D. E. W. Vandenhoudt

Ion‐beam synthesis of a Si/β‐FeSi2/Si heterostructure

Ion‐beam synthesis of a buried β‐FeSi2 layer in Si is demonstrated. In the experiments Si(111) substrates have been implanted with 450‐keV Fe+ ions. Samples have been analyzed by Rutherford backscattering spectrometry, x‐ray diffraction, and transmission electron microscopy. Annealing at 900 °C of samples implanted with 6×1017 Fe+/cm2 causes formation of a buried layer consisting of grains with lateral dimensions of approximately 5 μm. The epitaxy of β‐FeSi2 (110) and/or (101) planes parallel to the Si(111) substrate plane is observed.

β‐FeSi2 in (111)Si and in (001) Si formed by ion‐beam synthesis

Ion‐beam synthesis of β‐FeSi2 is demonstrated both in (111) Si and (001) Si substrates by 450 keV Fe ion implantation at elevated temperatures using a dose of 6×1017 Fe/cm2 and subsequent annealing at 900 °C. The structure of the buried layers has been analyzed using Rutherford backscattering spectrometry, x‐ray diffraction, and (cross‐section) transmission electron microscopy. In (111) Si an epitaxial layer is formed consisting of grains with lateral dimensions of approximately 5 μm. Epitaxy of β‐FeSi2 (110) and/or (101) planes parallel to the (111) Si substrate plane is observed. In (001) Si a layer is formed consisting of grains with lateral dimensions of typically 0.5 μm. Several grain orientations have been observed in this material, among others β‐FeSi2 {320}, {103}, and {13,7,0} parallel to (001) Si. Selected (111) Si samples were investigated optically using spectroscopic ellipsometry, and near‐infrared transmittance and reflectance spectroscopy. The results confirm that the β‐FeSi2 layer has an o...

MICROSTRUCTURE OF OXIDIZED LAYERS FORMED BY THE LOW-TEMPERATURE ULTRAVIOLET-ASSISTED DRY OXIDATION OF STRAINED SI0.8GE0.2 LAYERS ON SI

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.

Ion beam synthesis of cobalt silicide: effect of implantation temperature

Abstract In order to understand the physical processes which occur during ion beam synthesis of CoSi2, we have studied the effect of implantation temperature. The experiment consisted of 170 keV Co implantations (dose =1.7 × 1017 ions/cm2) in Si(100) targets at temperatures varying between 250°C and 500°C. Both as-implanted and annealed samples have been analyzed by several techniques, such as cross-section transmission electron microscopy, X-ray diffraction, Rutherford-backscattering spectrometry and the four-point probe technique. Our data indicate that an optimum implantation temperature interval exists where pinhole-free buried layers of CoSi2 can be synthesized. Outside this interval, the evolution of the precipitate size distribution and/or strain situation in the as-implanted state effectively reduce the necessary depth variation in precipitate stability.

Low temperature synthesis of Ge nanocrystals in SiO2

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.

Microstructure of buried CoSi2 layers formed by high‐dose Co implantation into (100) and (111) Si substrates

Heteroepitaxial Si/CoSi2/Si structures have been synthesized by implanting 170‐keV Co+ with doses in the range 1–3×1017 Co+ions/cm2 into (100) and (111) Si substrates and subsequent annealing. The microstructure of both the as‐implanted and annealed structures is investigated in great detail by transmission electron microscopy, high‐resolution electron microscopy, and x‐ray diffraction. In the as‐implanted samples, the Co is present as CoSi2 precipitates, occurring both in aligned (A‐type) and twinned (B‐type) orientation. For the highest dose, a continuous layer of stoichiometric CoSi2 is already formed during implantation. It is found that the formation of a connected layer, already during implantation, is crucial for the formation of a buried CoSi2 layer upon subsequent annealing. Particular attention is given to the coordination of the interfacial Co atoms at the Si/CoSi2 (111) interfaces of both types of precipitates. We find that the interfacial Co atoms at the A‐type interfaces are fully sevenfold ...

Investigation of the defect structure of thin single‐crystalline CoSi2 (B) films on Si(111) by transmission electron microscopy

Thin epitaxial single‐crystalline B‐type CoSi2 films (twin‐oriented) have been grown in ultrahigh vacuum by stoichiometric codeposition of Co and Si on slightly misoriented (0.1°–0.3°) Si(111) substrates. The microstructure as well as the nature of interfacial defects has been investigated in detail by transmission electron microscopy. The defect structure is found to depend closely on the initial deposition parameters, annealing temperature, and the topography of the Si substrate. It will be shown that even during the early stages of layer growth, loss of coherence is obtained and lattice strain already starts to occur with the introduction of misfit dislocations with Burgers vector b=a/2〈110〉 inclined to the interface or with Burgers vector b=a/6〈112〉 parallel to it. It is demonstrated that ultrathin CoSi2 films with thickness of about 1 nm grown on slightly misoriented substrates with parallel surface steps, exhibit quite different defect structures at annealing temperatures between 300 °C and 550 °C. ...

Epitaxial explosive crystallization of amorphous silicon

It is shown that amorphous silicon can be transformed to monocrystalline silicon via an explosive epitaxial crystallization process induced by pulsed laser irradiation. 370‐nm‐thick amorphous Si layers, buried beneath a 130‐nm‐thick crystalline surface layer, were irradiated with a 32 ns ruby laser pulse. Real‐time reflectivity measurements indicate that internal melting can be initiated at the amorphous‐crystalline interface, immediately followed by explosive crystallization of the buried amorphous Si layer. Channeling and cross‐sectional transmission electron microscopy reveal that explosive crystallization proceeds epitaxially with formation of twins extending into the sample. The crystal growth velocity is determined to be 16.2±1.2 m/s, close to the fundamental limit for crystalline ordering at a liquid Si/Si(100) interface.

Pulsed-laser crystallization of amorphous silicon layers buried in a crystalline matrix

Ion implantation, employing Si, Ar, and Cu ions in the energy range from 275 to 600 keV, was used to form amorphous silicon layers buried in a crystalline matrix. Different layer geometries were produced, with 150–620‐nm‐thick amorphous layers, separated from the surface by 120–350‐nm‐thick crystalline layers. Crystallization of the amorphous layers was induced by 32‐ns pulsed ruby laser irradiation. Real‐time reflectivity and conductivity measurements indicate that internal melting can be initiated at the amorphous‐crystalline interface, immediately followed by explosive crystallization of the buried layer. Channeling and cross‐section transmission electron microscopy reveal that in both Si(100) and Si(111) samples explosive crystallization proceeds epitaxially with twin formation, the twin density being higher in Si(111) than in Si(100). The measured crystal growth velocities range from 15 to 16 m/s, close to the fundamental limit for crystalline ordering at a Si liquid‐crystalline interface. Computer m...

Thin buried cobalt silicide layers in Si(100) by channeled implantations

Si(100) wafers have been implanted with 50 keV Co ions at elevated substrate temperatures (320 °C) in the dose range 7.8×1014–7.8×1016 at. cm−2. A comparison is made between channeled (along the Si 〈100〉 surface normal) and random (tilted by 7°) implantations. Co depth distributions are measured with secondary‐ion mass spectrometry and compared to marlowe and trim simulations. Annealed samples are characterized by Rutherford backscattering spectrometry and transmission electron microscopy. Our data indicate that for channeled implantations the sputtering effect is strongly reduced as compared to random implantations. Also, the average penetration depth is increased by about 20%. As a consequence, annealing of our high‐dose implanted samples yields either a discontinuous surface silicide layer (random case) or a pinhole‐free buried silicide layer (channeled case).