The thermal annealing of 1.5 μm thick SiO2 layers deposited on Si with a High Density Plasma (HDP) has been monitored by Thermal Desorption Spectrometry (TDS), Fourier Transform Infra-Red absorption (FTIR) and Positron Annihilation Doppler Broadening (PADB). Two samples were prepared with different production conditions (substrate temperature, Ar flow, ratio) in order to get oxide layers rich in SiH bonds or rich in SiOH bonds. The deposition temperatures of these layers were 545 K and 575 K, respectively. The formation of SiH rich and SiOH rich oxides was confirmed by FTIR absorption measurements. Desorption measurements showed that at a heating rate of 5 K/s release of hydrogen takes place around 1100 K. For the layer deposited at 575 K additional release of hydrogen is observed at 900 K. In both samples argon release is seen around 1200 K. The release of hydrogen at 1100 K is consistent with FTIR measurements at annealed samples. The absorption peaks associated with the SiH and SiOH bonds only disappear after heating above 1000 K. For the PADB measurements thermal anneals were carried out from 300 to 1300 K in steps of 50 and 100 K of 16 min duration. The positron measurements show different annealing behavior of the two oxides. It is observed that up to 1200 K the 545 K oxide shows a significant higher value for the defect parameter. The argon and hydrogen release is observed by an increase of the defect parameter at 1000 K.

Currently the trend in the Si IC industry is to produce epitaxial material layers by advanced growth and deposition techniques. Examples of these are Si and SiGe low temperature epitaxy, Si selective epitaxy and metallic silicide epitaxy. In order to obtain good electrical properties it is important that the epitaxial material shows no extended lattice defects and has a minimal concentration of lattice point defects. Given the concentrations of these phenomena a sensitive experimental technique is required to characterise the materials. The application of the positron annihilation technique in this IC research area is demonstrated by two examples, namely, characterization of Si Molecular Beam Epitaxy (MBE) and Atmospheric Pressure Chemical Vapour Deposition (APCVD) epi-layers and the assessment of the quality of CoSi2 epi-layers produced by the solid-state reaction with the Si substrate and an amorphous Co75W25 sputtered layer. Results will be presented in terms of defect concentrations derived from positron diffusion lengths.

We describe a novel technique fully compatible with silicon microelectronic technology for the synthesis of Ge nanocrystals. The approach followed involves UV-assisted low temperature dry oxidation of a strained Si0.8Ge0.2 layer. Initially, oxidation results in the selective formation of SiO2 under which accumulates a Ge-rich SiGe layer. Further irradiation and oxidation of this structure result in the incorporation of Ge nanocrystalline regions from 2 to 8 nm in diameter into the growing SiO2 layer. These Ge nanoparticles exhibit visible photoluminescence in the 550–800 nm range. The temperature of only 550 °C employed in our process is significantly less than the 800–850 °C levels necessary up till now for the reduction of SiGe oxides to form Ge nanocrystals. Regardless of size, the nanoparticles, being directly formed from the underlying substrate, always exhibit the diamond crystalline structure, as shown by high resolution transmission electron microscopy and Raman spectroscopy.

We have studied the incorporation of Ga in silicon during the fabrication of delta-doping layers. The delta-function doping profiles were grown by molecular beam deposition following a solid phase epitaxial growth method. Medium-energy ion scattering, secondary ion mass spectrometry, and Rutherford backscattering spectrometry were used to determine the structure and composition of the grown films. The interface velocity of the crystallization front and the diffusion coefficient of the impurity atoms in the Si matrix, both relevant parameters of the growth process, were measured. Optimum growth conditions were found that yield Ga doping profiles of less than 1.0 nm (full width at half maximum), with more than 95% of the buried dopant atoms on lattice sites. For these optimum growth conditions, a model is derived explaining the observed incorporation of the Ga atoms.

The redistribution of Ga in amorphous silicon (a-Si) in the temperature range of 560–830 K by means of medium-energy ion scattering has been studied. During the initial 10 s of the annealing the diffusivity shows a transient behavior that is attributed to the change in the relaxation state of the amorphous matrix. From 560 to 830 K the diffusivity during relaxation is enhanced by seven to two orders of magnitude compared to the value for bulk a-Si. Possible models that show the observed transient diffusion behavior are discussed.

Ultraviolet-assisted low-temperature (550 °C) dry oxidation of Si0.8Ge0.2 strained layers on (100)Si has been studied. The oxidation rate of this material was found to be a factor of 2 greater than that of pure Si oxidation under identical irradiation conditions. Initially, the structure of the oxidized material consists of a SiO2 layer on top of a strained Si1−xGex layer with a Ge concentration significantly higher (x≳0.2) than the initial value. Increasing the oxidation time produces more SiO2 and a Si1−xGex layer further enriched with Ge. However, the oxidation rate is reduced and some of the Ge becomes trapped inside the growing SiO2 layer. For a prolonged irradiation time (≳5 h) SiGe oxidation still continues, unlike the case for pure Si, while the Ge trapped inside the SiO2 forms isolated microcrystalline regions.

The defect structure in epitaxial silicon films grown by solid phase epitaxy (SPE) and by molecular beam epitaxy (MBE) has been studied by probing with implanted helium. It was found that SPE layers contain large vacancy clusters (voids) at a low density. In both SPE and MBE films, other not yet fully identified but smaller defects which trapped helium were detected. The detection of voids is in agreement with results of cross-sectional transmission electron microscopy observations of the SPE film. Defect concentrations found in the SPE and MBE films are similar to earlier results obtained with positron beam analysis on these layers.

A novel and simple technique for the synthesis of Ge nanocrystals embedded in SiO2 is reported. The method is fully compatible with silicon microelectronic technology and relies solely upon low temperature (only 550 °C) ultraviolet oxidation of Si0.8Ge0.2 strained layers. This temperature is significantly lower than that usually used for the formation of Ge nanocrystals from SiGe oxides by H2 reduction.

S‐parameter positron beam measurements have been done on several kinds of a‐Si: Kr‐sputtered a‐Si, PECVD a‐Si, MeV ion beam amorphized Si and a‐Si grown in an MBE‐system at a low deposition temperature. Kr sputtered a‐Si becomes denser for higher Kr concentration. PECVD a‐Si:H contains micro‐cavities with a size depending on growth temperature. MeV ion beam amorphized Si contains 1.2 at. % small vacancies, which decreases upon annealing (relaxation) to 0.4 at. %. This effect can be mimicked by H‐implantation and subsequent annealing, showing that at least some of the dangling bonds in a‐Si are located at these vacancy‐type defects. Finally positron measurements show that MBE‐system grown a‐Si contains large open‐volume defects. The positron annihilation data are supplemented by data from some other techniques.

The formation of epitaxial CoSi2 thin films by reactive deposition of cobalt onto silicon (001) substrates at temperatures around 600-degrees-C is described. When the deposition rate is below a certain critical value for a particular substrate temperature (for example below 0.02 nm s-1 at 600-degrees-C), epitaxial disilicide formation can be achieved. Deposition rates above this critical value lead to the production of polycrystalline disilicide. A mechanism is described to explain the influence of the deposition rate on the formation of epitaxial material.

The structure evolution and the defects present in epitaxial CoSi2 formed using the solid-state reaction between an amorphous Co75W25 sputtered layer and Si(001) have been studied by transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), positron annihilation and resistivity measurements. By employing anneals between 500 and 600 °C, Co diffuses out of the amorphous alloy into the substrate to form a CoSi2 layer. After the anneal, the remaining amorphous alloy on top of the silicide has been removed by a selective wet etch. It has been found that the greater part (∼68%) of the so-formed CoSi2 film is epitaxial and that a high density of vacancy-type defects (2.6×1019/cm3) is present in the material. A second anneal at a higher temperature has been performed to improve the quality of the silicide. This results in a decrease of the RBS minimum yield and the residual resistivity to values of ∼25% and 2.6 μΩ cm, respectively. Only a few grains of twinned CoSi2 could be detected after the second anneal. By plan-view TEM and RBS dechanneling energy dependence measurements, a total projected length of dislocation lines of ∼1.7×106 cm/cm2 has been estimated. By positron annihilation a density of 1.1×1018 vacancies/cm3 has been measured.

Epitaxial β-FeSi2 has been formed by depositing iron (Fe), at a rate of 0.01 nm/s, onto hot Si(001) substrates at 630°C. Epitaxial films were formed as long as the disilicide thickness was less than 320 nm. Post-annealing at around 800°C improved the epitaxial quality of the films.

Si1-xGex channel p-MOSFETs and MODFETs containing Ge fractions from x=0 to 1.0 have been fabricated in material grown at 550°C. An improved carrier mobility was recorded for a Si0.8Ge0.2 device over that for a control MOSFET fabricated in Si also grown at this low temperature. It is argued that this growth temperature is responsible for the low absolute values of mobility recorded in these devices.

We studied the influence of a thin Fe interface layer between W and the substrate Si and of a surface W–oxide on the formation kinetics of WSi2. Auger depth profiling, Rutherford backscattering spectrometry and x-ray diffraction have been used to investigate the reaction between the layers and the Si substrate. W layers with a thickness of 20 nm were deposited by electron beam evaporation on HF dipped Si(100) samples. If deposition and subsequent annealing are performed in ultrahigh vacuum, the complete conversion of a W layer into tetragonal WSi2 occurs within 1 h at 800 °C. The intercalation of a 5 nm-thick Fe layer between the W layer and the substrate reduces the conversion temperature to 650 °C. Ironsilicide is formed at a relatively low temperature. This silicide acts as a medium through which Si can easily diffuse towards the surface, thus maintaining a fast Si supply to the W layer. This experiment indicates that reactions at the metal/Si interface are rate determining in the formation of WSi2. Both with and without an Fe intermediate layer, the reaction proceeds via the migration of Si to the film surface followed by the formation of WSi2 at the surface. Continuation of the reaction occurs from the surface to the substrate. Furthermore, we found that the presence of a native oxide layer at the W surface retards the reaction between W and Si. Oxygen migrates via the open structure of the W film to the interface where it probably forms a thin SiO2 layer that hampers the transport of Si into the W film.

Studies of the properties and characteristics of transition metal silicides have been stimulated by their (potential) use in integrated circuit technology. This review describes some of the most recent studies in this field of research. Formation mechanisms of silicides are discussed in some detail. A division is made between near-noble and refractory metal silicidation which aids in the understanding of differences in formation mechanisms of the various silicides. The evolution of the components of thin film stress during metal silicidation is also elucidated. In the review of the practical uses of these materials, emphasis is placed on specific processes involving laterally confined (self-aligned) silicide film formation as more advanced applications require film formation only in certain localized regions on a Si wafer.

The formation and characterization of epitaxial CoSi2 layers using the solid-state reaction between an amorphous Co75W25 sputtered layer and Si(001) has been studied by transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), positron annihilation and resistivity measurements. In the temperature range 500–600°C, Co diffuses out of the amorphous alloy into the substrate to form a CoSi2 layer. After the anneal the remaining amorphous alloy on top of the silicide has been removed by a selective wet etch. It has been found that the greater part (about 68%) of the so-formed CoSi2 film is epitaxial and that a high density of vacancy-type defects (2.6 × 1019/cm3) is present in the material. A second anneal at a higher temperature has been performed to improve the quality of the silicide. This results in a decrease of the RBS minimum yield and of the residual resistivity to values of about 25% and 2.6 μΩ·cm, respectively. Only few grains of twinned CoSi2 could be detected after the second anneal. By positron annihilation a density of 1.1 × 1018 vacancies/cm3 has been measured. The Schottky barrier height shows a clear dependence on the CoSi2 film properties.

The formation of CoSi2 from an amorphous Co70Ti30 alloy film on Si(100) has been studied by Auger depth profiling, Rutherford backscattering spectrometry, cross-section transmission electron spectroscopy and x-ray diffraction. The solid-state reaction starts around 400-degrees-C with the diffusion of Co out of the alloy into the substrate, forming an interface layer consisting of CoSi and CoSi2. The simultaneous diffusion of Si into the Co-depleted region of the film is limited for annealing temperatures below 600-degrees-C. After removing the remaining top layer by selective etching, an extra heat treatment is performed to transform the mixed silicide layer completely into CoSi2. The latter is found to be partially aligned with the substrate. The amount of epitaxial CoSi2 increases with the use of higher post-anneal temperatures.

The formation of epitaxial CoSi2 on (001) Si using the solid state reaction between an amorphous Co75W25 sputtered layer and Si has been studied. Auger electron spectroscopy depth profiling, Rutherford backscattering spectrometry, x-ray diffraction, transmission electron microscopy, and resistivity and mobility measurements on Van der Pauw structures have been used to investigate the interaction between the amorphous alloy and Si. By employing anneals in vacuum between 500 and 600 °C for 60 or 120 min, Co diffuses out of the alloy into the substrate to form CoSi2. X-ray diffraction measurements indicate that the greater part (about 75%) of the disilicide film is epitaxial. The CoSi2 film is unstrained at the growth temperature. At room temperature a tetragonal distortion of the silicide lattice is noted, which results from cooling from the growth temperature, and is caused by the difference in the thermal expansion coefficients of Si and CoSi2. After a selective etch to remove the remaining amorphous alloy, a second anneal at a higher temperature has been performed to improve the quality of the silicide. As a result of the second anneal, the Rutherford backscattering channeling minimum yield and the residual resistivity of the film decrease to values of about 25% and 2.6 μΩ cm, respectively. Only the epitaxial (A type) orientation of CoSi2 could be detected after the second anneal by x-ray pole figure measurements. Both the vertical and the lateral distortions in the silicide lattice, measured at room temperature, appear to decrease during this anneal. The Debye temperature, obtained from electrical measurements, increases from 382 K, after Co outdiffusion, to 412 K after the second anneal.

Results are presented for mesa-structured Si0.87Ge0.13 base heterojunction bipolar transistors (HBTs), grown by means of silicon molecular beam epitaxy. By using arsenic poly emitters, the diffusion of boron in the base during processing could be largely prevented. Ideal Gummel plots were found. An improvement in the current gain to base resistance ratio from 9.6 to 156 □/kΩ was found by introduction of the Si0.87Ge0.13. The Early voltage in the HBT was 40 V. Analysis of the temperature dependence of the collector current in an HBT and a reference silicon transistor showed the band gap narrowing to be 80 mV which is somewhat less than expected. Indications were found that even in this case a small parasitic barrier is present.

Low-temperature dry oxidation of Si-capped and uncapped MBE-grown Si0.8Ge0.2, assisted by the UV radiation from a low-pressure Hg grid lamp, has been studied. For short processing times, the oxidation rate of Si0.8Ge0.2 was found to be a factor of 2–3 higher than that induced by the same method for elemental monocrystalline Si. After more than 80% of the initial thickness of the Si0.8Ge0.2 was oxidized, the growth rate of the oxide film approached that found for Si. The photo-oxidation rate of the Si capped layer was identical with that of single-crystal silicon. Because of the low temperature (550 °C) employed for this UV-assisted oxidation, no measurable relaxation of the strained layers was detected.