Selective Low Pressure Chemical Vapor Research Articles

Study of Cu-growth feature by selective low-pressure chemical vapor deposition using a CuI precursor

In this study, Cu-growth features are investigated using selective low-pressure CVD of Cu on Ru(001) using a copper(I) iodide precursor. While discrete columnar grains are formed below 320 °C, lateral Cu islands are grown above 380 °C. The CuI dissociation efficiency, which depends on the growth temperature, indicates two activation energies corresponding to I2 desorption from Cu and Ru. The activation energy below 320 °C and above 380 °C are identified as the energies required for the desorption of I2 from Cu(111) and Ru(001), respectively. At 400 °C, nucleation occurs at the initial stage, followed by the lateral growth of Cu-islands. A proposed growth model, involving dissociated Cu-atom contributions toward increasing the Cu-island height and Cu coverage on Ru, can explain the island growth features dependent on the growth time. Further, the growth model reveals an important factor to achieve thinner Cu layers growth entirely covering Ru.

Influence of thermal annealing on compositional mixing and crystallinity of highly selective grown Si dots with Ge core

We have studied the compositional mixing and the crystallinity of Si dots with Ge core (∼20 nm in average dot diameter), which were prepared on thermally grown SiO 2 by highly selective low-pressure chemical vapor deposition (LPCVD), as a function of annealing temperature in the range of 540–1000 °C. Raman scattering spectra of multiply stacked structures consisting of dots with Ge core and 2 nm-thick SiO 2 interlayers indicate that compositional mixing occurs partly at Si/Ge interface during the sample preparation, where the sample was heated up to 600 °C. Also, 800 °C annealing promotes Si–Ge alloying between Si clad and Ge core, and degrades the crystallinity. By 950 °C annealing, SiO 2 reduction with diffused Ge atoms to form volatile GeO x units becomes significant, resulting in the generation of SiSi bonds. Additionally, XPS analysis of annealed single layer structures confirms the incorporation of Ge atoms into Si clad from Ge core and the formation of GeO x at the Si clad surface.

19 GHz vertical Si p-channel MOSFET

Vertical Si p-MOSFETs with channel lengths of 100 nm were fabricated using selective low pressure chemical vapour deposition (LPCVD) epitaxial growth and conventional i-line lithography. The layout, called VOXFET, reduces gate to source/drain overlap capacitances, thus improving high speed applications. Transistors with a gate width of 12 /spl mu/m and gate oxide thickness of 10 nm show transconductances g/sub m/ of 200 mS/mm and measured cutoff frequencies of f/sub T/=8.7 GHz and f/sub MAX/=19.2 GHz.

Determination of the activation energy for the heterogeneous nucleation of misfit dislocations in Si1−xGex/Si deposited by selective epitaxy

Si 0.84 Ge 0.16 /Si heterostructures with variable finite lateral dimensions (10–300 μm) and different layer thicknesses grown by selective low pressure chemical vapor deposition epitaxy at a temperature of 700 °C were investigated with regard to relaxation by formation of misfit dislocations. While in small structures only nucleation and propagation occur, the dislocation–dislocation interaction (mainly multiplication) becomes more and more important in larger structures. Therefore it was possible to separate the three different mechanisms which play a role in relaxation, i.e., nucleation, propagation, and multiplication, and to study them independently. From the analysis of the misfit dislocations at the initial stage of relaxation it was possible to determine the nucleation site density and an activation energy of 2.8 eV for the heterogeneous nucleation of misfit dislocations.

Strain and misfit dislocation density in finite lateral size Si 1− x Ge x films grownby selective epitaxy

Strain and misfit dislocation density in small-area Si 1− x Ge x filmsgrown by selective low-pressure chemical vapour deposition on Si (100)have been investigated as a function of lateral size by Rutherford backscattering spectrometry, ion channeling, photoluminescence spectroscopy and transmission electron microscopy. The results show that a large-area Si 0.84Ge 0.16 film with a thickness of 430 nm has relieved more than 60% of the pseudomorphic strain by formation of misfit dislocations while 100X100 μ 2 square-shaped structures exhibit full pseudomorphic strain. In comparison to large-area growth, a significant decrease of the dislocation density was already observed in structures as largeas 5000X300 μ 2. The experimental results are in good agreement with theoretical estimations assuming a fixed density of nucleation sources. Selective growth and size-dependent reduction of the dislocation density may be important regarding future device applications and low dimensional semiconductor heterostructures as quantum wires and quantum dots based on the Si/Si 1− x Ge x materials system.

Modeling of selective tungsten low-pressure chemical vapor deposition

A comprehensive numerical model for selective low-pressure chemical vapor deposition (LPCVD) of tungsten from hydrogen and WF 6 in a single-wafer reactor has been developed. The computational fluid dynamics (CFD) code PHOENICS-CVD is used for transient solutions of the two-dimensional transport equations of heat, momentum and chemical species in the reactor. A detailed model is used for the kinetics of tungsten deposition at the surface. A model for the nucleation of intermediates, which are formed at the surfaces where tungsten is deposited and are transported through the gas phase, is used to describe the loss of selectivity. This opens the way for qualitative study of the influence of process conditions and reactor configurations on the selectivity of this process. The selectivity is found to improve at high flow rates, low total pressures and low partial pressures of WF 6.

Selective low pressure chemical vapour deposition epitaxy using silane only for advanced device applications

AbstractSelective epitaxial growth of silicon in windows opened in a mask is usually carried out using source gases in the Si–Cl–H system in low pressure chemical vapour deposition (LPCVD) systems. These gases offer good control over growth but are associated with mask distortion, which is intolerable in submicrometre device geometries. The silane only selective growth process possible in the Southampton University Microelectronics Centre (SUMC) LPCVD machine is highly selective, allowing growth of epitaxial layers four times thicker than the mask without lateral overgrowth. Surface facets are observed at the edges of 〈110〉 direction oxide features, in common with selective epitaxy by other techniques. The material under the facets is shown to include defects. Increased planarity can be obtained by orienting mask features along 〈100〉 directions, where faceting is not observed. The selectively grown material can be doped n type to give carrier concentrations from 2×1015 to 2×1019 cm−3, and p type from 1×10...

Selective low pressure chemical vapour deposition epitaxy using silane only for advanced device applications

Selective epitaxial growth of silicon in windows opened in a mask is usually carried out using source gases in the Si–Cl–H system in low pressure chemical vapour deposition (LPCVD) systems. These gases offer good control over growth but are associated with mask distortion, which is intolerable in submicrometre device geometries. The silane only selective growth process possible in the Southampton University Microelectronics Centre (SUMC) LPCVD machine is highly selective, allowing growth of epitaxial layers four times thicker than the mask without lateral overgrowth. Surface facets are observed at the edges of 〈110〉 direction oxide features, in common with selective epitaxy by other techniques. The material under the facets is shown to include defects. Increased planarity can be obtained by orienting mask features along 〈100〉 directions, where faceting is not observed. The selectively grown material can be doped n type to give carrier concentrations from 2×1015 to 2×1019 cm−3, and p type from 1×1017 to 1×1019 cm−3. In terms of selectivity, planarity, and carrier concentration, the material produced by the SUMC LPCVD epitaxy machine is suitable for device production.MST/3221

LPCVD WSi2 Films Using Tungsten Chlorides and Silane

This paper makes a systematic study of blanket and selective low pressure chemical vapor deposition (LPCVD) films from tungsten chlorides, silane, hydrogen, and argon on silicon as well as on patterned oxidized silicon substrates. Experiments were performed by varying the initial gaseous to ratio or the deposition temperature . Initially, yield and CVD‐phase diagrams of the W‐Si‐Cl‐H‐Ar chemical system were drawn, based on thermodynamic simulations. The deposition of pure phase and mixed solid phases involving W, , , and Si was predicted to occur in relation to process parameters. The corresponding films were grown in a cold‐wall reactor and characterized by x‐ray diffraction, scanning electron microscopy, four‐point probe, and Auger electron spectroscopy studies. Good agreement was found between experimentally observed solid phases and thermodynamically simulated results, under the same conditions. The growth rate of films for an value varying between 0.3 and 1.0 at 873 K reaches a maximum at . The Arrhenius plot of films grown between 773 and 1073 K shows a linear increase in growth rate up to 923 K, followed by saturation at high temperatures. Films processed above 823 K have a smooth surface and interface, indicating that the chloride‐based chemistry does not affect the silicon substrate even at high temperatures. Based on the above mentioned studies, a set of process parameters was defined, and selective LPCVD films were deposited on fine‐patterned oxidized silicon.

Selective low pressure chemical vapor deposition of copper: Effect of added water vapor in hydrogen or helium carrier gas

The low pressure chemical vapor deposition (LPCVD) of copper from its bis-hexafluoroacetylacetonate is studied on oxidized silicon substrates partially covered with a platinum seeding layer. With a known concentration of water vapor in the gas mixture, almost equal copper film growth rates are obtained when using either hydrogen or helium as carrier gas. For both carrier gases, an increase of the copper growth rate is observed with an increasing amount of water vapor added to the gas mixture, and deposition rates above 500 Å/min are obtained. The chemical purity and electrical conductivity of the copper deposit are as high in the case of a helium carrier gas as in the case of a hydrogen carrier gas. Implications for the mechanism of copper LPCVD are discussed.

Selective low pressure chemical vapor deposition of copper and platinum

The low pressure chemical vapor deposition of copper and platinum is studied on SiO2 substrates which have been locally prenucleated with ultrathin metal layers of Pt, Cu, Pd, Au, and W. These layers were between 0.1 and 30 Å thick and were produced by vacuum evaporation. Copper metal is deposited selectively on top of the prenucleation layers from the gaseous bis-hexafluoroacetylacetonate {Cu(hfa)2} diluted in hydrogen. High quality copper could be grown at temperatures in the range of 300–400 °C with electrical resistivities as low as 2.5 times the bulk copper value. In contrast, platinum deposited from gaseous Pt(hfa)2 in H2 grows selectively on the clean oxide surface rather than on the areas prenucleated with vacuum evaporated platinum.

Experimental and thermodynamical investigation of selective low pressure chemical vapour deposition of tungsten using WCl 6 as tungsten source

Selective low pressure chemical vapour deposition of tungsten using WCl 6 as the tungsten source was investigated both experimentally and thermodynamically. The process was found to be very sensitive to the thickness of the native oxide, thus making it difficult to obtain good reproducibility. The selectivity of the chloride process was good for both Ar-WCl 6 and H 2-WCl 6 reaction gas mixtures. Tungsten layers thicker than 2000 Å were occasionally deposited from the Ar-WCl 6 reaction gas mixture. This is explained by the porosity of the coatings, allowing for WCl 6 diffusion through the tungsten layer and permitting continued tungsten growth. Channel-like growth of tungsten into the silicon windows of patterned Si/SiO 2 was also observed when the Ar-WCl 6 gas mixture was employed. It is suggested that oxygen-containing species from the simultaneous etching of SiO 2 may promote the formation of channels.

Interfacial Structure of Tungsten Layers Formed by Selective Low Pressure Chemical Vapor Deposition

We have analyzed the interfacial structure of selectively deposited LPCVD tungsten on monocrystalline silicon, polycrystalline silicon, and polycrystalline aluminum substrates. Cross‐sectional specimens were examined by transmission electron microscopy to determine the amount of substrate consumed by the selective deposition process and to assess the degree of lateral encroachment under masking layers for different conditions of deposition and surface preparation. The tungsten‐silicon interfacial structure was found to depend strongly on the initial surface preparation. Immersion in a dilute solution resulted in a smooth interface, while a glow‐discharge treatment led to highly irregular interfaces, which, in extreme cases, contained tunnels extending 1 μm or more into the silicon substrate. Layers formed in plus were found to consist of two layers, of which the lower layer is formed by the substrate reduction of .