S Jin

Comparative study of Ni-silicide and Co-silicide for sub 0.25-mm technologies

In this work, the phase formation is compared for Ni- and Co-silicidation with and without Ti cap. In addition, the electrical performance of Ni-silicidation with and without Ti-cap is investigated and compared to the performance of a Co-silicidation process with a Ti cap that has the same Si consumption. The lateral confinement of the silicide in the active areas is also studied.

Characterization of WF6/N2/H2 plasma enhanced chemical vapor deposited WxN films as barriers for Cu metallization

WxN is a promising candidate as a barrier material for Cu metallization. In this work, we report the characterization of WxN films deposited by plasma enhanced chemical vapor deposition using WF6/N2/H2 gas mixtures. The films are analyzed by Rutherford backscattering spectrometry, Auger electron spectroscopy, atomic force microscopy, x-ray diffraction, transmission electron microscopy, differential scanning calorimetry, and sheet resistance combined with thickness measurements. The diffusion barrier properties are studied by using Cu-gate metal–oxide–semiconductor capacitors and subjecting to either bias-temperature stress (BTS) of 2 MV/cm at 250 °C or thermal anneal up to 700 °C, and evaluated by capacitance–voltage measurement. It is found that the as-deposited films with W/N ratios from 2–19 have an “amorphous-like” nature. Study of the initial growth shows that the WxN films form by nucleation and grow through coalescence, and the films exhibit a granular structure. The transformation from the amorpho...

Transmission electron microscopy investigation of the crystallographic quality of silicon films grown epitaxially on porous silicon

Epitaxial growth of thin crystalline layers on porous silicon can provide opportunities for silicon-on-insulator applications and silicon-based solar cells provided that the epitaxial layer has a sufficient crystallographic quality. Transmission electron microscopy (TEM) is used in this work to study the microstructural properties of porous silicon (PS) and of epitaxial Si layers grown on top of the PS. A more dense silicon layer exists in the upper part of the as-prepared porous silicon. The quality of the epitaxial layers is found to depend strongly on the morphology of the initial porous Si layers, and on the deposition temperature of the epitaxial silicon growth. The porous structure is completely destroyed after thermal CVD deposition of Si at too high temperature, resulting in a highly defective epitaxial layer. A high-quality epi-Si layer is obtained when depositing on a low porosity layer at 725°C. A stacked porous layer with a low porosity in the upper-part and a high porosity in the bulk can be formed by changing the conditions during the formation of the layer. On such a dual porous layer, an epitaxial silicon layer with a low defect density can be grown.

Interaction between Co and SiO2

Abstract Cobalt thin films deposited on SiO2 were processed by rapid thermal annealing. Agglomeration of Co takes place during the annealing, and the formed Co globules penetrate into the SiO2, resulting in crater-like erosion pits. The presence of reaction is evidenced by the formation of a crystalline orthosilicate compound (Co2SiO4). The reaction mechanism is discussed in view of the presence of water at the oxide surface.

Formation of ultra-thin PtSi layers with a 2-step silicidation process

We propose a new technique to form ultra-thin PtSi layers based on sputter deposition of the metal and two-step silicidation by rapid thermal processing, which are production tools used in standard silicon processing technologies.

Epitaxial growth of Gd silicides prepared by channeled ion implantation

A continuous buried GdSi1.7 layer is formed by channelled implantation of 90 keV Gd ions into Si(111). In the case of (001) oriented silicon substrates, the silicide film is formed on the silicon surface. Its worse crystalline quality is due to the epitaxy occurring relative to all four {111}Si planes resulting in a textured GdSi1.7 layer. Annealing at a temperature of ⩾850 °C for 30 min results in the presence of only the orthorhombic GdSi2 phase on the silicon surface for both (111) and (001) silicon substrates. However, the precipitates embedded in the silicon substrate are still hexagonal GdSi1.7. The phase transformation temperature is higher for (111) than for (001) silicon.

Ternary CoxFe(1−x)Si2 and NixFe(1−x)Si2 formed by ion implantation in silicon

Co1−xFexSi2 and Ni1−xFexSi2 metastable ternary phases were formed by sequentially implanting Co, Ni, and Fe into Si (111) at 623 K. In order to compare the phases formed by ion implantation, the Ni1−xFexSi2 stable bulk ternary phase with a wide variety of x values was synthesized. The samples were studied by Mossbauer effect, transmission electron microscopy (TEM), x-ray diffraction, and Rutherford backscattering and channeling. X-ray diffraction and TEM results on the as-implanted samples with x=0.5 indicate a cubic (fluorite) structure. 57Fe Mossbauer spectra show three resonanceline components. Comparison of the isomer shift values of the components with those measured in the stable and metastable transition-metal silicide phases indicated three different sites for iron atoms: Fe substituting Co or Ni; Fe in the empty cubes of the fluorite-type lattices; and Fe populating sites in the CsCl-type B2 lattice. In samples of Ni1−xFexSi2 annealed at 1273 K, α-FeSi2 and a fraction of Fe dissolved in NiSi2 app...

Low-thermal-budget treatments of porous silicon surface layers on crystalline Si solar cells: A way to go for improved surface passivation?

Porous silicon (PS) has several potential interests for crystalline Si solar cells. Besides the use as an anti-reflection coating, the porous layer also acts as a light-diffusor. However, major drawbacks are the light absorption within the porous layer and both insufficient as well as unstable surface passivating capabilities. This work deals with a comparative analysis of different PS treatments with the aim of maintaining the light diffusing property while both the absorption losses are reduced and surface passivation is improved and stabilized. In order to obtain a surface layer with a controlled and stable structure and composition, rapid thermal oxidation (RTO), plasma-nitridation and anodic oxidation have been selected as potentially interesting pathways with a low thermal budget in common. The effects of these different treatments are studied simultaneously on the level of the porous material as well as on solar cell structures (IQE-analysis). A solar cell process is applied which provides an identical emitter for all conditions allowing an analysis of the blue response and an assessment of the most suited porous Si treatment. An improvement of the blue response is observed for RTO treatments at high temperatures, which is due to the creation of an intermediate oxide at the PS/Si interface. No passivation effects are observed in the case of nitridation or anodic oxidation. The modified porous material preserves its light diffusing properties and suffers less from light absorption. The conclusions are drawn up as a strength-weakness analysis for each of the investigated treatments. This balance is not in favour of applying any of the PS modification techniques since in all three cases important drawbacks are the presence of an additional process step as well as the fact that the refractive index decreases which is unfavourable from the viewpoint of ARC-properties.

Ion beam synthesis of Ni-Fe-Si layer by TEM

Nickel and iron ions were selected to be implanted sequentially into (100) orientation silicon wafers to synthesize Ni-Fe-Si ternary silicide film. By using the metal-vapour vacuum-are ion-implantation system MEVVA 80-10, a ternary silicide layer of gamma-Fe0.6Ni0.4Si2 with CaF2 structure has been formed at implantation conditions of 7 x 10(16) Ni ions cm(-2) and 1.4 x 10(17) Fe ions cm(-2). With increase in annealing temperature, the grain size in the layer grows and the gamma phase is decomposed into nickel-rich and iron-rich phases. In the temperature range from 500 to 600 degrees C, a valuable structure of beta-Feo(0.6)Ni(0.4)Si(2)/CaF2-Fe0.35Ni0.65Si2/Si can be obtained. At proper annealing conditions, the gamma phase is decomposed into NiSi2 and FeSi2 phases. The morphology evolution of Ni-Fe-Si ternary silicide with increasing annealing temperature ranges from the layer thickness increasing to the film shrinking into isolated islands at 850 degrees C

Effects of Low-Thermal-Budget Treatments on the Porous Si Material Properties

Our interest in porous silicon is due to its potential benefits in crystalline Si solar cells. Besides the use as an anti-reflection coating, the porous layer also acts as a light-diffusor. However major drawbacks are the significant light absorption within the porous layer and both insufficient as well as unstable surface passivating capabilities. The unstable nature of the porous Si is also reflected in the presence of suboxides after storage in ambient. In this work we focus on rapid-thermal-oxidation (RTO) and plasma-nitridation as low-thermal-budget chemical modification techniques in order to obtain a surface layer with a controlled and stable structure and composition. RTO of porous Si converts the material into SiO2 in conjunction with a drastically decreased porosity. Both a remote- and a direct-plasma nitridation of porous Si are able to incorporate nitrogen uniformly throughout the porous layer while preserving the porous character.