Epitaxial Pd2Si Research Articles

Formation of Palladium Silicide Thin Layers on Si(110) Substrates

The formation of palladium silicide thin films from Pd/Si(110) and Pd/Si(001) systems with and without a Ti intermediate layer has been investigated. The existence of a Ti layer could improve the thermal stability of Pd2Si thin layers in Pd/Ti/Si(001). In addition, an epitaxial or highly oriented Pd2Si layer is formed in Pd/Ti/Si systems. However, the roughness of the Pd2Si/Si interface is observed in Pd/Ti/Si(110) systems, while the flatnesses of the Pd2Si/Si interface is observed in Pd/Ti/Si(001).

Formation of Palladium Silicide on Heavily Doped Si(001) Substrates Using Ti Intermediate Layer

The formation of palladium silicide on Pd/Ti/Si systems with and without heavy B-doping has been investigated. For comparison, Pd2Si was also formed on Pd/Si systems. The agglomeration of Pd2Si could be retarded in Pd/Ti/Si systems with and without B-doping after annealing at 600 °C. The existence of the Ti layer could improve the thermal stability of Pd2Si. In addition, epitaxial or highly oriented Pd2Si formed in Pd/Ti/Si systems. The two orientation relationships of Pd2Si layers were identified to be Pd2Si[110]∥Si[110] and Pd2Si[110]∥Si[001], and Pd2Si[100]∥Si[110] and Pd2Si[001]∥Si[001]. The formation of strained epitaxial Pd2Si layers was found in Pd/Ti/Si systems. The improvement in the thermal stability of Pd2Si and the formation of epitaxial or highly oriented Pd2Si in Pd/Ti/Si systems were observed with and without B-doping.

Dynamic transformation in the morphology of Pd-deposited Si(111) with thermal treatment using UHV STM

From the dynamic transformation in the morphology of Pd-deposited Si(111) surfaces with thermal treatment, observed by ultrahigh vacuum scanning tunneling microscopy (UHV-STM), the surface reactions of Pd on the Si(111) surface were clarified for the first time with appropriate models on a sound basis. At a low coverage below one monolayer (ML), 2D islands composed of Pd 2Si single crystals were clearly observed to be formed via a surface thermal reaction. At high coverages (> 2ML), following the growth of the epitaxial Pd 2Si film a (3√3 × 3√3)R30° superstructure appeared over the Pd 2Si surface at 300°C. This specific structure was demonstrated to be due to Si segregation.

Epitaxial growth and thermal stability of thin Pd2Si films on (001), (011) and (111) Si

Epitaxial growth and thermal stability of Pd2Si on (001), (011), and (111)Si substrates have been investigated by transmission electron microscopy, X-ray diffraction and sheet resistance measurements.Pd2Si was found to be most stable in (111) samples. Full surface coverage was observed in samples annealed at 800 °C for 1 h. The general trends of the thermal stability of Pd2Si are similar in (001) and (011) samples. Agglomeration of Pd2Si was found to start in samples annealed at a temperature as low as 600 °C. The growth of laterally uniform Pd2Si and resistance to island formation at high temperatures in (111) samples are attributed to the extensive growth of the epitaxial Pd2Si regions.The growth of four different modes of Pd2Si epitaxy on silicon was observed and analyzed. The prominence of a certain mode of Pd2Si epitaxy was found to correspond to a good lattice match with the silicon substrate. Sheet resistance data were found to correlate well with the morphological and microstructural observations.

Epitaxial growth and thermal stability of thin Pd2Si films on (001), (011) and (111) Si

Epitaxial growth and thermal stability of Pd2Si on (001), (011), and (111)Si substrates have been investigated by transmission electron microscopy, X-ray diffraction and sheet resistance measurements. Pd2Si was found to be most stable in (111) samples. Full surface coverage was observed in samples annealed at 800 °C for 1 h. The general trends of the thermal stability of Pd2Si are similar in (001) and (011) samples. Agglomeration of Pd2Si was found to start in samples annealed at a temperature as low as 600 °C. The growth of laterally uniform Pd2Si and resistance to island formation at high temperatures in (111) samples are attributed to the extensive growth of the epitaxial Pd2Si regions. The growth of four different modes of Pd2Si epitaxy on silicon was observed and analyzed. The prominence of a certain mode of Pd2Si epitaxy was found to correspond to a good lattice match with the silicon substrate. Sheet resistance data were found to correlate well with the morphological and microstructural observations.

Transmission electron microscopy and X-ray diffraction investigation of phase formation and transition between Pd 2Si and PdSi in Pd thin films on (111)Si

Phase formation and transition between Pd 2Si and PdSi in Pd thin films on (111)Si has been investigated by X-ray diffraction and transmission electron microscopy. In as-deposited and 200 °C/1 h annealed Pd(30nm)/(lll)Si samples, epitaxial Pd 2Si was found to coexist with the unreacted Pd layer. In samples annealed at 250–800 °C, epitaxial Pd 2Si is the only suicide phase present. PdSi was found to form along with Pd 2Si in samples annealed at 850 °C. Pd 2Si was found to be the predominant phase along with PdSi in samples annealed at 900–1000 °C. Pd 2Si and PdSi were found to be the stable phases at 300–800 and 850–875 °C, respectively. The phase transition between Pd 2Si and PdSi is reversible. In samples annealed at 900 °C, epitaxial Pd 2Si is initially the only suicide phase present; then polycrystalline PdSi becomes the dominant phase. After annealing for more than 240 s, polycrystalline Pd 2Si predominates over PdSi. The peculiar Pd 2Si to PdSi, then back to Pd 2Si phase transition behavior is correlated with the formation of PdSi islands, which is thought to alter the order of the total energy of the system.

AES and LEED studies of surface stoichiometry of palladium silicide epilayers on Si(111)

The stability region of the (1×1) surface structure for ultrathin epitaxial Pd 2Si (0001) films grown on Si (111) under UHV conditions was studied by AES and LEED. It is shown that solid state epitaxy of a Pd 2Si layer (5–20nm thick) on Si causes Si-enrichment of the silicide, both its surface and the film. Monolayer Pd deposition on the silicide surface at room temperature and recording of Si L 2,3VV Auger line shape variation allows the stoichiometric Pd 2Si formation to be determined. At Pd deposition being carried on the two-phase Pd 2Si+Pd system is formed. At the metal atom concentration being critical the silicide is formed which is more Pd-rich than Pd 2Si. The stoichiometry thereof is yet not understood. This new compound is unstable and after being held in vacuum it transforms back into Pd 2Si+Pd or Pd 2Si depending on the relative Pd or Si concentration. For all the phase transitions found the only (1×1) surface structure having a different spot/background ratio in the diffraction pattern is characteristic.

Tem study of the growth of pd2si islands from pd—ta films on si

Abstract The crystallization of amorphous Pd-Ta films and their reactions with Si(001) substrates were studied by transmission electron microscopy. The diffusion of Pd from the amorphous film is hightly enhanced during its relaxation, followed by the formation of epitaxial Pd2Si islands. The crystallization of the film leads to a considerable increase of the Pd diffusion and to the formation of TaSi2-Pd2Si-Si structure. The structure of islands, their coincidence with the Si lattice and the kinetics of their growth are determined. It is found that some islands, formed at the initial stage of the reaction, start to dissolve at the later stages. Here we propose the model of the growth and dissolution of Pd2Si islands during the reaction of Pd-Ta films with Si and the model of Pd diffusion taking into account the relaxation processes in the film.

Diffusion of silicon in Pd2Si during growth

The diffusion of silicon in Pd2Si during silicide formation has been studied with the aid of radioactive 31Si. Annealing samples with the structure Si〈 〉/31Si/Pd at 350 °C produces Pd2Si in which the 31Si is broadly distributed throughout the silicide, thereby indicating a very high silicon self-diffusion in Pd2Si during silicide formation. Since silicon self-diffusion in Pd2Si in the absence of growth is low at these temperatures, this suggests that silicon diffuses by a vacancy mechanism during polycrystalline Pd2Si growth. If samples with the structures Si〈111〉/epitaxial Pd2Si/31Si/Pd are annealed at the same temperature, the 31Si is found to be broadly distributed throughout the subsequently grown Pd2Si, but very little diffusion of 31Si back into the epitaxial region is observed. It is argued that a silicon vacancy mechanism is the most probable diffusion mechanism to have produced the observed 31Si distribution and it is therefore proposed that silicon diffuses by a vacancy mechanism in both polycrystalline and epitaxial Pd2Si growth.

Reordering of polycrystalline Pd2Si on epitaxial Pd2Si

Polycrystalline Pd2Si is found to reorder on top of epitaxial Pd2Si during silicide growth. The interface between polycrystalline Pd2Si and epitaxial Pd2Si is, thus, not immobile with respect to the silicide lattice during silicide formation and it is, therefore, not possible to use this interface as a structural marker in order to monitor diffusion in epitaxial Pd2Si. The use of Ti as an inert marker has shown that Si is the dominant diffusing species in epitaxial Pd2Si during silicide formation.

I n s i t u x-ray diffraction measurement of Pd2Si transformation kinetics using a linear position-sensitive detector

The x-ray diffraction technique described previously for measurement of growth kinetics of Pd2Si layers from their solid state reaction couples has been extended by the use of a one-dimensional position-sensitive detector (PSD). Additionally, the method has been extended to include measurement of the Pd layer. A detailed description of the experimental arrangement and analytical procedures is presented. The kinetics of epitaxial Pd2Si film growth were measured in situ over a range of 170–230 °C. The PSD results, using data obtained from both the Pd2Si and Pd layers, were able to confirm parabolic growth behavior for the Pd2Si film. The rate constants followed Arrhenius behavior and yielded an activation energy of E=1.32±0.07 eV with a prefactor k0=0.49 cm2/s for the Pd2Si layer analysis and E=1.34±0.17 eV with a prefactor of 0.72 cm2/s for the Pd layer analysis. The PSD technique significantly enhances data collection and provides extended analytical capabilities. The method has the potential for measuring rate kinetics of other solid state reactions/transformations such as surface oxidation and alloy decomposition.

On the atomic structure of the Pd2Si/(111)Si interface

Abstract The structure of the epitaxial Pd2Si/(111)Si interface has been investigated by transmission electron microscopy (TEM). Lattice imaging and conventional TEM on plan-view specimens show that the Pd2Si grains are often misoriented, by typically 4° → 7°, from the epitaxial relation of (0001)Pd2Si//(111)Si, [1010]Pd2Si//[011]Si. Quantitative texture measurements made by taking convergent-beam diffraction patterns from areas containing individual Pd2Si grains show that misorientations are mostly described by tilting about <110> directions in the film plane. Lattice imaging in (100) cross-sectional samples reveals more clearly the nature of the Pd2Si/(111)Si interface and also shows that individual Pd2Si grains may be considerably bent. The origin of the grain misorientations and their significance in understanding the atomic structure of the Pd2Si/(111)Si interface is discussed.

Kinetics of Pd2Si layer growth measured by an x-ray diffraction technique

An x-ray diffraction approach has been developed for determination of the kinetics of growth of Pd2Si layers. Epitaxial Pd2Si films were grown on Si(111) substrates over a temperature range of 160–222 °C by a solid-state reaction between the substrates and the Pd overlayers. The parabolic rate equation was verified and rate constants showed Arrhenius behavior with an activation energy Ea=1.06 eV and prefactor k0=7×10−4 cm2/s. The low value of Ea suggests a short-circuit diffusion mechanism. It is reasonable to expect that impurities and microstructure may play important roles in the growth process. Impurity levels in the specimens were evaluated by analytic techniques suited to thin-film study: Rutherford backscattering spectrometry, secondary ion mass spectrometry, and Auger electron spectrometry. No impurities were present at concentrations approaching 1 at. %. Some O, C, and F were detected at the Pd2Si/Si interfaces. The annealing ambient was the major source of further contamination. Upon emergence of the growth interface through the sample surface (some Pd2Si on surface), impurity pickup was detected. Interfacial roughness was indicated by all the techniques to be on the order of 20 nm.

Measurement of thermal stress in Pd 2Si film on Si(111) by absorption edge contour mapping

The film stress due to thermal mismatch between the Si(111) substrate and the overlying epitaxial Pd 2Si thin film has been measured by a novel technique named absorption edge contour (AEC) mapping using synchrotron radiation. The thermal expansion coefficient for Pd 2Si has been determined to be 23 × 10 −6 K −1. Stress relaxation was observed after prolonged annealing at temperatures greater than 200°C.

Étude de l'adsorption du palladium sur les faces vicinales de Si(111) par diffraction d'électrons rapides, diffraction d'électrons lents et spectroscopie Auger

The structural properties of palladium deposited onto clean silicon surfaces inclined at small angles to a (111) plane were studied by low energy electron diffraction, reflection high energy electron diffraction and Auger electron spectroscopy techniques. For all palladium deposits (the maximum mean thickness of palladium condensed is about 20 Å) on steps with edges towards [ 2 11], annealing at high temperatures (600–1000°C) produces (122) facets with 2×2 reconstruction. Also at low coverage (1 monolayer), only a (3×1) structure in a single orientation is observed after an annealing at 200°C. For higher coverage (5 to 10 Å), annealing produces epitaxial Pd 2Si islands. In the case of steps with edges towards [2 1 1 ] annealing of palladium deposits smaller than 10 Å at temperatures between 200 and 400°C gives flat smooth Pd 2Si islands epitaxially grown on the substrate. The surface structure of these islands is Si(111)√3×√3R(30°). Between these islands, the silicon surface presents the structure Si(111)3×1 Pd. For higher coverage (10–20 Å) annealing at 400°C gives a Si(111)3√3×3√3R(30°) structure. These results are the same as those we have observed on cleaved (111) surfaces.

The Influence of Predeposition of Nonolayer Thin Titanium Filns Upon the Crystallography of Subsequently Formed Pd2Si Layers on (100) Silicon

ABSTRACTThis paper reports upon a new technique for the formation of epitaxial Pd2Si on (100) silicon using thin predeposited titanium layers. Improvements in the quality of epitaxy in Pd2Si on {111} silicon by this technique will also be shown. A preliminary model for the formation of epitaxy will be given. Discrepancies between this model and results in the literature will be discussed and experiments suggested to resolve the uncertainties.

A TEM STUDY OF Pd-Si THIN FILM SOLID-PHASE REACTION

The initial silicide formation during the deposition of Pd to room-temperature Si (111) substrate and the dependence of Pd2Si-Si orientation relationship on Pd film thickness have been studied by TEM. The results show that the only silicide phase formed is Pd2Si under annealing temperature from 170℃ to 600℃. A thin layer of Pd2Si has grown without annealing, even when the substrate is kept in room-temperature. The Pd film thinner than 100 nm leads to epitaxial Pd2Si layer on Si (111), while the Pd film of about 400 nm gives the [0001] Pd2Si fiber texture. Various kinds of defect with high density exist in the silicide film and the interface.

Epitaxial PtSi and Pd 2Si formed by rapid thermal annealing

Thin films of PtSi and Pd 2Si were formed by short duration incoherent light exposure of evaporated Pt or Pd films on 〈111〉 or 〈100〉 Si single crystals. After processing for time intervals of 15 s and temperatures between ≈ 500 and ≈ 800°C, the suicides were characterized by their sheet resistivities. Stoichiometry and thickness were determined by Rutherford backscattering spectrometry, and epitaxy was studied by ion channeling measurements. Schottky barrier heights and diode ideality factors were deduced from current-voltage characteristics. The quality of these suicides is demonstrated by the low resistivity of respectively 28 and 32 μΩ cm for Pd 2Si and PtSi, and the low χ min values from ion channeling measurements of respectively 13 and 19% for Pd 2Si and PtSi grown on 〈111〉 Si.

A structure marker study for Pd2Si formation: Pd moves in epitaxial Pd2Si

A sample with the configuration Si (111)/single crystalline Pd2Si/polycrystalline Pd2Si/Pd is used to study the dominant moving species during subsequent Pd2Si formation by annealing at 275 °C. The interface between monocrystalline and polycrystalline Pd2Si is used as a marker to monitor the dominant moving species. The result shows that Pd is the dominant moving species in the monocrystal. off

LEED investigations on the interaction of Pd and Ni with different Si(111) surfaces

The structural properties of Pd and Ni on cleaved Si(111)-2 × 1 and − 7 × 7 surfaces have been studies under ultrahigh vacuum conditions by LEED to evaluate the microstructure in the early stages of suicide-silicon interface formation. In contrast to the indifferent behavior of Ni, the reaction of Pd reveals strong evidence for the dependence of the nucleation and growth of epitaxial Pd 2Si on the initial surface reconstruction. A 5 × 1 superstructure emerges on the 2 × 1 surface after deposition of submonolayer Pd at room temperature, suggesting a rather well ordered lateral arrangement of Pd 2Si(1000)-1 × 1 nuclei, whereas epitaxial Pd 2Si on 7 × 7 is only established at much higher coverage ( θ ⩾ 3). An unexpected 3 × 3 reconstruction is formed after annealing at ∼ 200 ° C for θ ⩽ 3 monolayers of Ni, independent of the initial reconstruction and well below the formation temperature of epitaxial NiSi 2. The coverage dependence of the 3 structure implies the presence of an unknown epitaxial film. This finding represents the first evidence of a well defined intermediate state of reaction between unreacted Ni and NiSi 2, which has not been anticipated from other UHV experiments. The qualitative difference in the interaction of Pd and Ni with the Si lattice is demonstrated further by the reappearance of the 7 × 7 reconstruction even after several monolayers of Ni, which has not been achieved with Pd under any process condition, and the pronounced faceting of stepped surfaces under Pd.