C. C. Peng

Rapid thermal annealing enhanced crystalline SiC particles at lower formation temperature

Formation of nanoparticle SiC (np-SiC) from three-layer Si/C/Si multilayers on Si(100) substrates were investigated using ultra-high-vacuum ion beam sputtering and post annealing by conventional furnace annealing (FA) and rapid thermal annealing (RTA). Fixing the thickness of bottom Si-layer at 50 nm, different thicknessses of the top Si and C layers were designed to study the effect of annealing on the reaction of np-SiC formation, that is, three-layer Si/C/Si structures with thicknesses of 50/200/50 nm by FA and 10/100/50 nm by RTA. There are almost no particle appears at 700degC 1.0 h by FA due to low thermal energy. It was observed that np-SiC appeared at a density order about 108 cm-2 by FA at 900degC for 1.0 h, but many np-SiC can be realized at 750degC for annealing time as short as 1 min at a density order about 1010 cm-2 by RTA. The density is much higher than conventional nanoparticles synthesis using CVD or PVD. The reaction temperature of SiC is also lower than the conventional CVD or FA because of RTA enhanced SiC crystallization behavior at high heating rate. The annealing method influences the particle formation. The particle size, distribution and density are concerned with the top and middle layer thickness. Thermal energy is the diving force for the crystalline SiC formation through interdiffusion between C and Si.

Effect of residual stress on nanoindented property of Si∕C∕Si multilayers

The effect of residual stress on the nanoindentation property of Si/C/Si multilayers has been investigated. Sandwiched Si/C/Si multilayers were deposited on Si(100) substrates by means of ultrahighvacuum ion-beam sputtering at room temperature (RT). Four structures with different Si top-layer thickness of 5, 10, 25, and 50 nm and the constant thickness of C/Si underlayer at 100/50 nm were investigated in this study. The residual stress of the Si/C/Si (5/100/50 nm/nm/nm thick) film was about -17.76 GPa under compression, and its hardness was 20.39 GPa at RT. The compressive residual stress was decreased to -5.54 GPa with the increased thickness of Si toplayer up to 50 nm, and its hardness was reduced to (16.22 GPa at RT. The effect of Si top-layer thickness (5-50 nm) on Si/C/Si residual stress on the nanoindentation property were also discussed. The results showed that the thicker was the Si toplayer, the lower was the residual stress and hardness, which was good for the suppression of the buckling or wrinkling in the C/Si-nanocomposite film.

Annealing effect on the microstructure and morphology of the nanostructured Ta-Si-N thin films

Ta-Si-N thin films were potentially applied as diffusion barriers for Cu interconnections. However, the thermal stability of Ta-Si-N is related to the composition and annealing methods. In this paper, we have investigated the effect of high- vacuum furnace annealing and vacuum rapid thermal annealing (RTA) on the microstructure and morphology of different nanostructured Ta-Si-N thin films fabricated by reactive cosputtering at varied Ta and Si powers and nitrogen flow ratio (FN2%= FN2/( FN2+FAr) x 100%). As Si is added to the Ta-N compound to form Ta-Si-N, the microstructure becomes nanocrystalline grains embedded in an amorphous matrix i.e. amorphous-like microstructure, which is also affected by the nitrogen flow ratio. Amorphous-like Ta-Si-N films obtained at small 3-6 FN2% had smoother morphology and lower resistivity compared to the polycrystalline film at high 20 FN2%. The thermal stability of Ta-Si-N films increases with the Si/Ta ratio and magnitude of vacuum. Higher vacuum furnace annealing at 5 times 10-5 Torr may make both amorphous-like and polycrystalline Ta-Si-N films enduring higher temperature up to 900degC for a longer time of 1 h while the higher pressure RTA at 2 times 10-2 Torr make Ta-Si-N films transform of phase and morphology at 750-900degC just in 1 min. The increase of Si/Ta ratio may also increases the stability of Ta-Si-N films.

Fabrication and Characterization of Nanostructured Ta-Si-N Films

In this paper, the morphology and properties of nanostructured Ta-Si-N thin films fabricated by reactively cosputtering have been studied. The Ta-Si-N film is a mixed composite consisting of the Ta-Si, Ta-N and Si-N compounds. The TaN phase is polycrystalline while SiNx is amorphous. As Si is added to the Ta-N compound to form Ta-Si-N, the micro structure becomes nanocrystalline grains embedded in an amorphous matrix i.e. amorphous-like micro structure, which is also affected by the nitrogen flow ratio i.e. FN2%= FN2/( FN2+FAr) times 100% during sputtering. Amorphous-like Ta-Si-N films obtained at small FN2% of 2-10% had smaller roughness, lower resistivity and larger nanohardness compared to polycrystalline films at high FN2% of 20- 30%. The variation of Ta-Si-N micro structure leads to the different electrical and mechanical properties of films. The electric resistivity of Ta-Si-N increases with increasing FN2% while the nanohardness first increases to a maximum of 15.19 GPa from FN2% of 2% to 3%, then decreases with increasing FN2%. The higher hardness in amorphous-like Ta-Si-N exhibits a larger stiffness and resilience than polycrystalline one.

Effect of Amorphous Si Thickness on the Formation of SiC Nanoparticles during High Vacuum Annealing

In this paper, a novel approach for the formation of SiC nanoparticles (np-SiC) has been demonstrated by annealing the three-layer a-Si/C/a-Si film on a Si(100) substrate. The np-SiC formation strongly depends on the amorphous Si (a-Si) thickness and annealing temperature. Both three-layer a-Si/C/a-Si structures in different thickness i.e. 50/200/50 nm and 75/150/75 nm were studied at annealing temperatures of high vacuum annealing at 500-900 degC at 10-4 Pa. The a-Si thickness and annealing temperature significantly affected the particle size, density, and distribution of np-SiC. No nanoparticles were formed for multilayers annealed at 500 degC, while a few particles started to appear as the annealing temperature was increased to 700 degC at both structures. Many np-SiC appeared at 900 degC at a density order about 108 cm-2 for both structure, but the thicker a-Si structure i.e. a-Si/C/a-Si (75/150/75 nm) has a particle density approximately 1.8 times higher than a-Si/C/a-Si (50/200/50 nm). This is attributed to the variation of activation energy, surface energy and atomic mobility during reaction of Si and C at different a-Si thickness and temperature. The higher the annealing temperature, the higher the particle density. The thicker a-Si structure with higher density implies that it has lower activation energy of SiC formation than the thin a-Si structure.