

The growth kinetics of ternary Co1−xNixSi2 thin films was studied in real time. The “Kissinger” method was applied to the results of ramped sheet resistance measurements to extract the apparent activation energy for the growth process. By simultaneously acquiring sheet resistance, x-ray diffraction and laser light scattering data on one hand and combining resistance measurements and Rutherford backscattering spectrometry on the other hand, we could distinguish between the initial, nucleation controlled thin film growth, and the subsequent diffusion controlled growth. The apparent activation energy for the initial growth decreases with increasing Ni concentration as a result of a lower nucleation barrier for the ternary disilicide. The markedly different microstructure of the ternary Co1−xNixSi2 films with respect to pure CoSi2 layers lies at the origin of a lower activation energy for the diffusion controlled growth of the ternary films. Despite the low activation energy, these films grow at a much slower...

Texture in thin film silicides and germanides: A review

Silicides and germanides are compounds consisting of a metal and silicon or germanium. In the microelectronics industry, silicides are the material of choice for contacting silicon based devices (over the years, CoSi2, C54-TiSi2, and NiSi have been adopted), while germanides are considered as a top candidate for contacting future germanium based electronics. Since also strain engineering through the use of Si1−xGex in the source/drain/gate regions of MOSFET devices is an important technique for improving device characteristics in modern Si-based microelectronics industry, a profound understanding of the formation of silicide/germanide contacts to silicon and germanium is of utmost importance. The crystallographic texture of these films, which is defined as the statistical distribution of the orientation of the grains in the film, has been the subject of scientific studies since the 1970s. Different types of texture like epitaxy, axiotaxy, fiber, or combinations thereof have been observed in such films. In...